Metachromatic leukodystrophy (MLD) is an inherited lysosomal storage disease caused by arylsulfatase A (ARSA) deficiency. Patients with MLD exhibit progressive motor and cognitive impairment and die within a few years of symptom onset. We used a lentiviral vector to transfer a functional ARSA gene into hematopoietic stem cells (HSCs) from three presymptomatic patients who showed genetic, biochemical, and neurophysiological evidence of late infantile MLD. After reinfusion of the gene-corrected HSCs, the patients showed extensive and stable ARSA gene replacement, which led to high enzyme expression throughout hematopoietic lineages and in cerebrospinal fluid. Analyses of vector integrations revealed no evidence of aberrant clonal behavior. The disease did not manifest or progress in the three patients 7 to 21 months beyond the predicted age of symptom onset. These findings indicate that extensive genetic engineering of human hematopoiesis can be achieved with lentiviral vectors and that this approach may offer therapeutic benefit for MLD patients.

Wiskott-Aldrich Syndrome (WAS) is an inherited immunodeficiency caused by mutations in the gene encoding WASP, a protein regulating the cytoskeleton. Hematopoietic stem/progenitor cell (HSPC) transplants can be curative but, when matched donors are unavailable, infusion of autologous HSPCs modified ex vivo by gene therapy is an alternative approach. We used a lentiviral vector encoding functional WASP to genetically correct HSPCs from three WAS patients and re-infused the cells after reduced-intensity conditioning regimen. All three patients showed stable engraftment of WASP-expressing cells and improvements in platelet counts, immune functions, and clinical score. Vector integration analyses revealed highly polyclonal and multi-lineage haematopoiesis resulting from the gene corrected HSPCs. Lentiviral gene therapy did not induce selection of integrations near oncogenes and no aberrant clonal expansion was observed after 20–32 months. Although extended clinical observation is required to establish long-term safety, lentiviral gene therapy represents a promising treatment for WAS.

Hepatitis C virus (HCV) envelope glycoproteins E1͞E2 can pseudotype retroviral particles and efficiently mediate entry into target cells. Using this experimental system, we determined HCV tropism for different cell types. Only primary hepatocytes and one hepatoma cell line were susceptible to HCV pseudovirus entry, which could be inhibited by sera from HCV-infected individuals. Furthermore, expression of the putative HCV receptor CD81 on nonpermissive human hepatic but not murine cells enabled HCV pseudovirus entry. Importantly, inhibition of viral entry by an anti-CD81 mAb occurred at a step following HCV attachment to target cells. Our results indicate that CD81 functions as a postattachment entry coreceptor and that other cellular factors act in concert with CD81 to mediate HCV binding and entry into hepatocytes.I t is estimated that 170 million people worldwide are infected with the hepatitis C virus (HCV) and are at risk of developing chronic hepatitis or cirrhosis, the latter often leading to hepatocellular carcinoma (1, 2). In the past, difficulties with culturing the virus and expressing fusogenic envelope glycoproteins limited studies of HCV tropism and entry. RT-PCR-and electron microscopy-based approaches were relied on to demonstrate the presence of HCV RNA and proteins in primary hepatocytes and certain hepatoma cell lines (3-8). Furthermore, the existence of extrahepatic HCV reservoirs was suggested by the detection of viral RNA in serum and peripheral blood mononuclear cells (PBMC) (9-11). Recently, a major technical advance in the field has been the discovery that unmodified HCV envelope glycoproteins can pseudotype retroviral particles and mediate entry into target cells (12)(13)(14)(15). This model seems to authentically replicate the early steps of the HCV life cycle, enabling detailed studies of HCV tropism and entry into target cells.The cellular tropism of enveloped viruses is largely determined by selective interactions of viral envelope glycoproteins with specific cell-surface receptors. Entry generally proceeds by a cascade of coordinated events wherein virus binding to a host molecule triggers exposure of cryptic envelope glycoprotein domains that mediate downstream interactions and functions. We and others recently demonstrated that DC-SIGN (dendritic cell-specific ICAM-3 grabbing nonintegrin; CD209) and L-SIGN (DC-SIGNR, liver and lymph node specific; CD209L) function as HCV capture receptors but do not mediate viral entry into target cells (16,17). Candidate HCV entry receptors include CD81, scavenger receptor class B type 1, low density lipoprotein receptor, and glycosaminoglycans (18)(19)(20). CD81 is the most extensively characterized putative HCV receptor. A number of groups have demonstrated that the soluble ectodomain of HCV envelope glycoprotein E2 binds specifically and with relatively high affinity (K d Ϸ10 Ϫ8 M) to human and chimpanzee CD81 (21-24). However, CD81 is widely expressed on human cells and therefore cannot account for the restricted tropism of HCV to hepatocytes...

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