First-in-Human Evaluation of the Safety and Immunogenicity of a Recombinant Vesicular Stomatitis Virus Human Immunodeficiency Virus-1 gag Vaccine (HVTN 090)

Abstract

Background. We report the first-in-human safety and immunogenicity evaluation of a highly attenuated, replication-competent recombinant vesicular stomatitis virus (rVSV) human immunodeficiency virus (HIV)-1 vaccine. Methods. Sixty healthy, HIV-1-uninfected adults were enrolled in a randomized, double-blinded, placebo-controlled dose-escalation study. Groups of 12 participants received rVSV HIV-1 gag vaccine at 5 dose levels (4.6 × 10(3) to 3.4 × 10(7) particle forming units) (N = 10/group) or placebo (N = 2/group), delivered intramuscularly as bilateral injections at 0 and 2 months. Safety monitoring included VSV cultures from blood, urine, saliva, and swabs of oral lesions. Vesicular stomatitis virus-neutralizing antibodies, T-cell immunogenicity, and HIV-1 specific binding antibodies were assessed. Results. Local and systemic reactogenicity symptoms were mild to moderate and increased with dose. No severe reactogenicity or product-related serious adverse events were reported, and all rVSV cultures were negative. All vaccine recipients became seropositive for VSV after 2 vaccinations. gag-specific T-cell responses were detected in 63% of participants by interferon-γ enzyme-linked immunospot at the highest dose post boost. Conclusions. An attenuated replication-competent rVSV gag vaccine has an acceptable safety profile in healthy adults. This rVSV vector is a promising new vaccine platform for the development of vaccines to combat HIV-1 and other serious human diseases.

Keywords: HIV vaccine; dose-escalation; immunogenicity; safety; vesicular stomatitis virus.

Figure 1.

(A) Wild-type vesicular stomatitis virus (VSV) genome organization and virion structure. Viral transcription is polar, initiating at the single 3′ promoter and proceeding to the 5′ end of the genome, producing a steep 3′ to 5′ gradient of gene expression. The N protein encapsidates viral genomic RNA forming viral nucleocapsid; the M protein drives virus assembly and budding from infected cells, and the G protein forms trimers in host cell plasma membrane, which becomes the envelope of budding virus particles. The P and L proteins associate to form the viral RNA polymerase that copackages into virus particles with nucleocapsid, providing the components needed to initiate the next infectious cycle. The mature virus particle is bullet shaped (60 nm × 180 nm) with a lipid envelope and underlying M protein surrounding a dense nucleocapsid core. (B) The recombinant VSV human immunodeficiency virus (HIV)-1 vaccine vector (rVSVN4CT1gag1). The vaccine construct encodes the HIV-1 gag transgene (strain HXB-2 p55 gag) in position one of the genome (gag1) to maximize gene expression, has the N gene translocated from first to fourth position (N4), and encodes a G protein that has the cytoplasmic tail truncated from 29 to 1 amino acid (CT1).

Figure 2.

Vesicular stomatitis virus (VSV)-neutralizing antibody titers. Neutralizing antibody titer responses are represented as the reciprocal of the lowest serum dilution, demonstrating complete protection of Vero cell monolayers from VSV-induced cytopathic effects using serum from 2 weeks after the first vaccination (d14) and 2 weeks after the second vaccination (d70), by group. Responders are shown as red dots, and nonresponders are shown as blue triangles. Box plots show the distribution of titers among positive responders only. The box indicates the median and interquartile range (IQR); whiskers extend to the furthest point within 1.5 times the IQR from the upper or lower quartile. Numbers above the panel show the number of responders with an assay result out of the evaluable subjects and the percentage with positive responses. Abbreviations: T1, 4.6 × 10³ PFU; T2, 4.6 × 10⁴ PFU ; T3, 4.8 × 10⁵ PFU; T4, 4.2 × 10⁶ PFU; and T5, 3.4 × 10⁷ PFU. d, day; PFU, particle-forming units.

Figure 3.

Intracellular cytokine staining assay. CD4⁺ T-cell responses to Gag Consensus (Con) B peptides. The percentage of CD4⁺ T cells expressing interleukin (IL)-2 or interferon (IFN)-γ (A) or expressing CD40 ligand (CD154) (B), in response to Gag Con B peptide pools. Human immunodeficiency virus-1-specific CD4⁺ and CD8⁺ T-cell responses were measured using a validated Intracellular cytokine staining assay. Results shown are from samples obtained 2 weeks after the prime (d14) and 2 weeks after boost vaccination (d70) for each treatment group. Responders are shown as red dots, and nonresponders are shown as blue triangles. Box plots show the distribution of the magnitude of response in positive responders only. The box indicates the median and interquartile range (IQR); whiskers extend to the furthest point within 1.5 times the IQR from the upper or lower quartile. Numbers at the top of each panel show the number and percentage of responders from each group. One Group 4 participant had a CD8⁺ T-cell response to Gag Con B at day 14 (data not shown). Abbreviations: T1, 4.6 × 10³ PFU; T2, 4.6 × 10⁴ PFU; T3, 4.8 × 10⁵ PFU; T4, 4.2 × 10⁶ PFU; and T5, 3.4 × 10⁷ PFU. d, day; PFU, particle-forming units.

Figure 4.

T-cell responses to Gag Consensus B peptides by interferon (IFN)-γ enzyme-linked immunospot (ELISPOT). The validated IFN-γ ELISPOT assay demonstrates a dose-response relationship, with a higher response rate and magnitude with a 10-fold higher dose and a second vaccination. Results are shown from 2 weeks after the first vaccination (d14) and 2 weeks after the second vaccination (d70), for study groups T4, 4.2 × 10⁶ PFU and T5, 3.4 × 10⁷ PFU. Responses are expressed as the number of spot-forming units (SFUs) per 10⁶ cells. Responders are shown as red dots, and nonresponders are shown as blue triangles. Box plots show the distribution of the magnitude of response in positive responders only. The box indicates the median and interquartile range (IQR); whiskers extend to the furthest point within 1.5 times the IQR from the upper or lower quartile. Numbers above the panel show the number and percentage of responders from each group. Abbreviations: d, day; PBMC, peripheral blood mononuclear cells.