Seroprotection of HIV-infected subjects after influenza A(H1N1) vaccination is directly associated with baseline frequency of naive T cells

Human immunodeficiency virus type 1 (HIV-1)-infected individuals, despite receipt of antiretroviral therapy (ART), often have impaired vaccine responses. We examined the role that immune activation and cellular phenotypes play in influenza A(H1N1) vaccine responsiveness in HIV-infected subjects receiving ART. Subjects received the H1N1 vaccine (15-μg dose; Novartis), and antibody titers at baseline and after immunization were evaluated. Subjects were classified as responders if, by week 3, seroprotection guidelines were met. Responders had higher percentages of baseline naive T cells and lower percentages of terminally differentiated T cells, compared with nonresponders. Additionally, the naive CD4⁺ T-cell percentage and age were negatively correlated. Preservation of naive T-cell populations by starting therapy early could impact vaccine responses against influenza virus and other pathogens, especially as this population ages.