Hemophilia B is an X-linked coagulopathy caused by absence of functional coagulation factor IX (F.IX). Previously, we established an experimental basis for gene transfer as a method of treating the disease in mice and hemophilic dogs through intramuscular injection of a recombinant adeno-associated viral (rAAV) vector expressing F.IX. In this study we investigated the safety of this approach in patients with hemophilia B. In an open-label dose-escalation study, adult men with severe hemophilia B (F.IX < 1%) due to a missense mutation were injected at multiple intramuscular sites with an rAAV vector. At doses ranging from 2 ؋ 10 11 vector genomes (vg)/kg to 1.8 ؋ 10 12 vg/ kg, there was no evidence of local or systemic toxicity up to 40 months after injection. Muscle biopsies of injection sites performed 2 to 10 months after vector administration confirmed gene transfer as evidenced by Southern blot and transgene expression as evidenced by immunohistochemical staining. Preexisting high-titer antibodies to AAV did not prevent gene transfer or expression. Despite strong evidence for gene transfer and expression, circulating levels of F.IX were in all cases less than 2% and most were less than 1%. Although more extensive transduction of muscle fibers will be required to develop a therapy that reliably raises circulating levels to more than 1% in all subjects, these results of the first parenteral administration of rAAV demonstrate that administration of AAV vector by the intramuscular route is safe at the doses tested and effects gene transfer and expression in humans in a manner similar to that seen in animals. (Blood.

Pre-clinical studies in mice and haemophilic dogs have shown that introduction of an adeno-associated viral (AAV) vector encoding blood coagulation factor IX (FIX) into skeletal muscle results in sustained expression of F.IX at levels sufficient to correct the haemophilic phenotype. On the basis of these data and additional pre-clinical studies demonstrating an absence of vector-related toxicity, we initiated a clinical study of intramuscular injection of an AAV vector expressing human F.IX in adults with severe haemophilia B. The study has a dose-escalation design, and all patients have now been enrolled in the initial dose cohort (2 x 10(11) vg/kg). Assessment in the first three patients of safety and gene transfer and expression show no evidence of germline transmission of vector sequences or formation of inhibitory antibodies against F.IX. We found that the vector sequences are present in muscle by PCR and Southern-blot analyses of muscle biopsies and we demonstrated expression of F.IX by immunohistochemistry. We observed modest changes in clinical endpoints including circulating levels of F.IX and frequency of FIX protein infusion. The evidence of gene expression at low doses of vector suggests that dose calculations based on animal data may have overestimated the amount of vector required to achieve therapeutic levels in humans, and that the approach offers the possibility of converting severe haemophilia B to a milder form of the disease.

In a clinical study of recombinant adenoassociated virus-2 expressing human factor IX (AAV2-FIX), we detected 2 impediments to long-term gene transfer. First, preexisting anti-AAV neutralizing antibodies (NABs) prevent vector from reaching the target tissue, and second, CD8 ؉ T-cell responses to hepatocyte-cell surface displayed AAV-capsid-terminated FIX expression after several weeks. Because the vector is incapable of synthesizing viral proteins, a short course of immunosuppression, until AAV capsid is cleared from the transduced cells, may mitigate the host T-cell response, allowing longterm expression of FIX. To evaluate coadministration of immunosuppression, we studied AAV8 vector infusion in rhesus macaques, natural hosts for AAV8. We administered AAV8-FIX in 16 macaques via the hepatic artery and assessed the effects of (1)

Long-term cures of hemophilia B have been achieved using AAV2 delivering the factor IX gene to the liver of adenoassociated virus (AAV)-naive hemophilic animals. However, the clinical success of this approach requires overcoming preexisting AAV neutralizing antibodies prevalent in humans. To better define the inhibition of neutralizing antibodies on AAV2-mediated liver transduction, we developed an in vivo passive immunity model. SCID mice were first reconstituted to a defined neutralizing titer with pooled plasma-derived human immunoglobulin. AAV2-FIX vectors then were administered to the liver, and the transduction efficiency was measured by plasma FIX levels. Unexpectedly, AAV2 neutralizing titers lower than 1:10 were sufficient to neutralize 4 to 20 ؋ 10 12 vg/kg of AAV2 vectors in vivo, a capacity that was underestimated by in vitro neutralizing assays. We also evaluated strategies to evade neutralization, including the use of alternative delivery routes, infusion parameters, empty capsids, and alternative AAV serotypes 6 and 8. The results indicate that low AAV2 neutralizing titers can be inhibitory to the tested human and primate AAV vectors delivered into the circulatory system. Therefore, novel nonprimate AAV vectors or compartmentalized delivery may offer more consistent therapeutic effects in the presence of preexisting AAV neutralizing antibodies.

