Acute graft-versus-host disease (aGvHD) is induced by immunocompetent alloreactive T lymphocytes in the donor graft responding to polymorphic and non-polymorphic host antigens and causing inflammation in primarily the skin, gastrointestinal tract and liver. aGvHD remains an important toxicity of allogeneic transplantation, and the search for better prophylactic and therapeutic strategies is critical to improve transplant outcomes. In this review, we discuss the significant translational and clinical advances in the field which have evolved based on a better understanding of transplant immunology. Prophylactic advances have been primarily focused on the depletion of T lymphocytes and modulation of T-cell activation, proliferation, effector and regulatory functions. Therapeutic strategies beyond corticosteroids have focused on inhibiting key cytokine pathways, lymphocyte trafficking, and immunologic tolerance. We also briefly discuss important future trends in the field, the role of the intestinal microbiome and dysbiosis, as well as prognostic biomarkers for aGvHD which may improve stratification-based application of preventive and therapeutic strategies.
Allogeneic hematopoietic stem cell transplantation (HSCT) remains one of the most important curative modalities for marrow failure and various advanced/aggressive hematologic malignancies. Acute graft-versus-host disease (aGvHD) remains an important HSCT toxicity with significant associated morbidity and mortality. aGvHD clinical manifestations typically involve skin (rash), upper (nausea, anorexia) or lower (diarrhea, abdominal pain) gastrointestinal (GI) tract, or liver dysfunction (elevated bilirubin, transaminases).1 Its pathology is typically induced by immunocompetent effector T lymphocytes responding to donor/recipient polymorphic and non-polymorphic antigens on host tissues, with activation, inflammation and eventual cytolytic activity.
Despite advances in HSCT, such as high resolution HLA genotyping and the routine use of calcineurin-inhibitor (CNI)-based prophylaxis, aGvHD incidence remains in the 30-35% range with HLA-matched donors. While aGvHD outcomes have improved (largely due to advances in supportive care, e.g., infectious disease interventions), patients with severe and steroid-refractory (SR) aGvHD still have impaired survival, estimated to be in the 5-30% range.
aGvHD control is a cornerstone of successful transplantation. Effective interventions should not cause excessive toxicity, impair the curative graft-versus-leukemia (GvL) effect of allotransplantation, or contribute to graft failure. In this review, we summarize aGvHD pathogenesis and discuss novel advances in the prevention and treatment of aGvHD that have evolved as our understanding of pathogenesis has grown. In addition, we highlight areas of burgeoning interest in the field: microbiota dysbiosis, and the development of aGvHD biomarkers.
Biology of acute graft-versus-host disease
In an early model of aGvHD, Antin and Ferrara described a three-step process comprising: (i) host tissue injury due to the conditioning regimen, with the production of inflammatory cytokines; (ii) stimulation and proliferation of effector T lymphocytes (Teff); and, finally, (iii) recruitment and activation of additional mononuclear effectors and amplification of a ‘cytokine storm’.2 This basic model has stood the test of time, although it has been refined thanks to a deeper and more sophisticated understand ing of transplant biology, briefly outlined below.
In the initial host tissue injury phase, exogenous and endogenous antigens classified as sterile damage-associated molecular patterns (DAMP; e.g., uric acid, ATP, heparan sulfate, HMGB-1 or IL-33) and pathogen-associated molecular patterns (PAMP; e.g., bacterial lipopolysaccharides) interact with antigen-presenting cells (APC) in the innate and adaptive immune systems, with activation of cytokine cascades (IL-1, IL-6, TNF-, etc.) that set the stage for T-cell priming and expansion.1
The second phase involves Teff trafficking (mediated by L-selectin, CCR7, etc.) to lymphoid organs and host tissues. CD8+ and CD4+ Teff cells homing to the gut express high levels of integrin 7 (47) which bind corresponding host tissue ligands. At their destination, Teff activation via APCmediated host tissue:TCR interaction is initiated. This step, modulated by anti- versus co-stimulatory pathways and cytokine cascades, finally leads to the third phase, selfpotentiating Teff cell proliferation and activation causing tissue damage via direct cellular cytotoxicity and indirectly via release of soluble mediators (TNF-, IFN-, IL-1 and nitric oxide).3 The canonical NOTCH pathway is involved in regulating GvHD pathogenesis4 and using humanized monoclonal antibodies, it was shown that Notch-deprived T cells (with predominant roles for NOTCH1 and Dll-4) produce less inflammatory cytokines but proliferate normally, with a preferential increase in regulatory T cells (Tregs), without compromising GvL.5 Selective NOTCH blockade offers potential for clinical translation.
Such immune activation is opposed by anti-inflammatory Tregs, a T-cell subset important in immunologic tolerance, in part via release of anti-inflammatory cytokines such as IL-10 and TGF-.6 Additionally, the balance of effector T-helper (Th) type 1 (IL-2, INF-) and type 2 (IL- 4, IL-10) cytokine responses may govern the ultimate outcomes of inflammation since type 2 cytokines can inhibit potent proinflammatory type 1cytokines, and a Th1 to Th2 shift could be beneficial in aGvHD.7 A distinct subset of CD4+ cells (characterized by production of IL-17A and F, IL-21 and IL-22) called Th17 cells has also been identified, which in murine models migrate to GvHD target organs causing severe pulmonary and GI lesions and GvHD lethality,8 and may play a critical role in GvHD pathogenesis9 antagonistic to Tregs. Invariant natural killer T (iNKT) cells (discussed below) are another cellular subset with putative immunoregulatory functions, in part via an increase in Treg numbers and IL-4 secretion, that may be important in GvHD pathophysiology.
Here we discuss novel advances in the prevention and therapy of aGvHD built on the understanding of these concepts.
Acute graft-versus-host disease prevention
Established determinants of acute graft-versus-host disease
The well-established impact of conditioning regimen intensity, donor-recipient HLA-mismatch and graft source (bone marrow [BM], peripheral blood stem cell [PBSC]) on aGvHD outcomes is briefly discussed below.
Conditioning regimen intensity - the impact of conditioning intensity on aGvHD is primarily due to tissue damageinduced DAMP/PAMP release (see above). In general, myeloablative conditioning (MAC) (particularly total body irradiation [TBI])-containing regimens are associated with higher aGvHD rates, an effect more pronounced with PBSC grafts.10 Non-myeloablative (NMA) and reduced-intensity conditioning (RIC) transplants have been associated with lower aGvHD rates11,12 than MAC, and even the newer reduced-toxicity regimens (e.g., ablative busulfan/fludarabine) as per a large randomized controlled trial (RCT).13 There has, therefore, been a shift towards minimizing TBI except when absolutely necessary (e.g., acute lymphoblastic leukemia).
Novel therapeutic targeting of DAMP/PAMP:immune cell interactions are being investigated. For example, ATP (a DAMP) interacts with APC to activate inflammatory STAT1 signaling. Interruption of this pathway reduced GvHD in murine models14 although translation into clinical practice is still awaited.
Donor-recipient human leukocyte antigen (HLA)-mismatch - HLA-mismatch is an aGvHD risk factor. Large registry studies document increased aGvHD rates (including severe aGvHD grades III-IV) and impaired survival for 1-2 locus HLA-mismatch versus 8 of 8 HLA-matched MAC and RIC HSCT.15,16 With the advent of post-transplant cyclophosphamide (PTCy)-based regimens, the effect of HLA-mismatch may be less deleterious. PTCy was initially introduced in haploidentical (haplo) HSCT, but in a trial of matched and single-antigen mismatched unrelated donors (MUD, MMUD) it was found superior to standard CNIbased prophylaxis (discussed below).17 The role of PTCy in single-antigen MMUD HSCT is being further explored, with one study showing better rates of acute and chronic GvHD, non-relapse mortality (NRM), and relapse with PTCy compared to anti-thymocyte globulin (ATG).18 Many centers are adopting a PTCy-based platform for MUD/MMUD HSCT.
Graft source - while unmanipulated donor BM grafts were initially used in transplantation, there is now a secular trend towards use of PBSC grafts, due to logistical reasons and donor preference. In a large meta-analysis comparing the two graft sources, there was no difference in overall aGvHD rates, although severe grade III-IV aGvHD and chronic severe GvHD was lower with BM. However, relapse in that analysis appeared higher with BM grafts leading to impaired disease-free survival (DFS) and overall survival (OS) in late stage disease.19 In a phase III RCT of MUD PBSC versus BM HSCT, OS was similar (albeit with relatively short follow-up) with no differences in aGvHD or relapse, but chronic GvHD rates were lower with BM.20 Hence BM is arguably the better graft source, although the effect on relapse needs longer term follow-up. Cord blood transplants have resulted in similar rates of aGvHD as conventional sources although with lower rates of cGvHD.21 It should be mentioned that many GvHD prophylaxis regimens have been tested in association with specific stem cell sources making the interpretation of these data difficult.
Innovations in acute graft-versus-host disease prophylaxis
Since the cardinal events in aGvHD etiopathogenesis involve T-cell trafficking, interaction with host antigens and activation to cause tissue injury, the cornerstone of aGvHD prevention remains depletion or modulation of donor T lymphocytes.
