Extra‐vascular clotting factor VIII protein protects against development of haemophilic synovitis in the presence of pre‐existing anti‐factor VIII inhibitor

Abstract

Objective: Progressive destruction of joints resulting from recurrent intra‐articular haemorrhage represents the major morbidity resulting from haemophilia A or B. In addition to systemic clotting factor replacement, therapies localized to haemophilic joints may provide adjunctive protection. In a factor VIII‐/‐ mice model, we investigated if extra‐vascular delivery of recombinant human clotting factor VIII (rhFVIII) via intra‐articular (IA) injection can prevent bleeding‐induced joint damage, and also examined the possibility that IA delivery of FVIII carries greater risk of developing anti‐rhFVIII inhibitor antibody.Methods: FVIII‐/‐ mice received rhFVIII by inserting a 30.5 G needle into the left knee joint, along with a range doses of FVIII(100, 25 and 5 IU kg−1) in 5 μL, normal saline as the control. Comparison group received the same needle injury and intravenous (IV) rhFVIII (100, 25 and 5 IU kg−1). 14 days after injury, both knee joints were collected for histological examination. To exclude the possibility that IA clotting factor was entering into circulation, mice received 100 IU kg−1 rhFVIII IA, and FVIII activity was measured by aPTT. To see if IA rhFVIII delivery can carry greater risk of developing anti‐FVIII antibody, mice were treated with a total dose of 300 IU kg−1 rhFVIII over 10 days, either by IA or IV. 14 days after exposure, anti‐FVIII was detected. After induction of anti‐FVIII antibody by IV rhFVIII, mice were subjected either to needle puncture under coverage of bypassing agent (FEIBA) 100 IU kg−1 or 100 IU kg−1 IV rhFVIII, or needle puncture with 25 IU kg−1 rhFVIII. Control mice received needle puncture with normal saline. Two weeks later, knee joints were collected for histological examination.Summary: Mice receiving only saline at the time of needle puncture developed synovitis (mean score 5.0 ± 0.5). Mice treated with 25 IU kg−1 IA rhFVIII developed better protection than mice treated with 100 IU kg−1 IV rhFVIII (lower pathology score for IA, 0.733 ± 0.278 vs. IV 2.57 ± 1.70) and even better protection was achieved by the dose of 100IU IU kg−1 IA (Pathology score of 0.25 ± 0.31). IA injection of 100 IU kg−1 rhFVIII did not lead to increased circulating FVIII activity at any time point up to 48 h. In IV‐treated mice, 100% of mice developed anti‐FVIII antibody (8.06BU), while only 50% of mice developed anti‐FVIII inhibitor at the lowest detection limit (0.61BU). In the presence of inhibitory antibody, only 46% of mice receiving IV FVIII survived the needle injury, 58% with FEIBA and 100% of mice survived with 25 IU kg−1 FVIII IA injection. In the saline‐injected control mice, needle injury led to a mean pathology score of 6.8. Neither IV FVIII nor FEIBA provided effective protection, with pathology scores of 6.3 and 5.4, respectively. Surprisingly, 25 IU kg−1 IA rhFVIII produced a pathology score of only 1.7.Conclusion: Extravascular rhFVIII in the joint space can contribute protection against bleeding‐induced joint damage. Intra‐articular rhFVIII delivery did not induce greater risk of inhibitory antibody formation in FVIII knockout mice than circulating factor VIIII challenge; in fact, a lower incidence was observed. In the presence of anti‐FVIII inhibitory antibodies, IA delivery of FVIII still can offer protection from bleeding‐induced joint damage.