• ClinicalTrials.gov Identifier: NCT00979238¹
• PI open-label, dose-escalation study²

• Active, not recruiting¹
• Last Update Posted: 2024-11-22¹

• Males ≥ 18 years of age with established severe HB (FIX:C<1u/dl)
• Treated/exposed to FIX products for at least10 years or 50 EDs

• Detectable antibodies reactive with AAV8 
• Received an AAV vector or any other gene transfer agent in the previous 6 months

AAV8/ HEK293T^{3 [supplementary appendix]}

Codon-optimized FIX encoded in a self-complementary AAV vector³

LP1 that is based on the earlier described liver-specific APOE-HCR/hAAT enhancer/ promoter construct that is encoded by:

• A compact sequence length of 448 bp instead of 754 bp⁴

Further expression cassette elements include:

• A modified simian virus 40 (SV40) small t antigen intron
• A SV40 late polyA signal (SV40 LpA)⁴

Systemic⁵

Co. 1 - Co. 3 were treated with an initial vector preparation (full: empty capsidratio at 1:10) as follows^2-3, 7

• Co. 1: 2e11 (2)
• Co. 2: 6e11 (2)
• Co. 3: 2e12 (6)

Co. 4 and Co. 5 were treated with a new vector preparation (full: empty capsid ratio at 1:3) as follows⁶: 

• Co. 4: 2e12 (2)
• Co. 5: 5e12 (2)

Follow-up periods reported across different publications were as follows:

• Up to 3 years, as reported in reference #2
• 6 to 16 months of follow-up, as reported in reference #3
• A median follow-up of 6.7 ± 1.0 years, as reported in reference #6
• A median follow-up of 13.0 years (range: 11.1 to 13.8 years), as reported in reference #7

OS

Data on FIX activity following gene therapy, as reported in multiple publications from a single clinical trial, are summarized below, including follow-up durations, dose cohorts, and FIX expression levels:

FIX levels in P4 increased to a peak of 4%, 4 weeks after gene transfer³

Data on annualized bleeding rates across the three dose cohorts were presented in Table 2 of reference #2 and are summarized as follows:

Long-term data on annualized bleeding rates, as reported in reference #7, are summarized in the table below:

Data on FIX concentrate use from the year before and the year after vector infusion were published in reference #2 and are summarized in the table below:

Data on FIX concentrate use 13 years after gene therapy, as reported in reference #7, are summarized in the table below:

The systemic infusion of scAAV2/8-LP1-hFIXco was not associated with clinically significant changes² like:

• Pulse
• Respiration rate
• Blood pressure 
• Temperature either during or after vector infusion

As reported in reference #6, P5 (Co. 3: 2e12 vg/kg) experienced a grade III SAE related to study agent considering ALT and AST elevation peaks at D58 as follows:

• By week 10 post–gene transfer, P5 received a short course of corticosteroids, and liver enzyme levels had returned to the normal range⁶

Additionally, study agent–related or possibly related Adverse Events, among other AEs, were extracted from reference #2 and are summarized as follows:

Most recent update on Adverse Events, were extracted from Table S2 in reference #7, is summarized below:

Not reported

• 4/6 pts. in Co. 3 (40-202 IU/L/7-10 weeks)^2-3
• 3/4 pts. in Co. 4+5⁶ (peak level/timing not reported)

• AST levels: (143 IU/L, week 7)^2-3 in P5 (Co. 3) 
• The same pt. had an ALT level of 202 IU/L /6 
• AST levels for Co. 4-5 were not reported⁶

• Yes, in Co. 2 and Co. 3^2-3: (200-400 SFU/ million PBMC/within 12 weeks to > 1 year) 
• Co. 4-5: not reported ⁸

Yes (8-12 weeks)² 

Data on declines in FIX levels associated with ALT elevations, as reported across different publications, are summarized below:

• Reference #2: Yes, 50-70% reduction in 3/4 participants in Co. 3 (2×10¹² vg/kg) with ALT elevations + T-cell response
• Reference #6: In two-thirds of patients in the 2×10¹² vg/kg dose cohort, a decline in FIX levels within 3 months of gene transfer was associated with an asymptomatic increase in liver enzyme levels
• Reference #7: Transient grade 1 or 2 elevations in liver aminotransferase levels were observed in four of six participants treated with the high vector dose
  • In two of these participants, delayed glucocorticoid treatment led to a considerable reduction in transgene expression

Data on reported cancer cases, as published in reference #7, are summarized below:

• In accordance with the study protocol, two cancers were reported to regulators as serious adverse events.
  • Lung adenocarcinoma in situ:
    • Detected incidentally after bullectomy for recurrent pneumothorax.
    • Occurred 7.0 years after gene therapy in a 44-year-old participant.
    • The participant had a smoking history of approximately 10 pack-years over 27 years.
  • Prostate adenocarcinoma:
    • Diagnosed in a 74-year-old participant
    • Occurred 11.6 years after gene therapy
• Molecular analyses and expert multidisciplinary review indicated that both cancers were likely unrelated to gene therapy
• Additional details are provided in the Supplementary Appendix in reference #7

