CD28 and cancer: Yet, the expression levels of CD137L, CD28, CD27 and TIGIT on cancer patients’ CD8+ T cells were significantly lower (cancer patients vs. healthy donors, 9.143 ± 1.450% vs. 21.53 ± 3.323%, p = 0.0031; 21.84 ± 2.707% vs. 56.12 ± 6.641%, p = 0.0001; 33.45 ± 4.259% vs. 57.36 ± 5.452%, p = 0.0028; 89.55 ± 1.816% vs. 96.66 ± 0.6024%, p = 0.0016; Figure 2).