Compressed sequential infection regimen to model immune responses to systemic and mucosal vaccination - PROJECT SUMMARY/ABSTRACT Laboratory mice exhibit underdeveloped immune systems which fail to accurately predict human responses to challenges such as vaccination. Intentional exposure of these mice to environmental microbes (creating “dirty” mice) through various approaches has been shown to confer effective maturation of the immune system, but generally requires specialized facilities which are not widely available to the research community. Rapid sequential infection with six murine viral pathogens, beginning in early life to mimic human viral exposures, is sufficient to drive immune maturation and yields mice available for subsequent challenge at 10 weeks of age. Viral pathogens selected include those frequently identified in and transferred from other “dirty” mouse models. This rapid sequential infection regimen dramatically alters circulating immune cells as well as total serum antibody and cytokine levels, and critically, also diminishes specific serum antibody responses to both intramuscular and intranasal SARS-CoV-2 vaccination. Intriguingly, the regimen also stimulates robust changes in the endogenous bacterial microbiota. Thus, this sequential infection model mimics phenotypes observed in other microbially-experienced mice and in human adults, and it can be readily implemented in standard animal facilities without special containment protocols. In the studies proposed here, this sequential infection regimen will be further refined and simplified, and the role of microbiota changes in immune maturation in this model will be explored. In Aim 1, the sufficiency and necessity of combinations of and individual viral exposures to stimulate immune maturation will be defined. Antibody responses to systemic and mucosal SARS-CoV-2 vaccination, as well as robust immunophenotypes observed in the sequential infection model, will serve as key assays. In Aim 2, the effects of sequential infections on the bacterial, viral and fungal microbiome will be defined, and the functional contributions of the endogenous microbiota to immune maturation will be tested. Microbiome profiling, germ-free mice, and antibiotic treatment with fecal transplants will be used to elucidate microbiota contributions. These studies will use established approaches supported by extensive published and preliminary data to reveal the contributions of individual viral pathogen exposures as well as endogenous microbial communities to immune maturation following the rapid sequential infection regimen. Completion of this proposal will yield a simplified “dirty” mouse model that is tractable and affordable for the majority of investigators studying infectious diseases, vaccine responses, or immune outcomes. Additionally, the proposed experiments will address an important open question about the relative importance of the endogenous microbiota versus specific viral pathogen exposures in immune maturation of “dirty” mice. Finally, they will serve to provide novel insights into immune responses directed against mucosal vaccines, which may have predictive value as this vaccination approach is increasingly implemented in humans.
