NEW YORK ( TheStreet) -- An experimental stem-cell therapy developed by Brainstorm Therapeutics (BCLI) - Get Report continues to demonstrate early but encouraging activity in patients with amyotrophic lateral sclerosis (ALS), the degenerative and fatal nerve disease which has stymied drug developers for years.

Brainstorm shares are down over 20% to about $6 Monday but that's more of an expected, sell-on-the-news reaction than a negative referendum on the updated, final results from the NurOwn phase IIa study. Brainstorm's stock price more than doubled in the previous eight trading days, so profit taking on today's data announcement isn't surprising at all.

I last wrote about Brainstorm in October. The company's experimental NurOwn stem-cell therapy starts with the harvesting of bone marrow from each ALS patient. Mesenchymal stem cells are isolated from the bone marrow sample and sent to a lab, where a proprietary Brainstorm process first expands their numbers and then transforms them into specialized cells secreting nerve growth factors. After the function and potency of the NurOwn cells are confirmed, the "drug" is delivered back into the ALS patient via injections into muscle and the spine.

Once injected, the NurOwn stem cells bathe the damaged neurons of ALS patients with secretions of nerve growth factors. Brainstorm has a home run on its hands if NurOwn can be shown to slow or halt the progressive destruction of neurons, and if that disease-modifying effect translates into improved muscle function for ALS patients.

Monday's update comes from a Phase IIa trial in which 14 ALS patients were followed for the three months without treatment. At month four, each patient was transplanted with their own personalized NurOwn therapy and then assessed every month for six months. Brainstorm evaluated NurOwn's impact on ALS disease progression using the ALSFRS score, a commonly used assessment of treatment response and muscle function in ALS patients. Lung function, another commonly used measure of efficacy in ALS clinical trials, was also measured.

Twelve ALS patients were evaluable for response. Of these, 11 patients showed a slowing of ALS disease progression at six months compared to baseline, measured either by improved ALSFRS or lung function scores, Brainstorm said. Two other patients enrolled in the study died. Administration of the NurOwn therapy was well tolerated by patients, the company said.

The final Phase IIa data announced Monday were a small improvement over interim results from the same study presented last June. Further, detailed data from the study will be presented at a medical meeting later this year. For perspective purposes, it's important to note that this phase IIa study enrolled a relatively small number of ALS patients and was conducted at a single hospital in Israel. This doesn't necessarily discredit the positive results, but conclusions about NurOwn's ultimate benefit as an ALS therapy can't be drawn until data from larger studies are gathered.

Brainstorm is conducting another, larger Phase II study in the U.S., enrolling 48 ALS patients who will be randomized 3:1 to receive a single NurOwn treatment in the muscle and spine, or a placebo treatment. The study is being conducted at two hospitals in Massachusetts, UMass Medical Center and Massachusetts General, and the Minnesota-based Mayo Clinic. The study's primary endpoint is the safety and tolerability of NurOwn, but investigators will also assess ALS patients for efficacy using measures of ALS disease activity and muscle function. The first patient was enrolled into the Phase II study last June and Brainstorm expects results to be ready in the first half of 2016.

The company is also in the planning stages for another Phase II study in which ALS patients will be treated with multiple doses of NurOwn.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

click here

to send him an email.