T memory stem cells after allogeneic haematopoietic cell transplantation: unique long-term kinetics and influence of chronic graft-versus-host disease.

T memory stem cells (TSCMs) are a subset of primitive T cells capable of both self-renewal and differentiation into all subsets of memory and effector T cells. Therefore, TSCMs may play a role in immune reconstitution and graft-versus-host disease (GVHD) in patients receiving allogeneic haematopoietic cell transplantation (HCT). We conducted a cross-sectional study to evaluate the proportions, absolute counts, phenotypes and functions of TSCMs in 152 adult patients without disease recurrence at least 12 months after undergoing HCT. CD4+ TSCMs were negatively correlated with number of months after transplantation in HCT patients that received cord blood transplantation, but not in patients that received bone marrow transplantation or peripheral blood stem cell transplantation. The proportions and absolute counts of CD4+ TSCMs and expression levels of inducible co-stimulator (ICOS) in CD8+ TSCMs were significantly higher in patients with mild and moderate/severe cGVHD compared to patients without cGVHD. These data suggested that, more than 12 months after allogeneic HCT, the kinetics of CD4+ TSCMs were dependent on the type of donor source, and further that CD4+ TSCMs and ICOS levels in CD8+ TSCMs were associated with cGVHD.