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HIV C.1086 Envelope Gp140 Protein Boosts Following DNA/MVA Vaccination Fail to Enhance Heterologous Anti-V1V2 Antibody Response and Protection Against Clade C SHIV Challenge.

The RV144 HIV-1 vaccine trial showed a strong association between anti-gp70 V1V2 scaffold (V1V2) and anti-V2 hotspot peptide (V2 HS) antibody responses and reduced risk of HIV infection. Accordingly, a primary goal for HIV vaccines is to enhance the magnitude and breadth of V1V2 and V2 HS antibody responses in addition to neutralizing antibodies. Here, we tested the immunogenicity and efficacy of HIV-1 C.1086 gp140 boosts administered sequentially after priming with CD40L-adjuvanted DNA-SHIV and boosting with modified vaccinia Ankara (MVA)-SHIV vaccines in rhesus macaques. The DNA/MVA vaccination induced robust vaccine-specific CD4 and CD8 T cell responses with a polyfunctional profile. Two gp140 booster immunizations induced very high levels (∼2mg/ml) of gp140 binding antibodies in serum with strong reactivity directed against the homologous (C.1086) V1V2, V2 HS, V3 and gp41 immunodominant (gp41 ID) proteins. However, the vaccine induced antibody showed 10-fold (peak) and 32-fold (prechallenge) weaker binding to the challenge virus (SHIV1157ipd3N4) V1V2 and failed to bind to the challenge virus V2 HS due to a single amino acid change. Point mutations in the immunogen V2 HS to match the V2 HS in the challenge virus significantly diminished the binding of vaccine-elicited antibodies to membrane-anchored gp160. Both vaccines failed to protect from infection following repeated SHIV1157ipd3N4 intrarectal challenges. However, only the protein boosted animals showed enhanced viral control. These results demonstrate that C.1086 gp140 protein immunizations administered following DNA/MVA vaccination do not significantly boost heterologous V1V2 and V2HS responses, and fail to enhance protection against heterologous SHIV challenge.IMPORTANCE - HIV, the virus that causes AIDS, is responsible for millions of infections and deaths annually. Despite intense research for the past 25 years, there remains no safe and effective vaccine available. The significance of this work is in identifying the pros and cons of adding a protein boost to an already well-established DNA/MVA HIV vaccine that is currently being tested in the clinic. Characterizing the effects of the protein boost can allow researchers going forward to design vaccines that generate responses that will be more effective against HIV. Our results in rhesus macaques show that boosting with a specific HIV envelope protein does not significantly boost antibody responses that were identified as immune correlates for protection in a moderately successful RV144 HIV vaccine trial in humans, and highlight the need for the development of improved HIV envelope immunogens.