Role of antigen valency and pattern recognition receptor ligands in HPV vaccine-induced durable B cell memory

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ABSTRACT Most vaccines protect by generating antibodies. Live attenuated vaccines induce lasting humoral immunity; however, humoral immunity for many subunit vaccines wanes over time. Because live attenuated vaccines may not be feasible for all pathogens or recipients, the development of subunit vaccines that elicit potent and long- lived antibody responses is essential. Vaccinology has focused for decades on developing subunit vaccines that elicit robust and/or broad antibody responses to human pathogens. However, it is crucial to public health that subunit vaccines also generate durable antibody responses. Thus, basic research is needed to know how to reliably design such vaccines. The highly effective 9-type human papillomavirus subunit vaccine (HPV-9) protects against nine HPV types that commonly cause cancer (e.g., HPV 16). Moreover, its antibody durability is superior to that of many other approved subunit vaccines. Thus, HPV-9 represents a model subunit vaccine for studying the generation of robust and enduring antibody responses. Unlike most other subunit vaccines, HPV vaccines are comprised of a highly repetitive, high valency antigen: virus like particles (VLP). Each VLP HPV type assembles from 360 units of its major capsid protein, L1. In addition, L1 binds DNA, and HPV-9 contains recombinant L1 DNA. Whether high antigen valency or antigen-associated DNA generally enhances the formation of durable B cell memory is not well studied. With regard to HPV, L1 VLPs elicit higher peak neutralizing antibody responses than L1 pentamers and anti-VLP antibody responses depend on MyD88, a component of a DNA sensing pathway. What is lacking is an understanding of whether vaccine DNA enhances the magnitude of antibody responses to HPV-9 and whether antigen valency or vaccine DNA plays a role in the induction of durable HPV-specific B cell memory. This proposal will address those gaps through two aims. The first aim is to test the dependency of peak and long-lived HPV-9-elicited B cell responses on DNA sensors. Wildtype mice and mice deficient in various DNA sensing pathways will be immunized with HPV-9 or alum. Before and at various time points after each HPV-9 dose, HPV-specific neutralizing antibody, memory B cell, and bone marrow plasma cell responses will be analyzed. In this way, the role of DNA sensing in stimulating peak, recall, and long-term (≥12 months) B cell responses will be assessed. The second aim is to evaluate the dependency of long-lived HPV-specific B cell memory on antigen valency. Mice will be immunized with three doses of monomeric HPV 16 L1 (1-mers), HPV 16 L1 pentamers (5-mers), or HPV 16 L1 VLPs (360-mers). Before and at various times after each antigen dose, HPV 16-specific neutralizing antibody, germinal center B cell, memory B cell, and bone marrow plasma cell responses will be analyzed. Responses to 1-mer, 5-mer, and 360-mer antigens will be compared. In this way, the role of antigen valency in the induction of long-term B cell memory will be tested. This work will advance knowledge of how HPV-9 achieves durable antibody responses and inform the development of vaccines with longer-lasting humoral immunity and improved protection against other pathogens.