MESA Correspondents bring you cutting-edge coverage from the 67th ASTMH Annual Meeting
Session 19: “Transmission Blocking Immunity: From Biology to Interventions”
The large audience attracted to the symposium on ‘Transmission Blocking Immunity: from Biology to Interventions’ heard five presentations, each containing some original unpublished data.
The role of naturally acquired infections in stimulating immunity that reduces transmission has been the subject of great debate.
Will Stone showed that antibodies produced following natural exposure, when affinity purified against established vaccine candidates Pfs230 and Pfs48/45 then added to gametocytes in vitro, were capable of blocking transmission. Responses to novel gametocyte antigens were detected by protein microarray and antibody prepared in the same way also reduced mosquito infection rates. Early results from mouse immunization studies confirmed that some of these newly identified proteins may be viable targets for vaccine development.
Matthias Marti presented a comprehensive assessment of naturally acquired responses to antigens that are present on the surface of gametocyte-infected red blood cells. Such antigens were detected on the red blood cell membrane for early developing gametocytes but not mature gametocytes. Naturally acquired antibody responses to these antigens were associated with phagocytosis of gametocyte-infected red blood cells and with reduced gametocyte burden during natural infections. Genetic analysis revealed minimal variation of key antigens across strains, supporting their further examination as vaccine candidates.
Two groups updated progress on identification and assessment of candidate transmission-blocking candidates
Carolina Barillas-Mury showed that antibodies against the different domains of the vaccine candidate Pfs47 protein showed markedly different potency to block transmission. Antibodies against the immunodominant domains showed negligible effects whereas antibodies against a non-dominant domain reduced parasite development dramatically. The data suggested that the effective anti-Pfs47 antibodies interact with female gametocytes and prevent fertilization.
Arianna Marini presented progress on the characterization and expression of established and novel Transmission Blocking Vaccine antigen candidates. In addition, she presented promising tools to enhance immune responses generated by such antigens, including a novel approach with the decoration of Virus Like Particles by Plug-and-Display technology.
Ashley Birkett summarized historical and recent clinical trial results with transmission blocking vaccine candidates from a funders perspective. Whereas early results with Pfs25 were disappointing, recent findings with Pfs230 hold great promise. He highlighted the need for novel candidate antigens and stressed the importance of assays that bridge early clinical testing to field deployment.
Taken together, these presentations exemplified recent achievements in understanding naturally acquired transmission reducing immunity and considerable progress in moving towards promising transmission blocking vaccines.
Co-chairs: Matthias Marti (University of Glasgow, Glasgow, United Kingdom) and Teun Bousema (Radboudumc, Nijmegen, Netherlands)
This report was written by Teun Bousema with editorial support from Professor Graham Brown.