Questioning the Efficacy of Steroid Prophylaxis and Identifying Gender as a Variable in Gene Therapy for Hemophilia A
Background
Adeno-associated virus (AAV)-based gene therapy has been anticipated as a fundamental solution for rare diseases. In fact, a gene therapy for severe hemophilia A has been approved, but it was withdrawn due to unclear durability and significant inter-patient variability. In particular, hepatic toxicity and elevated alanine aminotransferase (ALT) levels during treatment have been identified as major obstacles that reduce therapeutic efficacy.
In clinical practice, corticosteroids have been administered before and after infusion to prevent adverse effects and promote stable gene integration. The rationale is to suppress immune responses, reduce liver inflammation, and enhance expression efficiency. However, the extent to which this regimen actually improves therapeutic outcomes and reduces treatment uncertainty has not been clarified, necessitating a clear validation of the prescription criteria.
Key Findings
Recently, researchers evaluated the impact of prophylactic steroids in a model of seven dogs with severe hemophilia A. The experimental animals received an AAV5-based canine factor VIII (AAV5-cFVIII) gene therapy at a dose of 6e13 vector genomes (vg)/kg. Among them, four dogs were orally administered prednisolone (1 mg/kg/day) starting 3 hours before infusion, with the dosage gradually reduced over 6 weeks. The control group of three dogs received the therapy alone.
Over two years post-infusion, all dogs maintained therapeutic factor VIII activity levels between 8.7% and 56.1%. Improvements were observed in shortened whole blood clot times and a significant reduction in annual bleeding frequency from 6.11 to 1.42 bleeds/year. However, the difference in therapeutic efficacy between the steroid-treated group and the control group was minimal. The average factor VIII activity at two years, as measured by chromogenic substrate assay (CSA), was 39.1% in the treated group and 29.5% in the control group. This difference was largely driven by one female dog that exhibited significantly elevated expression levels from day 54 onward.
Gender analysis proved to be key in eliminating this statistical artifact. Regardless of steroid use, the average factor VIII activity at two years was 49.3% in females, compared to only 9.1% in males. In addition, steroids failed to prevent the initial rise in inflammatory cytokines or antibody formation. There was also no significant regulation of ALT levels, a marker of liver injury. In fact, one treated dog showed an ALT level 4.3 times the normal range at 18 weeks. A biopsy revealed mild, diffuse periportal lymphocyte and neutrophil infiltration, consistent with non-specific minimal hepatitis, but no long-term impact on therapeutic efficacy was observed.
Implications and Outlook
This study raises questions about the utility of the prophylactic steroid regimen that has been routinely applied in clinical settings. It reveals that a one-size-fits-all steroid administration may not provide meaningful benefits. Particularly, the demonstrated limitations in controlling immune responses and antibody formation suggest the need to focus on more precise and targeted immune modulation strategies.
The observed difference in therapeutic efficacy based on gender has also emerged as an important variable. The fivefold difference in activity levels between males and females suggests that hormonal or genetic factors may influence vector liver integration. Without overcoming this limitation, the development of precision therapies may be delayed. To ensure stable efficacy, it is essential to investigate gender-specific gene delivery mechanisms and explore alternative drugs for adverse effect control.
INTRODUCTION: Prior to commercial withdrawal, adeno-associated virus (AAV) gene therapy was approved for the treatment of adults with severe hemophilia A. Mechanisms underlying variability, durability, and liver transaminitis are largely uncharacterized. OBJECTIVES: To evaluate the effects of prophylactic corticosteroid administration on AAV gene therapy outcomes in severe hemophilia A dogs. METHODS: Seven hemophilia A dogs received 6e13 vector genomes/kg AAV5-canine factor VIII (AAV5-cFVIII). Four dogs received oral prednisolone (1 mg/kg/day) starting 3 hours pre-infusion with dose-tapering over 6 weeks; three control dogs received no corticosteroids. Percutaneous liver biopsies were performed on detection of alanine transaminase (ALT) >2-fold the upper limit of normal (ULN). RESULTS: All dogs expressed therapeutic FVIII:C (8.7-56.1%), improved whole blood clot time, and decreased bleeding rates (pre=6.11 vs. post=1.42 bleeds/year, p=0.016) over 2 years post-AAV5-cFVIII. Corticosteroid-treated dogs demonstrated a modest increase in mean FVIII:C at two years by chromogenic substrate assay (CSA) (39.1%) compared with controls (29.5%), driven by one female with markedly elevated FVIII:C from day 54 onward. When analyzed by sex, all female dogs exhibited increased mean FVIII:C CSA at 2 years (49.3%) compared with males (9.1%), regardless of prophylactic corticosteroid use. Prophylactic corticosteroids did not impact transient post-treatment elevations of pro-inflammatory cytokines, anti-AAV antibody formation, or ALT levels. One corticosteroid-treated dog experienced ALT >4.3-fold ULN at 18 weeks without impacting long-term FVIII:C expression. A liver biopsy showed diffuse, minimal periportal lymphocyte and neutrophil infiltration, consistent with non-specific minimal hepatitis. CONCLUSIONS: Prophylactic corticosteroids were not clearly associated with increased transgene expression in hemophilia A dogs.
These research findings provide a foundation for developing personalized treatment scenarios in clinical practice, where gene therapy dosing is adjusted according to a patient's gender. For male patients, increasing vector dosage or combining it with hormone-regulating therapies could enhance gene delivery efficiency, while for female patients, relatively lower dosages could be administered to preemptively reduce the risk of immune-related adverse effects. Furthermore, the establishment of patient-specific management guidelines that avoid routine steroid prescriptions and instead respond to individual liver enzyme changes or cytokine profiles during treatment monitoring becomes feasible. From a pharmaceutical industry perspective, this study is expected to contribute to the establishment of regulatory standards that strictly control gender balance in clinical trial designs and incorporate gender stratification as a mandatory step in data analysis.