Reduced-intensity conditioning regimen preserves thymic function in the early period after hematopoietic stem cell transplantation

Objective To compare T-cell reconstitution in two groups of patients submitted to allogeneic stem cell transplantation (SCT): those receiving reduced-intensity conditioning (RIC, n = 24) and those receiving myeloablative conditioning (MA, n = 27). Methods Fifty-one consecutive patients undergoing SCT were evaluated. Serial assessments of lymphocyte subsets and T cell receptor excision circles (TRECs) levels were performed using multiparametric flow cytometry and real-time PCR, respectively. Results During the first 6 months posttransplant, total and naïve CD4+ T cell counts were higher after RIC-SCT than after MA-SCT (total CD4+: p = 0.04, p = 0.08, and p = 0.058; naïve CD4+: p = 0.14, p = 0.05, and p = 0.01 at 1, 3, and 6 months, respectively). In both groups of patients, TRECs levels were low or undetectable in the first 3 months after SCT and progressively increased during the study. However, a higher proportion of patients with detectable levels of TRECs was observed in RIC-SCT at 1 and 3 months and more patients in this group reached normal levels of TRECs at 6 months post-SCT. In the multivariate analysis, including factors such as type of donor (sibling vs unrelated), dose of CD34+ cells infused with the graft, patient age, and graft-vs-host disease (GVHD), the most important factor influencing TRECs recovery in the early period after SCT was the type of conditioning regimen. Conclusions In this study, the pattern of immune reconstitution after RIC-SCT was different from that of MA-SCT and was characterized by higher posttransplant naïve CD4+ T cell counts and TRECs levels in the early period after transplant.