Results of the first-in-human trial of a vaccine against Chlamydia trachomatis infections indicate that the use of the antigen CTH522 with either CAF01 liposomes or aluminium hydroxide (AH) as adjuvant is safe and well tolerated. Both vaccine formulations induced anti-CTH522 IgG seroconversion, but the formulation containing the liposomal adjuvant had an overall better immunogenicity profile than the one containing AH.

Chlamydia is the most common sexually transmitted bacterial disease, but an effective preventive medication is currently lacking. The recombinant antigen CTH522 is a version of the major outer membrane protein of C. trachomatis, which has shown promising results in animal vaccination studies. In this phase I, randomized, parallel, double-blind, placebo-controlled trial, women were randomly assigned to receive CTH522 (with either adjuvant CAF01 (CTH522:CAF01) or AH (CTH522:AH); n = 15, respectively) or saline (n = 5). Intramuscular injections were given at 0, 1 and 4 months, followed by intranasal administrations of CTH22 without adjuvant or placebo at 4.5 and 5 months. Previous studies with CAF01 showed that systemic administration followed by mucosal boosting is highly effective in inducing mucosal immunity and IgA and, although genital mucosa does not have immune inductive sites, intranasal immunization induced mucosal immunity also in the genital tract. The trial primary outcome was safety and the secondary outcome was humoral immunogenicity.

both vaccine formulations resulted in strong responses

Overall, 91% of women received all five vaccinations. No treatment-related serious adverse events occurred. Mild injection site reactions were reported in all participants in the vaccine groups and in 60% in the placebo group; local reactions to intranasal administration were similar in the vaccination and placebo groups (all comparisons not statistically significant). In the CTH522:CAF01, CTH522:AH and placebo groups, 100%, 93% and 0% of women, respectively, had more than fourfold IgG seroconversion after the intramuscular immunizations. Post-hoc analysis showed that both vaccine formulations resulted in strong responses after the first immunization, which increased with each additional injection. Overall, the CTH522:CAF01 group had a faster seroconversion, higher IgG titres, a superior mucosal antibody profile and a more consistent profile of cell-mediated responses than the CTH522:AH group.