T cell responses have been implicated in reduced risk of HIV acquisition in uninfected persons and control of viral replication in HIV-infected individuals. HIV Gag-specific T cells have been predominantly associated with post-infection control, whereas Env antigens are the target for protective antibodies; therefore, inclusion of both antigens is common in HIV vaccine design. However, inclusion of multiple antigens may provoke antigenic competition, reducing the potential effectiveness of the vaccine. HVTN 084 was a randomized, multicenter, double-blind phase 1 trial to investigate whether adding Env to a Gag/Pol vaccine decreases the magnitude or breadth of Gag/Pol-specific T cell responses. Fifty volunteers each received one intramuscular injection of 1 × 1010 particle units (PU) of rAd5 Gag/Pol and EnvA/B/C (3:1:1:1 mixture) or 5 × 109 PU of rAd5 Gag/Pol. CD4+ T cell responses to Gag/Pol measured 4 weeks after vaccination by cytokine expression were significantly higher in the group vaccinated without Env, whereas CD8+ T cell responses did not differ significantly between the two groups. Mapping of individual epitopes revealed greater breadth of the Gag/Pol-specific T cell response in the absence of Env compared to Env coimmunization. Addition of an Env component to a Gag/Pol vaccine led to reduced Gag/Pol CD4+ T cell response rate and magnitude as well as reduced epitope breadth, confirming the presence of antigenic competition. Therefore, T cell-based vaccine strategies should aim at choosing a minimalist set of antigens to reduce interference of individual vaccine components with the induction of the maximally achievable immune response.

BACKGROUND: HVTN 120 is a phase 1/2a randomized double-blind placebo-controlled human immunodeficiency virus (HIV) vaccine trial that evaluated the safety and immunogenicity of ALVAC-HIV (vCP2438) and MF59- or AS01B-adjuvanted bivalent subtype C gp120 Env protein at 2 dose levels in healthy HIV-uninfected adults. METHODS: Participants received ALVAC-HIV (vCP2438) alone or placebo at months 0 and 1. At months 3 and 6, participants received either placebo, ALVAC-HIV (vCP2438) with 200 μg of bivalent subtype C gp120 adjuvanted with MF59 or AS01B, or ALVAC-HIV (vCP2438) with 40 μg of bivalent subtype C gp120 adjuvanted with AS01B. Primary outcomes were safety and immune responses. RESULTS: We enrolled 160 participants, 55% women, 18-40 years old (median age 24 years) of whom 150 received vaccine and 10 placebo. Vaccines were generally safe and well tolerated. At months 6.5 and 12, CD4+ T-cell response rates and magnitudes were higher in the AS01B-adjuvanted groups than in the MF59-adjuvanted group. At month 12, HIV-specific Env-gp120 binding antibody response magnitudes in the 40 μg gp120/AS01B group were higher than in either of the 200 μg gp120 groups. CONCLUSIONS: The 40 μg dose gp120/AS01B regimen elicited the highest CD4+ T-cell and binding antibody responses. Clinical Trials Registration . NCT03122223.

Background

Elicitation of broad immune responses is understood to be required for an efficacious preventative HIV vaccine. This Phase 1 randomized controlled trial evaluated whether administration of vaccine antigens separated at multiple injection sites vs combined, fractional delivery at multiple sites affected T-cell breadth compared to standard, single site vaccination.

Methods

We randomized 90 participants to receive recombinant adenovirus 5 (rAd5) vector with HIV inserts gag, pol and env via three different strategies. The Standard group received vaccine at a single anatomic site (n = 30) compared to two polytopic (multisite) vaccination groups: Separated (n = 30), where antigens were separately administered to four anatomical sites, and Fractioned (n = 30), where fractions of each vaccine component were combined and administered at four sites. All groups received the same total dose of vaccine.

Findings

CD8 T-cell response rates and magnitudes were significantly higher in the Fractioned group than Standard for several antigen pools tested. CD4 T-cell response magnitudes to Pol were higher in the Separated than Standard group. T-cell epitope mapping demonstrated greatest breadth in the Fractioned group (median 8.0 vs 2.5 for Standard, Wilcoxon p = 0.03; not significant after multiplicity adjustment for co-primary endpoints). IgG binding antibody response rates to Env were higher in the Standard and Fractioned groups vs Separated group.

Interpretation

This study shows that the number of anatomic sites for which a vaccine is delivered and distribution of its antigenic components influences immune responses in humans.

Funding

National Institute of Allergy and Infectious Diseases, NIH.