From www.bloodjournal.org at Wyeth Research on March 3, 2009. For personal use only.
CLINICAL OBSERVATIONS, INTERVENTIONS, AND THERAPEUTIC TRIALS
Human recombinant factor IX: safety and efficacy studies in hemophilia B
patients previously treated with plasma-derived factor IX concentrates
David A. Roth, Craig M. Kessler, K. John Pasi, Bonita Rup, Suzanne G. Courter, and Karen L. Tubridy,
for the Recombinant Factor IX Study Group
Human plasma–derived factor IX (pdFIX)
concentrates are routinely used to treat
patients with hemophilia B, an X-linked
bleeding disorder that affects 1 in 30 000
males, but concerns remain regarding
transmission of blood-borne pathogens.
Therefore, the safety and efficacy of recombinant human factor IX (rFIX) were
evaluated. A 20-center international trial
was conducted in previously treated patients with severe or moderate (< 5 IU/dL
factor IX activity) hemophilia B. Participants received rFIX for pharmacokinetic
studies, treatment of or prophylaxis
against hemorrhage, or surgical hemosta-
sis, and were assessed at 3-month intervals for 2 years. Fifty-six subjects were
treated. Mean incremental rFIX recovery
was 0.75 IU/dL per IU/kg, 30% lower than
expected for pdFIX, although the mean
half-life was similar. Pharmacokinetic parameters were stable over time. Somewhat lower recoveries were seen in subjects younger than 15 years of age and in
those with no detectable factor IX antigen. A total of 7362 infusions of rFIX were
administered. All 1796 hemorrhages were
controlled, 80.9% of which required only
one rFIX infusion. Effective hemostasis
was also achieved in prophylactic and
surgical settings. One individual developed a low titer (1.2 Bethesda unit) transient inhibitor that spontaneously resolved. rFIX was not associated with
serious adverse events, thrombogenicity,
or virus transmission. rFIX is safe and
effective for the treatment of hemophilia
B. Despite a lower recovery compared
with pdFIX, rFIX controlled hemorrhage in
a wide variety of settings and may provide a safety advantage in terms of risk
from blood-borne pathogens. (Blood.
2001;98:3600-3606)
© 2001 by The American Society of Hematology
Introduction
A
B
Human plasma–derived factor VIII and factor IX replacement products
are used routinely to treat individuals with hemophilia A (factor VIII
deficiency) and hemophilia B (factor IX deficiency).1,2 Low-purity,
low-specific activity factor VIII concentrates and factor IX concentrates
(prothrombin complex concentrates [PCCs]) became available over 30
years ago, and their use led to dramatic improvements in duration and
quality of life for persons with hemophilia. However, these products
infected patients with hepatitis B virus (HBV), hepatitis C virus (HCV),
and human immunodeficiency virus (HIV). PCCs also contained
prothrombin, factor VII, and factor X and their use in hemophilia B was
further complicated by thrombosis, generally attributed to the accumulation or delayed clearance of these unactivated and activated vitamin
K–dependent proteins.2-5 Subsequently, high-purity plasma-derived factor IX concentrates (pdFIX) were developed. These have largely
replaced PCCs and have been used successfully for those with a history
of thrombosis due to PCCs.
Despite the availability of high-purity virus-inactivated plasmaderived factor VIII concentrates (pdFVIII) and pdFIX products, concerns remain about their contamination with infectious prions causing
new variant Creutzfeldt-Jakob disease (vCJD).6-9 Outbreaks of hepatitis
A virus (HAV)10,11 and the transmission of parvovirus12,13 in persons
with hemophilia, including those treated exclusively with clotting-factor
concentrates considered safe against HIV and HCV,14 raise further
concerns about the transmission of small nonenveloped viruses with
pooled human plasma–derived clotting factor concentrates. This concern has stimulated intense efforts to develop recombinant human factor
VIII (rFVIII) and factor IX (rFIX) products for use in persons with
hemophilia A and B. Several rFVIII products have been available since
1992. Although the human F9 gene was first cloned nearly 2 decades
ago,15 development of rFIX for clinical use was hampered by the
complex posttranslational modifications required for biosynthesis of
factor IX.16
These barriers have been overcome, and rFIX, a pathogen-free
source of factor IX, is available to treat individuals with hemophilia
B. In contrast to rFVIII products for hemophilia A, no animal or
human plasma–derived protein is used during the manufacture17 or
formulation of rFIX, distinguishing rFIX18 as a unique replacement
product for use in routine hemophilia care. Herein, we report on the
safety and efficacy of rFIX in persons with severe and moderate
hemophilia B for the treatment or prevention of bleeding episodes.
