Nucleotide mixtures in human immunodeficiency virus type 1 (HIV-1) population sequences reflect sequence diversity. We evaluated gag and pol ambiguous nucleotide frequencies during an analytic treatment interruption (ATI) in an HIV-1 therapeutic vaccine study. The proportion of ambiguous nucleotides was significantly higher at ATI week 16 than at either the time of first detectable viremia (P < 0.001 gag and P = 0.03 reverse transcriptase) or preantiretroviral therapy (P = 0.007 gag). No significant differences were observed in the proportion of ambiguous nucleotides between those receiving vaccine and placebo. Increased HIV diversity during the ATI may represent a potentially higher barrier to success for a therapeutic as compared with a preventative vaccine targeting cell-mediated immunity.
Trial registration: ClinicalTrials.gov NCT00080106.