Limited rescue of osteoclast-poor osteopetrosis after successful engraftment by cord blood from an unrelated donor.
We report on a case of osteoclast-poor osteopetrosis who received a hematopoietic stem cell graft and, despite hematological engraftment, showed little signs of response in the skeletal defect. Clinical and laboratory studies supported the concept that the bone microenvironment remained abnormal, thus reducing the clinical response to transplantation.


BACKGROUND
Osteopetrosis is a rare genetic disorder characterized by severely reduced bone resorption resulting from a defect in either osteoclast development (osteoclast-poor osteopetrosis) or activation (osteoclast-rich osteopetrosis). Patients with osteoclast-rich osteopetrosis can be rescued by allogenic hematopoietic stem cell transplantation; however, little information exists concerning the success of transplantation as a treatment for osteoclast-poor osteopetrosis. We report on a child with osteoclast-poor osteopetrosis whose diagnosis was delayed, consequently receiving a cord blood transplant from an unrelated donor at the age of 8 years. Engraftment was deemed successful by peripheral blood genotyping, although >3 years after transplantation there was little rescue of the skeletal defect and anemia, and extramedullary hematopoiesis persisted.


METHODS
Peripheral blood mononuclear cells from the osteopetrosis patient, before and after transplantation, were used to generate osteoclasts in vitro in the presence of macrophage colony-stimulating factor (M-CSF) and RANKL.


RESULTS
Before transplantation few, small mononuclear osteoclasts formed (F-actin ring-positive cells, co-localizing with vitronectin receptor [alphavbeta3 integrin] and TRACP) associated with occasional, small resorption lacunae. Low levels of collagen C-terminal telopeptide (CTx) fragments were released from these cultures as assessed by ELISA (CrossLaps; patient, 12.85 nM; control, 448.6 nM). In contrast, osteoclasts formed in cultures after transplantation formed to a similar degree to control cultures from healthy individuals: large numbers of osteoclasts containing numerous nuclei were present, and approximately 50% of the surface of bone slices was resorbed, associated with intermediate levels of collagen fragment release (116.48 nM). The culture data reflect the histopathology and radiological findings and also support previous studies showing that neither M-CSF nor RANKL rescues osteoclast-poor osteopetrosis.


CONCLUSIONS
This is the first case reported in which a successful hematopoietic engraftment failed to correct an osteopetrotic skeletal defect, and this finding may be credited to the age at which the child was transplanted.
Nicholls
Brian M
BM
Department of Medicine, Bone and Mineral Centre, University College London, United Kingdom.
Bredius
Robbert G M
RG
Hamdy
Neveen A T
NA
Gerritsen
Egbert J A
EJ
Lankester
Arjan C
AC
Hogendoorn
Pancras C W
PC
Nesbitt
Stephen A
SA
Horton
Michael A
MA
Flanagan
Adrienne M
AM
D000135:Acid Phosphatase / Q000032:analysis; D001706:Biopsy; D039521:CD11c Antigen / Q000032:analysis; D018821:CD18 Antigens / Q000032:analysis; D002352:Carrier Proteins / Q000494:pharmacology; D002356:Cartilage / Q000473:pathology; D002454:Cell Differentiation / Q000187:drug effects; D002648:Child; D003094:Collagen / Q000378:metabolism; D024042:Collagen Type I; D036101:Cord Blood Stem Cell Transplantation; D004252:DNA Mutational Analysis; D005260:Female; D005269:Femur / Q000473:pathology; D006023:Glycoproteins / Q000097:blood; D006402:Hematologic Diseases / Q000209:etiology; D006801:Humans; D006811:Humerus / Q000473:pathology; D039302:Integrin alphaVbeta3 / Q000032:analysis; D007527:Isoenzymes / Q000032:analysis; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000473:pathology; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000494:pharmacology; D010010:Osteoclasts / Q000737:chemistry / Q000378:metabolism / Q000473:pathology*; D010022:Osteopetrosis / Q000150:complications / Q000473:pathology / Q000628:therapy*; D053244:Osteoprotegerin; D010455:Peptides / Q000378:metabolism; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear / Q000097:blood; D018124:Receptors, Tumor Necrosis Factor / Q000097:blood; D000071681:Tartrate-Resistant Acid Phosphatase; D014184:Transplantation, Homologous; D016896:Treatment Outcome
D039521:CD11c Antigen; D018821:CD18 Antigens; D002352:Carrier Proteins; D024042:Collagen Type I; D006023:Glycoproteins; D039302:Integrin alphaVbeta3; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D053244:Osteoprotegerin; D010455:Peptides; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018160:Receptors, Cytoplasmic and Nuclear; D018124:Receptors, Tumor Necrosis Factor; C505686:TNFRSF11A protein, human; C506030:TNFRSF11B protein, human; C505688:TNFSF11 protein, human; C052929:collagen type I trimeric cross-linked peptide; D016173:Macrophage Colony-Stimulating Factor; D003094:Collagen; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase