Directed evolution of TCRs with improved antigen sensitivity

Project Summary
T cells express T cell receptors (TCRs), which recognize antigens presented as peptides displayed by major
histocompatibility complexes (pMHC). Recognition of pMHC antigens activates the T cell, enabling immune
effector functions leading to the clearance of infected or transformed cells. TCR-T cell therapies are an
engineered immunotherapy that take advantage of this biology to engineer T cells to express a tumor-specific
TCR to redirect T cell responses against cancer cells. These therapies have achieved objective responses for
some cancer patients in clinical trials but have also suffered from limitations in efficacy and toxicity.
Since TCRs against many classes of tumor antigens are naturally low affinity, the TCRs used for these therapies
often require affinity maturation to achieve efficacy. Unfortunately, this process can also increase the affinity for
off-target peptides on healthy cells. Several clinical trial patients have suffered fatal toxicities as a result. Further,
affinity maturation is labor intensive, and the resulting mutations are only applicable to one TCR. Cancer antigens
are highly diverse, so it is limiting to repeat this process for every new antigen.
We propose a new TCR engineering strategy that we hypothesize will address these limitations. We will
implement high throughout library screens of TCR constant region variants to select for mutations that improve
TCR signaling strength. Because these modifications are not in the TCR antigen recognition domains, they have
the potential to improve efficacy without introducing cross-reactivity. Further, they could be applicable to all
TCRs, regardless of their targets, which would eliminate the need to re-engineer the TCR for each different
antigen. Together, these approaches could identify efficacious, safe, and broadly applicable TCRs as candidates
for TCR-T cell therapies.

Grant Number: 1R21CA305319-01
NIH Institute/Center: NIH
Principal Investigator: Michael Birnbaum