Purifying Selection in Human Immunodeficiency Virus-1 pol Gene in Perinatally Human Immunodeficiency Virus-1-Infected Children Harboring Discordant Immunological Response and Virological Nonresponse to Long-Term Antiretroviral Therapy

BACKGROUND: Biological monitoring of antiretroviral treatment (ART) in human immunodeficiency virus (HIV)-infected pediatric population remains challenging. The aim of the present study was to assess the long-term HIV-1 genetic diversity in pol gene in HIV-1-infected children in virological failure under antiretroviral regimen adapted according to the successive World Health Organization (WHO) guidelines for resource-constrained settings. METHODS: HIV-1 diversity in pol gene was assessed in HIV-1-infected children and adolescents born from HIV-infected mothers (median age at follow-up: 13.8 years) in virological failure (VF(+)) despite long-term regimen recommended by the WHO. The numbers of nonsynonymous substitutions per potential nonsynonymous site (dN) and of synonymous substitutions at potential synonymous sites (dS) in HIV-1 pol gene and the dN/dS ratios were used to estimate the selective pressure on circulating HIV-1. RESULTS: The immunological responses to ART basically corresponded to: 1) Full therapeutic failure with immunological (I(-)) and virological nonresponses in one-quarter (24.6%) of study children ((I(-), VF(+)) subgroup); 2) Discordant immunovirological responses with paradoxical high CD4 T cell counts (I(+)) and high HIV-1 RNA load in the remaining cohort patients (75.4%) ((I(+), VF(+)) subgroup). The mean dS was 1.8-fold higher in (I(+), VF(+)) than (I(-), VF(+)) subgroup (25.9 ± 18.4 vs. 14.3 ± 10.8). In the (I(+), VF(+)) subgroup, the mean dS was 1.6-fold higher than the mean dN. Finally, the mean dN/dS ratio was 2.1-fold lower in (I(+), VF(+)) than (I(-), VF(+)) subgroup (0.6 ± 0.3 vs. 1.3 ± 0.7), indicating purifying selection in the immunovirological discordant (I(+), VF(+)) subgroup and positive selection in the immunovirological failure (I(-), VF(+)) subgroup. CONCLUSIONS: Children and adolescents in immunovirological therapeutic failure harbor positive selection of HIV-1 strains favoring diversifying in pol-encoded amino acids. In contrast, children with persistent discordant immunovirological responses show accumulation of mutations and purifying selection in pol gene sequences, indicating limited genetic evolution and likely suggesting genetic adaptation of viruses to host functional constraints.