A VAR2CSA:CSP conjugate capable of inducing dual specificity antibody responses

Sungwa Matondo, Susan Thrane, Christoph Mikkel Janitzek, Reginald Adolph Kavishe, Steven Boniface Mwakalinga, Thor Grundtvig Theander, Ali Salanti, Morten Agertoug Nielsen, Adam Frederik Sander
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Background: Vaccine antigens targeting specific P. falciparum parasite stages are under pre-clinical and clinical development. It seems plausible that vaccine with multiple specificities will offer higher protection. With this hypothesis, we exploited the Spy- Tag/SpyCatcher conjugation system to make a, post expression, dual antigen conjugate vaccine, comprising two clinically tested antigen candidates (CSP and VAR2CSA).

Methods: The DBL1x-DBL2x-ID2a region of VAR2CSA was genetically fused with SpyTag at N-terminus. The full-length CSP antigen was genetically fused to C-terminal SpyCatcher peptide. The covalent interaction between SpyTag/ SpyCatcher enables the formation of DBL1x-DBL2x-ID2a:CSP conjugate vaccine. Immunogenicity and quality of antibody responses induced by the conjugate vaccine, as well as a control CSP-SpyCatcher vaccine, was tested in BALB/c mice.

Results: Serum samples obtained from mice immunized with the conjugate vaccine were able to recognize both untagged DBL1x-DBL2x-ID2a as well as CSP antigen. Moreover, the geometric mean anti-CSP antibody titer was 1.9-fold higher in serum (at day 35 and 55 post-first immunization) from mice immunized with the conjugate vaccine, as compared to mice receiving the control vaccine.

Conclusion: The data obtained in this study serves as proof-of-concept for the simultaneous induction of antibodies directed against individual antigen components in a dual stage anti-malaria vaccine.