Faculty Bibliography

Recombinant factor VIII and IX products have well-established efficacy and safety records. However, concerns about the possibility of viral transmission have prompted efforts to develop recombinant products that are free of added human and animal proteins. The currently licensed second-generation recombinant factor VIII concentrates were introduced in 2000. Two new third-generation products, manufactured without any human- or animal-derived materials, are currently in development and clinical testing. As an alternative to exogenous factor replacement, gene therapy is under investigation for use in the treatment of hemophilia. Gene therapy involves the stable insertion of a functional gene for long-term expression and secretion of endogenous factor VIII or IX protein. Methods used to date have been based on retroviral, adenoviral, and adeno-associated viral vectors, as well as nonviral electroporation. Three phase I trials using these approaches have been completed as of 2002, and one more is ongoing. This article reviews the results of recent clinical studies investigating third-generation recombinant products and gene-based approaches to hemophilia treatment

The goal of gene therapy for bleeding disorders is to provide stable insertion and expression of a particular gene whose absence is responsible for a particular disease. The bleeding disorders for which the most basic and clinical research has been completed are the hemophilias factor VIII deficiency and factor IX deficiency. These X-linked diseases are caused by single-gene mutations; replacement of the defective gene has not only resulted in clinical and biochemical improvement in animal models but also provided promising results in phase I clinical trials. An ideal gene transfer approach to the treatment of hemophilia would require a minimally invasive procedure for gene delivery, have minimal associated morbidity, and result in long-term transgene expression, ideally yielding factor levels in the therapeutic range. Multiple approaches to gene transfer in the hemophilias are currently under investigation

Two boys with severe factor VIII deficiency that initially presented with acute onset of joint pain and swelling consistent with an uncomplicated hemarthrosis are reported. When appropriate management failed to provide resolution of symptoms, alternate diagnoses were considered. Both boys ultimately had complex regional pain syndrome (CRPS) diagnosed. The delay in diagnosis contributed to prolonged patient discomfort and lack of appropriate therapy. Complex regional pain syndrome encompasses a group of disorders that are characterized by pain severity or duration disproportionate to that expected. It is uncommon in the pediatric population. Because early diagnosis and appropriate treatment may improve outcome, it is important for practitioners to consider CRPS in the differential diagnosis of persistent pain in children with hemophilia

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