ISTH 2021 Congress Review

ISTH 2021 Virtual Congress Review
Thinking Differently in Haemophilia:
Gene therapy at ISTH 2021
Welcome to the ISTH 2021 Congress Review.
The 29th annual ISTH Congress welcomed more than
7000 attendees from over 120 countries. We have selected
the most relevant abstracts, plenaries and symposiums to
gene therapy in haemophilia for this review.
Dr Katherine High gave an engaging opening plenary charting
the progress of gene therapy for haemophilia (page 2), and
Professor Edward Tuddenham gave an interesting view of the
history of gene therapy with a focus on the immune response
and potential mechanisms for transaminitis (page 3). New
data was presented from the ROCTAVIAN ® (valoctocogene
roxaparvovec), SPK-8011 and BAY 2599023 programmes in
haemophilia A and etranacogene dezaparvovec in haemophilia B
as well as investigational studies into platelet gene therapy.
I hope you enjoy this summary of the key data from ISTH 2021.
Professor Cem Ar
MORE INSIDE:
Investigating Antibodies to AAV page 12
Liver Health in Gene Therapy page 13
The Impact of Gene Therapy: The Exigency Study page 14
The WFH Gene Therapy Register page 15
Developments in
Haemophilia A
Data from the valoctocogene
roxaparvovec, BAY 2599023*
and SPK-8011* programmes.
Read more on page 4
Developments in
Haemophilia B
5-year results from a study
of AMT-060*, Phase 1/2
data, and abstracts from
the HOPE-B Phase 3 trial of
etranacogene dezaparvovec.
Turn to page 8
Platelet Gene Therapy
Intranasal delivery of
lentiviral vectors, the impact
of platelet aggregation, and
a preconditioning approach
for platelet gene therapy.
Find out more on page 11
The abstract presentations,
plenary presentations and
symposiums can be found here
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EU-ROC-00184 October 2022
1

ISTH 2021 Virtual Congress Review
The Progress of Gene Therapy
for Haemophilia
Dr Katherine High opened the congress with an overview of the gene
therapy journey in haemophilia, and presented her thoughts on the future
of haemophilia treatment. Professor Edward Tuddenham provided focus on
the immune response to AAV and potential mechanisms of transaminitis.
Dr Katherine High reviewed the goals of gene
therapy in haemophilia: Long-term treatment
that is durable, with predictable expression
resulting in factor levels adequate to prevent
bleeds in someone with a normal active lifestyle.
There should also be the lowest possible
incidence and magnitude of immune response.
Dr High shared data from Nathwani and
colleagues which showed that a short course
of immunomodulatory therapy could block
the immune response to the capsid and
rescue some of the FIX expression. In 3 of 4
participants treated with prednisone, 50–70%
of the expression was still lost. With the
identification that this response was due to
memory CD8 T cells, and that the response
was dose dependent, it was noted that a more
potent vector, better capsid, stronger promoter,
or better transgene was needed. A naturallyoccurring
FIX variant, (FIX-Padua) was shown
to be 8 times more active compared to wild type
FIX. Results from clinical trial programmes with
this variant have shown much higher circulating
levels of FIX, leading to a marked reduction
in bleeding rate. However, it is important that
elevations in transaminases are detected early
and controlled to avoid loss of expression.
Multiple programmes are underway in
haemophilia A using different capsids,
strategies for codon-optimising the F8
gene and manufacturing systems. Data for
valoctocogene roxaparvovec were shared, this
is the most advanced in terms of regulatory
pathway. Roctavian ® is indicated for the
treatment of severe haemophilia A (congenital
factor VIII deficiency) in adult patients without
a history of factor VIII inhibitors and without
detectable antibodies to AAV5. This medicine
received a conditional marketing authorisation.
The declining level of expression over time
was discussed, and Dr High commented
that this has not been reported for other
liver-directed AAV gene therapies.
Potential explanations for the decline in FVIII
levels were discussed. Inverted terminal
repeats that are clipped off during the
packaging process could lead to concatemer
stabilisation failure and subsequent loss of
expression. However, as all FVIII cassettes
are similarly sized, Dr High commented that
it is hard to understand why this would apply
to some but not all programmes.
On the hypothesis that misfolded FVIII
could induce stress response genes through
the unfolded protein response, which can
generate apoptosis of the cells, Dr High added
that it may be valuable to achieve modest
levels of transduction for many hepatocytes
rather than high-level transduction for a
smaller number. The question remains
whether factor levels will continue to fall
over time, or if they will stabilise.
