Preclinical prophylactic efficacy testing of Sm-p80-based vaccine in a nonhuman primate model of Schistosoma mansoni infection and immunoglobulin G and E responses to Sm-p80 in human serum samples from an area where schistosomiasis is endemic

Abstract

The prophylactic efficacy of a schistosome antigen (Sm-p80) was tested in a nonhuman primate model, the baboon. Using a total of 28 baboons, different vaccination strategies were used including recombinant Sm-p80 protein formulated in Toll-like receptor 7 and Toll-like receptor 9 agonists, and DNA priming followed by boosting with protein plus adjuvants. Recombinant protein approaches provided levels of prophylactic efficacy of 52%-58%, whereas prime-boost approaches conferred 38%-47% protection in baboons. An appropriately balanced pro-inflammatory (T-helper 17 [Th17] and Th1) and anti-inflammatory (Th2) type of response was generated; the Th1 and Th17 types of immune responses appear to be indicative of increased prophylactic efficacy. Production and expression of several cytokines (interleukin 2 [IL-2], interferon γ, IL-12α, IL-1β, IL-6, and IL-22) were up-regulated in vaccinated animals. Human correlate studies revealed Sm-p80 reactivity with immunoglobulin G in human serum samples from schistosome-infected individuals. In addition, a complete lack of prevailing Sm-p80-specific immunoglobulin E in a high-risk or infected population was observed, thus minimizing the risk of hypersensitivity reaction following vaccination with Sm-p80 in humans. This study provided the proof of concept to move Sm-p80 forward into further preclinical development leading to human clinical trials.

Figure 1.

Titers of anti–Sm-p80 antibodies in immunized baboons. Enzyme-linked immunosorbent assay was performed with serum samples from each baboon in their respective control and experimental groups of recombinant protein vaccine formulations (rSm-p80 + CpG ODN or Resiquimod [R848]). Shown are total immunoglobulin G (IgG) (A), IgG1 (B), IgG2 (C), IgM (D), and IgA (E) levels in individual control (HE13, WA84, LA15, and GE35) and vaccinated (ST88, NI31, SE83, and AN25) baboon serum samples collected every 4 weeks. The values represent the mean (± SE) of 3 experiments.

Figure 2.

Titers of anti–Sm-p80 antibodies in immunized baboons. Enzyme-linked immunosorbent assay was performed with serum samples from each baboon in their respective control and experimental groups of DNA-prime and protein-boost vaccine formulations (Sm-p80-VR-1020 + rSm-p80 + ODN-10104; Sm-p80 + VR-1020 + rSm-p80 + R848). Shown are total immunoglobulin G (IgG) (A), IgG1 (B), IgG2 (C), IgM (D), and IgA (E) levels in individual control (CA21, TR02, and NA25) and vaccinated (KE04, TA76, and CR03) baboon serum samples collected every 4 weeks. The values represent the mean (± SE) of 3 experiments.

Figure 3.

Relative fold differences in cytokine messenger RNA expression levels by peripheral blood mononuclear cells (A), splenocytes (B), and lymph node cells (C) after 24 hours of stimulation with recombinant Sm-p80 in vitro. The relative cytokine messenger RNA expression level was calculated by comparing the differences in the levels of the control group with those of the respective experimental group after standardization using respective glyceraldehyde 3-phosphate dehydrogenase.

Figure 4.

Quantification of intracellular interferon γ (IFN-γ)– and interlekin 4 (IL-4)–producing CD3⁺CD4⁺ and CD3⁺CD8⁺ cells from control and vaccinated baboon peripheral blood mononuclear cells. Initial gating was performed using the CD3 marker. A, IFN-γ–producing cells in recombinant Sm-p80 + CpG ODN and Sm-p80 + R848 groups. B, IL-4–producing cells in recombinant Sm-p80 + CpG ODN and Sm-p80 + R848 groups. C, IFN-γ–producing cells in prime-boost groups (Sm-p80− VR-1020 + rSm-p80 + ODN-10104; Sm-p80-VR-1020 + rSm-p80 + R848). D, IL-4–producing cells in prime-boost groups (Sm-p80-VR-1020 + rSm-p80 + ODN-10104; Sm-p80-VR-1020 + rSm-p80 + R848).

Figure 4.

Quantification of intracellular interferon γ (IFN-γ)– and interlekin 4 (IL-4)–producing CD3⁺CD4⁺ and CD3⁺CD8⁺ cells from control and vaccinated baboon peripheral blood mononuclear cells. Initial gating was performed using the CD3 marker. A, IFN-γ–producing cells in recombinant Sm-p80 + CpG ODN and Sm-p80 + R848 groups. B, IL-4–producing cells in recombinant Sm-p80 + CpG ODN and Sm-p80 + R848 groups. C, IFN-γ–producing cells in prime-boost groups (Sm-p80− VR-1020 + rSm-p80 + ODN-10104; Sm-p80-VR-1020 + rSm-p80 + R848). D, IL-4–producing cells in prime-boost groups (Sm-p80-VR-1020 + rSm-p80 + ODN-10104; Sm-p80-VR-1020 + rSm-p80 + R848).

Figure 5.

Antibody responses to Sm-p80 in human serum samples from an area in Kenya where schistosomiasis is endemic. A, Immunoglobulin G (IgG) reactivity to Sm-p80 in serum samples obtained from schistosome-carrying pediatric patients (n = 9) and hyperexposed adults (n = 43) as well as uninfected adults (n = 9) in Kenya. P > .05 for pediatric patients with schistosomiasis versus hyperexposed adults; P > .05 for pediatric patients with schistosomiasis versus uninfected adults; P < .01 for hyperexposed adults versus uninfected results (Dunn multiple comparison test). B, IgE reactivity to Sm-p80 and schistosome soluble egg antigen (SEA) in the serum samples of schistosome-infected individuals. P < .001 for anticalpain antibodies versus anti-SEA antibodies (Mann–Whitney U test).