Generation of suppressive blood cells for control of allograft rejection

Abstract

Our previous studies in rats showed that incubation of monocytic dendritic cells (DCs) with the chemotherapeutic drug mitomycin C (MMC) renders the cells immunosuppressive. Donor-derived MMC-DCs injected into the recipient prior to transplantation prolonged heart allograft survival. Although the generation of DCs is labour-intensive and time-consuming, peripheral blood mononuclear cells (PBMCs) can be easily harvested. In the present study, we analyse under which conditions DCs can be replaced by PBMCs and examine their mode of action. When injected into rats, MMC-incubated donor PBMCs (MICs) strongly prolonged heart allograft survival. Removal of monocytes from PBMCs completely abrogated their suppressive effect, indicating that monocytes are the active cell population. Suppression of rejection was donor-specific. The injected MICs migrated into peripheral lymphoid organs and led to an increased number of regulatory T-cells (Tregs) expressing cluster of differentiation (CD) markers CD4 and CD25 and forkhead box protein 3 (FoxP3). Tolerance could be transferred to syngeneic recipients with blood or spleen cells. Depletion of Tregs from tolerogenic cells abrogated their suppressive effect, arguing for mediation of immunosuppression by CD4⁺CD25⁺FoxP3⁺ Tregs. Donor-derived MICs also prolonged kidney allograft survival in pigs. MICs generated from donor monocytes were applied for the first time in humans in a patient suffering from therapy-resistant rejection of a haploidentical stem cell transplant. We describe, in the present paper, a simple method for in vitro generation of suppressor blood cells for potential use in clinical organ transplantation. Although the case report does not allow us to draw any conclusion about their therapeutic effectiveness, it shows that MICs can be easily generated and applied in humans.

Cell therapy for immunosuppression after kidney transplantation

“…Subsequently, continuously decreasing percentages of autologous NK , T, and B cells were noted, resulting in a stable, complete hematopoietic donor chimerism for more than 1 year. The patient received no further immunosuppressive treatment but was supported with additional donor stem cell boosts, one mesenchymal stem cell transfusion, and one administration of CMV-specific donor T cells [48]. Even though this clinical case does not allow us to draw any conclusion about the effectiveness of tolerogenic MIC therapy, it clearly demonstrates that MICs can be easily generated and safely translated into the clinic for human treatment.…”

“…Approximately 50 % of the recipients developed operational tolerance (more than 70 days without rejection episode) towards heart allografts from the same original donor. Depletion of CD4 + CD25 + Tregs before transfer abrogated the protective effect [48].…”

“…When the monocytes were depleted from the PBMCs, the tolerogenic properties were lost [48]. When MMC-treated monocytes were cultured in the presence of certain cytokines, the resulting myeloid cells exhibited an immature phenotype resembling that of myeloid-derived suppressor cells (MDSCs).…”

“…MICs were also tested in a large animal kidney transplantation model in the pig. Even the low dose of 1×10 8 MICs significantly prolonged mean allograft survival when compared to untreated kidney recipients [48].…”

“…1). Prophylactic immunomodulation with MICs solely targets the unwanted immune responses against the allograft, a central prerequisite for their application in clinical transplantation [48]. In composite tissue rat hind limb allotransplantation, MICs significantly prolonged allograft survival when given at the day of surgery [49].…”