Data was shared from the Spark programme in
haemophilia A, in which the SPK-8011 vector
has demonstrated durable FVIII expression
over 2–3 years. Whether there are specific
characteristics that differ between vectors
that lead to stabilisation over time, is not yet
understood. Data from all trial programmes
indicate that above certain levels of FVIII
expression, ABR is reduced to 0.
Dr High concluded that, while unanswered
questions remain on the use of gene therapy
in haemophilia, her belief is that it will soon
become part of the treatment options available
to the community and will usher in a new era of
treatment. With recent success in transthyretin
amyloidosis, gene editing in vivo may also
become an option for haemophilia in the future.
Professor Edward Tuddenham reviewed the
history of gene therapy, focussing on immune
response and potential mechanisms for
transaminitis. He discussed the first patient
infused with AAV-mediated FIX gene therapy
reported by Manno et al and examined the
initial rise in FIX expression, which reduced
following an immune response to the vector
capsid. A further study was described in which
a self-complementary expression cassette
packaged in an AAV8 vector was administered
via peripheral vein infusion. Two participants
were administered prednisolone in response
to rising ALTs, with final FIX expression of
2–3% and 6%, both of which were sustained
to 10 years. The rise in ALTs correlated with a
rise in detectable ELISPOT assay response to
a pool of vector peptides corresponding to the
peptides for the AAV8 capsid.
The landmark publication of data from
the first 10 patients dosed 1 demonstrated
a consistent, durable response to FIX
gene therapy, controlled liver enzyme
rate and substantially reduced bleed rate.
However, there is considerable variation in
the expression levels achieved and in the
immune response observed.
Details of the Freeline trial using FIX-Padua
were provided. Two patients dosed at
6x10 11 vg/kg and receiving prophylactic
prednisolone achieved FIX levels in the
high–mild range, and neither experienced
spontaneous bleeding up to 3 years postinfusion.
However, with a mild phenotype,
supplementary FIX would be required in the
case of severe trauma or surgery. One patient
receiving a 1x10 12 vg/kg dose was administered
a greater immunosuppression regimen, and
subsequently obtained steady state FIX levels
in the normal range with no bleeding episodes.
Most participants in the Spark trial obtained
levels of FIX activity in the mild–normal range,
with one case of particularly high levels
and one in the low–mild range. Decline in
FIX expression was briefly mentioned, with
limited clarity on whether the levels will
stabilise with time or continue to fall.
Potential mechanisms for transaminitis
were explored. Currently the mechanisms
are not well understood as transaminitis was
not an observation in animal studies. With
unpredictable dose and immune response to
gene therapy, it may be necessary to redesign
vectors to avoid an impact on expression levels
at the higher doses that are now in use.
2 3

ISTH 2021 Virtual Congress Review
Developments in Haemophilia A
Data from the Phase 3 GENEr8-1 and Phase 1/2 trial of valoctocogene
roxaparvovec were presented, in addition to Phase 1/2 data of BAY 2599023
and SPK-8011. Results of novel codon-optimised variants in a canine model
and immunogenicity of FVIII in a mouse model were also presented.
Individual participant FVIII infusion rate, ABR, and FVIII activity
Participant 7
Participant 9
Current FVIII
range
CS
OS
40
Annualized treated
bleed rate
Baseline After week 4
0
0
0
157
105
Annualized FVIII
infusion rate
Baseline After week 4
0
0.2
Results of the GENEr8-1 Phase 3 openlabel
trial of valoctocogene roxaparvovec
were presented by Ozelo et al. Participants
received prophylaxis at baseline and did not
have inhibitors to FVIII. In 132 HIV-negative
participants, FVIII activity increased by a
mean of 41.9 IU/dL at Weeks 49–52. Of
112 participants who rolled over from a
noninterventional study, 89 had no treated
bleeds versus 36 at baseline, and two of the
total 134 participants resumed prophylaxis.
Elevations in ALT occurred in 115 patients;
95.6% resolved. No participants developed
inhibitors to FVIII. The authors concluded
that this – the largest haemophilia gene trial
to date – demonstrated meaningful FVIII
expression resulting in reduction in bleeds
and replacement FVIII use. [OC 26.1]
Professor Michael Laffan reported the 5-year
results from the Phase 1/2 clinical study of
valoctocogene roxaparvovec from Pasi et al. A
single 6x10 13 (n=7) or 4x10 13 vg/kg (n=6) infusion
was administered to 13 adult men with severe
haemophilia A. At the end of Year 5 in the
6x10 13 vg/kg cohort, mean ABR was reduced
by 95% compared to pre-treatment (baseline
mean 16.3% and Year 5 mean 0.7%), and mean
FVIII activity was 8.2 IU/dL. In the 4x10 13 vg/kg
cohort at the end of Year 4, mean ABR was
reduced by 92%, and mean FVIII activity
was 4.8 IU/dL. Reduction in FVIII usage was
maintained in all participants, and all remained
prophylaxis-free. Haem-A-QoL scores
demonstrated maintenance of improvement
from baseline QoL in the 6x10 13 vg/kg cohort.