Since the 1990s, standard of care (SOC) aGvHD prophylaxis has incorporated a CNI (e.g., tacrolimus [Tac], cyclosporine [CyA]) plus another agent (e.g., methotrexate [MTX]), mycophenolate mofetil [MMF], sirolimus [Siro]).22,23 CNI inhibit alloreactive T-cell proliferation and activation. However, even with CNI-based platforms, rates of grade II-IV aGvHD are 30-40%, with 10-15% severe grade III-IV aGvHD. Furthermore, CNI are associated with various toxicities (e.g., renal dysfunction, thrombotic microangiopathy [TMA]) which can add to transplant-related mortality (TRM). Hence novel prophylactic therapies with improved efficacy and less toxicity are of great interest in transplantation. Recent advances in aGvHD prevention, some of which are challenging the established CNI-based platform, are discussed below.
In vivo T-cell depletion/modulation
Anti-thymocyte globulin - ATG is the polyclonal purified IgG fraction of sera from horses or rabbits immunized with human thymocytes or T-cell lines. In vivo T-cell depletion (TCD) with ATG has been extensively evaluated to reduce the incidence of acute and chronic GvHD with HLA-matched as well as cord blood and haploHSCT.
In the CNI-era, four RCT evaluated CNI/MTX prophylaxis ± ATG.24 In the first, using horse ATG, a reduction in aGvHD was offset by higher rates of infection with no difference in NRM or OS; however, there was a reduction in severe chronic GvHD.25,26 In the second, using rabbit ATG,27,28 and the third, mainly using PBSC grafts, there was no effect on aGvHD, with a reduction in cGvHD.29 These studies concluded that reduction in severe cGvHD with no deleterious effect on OS is a true ATG effect; however, aGvHD was not reduced. More recently, an RCT evaluated Tac/MTX ± anti T-lymphocyte globulin (ATLG) in MAC MUD HSCT, with a significant reduction in grade II-IV aGvHD and moderate/severe cGvHD. However, NRM and OS was impaired in the ATLG arm.30 A higher dose of ATLG in the trial may have contributed to increased infections and mortality.
In pioneering studies by Storek et al., persistence of therapeutic ATG levels on days +7 and +28 were found to reduce acute and chronic GvHD.31 There is also evidence that excessive persistence or dosing of ATG may have immunosuppressive toxicity with increased NRM and relapse. Individualized ATG dosing, based on absolute lymphocyte count beyond recipient weight, could be a way forward to control GvHD without impairing NRM and relapse.32
Post-transplant cyclophosphamide - the use of PTCy-based GvHD prophylaxis has been a major advance allowing the widespread use of haploHSCT with increasing importance also in HLA-matched and mismatched HSCT.
Haplo-hematopoietic stem cell transplantation was initially associated with increased graft rejection and GvHD due to strong bidirectional donor versus recipient alloreactive responses. HaploHSCT regimens utilized highly immunosuppressive conditioning with high transplantassociated toxicity. The innovative use of PTCy dosed at 50 mg/kg on days +3 and +4 following NMA haploHSCT resulted in a grade II-IV aGvHD rate of 34%, with a low grade III-IV aGvHD rate of 6% and a trend towards reduction in severe cGvHD. Relapse rates were around 50%.33 Numerous subsequent studies replicated these results, and PTCy is now the most widely used haploHSCT regimen. It is worth noting that overall aGvHD rates with PTCy, at 30-80%, are not necessarily lower than SOC, but severe aGvHD and cGvHD rates are lower.
PTCy was initially thought to act via depletion of alloreactive T cells by elimination of proliferating cells and intrathymic clonal deletion of alloreactive T-cell precursors. 34 More recent data suggest important roles for Treg preservation and Teff exhaustion as additional mechanisms of effect.34
PTCy has also been evaluated in alternative donor HSCT. In a phase II RCT of MUD/MMUD PBSC HSCT, three GvHD prophylaxis regimens were compared with SOC Tac/MTX: PTCy/Tac/MMF, Tac/MTX/bortezomib, and Tac/MTX/maraviroc. The primary 1-year GvHD free, relapse-free survival (GRFS) endpoint was improved in the PTCy-based arm.17 Interestingly, grade II-IV aGvHD was similar; however, impressive gains were seen for severe grade III-IV aGvHD. Chronic GvHD requiring immunosuppression also fared much better with PTCy.
Recently, a small European RCT compared PTCy/Tac/MMF to CyA/MMF in HLA-matched RIC PBSC HSCT. Grade II-IV aGvHD was lower with PTCy (P=0.014) while severe grade III-IV aGvHD was 6% versus 12%, respectively.35 Importantly, CyA/MMF is considered inferior to Tac/MTX, and hence PTCy-based prophylaxis is being definitively evaluated in a large multi-center phase III RCT (BMT CTN 1703) of MUD PBSC RIC HSCT comparing PTCy/Tac/MMF with Tac/MTX.
Sirolimus - Siro is an mTOR inhibitor that synergizes with CNI in reducing Teff proliferation and activity. Siro inhibits CD8+ cells36 while promoting Treg proliferation in vitro,37 an attractive immunologic profile for GvHD prevention. Importantly, unlike CNI, it does not cause nephrotoxicity. Siro/MTX prophylaxis has been investigated in a large RCT of MAC HSCT, documenting similar grade IIIV but lower grade III-IV aGvHD compared to Tac/MTX.38 In RIC transplants, a phase II RCT showed that combined Siro/Tac/MTX had less grade II-IV aGvHD but no survival benefit.39 A recent phase III RCT of NMA HSCT concluded that adding Siro to CyA/MMF was superior to CyA/MMF.40 Given that the combination of Tac and MMF is inferior to Tac/MTX in a phase II RCT in preventing grade II-IV aGvHD,41 and CyA has also been shown to be inferior to Tac in the past for GvHD prophylaxis, it is unclear how these data impact centers that primarily use Tac/MTX-based regimens. Although less nephrotoxic, Siro has also been associated with higher rates of venoocclusive disease (VOD), particularly with ablative busulfan and cyclophosphamide,42 and is avoided in patients at a higher risk for VOD. It has also been associated with increased rates of TMA, particularly in combination with CNI.43 Discontinuation of CNI typically resolves TMA in this setting.
Finally, the combination of Siro/PTCy as a CNI-free, less nephrotoxic regimen with acceptable rates of engraftment and aGvHD has been evaluated.44 This is currently reserved for scenarios precluding CNI use (e.g., sickle cell HSCT, with renal dysfunction). Given the Treg-sparing effect of Siro,45 novel combinations (e.g., with OX40L blockade) are being explored as GvHD prophylaxis platforms.46
Ex vivo T-cell depletion
A deeper understanding of transplant biology and the availability of sophisticated clinical-grade cell separation technology underpins advances in graft manipulation involving both pan-T-cell and selective T-cell subset depletion for the clinic, reviewed below.
Pan-T-cell depletion - ex vivo TCD of the donor graft has been utilized as a method to prevent GvHD, considering competing risks of relapse and NRM. Methods have included monoclonal antibodies with or without complement,47-50 immunotoxins,51 and counter flow elutriation.52
Ex vivo TCD was evaluated in a multi-center RCT of TCD grafts versus CNI-based prophylaxis.53 TCD was associated with lower rates of grade III-IV but not grade II-IV aGvHD, with no change in DFS. Graft failure and increased disease relapse (20% vs. 7%) was a concern, with increased relapse also noted in a seminal registry analysis.54 Other studies also suggested increased rates of graft failure with TCD grafts, ameliorated by ATG or thiotepa conditioning to prevent host immune-mediated graft rejection.
T-cell depletion based on immunomagnetic CD34+ graft selection (to eliminate contaminating immune cells) was evaluated in a single-arm phase II multicenter trial and showed low rates of cGvHD and relapse.55 This was compared to CNI-based prophylaxis in a retrospective analysis, where outcomes were similar, with lower rates of cGvHD in the CD34 arm.56 Ex vivo TCD remains the primary mode of transplantation in certain centers, although infectious complications, particularly viral infections, can be problematic. To better define optimal GvHD prophylaxis, results from an ongoing RCT of ex vivo TCD versus PTCy with MMF only versus standard CNI-based regimen are eagerly awaited (clinicaltrials.gov identifier: NCT02345850).
Beyond pan-T-cell depletion, subset-selective T-cell depletion and modulation strategies to ameliorate GvHD without compromising GvL effect by using antibodies with narrow specificities has become an area of great interest.50 Depletion of CD5+ T cells51 and CD8+ T cells were tried in the 1990s, but abandoned primarily due to higher rates of relapse. Other novel strategies are discussed below.
/T-cell depletion - the majority of T lymphocytes express /T-cell receptors (TCR), while /TCR are expressed by 2-10% of circulating T cells. /T cells have important innate immune functions including rapid release of cytokines, and killing of tumor and virally infected cells without inducing GvHD.57 They may have an important role in GvL effect and the preservation of NRM. Selective depletion of /T cells would preserve NK cells as well as /T cells. In a prospective study of 80 pediatric patients with acute leukemia, /TCD was studied with encouraging GRFS of 70%.58 Ongoing studies are further evaluating this approach in adult and pediatric populations, including a CNI-free GvHD prophylaxis strategy for acute leukemia patients undergoing 1-2 locus MMUD MAC HSCT (clinicaltrials. gov identifier: NCT03717480).
