The main characteristics of LTNP infections are (i) infection for more than 7 years; (ii) stable CD4+ T cell counts greater than 600 cells/μl; (iii) low/undetectable levels of HIV in the peripheral blood; (iv) no symptoms of HIV-induced disease; and (v) presence of a vigorous immune response against HIV, with multifunctional, persistent CD4 and CD8 responses. Here, CD4 is linked to infection.