From the Beth Israel Deaconess Medical Center, Harvard Medical School,
Boston, MA; Georgetown University Medical Center, Georgetown University,
Washington, DC; Royal Free Hospital, Royal Free Hampstead NHS Trust,
London, United Kingdom; and Genetics Institute, Cambridge, MA. A complete
list of the members of the Recombinant Factor IX Study Group is provided in
the Appendix.
Reprints: David A. Roth, Beth Israel Deaconess Medical Center, Center for
Hemostasis and Thrombosis Research, RE-302, 41 Ave Louis Pasteur,
Boston, MA 02115; e-mail: [email protected].
Submitted May 21, 2001; accepted August 14, 2001.
Supported by the Genetics Institute, Cambridge, MA.
3600
C
Patients, materials, and methods
Patients
Eligible participants had severe (factor IX activity ⬍ 1 IU/dL) or moderate
(factor IX activity 1-5 IU/dL) hemophilia B and all had been previously
treated with high-purity, monoclonal antibody–purified factor IX (pdFIX). D
Subjects with a history or evidence of a factor IX inhibitor by Bethesda
The publication costs of this article were defrayed in part by page charge
payment. Therefore, and solely to indicate this fact, this article is hereby
marked ‘‘advertisement’’ in accordance with 18 U.S.C. section 1734.
© 2001 by The American Society of Hematology
BLOOD, 15 DECEMBER 2001 䡠 VOLUME 98, NUMBER 13
From www.bloodjournal.org at Wyeth Research on March 3, 2009. For personal use only.
BLOOD, 15 DECEMBER 2001 䡠 VOLUME 98, NUMBER 13
inhibitor assay (BIA) or history of anaphylaxis to any factor IX–containing
product were excluded. Both HIV seropositive and seronegative individuals
were enrolled, but HIV⫹ individuals with a blood CD4 cell count of less
than 400/␮L were excluded. Subjects were excluded if they had serum
alanine aminotransferase in excess of 5 times the upper limit of the normal
range, total bilirubin more than 2 mg/dL, serum creatinine in excess of 1.25
times the upper limit of the normal range, or a platelet count of less than
140 000/␮L. The presence of antibodies against HIV-1, HIV-2, HAV, HBV
(surface antigen and core), and HCV was determined at baseline and
throughout the study. The study was approved at each center by the local
institutional review board. Informed consent was obtained from each
individual (or guardian) prior to enrollment.
Study design
Clinical studies with rFIX began in February 1995. Fifty-seven individuals
were enrolled at 20 sites throughout North America and Europe. One person
withdrew consent prior to treatment. The final subject completed his course
E of treatment in April 1999. The study comprised pharmacokinetic (PK)
assessment; assessment of thrombogenicity; and safety and efficacy during
home treatment and management of surgical procedures. The PK assessment was repeated every 6 months, with routine clinical and laboratory
evaluations at 3-month intervals. The planned study duration for each
participant was 2 years.
PK assessment
A baseline PK evaluation was performed on first infusion with rFIX using a
single 50 IU/kg intravenous dose. At the time of infusion, all subjects were
in a nonbleeding state and without any factor IX or antifibrinolytic products
during the preceding 7 days. Blood samples were drawn prior to infusion
and then at 0.25, 0.5, 1, 2, 4, 8, 12, 24, 36, 48, and 72 hours. The PK
parameters were derived using the observed maximum factor IX activity
F and the elimination half-life. Changes over time for incremental recovery
and half-life were assessed using repeated measures analysis of variance.
Half-life was estimated using compartmental and noncompartmental methods. Factor IX activity was measured in a central laboratory by a one-stage
clotting assay using a normal plasma reference standard calibrated against a
World Health Organization standard. The recovery of rFIX was calculated
as the observed maximum postinfusion plasma factor IX activity (IU/mL)
divided by the expected maximum plasma factor IX activity (the rFIX dose
administered [IU] divided by the subject’s estimated plasma volume [mL],
assuming 45 mL plasma per kilogram body weight).
