Expansion of phenotypically senescent CD57+CD8 T cells is associated with impaired immunocompetence after allogeneic hematopoietic stem cell transplantation

Background: T cell senescence is a physiological process typically associated with aging. In addition, lymphopenia and chronic immune activation can result in T cell senescence. CD57, a member of the N-CAM family initially described as a natural killer cell marker, has been reported as a marker of human senescent CD8 T cells. Percentages of CD57+ CD8 T cells increase during aging as well as during chronic viral infections. Early studies have reported increased proportions of CD57-expressing CD8 T cells after autologous and allogeneic hematopoietic stem cell transplantation (HSCT). Whether these cells can be considered a counterpart of the senescent population found during aging is at present unknown. More importantly, whether the expansion of CD57+ CD8 T cells is associated with impaired immunocompetence after allogeneic HSCT remains to be investigated.