Abstract A170: Transient microbiota depletion enhances mucosal CD8 T-cell responses

CD8+ tissue resident memory T-cells (Trm) are poised for immediate reactivation in peripheral organs and have enhanced protective potential in comparison to circulating T-cells. Trm represent potential players in antitumor immunity that might be enhance the effectiveness of cancer vaccines. Vaccination strategies increasing accumulation of Trm cells in skin or in the genital tract augmented protection against tissue-specific pathogens in vivo. However, to date, no specific approach has been proposed to reinforce Trm in the intestinal mucosa. The microbiota shapes composition and functions of host immune populations, particularly in the intestinal tissue, where it determines the ratio between conventional and regulatory T-cells. This suggests that modulation of commensal communities might be exploited to augment numbers and function of gut-resident CD8 T-cells. Listeria monocytogenes attenuated strains are employed in clinical trials to promote immunity against tumor antigens and have been administered orally to healthy volunteers to promote mucosal immunity, proving safety of this approach. Developing more effective mucosal vaccination strategies based on oral administration of Listeria-based vectors, would have a great impact in the fight against tumors of the gastrointestinal tract, such as colorectal cancer, for which neoantigens are being discovered. Based on our recent observation that antibiotic treatment favors intestinal expansion of Listeria, we have devised an oral immunization strategy (TMDI, Transient Microbiota Depletion prior to Immunization) consisting of oral vaccination with an antigen-carrying Listeria strain following administration of a single dose of antibiotics. In mice, TMDI promoted expansion of engineered avirulent Listeria strains, resulting in striking expansion of the antigen-specific CD8+ Trm population (~20 fold), that additionally displayed potent effector functions. Mice immunized with this approach showed augmented protection upon rechallenge with high doses of pathogen.We found that increased accumulation of T-cells was dependent on both increased antigen load and stronger inflammatory stimuli; surprisingly, even when the vector was forcedly maintained at high levels in the intestinal lumen for several weeks, the elicited CD8+ Trm cells did not show any sign of exhaustion and retained the capacity to rapidly produce inflammatory cytokines upon antigen stimulation. In conclusion, we have identified a novel strategy to harness tissue resident CD8 T-cells against an epitope of choice by modulating microbiota density at the time of immunization, and set up a system to dissect the requirements for obtaining potent T-cell responses in the intestine. This tool can potentially be utilized to design improved vaccines against tumors of the intestinal tract. Citation Format: Simone Becattini, Alexander Louie, Ingrd M. Leiner, Eric Pamer. Transient microbiota depletion enhances mucosal CD8 T-cell responses [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A170.