RECOMBINANT FACTOR IX FOR HEMOPHILIA B
products for similar bleeds or procedures: excellent (as much and as
rapid an improvement as the best pdFIX-related responses), good (as
much and as rapid an improvement as most pdFIX-related responses),
moderate (not as good as most pdFIX-related responses), or no response
(no improvement). For those who were maintained on secondary
prophylaxis, the rFIX dosing and frequency of administration were
determined by the investigator based on the individual’s prior experience with pdFIX, clinical responses to therapy with rFIX or results from
PK assessments with rFIX or both. The response to secondary prophylaxis was assessed once every 3 months by the investigator using a
3-point scale: excellent (no spontaneous bleeding of any kind, no change
in dosing regimen necessary), effective (no spontaneous musculoskeletal bleeding, no change in dosing regimen necessary), or inadequate
(inadequate prevention of bleeding requiring a change in dosing
regimen). When surgery was required, rFIX was prescribed by the
investigator as indicated for the procedure following recommended
guidelines.1 The investigator and surgeon assessed hemostasis, estimated blood loss, and rFIX efficacy during the perioperative period
using the same 4-point scale described above.
Human rFIX
Human rFIX was manufactured in the presence of vitamin K in a
I
characterized Chinese hamster ovary cell line free of infectious agents.19
Fibrinopeptide A and prothrombin fragment 1 ⫹ 2 (F1 ⫹ 2) were measured
to assess thrombogenicity in participants during their initial PK study, at 1
G hour before infusion, and 4 to 8 hours and 24 hours after infusion. A
subgroup of 6 subjects consented to additional testing for D-dimer,
thrombin-antithrombin complex, and F1 ⫹ 2 by separate venipuncture at 15
minutes and at 1, 2, 4, and 24 hours after infusion.
Table 1
Table 1. Baseline characteristics of patients treated with rFIX
Characteristic
Sex, male
No. (%)
56 (100)
Race
White
African American
51 (91.1)
2 (3.5)
Asian
1 (1.8)
Asian-white
1 (1.8)
Hispanic
1 (1.8)
Age, y
Median
23
Range
4-56
Hemophilia severity, %*
Below 1
46 (82.1)
From 1 to 3
9 (16.1)
Higher than 3 to 5
1 (1.8)
Previous exposure days
From 20 to 100
Thrombogenicity testing
3601
8 (14.0)
More than 100 to 250
22 (39.2)
More than 250
26 (46.4)
HIV antibody status†
Negative
49 (87.5)
Positive‡
7 (12.5)
Hepatitis A antibody status†
Negative
32 (57.1)
Positive
24 (42.9)
Hepatitis B antibody status†
Safety and efficacy in treatment of or prophylaxis
against hemorrhage
Negative
5 (8.9)
Positive
51 (91.1)
Hepatitis C antibody status†
H
Subjects used rFIX as needed to treat hemorrhage (on demand), as
prophylaxis to prevent hemorrhage, or to control surgery-related
bleeding. The investigator determined the dose and frequency of rFIX
administration following dosing protocols as described.1 All individuals
initially used rFIX at doses similar to those used previously with pdFIX.
Individualized PK testing results were used to adjust rFIX dosing when
appropriate. The prescribed dosing regimen was based on body weight,
vial potency, and the nature of the hemorrhage or surgery following
standard guidelines.1 Each individual recorded administration details
and the reason for each rFIX infusion. Participants (and the investigator
if administered in the clinic) were asked to judge the bleeding response
to each rFIX infusion after 24 hours, or just prior to the next dose, using
a 4-point scale based on a comparison with previously used pdFIX
Negative
13 (23.2)
Positive
43 (76.8)
Factor IX antigen status
Negative
33 (59)
Positive
22 (39)
Indeterminate§
1 (2)
N ⫽ 56.
*Percent circulating FIX activity measured by the one-stage clotting assay before
administration of the initial dose of rFIX in the baseline PK evaluation. Normal is
100% or 100 IU/dL.
†Antibody status was determined at study entry.
‡All 7 HIV⫹ patients were positive for HAV, HBV, and HCV in some combination.
§Assay interference precludes the assessment of factor IX antigen status.
From www.bloodjournal.org at Wyeth Research on March 3, 2009. For personal use only.
3602
Table 2
BLOOD, 15 DECEMBER 2001 䡠 VOLUME 98, NUMBER 13
ROTH et al
Table 2. rFIX dosing and exposure days
PK
On-demand
Prophylaxis*
Surgery-related
Total
56
55
47
20
56
Cumulative
907 264
8 552 140
9 252 060
2 212 170
20 923 634
Median
17 124
118 440
60 600
33 500
258 462
Range
2055-31 670
7200-810 200
1000-1 477 780
2200-423 700
11 778-2 141 525
No. of patients
Total rFIX units (IU)
administered per patient
Dose (IU/kg)
Median
50.0
42.80
35.10
60.40
40.90
49.95 ⫾ 3.53
46.56 ⫾ 23.48
38.00 ⫾ 17.06
66.25 ⫾ 29.47
43.07 ⫾ 21.32
25.0-90.3
6.5-224.6
9.7-170.6
13.8-169.0
6.5-224.6
Total
263
2 758
3 909
432
7 362
Median
5.00
41.00
24.00
10.00
85.00
4.70 ⫾ 1.04
50.15 ⫾ 42.34
83.17 ⫾ 130.28
21.60 ⫾ 26.53
131.46 ⫾ 128.69
1-7
3-196
1-656
1-96
4-669
Total†
263
2 633
3 620
320
6 823
Median
5.00
41.00
24.00
9.00
83.50
4.70 ⫾ 1.04
47.87 ⫾ 38.04
77.02 ⫾ 108.28
16.00 ⫾ 18.30
121.84 ⫾ 103.27
1-7
3-195
1-492
1-62
4-496
Mean ⫾ SD
Range
No. of infusions
Mean ⫾ SD
Range
No. of exposure days
Mean ⫾ SD
Range
*Prophylaxis includes routine secondary prophylaxis 2 to 3 times each week for prevention of hemorrhage (this subgroup of patients is discussed separately in “Results”)
as well as intermittent prophylactic use for the prevention of anticipated bleeding, such as bleeding that might occur following strenuous exercise.
†A patient may be dosed more than once a day for different reasons.
The Chinese hamster ovary cell line was cotransfected with complementary
DNAs (cDNAs) encoding human factor IX and human paired basic amino
acid cleaving enzyme to ensure complete processing of profactor IX to
mature biologically active ␥-carboxylated factor IX.20 The cell line was
grown in medium without animal or human plasma-derived protein
supplements.17 A nanofiltration step was used for additional viral safety.
The rFIX dosage form contains no animal or human-derived carrier proteins
such as albumin.18
Results
J
Baseline characteristics of the 56 efficacy evaluable subjects are
shown in Table 1. Fifty subjects completed the 24-month study.
Five subjects withdrew from the study for personal reasons, and
one withdrew because of a recurring adverse event (the urge to
cough shortly after rFIX infusions), respectively. The median time
on study was 741 days (mean ⫾ SD, 710.9 ⫾ 154.2 days). The time
on study ranged between 30 days and 856 days. A total of 7362
infusions with a cumulative total of 20 923 634 IU rFIX were
administered (Table 2).
Treatment for hemorrhage on demand
All but one PTP who was being treated with a prophylaxis regimen
received rFIX for treatment of hemorrhage. A total of 2758
infusions were administered for on-demand treatment of 1796
hemorrhages (59% hemarthroses, 25% soft tissue/muscle, 16%
multiple-site or other bleeding episodes). Most bleeding episodes
(80.9%) were controlled with one infusion (Figure 2). The rFIX L
dosing used for treatment of these bleeding episodes is described in
the legend for Figure 2. The majority of hemorrhages (90.9%) had
an “excellent” or “good” response to rFIX treatment (Figure 3).
Despite a rating of “moderate” or “no response” following the
initial infusion of 7.8% of hemorrhages, 47% and 15% of these
bleeds still resolved without further therapy, respectively, and rFIX
was effective in all bleeds.
