The manifestation of HIV-1 infection is different in children and adults. Most of the children who acquire HIV perinatally progress to disease within the first two years of life, while adults can remain asymptomatic for up to ten years. However, a small minority group of children can control the virus for years in the absence of antiretroviral therapy. We characterized CD8+ T cell responses critical for the containment of HIV infection in a cohort of infants HIV infected from birth using IFN- γ ELISPOT, multicolour flow cytometry and viral sequencing of the Gag protein. We investigated whether the age at the time of infection, specificity and functionality of the generated responses, genetic make up and the maternal immune responses to HIV, influenced disease progression in the child. We found that the majority of in-utero infected infants mounted CD8+ T cell responses from the first days of life. In contrast to chronically infected children or adults, the specificity of the initial response in acutely infected infants was directed towards Env and Rev proteins and CD4+ T cell responses were minimal during the first 6 months of life. Slow progression to disease was associated with possession of one of the protective HLA-B alleles by either the mother or the child (P=0.007) and targeting of Gag epitopes presented by the protective HLA-B alleles. Mothers who expressed protective alleles but whose children did not possess these alleles, transmitted less fit viruses that benefited their children. Furthermore, slow progressor children had more polyfunctional CD8+ T cell responses in early infection when compared to rapid progressors (P=0.05). The ability of infants to induce CD8+ T cell responses early in life is encouraging for vaccine interventions. The differences in the specificity of the initial responses between adults and children, insufficient priming of these responses as a result of minimal CD4+ T cell help during infancy and possession of non-protective HLA alleles shared between mother and child, may explain the rapid disease progression generally noted in most infants. However, slow progression to disease in the minority group of children may be attributed to functional capacity of the CD8+ T cells generated by the child, mediation by protective HLA alleles, acquisition of low fitness viruses from the mother or de novo attenuation of the virus by the child’s own immune responses.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2011.