Outcomes after Double Umbilical Cord Blood Transplantation in Children: A Survey on Behalf of Eurocord and PDWP-EBMT

Double UCBT (dUCBT) has been used in adults to reach an acceptable cell dose. For most children a single unit with a total nucleated cell (TNC) dose >3x10⁷/Kg can be easily identified, but that is not always the case for heavier patients (pts). Use of dUCBT might decrease relapse and increase graft-versus-host-disease (GvHD). Data on dUCBT in children are scarce in the literature. A recent randomized study in children has described similar outcomes after double compared to single UCBT. Our study provides an overview of the use of dUCBT in the pediatric population reported to Eurocord.

We retrospectively analyzed the outcomes of unrelated dUCBT in 177 children transplanted between 2002 and 2012 in 61 EBMT centres. Analysis was performed separately for pts with malignant (n=139) and non-malignant (NM, n=38) diseases.

Among pts with malignancies, 76 had ALL, 40 AML, 6 MDS, 2 CML, 11 NHL, 3 Hodgkin Lymphoma and 1 Multiple Myeloma. Median age at dUCBT was 15 years (1.3-17.9) and median weight was 55 kg (13-97). Disease status at dUCBT was 1st complete remission (CR) (36%), ≥2nd CR (34%) or advanced (25%), and missing in 5% of the pts. In this group, 117pts received a myeloablative conditioning (MAC) and 22 a reduced intensity regimen (RIC). Cyclophosphamide+fludarabine+TBI was administered to 41% of the pts; 55% received ATG in the conditioning. Median number of collected TNC was 5.7x10⁷/kg (3,6-12,8). Considering the unit with the higher number of HLA incompatibilities with the recipient, 56% had 2 mismatches. GvHD prophylaxis was cyclosporine-A (CSA) based in 93% of the pts (58% received CSA + mycofenolate mofetil). Median follow-up was 31 months. Cumulative incidence (CI) of neutrophil (PMN) and platelet (PLT) engraftment was 88% at 60 days and 64% at 180 days after dUCBT, and it was achieved with a median time of 24 and 45 days, respectively. Among the 122 pts with PMN engraftment, 85/94 with available data on chimerism were full donor and, of these, 20% had dual chimerism. CI of acute GvHD grade II-IV and grade III-IV at 100 days was 51% and 26%, respectively; it was significantly higher in pts who did not receive ATG (grade II-IV: 35% vs 67%, p=0.004; grade III-IV: 12% vs 37%, p=0.0075). Chronic GvHD was observed in 24/104 pts at risk (60% extensive; 2-year (yr) CI: 18%). The 2-yr CI of relapse was 31%. In univariate analysis, RIC, advanced stage at transplantation and a collected TNC dose lower than the median, were significantly associated with higher rates of relapse.The 2-yr CI of transplant related mortality (TRM) was 27%. Overall, 73 pts died: 35 of relapse, 15 of infections, 9 of GvHD and 14 of other causes. The 2-yr disease free survival (DFS) and overall survival (OS) were 42% and 45%, respectively.

Among pts with NM disorders, 24 had bone marrow failure syndrome (BMFS) (10 Fanconi Anemia, 13 Acquired Aplastic Anemia and 1 other inherited BMFS), 2 hemoglobinopathies, 7 immune deficiencies and 5 metabolic disorders. Median age at dUCBT was 11 years (0.7-17.9) and the median weight was 40 kg (13-70). In this group, 27 pts received a RIC (40% TBI based), 10 a MAC (90% busulfan based), and 1 no conditioning regimen. ATG was administered to 82% of the pts and GvHD prophylaxis was CSA-based in 77%. The median number of collected TNC was 8.4x10⁷/kg (1,2-11,2) and 60% of the grafts had ≥2 HLA mismatches with the recipient. Median follow-up was 39 months. Overall, 28 pts achieved PMN engraftment and 16 PLT engraftment, with a median time of 23 and 61 days, respectively. In univariate analysis, pts with BMFS compared to others had a significantly lower CI of PMN engraftment (58% vs 100%, p=0.002). Among the 10 pts who did not engraft, 3 had autologous reconstitution and 3 had a subsequent allogeneic HSCT. Forteen pts developed acute GvHD grade II-IV and 10/25 pts at risk had chronic GvHD (3 extensive). Overall 21 pts died (17 with BMFS): 9 of infections, 5 of GvHD and 7 of other causes. The 2-yr OS was 42% and it was significantly lower in pts with BMFS compared to those affected by other NM disorders (28% vs 70%, p=0.03).

In pts with malignancies, despite a higher incidence of acute GvHD, DFS and OS seem to be comparable to those reported in the literature for single UCBT or HSCT from other alternative stem cell sources. In the NM disorders group, despite the high cell dose, dUCBT did not seem to improve results in pts with BMFS. This survey suggests that dUCBT is feasible in children and should be considered when a single unit with an adequate cell dose is not available.