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Shares of Sangamo Therapeutics  (SGMO - Get Report)  rose sharply Monday after the release of encouraging test results for a new drug to treat severe hemophilia A.

Sangamo's stock price surged 10.53% to $12.58 after a pair of patients reported no bleeding events for as long as 24 weeks - the length of the follow-up period - after treatment with investigational SB-525 gene therapy for severe hemophilia A.

"The data showed that SB-525 was generally well-tolerated and demonstrated a dose-dependent increase in Factor VIII (FVIII) activity levels," according to an announcement by Sangamo, a genomic medicine developer, and partner Pfizer  (PFE - Get Report) , of updated results from the Phase 1/2 Alta study.

Sangamo and Pfizer said they were also seeing encouraging results from a pair of patients more recently treated, both of whom are "demonstrating FVIII activity kinetics that appear consistent with the first two patients treated in this dose cohort."

The Phase 1/2 Alta study looked at a total of 10 patients, with the best results coming from the four who were given the highest doses of SB-525.

Researchers presented the test results of the new, SB-525 gene therapy treatment on July 6 at the XXVII Congress of the International Society on Thrombosis and Haemostasis (ISTH), in Melbourne, Australia.

Sangamo currently faces competition from BioMarin Pharmaceutical (BMRN - Get Report) and Spark Therapeutics (ONCE - Get Report) , with the two companies in Phase 3 testing with their own treatments and as a result, further along in the Food and Drug Administration process.