Hematopoietic Stem Cell Transplantation in Children with Refractory Langerhans Cell Histiocytosis
Authors: Kudo Kazuko , Maeda Miho , Suzuki Nobuhiro , Kanegane Hirokazu , Ohga Shouichi , Ishii Eiichi , Shioda Yoko , Imamura Toshihiko , Imashuku Shinsaku , Tsunematsu Yukiko , Endo Mikiya , Shimada Akira , Koga Yuuki , Hashii Yoshiko , Inagaki Jiro , Inoue Masami , Tabuchi Ken , Morimoto Akira 
Published: October 2019

Abstract
Introduction
Hematopoietic stem cell transplantation (HSCT) is one of the promising treatment strategies for children with refractory Langerhans cell histiocytosis (LCH), because of its immunomodulatory effects.Efficacy and indication of HSCT has been still undetermined. We analyzed the outcomes of HSCT in children with refractory LCH registered in the Transplant Registry Unified Management Program (TRUMP) conducted by the Japanese Society for Hematopoietic Cell Transplantation.
Patients and methods
Between 1996 and 2014, 30 patients <15 years old with refractory LCH who underwent an allogeneic HSCT were registered in the TRUMP database. Data collected as of March 2017 were analyzed. The histiocyte committee of the Japanese Society of Pediatrc Hematology and Oncology (JSPHO) sent the questionnaires to the institutions where HSCT was done for LCH, and clinical data of 25 patients were collected. Definition of response to initial therapy and disease state at HSCT was described previously. Failures were defined as relapse after HSCT, secondary malignancy, and death from any causes.
Results
Patients' characteristics
The male/female ratio was 18/12. Ages of onset of LCH and at BMT were median 9 months (range 3-23 months) and median 1 years (range 0-11 years), respectively. At diagnosis of LCH, 19 patients were positive for risk organ involvement, 6 were negative. Eleven patients underwent HSCT using myeloablative conditioning (MAC) regimen, whereas 19 patients reduced intensity conditioning (RIC) regimen. Eight patients received total body irradiation (TBI) > 8Gy (10-12Gy) regimen, 3 received full dose busulfan (BU: 16mg/kg po or 17.6mg/kg iv) regimen. Seven received fludarabine (FLU: 125-180mg/m2) + melphalan (MEL: 70-180mg/m2) without TBI and 9 received FLU(120-180mg/m2)+MEL (140-180mg/m2) with low dose irradiation (2-5.1Gy) and the remaining 3 received other RIC regimens. Cyclosporine was used in 13 patients and tacrolimus was used in 16 patients for graft versus host disease (GVHD) prophylaxis. Donor sources were related donor in 9 patients and unrelated in 21 patients (cord blood 19 and bone marrow 2). Four related donors were father or mother and 3 of them were haplo-identical. In these patients, induction therapy at onset achieved a good (5/25), partial (8/25), no (4/25) and progressive (8/25) diseases. In regard to disease status at HSCT, recipients with no active diseae (NAD) were 4/25, active disease-regression (AD-r) 2/25, active disease-stable (AD-s) 4/25 and progressive (AD-p) 15/25. Eight patients received 2-chlorodeoxyadenosine (2-CdA), including 4 patients who received the combination of 2-CdA and high dose Ara-C before HSCT as salvage therapy. At HSCT, 15/23 (65%) patients were in primary induction failure and 8/23 (35%) experienced first or additional relapse, respectively.
Transplantation outcomes
Neutrophil recovery was observed in 24 patients and the median time to engraftment was 21 days. Platelets engraftment was observed in 17 patients and the median time to engraftment was 52 days. Acute GVHD of grade II - IV, chronic GVHD (cGVHD) were observed in 6 and 4 patients, respectively. Extensive cGVHD was observed in 3 patients who received MAC regimens (p= 0.079). Relapse after HSCT were observed 1 patient in RIC regimens and 2 patients in MAC (P=0.613).
With follow-up of median 433 days (range 9-5307days) after HSCT, 17/30 (57%) patients are alive and 13 died. Death occurred within 3 months after HSCT in 8/13. The overall survival (OS) was not different between RIC and MAC (56.8% vs 63.6%, p=0.843). In regard to the correlation of disease status at HSCT and outcome, 6 patients with NAD/ AD-r had better outcome than 19 with AD-s/ AD-p (5-year OS 100% vs 52.1%, p=0.035). The 5-year FFS of the 16 patients who received FLU+ MEL based regimen were 68.8%, and were marginally better than those of the 14 patients who were conditioned with other regimens (68.8% (95%CI: 46.0-91.5) vs 42.9% (95%CI: 16.9-68.8), P=0.209).
Discussion
In conclusions, of 30 HSCT-recipients for refractory LCH, 17/30 (57%) are alive while post-transplant death occurred in 13/30 (43%). Our study showed that in regard to the correlation of disease status at HSCT and outcome, 6 patients with NAD/ AD-r had better outcome than 19 with AD-s/ AD-p (5-year OS 100% vs 52.1%, p=0.035). Novel bridging measures, such as targeted inhibition of the MAPK pathway, are required to stabilize the disease activity before HSCT.

Disclosures
No relevant conflicts of interest to declare.