Non-T-cell-depleted HLA haploidentical stem cell transplantation based on feto-maternal microchimerism in pediatric patients with advanced malignancies

The persistence of fetal hematopoietic cells in maternal blood after birth, or feto-maternal microchimerism, has recently been suggested to be an indicator of immunologic hyporesponsiveness between mother and offspring.1, 2 Guided by the hypothesis that persistent maternal microchimerism indicates tolerance to fetally inherited paternal antigens (IPA) in children and that microchimerism among siblings with mismatched maternal antigens results in mutual tolerance to noninherited maternal antigens (NIMA), feto-maternal immunologic tolerance in allogeneic stem cell transplantation (SCT) has recently been investigated.2, 3, 4, 5, 6 Based on this premise, we used non-T-cell-depleted (TCD) stem cells from haploidentical family donors for transplantation. We report here a total of 11 pediatric patients with advanced hematologic malignancies or solid tumors who underwent non-TCD haploidentical SCT.

Patient characteristics are shown in Table 1. All patients lacking HLA-matched family member donors were acutely ill and time was not available to search for unrelated HLA-matched donors. Non-TCD haploidentical SCT was performed as a second allogeneic transplant in these four patients because of early primary rejection after unrelated cord blood transplantation (UCBT) (cases 3, 6 and 10) and chemorefractory relapse after UCBT (case 4). Non-TCD haploidentical SCT was performed after autologous SCT in two solid tumor patients (cases 9 and 11). In the remaining five patients, non-TCD haploidentical SCT was employed as the first transplant. After informed consent and permission were obtained from guardians and from the ethical committee at the transplant hospitals, healthy haploidentical family donors were selected based on feto-maternal microchimerism. Nine of the donors were mothers and two were NIMA-mismatched siblings. HLA incompatibilities that increase susceptibility to graft-versus-host disease (GVHD) were three-loci mismatches in three patients, two-loci mismatches in five patients and one-locus mismatch in three patients, while incompatibilities that increase susceptibility to HVG were three-loci mismatches in two patients, 2-loci mismatches in five patients, one-locus mismatch in two patients and no mismatch in two patients, respectively.

Table 1 Patient characteristics

HLA-nested polymerase chain reaction with sequence-specific primer typing was employed to detect microchimerism semiquantitatively in peripheral blood mononuclear cells as described previously.3, 7 As summarized in Table 1, IPAs of the patients were detected in the peripheral blood of the mothers (cases 3–6, 8 and 9) and NIMA was detected in the peripheral blood of the donors (cases 2 and 10), suggesting immunologic tolerance to the recipient cells. IPA of two patients (cases 7 and 11) was undetectable in the peripheral blood of the donors.

A fludarabine-based reduced-intensity SCT conditioning regimen was used in seven patients (cases 3, 4, 6, 7, 9–11) and a myeloablative SCT conditioning regimen was used in four patients (Table 2). Prophylactic treatment for GVHD mainly consisted of short-term methotrexate (10–15 mg/m2, day 1; 7–10 mg/m2, days 3 and 6) combined with cyclosporin A (CsA) (starting dose, 3 mg/kg/day intravenously) or tacrolimus (starting dose, 0.02 mg/kg/day intravenously). Grafts were bone marrow cells in nine patients and peripheral blood stem cells in two patients. The median time required to achieve a neutrophil count above 0.5 × 109/l, a reticulocyte count above 1.0% and a platelet count above 50 × 109/l was 14 (range 10–26) days, 22 (range 14–48) days, and 44 (range 16–) days, respectively. All patients had attained full donor chimera by day 30, as analyzed by sex-specific fluorescence in situ hybridization or microsatellite polymorphism. Two out of three patients with three-loci mismatches predisposed to GVHD (cases 6, 7 and 9) developed grade 3 acute GVHD, while the remaining patients developed grade 1–2 acute GVHD. None of the patients developed grade 4 acute GVHD. Methylprednisolone (mPSL) pulse therapy was required in cases 1, 2 and 9 and lower dose (1–5 mg/kg/day) mPSL treatment was necessary in most of the remaining cases to control effectively acute GVHD. Two patients in whom microchimerism was undetectable (cases 7 and 11) developed grade 3 and 2 acute GVHD, respectively. Chronic GVHD developed in five patients, which was extensive in two patients. Cytomegalovirus (CMV) antigenemia developed in four patients (cases 2–5) and mild CMV retinitis developed in case 2. Case 8 developed acyclovir-resistant herpes simplex infection, case 9 developed Candida septicemia and case 10 had adenoviral cystitis and Varicella zoster infection. As summarized in Table 2, at this writing, seven patients are alive and have been in complete remission for 146–1273 (median 387) days, with Karnofsky scores of 90–100%. One patient died of interstitial pneumonia (case 6) and three died of disease progression (cases 8, 9 and 11). Six out of eight patients who had two-loci or fewer HLA mismatches predisposed to GVHD are alive and in complete remission, while two out of three patients who had three-loci mismatches died.

Table 2 Stem cell transplantation and outcome

Detection of microchimeric cells has been the only method used thus far to determine immunologic tolerance. Engraftment appeared to be successful and lasting in the non-TCD transplants. Acute GVHD was controlled and grade 4 acute GVHD was not observed, suggesting immunologic tolerance to IPA or NIMA. So far, none of our patients has developed fatal infectious complications. However, immune reconstitution after non-TCD haploidentical SCT is slow due to strong immunosuppression; therefore, patients should be monitored closely for infectious complications for an extended period. Remarkably, four out of six patients with chemorefractory hematologic malignancies (cases 1, 4–6, 8 and 10) have maintained complete remission, suggesting that the graft-versus-leukemia effect in this non-TCD haploidentical SCT is beneficial.

Our limited experience currently suggests that non-TCD haploidentical SCT is effective for primary as well as back-up transplantations. Three of our patients (cases 3, 6 and 10) who experienced early graft failure after UCBT were saved by non-TCD SCT from a haploidentical donor. Thus, non-TCD SCT from haploidentical and microchimeric family donors can be performed safely in children, especially when donors are mismatched by no more than HLA two-loci. Two of our patients in whom microchimerism could not be detected also achieved successful engraftment, with grade 2–3 acute GVHD. Thus, microchimerism may not be an absolute prerequisite for successful transplantation.8 More studies and longer observation periods are required to establish this transplantation procedure.

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Yoshihara, T., Morimoto, A., Inukai, T. et al. Non-T-cell-depleted HLA haploidentical stem cell transplantation based on feto-maternal microchimerism in pediatric patients with advanced malignancies. Bone Marrow Transplant 34, 373–375 (2004). https://doi.org/10.1038/sj.bmt.1704597

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