Results from just two haemophilia A patients sent Sangamo’s stock soaring in April, and the company will hope to repeat the trick on Monday. The group’s latest data drop with its Pfizer-partnered gene therapy, SB-525, shows persistent longer-term responses and promising but early results in two further patients receiving the highest dose.

Still, only one of the recently dosed subjects has reached normal levels of factor VIII so far, and there was another case of the liver enzyme elevations previously seen. While Sangamo is confident of managing these adverse events, it still has some way to go to prove that its therapy is effective, durable and safe.

Alta right

The latest data from the phase I/II Alta trial were presented on Saturday at the International Society on Thrombosis and Haemostasis (ISTH) meeting in Melbourne.

The trial has so far enrolled 10 patients. Four of these received the highest SB-525 dose of 3x1013 vector genomes (vg)/kg, and it is this group that has produced the most promising data.

Sangamo will recruit one more patient into this dose cohort, the company’s chief executive, Sandy Macrae, told Vantage. The company does not plan to evaluate higher doses in the study, he added.

A phase III trial should also begin soon, and will be run by Pfizer. Mr Macrae would not confirm whether this would also use 3x1013vg/kg, but did say that both Pfizer and Sangamo were “very happy” with the results being generated from this cohort.

This optimism looks justified based on the data available so far on levels of factor VIII, the clotting factor that is missing in haemophilia A. In the two patients treated with the highest dose who have been followed for the longest, FVIII levels, which had reached normal levels at the April data cut, stayed within the normal range as determined by chromogenic assay.

The two more recently dosed patients also showed a rapid rise in FVIII levels, although only one has reached the normal range so far; however, this patient has only been followed for four weeks.