Improved Outcome of Unrelated Cord Blood Transplantation in Children with Severe Aplastic Anemia

Introduction

Hematopoietic stem cell transplantation (HSCT) from an HLA-matched related donor is a first-line treatment for children with severe aplastic anemia (SAA). HSCT from an HLA-matched unrelated donor (MUD) is indicated as a salvage treatment for non-responders to immunosuppressive therapy (IST).Because unrelated cord blood transplantation (UCBT) has been considered as an experimental therapy, information of UCBT in patients with SAA is scarce, especially in pediatric patients. We analyzed the outcomes of UCBT in children with AA registered in the Transplant Registry Unified Management Program (TRUMP) conducted by the Japanese Society for Hematopoietic Cell Transplantation.

Patients and Methods

Between 1998 and 2013, 27 patients <15 years old who underwent an UCBT as the first HSCT were registered in the TRUMP database. Patients with congenital bone marrow failure syndrome such as Fanconi anemia were excluded from the analysis. Treatment failure were defined as death by all causes, graft failure (GF) and secondary malignancy. Data collected as October 2014 were analyzed.

Results

Patients' characteristics

Among the 27 patients, 10 patients underwent UCBT during 1998 - 2005 and 17 patients underwent UCBT during 2006 - 2013. The median age at the time of UCBT was 6 years (range, 0 - 14). The male/female ratio was 12/15. The median interval between the diagnosis of AA and CBT was 212 days (range, 39 - 2,982). Sixteen patients received antithymocyte globulin (ATG) as immunosuppressive therapy (IST) before UCBT. The median total nucleated cell number and CD34 positive cell number at cryopreservation were 3.99 x 10⁷/kg (range, 0.09 - 16.11 x 10⁷/kg) and 1.31 x 10⁵/kg (range, 0.39 - 6.17 x 10⁵/kg), respectively. Ten patients received fludarabine (FLU) + cyclophosphamide (CY) + irradiation ± ATG. Six received FLU + CY + ATG. Four received FLU + melphalan (MEL) + irradiation and the remaining 7 received other various conditioning regimens. Cyclosporine was used in 9 patients and tacrolimus was used in 17 patients for graft-versus-host disease (GVHD) prophylaxis.

Transplantation outcomes

Neutrophil recovery was observed in 19 patients and the median time to engraftment was 20 days. Platelets engraftment was observed in 17 patients and the median time to engraftment was 50 days. One patient experienced secondary GF. Sustained engraftment was observed in 18 patients. Grade II - IV acute GVHD, limited chronic GVHD, and extensive chronic GVHD were observed in 6 (26%), 2 (10%), and 2 patients (10%), respectively.

With median follow-up times of 18 months after CBT, 19 of 27 patients were alive. Causes of death included bacterial/fungus infections in 3, veno-occulusive disease (VOD) in 2, EBV-LPD, hematologic malignancy, and secondary GF in each 1 patient.

The 5-year overall and failure-free survival (OS, FFS) of all patients were 69.5±9.0% and 59.3±9.5%, respectively. The 5-year OS and FFS of 17 patients who underwent UCBT after 2006 was 93.8±6.1% and 76.0±10.5%, respectively. Primary GF was observed in 8 patients, including 3 who underwent UCBT during 2006 - 2013. Two patients, who underwent UCBT after 2006, received FLU + CY + ATG without irradiation and remaining one patient received CY + ATG + total body irradiation (TBI). We screened anti-HLA antibodies in 8 patients but none of them were positive. The conditioning regimens including ATG exhibited a significantly worse FFS than those without ATG (33.3±12.2 % vs 91.7±8.0 %, P=0.004). On the other hand, the conditioning regimens including irradiation exhibited a better FFS than those without irradiation (75.0±9.7 % vs 14.3±13.2 % , P=0.01). The 5 year FFS of FLU + MEL + irradiation regimen (n=4) and FLU + CY + irradiation regimen (n=10) was 100% and 90%±9.5%, respectively.

Univariate analysis resulted in no statistical significant differences in OS and FFS in HLA disparities, total nucleated cell number and CD34 positive cell number at cryopreservation, and methods of GVHD prophylaxis. One patient developed secondary malignancy.

Discussion

Our study showed that a reduced conditioning regimen with Flu, MEL/CY and low-dose irradiation may be an optimal regimen for SAA children receiving UCBT. An important finding is that ATG has no benefit in this setting. A prospective study with larger number of patients is warranted to confirm our promising results.