Safety and immunogenicity of a pneumococcal histidine triad protein D vaccine candidate in adults

Abstract

Background: Pneumococcal vaccines based on conserved protein antigens have the potential to offer expanded protection against Streptococcus pneumoniae.

Objective: To explore safety and immunogenicity of a recombinant protein vaccine candidate against S. pneumoniae composed of adjuvanted pneumococcal histidine triad protein D (PhtD).

Methods: This phase I, exploratory, open-label, single-center clinical study enrolled adults (18-50 years). Participants in a pilot safety cohort received a single intramuscular injection of 6 μg. Following safety review, 3 dose cohorts were enrolled (6, 25, and 100 μg); participants received 2 injections administered approximately 30 days apart. Assignment of the second injection and successive dose cohorts were made after blinded safety reviews after each injection at each dose level. Safety endpoints included rates of solicited injection site and systemic reactions, unsolicited adverse events, serious adverse events, and safety laboratory tests. Immunogenicity endpoints included levels of anti-PhtD antibodies as measured by ELISA.

Results: Sixty-three participants were enrolled and received the pilot safety dose (n=3) or at least 1 dose of PhtD vaccine candidate at 6 μg (n=20), 25 μg (n=20), or 100 μg (n=20). No safety concerns were identified. No vaccine-related serious adverse event was reported. The most common solicited injection site reaction was pain and most common solicited systemic reactions were myalgia and headache; most reactions were mild and transient. Observed geometric mean concentrations (95% CI) were 200.99 ELISA units (148.46, 272.10), 352.07 (193.49, 640.63), and 699.15 (405.49, 1205.48) post-injection 1 in the 6, 25, and 100 μg dose cohorts, respectively, and 378.25 (275.56, 519.21), 837.32 (539.29, 1300.04), and 1568.62 (1082.92, 2272.16) post-injection 2.

Conclusions: All dose levels were safe and immunogenic. The frequency of solicited reactions was highest at the 100 μg dose. Administration of a second injection significantly increased the levels of anti-PhtD antibodies (ClinicalTrials.gov registry no. NCT01444001).