Randomized, observer-blind, controlled Phase 1 study of the safety and immunogenicity of the Na-GST-1/Alhydrogel hookworm vaccine with or without a CpG ODN adjuvant in hookworm-naïve adults.

BACKGROUND

Recombinant Necator americanus Glutathione-S-Transferase-1 (Na-GST-1) formulated on Alhydrogel (Na-GST-1/Alhydrogel) is being developed to prevent anemia and other complications of N. americanus infection. Antibodies induced by vaccination with recombinant Na-GST-1 are hypothesized to interfere with the blood digestion pathway of adult hookworms in the host. Phase 1 trials have demonstrated the safety of Na-GST-1 formulated on Alhydrogel, but further optimization of the vaccine adjuvant formulation may improve humoral immune responses, thereby increasing the likelihood of vaccine efficacy.

METHODS

A randomized, observer-blind, dose escalation Phase 1 trial was conducted in 24 healthy, hookworm-naïve adults. In each cohort of 12 participants, 4 were randomized to receive 100 µg of Na-GST-1/Alhydrogel and 8 to receive 30 µg or 100 µg of Na-GST-1/Alhydrogel plus the Cytosine-phospho-Guanine (CpG) oligodeoxynucleotide Toll-like receptor-9 agonist, CpG 10104, in the first and second cohorts, respectively. Progression to the second cohort was dependent upon evaluation of 7-day safety data after all participants in the first cohort had received the first dose of vaccine. Three intramuscular injections of study product were administered on days 0, 56, and 112, after which participants were followed for 6 months. IgG and IgG subclass antibody responses to Na-GST-1 were measured by qualified indirect ELISAs at pre- and post-vaccination time points.

RESULTS

Na-GST-1/Alhydrogel administered with or without CpG 10104 was well-tolerated. The most common solicited adverse events were mild injection site tenderness and pain, and mild headache. There were no vaccine-related serious adverse events or adverse events of special interest. Both dose concentrations of Na-GST-1/Alhydrogel plus CpG 10104 had significantly higher post-vaccination levels of antigen-specific IgG antibody compared to Na-GST-1/Alhydrogel without CpG, starting after the second injection. Peak anti-Na-GST-1 IgG levels were observed between 2 and 4 weeks following the third dose, regardless of Na-GST-1 formulation. IgG levels decreased but remained significantly above baseline in all groups by day 290, at which point all participants (20 of 20 evaluable participants) still had detectable IgG. Longitudinal antigen-specific IgG1 and IgG3 subclass responses mirrored those of total IgG, whereas IgG4 responses were lower in the groups that received the vaccine with the CpG adjuvant compared to the non-CpG group.

CONCLUSIONS

Vaccination of hookworm-naïve adults with Na-GST-1/Alhydrogel plus CpG 10104 was safe and minimally reactogenic. Addition of CpG 10104 to Na-GST-1/Alhydrogel resulted in significant improvement in IgG responses against the vaccine antigen. These promising results have led to inclusion of the CpG 10104 formulation of Na-GST-1/Alhydrogel in a Phase 2 proof-of-concept controlled human infection trial.