# Immune tolerance induction by AAV-FVIII gene therapy for canine hemophilia A with inhibitors

> **NIH NIH R01** · CHILDREN'S HOSP OF PHILADELPHIA · 2021 · $746,236

## Abstract

Hemophilia A (HA) is an X-linked bleeding disorder caused by a deficiency in factor VIII (FVIII) due to mutations
in the F8 gene. The disease affects 1:5,000 male born worldwide. Replacement therapy with FVIII protein is
effective in preventing/controlling bleeding but ~30% of patients develop inhibitors to FVIII (neutralizing
alloantibodies) that renders FVIII ineffective; thus, increasing morbidity and mortality. Immune tolerance
induction (ITI) is the only successful strategy for eradication of inhibitors/restore immune tolerance to FVIII. ITI
regimens are based on FVIII protein injections for months/years and is efficacious in ~60% of cases, but the high
cost (~1million/year) prevents its use outside the developed word. Thus, new approaches for inhibitor eradication
are urgently needed. Ongoing AAV liver gene therapy clinical trials for HA without inhibitors resulted in
therapeutic FVIII. These studies are using vectors manufactured in either HEK-293 or Sf9 cells that differ in their
basic biology and clinical outcomes. Our central hypothesis is that AAV-FVIII liver gene therapy is an ideal
ITI regimen based on our proof-of-concept report in inhibitor HA dogs (Finn et al Blood, 2010) and novel
preliminary data. We will use 2 novel distinct high-responding inhibitor HA dog models with the canine F8 gene
mutations associated with the most challenging inhibitor patient group that likely would benefit from AAV ITI. The
rationale of this proposal is that a single injection of AAV liver gene therapy provides (A) efficient eradication of
high titer inhibitors, (B) restoration and maintenance of immune tolerance to FVIII in high responding HA dogs
and (C) continuous FVIII expression that improves the bleeding phenotype after inhibitor eradication. The
specific aims are Aim 1: Determine the efficacy of AAV gene therapy in inducing immune tolerance in
high-responding HA dog models.We will advance our efforts testing AAV gene therapy in dog models across
several distinct breeds to define the factors associated with kinetics of inhibitor eradication (transgene
levels/duration). Aim 2: Determine the potential of ITI by rAAV-Sf9-derived AAV-cFVIII gene therapy in
high-responding HA dog models. Recent unexpected decline of FVIII expression after 3 years post- AAV-Sf9-
FVIII in HA patients raised concerns of durability. To date, the underlying mechanism is unknown. We
hypothesized that this could be a combination of Sf9-derived vector and/or FVIII. We will determine in dogs if
AAV-Sf9 impacts FVIII expression levels over time and its ability to eradicate inhibitors and to induce tolerance
to FVIII. Aim 3: Define the mechanism(s) underlying AAV-mediated ITI. In these novel dog models, we will
characterize specific B cells and especially T regulatory cells pool and function following AAV-ITI and to
determine the underlying mechanism of immune tolerance in both cell line-derived vector systems. Successful
completion of this proposal would support AAV liver gene...

## Key facts

- **NIH application ID:** 10276571
- **Project number:** 1R01HL158781-01
- **Recipient organization:** CHILDREN'S HOSP OF PHILADELPHIA
- **Principal Investigator:** Valder R. Arruda
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $746,236
- **Award type:** 1
- **Project period:** 2021-09-01 → 2025-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10276571

## Citation

> US National Institutes of Health, RePORTER application 10276571, Immune tolerance induction by AAV-FVIII gene therapy for canine hemophilia A with inhibitors (1R01HL158781-01). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10276571. Licensed CC0.

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