Routine secondary prophylaxis for prevention of hemorrhage
In addition to those individuals who used rFIX for intermittent
bleeding prophylaxis (eg, in advance of occasional physical
activities that were anticipated to result in bleeding, such as
strenuous exercise), 19 PTPs used rFIX for regular secondary
M
PK assessments
K
At baseline, rFIX infusion of 50 IU/kg resulted in a mean factor IX
activity increase of 0.75 IU/dL per IU/kg (range, 0.34-1.38 IU/dL
per IU/kg), corresponding to a recovery of 33.7% (range, 15.3%62.2%). The mean elimination half-life was 19.3 hours (range,
11.1-36.4 hours). Repeat PK assessments every 6 months demonstrated the stability of these parameters during 2 years of exposure
to rFIX (Figure 1). No significant reduction in baseline rFIX
recovery or elimination half-life occurred in any previously treated
patients (PTPs) over time, with the exception of one subject in
whom a low-titer inhibitor developed. Subgroup analyses revealed
the lowest recoveries in subjects younger than 15 years old. Lower
recoveries were also seen in patients who were negative for factor
IX antigen, although neither of these trends reached statistical
significance (Table 3).
Figure 1. Mean factor IX activity versus time at months 0, 6, 12, 18, and 24. PK
parameters were estimated for 56 patients at baseline. Fifty-three patients had PK
parameters estimated at 6 months, 51 patients at 12 months, and 48 patients at 18
and 24 months. The data from one patient (months 12, 18, 24) were excluded after
inhibitor development.
Figure 1
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BLOOD, 15 DECEMBER 2001 䡠 VOLUME 98, NUMBER 13
Table 3
RECOMBINANT FACTOR IX FOR HEMOPHILIA B
3603
Table 3. Factor IX pharmacokinetic estimates stratified by age and factor IX–antigen status*
No.
Incremental recovery, %
FIX activity rise, IU/dL
Half-life, h
20.2 ⫾ 4.0 (14.2-28.2)
Age, y
⬍ 15
19
29.8 ⫾ 9.9 (15.3-50.4)
0.66 ⫾ 0.22 (0.34-1.12)
15-40
28
34.7 ⫾ 9.2 (18.0-57.6)
0.77 ⫾ 0.20 (0.4-1.28)
19.4 ⫾ 5.5 (12.4-36.4)
⬎ 40
9
37.7 ⫾ 12.3 (23.3-62.2)
0.84 ⫾ 0.27 (0.52-1.38)
17.2 ⫾ 4.8 (11.1-25.0)
Factor IX antigen
Positive
22
36.9 ⫾ 11.0 (17.1-62.2)
0.82 ⫾ 0.25 (0.38-1.38)
18.7 ⫾ 6.2 (11.1-36.4)
Negative
33
31.0 ⫾ 8.9 (15.3-50.4)
0.69 ⫾ 0.20 (0.34-1.12)
19.8 ⫾ 4.1 (12.7-28.2)
Values represent the mean ⫾ SD; range is shown in parentheses.
*Assay interference precluded assessment of factor IX–antigen status in one patient.
prophylaxis regimens (average dose 40.3 IU/kg; range, 13-78
IU/kg) 2 to 3 times per week. At times, intervals between doses
exceeded 72 hours. Three of the 19 PTPs did not experience
breakthrough hemorrhages. The other 16 subjects had a total of 203
hemorrhages; 64 related to injury and 139 were spontaneous.
Eighty-five (61%) of the 139 spontaneous hemorrhages occurred
more than 72 hours after rFIX infusion, whereas only 27 (19%) of
spontaneous hemorrhages were true breakthrough hemorrhages,
occurring within 48 hours of rFIX infusion. This low frequency of
breakthrough bleeding occurred in only 7 patients (37%) who used
prophylaxis regimens. Overall, 93% of prophylaxis regimen responses were rated as “excellent” or “effective,” typical for
effective secondary prophylaxis with pdFIX.
Surgical prophylaxis
N
Twenty-seven surgical procedures were performed in 20 PTPs,
including 11 dental, 9 orthopedic (2 ankle arthrodeses, 3 total knee
arthroplasties, 2 arthroscopic synovectomies, 1 hip prosthesis, 1
Achilles tendon lengthening), 2 ingrown toenail removals, 1
vasectomy, 1 lymph node biopsy, 2 cyst excisions, and 1 birthmark
removal. Of all infusions administered for surgical procedures,
98% provided “excellent” or “good” hemostasis. Estimated blood
loss was comparable to individuals without a coagulation disorder.
One dental extraction was complicated by dislodged fibrin glue, but
bleeding was controlled with rFIX.
