CD4 T Cell-Mediated Alloresistance to Fully MHC-Mismatched Allogeneic Bone Marrow Engraftment Is Dependent on CD40-CD40 Ligand Interactions, and Lasting T Cell Tolerance Is Induced by Bone Marrow Transplantation with Initial Blockade of this Pathway

Abstract

Costimulatory blockade can be used to promote allogeneic marrow engraftment and tolerance induction, but on its own is not 100% reliable. We sought to determine whether one or the other of the CD4 or CD8 T cell subsets of the recipient was primarily responsible for resistance to allogeneic marrow engraftment in mice receiving costimulatory blockade, and to use this information to develop a more reliable, minimal conditioning regimen for induction of mixed chimerism and transplantation tolerance. We demonstrate that a single anti-CD40 ligand mAb treatment is sufficient to completely overcome CD4 cell-mediated resistance to allogeneic marrow engraftment and rapidly induce CD4 cell tolerance, but does not reliably overcome CD8 CTL-mediated alloresistance. The data suggest that costimulation, which activates alloreactive CTL, is insufficient to activate alloreactive CD4 cells when the CD40 pathway is blocked. The addition of host CD8 T cell depletion to anti-CD40 ligand treatment reliably allows the induction of mixed chimerism and donor-specific skin graft tolerance in 3 Gy-irradiated mice receiving fully MHC-mismatched bone marrow grafts. Thus, despite the existence of multiple costimulatory pathways and pathways of APC activation, our studies demonstrate an absolute dependence on CD40-mediated events for CD4 cell-mediated rejection of allogeneic marrow. Exposure to donor bone marrow allows rapid tolerization of alloreactive CD4 cells when the CD40 pathway is blocked, leading to permanent marrow engraftment and intrathymic tolerization of T cells that develop subsequently.

Lack of Role for CsA‐Sensitive or Fas Pathways in the Tolerization of CD4 T Cells Via BMT and Anti‐CD40L

“…Thus, Fas-mediated apoptosis is not crucial for either the deletion of these donor-reactive cells, or for other mechanisms establishing tolerance in this model. Although these results differ from those in the model involving CD40L plus CTLA4Ig, the addition of CD8-depleting mAb precludes the observation of the same early (1 week post-BMT) deletion of donor-reactive T cells (23). While Fasmediated deletion may still occur in this model, these new data demonstrate that it is not necessary for the induction of mixed chimerism or CD4 cell tolerance following BMT.…”

“…Short course of CsA administration does not impair the establishment of mixed chimerism or tolerance When recipient CD8 + cells are depleted, a single injection of anti-CD40L mAb MR1 is able to completely overcome CD4 + T cell-mediated resistance to allogeneic BMT in 3 Gy irradiated mice, and lasting mixed chimerism and tolerance are reliably induced (23). This donor-specific tolerance develops rapidly, and is not the result of specific targeting or signaling of activated CD4 + T cells by anti-CD40L mAb (24).…”

“…I-E is necessary to present superantigens encoded by the mammary tumor virus (Mtv)-8 and -9 retroviruses, which are encoded in both the B10.A and B6 genomes. These superantigens bind to thymocytes expressing T-cell receptors (TCRs) containing Vb5 or Vb11, resulting in their deletion during intrathymic development and establishing a hole in the repertoire of I-E + strains, such as B10.A (29-31), but not of I-E -strains, such as B6 (31,32 and Vb11 + T cells, so CD8 + -cell depletion precludes the ability to examine early (week 1) Vb5 + and Vb11 + deletion in the peripheral blood after BMT in mice treated with anti-CD40L and anti-CD8 mAb (23). Such deletion is usually apparent between 2 and 3 weeks post-BMT (24).…”

“…We have previously demonstrated that when recipient CD8 + T cells are depleted, mixed chimerism can reliably be established in mice receiving only 3 Gy TBI and one injection of anti-CD40L mAb (23), and that the peripheral CD4 + T-cell population is rapidly tolerized by donor antigens by blocking CD40/CD40L interactions (24). The low dose of TBI can be removed from the regimen if the marrow dose is increased approximately 10-fold (H. Ito et al, unpublished data).…”

Deletional and regulatory mechanisms coalesce to drive transplantation tolerance through mixed chimerism

“…While some form of (local) irradiation was universally required even when very profound doses of T-cell depleting antibodies (anti-CD4 and anti-CD8 mAb) were given as part of the conditioning [9,10], costimulation blockade allowed the elimination of any irradiation from recipient conditioning if very high doses (mega doses) of allogeneic BM were transplanted [7,11]. Anti-CD40L is sufficiently effective alone (without CTLA4Ig) in strain combinations without minor antigen barriers (e.g., donor B10.A → recipient C57BL/10) [12,13] [8,14,18,19]. As long as no effective anti-CD40L mAb is available for clinical use, its elimination from recipient conditioning would be desirable.…”