CD4 and HIV-1 infection: Several studies have detailed the emergence of CD4 T cells with cytolytic activity and HIV-1-specificity in the blood during HIV infection.21–33 Frequencies of cytotoxic CD4 T cells (CD4 CTLs), variably identified by granzyme type (i.e. GZA, GZB, GZK) and co-expression of other cytolytic molecules such as perforin and/or degranulation molecules (e.g. CD107a), increased early during HIV-1 infection.