The previously observed shallow decline in
FVIII activity continued in these participants.
FVIII rose to a peak in Year 1 and began to
decline in Year 2 in both cohorts, in proportion
to the peak FVIII expression. The safety profile
remained unchanged over 5 years, with
transient, asymptomatic ALT elevation the most
common AE reported. No participant developed
inhibitors to FVIII. The authors concluded that
valoctocogene roxaparvovec demonstrates
durable haemostatic efficacy and a generally
tolerable safety profile, and that the 5-year
data provide increased clarity on the trajectory
of FVIII activity over time. [OC 67.1]
The safety and efficacy of BAY 2599023
(AAVhu37.hFVIIIco) from the Phase 1/2 openlabel
study in haemophilia A was reported by
Pipe et al. Sustained FVIII levels ≤21 months
were seen in 6 patients who received
BAY 2599023. Asymptomatic elevations
in ALT were observed in three patients and
were managed with corticosteroids. No AEs
were observed, and the authors concluded
that, with its generally tolerable safety profile
and sustained efficacy, BAY 2599023 is a key
option in the evolution of gene therapy in
haemophilia A. [PB0652]
6x10 13 vg/kg
dose cohort
(n = 7)
4x10 13 vg/kg
dose cohort
(n = 6)
Participant 5
Participant 4
Participant 8
Participant 6
Participant 3
Participant 11
Participant 14
Participant 10
Participant 12
Participant 13
Participant 15
Nonhemophilic
(>40 IU/dL)
FVIII activity are for week 260 for the 6x10 13 vg/kg cohort and week 208 for the 4x10 13 vg/kg cohort.
Annualised infusion rate includes infusions for surgery/procedures or one-time prophylaxis.
George et al reported results from the
ongoing Phase 1/2 trial of SPK-8011 in
haemophilia A. Participants received
SPK-8011 in four dose cohorts ranging from
5x10 11 to 2x10 12 vg/kg. These are the lowest
doses in use in trials for haemophilia A.
15 participants maintained FVIII expression
at 1 year, with 11 maintaining expression for
>2 years. No significant decline in expression
25
Mild
(>5 to 40 IU/dL)
24
24
9
1
0
0.4
0
41 0
0
5
15 0.3
4
1 0.7
0
0.5
0
12 4.8
184
183
152
159
156
155
121
120
125
Laffan et al [OC 67.1]
was observed over time. One year postadministration,
the majority of participants
maintained stable FVIII expression in the mild
range. This resulted in a mean reduction in
ABR of 91% from the year prior to treatment.
A 97% reduction in annualised infusion rate
was also observed, and all participants on
prophylaxis prior to infusion ceased use.
In two participants, a presumed cellular
54
27
0
1.2
0
6.6
1.0
0.5
1.9
24.6
15.2
0.8
27.3
40 20 0 20 40 200 100 0 100 200
bleeds/year
infusions/year
Moderate
(3 to 5 IU/dL with CS
1 to 5 IU/dL with OS)
Below LLOQ
(

ISTH 2021 Virtual Congress Review
immune response to the capsid resulted in
loss of FVIII expression, and six had vectorrelated
AEs. At a median of 3 years there
have been no deaths and no development
of inhibitors. The authors commented that
SPK-8011 demonstrated acceptable safety
and efficacy, and that expression of FVIII
can be stable and durable up to 3.5 years
after gene transfer. These data support that
hepatocyte expression of FVIII after AAV gene
transfer is a viable approach. [OC 67.2]
The efficacy and safety of novel codonoptimised
variants AAV8-hFVIII-CO-∆3-SP/
DE and AAV8-hFVIII-BDD in four haemophilia
A dogs tolerised to hFVIII, was presented by
Nguyen et al. FVIII expression was 2.4–5.7%
in two dogs receiving 2x10 12 vg/kg AAV8-
hFVIII-BDD and 10.9–16.7% in two receiving
the same dose of AAV8-hFVIII-CO-∆3-SP/DE,
sustained up to 2.5 years. No anti-hFVIII
IgG antibodies were observed, suggesting
no breakthrough immune response to AAV
occurred. FVIII expression after infusion of
Human FVIII activity after AAV administration at a dose of 2x10 12 vg/kg (Coatest assay)
hFVIII Activity (%)
20
18
16
14
12
10
8
6
4
2
AAV8-hFVIII-CO-∆3-SP/DE was 2–3 times
higher than AAV8-hFVIII-BDD, providing a
novel strategy for reducing the vector dose
for AAV gene therapy. [OC 75.4]
The results of a study examining the
immunogenicity of FVIII delivered via liverdirected
AAV vector in a FVIII-deficient mouse
model were presented by Lundgren et al.
