Induction of Donor-Specific Immune Tolerance with Clinical MIC Cell Infusion — a Phase I Study (TOL-1)

Background:

After transplantation of solid organs like allogeneic kidneys, the administration of immunosuppressive drugs such as cyclosporine A (CSA) and steroids is mandatory. This regimen exerts toxicity to the graft and makes transplant recipients prone to opportunistic infections. Replacement of the immunosuppressive drugs by a transfusion of tolerogenic cells might overcome these noxious side effects. Mitomycin-induced cells (MICs) are donor-derived monocytes that gain immunosuppressive properties after incubation with the proliferation inhibitor mitomycin C and have a myeloid-derived suppressor cell (MDSC) character.

Materials and methods:

Peripheral blood mononuclear cells (PBMCs) were harvested from living kidney donors by leukapheresis and MIC cells were manufactured under Good Manufacturing Practice (GMP) conditions in the clean room of our University Hospital. Kidney transplant recipients received either 1.5x10E6 MIC cells per kg body weight on day -2 (N=3, group A) or 1.5x10E8 MIC cells per kg body weight on day -2 (N=3, group B) or on day -7 (N=4, group C) before living donor kidney transplantation. Patients received immunosuppressive therapy with cyclosporine a (CSA), enteric coated mycophenolate sodium (EC-MPS) and corticosteroids. The primary outcome was measured by the frequency of adverse events (AEs) on post-transplant day 30 with a follow-up until post-transplant day 360 for all patients.

Results:

Clinically, all kidney transplant recipients showed a median serum creatinine of 1.4 mg/dL at day 30 and remained stable with a median creatinine of 1.48 mg/dL at day 180 without significant proteinuria (median 10 g/mol creatinine at day 180) and without rejection episode. In total 72 AEs were observed including three severe AEs which were not associated with the MIC cell transfusion. Besides two infectious complications, no positive cross match results, no de novo donor-specific antibodies or rejection episodes were recorded. In group C, a reduction of immunosuppressive therapy was effective in the observational phase with low-dose CSA and low-dose EC-MPS.

Immunologically, CD19⁺ B cells increased up to a median of 300/µL until day 30, followed by a decrease to a median of 35/µL at day 180 in group C. Notably, CD19⁺CD24^highCD38^high regulatory B cells were significantly increased from a median of 2% on day 30 to a median of 20% on day 180. The plasma IL-10/TNF-α ratio increased from a median of 0.05 before cell therapy to a median of 0.11 at day 180. Moreover, recipient lymphocytes showed no or only minimal reactivity against irradiated donor PBMCs, while reactivity against 3rd party healthy donor PBMCs in vitro was not impaired.

Additionally, the quality assessment demonstrated that MIC cells have the capability to induce tolerogenic dendritic cells (tDCs) by down-regulating the costimulatory molecules CD80 and CD86, and the maturation molecule CD83, while up-regulating the immunosuppressive molecule CD103. MIC-induced tDCs showed the capacity to inhibit donor specific allo-reactive CD4 and CD8 T cell proliferation.

Conclusion:

A stable function was observed in all transplant recipients receiving the MIC cells product without any allograft injury or rejection episodes even under reduction of conventional therapy with immunosuppressive drugs. MIC cells constitute a novel tool for immunotherapy with a high potential in transplantation medicine.