Consistent with previous reports, patients with cancer showed immune exhaustion phenotype as indicated by increased cell-surface expression of PD-1, TIGIT, and Tim-3 but reduced CD28 expression on CD8+ T cells and Vγ9Vδ2+ T cells, while cell surface CTLA-4 was barely detectable (online supplemental figure S1A, B). Here, CD28 is linked to cancer.