FVIII activity, anti-FVIII IgG, and inhibitor
titer incidence, magnitude and kinetics were
observed and several independent variables,
including vector dose, were tested. The
strongest predictor of inhibitor development
was initial FVIII production rate. When
challenged with recombinant FVIII protein,
mice with no inhibitors and steady-state
FVIII levels of 1.5–4.5 IU/mL were protected
from developing inhibitors; however, those
with levels

ISTH 2021 Virtual Congress Review
FIX activity by baseline NAb status: up to 26 weeks
FIX activity,
central one-stage (IU/dL)
FIX activity,
central one-stage (IU/dL)
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
NAb + (n=23)
1 2
N
3
21
NAb - (n=31)
1 2
N
3
31
Pipe et al provided a case report on a liver
safety incident from the HOPE-B trial. The
FDA placed the clinical trial programme on
hold until issues relating to this case had been
satisfactorily addressed. The hold was removed
in April 2021. The patient was a >65-year-old
man with multiple pre-existing risk factors for
HCC. His liver transaminase levels were within
normal limits in the preceding year, and FIX
activity was stable. There was no evidence of
a lesion on pre-entry ultrasound screening.
A liver lesion was observed on routine safety
ultrasound 1 year post dose. Biopsy indicated
predominantly normal liver tissue with a single
atypical focus consistent with HCC. Integration
of etranacogene dezaparvovec into the HCC
and HCC-adjacent tissue was very low
(0.027% and 0.018%, respectively). There
4
20
4
31
5
20
5
31
6
17
6
31
7
19
7
31
8
Week
20
8
Week
Uncontaminated central laboratory data (the visit did not occur within 10 days of exogeneous FIX use).
FIX levels beginning with the Week 3 assessment were used in the analysis.
31
9
19
9
28
10
19
10
26
11
21
11
28
12
22
12
30
Month
4
22
Month
4
28
Month
5
Leebeek et al [OC 67.3]
was no dominant integration event or site
in the HCC sample, and there was no clonal
outgrowth of the tumour shown on whole
genome analysis. An independent expert
molecular evaluation determined that
this case was unlikely to be treatment
related. Participants in the etranacogene
dezaparvovec trials will receive twice yearly
ultrasounds from now on. [OC 67.4]
Recht et al reported the AEs of special
interest on the day of dosing in the HOPE-B
trial. Seven participants (13%) experienced
a total of nine mild-to-moderate infusionrelated
reactions which occurred in those
with (5/7) and without (2/7) AAV5 NAbs.
All events except one were resolved on
the day of infusion. A moderate suspected
20
Month
5
27
Month
6
23
Month
6
31
Q1–Q3
Median
Mean
Min/Max
hypersensitivity reaction that occurred after
10% of the dose was administered was
managed through withdrawal of etranacogene
dezaparvovec followed by administration of
IV corticosteroids and antihistamines. The
authors recommended that mild reactions
were managed by decreasing the infusion
rate and moderate reactions by temporary
interruption or slowing of etranacogene
dezaparvovec infusion and supportive steroids
and/or antihistamines. [PB0659]
The 2-year results of the Phase 2b openlabel
trial of etranacogene dezaparvovec
were presented by von Drygalski et al. Three
participants with FIX ≤1%, requiring routine
prophylaxis and with AAV5 NAbs at baseline
received a single 2x10 13 gc/kg infusion of
etranacogene dezaparvovec. By Week 6, mean
FIX activity was 31%, increasing to 44.2% at
2 years, with levels of 45%, 36% and 52% in
participants 1, 2 and 3 respectively. There
was no observed relationship between FIX
activity and presence of NAbs at baseline,
no participants developed inhibitors to FIX,
there were no clinically significant elevations
in liver enzymes and no steroids were required
Platelet Gene Therapy
as a result of treatment. One participant
had a spontaneous bleed in Year 2 and
self-administered a single infusion of FIX
replacement. Sustained FIX activity in the mildnormal
range has been observed over 2 years,
and routine prophylaxis has been discontinued
in these participants. [LPB0020]
Shehu et al demonstrated the applicability
of a FIX-Padua activity Calculator to compare
results from FIX-R338L-based gene
therapy trials which used different assay
methodologies. FIX activity (FIX:C) ratios were
developed using results from the FIX-R338L
field study, indexed to SynthASil FIX:C results.
