TIGIT and HIV-1 infection: The flow cytometer charts (Figure 6A) showed the degranulation substance CD107a, a sensitive marker of NK cell activity (32), produced by NK cells in response to K562 tumor cells significantly increased as HIV-1 infection prolonged to the stage of chronic infection (P = 0.027, Kruskal–Wallis test); TIGIT−NK cells showed this change (P = 0.015, Kruskal-Wallis test), but TIGIT+NK cells did not (Figures 6B,C).