TIGIT and HIV-1 infection: Contrary to CD8 T-cell activation, which increased promptly within days of HIV-1 invasion and then gradually decreased with the progression of HIV-1 infection (31), CD38 and HLA-DR coexpression by NK cells, including TIGIT+NK and TIGIT−NK cells, increased in the first month after HIV-1 infection and did not decrease even in chronic infection over 2 years.