Concerns have been raised about vaccine-elicited CD4+ T cell responses enhancing susceptibility to infection by HIV (Fauci et al., 2014, Hu et al., 2014) or SIV (Fouts et al., 2015, Staprans et al., 2004) by providing more targets for infection at the mucosal site of transmission (Bukh et al., 2014, Carnathan et al., 2015, Martins and Watkins, 2018, Qureshi et al., 2012), most likely due to the presence of activated Th1 cells in the mucosa, which was correlated with CCR5, α4β7, or proliferation in different studies. This evidence concerns the gene CD4 and infection.