CD4 and infection: Briefly, despite being infected from a single source, SBBC members now comprise slow progressors (SP) who have eventually experienced decline in CD4 T-cells after many years of asymptomatic infection (subjects D36, C98, C54), and "elite" long-term nonprogressors (LTNP) who have had stable CD4 T-cell counts and low or below detectable plasma HIV RNA levels for more than 20 years without antiretroviral therapy (ART) and remain asymptomatic (subjects C49, C64, C135) [28,30,31].