CD4 and lymphoma: In an engineered T-NHL mouse model with forced ITK-SYK expression in CD4+ T cells, Pdcd1 deletion resulted in complete malignant transformation of T cells, and blockade of PD-1 signaling by the administration of anti–PD-1 or anti-PD-L1 antibodies accelerated the progression of lymphoma in vivo, suggesting that PD-1 functions as a powerful suppressor of lymphomagenesis under certain conditions and models (19).