Published FIX:C results for ACTIN-FSL,
CK Prest, PTT Automate and ROX assays,
as well as FLT180a ROX Factor IX data were
compared with predicted results from the
Calculator. A strong positive correlation was
observed between calculated results and all
published results (r>0.85, p

ISTH 2021 Virtual Congress Review
dexamethasone to reduce lung mucus and
immune response prior to lentiviral delivery.
Delivery of GFP containing 2.5x109 ifu/mL
lentiviral vectors produced ≤0.075% positive
GFP-expressing platelets after 4 days;
FVIII expression in platelets was detectable
at 0.4 mU/108 platelets when a F8-genecontaining
vector was delivered intranasally.
The authors concluded that the intranasal
delivery of lentiviral vectors encoding F8 gene
and targeting the lung is a potential option
for treatment of patients with haemophilia.
[PB0650]
The impact of platelet aggregation on
the clinical efficacy of platelet FVIII in
2bF8/FVIII-/- mice, was investigated by
Yu et al using an anti-mouse integrin αIIbβ3
antibody (Leo.H4). Platelet FVIII levels were
comparable between 2bF8/FVIII-/- and
wild type mice in the presence of Leo.H4.
However, clotting time, clot formation
time, maximal clot formation, α angle
and A10 were significantly impaired in
2bF8/FVIII-/- mice. Leo.H4 significantly
Investigating Antibodies to AAV
enhanced peak thrombin and endogenous
thrombin potential in 2bF8/FVIII-/- mice.
No occlusion occurred in FeCl3-induced
carotid injury when Leo.H4 was infused.
The authors concluded that αIIbβ3-mediated
platelet aggregation is critical in maintaining
haemostatic functions and clinical efficacy
of platelet-derived FVIII. [PB0651]
Shi et al reported a preconditioning approach
for platelet gene therapy of haemophilia A
with inhibitors in rhF8-primed mice, using
fludarabine on Days −7 to −4 and busulfan
on Days −2 and −1. Transplantation of 2bF8
lentivirus-transduced HSCs introduced platelet
FVIII expression. TBI preconditioning was used
as a parallel control. Anti-FVIII antibody titers
reduced in both groups; when challenged with
rhF8, no anti-FVIII inhibitors were apparent
in either group. However, all untransduced
control mice developed inhibitors. In this trial,
preconditioning with fludarabine and busulfan
led to immune tolerance and the introduction
of therapeutic levels of platelet FVIII expression
in rhF8 mice. [PB0654]
The seroprevalence of antibodies to AAV capsids was investigated and the
reasons for standardising the measurement of AAV NAbs elucidated. One
presentation provided support for the inclusion of participants with NAbs
in gene therapy trials, and the design and recruitment methods for the
Seroprevalence of AAV AntibodY (SAAVY) study were presented.
The results of a prospective study of 546
participants from nine countries to evaluate
the seroprevalence of antibodies to AAV2,
AAV5, AAV6, AAV8 and rh10 capsids were
reported by Klamroth et al. Geographic
variability was observed, although the
prevalence of AAV5 was generally the lowest
and AAV2 the highest. The percentage of
participants positive for antibodies to
AAV5 was lower in adolescents than adults
(29% versus 36%), and data from individuals
without haemophilia showed comparable
rates of seropositivity. The authors concluded
that the presence of antibodies to AAV
serotypes may play an important role in
eligibility considerations as trials for gene
therapies progress. [LPB0022]
Dr David Lillicrap gave a presentation on the
standardisation of measuring AAV NAbs. He
outlined that the number of vector particles
reaching the target cells is a key factor in the
success of gene therapy and that antibodies
in the plasma may affect this. The prevalence
and influence of AAV antibodies on efficacy
of gene therapy may depend on whether
the antibodies are pre-existing, developed
following exposure to the wild-type virus, or
developed after administration with AAVmediated
gene therapy. Development of
antibodies after gene therapy can result in
high titer and persistent antibodies, and can
prevent re-administration of the gene therapy
product. Two types of assay measure AAV
immunity, ELISA-based total antibody assay;
and transduction inhibition assay. Dr Lillicrap
expressed a critical need to standardise
the AAV antibody assay as the results can
influence the decision on eligibility for
gene therapy, may explain the success and
variability of outcomes, and would eliminate
one element of uncertainty concerning
vector delivery.
