Targeting Conserved Molecular and Structural Features of Apicomplexans Towards a Rational Vaccine Design

PROJECT SUMMARY_____________________________________________________________________ Parasitic diseases remain a problem worldwide largely due to the lack of vaccines to effectively interrupt transmission or infection, as parasites often develop resistance to drugs. A combination of different factors principally drives the lack of vaccines against parasitic diseases, including a limited understanding of the nature of the humoral immune response and difficulties in proper expression of the candidate immunogen. Our current work suggests that the GPI anchor has a vital role in humoral immune response to GPI-anchored proteins (GPI- APs) and most vaccine efforts have utilized GPI-APs - which constitute the bulk of surface proteins in parasites, as immunogens. However, in these vaccine formulations, the GPI-APs are without the GPI anchor to enable soluble expression of such proteins. In this grant submission, we have shown that de-lipidation of the GPI anchor significantly reduces antibody reactivity to GPI-APs of Toxoplasma gondii, a widespread Apicomplexa parasite of animals. We hypothesize a role of the GPI anchor in humoral immune response and propose using mRNA technology as an efficient method for accurate delivery of GPI-APs to the immune system to understand its role following vaccination. We also propose the use of mRNA vaccines for the efficient delivery of highly conserved antigens of the parasite's invasion machinery, a handful of which we propose as excellent targets to halt invasion of apicomplexans. Thus, we will employ tools in immunology, molecular parasitology, vaccinology, and biochemistry to dissect the aims of the study. In Aim 1, the role of the GPI anchor in humoral immunity to T. gondii will be deciphered by comparing vaccine efficacies of parasite GPI-APs with and without their GPI anchorage following immunization. In Aim 2, the invasion machinery of T. gondii will be targeted by vaccine- elicited antibodies against conserved apical proteins of the plasma membrane that confer fitness to the parasite. With the overall goal of the project being to block infection of T. gondii and apicomplexans in general, this R21 proposal will provide new insights in vaccine development against parasitic diseases.