Liver biopsy findings from Participant 8 (high-dose group), who had no evidence of cancer, in the high-dose group, as reported in reference #7, are summarized below:

• Ten years after gene therapy a transjugular liver biopsy was performed on Participant 8
• Histological analysis showed:
  • Preserved lobular architecture
  • No necrosis, fibrosis, or dysplasia
• In situ hybridization findings:
  • hFIXco DNA was detected in a mean of 10.3 ± 3.4% of hepatocytes.
  • RNA in situ hybridization showed active transcription in a mean of 5.5 ± 2.3% of hepatocytes
  • This indicates that just over half of the transduced hepatocytes were transcriptionally active
• No segregation was observed between active and inactive hepatocytes
• Note: This single liver-biopsy sample represents only the sampled region and may not fully reflect transgene expression throughout the liver
• Nonetheless, findings confirm persistent transgene transcription in a subset of transduced hepatocytes

1. Dose-Escalation Study Of A Self Complementary Adeno-Associated Viral Vector For Gene Transfer in Hemophilia B. Available at: Dose-Escalation Study Of A Self Complementary Adeno-Associated Viral Vector For Gene Transfer in Hemophilia B - Full Text View - ClinicalTrials.gov
2. Nathwani, A.C., et al., Adenovirus-associated virus vector-mediated gene transfer in hemophilia B. N Engl J Med, 2011. 365(25): p. 2357-65. Long-Term Safety and Efficacy of Factor IX Gene Therapy in Hemophilia B | NEJM
3. Nathwani, A.C., et al., Long-term safety and efficacy of factor IX gene therapy in hemophilia B. N Engl J Med, 2014. 371(21): p. 1994-2004. Adenovirus-Associated Virus Vector–Mediated Gene Transfer in Hemophilia B | NEJM
4. Nathwani, A.C., et al., Self-complementary adeno-associated virus vectors containing a novel liver-specific human factor IX expression cassette enable highly efficient transduction of murine and nonhuman primate liver. Blood, 2006. 107(7): p. 2653-61. Self-complementary adeno-associated virus vectors containing a novel liver-specific human factor IX expression cassette enable highly efficient transduction of murine and nonhuman primate liver | Blood | American Society of Hematology (ashpublications.org)
5. Nathwani, A.C., Gene therapy for hemophilia. Hematology Am Soc Hematol Educ Program, 2019. 2019(1): p. 1-8. Gene therapy for hemophilia | Hematology, ASH Education Program | American Society of Hematology (ashpublications.org)
6. Nathwani, A.C., et al., Adeno-Associated Mediated Gene Transfer for Hemophilia B: 8 Year Follow up and Impact of Removing "Empty Viral Particles" on Safety and Efficacy of Gene Transfer. Blood, 2018. 132(Suppl. 1): p. 491. Adeno-Associated Mediated Gene Transfer for Hemophilia B:8 Year Follow up and Impact of Removing "Empty Viral Particles" on Safety and Efficacy of Gene Transfer | Blood | American Society of Hematology (ashpublications.org)
7. Reiss UM, Davidoff AM, Tuddenham EGD, Chowdary P, McIntosh J, Muczynski V, Journou M, Simini G, Ireland L, Mohamed S, Riddell A, Pie AJ, Hall A, Quaglia A, Mangles S, Mahlangu J, Haley K, Recht M, Shen YM, Halka KG, Fortner G, Morton CL, Gu Z, Hayden RT, Neufeld EJ, Okhomina VI, Kang G, Nathwani AC. Sustained Clinical Benefit of AAV Gene Therapy in Severe Hemophilia B. N Engl J Med. 2025 Jun 12;392(22):2226-2234. doi: 10.1056/NEJMoa2414783. PMID: 40499172. Sustained Clinical Benefit of AAV Gene Therapy in Severe Hemophilia B - PubMed

AAV, Adeno-associated virus; ABR, Annualized bleeding rate; AEs: adverse events; AIR, Annualized FVIII/FIX infusion rate; ALT, alanine aminotransferase; AST, aspartate aminotransferase; CH, Chromogenic Assay; Co., cohort; DOACs, Direct oral anticoagulants; D, days; EDs, exposure days; FIX, factor IX; FIX-Padua, gain of function FIX variant; FVIII, factor VIII; gc, genome copies; HEK cells, human embryonic kidney cells; IQR, interquartile range; IRR, Infusion-related reaction; NAbs, neutralizing antibodies; OS, One-stage clotting assay; Pop., population; pt., patient/participant; pts., patients/participants; P1, Participant 1; PI, phase I; PBGD, porphobilinogen deaminase; PBMC, peripheral blood mononuclear cells; SAEs, serious adverse events; SFU, spot-forming units; TAC, tacrolimus; ULN, upper limit of normal; VCN, vector copy number; vg, vector genomes; W, weeks; WT, wild type; Y, year