Predictive factors and impact of full donor T-cell chimerism after reduced intensity conditioning allogeneic stem cell transplantation

Abstract

This study investigated the kinetics of CD3+-T cell chimerism (TCC) in 102 patients receiving reduced intensity conditioning allogeneic stem cell transplantation (RIC-allo-SCT) from an HLA-identical sibling. Patients with full donor TCC at day 30 had a higher incidence of grade 2–4 acute GVHD compared to patients in mixed TCC (cumulative-incidence, 61% vs. 35%; p=0.01). The delayed establishment of full donor TCC in myeloid malignancies was associated with a higher incidence of relapse (40% vs. 0; p=0.002), suggesting that monitoring of the kinetics of TCC is mandatory after RIC-allo-SCT.

Initial mixed donor/host chimerism has usually been observed in most patients after reduced-intensity conditioning allogeneic stem cell transplantation (RIC-allo-SCT). This retrospective single center study investigated the impact of different factors on the establishment of full donor CD3 T cell chimerism (TCC) in a series of 102 patients receiving RIC allo-SCT. Only patients who were alive at the third month after RIC-allo-SCT were included. All donors were HLA-A-, HLA-B-, and HLA-DR-identical siblings. Eligibility criteria for RIC allo-SCT are detailed elsewhere.1 The RIC regimen included either fludarabine, oral busulfan and low dose anti-thymocyte globulin (ATG 2.5 or 5 mg/kg total dose; Thymoglobulin, Genzyme, Lyon, France),1 or fludarabine (150 mg/m total dose) and low dose irradiation [TBI 2 Gy, or total lymphoid irradiation (TLI), 1.5 Gy total dose] with or without busulfan. Busulfan total dose was 8 mg/kg when ATG was used and 4 mg/kg with TLI. Choice of the RIC regimen type was not based on disease category. Supportive care has been previously reported and was similar during the whole study period.2 Graft-vs.-host disease (GVHD) prophylaxis was given with cyclosporine A (CSA) alone or with CSA and mycophenolate mofetil (MMF). According to protocols, MMF was discontinued at day 35 after allo-SCT. CSA tapering was started between day 80 and 100 if no GVHD appeared. All patients received peripheral blood stem cells mobilized with G-CSF.

TCC (on sorted peripheral blood T lymphocytes) was serially assessed approximately 30, 60 and 90 days after allo-SCT as previously described.3 Mixed T-cell chimerism was defined as between 5 and 94% recipient cells, and full chimerism was defined as the presence of more than 95% donor cells.4 Patients and RIC-allo-SCT characteristics are detailed in Table 1. Kinetics of full donor TCC are shown in Figure 1A. In univariate analysis, none of the patients’ graft, RIC type, or disease characteristics were predictive of establishment of an early full donor TCC at day 30. However, the 31 patients who achieved this experienced a higher incidence of grade 2–4 acute GVHD compared to the 71 patients who were still in mixed TCC at day 30 (cumulative incidence, 61% vs. 35%; p=0.01; Figure 1B). Univariate analysis of predictive factors for full donor TCC at day 90 is shown in Table 1. Diagnosis category (Figure 1C), the RIC regimen type (Figure 1D), a female donor, CD34 stem cell dose, and CD4 T cell dose infused with the graft, were significantly or had a trend towards significant association with full donor TCC at day 90. In the multivariate analysis, a diagnosis other than a myeloid malignancy, was predictive of full TCC at day 90 (p=0.007; OR=3.82;95%CI,1.4–10.1). The delayed full donor TCC in patients with myeloid malignancies (AML, CML, MDS) resulted in a poorer PFS (p=0.06; Figure 1E). This was also confirmed when analysis was restricted to the 24 patients with AML (p=0.017). Interestingly, there were no significant differences between disease risk factors in the AML patients’ sub-group who achieved full donor TCC when compared to the other sub-group. This poorer PFS for myeloid malignancies was due to a higher incidence of relapse (6 relapses/15 patients in mixed TCC; 40%) compared to none in the 26 patients in full TCC (p=0.002; Figure 1F).

Figure 1.Kinetics of T-cell chimerism (TCC) after RIC allo-SCT. (A)% of patients achieving full donor TCC in the first three months after allo-SCT. Patients included in this study were assessed at all time points. (B) Cumulative incidence of grade 2–4 acute GVHD according to the TCC status at the end of the first month after allo-SCT. (C) Kinetics of TCC in the first three months after allo-SCT according to disease category. (D) Kinetics of TCC in the first three months after allo-SCT according to the RIC regimen type. (E) Progression-free survival in patients with myeloid malignancies according to TCC status at the end of the third month after allo-SCT. (F) Cumulative incidence of relapse in patients with myeloid malignancies (AML, CML, MDS) according to TCC status at the end of the third month after allo-SCT.

Table 1.Univariate analysis of risk factors for full donor T-cell chimerism at day 90 after transplantation

In this study, we identified factors influencing TCC following RIC-allo-SCT. The intensity of immunosuppression included in the RIC regimen is likely to influence establishment of TCC. The association between grade 2–4 acute GVHD and early full donor TCC, suggests that close monitoring of TCC may help clinical decision-making, as previously shown.5,6 Disease category appears also to be a predictive factor for full donor TCC. This is delayed in patients with myeloid malignancies, which suggests that TCC is helped by prior exposure to high dose chemotherapy or to multiple lines of chemotherapy.7 Therefore, patients less exposed to chemotherapy would require more intensive conditioning to achieve full donor TCC. This is extremely important because these patients (MDS, CML, AML) were found to have a higher incidence of relapse if they failed to achieve rapid full donor TCC. However, one must also consider the potential role of residual disease. Monitoring CD34 cells chimerism at day 30 may prove to be useful and is currently under investigation. In conclusion, monitoring of the kinetics of donor TCC is mandatory after RIC-allo-SCT, and can improve patients’ outcome.

Acknowledgments

we would like to thank the nursing staff for providing excellent care for our patients, and the physicians of the Hematology and Medical Oncology Departements at the Institut Paoli-Calmettes for their important study contributions and dedicated patient care

Footnotes

• Funding: we also thank the “Association pour la Recherche sur le Cancer (ARC)” (Pole ARECA), the “Ligue Nationale contre le Cancer”, the “Fondation de France”, the “Fondation contre la Leucémie”, the “Agence de Biomédecine”, the “Association Cent pour Sang la Vie”, and the “Association Laurette Fuguain”, for their generous and continuous support for our clinical and research work. Our group is supported by several grants from the French Ministry of Health as part of the “Programme Hospitalier de Recherche Clinique (PHRC)”.