Biomedical Engineering Reference
In-Depth Information
the frequency of injections required by haemophilia A sufferers. However, any alteration of the
primary sequence of the molecule carries with it the strong possibility of rendering the resultant
mutant immunogenic.
12.2.6 Factors IX, IIVa and XIII
Individuals who display a defi ciency of factor IX develop haemophilia B, also known as Christmas
disease. Although its clinical consequences are very similar to that of a defi ciency of factor VIII,
its general incidence in the population is far lower. Persons suffering from haemophilia B are
treated by i.v. administration of a concentrate of factor IX. This was traditionally obtained by frac-
tionation of human blood. Recombinant factor IX is now also produced in genetically engineered
CHO cells (Table 12.2 and Box 12.1).
Factor IX obtained from blood donations is normally only partially pure. In addition to factor
IX, the product contains lower levels of factors II, VII and X and has also been used to treat bleed-
ing disorders caused by a lack of these factors.
Factor IX may also be purifi ed by immunoaffi nity chromatography, using immobilized anti-
IX murine monoclonals. Purifi cation to homogeneity is particularly important in the case of
Box 12.1
Product case study: BeneFix
BeneFix (tradename, also known as nonacog alfa) is a recombinant human blood factor IX
approved for general medical use in the USA and EU since 1997. It is indicated for the control
and prevention of haemorrhagic episodes in patients with haemophilia B (Christmas disease),
including use in a surgical setting. The 55 kDa, 415 amino acid, single-chain protein displays
identical amino acid sequence and a relatively similar post-translational modifi cation profi le to
that of native, serum-derived factor IX. Post-translational modifi cations present include both
N- and O-linked glycosylation, γ-carboxylation, β-hydroxylation, sulfation and phosphoryla-
tion. The recombinant blood factor IX is produced in an engineered CHO cell line, and down-
stream processing entails multiple chromatographic steps, ultrafi ltration and diafi ltration. The
fi nal product is presented in lyophilized form in single-use vials and contains histidine, su-
crose, glycine and polysorbate 80 as excipients. Vials contain 250, 500 or 1000 IU of factor IX
(as determined by a one-stage clotting assay against a World Health Organization international
standard). The product is intended for i.v. administration and exact dosage/administration re-
gimes depend upon the severity of the factor IX defi ciency, the location and extent of bleeding,
and the patient's clinical condition.
The product displays a mean serum half-life of 18.8 h in humans. It has been evaluated in four
clinical trials involving a total of 128 subjects and in the context of both spontaneous bleeding
and surgery. Some 88 per cent of the total infusions administered for bleeding were rated as
providing a 'good' or 'excellent' response. Reported side effects, although uncommon, included
hypersensitivity, as well as headache, fever and nausea. BeneFix is marketed by Wyeth.
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