Critical role of CCR7 for the initiation of acute GVHD. The top halves of the schemes represent models of transplanted allogeneic CCR7-deficient T-cell subsets. In the bottom halves, allogeneic T cells express CCR7. (A) CCR7-deficient T cells cannot efficiently enter the T-cell zones where antigen presentation occurs. Instead, they accumulate in the red pulp. However, the antitumor effect is retained. (B) CCR7-deficient T_reg cells can suppress alloreactive T cells in myeloablative conditioned allogeneic recipients as well as wild-type T_reg cells.