Dosing adjustment of rFIX
Analysis of dosing patterns was evaluable for over 3 months in 54
of the 56 PTPs. Thirty-one subjects (57%) increased their dose and
23 (43%) had no change. Of the 31 PTPs who increased their dose,
11 changed because of a low recovery at baseline assessment, 15
changed because of suboptimal clinical response and low recovery,
and 5 had breakthrough bleeding episodes during prophylactic
treatment. Sixteen of the 31 PTPs (52%) who increased their dose
were younger than 15 years of age, the cohort in which a lower
recovery was observed (Table 3).
O
Viral transmission
There was no evidence of transmission of HAV, HBV, HCV, HIV-1, P
or HIV-2.
Inhibitors
A low-titer, transient inhibitor to rFIX was detected in one
individual who had severe hemophilia B due to a T (nucleotide 97) Q
to C point mutation in the F9 gene. This resulted in a Leu ⫺24 to
Figure 2
Figure 2. Number of infusions required for resolution of 1796 hemorrhages. A
total of 2641 infusions were administered for on-demand treatment in 55 patients.
The total number of infusions used to treat the site of any bleeding episode ranged
from 1 to 123. The data exclude those from one patient after evidence of factor IX
antibody was detected at month 9. Of the 2641 total infusions administered, 4% (101
of 2641) were at a dose of less than or equal to 20 IU/kg, 25% (663 of 2641) ranged
from above 20 to 30 IU/kg, 18% (470 of 2641) ranged from above 30 to 40 IU/kg, 20%
(537 of 2641) ranged from above 40 to 50 IU/kg, 15% (405 of 2641) ranged from
above 50 to 60 IU/kg, and only 17% (461 of 2641) were used at doses above 60
IU/kg; the dose was not reported for 4 infusions. Thirty-three of the 56 PTPs used
average doses for bleeding episodes and prophylaxis that were less than or equal to
50 IU/kg, whereas 23 used average doses of above 50 IU/kg. Twelve of these 23
patients used average doses between 50 and 60 IU/kg, 8 patients used average
doses between 60 and 70 IU/kg, and 3 patients used higher average doses. The
patient who used the far outlying average dose of 100.2 IU/kg is the patient who
showed the lowest recovery in the PTP population at baseline (0.34 IU/dL per IU/kg
rFIX given). The other 2 outlier patients used average doses between 70 to 80 IU/kg.
One patient used self-determined doses (outside physician guidelines) and engaged
in strenuous activity despite very severe hemophilic arthropathy. The other is the
single PTP who developed a transient, low-titer inhibitor.
Figure 3. Response ratings of rFIX used for treatment of 1796 hemorrhages. For
hemorrhages that required more than one treatment, only the initial response rating
24 hours following the first rFIX infusion was used in the response rating analysis.
The data exclude those from one patient after evidence of factor IX antibody was
detected at month 9.
Figure 3
From www.bloodjournal.org at Wyeth Research on March 3, 2009. For personal use only.
3604
ROTH et al
Pro missense mutation in the factor IX signal peptide sequence and
no circulating factor IX antigen was found in the pretreatment
blood sample. He had received in excess of 500 infusions of pdFIX
before receiving rFIX, including a single subcutaneous dose of
pdFIX (30 IU/kg) at 10 injection sites approximately 2 months
before study entry. Factor IX antibodies were detected on routine
enzyme-linked immunosorbent assay (ELISA) samples at month
9 after 39 rFIX exposure days, and by BIA at month 12 after
63 rFIX exposure days. PK assessment demonstrated a shortened
rFIX half-life (19.1 hours at baseline to 3.6 hours), although rFIX
recovery was unchanged. He continued to treat hemorrhages using
rFIX every 6 to 8 hours rather than every 12 to 24 hours. By month
19, the inhibitor had disappeared by BIA and rFIX half-life had
increased to 26 hours.
Thrombogenicity
R
There was no evidence that rFIX increased thrombin generation.
One individual experienced the acute onset of a segmental renal
infarction 12 days following a single dose of rFIX (3000 IU). He
had received only 2 rFIX infusions in the preceding month and
continued to receive rFIX for 2 days following this event.
Thrombophilia investigations were negative and his symptoms
resolved after 6 days. The investigator concluded that the relationship to rFIX was “unknown, but highly unlikely.” The patient
continued to use rFIX, and there were no other thrombotic events in
this or any other patient during the study period.
