Recombinant Full-length Plasmodium falciparum Circumsporozoite Protein–Based Vaccine Adjuvanted With Glucopyranosyl Lipid A–Liposome Quillaja saponaria 21: Results of Phase 1 Testing With Malaria Challenge

Background. Malaria is preventable yet causes >600 000 deaths annually. RTS,S, the first marketed malaria vaccine, has modest efficacy, but improvements are needed for eradication. Methods. We conducted an open-label, dose escalation phase 1 study of a full-length recombinant circumsporozoite protein vaccine (rCSP) administered with adjuvant glucopyranosyl lipid A–liposome Quillaja saponaria 21 formulation (GLA-LSQ) on days 1, 29, and 85 or 1 and 490 to healthy, malaria-naive adults. The primary end points were safety and reactogenicity. The secondary end points were antibody responses and Plasmodium falciparum parasitemia after homologous controlled human malaria infection. Results. Participants were enrolled into 4 groups receiving rCSP/GLA-LSQ: 10 µg × 3 (n = 20), 30 µg × 3 (n = 10), 60 µg × 3 (n = 10), or 60 µg × 2 (n = 9); 10 participants received 30 µg rCSP alone × 3, and there were 6 infectivity controls. Participants experienced no serious adverse events. Rates of solicited and unsolicited adverse events were similar among groups. All 26 participants who underwent controlled human malaria infection 28 days after final vaccinations developed malaria. Increasing vaccine doses induced higher immunoglobulin G titers but did not achieve previously established RTS,S benchmarks. Conclusions. rCSP/GLA-LSQ had favorable safety results. However, tested regimens did not induce protective immunity. Further investigation could assess whether adjuvant or schedule adjustments improve efficacy.