Induction of Tolerance across Fully Mismatched Barriers by a Nonmyeloablative Treatment excluding Antibodies or Irradiation Use

Abstract

A mixed-chimerism approach is a major goal to circumvent sustained immunosuppression, but most of the proposed protocols need antibody treatment or host irradiation. Another promising experience involves busulfan combined with cyclophosphamide treatment. Additionally, recent publications demonstrated that, differing from busulfan, treosulfan administration does not present severe organ or hemato toxicities. Currently, Duchenne muscular dystrophy (DMD) patients are treated with chronic immunosuppression for muscle precursor cell transplantation (MT). We have developed a safe tolerance approach within this cellular allotransplantation therapy background. Thus, we have conditioned, prior to a donor BALB/c MT, the dystrophic mouse model C57Bl10J mdx/mdx, with our treatment based on a donor-specific transfusion, then a treosulfan treatment combined with single cyclophosphamide dose, and finally a donor bone marrow transplantation (TTCB). A first MT was performed in all mixed chimeric mice resulting from the TTCB treatment in the left tibialis anterior (TA) muscles. A second MT from the same donor strain was performed 100 days later in the right TA without any additional therapy. Results show that all treated mice developed permanent mixed chimerism. Long-lasting donor-positive fibers were present in both TAs of the mice, which received MT after the TTCB treatment. Only a basal level of infiltration was observed around donor fibers and mixed chimeric mice rejected third-party haplotype skin grafts. Thus, mixed chimerism development with this TTCB conditioning regimen promotes donor-specific stable tolerance, avoiding costimulatory blockade antibodies or irradiation use and side effects of sustained immunosuppressive treatments. This protocol could be eventually applied for MT to DMD patients or others tissue transplantations.

Transplantation of Myogenic Cells in Duchenne Muscular Dystrophy Patients

“…Currently, there is no protocol for induction of tolerance regularly applicable in humans. Regarding myoblast transplantation, there were experiments testing strategies of immune tolerance in mice with variable outcomes [84][85][86]. However, tolerance is much harder to obtain in humans and nonhuman primates than in mice, and "positive" results in mice should be relativized because they involve graft survival of a few months, while in DMD patients the graft must survive for decades.…”

Transplant Tolerance: New Insights and Strategies for Long-Term Allograft Acceptance

“…Nonmyeloablative conditioning consists of the administration of sufficient immunosuppression (e.g., antithymocyte globulin, costimulation blockage, and immunosuppressive drugs) to allow the engraftment of fully mismatched BMT, but at the same time, minimal enough to avoid toxic secondary effects. Although some physical and pharmacological strategies such as total body irradiation, thymic irradiation, or the use of depleting antibodies are able to induce mixed chimerism; however, it is still necessary to generate conditioning protocols that minimize systemic immunosuppression [58, 71–74]. …”

Cell Transplantation and “Stem Cell Therapy” in the Treatment of Myopathies: Many Promises in Mice, Few Realities in Humans

“…Our team has specifically tried some protocols to induce tolerance for myoblast allotransplantation in mice. Central tolerance via mixed chimerism [194,195] was superior to anti-CD154 administration and donor-specific transfusion [196]. Nevertheless, central tolerance in the context of myogeniccell allotransplantation would not include neoantigens in the hybrid myofibers and would need also peripheral tolerance [197].…”