Early administration of calcineurin inhibitors limits tolerogenic effect of PTCy in allogeneic hematopoietic transplant

Abstract

We recently demonstrated early administration of calcineurin inhibitors (CNIs) after murine allogeneic hematopoietic cell transplantation (allo-HCT) inhibits terminal exhaustion of donor T cells and hampers tolerance induction. However, the role of CNIs in regulating T-cell exhaustion in clinical allo-HCT remains to be clarified. It also remains to be elucidated why posttransplant cyclophosphamide (PTCy) could reduce chronic graft-versus-host disease (cGVHD), despite the administration of CNIs. In this study, we explored the impact of CNIs on donor T-cell exhaustion after PTCy-based haploidentical HCT. In mice, early administration of cyclosporine before PTCy preserved a population of Ly6C⁺ donor T cells with less exhausted characteristics, as has been shown in non-PTCy allo-HCT. In single-cell analysis of clinical samples from patients undergoing HLA-haploidentical peripheral blood stem cell transplantation with PTCy (PTCy-haplo-PBSCT), early administration of tacrolimus prior to PTCy promoted the expansion of effector-like CD8+ intermediate exhausted T cells (Tex-int) and CD4⁺ cytotoxic T cells (CTLs), with the former enriched for both effector- and exhaustion-associated and the latter for effector- and CD4⁺ CTL-specific gene signatures. These subsets retained high responsiveness to TCR stimulation and PD-1 blockade, and their expansion on day 28 predicted subsequent cGVHD. In contrast, delaying tacrolimus administration on day 5 after PTCy-haplo-PBSCT significantly reduced the expansion of these effector-like T cells. These findings indicate early CNI exposure favors the persistence of incompletely exhausted and clonally expanded donor T cells with pathogenic potential. Tex-int and CD4⁺ CTLs may serve as prognostic biomarkers of cGVHD risk and as promising targets for preemptive therapy of cGVHD.