FVIII activity following FVIII protein infusion or FVIII gene transfer predicts the bleeding risk in hemophilia A rats.

BACKGROUND: Prophylactic replacement therapy in hemophilia A (HA) patients does not adequately prevent bleeds and arthropathic complications. A more refined understanding of the relationship between coagulation factor VIII (FVIII) levels and bleeding risk during protein prophylaxis, or with gene therapy, is needed to improve patient care. OBJECTIVES: Investigate this relationship in the HA rat, a model exhibiting spontaneous bleeds and development of arthropathy similar to HA patients. METHODS: Human B domain-deleted FVIII was delivered to HA rats via adeno-associated virus (AAV)-mediated gene transfer or multiple intravenous protein injections. RESULTS AND CONCLUSIONS: After 12 weeks of observation, both approaches significantly reduced bleeds per animal and increased the proportion of bleed-free animals compared with controls (43% vs 0%, respectively [AAV]; 75% vs 8%, respectively [injection]). Both approaches resulted in an anti-FVIII inhibitory response in 20% to 37% of treated animals, similar to HA patients. Inhibitory antibodies were refractory to clinical improvement (reduction of bleeds) only in the AAV-based prophylaxis. An integrated model-based analysis of data on FVIII exposure and bleeding events was performed. This predicted the bleeding risk at any given circulating FVIII activity. Specifically, 4.8 or 10 IU/dL FVIII (0.048 and 0.1 IU/mL, respectively) were predicted to reduce bleeding risk by 90% or 95%, respectively, compared with untreated controls. Our data establish the utility of the HA rat model in FVIII prophylaxis studies and describe how FVIII activity affects bleeding risk in this setting. These enable further studies on FVIII prophylaxis focusing on disease complications for an optimized treatment of HA patients.

Acute Haemarthrosis in the Haemophilia A Rat Generates a Local and Systemic Proinflammatory Response.

Background Replacement therapy with coagulation factor VIII (FVIII) concurrent with bleeds (on-demand) in haemophilia A (HA) patients has been hypothesized to increase the risk for antidrug antibodies (inhibitors). A danger signal environment, characterized by tissue damage and inflammation at the site of a bleed, is thought to contribute to the anti-FVIII response. The nature of this inflammatory reaction is, however, not fully known, and new insights will be valuable for both managing inhibitors and understanding arthropathy development. Objective To characterize the inflammatory response, locally and systemically, during the first 24 hours following a joint bleed in the HA rat. Methods HA rats received a needle-induced knee joint bleed (n = 83) or a sham procedure (n = 41). Blood samples were collected at selected time points from 0 to 24 hours post injury/sham. Synovial fluid, intra-articular knee tissue and popliteal lymph nodes were collected at 24 hours. Cytokine/chemokine concentrations and gene expression were measured. Results Gene expression analysis revealed a rapid inflammatory response in the injured knees, accompanied by significantly increased levels of specific gene products in the synovial fluid; IL-1ß, TNFα, KC/GRO, IL-6, Eotaxin, MCP-1, MCP-3, MIP-1α, MIP-2, RANTES, A2M and AGP. Plasma analysis demonstrated significantly increased systemic levels of KC/GRO and IL-6 in injured rats already after 5 to 6 hours. Conclusion A rapid proinflammatory response, locally and systemically, characteristic of innate immunity, was demonstrated. Results reveal a more comprehensive inflammatory picture than previously shown, with resemblance to human haemophilic arthropathy, and with unique correlation between gene expression level, synovial concentration and plasma concentration in individual rats.