Adverse events
S
No serious adverse events were related to rFIX. Nine subjects
experienced 55 treatment-related adverse events, including 4
subjects who showed some sign or symptom of minor allergic
reaction to rFIX, although ELISA tests for antifactor IX IgE
were negative. In 3 of these 4 participants, symptoms occurred
once or twice and did not recur despite continued treatment with
rFIX. There were no other clinically significant adverse experiences. The remaining adverse experiences were similar to those
reported with pdFIX.1,3
Discussion
T
U
An important and unexpected finding of this study was that despite
a mean circulating half-life similar to that of pdFIX,21 the mean
incremental recovery was typically 30% lower. Although minor
differences in the posttranslational modification of rFIX, such as
decreased complexity of N-linked glycans, decreased sulfation of
Tyr155, and absent phosphorylation of Ser158 have no influence on
the specific coagulant activity of rFIX,22,23 it has been speculated
that these differences contribute to the observed decreased recovery compared to pdFIX.24
Studies with pdFIX have shown that subjects 15 years of age
and younger have a significantly lower recovery than those who are
older.25 In our study, the average incremental recovery was also
lower in younger participants (⬍ 15 years of age), although this did
not reach statistical significance. Therefore, all individuals, and
particularly young children, should have their recoveries evaluated
to ensure proper dosing. Because the difference in recovery may
lead to higher rFIX doses, when combined with the higher price of
rFIX, the overall cost of hemophilia B treatment may be increased
compared to the cost of treatment with pdFIX.
BLOOD, 15 DECEMBER 2001 䡠 VOLUME 98, NUMBER 13
These results demonstrate that rFIX is safe and clinically
effective in the treatment and prevention of bleeding in individuals
with hemophilia B. All bleeding episodes were controlled exclusively with rFIX using standard dosing intervals, with the majority
of hemorrhages responding to one rFIX infusion. Although this was
not a comparative study, hemostatic efficacy of rFIX was rated
against participants’ previous experience with pdFIX in “ondemand” and “secondary prophylaxis” regimens, and was reported
as “excellent” or “good” in 90.9% to 98% of bleeding episodes,
consistent with those reported in other studies that evaluated pdFIX
in individuals with hemophilia B.25-30 In addition, an analogous
study testing rFVIII in PTPs with hemophilia A reported hemostatic efficacy as “excellent” or “good” in 91.2% of bleeding episodes,31 similar to our results with rFIX in PTPs with hemophilia B.
A crucial element of this study was the evaluation for
potential neoantigenicity and inhibitor formation following
exposure to rFIX in PTPs. There was no evidence that rFIX
increased the risk of inhibitor development. Only 1 of the 56
participants showed evidence of a low-titer, transient factor IX
inhibitor, which is consistent with the estimated prevalence of
factor IX inhibitors (1.5%-2%) in hemophilia B.32,33 The
majority of patients who develop inhibitors have gross deletions
or certain nonsense mutations in the F9 gene, whereas complete
F9 gene deletions also confer the risk of anaphylaxis.34-37 These
observations support the hypothesis that a lack of circulating
factor IX protein predisposes to an immune response following
factor IX replacement therapy. Although missense mutations are
less commonly associated with such immune responses, this
patient had a signal peptide missense mutation that prevented
secretion of his factor IX protein, resulting in his factor IX
antigen-negative phenotype and increased risk of inhibitor
development. Alternatively, we can speculate that his prior
subcutaneous administration of pdFIX contributed to the transient immune response to rFIX. PTPs with a history of inhibitor
or anaphylaxis to pdFIX were excluded from this study,
selecting a study population at low risk for developing immune
reactions to rFIX. Because it is important to understand the true
risk of immune responses to rFIX, including the development of
inhibitors and minor allergic reactions, additional studies with
rFIX in previously untreated hemophilia B patients are currently
in progress.
As anticipated, there was no evidence of viral transmission of
HIV, HAV, HBV, or HCV resulting from rFIX treatment. Continued
concerns about human blood-borne pathogens, the viral safety of
rFIX, and the demonstrated clinical efficacy and tolerability of
rFIX reported herein lead us to conclude that rFIX offers an
advantage to persons who depend on the availability of human
blood for survival. Multiple steps are in place throughout the
manufacturing process to ensure that rFIX is free of viral contamination. Moreover, both the production17 and formulation18 of rFIX
are done in the absence of animal or human plasma–derived
products, thus eliminating possible contamination with viruses,
vCJD, or unknown pathogens.
