Calcineurin inhibitor blocks tolerance by suppressing donor T cell terminal exhaustion after allogeneic hematopoietic cell transplantation

We read with great interest the recent article by Wang et al. ( 1), wherein the authors demonstrated calcineurin inhibitors (CNIs) administered after experimental allogeneic hematopoietic stem cell transplantation (allo-HCT) suppressed donor T cell exhaustion while promoting the expansion of CD62L + CD44 + central memory T cells (Tcm), which contribute to the development of chronic graft-versus-host disease (cGVHD).We previously reported that CNIs inhibited terminal exhaustion of donor T cells and contributed to the development of cGVHD after allo-HCT (2).Both studies share the concept that CNIs suppress the exhaustion of donor T cells and impair tolerance induction.However, the cell types induced by CNIs and contributing to cGVHD development differ between studies: transitory exhausted T cells (transitory-Tex) in our study, but Tcm in the Wang et al. study.In our study, single-cell RNA sequencing (scRNA-seq) on day 14 after transplantation showed that the majority of alloreactive donor T cells had completed differentiation toward terminally exhausted T cells (terminal-Tex) after allo-HCT without CNI.However, CNIs downregulated Tox expression and inhibited differentiation of transitory-Tex toward terminal-Tex.We identified transitory-Tex based on the expression of exhaustion markers such as Tox, Pdcd1, and Havcr2, along with effector molecules such as Cx3cr1 and Gzmb, and their self-renewal capacity, as has been previously shown (3).In Wang et al.'s study, scRNA-seq analysis was performed on day 7, which may be too early to assess T cell exhaustion.In our study, the majority of donor T cells were CD62L -PD-1 + irrespective of CNI treatment, while Wang et al. demonstrated the expansion of CD62L + PD-1 lo Tcm in CNI-treated recipients (Fig-