CTLA4 and hepatitis C virus infection: Although anti-CTLA-4 therapy is mostly used in combination with other immune checkpoint therapies, for example, after hepatitis C infection, the expression of PD-1 and CTLA-4 on CD8+ T cells in peripheral blood increases, inducing T cell exhaustion, and blocking PD-1 or CTLA-4 alone fails to obtain a satisfactory curative effect, and only the combination of PD-1 and CTLA-4 was able to reverse T cell dysfunction (51, 52).