Abstract
Abstract 654
Unrelated cord blood (UCB) transplantation is a useful alternative for patients with hematological malignancies or non-malignant hematological disorders lacking an HLA matched donor. However, outcomes for patients with severe aplastic anemia (SAA) undergoing either a single or dual UCB transplant have been disappointing. A recent EBMT/ Eurocord study reported engraftment and 3 year survival rates of only 51% and 38% respectively (Perrault de Latour, Biol Blood Marrow Transplant 2011). We investigated whether co-infusion of a single UCB unit with CD34+ selected cells from a haploidentical relative following a highly immunosuppressive conditioning regimen could improve transplant outcome for patients with SAA refractory to immunosuppressive therapy that lack an HLA matched donor. Subjects with SAA and life-threatening neutropenia (ANC <500) refractory to 2 or more immunosuppressive agents were eligible for enrollment if they lacked an HLA matched related or unrelated donor. Conditioning consisted of cyclophosphamide (120 mg/kg), fludarabine (125 mg/m2), equine ATG (160 mg/kg) and one dose of 200 cGy of total body irradiation. Patients received a G-CSF mobilized, T-cell depleted CD34+ selected stem cell product prepared from a haplo-identical donor using the Miltenyi CliniMacs system combined with a single ≥ 4/6 HLA antigen matched UCB unit. Eight patients with treatment refractory SAA (median age 18 years; range 9–20), including 1 patient with SAA evolved to MDS, have been transplanted. All patients were platelet and RBC transfusion-dependent with severe neutropenia (median ANC 60 neutrophils/ul; range 0–260). Patients were at high risk for graft rejection, being heavily transfused, having failed a median 3 (range 2–4) immunosuppressive regimens, and 4 (50%) were HLA alloimmunized. Six patients received a single 4/6 HLA matched UCB unit and 2 received a 5/6 HLA-matched unit. Transplanted allografts contained a median 2.9 × 107 CB TNCs/kg (range 2.6–7.3), 1.5 × 105 CB CD34+cells /kg (range 0.4–3.2), and 3.3 ×106 CD34+cells/kg (range 2.6–3.6) from the haploidentical relative. All patients achieved the primary study endpoint of donor engraftment with an ANC of >500 by day 42, 7 of 8 achieving a UCB-derived ANC >500 cells/μl. The median time to neutrophil recovery was 10 days (range 10–18 days). One patient failed to engraft with the cord unit, but has had sustained engraftment from the haploidentical donor, and is transfusion independent with a normal neutrophil count >25 months post transplant. Acute GVHD grade II developed in 2 patients and one developed limited chronic GVHD. Early T-cell engraftment was predominantly UCB in 7 cases; on day 21, T-cell chimerism was a median 100% cord in origin (range 0–100%). In contrast, myeloid chimerism at engraftment was predominantly haplo-donor in origin and showed 3 phases of engraftment: 1) early myeloid engraftment from the haplo-CD34+ cell donor 2) delayed myeloid engraftment from the cord unit resulting in dual myeloid chimerism and 3) disappearance of the haplo-donor cells with transition towards full cord donor myeloid chimerism (see figure).
Mixed lymphocyte reactivity assays performed on post transplant PBMCs showed increasing alloreactivity of cord blood T-cells against the haploidentical donor during the period when myeloid chimerism transitioned towards cord, indicating that the disappearance of haplo-donor myeloid cells occurred as a consequence of rejection by engrafting cord blood T-cells. At a median follow-up of 9 months (range 75 days to 3 years), 7 patients survive, and all are transfusion–independent. One patient died 14 months after transplantation from complications related to CMV pneumonitis.
Wilder:NCI: Funded in part by NCI contract No. HHSN261200800001E.
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