Interestingly, although tumor infiltrating SKAP55 KO or ADAP KO CD8+ T cells, as well as CD4+ effector/memory T cells, substantially reduced PD-1 expression during anti-tumor response, we did not observe any significant changes in CTLA-4 expression or infiltrating CD4+Foxp3+ Tregs in vivo. Here, CD4 is linked to neoplasm.