Avrobio shares more than halve on update from clinical studies of Fabry disease gene therapy

Shares in Avrobio fell as much as 52 percent after the company reported an update on four patients enrolled in two studies of its experimental gene therapy AVR-RD-01 for the treatment of Fabry disease. The ex vivo lentiviral gene therapy, which is designed to be a one-time treatment, works by inserting the GLA gene that encodes functional alpha-galactosidase A.

The Phase I study is assessing AVR-RD-01 in up to six patients with Fabry disease who have been treated with standard-of-care enzyme replacement therapy (ERT) for at least six months prior to receiving Avrobio's gene therapy. Meanwhile, the mid-stage FAB-201 trial is evaluating the efficacy and safety of AVR-RD-01 in eight to 12 treatment-naïve patients.

The company noted that two patients in the Phase I study continue to demonstrate AGA enzyme activity above the diagnostic range for classic Fabry disease at 18 months and six months after receiving AVR-RD-01, respectively. Avrobio added that the first patient is no longer receiving ERT, although the subject's levels of AGA have fallen markedly between six months and 18 months after receiving AVR-RD-01.

Avrobio also disclosed details on vector copy number (VCN), which the drugmaker said refers to the average number of copies of the lentiviral-vector inserted gene that are integrated into the genome of a cell. The company noted that the first patient in the Phase I study started with a VCN of 0.7, which fell to 0.1 after 18 months. Further, the second patient's VCN began at 1.4, dropping to 0.4 at six months, while a third subject's VCN fell from 0.8 at study start to 0.2 after one month. Meanwhile, in the mid-stage trial, the only patient to have received treatment, to date, started with a VCN of 0.7, which fell to 0.5 after three months.

"We are encouraged by the AGA enzyme activity we are seeing after treatment with AVR-RD-01 in the first two patients with Fabry disease in the Phase I study," remarked CEO Geoff MacKay. The executive added that in the mid-stage trial, the sole treated patient "is now demonstrating AGA activity above the diagnostic range for males with classic Fabry disease three months after receiving…treatment."

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