What happened

Shares of Sangamo Therapeutics (NASDAQ:SGMO) jumped 23% in June, according to data from S&P Global Market Intelligence, boosted by results from the phase 1/2 Alta clinical trial of SB-525 in patients with severe hemophilia A that were released in an abstract for a presentation at the International Society on Thrombosis and Haemostasis (ISTH) meeting.

So what

The abstract noted that two patients treated with the highest dose "reached factor VIII levels within the normal range." Factor VIII is the gene that's mutated in patients with hemophilia A and is expressed by the gene therapy SB-525, which is partnered with Pfizer (NYSE:PFE).

Woman in medical scrubs administering medicine to a man sitting in a chair.

Image source: Getty Images.

Last week, investors got to see the full results at the ISTH presentation with numbers to back up the claims in the abstract. Both patients in the higher-dose cohort reached 250% of normal factor VIII activity using the one-stage test, with both patients still over 150% of normal. Using the chromogenic assay to test factor VIII activity, both patients peaked around 150% of normal and were still above 100% of normal for their last measurements at 19 weeks and 24 weeks after treatment.

Two additional patients have been treated with the same dose, although they've been followed for only seven weeks or less. The most advanced of those additional patients achieved normal levels of factor VIII activity -- defined as 50% of normal -- seven weeks after the treatment.

The increased factor VIII expression resulted in none of the patients in the high-dose group having a bleeding event when measured starting at three weeks after the treatment.

Now what

Sangamo and Pfizer are trailing BioMarin Pharmaceutical and Spark Therapeutics (which is being purchased by Roche) in the race to treat hemophilia A patients with a gene therapy. Fortunately for Sangamo and Pfizer, the long-term winner will end up being the treatment that produces the best expression of factor VIII, and the data at ISTH suggests SB-525 could end up being the best of the bunch. Of course, gene therapies are designed to be lifetime cures, so we'll need to see longer-term factor VIII expression data in more patients to know for sure.