CD45RA (naïve) T-cell depletion - conceptually, it is naïve T cells in the donor allograft that are primarily alloreactive. In a study in healthy individuals, the bulk of allo-HLA reactivity was derived from subsets enriched for naïve T cells.59 Hence, removal of CD45RA+ naïve T cells from the donor graft could help prevent aGvHD alloreactivity. The CD45RA− target fraction contains effector and central memory T cells that show preserved reactivity to common viral and fungal pathogens.60 In a two-step immunomagnetic bead procedure for naïve TCD, Bleakley et al.61 reported on a first-in-human single-arm trial (n=35) for patients with acute leukemia transplanted with HLA-matched related donors. Although 34 of 35 patients engrafted with lower rates of cGvHD, rates of aGvHD remained relatively high (66%), suggesting a lack of efficacy with this approach alone.62 A combinatorial approach using /TCD combined with CD45RA naïve cell depletion was not much better, with aGvHD rates in the 58% range.63 Hence, for the moment, this approach remains only investigational.
CD6 depletion - CD6 is a co-stimulatory receptor, predominantly expressed on T cells that bind to activated leukocyte cell adhesion molecule (ALCAM), a ligand expressed on APC and various host tissues and plays an integral role in modulating T-cell activation, proliferation, differentiation and trafficking. CD6 depletion using a monoclonal antibody (mAb) (anti-T12, CD6) that recognized mature T cells but not other cellular elements (e.g., B, natural-killer [NK] cells, and myeloid precursors) was clinically evaluated in a single arm trial with 112 patients with a grade II-IV aGvHD rate of 18%.48 More recently, itolizumab a humanized anti- CD6 mAb, was evaluated in human xenograft models, suggesting that itolizumab can modulate pathogenic Teff activity. 64 Itolizumab has been provided fast track status by the US Food and Drug Administration (FDA) for this indication and is undergoing evaluation in a phase I/II study for firstline treatment (with steroids) of severe aGvHD (clinicaltrials. gov identifier: NCT03763318).
Graft engineering: Treg/Tcon add back strategies - in haploHSCT, in the early 1990s, CD34+ cell selection was used by the Perugia group to generate T-cell depleted peripheral blood progenitor cell grafts. Although GvHD rates were low, there was poor immune reconstitution (IR) and high rates of infection.65 The Perugia group then pioneered the use of a ‘megadose’ of CD34+ cells to facilitate engraftment and improve IR based on the increased tolerability effect of such a dose of CD34+ cells.66 Subsequently, further TCD by negative selection of CD3/CD19+ cells was used. Most recently, CD34+ selection followed by graduated add back of Tregs and conventional T cells (Tcons) (in a 2:1 ratio) have been adopted, with promising early results for enhanced IR and GvL, but aGvHD remains a concern.67 Further iterations of this approach may yield enhanced clinical benefit, despite their complexity and cost.
Regulatory T-cell enhancement
Tregs - Tregs are CD4+CD25+Foxp3+ cells which play an important role in immunologic homeostasis and the control of aberrant or overactive immune effectors. Tregs can be derived ‘naturally’ from the thymus (nTregs) or converted from CD4+CD25- cells (inducible or iTregs).6 iTregs require IL-2 and TGF-to fully develop their suppressive function. Blazar et al. showed that ex vivo activation and expansion of Treg is feasible, with efficacy in murine GvHD models.68 Other approaches have utilized fucosylation69 and TL1A/TNFRSF25 stimulation70 for ex vivo Tregs. In clinical transplantation, they have confirmed the feasibility and safety of ex vivo Treg expansion and adoptive transfer, with preliminary clinical efficacy for aGvHD prevention in both cord71 and haploHSCT.67 However, concerns about stability of expanded Tregs has been a barrier to translation into the clinic.
Invariant natural killer T cells - invariant NK T (iNKT) cells are a rare T-lymphocyte subset which co-express both Tand NK-cell markers and are considered a bridge between innate and adaptive immunity. Their semi-invariant TCR recognizes glycolipid antigens presented by the major histocompatibility complex (MHC) class I-like molecule Cd1d. Despite their rarity, they have strong immunomodulatory functions through the secretion of IL-4 and IL-10, as well as providing active immunologic surveillance against cancer.72 Murine models suggested that iNKT cells have a protective effect against GvHD without impairing the GvL effect. This occurs in part via a switch of donor T cells to a Th2 cytokine profile and/or IL-4 dependent Treg expansion.73,74 Observational studies suggest lower acute and chronic GvHD with improved iNKT cell reconstitution. Clinical translation has involved RIC HSCT utilizing total lymphoid irradiation plus ATG (TLI-ATG) conditioning (offering iNKT expansion in murine models) with promising outcomes,75 as well as more direct ex vivo expansion and adoptive iNKT transfer peri-transplant, where clinical data are eagerly anticipated. KRN7000 (synthetic derivative of -galactosylceramide and a CD1d ligand) when embedded in a lipid bilayer constitutes RGI- 2001or REGiMMUNE which can expand FoxP3+ Tregs via iNKT cells in mice to reduce aGvHD lethality.76 Recently a phase IIa trial of a combination of Siro and RGI-2001 showed lower incidence of overall and severe aGvHD in responders compared to non-responders.77 Although promising, iNKT targeted approaches have not been widely adopted for the moment and more mature data are awaited.
Tocilizumab - interleukin-6 (IL-6) is a key inflammatory cytokine in the early pathogenesis of aGvHD in murine models.78 A logical next step was to investigate the role of IL-6 blocking agents in preventing aGvHD. Tocilizumab is a humanized mAb against the IL-6 receptor (IL-6R). Based on promising phase II data,79 a placebo-controlled phase III study from Australia was reported, which, however, showed no significant difference in grades II-IV or III-IV aGvHD.80 This is a salient reminder that, given the complex pathophysiology of aGvHD, with crosstalk between myriad cytokines and immune effector cells, it is possible that targeting multiple cytokine pathways will be required for efficacy.
Targeting T-cell co-stimulatory pathways
As mentioned previously, following initial engagement of an APC with the TCR, a number of secondary co-stimulatory signals come into play which are necessary to complete alloreactive T-cell activation, proliferation and eventual development of aGvHD. CD28 is a co-stimulatory receptor while CTLA-4 is a co-inhibitory receptor on the T cell, both of which bind to B7-1/CD80 and B7-2/CD86 ligands on APC. CTLA-4-Ig (abatacept) is the soluble extracellular portion of CTLA-4 complexed with immunoglobulin heavy chain which blocks CD28/CTLA-4 (CD28>CTLA-4) co-stimulation with an eventual T-cell inhibitory signal. Blazar et al. showed in murine models that blockade of the CD28/CTLA-4 and CD80/CD86 interaction reduced aGvHD lethality.81 Following a promising feasibility study, Kean et al. then tested abatacept added to SOC versus SOC in a phase II RCT with 8/8 and 7/8 HLA-matched donors. There was significant reduction in grades III-IV aGvHD in the abatacept arm with improved OS82 leading to FDA breakthrough designation for this drug. To avoid the undesirable effect of concomitantly blocking inhibitory pathways, more selective approaches to CD28 blockade are being investigated. FR104, an antagonistic CD28-specific pegylated-Fab' has shown promise with and without Siro in non-human primate models, with the caveat that a worrying inhibitory effect was seen on the INF-axis with deaths secondary to sepsis.83 The modulation of co-stimulatory/inhibitory pathways is one of the important new frontiers in aGvHD prevention.
These prophylactic strategies, along with the level of evidence supporting them, are summarized in Table 1.
Advances in acute graft-versus-host disease therapy
Systemic steroids, while not FDA-approved for this indication, remain a cornerstone of the initial treatment of moderate-severe aGvHD. In a seminal study, Blazar et al. showed that first-line therapy of aGvHD with corticosteroids (60 mg daily followed by an 8-week taper) resulted in response rates of 50% and 1-year survival of 53%.84 Higher doses of steroids did not result in better outcomes. In a study comparing 10 mg/kg to 2 mg/kg of methylprednisone, both resulted in transplant mortality of 30% at one year with no improvement in aGvHD responses at higher doses.85 SR-aGvHD treatment remains a difficult problem, with 6-month survival in the 50% range, and long-term survival of only 5-30%.86 Stratification systems such as the Minnesota risk score that take into account patterns of aGvHD by target organ involvement can further refine the prediction of transplant-related mortality, and are being considered in clinical trial risk stratification.84 Finally, even when aGvHD is controlled, patients often succumb to infections exacerbated by additional immunosuppressive therapies. Novel therapies are, therefore, a critical unmet need. Here we outline some of the more promising approaches currently available or in early translation to the clinic.
JAK-STAT pathway - the Janus Kinases (JAK) are intracellular tyrosine kinases investigated as GvHD therapeutic targets given their important role in cytokine signaling and effects on immune effector cells. In murine models, the role of IFNon T-lymphocyte trafficking to GvHD target organs (particularly the GI tract) via CXCR upregulation was studied. Inhibition of interferon (IFN)R signaling via JAK1/JAK2 inhibitors resulted in decreased CXCR3 expression and altered Teff trafficking to target organs, reducing GvHD.87 Ruxolitinib (Rux) is a potent oral JAK-1/JAK-2 inhibitor. In a proof of concept study, Rux reduced Teff proliferation and activity, increased Tregs and decreased cytokine production, with excellent responses in six SRaGvHD patients.88
A retrospective survey of off-label Rux in SR aGvHD documented overall response rate (ORR) of 81.5% (complete responses [CR] 46%). Cytopenias and cytomegalovirus (CMV) reactivation were seen.89 A phase II single-arm multicenter study of Rux (REACH-1) in 71 patients documented ORR at 28 days of 54.9% (complete remission/CR, 26.8%), irrespective of aGvHD grade and steroid refractoriness.90 In addition to cytopenias and CMV reactivation, serious bacterial infections were reported. The phase III RCT of Rux versus investigator’s choice for SR aGvHD has now been reported (REACH-2). Rux was superior in terms of ORR; however, there was no difference in cumulative incidence of 18-month NRM.91 Infections and cytopenias remain limiting toxicities. The FDA has approved Rux for SR aGvHD.
