Modulation of T Cell Trafficking to the Small and Large Intestine Mucosa

Abstract

Infections of the gastrointestinal (GI) tract have a high disease burden globally, and effective vaccines are needed to reduce the spread of many GI pathogens. A majority of clinical and pre-clinical vaccines are delivered parenterally, such as by subcutaneous (s.c.) or intramuscular (i.m.) injections. While these routes are effective at establishing systemic protection, they are often poor at eliciting protective antibodies and T cell responses in the gut, leaving the mucosa susceptible to pathogen entry, and possibly replication and transmission. Therefore, a strategy that generates gut-tropic T cells in a parenteral immunization has the potential to improve vaccine efficacy, which is presented in my dissertation. Modulation of CD8+ T cell trafficking was achieved by adjuvantation with “gut-imprinting” signals – tissue-specific cues that promote entry (“homing”) of antigen-experienced lymphocytes into the gut, through up-regulation of homing molecules. I immunized mice s.c. with a model antigen chicken ovalbumin (OVA) and an adjuvant CpG, in combination with gut-imprinting compounds. Vaccine supplementation with all-trans retinoic acid (ATRA) as well as Am80, a synthetic retinoic acid receptor (RAR) agonist, increased expression of small intestine homing molecules α4β7 and CCR9, increased T cell trafficking to the small intestine, and established resident-memory T (Trm) cells. Additionally, an Am80-encapsulating polymeric nanoparticle was developed which showed equivalent gut-imprinting capacity and improved clinical translatability, compared to the un-encapsulated Am80. Unlike the small intestine, Am80 alone was sub-optimal at targeting CD8+ T cells to the large intestine. Optimal targeting to the cecum and colon required a combination of RAR agonist (Am80) and aryl-hydrocarbon receptor (AHR) agonist (10-CL-BBQ), respectively up-regulating α4β7 and the large intestine homing molecule GPR15. Both the RAR-α4β7 axis and AHR-GPR15 axis were indispensable for large intestine trafficking, whereas AHR was dispensable for small intestine trafficking, suggesting a mechanism for compartmentalized T cell entry into different segments of the GI tract. In the s.c. vaccination model, combined administration of Am80 and 10-CL-BBQ yielded the most robust large intestine trafficking α4β7+GPR15+ effector T (Teff) cells, established Trm cells in the total intestinal tract, and conferred protection against intra-rectal challenge with Listeria Monocytogenes. In summary, I conclude that CD8+ T cell trafficking to the small and large intestine are differentially regulated by the RAR and AHR signaling pathways, and that adjuvantation of parenteral vaccines with agonists of RAR and AHR are viable approaches to enhance T cell protection of the intestinal tract.