ALBERT

Description: Pre-clinical data in monkeys receiving non-myeloablative conditioning followed by MHC-mismatched kidney and bone marrow transplantation show that transient chimerism is sufficient to permit achievement of long-term tolerance to a simultaneous donor renal allograft. Our group has recently reported successful induction of tolerance to donor kidneys in patients with advanced multiple myeloma and renal failure through combined bone marrow and kidney transplantation in the HLA-identical setting. On the basis of these results, five end-stage renal failure patients without malignant disease received simultaneous kidney and bone marrow transplantation from haploidentical HLA mismatched related donor after non-myeloablative conditioning with MEDI-507 (anti-CD2 humanized mAb; MedImmune), cyclophosphamide, thymic irradiation and peritransplant cyclosporine. Transplantation of kidney and bone marrow were both performed on Day 0. All patients developed initial mixed chimerism but lost their chimerism by Day 21. We have analyzed three patients who successfully discontinued immunosuppression on Days +240, +422 and +244. At a follow-up of 47, 38, and 17 months, all three patients are off immunosuppression without allograft rejection. T-cell counts exceeded 100 cells/μL by Day +128, +21, +21, respectively, and a high early prevalence of CD4+CD25high cells was detected. Post-transplant in vitro alloreactivity assays (bulk MLR/CML) showed the development of long-lasting donor-specific unresponsiveness in all three patients. In patients in whom renal tubular epithelial cells (RTEC) were cultured from the donor kidney, no killing of donor RTEC was detected post-transplant. We also assessed alloresponses in chemorefractory lymphoma patients receiving haploidentical bone marrow transplantation with a similar conditioning regimen. In contrast to the recipients of combined kidney/bone marrow transplants, these patients showed sustained global hyporesponsiveness in CML and MLR. However, loss of donor chimerism was associated with the eventual appearance of measurable anti-donor CML and/or MLR responses. In contrast, donor-specific and host-specific unresponsiveness with strong anti-3rd party responses developed in a sustained mixed chimera who received haploidentical stem cell transplantation with a modification of this conditioning protocol (i.e. different dose of MEDI-507, Isolex-selected CD34+ cells from G-CSF mobilized PBMC and the addition of fludarabine). In summary, we have obtained proof of principle that durable multilineage mixed chimerism with donor- and host-specific tolerance can be achieved without GVHD in humans receiving haploidentical HCT. In recipients of combined kidney/bone marrow transplants but not in recipients of bone marrow alone, patients who lose chimerism develop donor-specific unresponsiveness. These studies point to a role for the renal allograft in maintaining long-term tolerance following loss of initial donor chimerism.

Description: Following an in vivo T cell depleting non-myeloablative conditioning regimen, 5 patients, aged 22–49, received combined kidney and bone marrow transplantation from a haploidentical related donor. Rituximab was included in the conditioning for patients 4 and 5. All patients developed initial mixed chimerism but lost it by day 21; no patient developed GVHD. Four patients discontinued immunosuppression from 240 to 422 days after BMT and have remained off immunosuppression for 9 to 52 months with no evidence of allograft rejection. Flow cytometry was used to assess lymphocyte subsets recovering after transplant. CD3 counts recovered slowly, exceeding 500 cells/μl at days +271, +365, +640 and +450. While memory CD45RO+ cells were most prevalent among CD4+ cells, naïve-type CD4+CD45RA+ cells, presumably arising from the recipient thymus, ranged from 8% to 56% at the time when total CD4 counts recovered to 〉100 cells/μl (days +165, +21, +352, +240). Notably, a very high proportion of initially recovering T cells were CD3+CD4+ expressing CD25 in all patients as early as day 7 and persisted over 1 year in 2 patients. At approximately day +120 and +365, we further characterized these cells for CD127, FOXP3, CD45RO, CD45RA, HLA-DR and CD62L expression. At Day +120, all 4 patients showed increased frequencies (10.7±4.6%) of CD25+CD127-FOXP3+ regulatory T cells (Treg) within the CD4 population compared to healthy subjects (3.8±0.4%). Expression of CD45RO, CD45RA, CD62L and HLA-DR was variable. By 1 year post-transplant, frequencies of Treg had decreased to levels similar to those in normal subjects. In vitro assays for CD8 and CD4 T cell-mediated alloreactivity (CML/MLR) showed development of long-lasting donor-specific unresponsiveness by 3 months after transplant in Patients 2, 4 and 5, and by 9 months in Patient 1. Responses to 3rd party recovered in all patients after a period of unresponsiveness. In Patient 1, in whom anti-donor CML reactivity declined gradually to become unresponsive by 9 months, depletion of CD4+CD25+ cells revealed a residual anti-donor CML and MLR response at 1year but not at 18 months. In 2 other patients, depletion of CD4+CD25+ cells did not reveal an anti-donor response at time points analyzed from day +122 to 2 years. In patients in whom renal tubular epithelial cells (RTEC) were cultured from the donor kidney, loss of killing activity against donor RTEC was observed post-transplant. The high percentage of Treg recovering early after transplant suggests that they may play a role in initial tolerance induction. This regulatory mechanism may be followed by later deletion of donor-reactive T cells. The variable ability to detect regulation of anti-donor reactivity may reflect the strength of the initial response, as patients with weak pre-transplant anti-donor responses and rapid post-transplant development of donor unresponsiveness did not reveal anti-donor response when Treg were depleted. In addition, infiltration of Treg at the graft site, not revealed by the assays described, might be responsible for tolerance in these patients.