Although most mature T cells exclusively expressed CD4 or CD8, but not both once leaving thymus, however, the frequency of CD4+CD8+ double positive T cells could be augmented for adaptive immune response under inflammatory conditions, such as autoimmune diseases, acute viral infections, and cancer.21 It might be assumed that influx of CD4+CD8+ double positive T subsets into a tumor resulted in the induction of an inflammatory microenvironment, which activated anti‐tumor immunity after PDT. Here, CD4 is linked to cancer.