(P15-LB) Developing a Synergistic, Multi-Epitope Antigen for use in a Cross-Serovar Chlamydia Trachomatis Vaccine.

Background
Chlamydia is the most common sexually transmitted infection reported to the CDC, with over 1,500,000 cases reported in 2020 alone, yet formulation of a protective chlamydia vaccine remains elusive. In humans, chlamydia is caused by infection with the gram-negative bacteria Chlamydia tracomatis (Ct). Amino acid sequence diversity of Ct strains classify Ct into 15 distinct serovars. Human infections have been found to be a heterologous mix of these serovars, with serovar E being the most prevalent. The porin protein, major outer membrane protein (MOMP), is the most abundant protein in all Ct life cycle stages, making it a desirable vaccine target.

Methods and Results
To determine the feasibility of a cross-serovar vaccine targeting MOMP, we performed a multi-protein sequence alignment of MOMP from all Ct serovars. As expected, the serovars are on average ~88% homologous to each other with majority of the sequence deviations concentrated within the previously described variable domain regions. To develop a cross-serovar vaccine against Ct, we then systematically analyzed the Immune Epitope DataBase (IEDB) to identify experimentally tested B- and T-cell epitopes against the aligned serovar E MOMP sequence. This computational analysis identified 11 linear sequences as putative epitope candidates. Of these candidates, 5 were predicted to bind T-cells, 2 were predicted to bind B-cells, and 4 were predicted to bind both immune cell types. To test these epitopes for desirable vaccine qualities, such as self-serovar/cross-serovar immunogenicity and specific CD8+ T-cell responses, we tested 14 antigen permutations containing 1-8 of the 11 putative epitopes in various immunological-based assays.

Conclusions
Through systemic analysis of established experiential data, we were able to identify 11 putative epitope sequences targeting Ct MOMP. We screened all 11 epitopes for single and synergistic effects promoting (or deterring) the desired qualities of a Ct vaccine, such as self-serovar and cross-serovar immunogenicity. Future iterations of the multi-epitope antigen identified in these studies can be used for development of either protein subunit or RNA-based Ct vaccines.