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AN IMPLANT that treats the blood of haemophiliacs should free patients from
the need for constant injections and the associated risk of diseases such as
HIV.

Haemophiliacs lack one of two vital blood-clotting agents called factors VIII
and IX. Without these factors their blood cannot clot and they may bleed for
longer than normal after the smallest accidents. Traditionally, they are given
injections of the missing factor. This must either be purified from donated
blood, risking virus contamination, or made artificially, which is extremely
expensive鈥攁t a cost of up to $100 000 a year, according to cell
biologist Harvey Pollard of the Uniformed Services University School of Medicine
in Maryland. Worse, many people develop antibodies to the artificial treatment,
rendering it ineffective.

So Pollard and his colleagues built an implant that makes the missing factors
redundant and restores clotting ability. 鈥淚t鈥檚 a good idea, and absolutely new,鈥�
says Paul Giangrande from the Oxford Haemophilia Centre. The thimble-sized,
Teflon implant contains tiny beads coated with the human clotting factor Xa.
This converts factor VII, which haemophiliacs already have in their blood, to an
active clotting version called VIIa.

鈥淚t鈥檚 like a salt shaker with holes,鈥� says Pollard. A semipermeable membrane
allows factor VII into the implant and factor VIIa out, back into the
bloodstream. But larger molecules are barred, sheltering the beads from any
possible immune response. The implant is placed in the peritoneal membrane,
which surrounds the major organs and is well supplied with blood vessels,
allowing blood to diffuse through the implant.

The researchers have tested the implant in guinea pigs, and in a rhesus
monkey, where clotting activity was restored for a month. Now they want to see
how it will work in humans. 鈥淲e have a lot of scaling up to do,鈥� Pollard
says.

Other researchers hoping to eliminate the need for injected clotting factors
have set their sights on gene therapy, a field that has offered a lot of promise
but few tangible successes. Now, Mark Kay of Stanford University School of
Medicine in California reports that two patients with severe haemophilia had
fewer bleeding episodes and required less factor IX after receiving an
experimental gene therapy.

To assess the safety of the technique, Kay and his colleagues injected low
levels of a virus containing the gene for factor IX into the thigh muscles of
three men whose bodies made less than 1 per cent of the amount of factor IX
required. Two of the patients needed to inject 50 to 80 per cent less factor IX
over the next 100 days. 鈥淲e鈥檙e hopeful that it鈥檚 going to last a long time,
maybe indefinitely,鈥� says Kay, who is planning to give seven more patients
higher doses in the trial.