In contrast, failure of the selective JAK1 inhibitor itacitinib when added to steroids (vs. steroids alone) for upfront therapy of aGvHD in the closed GRAVITAS 301 trial (clinicaltrials. gov NCT03139604) is notable. JAK-1 inhibition is capable of selectively suppressing Th1 and Th17 Teff cell subsets, with preserved activation of anti-inflammatory Treg cells dependent on the JAK2/JAK3 pathway; however, the drug failed clinical efficacy, highlighting limitations in clinical trial design, optimal therapeutic target identification, or both. Data on the efficacy of selective JAK2 inhibitors in aGvHD are eagerly awaited, but it is possible that combination JAK1/2 blockade may be required for appropriate suppression of activation in Teff cells.
Although a number of cytokine-directed therapies previously failed in the therapy of aGvHD (denileukin diftitox, tocilizumab, anti TNF-), the efficacy of Rux is a milestone in the field, and a testament to the critical role of a ‘cytokine storm’ in aGvHD.
Alpha-1-antitrypsin - alpha-1-antitrypsin (AAT) is a serine protease inhibitor produced by the liver which has myriad functions including inhibition of proinflammatory plasma cytokines and induction of anti-inflammatory IL10, and in vivo induction of Treg. In preclinical aGvHD models, AAT reduced inflammatory cytokines, altered the ratio of Teff and Tregs and reduced levels of DAMP.92 In a phase I/II open label single center study in SR aGvHD patients (n=12), responses were seen in 8 of 12 patients with no significant toxicity.93 In a larger phase II multicenter study (n=40), ORR at D28 was 65% (CR 35%).94 Upfront AAT is being evaluated in a Blood and Marrow Transplant Clinical Trials Network (BMT-CTN) phase III RCT evaluating corticosteroids ± AAT (clinicaltrials.gov NCT04167514) as a promising non-toxic agent for high-risk aGvHD.
Targeting lymphocyte trafficking
Vedolizumab - lymphocyte trafficking to GvHD target organs is a key event leading to aGvHD. In the lower GI tract, Peyer’s patches (PP) and gut-associated lymphoid tissue (GALT) are the targets for alloreactive CD8+ T cells. Guttropic CD8+ cells express high levels of integrin 7 (47) that binds its ligand mucosal addressin cell adhesion molecule 1 (MAdCAM 1) in the PP and GALT. Vedolizumab, a humanized mAb, targets 47 integrins and prevents Teff trafficking to the gut. A small proof of concept study (n=6) demonstrated responses in all patients with SR lower GI GvHD. In an international, retrospective review to evaluate the off-label use of vedolizumab (n=29), ORR was 64% and OS at 6 months was 54%.95 CMV reactivation and Clostridium difficile colitis were noted. Natalizumab, a selective 4 subunit adhesion molecule inhibitor was studied in a phase II study with a response rate of approximately 30%.96 Vedolizumab is being studied in larger prophylactic (clinicaltrials.gov NCT03657160) and therapeutic (clinicaltrials.gov NCT02993783) trials for aGvHD.
Targeting immunologic tolerance
Extracorporeal photochemotherapy - extracorporeal photochemotherapy (ECP) has been used for cGvHD for decades, and more recently for aGvHD with some suc- cess. Although the mechanism by which ECP improves GvHD is a matter of debate, its immunomodulatory effects include Treg upregulation, a change from Th1 to Th2 cytokine profile, as well as modulation of APC.97 Importantly ECP may not result in additional immunosuppression in GvHD patients. In a RCT evaluating ECP in cGvHD therapy, there was no increased risk of infection in the ECP arm,98 which, if also true in the aGvHD setting, would be a major benefit. Initially evaluated in pediatric cohorts, ECP resulted in a response rate of 67% in a small study of adult aGvHD.99 In another small ECP study (n=23), CR was achieved in 70%, 42% and 0% of patients with grades II, III and IV aGvHD respectively. With regards to end-organ based efficacy, complete responses were seen in 66%, 27% and 40% of patients with skin, liver and gut involvement, respectively.100 However, the data are limited to small non-randomized studies and efficacy needs to be confirmed.
Finally, another novel therapeutic intervention for aGvHD, fecal microbiota transplantation (FMT), is further discussed in the section on microbiome and the role of dysbiosis.
These therapeutic strategies, along with the level of evidence supporting them, are summarized in Table 2.
Finally, we highlight the emerging role of early prognostic biomarkers as well as the potentially critical role of the intestinal microbiome in influencing aGvHD and transplant outcomes.
Novel biomarkers in acute graft-versus-host disease
Identifying predictive biomarkers for aGvHD development and/or prognosis has been an important question in the field. Hypothesis-driven markers based on the pathophysiology of aGvHD include acute phase reactants (e.g., IL-6, C-reactive protein [CRP]), Th1 cytokines (e.g., IL-12, IL-18), anti-inflammatory cytokines (e.g., IL-10, TGF-), other circulating markers (e.g., IL-8, HGF, cytokeratin-18, CD30), and lymphocyte trafficking molecules (e.g., CXCL10, CCL8) have been evaluated with limited success. In contrast, unbiased marker discovery typically involved proteomic screening of GvHD and non-GvHD samples. In a discovery study from Ann Arbor, IL-2R, TNFR1, HGF and IL-8 identified early after aGvHD onset demonstrated impressive accuracy confirmed in a larger validation set.101 Another panel comprising IL-2R, TNFR1 and elafin has also been validated.102
The Mount Sinai Acute GvHD International Consortium (MAGIC) was established to identify potential biomarkers to risk stratify GvHD. Investigators tested previously identified biomarkers, namely suppressor of tumorigenicity-2 (ST2) and regenerating islet-derived protein 3-(REG3), in SR aGvHD and found that marker elevation 7 days after aGvHD was a better predictor of NRM than the Minnesota clinical risk score.103 Another approach has evaluated markers of endothelial toxicity documenting follistatin and endoglin as being associated with higher rates of grade IIIIV aGvHD and NRM.104
The appropriate clinical application of these biomarker panels is a complex issue, with the underlying principle that test results should change therapy and, ideally, outcome. Risk-adapted approaches have proposed using these panels in two different ways: (i) early post-transplant prior to diagnosis of aGvHD, with allocation of high-risk patients to novel GvHD trials; and (ii) after the diagnosis of aGvHD, to stratify patients at high NRM risk and risk-adapt therapy accordingly.
Future clinical trials that use biomarkers to risk stratify aGvHD patients for eligibility or therapy will be important to prospectively evaluate their utility as a first step to their broader use in clinical practice.
The microbiome in acute graft-versus-host disease
The many micro-organisms which constitute the human gut are collectively called the intestinal microbiota while their genetic make-up has often been referred to as the ‘microbiome’.105 Diversity is a hallmark of the healthy gut microbiome. There is a growing appreciation of the role of the microbiome in various health and disease states. In HSCT, the loss of microbiota diversity (dysbiosis) has been associated with the risk of aGvHD.105
This association between aGvHD and gut dysbiosis relates to immunologic and metabolic imbalances in the gut wrought by HSCT, with loss of diversity of the microbiome. Under normal circumstances, diverse gut commensals result in healthy tissue immune cells, including recruitment of Treg cells, secretion of TGF-and IL-10, as well as TH17 cells secreting IL-17 and IL-22.106 Another protective immune response modulated by gut bacteria relates to their production of short chain fatty acids (SCFA), a nutritional source for intestinal epithelial cells. Disruption of the intestinal microbiome triggered by conditioning chemoradiotherapy and antibiotic use during transplantation results in overgrowth of bacteria (e.g., enterococci, Proteus spp.), and reduction in firmicutes (e.g., Blautia spp.), which generally are producers of SCFA, is considered an inciting stimulus for GvHD.107
Further studies are needed to develop actionable targets in this arena. It is a complex endeavor given the variations in gut microbiome over different geographical areas, across transplant strategies, and inpatient and outpatient settings. It is heartening that a recent study from four international centers showed that the patterns of loss of microbiome diversity during HSCT was similar across countries, and that lower diversity at time of neutrophil engraftment was associated with higher mortality.108 A large biorepository of stool samples along with blood and other samples is being built as the correlative arm of the large BMT CTN RCT 1703 (Mi-immune) study in which the biology of the microbiome and correlations with transplant outcomes will be interrogated.
Fecal microbiota transplant as an effort to repopulate the gut with normal gut flora has been proposed as a means to control aGvHD, based on data limited to pilot studies109 and limited case series.110 Infection with extended spectrum lactamase (ESBL) producing Escherichia coli bacteria has been reported in at least two transplant patients post allogeneic transplantation who underwent FMT, one of whom died.111 Hence the safety and efficacy of FMT in aGvHD remains an open question.
To summarize, aGvHD remains an important problem in HSCT. However, where effective treatment options had previously been very limited, there are now multiple exciting translational advances.
