The objectives of this study were to investigate the relationships between polymorphisms at the interferon lambda (IFNL) locus and CD4+:CD8+ ratio normalisation in people living with HIV (PLWH) on effective antiretroviral therapy (ART); and to examine whether these polymorphisms influence the composition of T lymphocyte compartments in long-term treated HIV-1 infection. Here, CD4 is linked to HIV-1 infection.