CCR9 and lymphopenia: We demonstrated that the observed lymphopenia postinfusion is due to a combined RMD effect, consisting of (i) apoptosis; (ii) downregulation of cell surface markers CD3, CD4, and CD8; (iii) upregulation of homing markers α4β7, CCR7, and CCR9; and (iv) migration from the periphery to the gut and LNs.