In the arena of prevention, PTCy-based GvHD prophylaxis has been a significant advance and some selective methods of T-cell depletion and modulation of co-stimulatory pathways appear promising. In the therapeutic arena, cytokine targeting with Rux is an exciting novel therapy for SR-aGvHD, while immunomodulatory strategies (e.g., ECP, AAT) offer therapeutic potential without immunosuppressive toxicity, and strategies targeting lymphocyte trafficking and inhibition of key canonical pathways (e.g., Notch) offer future potential. For the more long-term future, the importance of the gut microbiome in aGvHD is becoming increasingly apparent, and offers an opportunity for future therapeutic targeting (e.g., probiotics, metabolic modifications).
A long-term rational approach to aGvHD care would involve precision prognostics pre- and peri-transplantation (e.g., plasma biomarkers, microbiota dysbiosis, etc.) to select patients for innovative GvHD preventive strategies, as well as the early identification of high-risk patients at aGvHD onset, for novel treatment trials, ideally avoiding additional immunologic dysfunction or impairing GvL.
- Received May 3, 2020
- Accepted July 29, 2020
- Zeiser R, Blazar BR. Acute graft-versus-host disease - biologic process, prevention, and therapy. N Engl J Med. 2017; 377(22):2167-2179. https://doi.org/10.1056/NEJMra1609337PubMedPubMed CentralGoogle Scholar
- Antin JH, Ferrara JL. Cytokine dysregulation and acute graft-versus-host disease. Blood. 1992; 80(12):2964-2968. https://doi.org/10.1182/blood.V80.12.2964.2964PubMedGoogle Scholar
- Ferrara JLM, Levine JE, Reddy P, Holler E.. Graft-versus-host disease. Lancet. 2009; 373(9674):1550-1561. https://doi.org/10.1016/S0140-6736(09)60237-3PubMedPubMed CentralGoogle Scholar
- Zhang Y, Sandy AR, Wang J. Notch signaling is a critical regulator of allogeneic CD4+ T-cell responses mediating graft-versus- host disease. Blood. 2011; 117(1):299-308. https://doi.org/10.1182/blood-2010-03-271940PubMedPubMed CentralGoogle Scholar
- Tran IT, Sandy AR, Carulli AJ. Blockade of individual Notch ligands and receptors controls graft-versus-host disease. J Clin Invest. 2013; 123(4):1590-1604. https://doi.org/10.1172/JCI65477PubMedPubMed CentralGoogle Scholar
- Sakaguchi S, Yamaguchi T, Nomura T, Ono M.. Regulatory T cells and immune tolerance. Cell. 2008; 133(5):775-787. https://doi.org/10.1016/j.cell.2008.05.009PubMedGoogle Scholar
- Krenger W, Ferrara JLM. Graft-versus-host disease and the Th1/Th2 paradigm. Immunol Res. 1996; 15(1):50-73. https://doi.org/10.1007/BF02918284PubMedGoogle Scholar
- Carlson MJ, West ML, Coghill JM, Panoskaltsis-Mortari A, Blazar BR, Serody JS. In vitro-differentiated TH17 cells mediate lethal acute graft-versus-host disease with severe cutaneous and pulmonary pathologic manifestations. Blood. 2009; 113(6):1365-1374. https://doi.org/10.1182/blood-2008-06-162420PubMedPubMed CentralGoogle Scholar
- Yu Y, Wang D, Liu C. Prevention of GVHD while sparing GVL effect by targeting Th1 and Th17 transcription factor T-bet and RORγt in mice. Blood. 2011; 118(18):5011-5020. https://doi.org/10.1182/blood-2011-03-340315PubMedPubMed CentralGoogle Scholar
- Jagasia M, Arora M, Flowers MED. Risk factors for acute GVHD and survival after hematopoietic cell transplantation. Blood. 2012; 119(1):296-307. https://doi.org/10.1182/blood-2011-06-364265PubMedPubMed CentralGoogle Scholar
- Couriel DR, Saliba RM, Giralt S. Acute and chronic graft-versus-host disease after ablative and nonmyeloablative conditioning for allogeneic hematopoietic transplantation. Biol Blood Marrow Transplant. 2004; 10(3):178-185. https://doi.org/10.1016/j.bbmt.2003.10.006PubMedGoogle Scholar
- Sorror ML, Maris MB, Storer B. Comparing morbidity and mortality of HLA-matched unrelated donor hematopoietic cell transplantation after nonmyeloablative and myeloablative conditioning: influence of pretransplantation comorbidities. Blood. 2004; 104(4):961-968. https://doi.org/10.1182/blood-2004-02-0545PubMedGoogle Scholar
- Scott BL, Pasquini MC, Logan BR. Myeloablative versus reduced-intensity hematopoietic cell transplantation for acute myeloid leukemia and myelodysplastic syndromes. J Clin Oncol. 2017; 35(11):1154-1161. https://doi.org/10.1200/JCO.2016.70.7091PubMedPubMed CentralGoogle Scholar
- Wilhelm K, Ganesan J, Müller T. Graftversus- host disease is enhanced by extracellular ATP activating P2X7R. Nat Med. 2010; 16(12):1434-1438. https://doi.org/10.1038/nm.2242PubMedGoogle Scholar
- Lee SJ, Klein J, Haagenson M. High-resolution donor-recipient HLA matching contributes to the success of unrelated donor marrow transplantation. Blood. 2007; 110(13):4576-4583. https://doi.org/10.1182/blood-2007-06-097386PubMedGoogle Scholar
- Verneris MR, Lee SJ, Ahn KW. HLA mismatch is associated with worse outcomes after unrelated donor reduced-intensity conditioning hematopoietic cell transplantation: an analysis from the Center for International Blood and Marrow Transplant Research. Biol Blood Marrow Transplant. 2015; 21(10):1783-1789. https://doi.org/10.1016/j.bbmt.2015.05.028PubMedPubMed CentralGoogle Scholar
- Bolaños-Meade J, Reshef R, Fraser R. Three prophylaxis regimens (tacrolimus, mycophenolate mofetil, and cyclophosphamide; tacrolimus, methotrexate, and bortezomib; or tacrolimus, methotrexate, and maraviroc) versus tacrolimus and methotrexate for prevention of graft-versushost disease with haemopoietic cell transplantation with reduced-intensity conditioning: a randomised phase 2 trial with a nonrandomised contemporaneous control group (BMT CTN 1203). Lancet Haematol. 2019; 6(3):e132-e143. https://doi.org/10.1016/S2352-3026(18)30221-7PubMedPubMed CentralGoogle Scholar
- Nykolyszyn C, Granata A, Pagliardini T. Posttransplantation cyclophosphamide vs. antithymocyte globulin as GVHD prophylaxis for mismatched unrelated hematopoietic stem cell transplantation. Bone Marrow Transplant. 2020; 55(2):349-355. https://doi.org/10.1038/s41409-019-0682-2PubMedGoogle Scholar
- Stem Cell Trialists’ Collaborative Group. Allogeneic peripheral blood stem-cell compared with bone marrow transplantation in the management of hematologic malignancies: an individual patient data meta-analysis of nine randomized trials. J Clin Oncol. 2005; 23(22):5074-5087. https://doi.org/10.1200/JCO.2005.09.020PubMedPubMed CentralGoogle Scholar
- Anasetti C, Logan BR, Lee SJ. Peripheral-blood stem cells versus bone marrow from unrelated donors. N Engl J Med. 2012; 367(16):1487-1496. https://doi.org/10.1056/NEJMoa1203517PubMedPubMed CentralGoogle Scholar
- Chen Y-B, Wang T, Hemmer MT. GVHD after umbilical cord blood transplantation for acute leukemia: an analysis of risk factors and effect on outcomes. Bone Marrow Transplant. 2017; 52(3):400-408. https://doi.org/10.1038/bmt.2016.265PubMedPubMed CentralGoogle Scholar
- Nash RA, Antin JH, Karanes C. Phase 3 study comparing methotrexate and tacrolimus with methotrexate and cyclosporine for prophylaxis of acute graftversus- host disease after marrow transplantation from unrelated donors. Blood. 2000; 96(6):2062-2068. Google Scholar
- Ratanatharathorn V, Nash RA, Przepiorka D. Phase III study comparing methotrexate and tacrolimus (prograf, FK506) with methotrexate and cyclosporine for graft-versus- host disease prophylaxis after HLAidentical sibling bone marrow transplantation. Blood. 1998; 92(7):2303-2314. Google Scholar
- Bacigalupo A. ATG in allogeneic stem cell transplantation: standard of care in 2017? Point. Blood Adv. 2017; 1(9):569-572. https://doi.org/10.1182/bloodadvances.2016001560PubMedPubMed CentralGoogle Scholar
- Bacigalupo A, Lamparelli T, Bruzzi P. Antithymocyte globulin for graft-versus-host disease prophylaxis in transplants from unrelated donors: 2 randomized studies from Gruppo Italiano Trapianti Midollo Osseo (GITMO). Blood. 2001; 98(10):2942-2947. https://doi.org/10.1182/blood.V98.10.2942PubMedGoogle Scholar
