Local and systemic immune responses during syphilis infection

PROJECT SUMMARY Syphilis has been a scourge for thousands of years. It has been impossible to eradicate due to biological and societal barriers. Despite curative therapy and public health work, incidence is rising in underrepresented minorities, men who have sex with men, women, and children. An effective syphilis vaccine will be a key tool

for control and eradication. During infection, Treponema pallidum (Tp) bacteria are largely cleared from primary and then secondary infectious lesions by immune mechanisms, including antibody-mediated phagocytosis by IFNγ-activated tissue macrophages. Prior efforts to create a syphilis vaccine focused on antibodies against

rare outer membrane proteins. These only generate partial protection in rabbits and have not advanced to human trials. Notably, these candidates did not specifically target T-cell responses. The premise of this K08 application is that inclusion of T cell antigens will drive effective antibody responses and macrophage

activation, and should be a goal for vaccine design. We hypothesize that there are population prevalent Tp T cell antigens. Prior to my work, there are no reported human Tp T cell antigens with epitope validation. Aim 1 focuses on acquired immunity, including identification of dominant/prevalent CD4 T cell antigens. I will use a

suite of methods established in my mentor’s lab to detect, enrich, and expand Tp-specific CD4 T cells from blood. We have also shown that Tp-specific CD4 T cells are naturally enriched in situ in small biopsies of secondary syphilis lesions. My established IRB protocols and subject referral pathways have allowed me to

demonstrate that Tp-specific T cells remain in skin for at least 6 months after therapy. CD4 T cells from blood and biopsies will be screened with a large panel of rationally chosen recombinant Tp proteins and T cell reactivity thoroughly validated. Syphilis lesions are rich in B cells that secrete antibodies (plasma cells, PC).

Aim 1 will examine the hypothesis that lesion PC secrete Tp-specific IgG. While Tp is canonically an extracellular pathogen, not expected to elicit peptide-specific CD8 T cells, abundant CD8α-expressing cells do occur in lesions. If Aim 2 confirms the presence of CD8αβ T cells with hypervariable T cell receptors in lesions,

Aim 1 will examine their fine specificity for potential vaccine use. Aim 2 focuses on the innate immune response to Tp in active and healed syphilis lesions. Immunohistochemistry and single cell RNAseq will examine the hypothesis that parenchymal dermal cells express interferon and ISG genes in syphilis rashes,

and that innate leukocytes are also involved in the inflammatory reaction. Aim 2 Approaches will also yield IgG and CD4 T cell TCR sequences suitable for synthetic reconstruction of antibodies and TCR-bearing reporter cells, cutting-edge technologies in use in my mentors’ labs, to further address Aim 1 acquired immunity

hypotheses. Overall, knowledge of Tp T cell antigens will significantly improve our ability to design next- generation candidate vaccines against syphilis.