HLA-Haploidentical Hematopoietic Stem Cell Transplantation In An Infant with Malignant Infantile Osteopetorosis.
Authors: Omachi Taichi , Kawasaki Hirohide , Noda Yukihiro , Kaneko Kazunari 
Published: October 2019

Abstract
Abstract 4585
Malignant infantile osteopetrosis is an autosomal recessive disease characterized by a lack of osteoclastic function with incidence of 1: 200,000 to 1: 300,000. In consequence of disturbed bone building and remodeling, affected patients have osteosclerosis, dense fragile bone, and a marked reduction in the bone marrow cavity. Clinical features, such as anemia, thrombocytopenia, hepatosplenomegaly, bone fractures, bone deformity, and cranial nerve entrapment, appear soon after birth or within the first years of life. In the natural course of the disease, only 30% of children can survive to more than six years old. Because osteoclasts are of hematopoietic origin, allogeneic stem cell transplantation is the only curable therapy. Recently, successful HLA-haploidentical hematopoietic stem cell transplantation (HSCT) has been reported for patients without HLA- matched donors. We also present an infant with malignant infantile osteopetrosis who underwent HLA-haploidentical HSCT. A four-month-old boy was referred to our hospital for splenomegaly and pancytopenia. A physical examination revealed failure to thrive, distention of anterior fontanel, and hepatosplenomegaly. Laboratory findings indicated thrombocytopenia and anemia, and elevated alkaline phosphatase. Osteoclasts were hyperplastic in bone marrow. Radiography showed homogeneous and sclerotic bones with absence of corticomedullary junction, and bone marrow scintigraphy showed no accumulation of bone marrow. Subsequently, TCIRG1 mutations are identified. All these findings are compatible with malignant infantile osteopetrosis and the diagnosis was made. We conducted HSCT to revive his osteoclastic function. However, he didn't have HLA-matched donors not only in relatives but also in the bone marrow bank and the cord blood bank of Japan. We attempted HLA-haploidentical bone marrow transplantation (BMT) from his father with written informed consent. The patient was prepared for BMT at 11 months of age by conditioning with busulfan (6 mg/kg × 4/day × 4 days), cyclophosphamide (360mg/m2 × 2 days) and antithymocyte globulin (2 mg/kg/day × 3 days). Prophylaxis for graft-versus-host disease (GVHD) included tacrolimus and short-term methotrexate. Bone marrow nuclear cells (1×109/kg) were collected from his father and transplanted without any manipulations. The engraftment of neutrophils was confirmed on day 9 after BMT. Acute GVHD was limited to the skin (grade I). At 2 months after BMT, neutrophil counts, platelet counts, and hemoglobin level were all within normal limits. Bone marrow scintigraphy revealed a significant uptake in bone marrow. There have been no chronic GVHD up to six months after BMT.HSCT for patients with osteopetrosis is challenging as it is reported that HLA-haploidentical HSCT has the high rate of acute and chronic GVHD. Fortunately, HLA-haploidentical BMT was successful in our patient. This might be due to our regimen for prophylaxis of rejection and GVHD. We used ATG in conjunction with tacrolimus: this regimen may be prophylactic not only for rejection but also for GVHD as previously reported (Schulz et al. Blood 2002; 99: 3458–3460). In conclusion, HLA-haploidentical family donors should be considered as the alternative hematopoietic stem cell source for patients with malignant infantile osteopetrosis in condition without HLA-matched donors.

Disclosures:
No relevant conflicts of interest to declare.