Since CCR6 transduced T cells showed increased PD-1 expression in the tumor and CCR4 transduced T cells in draining lymph nodes (Fig. 4D), one possible reason why this combination approach did not work was that CCR4/CCR6 double-transduced T cells become exhausted by additive PD-1 upregulation via CCR4 and CCR6. The gene discussed is CCR4; the disease is neoplasm.