Tfh induction can be traced as early as 14 days post-infection in NHPs challenged with SIV [49] and studies in humans and NHPs show that despite CD4 T cells being depleted during chronic HIV-1/SIV infection, the frequency of CXCR5+ PD-1hi CD4 T cells significantly increases both in the blood as well as in the LNs [50–53]. The gene discussed is CD4; the disease is infection.