Conserved Protective Mechanisms in Radiation and Genetically Attenuated uis3(-) and uis4(-) Plasmodium Sporozoites

Immunization with radiation attenuated Plasmodium sporozoites (RAS) elicits sterile protective immunity against sporozoite challenge in murine models and in humans. Similarly to RAS, the genetically attenuated sporozoites (GAPs) named uis3(-), uis4(-) and P36p(-) have arrested growth during the liver stage development, and generate a powerful protective immune response in mice. We compared the protective mechanisms in P. yoelii RAS, uis3(-) and uis4(-) in BALB/c mice. In RAS and GAPs, sterile immunity is only achieved after one or more booster injections. There were no differences in the immune responses to the circumsporozoite protein (CSP) generated by RAS and GAPs. To evaluate the role of non-CSP T-cell antigens we immunized antibody deficient, CSP-transgenic BALB/c mice, that are T cell tolerant to CSP, with P. yoelii RAS or with uis3(-) or uis4(-) GAPs, and challenged them with wild type sporozoites. In every instance the parasite liver stage burden was approximately 3 logs higher in antibody deficient CSP transgenic mice as compared to antibody deficient mice alone. We conclude that CSP is a powerful protective antigen in both RAS and GAPs viz., uis3(-) and uis4(-) and that the protective mechanisms are similar independently of the method of sporozoite attenuation.