Cd4+Cd25+ Immune Regulatory Cells Are Required for Induction of Tolerance to Alloantigen via Costimulatory Blockade

TLDR

Immune regulatory CD4+CD25+ cells are essential for self‑tolerance, T‑cell homeostasis, and preventing autoimmunity, and inducing tolerance to allogeneic grafts is a key goal in transplantation. The study aimed to test whether CD4+CD25+ cells regulate alloantigen responses and are essential for tolerance induction. This was investigated by tolerizing murine CD4+ T cells ex vivo with CD40L/CD40 or CD28/CTLA‑4/B7 blockade, leading to mixed leukocyte reaction hyporesponsiveness and in vivo tolerance. CD4+CD25+ T cells are potent regulators of alloresponses, and depletion abrogated tolerance induction while addback restored it, demonstrating their essential role in alloantigen tolerance and informing costimulatory pathway–targeted strategies.

Abstract

Immune regulatory CD4+CD25+ cells play a vital role in the induction and maintenance of self-tolerance and are essential for T cell homeostasis and the prevention of autoimmunity. Induction of tolerance to allogeneic donor grafts is a clinically desirable goal in bone marrow and solid organ transplantation. To determine whether CD4+CD25+ cells regulate T cell responses to alloantigen and are critical for tolerance induction, murine CD4+ T cells were tolerized to alloantigen via ex vivo CD40 ligand (CD40L)/CD40 or CD28/cytotoxic T lymphocyte–associated antigen 4/B7 blockade resulting in secondary mixed leukocyte reaction hyporesponsiveness and tolerance to alloantigen in vivo. CD4+CD25+ T cells were found to be potent regulators of alloresponses. Depletion of CD4+CD25+ T cells from the CD4+ responder population completely abrogated ex vivo tolerance induction to alloantigen as measured by intact responses to alloantigen restimulation in vitro and in vivo. Addback of CD4+CD25+ T cells to CD4+CD25− cultures restored tolerance induction. These data are the first to indicate that CD4+CD25+ cells are essential for the induction of tolerance to alloantigen and have important implications for tolerance-inducing strategies targeted at T cell costimulatory pathways.