David Cooper (UniQure) presented data
supporting the inclusion of patients with
pre-existing NAbs to AAV in the clinical
trial programme. NAb titers up to 1030 in
NHP, 340 in the Phase 1/2 and 678 in the
Phase 3 trial of etranacogene dezaparvovec
have not impacted on the efficacy of AAVmediated
therapy in these groups. Based on
these titers, potentially up to 96% of donors
would be eligible for gene therapy. These
observations support the lack of impact of
pre-existing AAV5 NAbs measured in vitro on
the efficacy of AAV5-mediated gene therapy
transduction when compared to pre-existing
NAbs to AAV2 and AAV8.
The design and recruitment methods
for the Seroprevalence of AAV AntibodY
(SAAVY) study, designed to minimise
in-person interactions during the COVID-19
pandemic, were presented by Vaghela et al.
The SAAVY study aims to characterise
AAV antibody prevalence and titers, and
evaluate changes and influencing factors on
titer, antibody positivity and seroconversion.
With the COVID-19 pandemic interrupting
clinical trials, adaptability in recruiting
participants and study design is a necessary
evolution. SAAVY uses a mobile app,
various routes of engagement to reach
HCPs, patients and PAGs, remote
recruitment through e-consent, and a
network of >1800 laboratories in the US
for collection of biospecimens, thereby
minimising travel, face-to-face contact
and burden on HTC staff. 105 participants
have consented to date. The authors
concluded that multi-modal engagement
with the haemophilia community can
facilitate the conduct of studies and may
improve clinical trial recruitment and
patient experience. [PB0663]
10 11

ISTH 2021 Virtual Congress Review
Liver Health in Gene Therapy
Liver health up to 60 months in the Phase 1/2a study of fidanacogene
elaparvovec was reported in addition to the results of a canine model
examining hepatic outcomes and mechanisms of elevation of ALT.
George et al evaluated the liver health of 14
men with haemophilia B in a long-term follow
up study of fidanacogene elaparvovec following
completion of a Phase 1/2a study. Follow up
ranged from 32–60 months, 10 participants
had a history of resolved HCV and seven had
prior HBV. Annual liver ultrasound indicated
fatty liver in one participant. The most common
finding was mild sustained elevations of ALT,
the aetiology of which was unclear. The longterm
impact of fidanacogene elaparvovec on
liver health was considered mild, and further
monitoring is required. [PB0532]
Batty et al reported the results of a canine
AAV gene therapy model to investigate factors
influencing FVIII expression and examine
hepatic outcomes and mechanisms of elevated
ALT. Five male dogs were treated with one of
three AAV5 BDD canine FVIII vectors with a
The Impact of Gene Therapy:
The Exigency Study
hybrid liver promoter (AAV5-HLP-cFVIII) at
doses of 6.8x10 13 –2x10 14 vg/kg. Three dogs
receiving non-codon-optimised-AAV5-cFVIII-SQ
vector did not demonstrate significant FVIII
expression, although improvement in whole
blood clot time and TEG was observed. Two
dogs treated with codon-optimised constructs
demonstrated FVIII expression which was
maintained at 6 months. Whole blood clot
time was normalised. Transaminitis and
transient loss of FVIII expression was seen
in one dog treated with co-cFVIII-V3, although
ultrasound and biopsies showed no underlying
histopathology. There was no evidence of
hepatocyte cell death, inflammation, or
upregulation of the unfolded protein response.
This is the first incidence of transaminitis and
loss of FVIII expression in a preclinical model;
further investigation into the mechanisms
behind these is ongoing. [OC 75.2]
Results from the Exigency study, designed to capture the experience of gene
therapy in individuals with haemophilia and their families, were reported.
apparent: freedom, altruism, side effects
of immunosuppression, loss of factor
expression and loss of control. Gene therapy
was largely viewed as a positive experience,
although concerns were raised over the side
effects of immunosuppression. Participants
reported a lack of psychological support and
The WFH Gene Therapy Registry
a loss of control. The study is ongoing; the
authors commented that this data indicates
psychological support should be an integral
part in gene therapy programmes to enable
participants and families to process their
experiences of gene therapy, whether positive
or negative. [PB0660]
The reasons behind the development of the WFH Gene Therapy Registry were
presented, as well as details on how data will be collected.
