Antigen diversity and antibody-mediated immunity to malaria

The malaria parasite Plasmodium falciparum exhibits extensive complexity and antigenic polymorphism which are challenges for malaria control and elimination efforts, especially for vaccines. To overcome these challenges, we need to better understand its genetic complexity and immune responses towards it.

In Study I we developed a novel tool to study sequence diversity of the polymorphic msp2 locus. This tool can be used to analyze structural variation and sequence conservation in msp2 and other polymorphic markers. In Study II we assessed the genetic diversity of msp2 across sub-Saharan Africa using fragment size genotyping and long-read sequencing. We observed prevalent size variants that were maintained in the parasite population across a broad spatiotemporal scale, presenting a possible target for vaccine development. We revealed the extensive sequence diversity of full-length msp2 within single size variants. Maintenance of size variants with high sequence diversity supports the biological importance of gene length. In Study III we assessed genetic diversity over time in a village in Tanzania with declining malaria transmission. Prevalent msp2 size variants were maintained over four decades with declining transmission. Our results support the further study of MSP2 in relation to immunity and potential as a malaria vaccine candidate.

In Study IV we evaluated the targets of naturally acquired, antigen-specific antibody responses to variants of MSP2 isolated from the field. We show that IgG responses to MSP2 are variant-specific, and do not target the conserved termini. We detected cross-reactivity to MSP2 variants in minimally exposed Swedish travelers. IgG responses to the termini may be reliant on protein structure and epitope accessibility. In Study V we assessed memory B-cell responses to MSp2 variants in highly exposed individuals and non-immune travelers using a multiplex FluoroSpot assay, which has not been done before. We detected memory B-cell responses to MSP2 in both groups. Breadth of response was greater in highly exposed Kenyan individuals than travelers. We detected simultaneously cross-reactive, MSP2-specific memory B-cells in highly exposed individuals, , showing they are developed under repeated exposure.

This PhD project reveals extensive diversity of msp2 across Africa and identifies MSP2 variants of interest for future study and targets for vaccination. Finally, it helps to understand the development of immune responses targeting the highly polymorphic vaccine candidate antigen MSP2.

List of scientific papers

I. A genomic platform for surveillance and antigen discovery in Plasmodium spp. using long-read amplicon sequencing. Plaza DF, Zerebinski J, Broumou I, Lautenbach MJ, Ngasala B, Sundling C, Färnert A. Cell Reports Methods, 2023;3(9):100574. https://doi.org/10.1016/j.c…

II. Widespread variants of the highly polymorphic Plasmodium falciparum vaccine candidate antigen MSP2 across Sub- Saharan Africa. Zerebinski J, Broumou I, Kimenyi KM, Aklillu E, Andrade CM, Babiker H, Bejon P, Cherif MK, Crompton PD, Fançony C, Foroogh F, Gil JP, Homann MV, Trovoada MdJ, Kapulu M, Kiwuwa SM, Kweku MA, Liljander A, Lopes D, Marsh K, Mutemi DD, Ngasala B, Normark J, Orikiiriza J, Persson KEM, Portugal S, Ribacke U, Sirima SB, Sonden K, de Sousa TN, Traore B, Tijani MK, Eckerdal N, Villner P, Ochola-Oyier LI, Plaza DF, Färnert A. J Infect Dis 2026. https://doi.org/10.1093/INF…

III. Naturally acquired IgG responses to Plasmodium falciparum do not target the conserved termini of the malaria vaccine candidate Merozoite Surface Protein 2. Zerebinski J, Margerie L, Han N, Moll M, Ritvos M, Jahnmatz P, Ahlborg N, Ngasala B, Rooth I, Sjoeberg R, Sundling C, Yman V, Färnert A, Plaza DF. Frontiers in Immunology, 2024;15:1501700. https://doi.org/10.3389/fim…

IV. Diversity of the polymorphic Plasmodium falciparum merozoite surface protein 2 in a Tanzanian village over nearly four decades with declining transmission. Zerebinski J, Broumou I, Mutemi DD, Kinabo CM, Jesaja S, Mhoja L, Ally J, Rono J, Homann MV, Rooth I, Foroogh F, Yman V, Ngasala B, Plaza DF, Färnert A [Manuscript]

V. Memory B cell responses to variants of the polymorphic P. falciparum antigen MSP2 using multiplex FluoroSpot. Zerebinski J, Makusa P, Borgenstam A, Tishadas S, Mwacharo J, Foroogh F, Musyoki J, Jahnmatz P, Plaza DF, Hanke L, Yman V, Sundling C, Ndungu FM, Färnert A [Manuscript]