Tuesday, September 26, 2023
9/26/2023
ABSTRACT Gonorrhea affects over 87 million people annually globally. In 2019, over 600,000 cases of gonorrhea were reported to the CDC, a 92% increase since the historic low in the US in 2009. However, the true incidence of cases annually in the US is estimated to be ~1.5 million. The spread of antimicrobial resistance has severely limited treatment options – currently, ceftriaxone is the only approved first line of treatment. A safe and effective vaccine against gonorrhea is urgently needed. Lipooligosaccharide (LOS) is the most abundant molecule on the gonococcal surface and plays multifaceted roles in bacterial virulence. A LOS epitope recognized by mAb 2C7 (therefore called the 2C7 epitope) is expressed by >95% of Ng in vivo; Ng mutants that do not express the 2C7 epitope are attenuated in mice. Our group has developed a peptide mimic (mimitope) of the 2C7 epitope, which when configured as a multi-antigen peptide (MAP) elicits bactericidal Abs and attenuates Ng colonization in mice. Further, we have elucidated the mechanism of action of MAP as complement-mediated killing (killing through membrane attack complex), strongly suggesting serum bactericidal activity as a mechanistic correlate of protection. In a collaborative venture with Evaxion Biotech, we screened 30 antigens that were identified by EDEN, Evaxion’s proprietary in silico platform, for immunogenicity, bactericidal activity and efficacy in the mouse vaginal colonization model. These studies identified two cell division proteins as promising candidates based on efficacy in vivo. When configured as a fusion protein (chimera), the cell division proteins showed improved ac- tivity in vivo compared to individual proteins and currently is our lead protein vaccine candidate. DNA and mRNA vaccines have proven very successful in the fight against the Covid-19 pandemic. These platforms elicit high levels of protection, have proven safe, are rapidly adaptable and economical. Here, we will leverage these two newer vaccine platforms to deliver the protective gonococcal antigens. A multivalent vaccine has the advantage of broader strain coverage, improved efficacy and would also raise the barrier for development of resistance. In Aim 1, we will evaluate DNA vaccine constructs that contain the 2C7 LOS mimitope (PEP1) configured as an octameric concatemer (PEP1_OCT), the cell division protein chimera, or a combination of the two. Serum will be assessed for antibody titers and complement-dependent bactericidal activity, as well durability of responses. Comparisons will be made with the protein versions of these vaccines currently under development. Mucosal (vaginal) Ab responses will also be measured. T cell responses will be measured by ELISpot. Based on data in vitro, the lead DNA vaccine formulation(s) will be assessed for efficacy in the mouse vaginal colonization model. In Aim 2 the constructs described in Aim 1 will be expressed using an mRNA vaccine delivery platform. As in Aim 1, we will evaluate Ab titers in serum and vaginal fluid, measure serum bactericidal activity, T cell responses and efficacy of the lead mRNA vaccine formulation(s) in the mouse model of gonorrhea. Successful completion of the work in this proposal will identify a lead gonococcal DNA and/or mRNA vaccine for further pre-clinical development.
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