PDCD1 and infection: In addition, PD-1+CD8+ TSCM-like regulatory cells can survive for a long time in recipients to resist early risk events such as the suppression of aGVHD and infection, which may help to promote immune reconstitution.88,89 The underlying mechanism of the PD-1+CD8+ TSCM-like regulatory subset, including the establishment of bone marrow niche, the relevant biological pathways, the interaction of these T cells with the bone marrow microenvironment and deep function such as long-term anti-infection in recipients, are tasks waiting for us to explore.