Professor Barbara Konkle addressed why
long-term follow up for gene therapy is
necessary. Unanswered questions remain in
gene therapy including duration of response,
variability of response, optimal use of
immunosuppression (if needed), and risk
of integration. Lifelong follow up is crucial
to monitor long-term safety issues such as
long-term liver toxicity, risk of insertional
mutagenesis, and germline transfer. Canine
studies have demonstrated no evidence of
clonal expansion and increasing data from
human studies have shown no long-term
liver toxicity or tumorigenesis. Gene therapy
used in NHPs with disorders other than
haemophilia have indicated that random,
low-frequency integration events have
occurred over time. In the haemophilia field,
it is expected that genotoxicity may be a
longer-term event that will require follow up.
To address the unknown long-term safety,
the WFH developed the gene therapy registry
with the goal of collecting data on all patients
who receive gene therapy for haemophilia,
either as part of a trial or post-marketing. It
is essential to ensure inclusion of a maximum
number of patients worldwide to increase
the likelihood of identifying low-incidence
events. A core data set has been developed
and includes demographics, medical
history, infusion details, efficacy and safety
data, PROs, and mortality. The registry is
designed to be completed by HTCs or through
compatible national registries. The database
is under development and will be ready to
receive data early in 2022. [PB0661]
Data from nine participants in the Exigency
study were reported by Fletcher et al.
The mean time from transfection was
1.89 years (range 1–5 years). Semi-structured
interviews were conducted, and responses
analysed thematically, with five key themes
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ISTH 2021 Virtual Congress Review
Symposiums Review
There were several high-quality industry-sponsored symposiums at
ISTH. In addition to those covered in this section, there were symposiums
on personalised care in haemophilia (Takeda), advancements in the
management of bleeding in patients with inhibitors (LFB-HEMA Biologics),
elevating expectations for factor replacement beyond current paradigms
(Sanofi Genzyme and Sobi), therapy, diagnostics, and devices (Novo Nordisk),
improving clinical outcomes through a better understanding of haemostasis
(Springer Healthcare IME) and immunomodulation with investigational AAV
gene therapy (Spark Therapeutics).
Gene Therapy Research in Haemophilia:
Liver Health and Patient Preparation;
Experience from Clinical Trials
Professor Flora Peyvandi chaired the BioMarin symposium, which included
a discussion on liver health and considerations on how to prepare a patient for
a gene therapy trial.
A review of the objectives of gene therapy
research and the different viral vectors
used in gene transfer in haemophilia was
presented, and an overview of the current
AAV haemophilia A and B gene therapy trials
provided. The case of HCC in the UniQure
haemophilia B clinical trial programme was
discussed, and an interesting discussion
was held between Professor Dan Hart and
Professor Graham Foster on liver health and
gene therapy. The concerns of haematologists
regarding elevated transaminases after
gene therapy, particularly in relation to
the potential subsequent loss of factor
expression were discussed and it was
noted that the population receiving
gene therapy for haemophilia may have
underlying liver issues prior to treatment.
A pre-treatment assessment of fibrosis,
liver function, and a baseline level of ALT
was recommended to enable a personalised
management plan to be established in
response to a rise in transaminases. It was
agreed that the importance of liver health
needs to be stressed to haematologists and
patients, and patients need to be educated
on the incremental risks associated with
lifestyle factors.
The preparation of patients for clinical
trials was discussed by Professor Wolfgang
Miesbach, including an overview of the
status of gene therapy research, as well
as eligibility criteria, and the requirements
for trial inclusion, such as liver health and
commitment to short- and long-term follow
up. The need for patients to understand the
different possible outcomes of gene therapy
was discussed, including ABR, factor levels,
change in factor levels over time, and impact
on their day-to-day QoL. It was noted that
clear communication and coordination
between the MDT will be essential to fully
implement the EAHAD ‘hub-and-spoke’ model
for following up gene therapy in practice.
Embarking on the Gene Therapy Journey with your
Patient: Key Topics for Shared Decision Making
This symposium, sponsored by UniQure, was chaired by Mark Skinner and focused on shared
decision making in preparation for gene therapy from both a patient and clinical perspective.
