Background
Reconstructive transplantation represents a valid therapeutic option after devastating tissue loss such as an extremity or face Immunosuppression-free donor-specific immunological tolerance has been successfully achieved in the setting of solid organ transplantation through mixed chimerism Routine clinical application of this approach, however, is hampered by the toxicity of the cytoreductive recipient conditioning The current study investigated a novel non-cytoreductive immunosuppressive strategy in a murine model of hind limb transplantation.
Methods
Fully MHC-mismatched allogeneic, orthotopic hind limb transplants were performed from Balb/C to C57BL/6 mice Recipient animals in the experimental groups received no treatment (Group 1); 025 mg CTLA4 Ig on postoperative days (POD) 0, 2, 4, and 6 (Group 2); 20 mg/kg anti-T cells (anti-Thy 12 mAb) on POD-1 plus CTLA4-Ig and 1 mg/kg Rapamycin (POD0-9) (Group 3) Flow cytometric analysis was performed to evaluate mixed chimerism and clonal deletion of alloreactive T cells.
Results
The CTLA4 Ig treated group showed increased graft survival compared to non-treated controls (mean survival time [MST] 17 d and 8 d, respectively, p < 001) Interestingly, combination of T cell depletion and CTLA4 Ig plus short-course of Rapamycin increased VCA survival significantly (MST 105 days; p < 001) Donor derived mixed chimerism was detected in recipients receiving the combined treatment protocol with 50 ± 12 % of donor derived CD11b+ cells on POD 55 VÎ2 – TCR staining profiles in recipients after combined treatment showed 16 ± 04 % of νÎ25+CD4+ T cells, while naïve C57BL/6 express 36 ± 04 % of νÎ25+CD4+ T cells, suggesting central deletion of donor-reactive T cells Also, we found infiltrating Foxp3+ regulatory T cells expressing donor derived marker (H-2Kb) at POD60 on combined treatment representing donor derived T reg cells were infiltrated.
Conclusion
This study shows that combination of T cell depletion and costimulation blockade and short-course of Rapamycin prevents VCA rejection and significantly prolongs graft survival Also, these data show that a clinically acceptable non-cytoreductive strategy could be applied in VCA to avoid long-term maintenance immunosuppression.