Compensatory Regulatory Networks between CD8 T, B, and Myeloid Cells in Organ Transplantation Tolerance

Abstract

In transplantation tolerance, numerous regulatory populations have the capacity to inhibit allograft rejection; however, their compensatory capacities have never been clearly evidenced. We have previously demonstrated that the tolerogenic effect mediated by CD8+CD45RClow regulatory T cells (Tregs) in a model of organ transplantation with CD40Ig could be abrogated by permanent depletion of CD8+ cells that resulted in allograft rejection in half of the recipients. This result demonstrated that CD8+ Tregs were essential, but also that half of the recipients still survived indefinitely. We also demonstrated that no other regulatory populations, besides CD8+ Tregs, could induce and maintain allograft tolerance in CD40Ig-treated tolerant animals. In the current study, we analyzed the mechanisms that arose following CD8+ Treg depletion and allowed establishment of networks of new regulatory cells to maintain allograft survival. We identified regulatory B cells (Bregs) and regulatory myeloid cells (RegMCs) as being responsible of the maintenance of the long-term allograft survival. We demonstrated that both regulatory cell subsets efficiently inhibited antidonor immune responses in adoptively transferred recipients. Although Bregs were induced, they were not essential for the maintenance of the graft as demonstrated in IgM-deficient recipients. In addition, we showed that RegMCs were the most suppressive and acted alone, whereas Bregs activity was associated with increased suppressive activity of other subsets in adoptively transferred recipients. Altogether, to our knowledge, we demonstrated in this study for the first time the emergence of both Bregs and RegMCs following Tregs depletion and highlighted the importance of regulatory cell networks and their synergistic potential in transplantation.

Transient antibody targeting of CD45RC induces transplant tolerance and potent antigen-specific regulatory T cells

“…Clinical protocols applying polyclonal or antigen-specific CD4 + Treg cell therapy in transplantation are underway and hold promise, but results are not yet available (36). In the last years, we have investigated the properties of a population of CD8 + Tregs that arise in a model of cardiac allograft tolerance following blocking of CD40-CD40L interactions (18,20,21,23,24,(37)(38)(39) and are characterized by the low expression or absence of the CD45RC marker, which is one of the less known and studied alternative splice variants of the CD45 molecule.…”

“…Rat spleens were harvested at day 120, and splenocytes or subpopulations were purified as previously described (18,23 A Canto II cytometer (BD Biosciences) was used to measure fluorescence, a FACS Aria II (BD Biosciences) was used to sort cells, and data were analyzed using the FLOWJO software (Tree Star Inc.). Cells were first gated by their morphology excluding dead cells by selecting DAPI-viable cells.…”

“…We have shown in a rat model of organ transplantation tolerance that antigen-specific regulatory CD8 + CD45RC low/-T cells transferred dominant donor-specific tolerance associated with production of IFNγ, fibroleukin-2, and IL-34 (18,(20)(21)(22)(23)(24). In humans, a high proportion of CD45RC high CD8 + T cells before transplantation has been correlated with decreased graft survival in kidney transplanted patients (25).…”

Importance of B cells to development of regulatory T cells and prolongation of tissue allograft survival in recipients receiving autologous bone marrow transplantation

“…In patients receiving autologous HSCT for systemic sclerosis, increased numbers of Breg cells (defined as CD19 + CD24 hi CD38 hi ) were reported at 6 and 12 months post transplant with no alteration in the levels of Foxp3 + CD25 hi CD4 + Treg cells . Regulatory networks between B and T cells, and a role for interleukin‐10 (IL‐10) ‐producing Breg cells, have been reported in a clinical graft‐versus‐host disease model following cord blood transplantation …”

Future prospects for CD8+ regulatory T cells in immune tolerance

“…36 We have also shown that IL-34, a recently discovered cytokine involved in monocyte/macrophage differentiation, was secreted by approximately half of FOXP3 + CD8 + and CD4 + Tregs. 39 Other more classical cytokines such as TGFβ have also been described as playing a role in CD8 + Treg suppressive activity. This was the first description of a role for this cytokine in T cell biology and transplantation.…”