Hemophilia clinical trials

White GC. Gene therapy in hemophilia Clinical trials update. Thromb Haemost 2001 86 172-177. 

Flowever, some associated materials might be perceived as toxic. For example, complexes of osmium find frequent use as electron mediators, because of their rich chemistry, stability, and redox activity. Osmium metal and most compounds are considered nontoxic, but the neat tetroxide of osmium is a strong oxidizer and is considered highly toxic in the U.S. and very toxic by the European Union. On the other hand, the aqueous solution, osmic acid, has been injected at 1% concentration in several European clinical trials, starting in the 1970s, for treatment of arthritis and hemophilia. - No toxic effects were observed. Thus, osmium toxicity might be a question not of in vivo chemistry, but of manufacture, where a concentrated form of the oxide might need to be handled. ... 

For ethical reasons, children enrolled in these clinical trials have also received standard therapy of enzyme infusions, so the results of these studies have been difficult to interpret and are controversial. Nevertheless, there is some evidence that the ex vivo gene transfer approach may evoke a biological response relevant to the treatment of ADA deficiency. Such interpretations have stimulated efforts to use the ex vivo strategy for other monogenic disorders, such as familial hypercholesterolemia, hemophilia B, and Gaucher s disease. 

Clinical trials have demonstrated excellent efficacy with recombinant human factor VIII concentrates available as Recombinate and Kogenate. These recombinant factor VIII products are purified from the cell culture of plasmids, not viral DNA-transfected hamster cells and therefore do not express viral sequences. The addition of human serum albumin for stabilization, constitutes the sole possible source for human viral contamination. More recently recombinant factor IX has been genetically engineered by insertion of the human factor IX gene into a Chinese hamster ovary cell line. It has been proved to be safe and effective in the treatment of patients with hemophilia B. 

Thee future prospects for naked DNA gene therapy include clinical trials for genetic diseases (e.g., Duchenne muscular dystrophy, ischemia, hemophilia), which would be initiated in the next few years, and tail vein injections in rodents, which will become a widely used technique for rapidly testing expression vectors/gene therapy approaches (101). 

Lyophilized factor VIII has been used as substitution therapy in patients with hemophilia A. Most, but not all, recombinant factor VIII (recFVIII) is structurally and immunologically similar to plasma-derived factor VIII, and it has been well tolerated by patients in clinical trials. A major concern about recombinant factor VIII has been the occurrence inhibitors (1). However, there is evidence that there is no difference in the occurrence of inhibitors between recombinant factor VIII and plasma-derived factor VIII (2). 

Protein purification, introduced in the 1990s, produced high-purity concentrates with increased amounts of factor VIII or factor IX relative to the product s total protein content. Recombinant factor VIII and then factor IX also became available. The first-generation recombinant factor VIII products utilize human and animal proteins in culture and add human albumin as a protein stablilizer. Second-generation recombinant factor VIII concentrates removed albumin as a protein stabilizer, and the third-generation products lack human and animal proteins in the culture media. Finally, gene therapy for the treatment of hemophilia is now in the early stages of clinical trials. 

First marketed in the United States in 1996,recombinant factor IX is produced in Chinese hamster ovary cells transfected with the factor IX gene. Blood and plasma products are not used to produce recombinant factor IX nor to stabilize the final product thus recombinant factor IX has an excellent viral safety profile. Clinical trials have shown the product to be safe and efficacious in the treatment of acute bleeding episodes and in the management of bleeding associated with surgical procedures. Although the half-life of recombinant factor IX is similar to that of the plasma-derived products, recovery is approximately 28% lower. As a result, doses of recombinant factor IX concentrate must be higher than those of plasma-derived products to achieve equivalent plasma levels. Because individual pharmacokinetics may vary, recovery and survival studies should be performed to determine optimal treatment. Recombinant factor IX is often considered the treatment of choice for hemophilia B. 

More recently, the ALN-AT3 (RNAi targeting antithrombin Sehgal et al, 2015) entered a phase I clinical trial with healthy volunteers (NCT02035605) and then patients with moderate or severe hemophilia A and B (NCT02554773). 

Using rAAV to deliver the fector IX gene in the treatment of hemophilia B demonstrates another excellent example of the efficacy and safety of rAAV vectors. Immediately following the successful use of rAAV in murine and canine hemophilia B models, a clinical trial was initiated (197). In this dose-escalation trial, rAAV particles were injected intramuscularly to three human patients. None of the patients revealed any significant side effects to the vector. Furthermore, modest therapeutic efficacy was demonstrated in some patients. Based on these exciting findings, a second human trial with direct portal vein delivery of rAAV is currently underway. 

Pharmacokinetic data were collected as well as pharmacodynamic measurements of platelet aggregation support (ristocetin cofactor activity) and cuticle wound blood flow. An important component of these studies was the suitability of the model. These models were chosen because of the biochemical deficiency of the particular factors and the parallel clinical syndromes. Such in vivo data can help in determining activity and dosing when such a product is first used in human trials. The Refacto molecule was also studied in rats and monkeys to determine its no observed adverse effect level, that was more than 10 times normal circulating levels. The major toxicity observed was the development of antibodies to the molecule that blocked activity and resulted in an acquired hemophilia syndrome. Similar findings were demonstrated when plasma-derived material was injected into monkeys [20]. 

In another clinical study, patients suffering from hemophilia B, which is a bleeding disorder caused by a deficiency of coagulation factor IX, were treated with AAV vectors expressing human factor IX (13 9). These patients participated in a Phase I trial and received intramuscular injections of AAV vectors. Although only very low levels of secreted factor IX could be detected in the plasma of one patient, the treated patients showed some clinical benefits and a reduced intake of factor IX infusions. Moreover, no vector-related toxicity and germ line transmission was observed. 

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