Development and characterization of the mait-boost knock-in (mbki) mouse to investigate mait cell biology and cancer immunotherapy

The National Institute of Allergy and Infectious Diseases (NIAID) awarded the Regents of the University of Colorado, doing business as University of Colorado-Denver, $429,000 on February 1, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855) to develop and characterize the MAIT-Boost Knock-In (MBKI) mouse model for investigating mucosal-associated invariant T (MAIT) cell biology and cancer immunotherapy.

The funded research addresses the limitation that MAIT cells are rare in commonly used laboratory mouse strains, including C57BL/6, restricting physiological study. The project uses genetic engineering to generate the MBKI mouse by replacing TRAV19 with TRAV1 and TRAJ56 with TRAJ33, redirecting T-cell receptor alpha (TCRA) recombination to favor the canonical TRAV1-TRAJ33 configuration required for MAIT cell development. This approach maintains natural TCR diversity and thymic selection while increasing MAIT cell frequency, avoiding the complications of existing transgenic or infection-based models.

The project will characterize the frequency, tissue distribution, and functional properties of MAIT cells in MBKI mice, assess the impact of these modifications on TCRA rearrangement dynamics and other immune subsets including gamma-delta T cells and invariant natural killer T cells, and evaluate whether increased MAIT cell frequency enhances melanoma tumor control for cancer immunotherapy applications. Performance takes place in Aurora, Colorado, with a period of performance from February 1, 2026, through January 31, 2028. This is a Project Grant, classified as assistance funding.

Abstract

This research project seeks to develop and characterize a novel mouse model to address the limitations of current systems for studying mucosal-associated invariant t (mait) cells. Mait cells are a conserved subset of t lymphocytes that bridge innate and adaptive immunity by recognizing microbial metabolites presented by MR1 molecules. They play critical roles in infection control, cancer immunity, and tissue homeostasis. Despite their functional importance, mait cells are rare in commonly used laboratory mouse strains, including C57BL/6 (B6), which restricts their study under physiological conditions. Existing approaches, such as TCR transgenic mice or artificial expansion through infection, alter the natural TCR repertoire or rely on inflammation, complicating the study of mait cells' development and function. This proposal leverages a genetic engineering strategy to generate the mait-boost knock-in (mbki) mouse model, which increases mait cell frequency while maintaining natural TCR diversity and thymic selection. By replacing TRAV19 with TRAV1 and TRAJ56 with TRAJ33, the mbki model redirects tcra recombination to favor the canonical TRAV1-TRAJ33 configuration required for mait cell development. This approach is designed to boost mait cell numbers without the unintended consequences of existing models, offering a physiologically relevant system for studying their biology. The project aims to characterize the frequency, tissue distribution, and functional properties of mait cells in mbki mice. IT will also assess the broader impact of these modifications on tcra rearrangement dynamics and other immune subsets, including GD t cells and inkt cells. Finally, the mbki model will be used to evaluate whether increased mait cell frequency enhances melanoma tumor control, addressing their potential for cancer immunotherapy. This work will provide fundamental insights into mait cell biology and create a platform for developing therapeutic strategies targeting infections, cancer, and immune dysregulation.