Recent evidence in a large animal model of vCJD demonstrates that this disease can be transmitted by transfusion with
whole blood obtained during the symptom-free phase of experimental bovine spongiform encephalopathy infection.38 Furthermore, it was reported that several blood coagulation proteins,
including purified factor IX, bind to PrP27-30, the proteaseresistant core of the vCJD-associated prion protein (PrPSc).39
Together, these data suggest that blood may be a carrier of
V
W
X
Y
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BLOOD, 15 DECEMBER 2001 䡠 VOLUME 98, NUMBER 13
prions. Although it is important to emphasize that no iatrogenic
cases of vCJD or other viruses have been confirmed in recipients
of pdFIX, there are justified concerns about the safety of
large-pool blood protein concentrates for patients such as those
with hemophilia for whom continuous usage results in exposure
to millions of blood donors during one’s life. Given these concerns,
rFIX provides a new option for the safe and effective management of
patients with hemophilia B.
Acknowledgments
We are indebted to the hemophilia B study patients and their
families for their participation in this study; Missy Magill,
biostatistician, and other members of the basic science and
RECOMBINANT FACTOR IX FOR HEMOPHILIA B
3605
clinical research teams of Genetics Institute in Andover and Cambridge, MA; the physician and nursing staffs of the numerous
clinical research centers at many of the participating institutions; Dr James Meade, UNC Coagulation Laboratory, University of North Carolina, Chapel Hill, for analysis of factor IX
activity and inhibitor data; Dr Steve S. Sommer, City of Hope
National Medical Center, Duarte, CA, for factor IX genotype
analyses; and Dr Kenneth A. Bauer, Beth Israel Deaconess
Medical Center, Boston, MA, for independent interpretation of
the thrombogenicity data. Lastly, we dedicate this work to the
memory of Suzanne G. Courter of Genetics Institute who died
unexpectedly during the final stages of preparing this manuscript. Her professional commitment to patients with hemophilia
and her passion for excellence in clinical investigation are largely
responsible for the execution and completion of this study.
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Appendix
The following institutions and investigators (alphabetical order) participated in this study as members of the Recombinant Factor IX Study Group:
V. S. Blanchette (The Hospital for Sick Children, Toronto, ON, Canada);
H.-H. Brackmann (Institute für Experimentelle Haematologie und Transfusionmedizin der Universität, Bonn, Germany); B. Ewenstein (Brigham and
Women’s Hospital, Boston, MA); P. Giangrande (Oxford Haemophilia
Centre, Oxford, United Kingdom.); M. A. Heisel (Children’s Health Care of
Minnesota, Minneapolis, MN); W. K. Hoots (University of Texas-Houston
Medical School, Houston, TX); C. M. Kessler (Georgetown University,
Washington, DC); Y. Laurian (Centre de Traitement de l’Hemophilie Centre
Hospitalier Universitaire Bicetre, Paris, France); J. Lusher (Children’s
Hospital of Michigan, Detroit, MI); C. Negrier (Hôpital Edouard Herriot
Centre Regional de l’Hemophilie, Lyon, France); C. Lee and K. J. Pasi
(Royal Free Hospital, London, United Kingdom); C. Philipp (Robert Wood
Johnson Medical School, New Brunswick, NJ); M.-C. Poon (University of
Calgary Foothills Hospital, Calgary, AB, Canada); M. V. Ragni (Hemophilia Center of Western Pennsylvania, Pittsburgh, PA); G. E. Rivard
(Hôpital Ste-Justine, Montreal, QC, Canada); D. A. Roth and C. G.
Rosenfield (New England Medical Center and the Floating Hospital for
Children, Boston, MA); A. Shapiro (Indiana Hemophilia and Thrombosis
Center, Indianapolis, IN); A. R. Thompson (Puget Sound Blood Center, Seattle,
WA); J. Vermylen (University Hospital Gasthuisberg Functiemetingen Bloedingsziekten, Leuven, Belgium); and G. White (University of North Carolina,
Chapel Hill, NC).