Highly Ambiguous HIV-1 Pol Positions Encoding Multiple Amino Acids Usually Result from Antiviral or Immune Selection Pressure.

HIV-1 nucleotide ambiguities encoding amino acid mixtures occur commonly during population-based genotypic drug resistance testing. However, few studies have addressed the validity of sequences with fully ambiguous codons (FACs) containing codons translatable to more than four amino acids. We identified 839 published HIV-1 sequences with 846 FACs at 131 positions and determined their distribution relative to 215 HLA-associated positions (HAPs) and 84 drug-resistance positions. Among HIV-1 reverse transcriptase (RT) and protease sequences from antiretroviral therapy (ART)-naive and -experienced persons, there was a strong correlation between the likelihood a position was a FAC and that it was an HAP (Spearman's correlation coefficient rho >0.40;  < 1e-6). Among HIV-1 RT sequences from ART-experienced persons, there was a correlation between the likelihood that a position was a FAC and that it was a drug-resistance position (rho = 0.2;  = 8e-4). In the context of population-based genotypic resistance testing, FACs usually result from antiviral or immune selection pressure.