Moreover, a second generation of immune checkpoint inhibitors (revised in [40]) is underway: among others, lymphocyte activation gene (LAG)-3, T-cell immunoglobulin mucin (TIM)-3, and T cell immunoglobulin and ITIM domain (TIGIT) represent the most promising cancer therapeutic targets, expressed by natural killer (NK), CD4+ and CD8+ T cells, as redundant co-inhibitory receptors [26,41,42,43]. Here, CD4 is linked to cancer.