- Bacigalupo A, Lamparelli T, Barisione G. Thymoglobulin prevents chronic graftversus- host disease, chronic lung dysfunction, and late transplant-related mortality: long-term follow-up of a randomized trial in patients undergoing unrelated donor transplantation. Biol Blood Marrow Transplant. 2006; 12(5):560-565. https://doi.org/10.1016/j.bbmt.2005.12.034PubMedGoogle Scholar
- Finke J, Bethge WA, Schmoor C. Standard graft-versus-host disease prophylaxis with or without anti-T-cell globulin in haematopoietic cell transplantation from matched unrelated donors: a randomised, open-label, multicentre phase 3 trial. Lancet Oncol. 2009; 10(9):855-864. https://doi.org/10.1016/S1470-2045(09)70225-6Google Scholar
- Socié G, Schmoor C, Bethge WA. Chronic graft-versus-host disease: long-term results from a randomized trial on graft-versus- host disease prophylaxis with or without anti–T-cell globulin ATG-Fresenius. Blood. 2011; 117(23):6375-6382. https://doi.org/10.1182/blood-2011-01-329821PubMedGoogle Scholar
- Kröger N, Solano C, Wolschke C. Antilymphocyte globulin for prevention of chronic graft-versus-host disease. N Engl J Med. 2016; 374(1):43-53. https://doi.org/10.1056/NEJMoa1506002PubMedGoogle Scholar
- Soiffer RJ, Kim HT, McGuirk J. Prospective, randomized, double-blind, phase III clinical trial of anti–T-lymphocyte globulin to assess impact on chronic graftversus- host disease–free survival in patients undergoing HLA-matched unrelated myeloablative hematopoietic cell transplantation. J Clin Oncol. 2017; 35(36):4003-4011. https://doi.org/10.1200/JCO.2017.75.8177PubMedGoogle Scholar
- Podgorny PJ, Ugarte-Torres A, Liu Y, Williamson TS, Russell JA, Storek J.. High rabbit-antihuman thymocyte globulin levels are associated with low likelihood of graftvs- host disease and high likelihood of posttransplant lymphoproliferative disorder. Biol Blood Marrow Transplant. 2010; 16(7):915-926. https://doi.org/10.1016/j.bbmt.2010.02.027PubMedGoogle Scholar
- Admiraal R, Nierkens S, de Witte MA. Association between anti-thymocyte globulin exposure and survival outcomes in adult unrelated haemopoietic cell transplantation: a multicentre, retrospective, pharmacodynamic cohort analysis. Lancet Haematol. 2017; 4(4):e183-e191. https://doi.org/10.1016/S2352-3026(17)30029-7Google Scholar
- Luznik L, O’Donnell PV, Symons HJ. HLA-haploidentical bone marrow transplantation for hematologic malignancies using nonmyeloablative conditioning and highdose, posttransplantation cyclophosphamide. Biol Blood Marrow Transplant. 2008; 14(6):641-650. https://doi.org/10.1016/j.bbmt.2008.03.005PubMedPubMed CentralGoogle Scholar
- Wachsmuth LP, Patterson MT, Eckhaus MA, Venzon DJ, Gress RE, Kanakry CG. Posttransplantation cyclophosphamide prevents graft-versus-host disease by inducing alloreactive T cell dysfunction and suppression. J Clin Invest. 2019; 129(6):2357-2373. https://doi.org/10.1172/JCI124218PubMedPubMed CentralGoogle Scholar
- De Jong CN, Meijer E, Bakunina K. Post-transplantation cyclophosphamide after allogeneic hematopoietic stem cell transplantation: results of the prospective randomized HOVON-96 trial in recipients of matched related and unrelated donors. Blood. 2019; 134(Suppl 1):1. https://doi.org/10.1182/blood-2019-124659PubMedGoogle Scholar
- Slavik JM, Lim DG, Burakoff SJ, Hafler DA. Uncoupling p70(s6) kinase activation and proliferation: rapamycin-resistant proliferation of human CD8(+) T lymphocytes. J Immunol. 2001; 166(5):3201-3209. https://doi.org/10.4049/jimmunol.166.5.3201PubMedGoogle Scholar
- Battaglia M, Stabilini A, Roncarolo M-G. Rapamycin selectively expands CD4+CD25+FoxP3+ regulatory T cells. Blood. 2005; 105(12):4743-4748. https://doi.org/10.1182/blood-2004-10-3932PubMedGoogle Scholar
- Cutler C, Logan B, Nakamura R. Tacrolimus/sirolimus vs tacrolimus/methotrexate as GVHD prophylaxis after matched, related donor allogeneic HCT. Blood. 2014; 124(8):1372-1377. https://doi.org/10.1182/blood-2014-04-567164PubMedPubMed CentralGoogle Scholar
- Armand P, Kim HT, Sainvil M-M. The addition of sirolimus to the graft-versus-host disease prophylaxis regimen in reduced intensity allogeneic stem cell transplantation for lymphoma: a multicentre randomized trial. Br J Haematol. 2016; 173(1):96-104. https://doi.org/10.1111/bjh.13931PubMedPubMed CentralGoogle Scholar
- Sandmaier BM, Kornblit B, Storer BE. Addition of sirolimus to standard cyclosporine plus mycophenolate mofetilbased graft-versus-host disease prophylaxis for patients after unrelated non-myeloablative haemopoietic stem cell transplantation: a multicentre, randomised, phase 3 trial. Lancet Haematol. 2019; 6(8):e409-e418. https://doi.org/10.1016/S2352-3026(19)30088-2PubMedPubMed CentralGoogle Scholar
- Perkins J, Field T, Kim J. A randomized phase II trial comparing tacrolimus and mycophenolate mofetil to tacrolimus and methotrexate for acute graft-versus-host disease prophylaxis. Biol Blood Marrow Transplant. 2010; 16(7):937-947. https://doi.org/10.1016/j.bbmt.2010.01.010PubMedGoogle Scholar
- Cutler C, Stevenson K, Kim HT. Sirolimus is associated with veno-occlusive disease of the liver after myeloablative allogeneic stem cell transplantation. Blood. 2008; 112(12):4425-4431. https://doi.org/10.1182/blood-2008-07-169342PubMedPubMed CentralGoogle Scholar
- Cutler C, Henry NL, Magee C. Sirolimus and thrombotic microangiopathy after allogeneic hematopoietic stem cell transplantation. Biol Blood Marrow Transplant. 2005; 11(7):551-557. https://doi.org/10.1016/j.bbmt.2005.04.007PubMedGoogle Scholar
- Solomon SR, Sanacore M, Zhang X. Calcineurin inhibitor-free graft-versus-host disease prophylaxis with post-transplantation cyclophosphamide and brief-course sirolimus following reduced-intensity peripheral blood stem cell transplantation. Biol Blood Marrow Transplant. 2014; 20(11):1828-1834. https://doi.org/10.1016/j.bbmt.2014.07.020PubMedGoogle Scholar
- Gooptu M, Kim HT, Howard A. Effect of sirolimus on immune reconstitution following myeloablative allogeneic stem cell transplantation: an ancillary analysis of a randomized controlled trial comparing tacrolimus/sirolimus and tacrolimus/methotrexate (Blood and Marrow Transplant Clinical Trials Network/BMT CTN 0402). Biol Blood Marrow Transplant. 2019; 25(11):2143-2151. https://doi.org/10.1016/j.bbmt.2019.06.029PubMedPubMed CentralGoogle Scholar
- Tkachev V, Furlan SN, Watkins B. Combined OX40L and mTOR blockade controls effector T cell activation while preserving Treg reconstitution after transplant. Sci Transl Med. 2017; 9(408):eaan3085. https://doi.org/10.1126/scitranslmed.aan3085PubMedPubMed CentralGoogle Scholar
- Reinherz EL, Geha R, Rappeport JM. Reconstitution after transplantation with T-lymphocyte-depleted HLA haplotypemismatched bone marrow for severe combined immunodeficiency. Proc Natl Acad Sci U S A. 1982; 79(19):6047-6051. https://doi.org/10.1073/pnas.79.19.6047PubMedPubMed CentralGoogle Scholar
- Soiffer RJ, Murray C, Mauch P. Prevention of graft-versus-host disease by selective depletion of CD6-positive T lymphocytes from donor bone marrow. J Clin Oncol. 1992; 10(7):1191-1200. https://doi.org/10.1200/JCO.19188.8.131.521PubMedGoogle Scholar
- Drobyski WR, Ash RC, Casper JT. Effect of T-cell depletion as graft-versus-host disease prophylaxis on engraftment, relapse, and disease-free survival in unrelated marrow transplantation for chronic myelogenous leukemia. Blood. 1994; 83(7):1980-1987. https://doi.org/10.1182/blood.V83.7.1980.1980PubMedGoogle Scholar
- Champlin RE, Passweg JR, Zhang MJ. T-cell depletion of bone marrow transplants for leukemia from donors other than HLAidentical siblings: advantage of T-cell antibodies with narrow specificities. Blood. 2000; 95(12):3996-4003. Google Scholar
- Antin JH, Bierer BE, Smith BR. Selective depletion of bone marrow T lymphocytes with anti-CD5 monoclonal antibodies: effective prophylaxis for graft-versus-host disease in patients with hematologic malignancies. Blood. 1991; 78(8):2139-2149. https://doi.org/10.1182/blood.V78.8.2139.2139PubMedGoogle Scholar
