Among the molecules detected by mass cytometry on CD4 + T cells the expression of CXCR5 indirectly correlated to the size of HIV-1 reservoirs; CXCR5 expression in the periphery characterizes circulating T follicular helper cells38, which have been identified in multiple studies as HIV-1 reservoirs in untreated HIV-1 infection (reviewed in39); the dynamics of decay of HIV-1 reservoir in Tfh cells during ART are less studied. The gene discussed is CXCR5; the disease is HIV-1 infection.