Hematopoietic cell transplantation for inherited metabolic diseases: an overview of outcomes and practice guidelines

Five-Year Follow-Up of Two Siblings with Aspartylglucosaminuria Undergoing Allogeneic Stem-Cell Transplantation from Unrelated Donors

BACKGROUND

Aspartylglucosaminuria is a rare, inherited lysosomal disease characterized by a slowly progressive mental retardation and coarse facial and body features. With the intent to provide the deficient enzyme aspartylglucosaminidase, allogeneic stem-cell transplantation (ASCT) has been attempted. Only a few cases of transplants have been reported.

METHODS

Two siblings with aspartylglucosaminuria underwent allogeneic bone marrow transplants using unrelated human leukocyte antigen-A, -B, and DR identical donors at ages 10 years 5 months and 5 years 10 months, respectively. They were followed during 5 years with biochemical, neuroradiologic, neuropsychologic, and clinical investigations.

RESULTS

During 5 years follow-up, no neuropsychologic or clinical deterioration was noted in the children. A stable expression of aspartylglucosaminidase was found during the whole follow-up period. The spinal fluid concentration of Tau-protein, a marker of neuronal and axonal degeneration and damage, peaked at approximately 12 months after bone-marrow transplantation and then declined to almost normal levels after 5 years. By magnetic resonance imaging (MRI), an improvement of myelination in the youngest sibling and an arrest of demyelination in the older one were observed.

CONCLUSION

The importance of long-term follow-up of children after ASCT in this rare, very slowly progressive lysosomal disease must be emphasized. We report that none of the children had lost any capabilities since the transplantation; moreover, an improvement is shown in biochemical markers and MRI white-matter signals, suggesting a beneficial effect.

Cell-based therapies for birth defects: a role for adult stem cell plasticity?

Cell therapy can offer a reasonable approach to the treatment of specific birth defects, particularly those for which hematopoietic stem cells (HSCs) can be used to restore (even partially) the number of cells, protein levels, or enzyme activity. Relatively few clinical experiences have been published on this subject, but when a natural selective advantage exists for the cell graft, a degree of "rescue" is possible. Strategies have been developed to confer a selective advantage through genetic engineering of donor cells, and this approach may prove valuable in the treatment of birth defects, as it is in hematological malignancy. Stem cell (SC) plasticity, or transdifferentiation, may offer another route for delivery of cells to established or developing organs. A wide variety of studies support the concept that adult tissue-specific SCs can, if displaced from their normal niche to another, be reprogrammed to produce cell types appropriate to their new environment. Clinical observations reveal that persistent tissue microchimerism develops not only in blood lineages after transfusion, but also in thyroid follicular epithelium via transplacental exchange. In addition, hepatic and renal parenchyma also become chimeric following allografts or bone marrow transplantation (BMT). Experimental models indicate that a renal glomerulosclerosis phenotype can be transferred by grafting whole BM, and that a severe liver disorder in fah-/- mice can be overcome by grafting HSCs and then exerting a selection pressure. It may be possible in the future to exploit the ability of adult SCs to contribute to diverse tissues; however, our understanding of the processes involved is at a very early stage.

Correction of metachromatic leukodystrophy in the mouse model by transplantation of genetically modified hematopoietic stem cells

Gene-based delivery can establish a sustained supply of therapeutic proteins within the nervous system. For diseases characterized by extensive CNS and peripheral nervous system (PNS) involvement, widespread distribution of the exogenous gene may be required, a challenge to in vivo gene transfer strategies. Here, using lentiviral vectors (LVs), we efficiently transduced hematopoietic stem cells (HSCs) ex vivo and evaluated the potential of their progeny to target therapeutic genes to the CNS and PNS of transplanted mice and correct a neurodegenerative disorder, metachromatic leukodystrophy (MLD). We proved extensive repopulation of CNS microglia and PNS endoneurial macrophages by transgene-expressing cells. Intriguingly, recruitment of these HSC-derived cells was faster and more robust in MLD mice. By transplanting HSCs transduced with the arylsulfatase A gene, we fully reconstituted enzyme activity in the hematopoietic system of MLD mice and prevented the development of motor conduction impairment, learning and coordination deficits, and neuropathological abnormalities typical of the disease. Remarkably, ex vivo gene therapy had a significantly higher therapeutic impact than WT HSC transplantation, indicating a critical role for enzyme overexpression in the HSC progeny. These results indicate that transplantation of LV-transduced autologous HSCs represents a potentially efficacious therapeutic strategy for MLD and possibly other neurodegenerative disorders.