IMMUNOREGULATION OF BONE MARROW INFUSED LRD RENAL TRANSPLANT RECIPIENTS BY CHIMERIC CELLS OF DONOR PHENOTYPE.

Abstract

120 A number of transplant centers, including our own, have adopted donor specific bone marrow cell infusions of organ transplant recipients to enhance donor chimerism with the aim of inducing allograft acceptance. However, to date there has been no direct evidence linking chimerism with specific tolerance induction in the transplant recipients. In this study in renal transplant recipients from living related donors (LRD) who had received perioperative donor bone marrow cell infusions, chimeric cells of donor phenotype were isolated from the peripheral blood and the iliac crest bone marrow one year post-operatively, using monoclonal antibodies to donor mismatched HLA class 1 antigens and magnetic microbeads. They were then characterized phenotypically and functionally. In contrast freshly isolated and similarly treated cells from blood and iliac crest marrow of the donors (non-chimeric donor cells) were similarly treated and tested at the same 1 year interval. The yield of such chimeric cells from the recipient marrow by this method of purification ranged as high as 0.5% at this time. Phenotypic characterizations of similarly isolated chimeric cells from the iliac crest marrow of cadaveric kidney recipients 1-3 years postoperatively (the purified chimeric cells from LRD recipients were sufficient only for the functional studies) showed that 51.8±6.3% of the chimeric cells were TcRαβ+ CD2+ CD3-dimly positive. 28.3±7.5% cells were also CD4− CD8−. In addition, 20.4±11.8% were CD4+ CD3+ and 15.0±4.9% were CD8+ CD3+ (n = 4). The regulatory activity of chimeric and non-chimeric donor cells was assessed by testing them as third party cells in MLC and CML responses of the recipients to the allogeneic LRD PBL as stimulating cells. Of the seven cases analyzed so far, two recipients did not respond to the donor in MLC, although this reaction was present preoperatively, so that the role of chimeric cells could not be ascertained. In the five patients with positive anti-donor MLC responses, the purified chimeric cells showed significantly stronger inhibition than non-chimeric donor marrow cells similarly treated (p < 0.01). Modulation experiments on CML responses could be performed only in three cases because of the low yield of the chimeric cells. The chimeric cells were also significantly more potent inhibitors (p < 0.05) of the generation cytotoxic T cells than the non-chimeric donor marrow cells. The inhibitions occurred with chimeric (regulatory) cell concentrations as low as 8% of the responder cells. These results clearly showed that donor bone marrow derived chimeric cells present in transplant recipients have evolved into even more potent immunoregulatory cells by 1 year postoperatively, supporting the notion that chimerism plays a major role in the induction and/or maintenance of transplant tolerance.