A history of prophylaxis in haemophilia

A bispecific antibody NXT007 exerts a hemostatic activity in hemophilia A monkeys enough to keep a nonhemophilic state

BACKGROUND

Emicizumab, a factor (F) VIIIa-function mimetic bispecific antibody (BsAb) to FIXa and FX, has become an indispensable treatment option for people with hemophilia A (PwHA). However, a small proportion of PwHA still experience bleeds even under emicizumab prophylaxis, as observed in the long-term outcomes of clinical studies. A more potent BsAb may be desirable for such patients.

OBJECTIVES

To identify a potent BsAb to FIXa and FX, NXT007, surpassing emicizumab by in vitro and in vivo evaluation.

METHODS

New pairs of light chains for emicizumab's heavy chains were screened from phage libraries, and subsequent antibody optimization was performed. For in vitro evaluation, thrombin generation assays were performed with hemophilia A plasma. In vivo hemostatic activity was evaluated in a nonhuman primate model of acquired hemophilia A.

RESULTS

NXT007 exhibited an in vitro thrombin generation activity comparable to the international standard activity of FVIII (100 IU/dL), much higher than emicizumab, when triggered by tissue factor. NXT007 also demonstrated a potent in vivo hemostatic activity at approximately 30-fold lower plasma concentrations than emicizumab's historical data. In terms of dose shift between NXT007 and emicizumab, the in vitro and in vivo results were concordant. Regarding pharmacokinetics, NXT007 showed lower in vivo clearance than those shown by typical monoclonal antibodies, suggesting that the Fc engineering to enhance FcRn binding worked well.

CONCLUSION

NXT007, a potent BsAb, was successfully created. Nonclinical results suggest that NXT007 would have a potential to keep a nonhemophilic range of coagulation potential in PwHA or to realize more convenient dosing regimens than emicizumab.

Musculo-skeletal problems of the hand in haemophilia

Musculo-skeletal complications of the hand in the haemophilia patient are rare, and they include synovitis, arthropathy, pseudotumours, carpal tunnel syndrome and vascular aneurysms and pseudoaneurysms.

The best way to prevent the aforementioned musculo-skeletal complications is early continuous haematological primary prophylaxis (intravenous infusion of the deficient coagulation factor, ideally from cradle to death).

There is a wide range of procedures that a hand surgeon treating these patients should be able to manage, including synovectomy, prosthetic replacement of small joints, removal or curettage of pseudotumours, release of carpal tunnel and, occasionally, vascular reconstruction of aneurysms.

The treatment of these patients should be made at an institution with close collaboration between haematologists and hand surgeons (all surgical procedures must always be performed under cover of the deficient coagulation factor).

Cite this article: EFORT Open Rev 2020;5:328-333. DOI: 10.1302/2058-5241.5.190078