Haematologica 2000;85:supplement to no. 10 - Supplements ...

Haematologica 2000; 85(suppl. to n.10)
p. 86-88
Immunetolerance:
Molecular and biological aspects
Characterization of antibodies to factor VIII in hemophilia A
patients treated by immune tolerance therapy
DOROTHEA SCANDELLA, HERBERT REYES, MATTHEW FELCH, YOSHIHIKO SAKURAI
American Red Cross, Holland Laboratory, Rockville, MD, USA
Abstract
The treatment of hemophilia A patients has
improved in this decade by production of recombinant
factor VIII (FVIII) in mammalian cells, which
has significantly reduced contamination by infectious
agents. A remaining serious problem in 25-
30% of patients with severe hemophilia A is the
appearance of antibodies that inactivate FVIII. The
present therapy for this condition is frequent treatment
with high doses of FVIII to induce tolerance,
which is defined as a negative Bethesda assay. Serial
plasma samples from 50 evaluable patients in a
large study of 72 previously untreated patients
were tested to determine whether tolerized
patients have actually lost all their anti-FVIII by
using a 10 fold more sensitive immunoprecipitation
(IP) method of measuring all anti-FVIII antibodies.
Six of the 22 patients with inhibitors were given tolerance
therapy, and 3 of them were only partially
tolerized as determined by IP assay. Seven patients
with 1-11 BU/mL lost their inhibitor spontaneously,
while 5 non-inhibitor patients with low level
immune responses similarly became antibody negative.
In a smaller study, a tolerized patient with 0
BU/mL had remaining non-inhibitory antibody levels
high enough to reduce the FVIII half-life significantly.
Plasmas from 2 patients who were not
tolerized, were tested by the IP assay for the A2
and/or C2 domain specificity of the anti-FVIII over
time.The antibodies detected were directed against
both the heavy and light chains of FVIII, and they
increased and decreased at the same rate before
and during tolerance therapy
©2000, Ferrata Storti Foundation
Key words: factor VIII, hemophilia A, immune tolerance,
anti-Factor VIII antibody
Treatment of individuals with hemophilia A
in past decades was often compromised
by factor VIII (FVIII) contamination with
infectious agents from the human plasma used
for the purification of FVIII. Both hepatitis A
and AIDS viral infections were detected in a significant
portion of these patients. Within the
past few years the FVIII therapeutic products
Correspondence: D. Scandella, Ph.D., American Red Cross, 15601
Crabbs Branch Way, Rockville, MD 20855, USA, Phone: international
+001-301-738-0750, Fax: international +1-301-738-0794
given for therapy of hemophilia A have been
improved by better viral inactivation steps and
by production of recombinant factor VIII in
mammalian, non-human cell lines. 1,2 So far the
recombinant FVIIIs have not caused the previous
problems or any new ones.
The most serious remaining problem of FVIII
therapy is the production of anti-FVIII inhibitor
antibodies that arise in about 25-30% of individuals
with severe hemophilia (1-2% FVIII) 3 and
less often in those with mild and moderate
hemophilia. As these antibodies can inactivate
FVIII and are consequently referred to as
inhibitors, they represent a serious challenge to
effective therapy. Patients with a common FVIII
gene inversion, large deletions, and some nonsense
mutations 4 are more likely to develop anti-
FVIII antibodies because they have no circulating
FVIII antigen and are therefore not tolerant to
FVIII infusion. The current clinical strategy for
significantly reducing or eliminating anti-FVIII is
to give frequent doses of FVIII in low, medium,
or high doses that eventually reduce antibody
levels to very low or non-existent levels, as measured
by the Bethesda assay. 5 A study using low
FVIII doses (25 U/kg every other day) led to
immune tolerance in 21 of 24 patients. 6 Another
study treated high titer inhibitor patients with
FVIII doses of 100 U/kg/day and FEIBA, a source
of factor IXa. Twelve of the 15 patients had
inhibitor titers that dropped to ≤1 BU/mL, and
their FVIII recovery and half-life was normal. 7
We examined the status of antibody development
in several studies of previously untreated
patients who received treatment with recombinant
FVIII and others who used either plasmaderived
or recombinant FVIII. We particularly
focused on those patients who had immune tolerance
therapy to determine whether all their
antibodies disappeared by using a highly sensitive
immunoprecipitation assay. Using this
method we also tested patient plasmas with low
or no Bethesda titer to determine whether such
titers corresponded to significant amounts of
antibody and whether the BU negative individuals
ever had low level immune responses to FVIII.
Haematologica vol. 85(supplement to n. 10):October 2000