Electrocardiographic and other cardiac anomalies in beta-glucuronidase-null mice corrected by nonablative neonatal marrow transplantation.

Cardiovascular manifestations of lysosomal storage disease (LSD) are a significant health problem for affected patients. Infantile-onset cardiac disease, because of its rapid progression, is usually treated symptomatically. Therapy in older patients includes valve replacement and bone marrow (BM) transplantation, both of which are life threatening in the already debilitated patients. Enzyme replacement therapy has potential benefit but has not yet been demonstrated to provide long-term relief for cardiac disease. Here, we demonstrate prevention of severe cardiac manifestations in beta-glucuronidase (GUSB) null mice BM-transplanted i.v. as neonates without myeloablative pretreatment. The mice, a model of mucopolysaccharidosis type VII (MPSVII, Sly syndrome), develop progressive LSD unless provided with GUSB early in life. The BM recipients retained GUSB+ donor cells in the peripheral blood and heart until necropsy at > or = 11 months of age. The enzyme beta-hexosamindase increased in tissues of GUSB null MPSVII mice was reduced significantly (P = 0.001) in treated MPSVII hearts. Electrocardiography demonstrated normalization of heart rate, PR, PQ, and QRS intervals in BM recipients. Storage was markedly reduced in the stroma of heart valves, adventitial cells of the aortic root, perivascular and interstitial cells of the myocardium, and interstitial cells of the conduction tissue. Heart/body weight ratio normalized. The aortic root was still grossly distended, and the conductive myocytes retained storage, suggesting neither plays a major role in ECG normalization. We conclude that transplantation of MPSVII neonates without toxic intervention can prevent many of the cardiovascular manifestations of LSD.

Donor cell replacement in mice transplanted in utero is limited by immune-independent mechanisms.

In utero transplantation (IUTx) therapy with allogeneic cells results in negligible peripheral blood (PBL) chimerism in nonablated humans with progressive diseases. IUTx has been successful only in immunocompromised fetuses. Because early treatment has great potential for halting disease progression, mechanisms preventing cell expansion must be identified and corrected. The hypothesis that factors in addition to allogenicity are responsible for low-level expansion is tested here by transplanting congenic cells into nonablated normal and mucopolycaccharidosis type VII (MPSVII) murine fetuses. MPSVII mice lack the enzyme beta-glucuronidase (GUSB-), accumulate glycosaminoglycans, and progressively develop severe storage disease. Low levels of enzyme can reverse storage. Evidence presented elsewhere showed that allogeneic donor cells overexpressing GUSB are negligible and their corrective effects are lost post-IUTx in MPSVII mice. We find that (1) congenic donor PBL cells, like allogeneic cells, are negligible in PBL of normal GUSB+ and MPSVII GUSB- hosts post-IUTx; (2) congenic, unlike allogeneic cells, are retained long term in both GUSB+ and GUSB- recipients; and (3) sufficient GUSB is produced to alleviate storage for up to 11.5 months in multiple tissues of GUSB- hosts. GUSB+ and GUSB- animals repopulate to a similar extent, indicating that donor GUSB enzyme does not initiate an immune response in the MPSVII null recipients. We conclude that the initial expansion of congenic and allogeneic cells is limited post-IUTx by non-immune-related mechanisms and the level of PBL cells is not necessarily indicative of graft failure following congenic IUTx. The mechanism limiting initial expansion may differ from that supporting long-term cell retention.

Nonablative neonatal marrow transplantation attenuates functional and physical defects of beta-glucuronidase deficiency.

The toxicity of preparative regimens render neonatal bone marrow transplantation (BMT) for progressive childhood diseases a controversial treatment. Ablative BMT in neonatal mice with or without the lysosomal storage disease mucopolysaccharidosis type VII (MPS VII) show high morbidity and developmental disruption of both brain and bone structure. In this investigation, BMT was performed with a high dose of congenic, normal bone marrow into nonablated newborn mice. Recipients had lifelong, multilineage, peripheral blood chimerism with the donor beta-glucuronidase-positive (GUS(+)) cells that was both well tolerated and therapeutic. Three daily injections of normal adult marrow increased the average life span by at least 6 months and corrected the functional breeding deficits typical of the MPS VII mice. Twelve months after injection, several structural features of femurs were more like that of normal mice than of untreated MPS VII mice. Periosteal circumference and bone cortical thickness were significantly improved in males and cortical density did not differ significantly from values in normal females. Significant reduction of lysosomal glycosaminoglycan storage corresponded directly with GUS enzyme activity and percentage of histochemically GUS(+) cells in visceral organs and hematopoietic tissues such as thymus, spleen, peripheral blood, and bone marrow. By all criteria tested, BMT into neonatal MPS VII mice in the absence of any preparative regimen is a successful therapy.