- Wagner JE, Donnenberg AD, Noga SJ. Lymphocyte depletion of donor bone marrow by counterflow centrifugal elutriation: results of a phase I clinical trial. Blood. 1988; 72(4):1168-1176. https://doi.org/10.1182/blood.V72.4.1168.1168PubMedGoogle Scholar
- Wagner JE, Thompson JS, Carter SL, Kernan NA, Unrelated donor marrow transplantation trial. Effect of graft-versus-host disease prophylaxis on 3-year disease-free survival in recipients of unrelated donor bone marrow (T-cell Depletion Trial): a multi-centre, randomised phase II-III trial. Lancet. 2005; 366(9487):733-741. https://doi.org/10.1016/S0140-6736(05)66996-6Google Scholar
- Horowitz MM, Gale RP, Sondel PM. Graft-versus-leukemia reactions after bone marrow transplantation. Blood. 1990; 75(3):555-562. https://doi.org/10.1182/blood.V75.3.555.555PubMedGoogle Scholar
- Devine SM, Carter S, Soiffer RJ. Low risk of chronic graft versus host disease and relapse associated with T-cell depleted peripheral blood stem cell transplantation for acute myeloid leukemia in first remission: results of the Blood and Marrow Transplant Clinical Trials Network (BMT CTN) Protocol 0303. Biol Blood Marrow Transplant. 2011; 17(9):1343-1351. https://doi.org/10.1016/j.bbmt.2011.02.002PubMedPubMed CentralGoogle Scholar
- Pasquini MC, Devine S, Mendizabal A. Comparative outcomes of donor graft CD34+ selection and immune suppressive therapy as graft-versus-host disease prophylaxis for patients with acute myeloid leukemia in complete remission undergoing HLA-matched sibling allogeneic hematopoietic cell transplantation. J Clin Oncol. 2012; 30(26):3194-3201. https://doi.org/10.1200/JCO.2012.41.7071PubMedPubMed CentralGoogle Scholar
- Daniele N, Scerpa MC, Caniglia M. Transplantation in the onco-hematology field: focus on the manipulation of and T cells. Pathol Res Pract. 2012; 208(2):67-73. https://doi.org/10.1016/j.prp.2011.10.006PubMedGoogle Scholar
- Locatelli F, Merli P, Pagliara D. Outcome of children with acute leukemia given HLA-haploidentical HSCT after Tcell and B-cell depletion. Blood. 2017; 130(5):677-685. https://doi.org/10.1182/blood-2017-04-779769PubMedGoogle Scholar
- Distler E, Bloetz A, Albrecht J. Alloreactive and leukemia-reactive T cells are preferentially derived from naïve precursors in healthy donors: implications for immunotherapy with memory T cells. Haematologica. 2011; 96(7):1024-1032. https://doi.org/10.3324/haematol.2010.037481PubMedPubMed CentralGoogle Scholar
- Teschner D, Distler E, Wehler D. Depletion of naive T cells using clinical grade magnetic CD45RA beads: a new approach for GVHD prophylaxis. Bone Marrow Transplant. 2014; 49(1):138-144. https://doi.org/10.1038/bmt.2013.114PubMedGoogle Scholar
- Bleakley M, Heimfeld S, Jones LA. Engineering human peripheral blood stem cell grafts that are depleted of naïve T cells and retain functional pathogen-specific memory T cells. Biol Blood Marrow Transplant. 2014; 20(5):705-716. https://doi.org/10.1016/j.bbmt.2014.01.032PubMedPubMed CentralGoogle Scholar
- Bleakley M, Heimfeld S, Loeb KR. Outcomes of acute leukemia patients transplanted with naive T cell-depleted stem cell grafts. J Clin Invest. 2015; 125(7):2677-2689. https://doi.org/10.1172/JCI81229PubMedPubMed CentralGoogle Scholar
- Poon LM, Linn YC, Tan PL. HLA-haploidentical hematopoietic cell transplantation after TCR-Aand CD45RA+ depletion following reduced intensity conditioning in adults and children with hematological malignancies - two-year follow-up of multicenter study in Singapore. Blood. 2019; 134(Suppl 1)https://doi.org/10.1182/blood-2019-128014PubMedGoogle Scholar
- Ng CT, Ampudia J, Soiffer RJ, Ritz J, Connelly S.. Itolizumab as a potential therapeutic for the prevention and treatment of graft vs host disease. Blood. 2019; 134(Suppl 1):5603. https://doi.org/10.1182/blood-2019-122787PubMedGoogle Scholar
- Aversa F, Pierini A, Ruggeri L, Martelli MF, Velardi A.. The evolution of T cell depleted haploidentical transplantation. Front Immunol. 2019; 10:2769. https://doi.org/10.3389/fimmu.2019.02769PubMedPubMed CentralGoogle Scholar
- Rachamim N, Gan J, Segall H. Tolerance induction by “megadose” hematopoietic transplants: donor-type human CD34 stem cells induce potent specific reduction of host anti-donor cytotoxic T lymphocyte precursors in mixed lymphocyte culture. Transplantation. 1998; 65(10):1386-1393. https://doi.org/10.1097/00007890-199805270-00017PubMedGoogle Scholar
- Di Ianni M, Falzetti F, Carotti A. Tregs prevent GVHD and promote immune reconstitution in HLA-haploidentical transplantation. Blood. 2011; 117(14):3921-3928. https://doi.org/10.1182/blood-2010-10-311894PubMedGoogle Scholar
- Taylor PA, Lees CJ, Blazar BR. The infusion of ex vivo activated and expanded CD4(+)CD25(+) immune regulatory cells inhibits graft-versus-host disease lethality. Blood. 2002; 99(10):3493-3499. https://doi.org/10.1182/blood.V99.10.3493PubMedGoogle Scholar
- Parmar S, Liu X, Najjar A. Ex vivo fucosylation of third-party human regulatory T cells enhances anti–graft-versus-host disease potency in vivo. Blood. 2015; 125(9):1502-1506. https://doi.org/10.1182/blood-2014-10-603449PubMedPubMed CentralGoogle Scholar
- Copsel SN, Barreras H, Lightbourn CO. IL-2/IL-2R, TL1A/TNFRSF25 or their combined stimulation results in distinct CD4+FoxP3+ regulatory T cell phenotype and suppressive function. Biol Blood Marrow Transplant. 2020; 26(3):S169. https://doi.org/10.1016/j.bbmt.2019.12.030Google Scholar
- Brunstein CG, Miller JS, Cao Q. Infusion of ex vivo expanded T regulatory cells in adults transplanted with umbilical cord blood: safety profile and detection kinetics. Blood. 2011; 117(3):1061-1070. https://doi.org/10.1182/blood-2010-07-293795PubMedPubMed CentralGoogle Scholar
- Mavers M, Maas-Bauer K, Negrin RS. Invariant natural killer T cells as suppressors of graft-versus-host disease in allogeneic hematopoietic stem cell transplantation. Front Immunol. 2017; 8:900. https://doi.org/10.3389/fimmu.2017.00900PubMedPubMed CentralGoogle Scholar
- Pillai AB, George TI, Dutt S, Teo P, Strober S.. Host NKT cells can prevent graft-versushost disease and permit graft antitumor activity after bone marrow transplantation. J Immunol. 2007; 178(10):6242-6251. https://doi.org/10.4049/jimmunol.178.10.6242PubMedGoogle Scholar
- Pillai AB, George TI, Dutt S, Strober S.. Host natural killer T cells induce an interleukin-4- dependent expansion of donor CD4+CD25+Foxp3+ T regulatory cells that protects against graft-versus-host disease. Blood. 2009; 113(18):4458-4467. https://doi.org/10.1182/blood-2008-06-165506PubMedPubMed CentralGoogle Scholar
- Lowsky R, Takahashi T, Liu YP. Protective conditioning for acute graft-versus- host disease. N Engl J Med. 2005; 353(13):1321-1331. https://doi.org/10.1056/NEJMoa050642PubMedGoogle Scholar
- Duramad O, Laysang A, Li J, Nguyen N, Ishii Y, Namikawa R.. A liposomal formulation of KRN7000 (RGI-2001) potently reduces GvHD lethality through the expansion of CD4+Foxp3+ regulatory T cells in murine models. Blood. 2008; 112(11):3500. https://doi.org/10.1182/blood.V112.11.3500.3500PubMedGoogle Scholar
- Chen Y-B, Efebera YA, Johnston L. Increased Foxp3+Helios+ regulatory T cells and decreased acute graft-versus-host disease after allogeneic bone marrow transplantation in patients receiving sirolimus and RGI-2001, an activator of invariant natural killer T cells. Biol Blood Marrow Transplant. 2017; 23(4):625-634. https://doi.org/10.1016/j.bbmt.2017.01.069PubMedPubMed CentralGoogle Scholar
- Tawara I, Koyama M, Liu C. Interleukin-6 modulates graft-versus-host responses after experimental allogeneic bone marrow transplantation. Clin Cancer Res. 2011; 17(1):77-88. https://doi.org/10.1158/1078-0432.CCR-10-1198PubMedPubMed CentralGoogle Scholar
- Drobyski WR, Szabo A, Zhu F. Tocilizumab, tacrolimus and methotrexate for the prevention of acute graft-versus-host disease: low incidence of lower gastrointestinal tract disease. Haematologica. 2018; 103(4):717-727. https://doi.org/10.3324/haematol.2017.183434PubMedPubMed CentralGoogle Scholar
