ABSTRACT HPV is one of the most common sexually transmitted diseases worldwide and is the caustic factor for about 5% of all human cancers. Most cases of cervical cancer (>96%) and oropharyngeal cancer (70%) are associated with HPV infections. Although current HPV vaccines have successfully decreased the prevalence of HPV types covered in the vaccinated groups, the prevalence of HPV types not covered by vaccines is still high. Currently, no curative treatments are available to millions of individuals with preexisting HPV infections. Our proposed study aims to address the knowledge gap raised in PAR-20-061 in understanding “the role of co- infection in cancer etiology and progression”. Emerging experimental and observational studies have demonstrated that vaginal microbiota may play a critical role in HPV-associated disease progression to cancer. We propose to test several novel hypotheses including vaginal bacteria and their metabolites as potential drivers or suppressors of immune responses linked with progression/regression of cervical cancers in humans. In healthy women, the vaginal microbial environment is dominated by lactobacillus species, polymicrobial microbiome profiles (CST-I). Several non-lactobacillus species, including polymicrobial microbiome profiles (CST-III and -IV), are associated with increased HPV infection/persistence and neoplasia formation. Interestingly, individuals with a relatively small lactobacillus (CST-I) community in the vagina are commonly colonized by non-lactobacillus bacteria (CST-III and -IV), which is characteristic of BV. Our preliminary in vivo studies have demonstrated that non-lactobacillus bacteria Gardnerella vaginalis and Mobiluncus mulieris (CST-IV) changed inflammatory pathways, thereby suggesting G. vaginalis and M. mulieris may promote papillomavirus persistence in the genital tract. We hypothesize that papillomavirus co-infection with BV- associated bacteria promotes viral persistence and genital mucosal dysplasia. To test our hypothesis, we will use our novel mouse papillomavirus and vaginal bacterial infection models to 1) determine the changes of endogenous vaginal microbiota that are associated with high vaginal dysplasia in both immunocompromised and immunocompetent mice (Aim 1); 2) determine the interaction between BV-associated bacteria and metabolites and papillomavirus associated tumor progression (Aim 2). This is the first such study in both the microbiome and papillomavirus fields. Our findings will shed light on an understudied yet significant problem in cervical cancer development that is relevant to humans.