Chimeric rodent malaria parasites put P. vivax vaccine antigens SSP3 and SPECT1 to the test

Developing an effective vaccine against Plasmodium vivax malaria remains one of the most pressing goals in global health, and a new preclinical study reports a practical step toward that goal. Researchers generated transgenic Plasmodium berghei parasite lines expressing two P. vivax pre-erythrocytic antigens, SSP3 and SPECT1, creating chimeric research tools that allow these candidates to be evaluated in a rodent malaria system before any testing in human volunteers. The work addresses a persistent bottleneck: screening new P. vivax vaccine candidates typically requires controlled human studies, so robust preclinical models are needed to triage antigens early.

The rationale for targeting pre-erythrocytic stages is rooted in the biology of P. vivax itself. Unlike P. falciparum, P. vivax forms hypnozoites, dormant liver stages that can reactivate months or even years after the initial infection, causing relapse malaria and sustaining transmission. Antigens expressed before the blood stage therefore offer the potential to prevent clinical malaria from both primary and relapse infections. The circumsporozoite protein (CSP) is the leading pre-erythrocytic candidate and forms the basis of the current P. falciparum vaccines RTS,S and R21/Matrix-M, but studies indicate that CSP provides limited protection against P. vivax, underscoring the need to identify additional antigens.

To build the models, the team engineered chimeric Pb-Pv SSP3 and Pb-Pv SPECT1 P. berghei lines, in which the P. vivax orthologs are expressed in the rodent parasite. Across the parasite life cycle, both lines showed normal development in mice and in mosquitoes, indicating that the transgenic constructs did not disrupt the biological processes required for parasite propagation. That functional compatibility is what makes the lines usable as standardized challenge tools for vaccine evaluation.

The immunological results were measured but modest. Antisera raised against recombinant Pv SSP3 and Pv SPECT1, formulated with TiterMax Gold adjuvant, reduced sporozoite invasion of hepatocytes in vitro, with mean inhibitions of 27 percent for SSP3 and 14 percent for SPECT1. In vivo sporozoite challenge studies showed sterile protection in 10 percent of mice immunized with recombinant Pv SPECT1, whereas recombinant Pv SSP3 provided no detectable protection under the conditions tested. Neither antigen, in other words, delivered substantial protection in this system.

The authors are careful about the interpretation. The failure to observe strong protection does not by itself disqualify either antigen; immunization conditions, antigen delivery, and adjuvant choice all shape outcomes in such experiments. What the study does deliver is infrastructure. The transgenic P. berghei lines generated here serve as platforms for evaluating SSP3 and SPECT1 across different delivery systems and adjuvanted formulations, allowing candidate combinations to be screened systematically before the most promising are advanced toward clinical testing in the effort to build a vaccine capable of blocking both primary and relapse P. vivax infections.

Subject of Research: Transgenic Plasmodium berghei models for evaluating Plasmodium vivax pre-erythrocytic vaccine antigens SSP3 and SPECT1

Article Title: Transgenic Plasmodium berghei expressing P. vivax pre-erythrocytic antigens SSP3 and SPECT1 to elucidate their efficacy towards vaccine development

Article References: Kolli, S. K., Annamalai Subramani, P., Ramesar, J., Nicholas, J., Ogbondah, M. M., Barnes, S. J., Mahdavi, P., Salman, A. M., Ntumngia, F. B., Janse, C. J., & Adams, J. H. (2026). Transgenic Plasmodium berghei expressing P. vivax pre-erythrocytic antigens SSP3 and SPECT1 to elucidate their efficacy towards vaccine development. PLOS Neglected Tropical Diseases, 20(10), e0014810. https://doi.org/10.1371/journal.pntd.0014810

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014810

Keywords: malaria, Plasmodium vivax, Plasmodium berghei, SSP3, SPECT1, pre-erythrocytic antigens, vaccine development, sporozoites, hypnozoites, sterile protection, Transgenic, Plasmodium