CD4 and cancer: This was supported by the following facts: inhibition of CD8+ CTL proliferation and function, and enhanced production of Foxp3+ Tregs from CD4+ T cells, resulting in peripheral immune tolerance303–306 of patients in several types of carcinomas, including NSCLC,307,308 lung squamous cell carcinoma,303 liver cancer,309 and myeloproliferative neoplasms.310 This functional connectivity suggests that the expression of PD-L1 in cancer cells, in some sense at least, may play a role as an indicator since the levels of immunosuppression rise during cancer progression.