Evolution of subtype C HIV-1 Env in a slowly progressing Zambian infant

Given the high prevalence of mother to child infection, the development of a better understanding of African subtype C HIV-1 transmission and natural evolution is of significant importance. In this study, we genotypically and phenotypically characterized subtype C viruses isolated over a 67-month follow-up period from an in utero-infected Zambian infant. Changes in genotype and phenotype were correlated to alterations of the host humoral immune response.

A comparison of baseline maternal and infant samples indicated that the infant sequences are monophyletic and contain a fraction of the diversity observed in the mother. This finding suggests that selective transmission occurred from mother to child. Peaks in infant HIV-1 Env genetic diversity and divergence were noted at 48 months, but were not correlated with changes in co-receptor usage or syncytia phenotype. Phylogenetic analyses revealed an accumulation of mutations over time, as well as the reappearance of ancestral lineages. In the infant C2-V4 region of Env, neither the median number of putative N-glycosylation sites or median sequence length showed consistent increases over time. The infant possessed neutralizing antibodies at birth, but these decreased in effectiveness or quantity with time. De novo humoral responses were detected in the child after 12 months, and corresponded with an increase in Env diversity.

Our study demonstrates a correlation between HIV-1 Env evolution and the humoral immune response. There was an increase in genetic diversification in the infant viral sequences after 12 months, which coincided with increases in neutralizing antibody titers. In addition, episodes of viral growth and successive immune reactions in the first 5-6 years were observed in this slow progressor infant with delayed onset of AIDS. Whether this pattern is typical of slow progressing subtype C HIV-1 infected infant needs to be further substantiated.