The current models put forth to explain how aGVHD affects T cell reconstitution relates to two primary factors: GVHD-mediated damage to the thymic microenvironment essential for T cell production (20); and the dysfunction of the peripheral niche essential for the survival and HP of naïve CD4+ and CD8+ T lymphocytes in the periphery (Figure 1B) (21–23). Here, CD8A is linked to graft versus host disease.