Optimizing precision Treg therapy to control anti-drug antibodies

The focus of this proposal is to develop and translate effective regulatory T cell (Treg) therapies to
suppress anti-drug antibody (ADA) responses to biotherapeutics such as clotting factor replacement
therapy for the monogenic disorder hemophilia. Despite high potential, current Treg-based treatments are
hampered by low starting numbers, challenges in scalability, and unwanted off-target suppression.
Redirecting specificity by engineering antibody-based synthetic receptors towards conformational
antigenic epitopes can surmount these obstacles. Whereas this concept has been highly successful in
generating chimeric antigen receptor (CAR) T cells for blood cancers, adapting engineered Tregs for
tolerance applications is still evolving. This proposal derives from our recent findings that a synthetic T cell
receptor fusion construct (TRuC) can suppress ADA responses to clotting factor VIII (FVIII) in a murine
model of hemophilia. TRuCs combine the specificity of an antibody with the internal signaling machinery
of a TCR by incorporating into the endogenous TCR-CD3 complex of the engineered Treg. We find that
the TCR-like signaling of TRuC Tregs can deliver suppression in a physiological manner. In contrast, the
non-physiological signaling of a CAR can negatively affect Treg suppressive capacity. Why different
engineered receptors with the same scFv would result in dramatically divergent signaling and functional
outcomes is as yet unclear.
This proposal combines mechanistic understanding of synthetic receptor engineering with targeted
potentiation of the Treg suppressive effect to achieve ADA tolerance. In Aim 1, we will test the hypothesis
that careful considerations in synthetic receptor design, such as receptor affinity need to be made such
that activation thresholds are regulated to maintain optimal suppressive function. Further, we will examine
mechanisms by which engineered Tregs with specificity to a soluble antigen like FVIII can suppress antigen
specific B cells. In Aim 2, we will explore strategies to enhance in vivo localization, persistence, and
functionality of TRuC Tregs. We will co-administer a novel single chain IL-2 immunocytokine to drive
selective proliferation of TRuC Tregs, biasing immune activation toward tolerogenic outcomes. In Aim 3,
we will evaluate TRuC Treg efficacy in the presence of established ADAs in combination with
pharmacological immunosuppressants to establish long term tolerance and lower the risk of ADA
recurrence. Successful completion of these aims will generate potent antigen specific Tregs for effective
suppression of ADA responses to biotherapeutics. These studies will provide proof of principle for the utility
and mechanism of action of engineered Tregs and provide steps for clinical translation. The modularity of
the components of this platform will allow ready extension to suppress ADAs for other conditions, in
autoimmune disease and transplantation tolerance.

Grant Number: 1R56AI175187-01A1
NIH Institute/Center: NIH
Principal Investigator: Moanaro Biswas