No Significant Benefit of Marrow and Blood HLA-Haploidentical Stem Cell Transplantations Given by Mothers with Long-Term Fetomaternal Microchimerism.

Non-T-cell-depleted maternal HLA-haploidentical hematopoietic stem cell transplantations(SCT) have been reported feasible based on the hypothesis that long-term fetomaternal microchimerism(FMC) is linked with hyporesponsiveness to inherited paternal antigens(IPAS),but the hypothesis is still in debate due to lack of direct evidence. To determine whether the existence of such microchimerism affect the outcome of maternal HLA-haploidentical SCT, we investigated the outcomes of 18 patients (median age 19) with hematologic malignancies (ALL 8, AML 6, CML 3, NHL 1) who underwent haploidentical SCT from mothers with the same regime from July 2003 to January 2005. Donor was treated with granulocyte colony stimulating factor subcutaneously at a dose of 300μg per day for 5 days before bone marrow harvesting. Leukaphereses were performed using a continuous-flow blood cell separator if CD34+ cells in the bone marrow harvest were less than 4.0×10⁶ cells/kg. Patients with CML or AML in CR received 7.5Gy TBI based standard-intensity regimen combined with cyclophosphamide plus cytarabine. The remaining received non-TBI standard-intensity regimen consisting of cytarabine, busulfan and cyclophosphamide. Antithymocyte globulin(ATG) at a dosage of 2.5mg/kg/day on days −5 to −3 was given as an additional immunosuppressive measure in all patients. To prevent GVHD, patients also received cyclosporin at a dose of 3mg/kg/day as a continuous infusion from day −10, 30mg/kg/day mycophenolate mofetil starting on day −10, and short-term methotrexate administered on days 1, 3, 6, 11 at doses of 15, 10, 10, and 10mg/m². Among all these patients, microchimerism were confirmed with nested polymerase chain reaction using sequence-specific primers(PCR-SSP) typing for HLA in 10 donor-recipient pairs. In the 2 categories as to whether the microchimeric status of the donor is positive or negative, they had similar characteristics in the background factors such as recipient sex, type of conditioning regime, stem cell source, and disparity of HLA except recipients of positive group had more CML. Engraftment was obtained in all patients. As of august 1, 2005, 5 patients died (1 of relapse, 4 of complication), other 13 patients were alive and free of disease. The 2-year overall survival for the whole cohort was 58%. Although there was a survival advantage for pairs with microchimerism over pairs without it, the influence on outcome was not statistically significant (P=0.9, log-rank test). The cumulative incidences of grade Ò/Ô acute graft-versus-host disease (GVHD) were 39% (95%CI, 17%–64%). Also no significant difference was observed between the two groups. Extensive chronic GVHD developed in 5 of 13 patients who could be evaluated. These results indicate maternal HLA-haploidentical hematopoietic SCT is a acceptable option for patients who lack immediate access to a conventional stem cell source, but the presence of fetomaternal microchimerism may not correlate to the existence of immunological tolerance between mother and offspring.