# Mechanistic studies on novel aspects of robust transplantation tolerance (Project 1)

> **NIH NIH P01** · UNIVERSITY OF CHICAGO · 2020 · $560,116

## Abstract

PROJECT SUMMARY
Transplantation tolerance, a state in which immunosuppression can be stopped while grafts remain functional,
is a major goal in the field to reduce the morbidity associated with long-term usage of immunosuppression.
Tolerance can be spontaneously achieved in rare patients. However, a proportion of tolerant patients lose
their grafts after years of tolerance, sometimes following episodes of infections, indicating that tolerance is not
always robust and persistent. The goal of Project 1 has been to investigate the mechanisms underscoring
tolerance when it is robust and durable. To address this question mechanistically, we used a mouse model of
donor-specific transplantation tolerance that we consider robust because it withstands many inflammatory
challenges, and tracked graft-reactive T cells using seeded TCR-Tg T cells, or using fluorescent pMHC Class I
and Class II multimers to identify endogenous populations. We have found that robust tolerance depends on
multiple redundant cell-intrinsic and -extrinsic (constraint of cell numbers, Tregs, engagement of PD-L1)
mechanisms to control alloreactive T cells. In this model, infection with Listeria monocytogenes (Lm) 60 days
after transplantation eroded the tolerance, in that elimination of single mechanisms of tolerance was sufficient
to precipitate graft rejection after, but not before infection. Therefore, our programmatic research revealed that
transplantation tolerance is not an all-or-none state but rather reflects a gradation of individual mechanisms of
T cell tolerance, each of which may be sufficient to prevent rejection, but several of which together maintain a
more robust tolerance. In this Competitive Renewal, we will concentrate on an important property of robust
tolerance, namely its resilience, defined as the ability to “spring back” after a period of stress. Indeed, Lm
infection in tolerant hosts precipitated rejection in about 50% of the mice, but tolerance re-emerged when the
inflammation subsided, and second donor-matched allografts were spontaneously accepted. This `memory of
tolerance' that dominated over a memory of rejection was dependent on regulatory T cells (Tregs) and their
suppression of the alloreactive conventional T cells (Tconv) that had not been deleted during the induction of
tolerance. Analysis of tolerant Tconv before and after infection revealed 2 novel properties: programmed T
cell-intrinsic dysfunction, and the preferential preservation of low avidity graft-reactive T cell clones. We
hypothesize that these two features make Tconv more susceptible to regulation, and are thus critical for
tolerance to be robust at initiation and to return after transient reactivation by inflammatory events. We propose
two aims: Aim 1. To define the molecular characteristics and functional defects of T cell-intrinsic dysfunction;
Aim 2. To assess the impact of controlling T cell `avidity maturation' in transplantation tolerance. We anticipate
that the completion of the...

## Key facts

- **NIH application ID:** 9985706
- **Project number:** 5P01AI097113-09
- **Recipient organization:** UNIVERSITY OF CHICAGO
- **Principal Investigator:** Maria-Luisa Alegre
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $560,116
- **Award type:** 5
- **Project period:** — → —

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9985706

## Citation

> US National Institutes of Health, RePORTER application 9985706, Mechanistic studies on novel aspects of robust transplantation tolerance (Project 1) (5P01AI097113-09). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9985706. Licensed CC0.

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