CD4 and HIV-1 infection: HIV-1 infection is associated with epithelial barrier dysfunction that results in microbial translocation into the underlying lamina propria and systemic circulation.2,4 Our previous study modeling the interactions between the microbiome and gut lymphocytes in vitro led to a surprising discovery: enteric bacteria readily upregulated the cytotoxic marker GZB in gut CD4 T cells.15 However, to date, it remained unknown if these findings were just an artifact of cell culture.