SAN DIEGO – A novel human factor VIII variant shows promise for the treatment of severe hemophilia A, according to preliminary findings from the ongoing Gene Therapy for Hemophilia A (GO-8) phase 1/2 dose-escalation study.
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A single peripheral vein infusion of the factor VIII (FVIII) variant resulted in FVIII activity levels of about 6% versus levels of no more than 1% of normal at study entry in the first four patients, Pratima Chowdary, MD, reported at the annual meeting of the American Society of Hematology.
The variant, known as scAAV2/8-LP1-hFIXco, is being investigated for safety and efficacy in the GO-8 investigator-led, open-label, nonrandomized trial at a low, mid, and high dose (2 x 1011 vector genomes/kg, 6 x 1011 vector genomes/kg, and 2 x 1012 vector genomes/kg), said Dr. Chowdary, a consultant hematologist at Royal Free Hospital London.
The main study period is 6 months and 15 years of follow-up are offered.
The first patient received the low dose and achieved FVIII of about 6% within 1 week. That level persisted for about 6 weeks when the patient developed a transaminitis, which promptly responded to steroids.
His steady-state FVIII within a few weeks was 7% by one-stage assay and about 3% by chromogenic assay, Dr. Chowdary said.
The remaining patients received the mid dose and also achieved FVIII levels of about 6% within a week. Patient 2 started on prophylactic steroids at week 6, per protocol, and did not experience transaminitis, but also had no increase in FVIII level, compared with the low-dose patient, which may be explained by the potential drug half-life, she noted.
Patient 3 reached a FVIII level of about 30% by week 4. He developed transaminitis at that time, which was about 2 weeks before planned prophylactic drug administration, but the transaminitis was controlled by steroids over a period of about 8-10 weeks.
“His steady-state FVIII level by one stage was 34% and by chromogenic assay was 17%. He has not had any bleeds since his gene transfer and has not required any FVIII concentrate either,” she said.
Patient 4 reached a FVIII level of about 40% by week 4. He was given prophylactic steroids at that time because of the occurrence of transaminitis at week 4 in Patient 3.
The patient developed transaminitis during steroid taper about 4 weeks later, perhaps because of the rapid taper, Dr. Chowdary said, adding that the transaminitis was well controlled with steroids, but follow-up in this patient has only been about 12 weeks.
“The characteristics of FVIII expression in this patient are very similar to the previous patient. ... We suspect he will have a steady-state level of about 30%,” she said. “Again, he’s had no bleeds since his gene transfer and has not required any FVIII concentrate.”
The single infusion of this novel vector was well tolerated in each patient, with no evidence of infusion-related reactions, neutralizing anti-FVIII antibodies, or vector-related adverse events.
“The transgene expression was achieved in all patients and at both vector dosages,” Dr. Chowdary said. “What is very important is that the levels of less than 10% had only a modest impact on the bleed rates and FVIII usage, whereas an expression of more than 10% resulted in zero bleeds and the patient did not require any additional FVIII treatment.”
The data are “encouraging,” she said. “We look forward to escalating the dose in the next patient.”
Dr. Chowdary reported financial relationships with Bayer, CSL Behring, Baxalta, Baxter, Biogen, Freeline, Novo Nordisk, Pfizer, Roche, Shire, and SOBI.
SOURCE: Chowdary P et al. ASH 2018, Abstract 489.