No abstract

IntroductionHemophilia A, a congenital deficiency or dysfunction of factor VIII (FVIII), is the most common severe inherited bleeding disorder in humans. Severe hemophilia A patients have less than 1% of normal FVIII activity, and suffer from spontaneous or traumatic joint and muscle hemorrhage, leading to a chronic painful and disabling arthropathy. Bleeding into body cavities or the brain can result in significant morbidity and mortality if not treated aggressively. 1 Current treatment in the developed world, FVIII protein replacement, has established that restoring circulating FVIII levels above 1% of normal prevents most spontaneous bleeding, and levels above 5% are sufficient to improve the disease from a severe to a mild form. However, the limited worldwide supplies of both plasma-derived and recombinant FVIII, its short half-life in vivo (ϳ 12 hours), and the high cost of treatment (Ͼ $150 000 per year) make gene therapy an attractive alternative to better manage and cure the disease.Previously, we have shown that gene therapy with an AAV2 vector encoding a B-domain-deleted (BDD) canine FVIII (cFVIII) cDNA under the control of a liver-specific promoter resulted in an average of 2% to 3% of normal canine FVIII activity in 2 hemophilia A dogs, 2 providing preliminary support for the feasibility of this approach in humans. In order to further improve the efficacy of liver-targeted AAV-cFVIII, we explored the possibility of using alternative serotypes of AAV. We also assessed the duration of therapeutic benefit following a single injection of AAV-cFVIII in hemophilia A dogs.Since the isolation of AAV2, many different AAV serotypes have been isolated from human and nonhuman primate tissues. 3 In comparison with the prototypic AAV2, AAV vectors pseudotyped with other serotypes show superior transduction efficiency in various tissues: AAV1 in muscle, 4 pancreatic islets, 5 heart, 6 vascular endothelium, 7 brain and central nervous system (CNS), 8,9 and liver 10 ; AAV3 in Cochlear inner hair cells 11 ; AAV4 in brain 12 ; AAV5 in brain and CNS, 8,13 lung, 14-16 eye, 17,18 arthritic joints, 19 and liver 20 ; AAV6 in muscle, 21,22 heart, 23 and airway epithelium 24 ; AAV7 in muscle 4 ; and AAV8 in muscle, 4,25 pancreas, 26 heart, 25 and liver. [27][28][29][30][31] The tissue tropism of different AAV serotypes may permit targeting of AAV vectors to human disease. However, as most of these tissue-specific tropisms have been reported in the rodent, it is important to evaluate cross-species fidelity of differential targeting among serotypes in larger animal modelsIn this report, we have compared the efficacy, gene transfer efficiency, and biodistribution of AAV-cFVIII vectors of serotypes 2, 5, 6, and 8 delivered by portal-vein injection in hemophilia A mice. Furthermore, since prior studies have demonstrated that the hemophilia dog model, compared with the mouse model, more accurately predicts the therapeutic outcomes in humans and other primates, 32,33 we have determined the long-term efficacy and safety of AAV2-cFVI...

Lactadherin, a major glycoprotein of the human milk fat globule membrane, is abundant in human breast milk and expressed in human breast carcinomas. Previously, we have shown that the mature protein, formerly known as BA46, has three domains: an epidermal growth factor (EGF)-like domain containing an Arg-Gly-Asp (RGD) cell adhesion sequence and C1 and C2 domains similar to those found in coagulation factors V and VIII. An alignment of lactadherin with its bovine (MGP57/53) and murine (MFG-E8) homologs shows that the RGD sequence has been conserved during evolution, suggesting that the RGD sequence is not fortuitous. We demonstrate that lactadherin purified using Triton X-114 phase partitioning promotes RGD-dependent cell attachment of green monkey kidney cells (MA104), mouse fibroblast cells (3T3-L1), and breast carcinoma cells (ELL-G). A lactadherin-specific monoclonal antibody, Mc3, inhibits attachment to purified lactadherin, suggesting that contaminants in the purification are not responsible for binding. In addition, the anti-integrin alpha(v)beta3 monoclonal antibody LM609 inhibits cell attachment of MA104 cells to lactadherin. These results demonstrate that lactadherin promotes RGD-dependent cell adhesion via integrins. Denaturation of lactadherin with heat and reducing conditions diminished cell attachment, suggesting that optimal cell attachment to RGD is dependent on the structural presentation of the sequence.

No abstract