CD4 and cancer: Furthermore, SMARTA cells showed low expression of PD-1 and CTLA4 on Day 7, but on Day 15, the percentage of PD-1 and CTLA4 positive cells were higher than that of the cells on Day 7 and the mean fluorescence intensity of PD-1 was also upregulated (Figures 4C–F), indicating that CD4+ T-cell subsets also exhibit altered phenotypes, including features of exhaustion, during cancer progression.