The shared decision-making process to
undergo gene therapy for haemophilia
was discussed from both a patient (Mark
Skinner) and clinician (Dr Robert Klamroth)
perspective. With the potential for gene
therapy to impact the patient’s future, a fully
informed patient and shared decision making
are vital to proceed with gene therapy, and
patient satisfaction and adherence can be
increased when a decision is mutual. The
necessity for clinicians to understand the
outcomes of importance to individual patients
was addressed, including dose frequency,
durability, and effect on ABR. Data were
provided on the varying prevalence of NAbs
dependent on the AAV type, and it was noted
that successful gene therapy is possible even
in patients with NAbs, as per the evidence in
the HOPE-B study. Data from the BioMarin 2
and AMT-061 trials were shared to illustrate
the variability of factor levels achieved after
gene therapy. It was noted that patients need
to be made aware that there are liver function
and factor levels tests required weekly for
the first 6 months, as well as consistent,
long-term follow up.
The reasons why patients considering gene
therapy should be cognisant of their liver
health, the tools for assessment, common
comorbidities, lifestyle modifications,
and when patients should be referred
to a hepatologist were discussed by
Dr Bruce Luxon. The importance of
documenting baseline ALT and AST to
establish the extent of elevation for each
individual patient was discussed, and
confounding issues such as previous HBV
and HCV infection identified as relatively
common in the haemophilia population.
Non-invasive measures to assess liver
fibrosis were addressed, including innovative
combinations of standard tests (e.g., APRI),
specialised proprietary tests (e.g., Fibrosure ,
FibroTest ), and elastography performed
by ultrasound or MRI.
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ISTH 2021 Virtual Congress Review
Long-term Monitoring of Clinical Efficacy and
Safety Parameters for Hemophilia Gene Therapy
Dr Steven Pipe chaired the Pfizer symposium, in which the importance of long-term safety
and efficacy monitoring, and liver health in relation to gene therapy were discussed.
The necessity for short- and long-term clinical
and laboratory monitoring after gene therapy
to address the unknown reliability, variability,
and durability of expression was discussed
by Dr Steven Pipe. In-depth pre-therapy
assessment to exclude participants with
abnormal laboratory values, active HBV, HCV,
HIV, NAbs to vector capsid and a history or
presence of inhibitors was recommended.
The importance of patient adherence to weekly
follow up for the first 6 months, and long-term
monitoring was discussed, and the specific
concerns both in the short- and long-term
explained. Dr Annette Bowyer explored the
monitoring parameters for clinical efficacy
after gene therapy, including frequency of
bleeding events, duration of expression, pain/
discomfort, factor activity level and emotional
functioning. The complexities of monitoring
factor levels were addressed, with discrepancies
seen between OS and CS assays, and a lack of
clarity on the methodologies and reagents used
in clinical trials. The importance of long-term
monitoring to address some of the current
unknowns of gene therapy was stressed, with
collection of registry data from all participants
who have received gene therapy a priority to
detect low incidence or delayed safety events
from a small, geographically widespread cohort.
The importance and methodologies for
monitoring liver health in gene therapy was
discussed by Professor Rajender Reddy. The
pathology of the immune response induced
by investigational gene therapy was explored,
with several potential factors explained,
including innate immunity in response to
acute toxicities, or adaptive immunity from
cytotoxic T-cell responses, high-titer NAbs
or transgene tolerance. The reliability of
elevated ALT as an assessment of liver health
was questioned, and considerations for gene
therapy participants with a history of HBV
and HCV elucidated. Options for assessing
liver fibrosis, such as biopsy, serum
biomarkers, and FibroScan were outlined.
LIST OF ABBREVIATIONS
AAV – adeno-associated virus
ABR – annualised bleeding rate
ALT – alanine aminotransferase
AST – aspartate transaminase
ATHN – American Thrombosis
and Hemostasis Network
BDD – B-domain deleted
EAHAD – European Association for
Haemophilia and Allied Disorders
EMA – European Medicines
Agency
FDA – US Food and Drug
Administration
gc/kg – genome copies/kilogram
GFP – green fluorescent protein
HBV – hepatitis B virus
HCC – hepatocellular carcinoma
HCV – hepatitis C virus
HSC – hematopoietic stem cell
transplantation
IgG – immunoglobulin G
ISTH – International Society of
Thrombosis and Haemostasis
MDT – multidisciplinary team
NAb – neutralising antibody
NHP – non-human primate
QoL – quality of life
TBI – total body irradiation
TEG – thromboelastography
vg/kg – vector genomes/
kilogram
WFH – World Federation of
Hemophilia
REFERENCES 1. Nathwani AC et al. N Engl J Med 2014 20;371:1994–2004.
2. Pasi J et al. N Engl J Med 2020;382:29–40.
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