Clinical Considerations for Capsid Choice in the Development of Liver-Targeted AAV-Based Gene Transfer.

As gene transfer with adeno-associated virus (AAV) vectors is starting to enter clinical practice, this review examines the impact of vector capsid choice in liver-directed gene transfer for hemophilia. Given that there are multiple clinical trials completed and ongoing in this field, it is important to review the clinical evidence, particularly as a range of AAV-vector serotypes including AAV2, AAV5, AAV8, and AAV10 have been tested. Although there have been a number of successful trials, the development of two investigational AAV vectors for hemophilia B has been discontinued because they did not meet efficacy and/or safety expectations. Whether this difference between success and failure of gene transfer approaches reflects capsid choice, vector design, manufacturing system, or other variables is a question of great interest. Here, we examine the body of evidence across trials to determine the possible influences of serotype choice on key clinical outcomes such as safety, vector clearance, treatment eligibility, occurrence of transaminase elevations, activation of capsid-directed cytotoxic T cell responses, and clinical efficacy. In summary, gene transfer requires a balance between achieving sufficient transgene expression and minimizing destructive immune responses, which may be affected by AAV-vector serotype choice.

Practical Implications of Factor IX Gene Transfer for Individuals with Hemophilia B: A Clinical Perspective.

Gene therapy for severe hemophilia is on the cusp of entering clinical practice. However, there is limited clinical experience in this area given that gene transfer is a relatively recent technology. Therefore, this clinical perspective article will review the evidence supporting gene therapy in this field, examine ways to open a dialogue about gene therapy with patients in the clinic setting, and present a case of a participant in a recent clinical trial of gene therapy for hemophilia. Clinical trials in hemophilia using adeno-associated virus (AAV) vectors to transfer functional factor IX (FIX) have reported increases in FIX activity to functional levels, reduced bleed frequency, and a lessening or abrogation of the need for costly FIX replacement. The safety profile of AAV-mediated gene therapy also appears positive, with manageable, asymptomatic increases in liver enzymes being the most commonly described adverse event. Examining a clinical case in hemophilia B more closely, gene transfer decreased annualized bleeds from six (unknown or spontaneous) bleeds before treatment to three (spontaneous) bleeds after treatment alongside a 55% reduction in FIX replacement. The participant experienced an increase in traumatic bleeds after treatment, which appears to reflect increased physical activity and early prophylaxis discontinuation. After the gene transfer, the participant considered his hemophilia to be "cured," which emphasizes the need to manage patient expectations, particularly regarding activity levels and bleed risk in the immediate post-treatment period. Gene therapy for hemophilia has the potential to transform the lives of affected individuals and is likely to create a new class of hemophilia patient who has shifted from a severe to a mild phenotype. Despite having a mild phenotype, these individuals may retain a legacy of increased bleed risk and joint damage from their years with severe hemophilia and will need different clinical management compared to a more typical individual with mild hemophilia.

Burden of disease in adult patients with hypophosphatasia: Results from two patient-reported surveys.

BACKGROUND: Hypophosphatasia (HPP) is a rare metabolic bone disease caused by loss-of-function mutation(s) in the tissue-nonspecific alkaline (TNSALP) phosphatase gene, which manifests as rickets and/or osteomalacia with systemic complications and affects patients of all ages. The burden of disease is poorly characterized in adult patients. AIMS: We assessed patient-reported burden of disease using two surveys reasonably specific for HPP symptomatology, the Hypophosphatasia Impact Patient Survey (HIPS) and the Hypophosphatasia Outcomes Study Telephone interview (HOST). METHODS: Patients with HPP were invited to participate via patient advocacy groups or their medical provider. Survey questions captured demography, HPP-related medical history, mobility, and health-related quality of life (using Short Form 12 [version 2] Health Survey [SF-12v2]) via internet report (HIPS) or telephone interview (HOST). RESULTS: One hundred twenty-five adults responded (mean [standard deviation, SD] age: 45 [14.3] years). Eighty-four patients (67%) reported pediatric-onset of their symptoms. Common clinical features in the study population included pain (95% of patients), fractures (86% of patients) muscle weakness (62%) and unusual gait (52%). Use of assistive devices for mobility (60%) was also prevalent. Twenty-six percent of patients reported more than 10 fractures. Seventy-four percent of patients had undergone orthopedic/dental surgical procedures. The health profile of patients responding on the SF-12 showed a broad and substantial impact of HPP on health-related quality of life, with domains related to physical ability showing the greatest decrement compared to normative data. CONCLUSIONS: In aggregate, these data indicate that HPP can confer a high burden of illness in adulthood.