- Kennedy GA, Tey S-K, Curley C. Results of a phase III double-blind study of the addition of tocilizumab vs. placebo to cyclosporin/methotrexate GvHD prophylaxis after HLA-matched allogeneic stem cell transplantation. Blood. 2019; 134(Suppl 1):368. https://doi.org/10.1182/blood-2019-126285PubMedGoogle Scholar
- Blazar BR, Taylor PA, Linsley PS, Vallera DA. In vivo blockade of CD28/CTLA4: B7/BB1 interaction with CTLA4-Ig reduces lethal murine graft-versus-host disease across the major histocompatibility complex barrier in mice. Blood. 1994; 83(12):3815-3825. https://doi.org/10.1182/blood.V83.12.3815.3815PubMedGoogle Scholar
- Watkins B, Qayed M, Bratrude B. T cell costimulation blockade with abatacept nearly eliminates early severe acute graft versus host disease after HLA-mismatched (7/8 HLA matched) unrelated donor transplant, with a favorable impact on disease-free and overall survival. Blood. 2017; 130(Suppl 1):212. Google Scholar
- Watkins BK, Tkachev V, Furlan SN. CD28 blockade controls T cell activation to prevent graft-versus-host disease in primates. J Clin Invest. 2018; 128(9):3991-4007. https://doi.org/10.1172/JCI98793PubMedPubMed CentralGoogle Scholar
- MacMillan ML, Weisdorf DJ, Wagner JE. Response of 443 patients to steroids as primary therapy for acute graft-versus-host disease: comparison of grading systems. Biol Blood Marrow Transplant. 2002; 8(7):387-394. https://doi.org/10.1053/bbmt.2002.v8.pm12171485PubMedGoogle Scholar
- Van Lint MT, Uderzo C, Locasciulli A. Early treatment of acute graft-versus-host disease with high- or low-dose 6-methylprednisolone: a multicenter randomized trial from the Italian Group for Bone Marrow Transplantation. Blood. 1998; 92(7):2288-2293. Google Scholar
- Jagasia M, Zeiser R, Arbushites M, Delaite P, Gadbaw B, von Bubnoff N. Ruxolitinib for the treatment of patients with steroidrefractory GVHD: an introduction to the REACH trials. Immunotherapy. 2018; 10(5):391-402. https://doi.org/10.2217/imt-2017-0156PubMedGoogle Scholar
- Choi J, Ziga ED, Ritchey J. IFNR signaling mediates alloreactive T-cell trafficking and GVHD. Blood. 2012; 120(19):4093-4103. https://doi.org/10.1182/blood-2012-01-403196PubMedPubMed CentralGoogle Scholar
- Spoerl S, Mathew NR, Bscheider M. Activity of therapeutic JAK 1/2 blockade in graft-versus-host disease. Blood. 2014; 123(24):3832-3842. https://doi.org/10.1182/blood-2013-12-543736PubMedGoogle Scholar
- Zeiser R, Burchert A, Lengerke C. Ruxolitinib in corticosteroid-refractory graftversus- host disease after allogeneic stem cell transplantation: a multicenter survey. Leukemia. 2015; 29(10):2062-2068. https://doi.org/10.1038/leu.2015.212PubMedPubMed CentralGoogle Scholar
- Jagasia M, Ali H, Schroeder MA. Ruxolitinib in combination with corticosteroids for the treatment of steroid-refractory acute graft-vs-host disease: results from the phase 2 REACH1 trial. Biol Blood Marrow Transplant. 2019; 25(3):S52. https://doi.org/10.1016/j.bbmt.2018.12.130Google Scholar
- Zeiser R, von Bubnoff N, Butler J. Ruxolitinib for glucocorticoid-refractory acute graft-versus-host disease. N Engl J Med. 2020; 382(19):1800-1810. https://doi.org/10.1056/NEJMoa1917635PubMedGoogle Scholar
- Tawara I, Sun Y, Lewis EC. Alpha-1- antitrypsin monotherapy reduces graft-versus- host disease after experimental allogeneic bone marrow transplantation. Proc Natl Acad Sci U S A. 2012; 109(2):564-569. https://doi.org/10.1073/pnas.1117665109PubMedPubMed CentralGoogle Scholar
- Marcondes AM, Hockenbery D, Lesnikova M. Response of steroid-refractory acute GVHD to 1-antitrypsin. Biol Blood Marrow Transplant. 2016; 22(9):1596-1601. https://doi.org/10.1016/j.bbmt.2016.05.011PubMedGoogle Scholar
- Magenau JM, Goldstein SC, Peltier D. 1-antitrypsin infusion for treatment of steroid-resistant acute graft-versus-host disease. Blood. 2018; 131(12):1372-1379. https://doi.org/10.1182/blood-2017-11-815746PubMedPubMed CentralGoogle Scholar
- Fløisand Y, Lazarevic VL, Maertens J. Safety and effectiveness of vedolizumab in patients with steroid-refractory gastrointestinal acute graft-versus-host disease: a retrospective record review. Biol Blood Marrow Transplant. 2019; 25(4):720-727. https://doi.org/10.1016/j.bbmt.2018.11.013PubMedGoogle Scholar
- Kekre N, Kim HT, Ho VT. Phase II trial of natalizumab (Tysabri®) with corticosteroids as initial treatment of gastrointestinal acute graft versus host disease. Biol Blood Marrow Transplant. 2018; 24(3):S81. https://doi.org/10.1016/j.bbmt.2017.12.649Google Scholar
- Klassen J. The role of photopheresis in the treatment of graft-versus-host disease. Curr Oncol. 2010; 17(2):55-58. https://doi.org/10.3747/co.v17i2.565PubMedPubMed CentralGoogle Scholar
- Flowers MED, Apperley JF, van Besien K. A multicenter prospective phase 2 randomized study of extracorporeal photopheresis for treatment of chronic graft-versus- host disease. Blood. 2008; 112(7):2667-2674. https://doi.org/10.1182/blood-2008-03-141481PubMedGoogle Scholar
- Greinix HT, Volc-Platzer B, Rabitsch W. Successful use of extracorporeal photochemotherapy in the treatment of severe acute and chronic graft-versus-host disease. Blood. 1998; 92(9):3098-3104. https://doi.org/10.1182/blood.V92.9.3098PubMedGoogle Scholar
- Perfetti P, Carlier P, Strada P. Extracorporeal photopheresis for the treatment of steroid refractory acute GVHD. Bone Marrow Transplant. 2008; 42(9):609-617. https://doi.org/10.1038/bmt.2008.221PubMedGoogle Scholar
- Paczesny S, Krijanovski OI, Braun TM. A biomarker panel for acute graft-versushost disease. Blood. 2009; 113(2):273-278. https://doi.org/10.1182/blood-2008-07-167098PubMedPubMed CentralGoogle Scholar
- Paczesny S, Braun T, Lugt MV. A three biomarker panel at days 7 and 14 can predict development of grade II-IV acute graft-versus- host disease. Biol Blood Marrow Transplant. 2011; 17(2):S167. https://doi.org/10.1016/j.bbmt.2010.12.048Google Scholar
- Major-Monfried H, Renteria AS, Pawarode A. MAGIC biomarkers predict longterm outcomes for steroid-resistant acute GVHD. Blood. 2018; 131(25):2846-2855. https://doi.org/10.1182/blood-2018-01-822957PubMedPubMed CentralGoogle Scholar
- Newell LF, Defor TE, Cutler CS. Follistatin and endoglin: potential biomarkers of endothelial damage and non-relapse mortality after myeloablative allogeneic hematopoietic cell transplantation in Blood and Marrow Transplant Clinical Trials Network (BMT CTN) 0402. Biol Blood Marrow Transplant. 2017; 23(3):S73-S74. https://doi.org/10.1016/j.bbmt.2017.01.030Google Scholar
- Staffas A, Burgos da Silva M, van den Brink MRM. The intestinal microbiota in allogeneic hematopoietic cell transplant and graftversus- host disease. Blood. 2017; 129(8):927-933. https://doi.org/10.1182/blood-2016-09-691394PubMedPubMed CentralGoogle Scholar
- Ivanov II, Atarashi K, Manel N. Induction of intestinal Th17 cells by segmented filamentous bacteria. Cell. 2009; 139(3):485-498. https://doi.org/10.1016/j.cell.2009.09.033PubMedPubMed CentralGoogle Scholar
- Jenq RR, Taur Y, Devlin SM. Intestinal blautia is associated with reduced death from graft-versus-host disease. Biol Blood Marrow Transplant. 2015; 21(8):1373-1383. https://doi.org/10.1016/j.bbmt.2015.04.016PubMedPubMed CentralGoogle Scholar
- Peled JU, Gomes ALC, Devlin SM. Microbiota as predictor of mortality in allogeneic hematopoietic-cell transplantation. N Engl J Med. 2020; 382(9):822-834. https://doi.org/10.1056/NEJMoa1900623PubMedPubMed CentralGoogle Scholar
- van Lier YF, Davids M, Haverkate NJE. Fecal microbiota transplantation can cure steroid-refractory intestinal graft-versushost disease. Biol Blood Marrow Transplant. 2019; 25(3):S241. https://doi.org/10.1016/j.bbmt.2018.12.237Google Scholar
- Qi X, Li X, Zhao Y. Treating steroid refractory intestinal acute graft-vs.-host disease with fecal microbiota transplantation: a pilot study. Front Immunol. 2018; 9:2195. https://doi.org/10.3389/fimmu.2018.02195PubMedPubMed CentralGoogle Scholar
- DeFilipp Z, Bloom PP, Torres Soto M. Drug-resistant E. coli bacteremia transmitted by fecal microbiota transplant. N Engl J Med. 2019; 381(21):2043-2050. https://doi.org/10.1056/NEJMoa1910437PubMedGoogle Scholar