Sangamo Therapeutics (SGMO -3.67%) recently thrilled investors with an update for its experimental gene therapy. It looks like SB-525 can help people with a rare bleeding disorder called hemophilia A, but it isn't the only potential new treatment for this condition.

Roche (RHHBY -0.60%) and BioMarin (BMRN -0.50%) have experimental gene therapies of their own aimed at the limited hemophilia population, and they're further along on the development timeline. Let's weigh Sangamo's update with results we've seen from its potential competitors so far.

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What happened

Recently, Sangamo held a conference call to give a long investor presentation that included a few exciting details about SB-525, an experimental therapy that plugs in a working gene for the clotting factor that hemophilia A patients can't produce on their own.

Last August, Sangamo Therapeutics and its collaboration partner, Pfizer (PFE 0.66%), excited the medical community and investors when it reported the fifth patient in an ascending dose study achieved therapeutic clotting factor activity levels. Patients seven and eight received three times as much SB-525 as patient five, which looks like an effective dose to move into a pivotal trial.

As of March 27, patients seven and eight haven't needed any clotting factor replacement infusions for 12 weeks and six weeks, respectively. Sangamo needs to show SB-525 lasts a lot longer, but the company's clearly on the right track with a therapy that might be able to rise above the competition.

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The numbers to beat

Roche recently agreed to acquire Spark Therapeutics for $4.8 billion to get its hands on Spark's approved gene therapy used to treat a rare cause of blindness. The Swiss pharmaceutical and diagnostics giant also received an investigational gene therapy for the treatment of hemophilia, SPK-8011.

Two out of seven patients given the highest dosage of SPK-8011 experienced an immune response that reduced their clotting factor levels to less than 5% of normal. We're still waiting for more data from the highest-dose group, but we know two patients who received half as much SPK-8011 showed clotting factor activity around 12% and 22% of normal that stayed steady through 52 weeks.

BioMarin is advancing a gene therapy, nicknamed ValRox, for the same limited population of hemophilia patients, and it's a bit further along the development timeline than SPK-8011 and miles ahead of Sangamo's SB-525. BioMarin is running a 130-patient phase 3 trial with a dosage that looks like it works early on and keeps working for hemophilia A patients. At the 104-week follow-up, the average patient's clotting factor activity level was within the normal range at 59% and the median was near normal at 46%.

Sangamo might have this one

So far, the proposed dose for Sangamo's candidate from now on looks like it could wipe the floor with Spark's candidate and BioMarin's. Patient seven started showing clotting activity at 150% of normal five weeks after treatment with SB-525 and sustained this level through week 12, the most recent observation.

Patient eight had only been observed twice, but this one is doing pretty good so far. Clotting factor activity burst out of the gate at 50% of normal two weeks after treatment with SB-525, and it reached 100% at week four.

Sangamo, Biomarin, and Roche are all trying to treat hemophilia A patients, but sample populations vary from study to study. Without a head-to-head trial, any comparisons should be taken with a grain of salt. That said, it looks like Sangamo's treatment could be the best one yet.

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Image source: Getty Images.

Beyond hemophilia

Sangamo also presented an early look at the first patient dosed with ST-400, an experimental gene therapy for the treatment of beta thalassemia and sickle cell disease. Unlike SB-525, this candidate uses zinc finger nucleases to snip a gene and restart production of fetal hemoglobin.

The first beta thalassemia patient treated with ST-400 experienced an allergic reaction but recovered without too much trouble. This beta thalassemia patient's total hemoglobin level has remained high enough to avoid transfusions seven weeks after treatment. The company was also encouraged to see fetal hemoglobin rise from around 1% of the total to 31% at week seven.

Looking ahead

Before you get too carried away with excitement for Sangamo, you should understand it's still too early to draw broad conclusions about SB-525, or any conclusions about ST-400. For SB-525, we'll need to see more than two hemophilia patients display normal clotting factor activity for a lot longer than 12 weeks. Of course, a repeat performance with a larger group of patients, without any signs of serious immune responses, could send the stock soaring again.

BioMarin plans on sending an application for ValRox to the FDA in the second half of the year. Meanwhile, Pfizer and Sangamo are still waiting for data so they can begin planning SB-525's pivotal study. By the time the partners get a chance to change the hemophilia treatment landscape, it might not look the same.