Acceleron Pharma (XLRN) - Get Report and Celgene (CELG) - Get Report are enrolling patients with low-risk myelodysplastic syndrome into a phase III study to determine if an experimental medicine, luspatercept, can increase the production of red blood cells so that transfusions are no longer needed.

While the phase III study progresses, Acceleron is searching for different populations of MDS patients where luspatercept might also be effective.

On Sunday, the company reported promising but early data from one such group of low-risk MDS patients: Those who not been treated previously with anti-anemia drugs like Amgen's (AMGN) - Get Report Epogen or Johnson & Johnson's (JNJ) - Get Report Procrit.

Following treatment with luspatercept, hemoglobin levels in these patients increased enough to obviate the need for red blood cell transfusions.

Acceleron estimates Amgen and J&J sell approximately $600 million of their anti-anemia drugs in the U.S. targeted at treating this specific group of MDS patients. These patients are not included in the ongoing luspatercept phase III study enrolling MDS patients who no longer respond to anti-anemia drugs. 

If luspatercept can demonstrate superiority over Epogen and Procrit in this MDS patient group, Acceleron and Celgene could capture a significant, additional commercial revenue opportunity for their drug.

Myelodysplastic syndrome (MDS) is a cancer-like disease in which the bone marrow is incapable of producing sufficient and healthy blood cells. Severe anemia is a problem for MDS patients, so erythropoietin-stimulating agents (ESAs) -- the aforementioned Epogen and Procrit -- are often prescribed to boost the production of early-stage red blood cells.

Acceleron's luspatercept is also targeted at treating anemia but in a different way from ESAs. The drug works differently by increasing the production and maturation of late-stage red blood cells.

As part of a phase II study, Acceleron enrolled 20 patients with low-risk MDS who would normally be eligible for ESAs but were treated with luspatercept instead.

Twelve of 20 patients, or 60%, treated with luspatercept for three months had a positive red blood cell response, Acceleron reported Sunday.

Among the 20 MDS patients, 12 were so anemic they required red blood cell transfusions. Nine of 12 (75%) of these patients treated with luspatercept for three months became transfusion independent.

These new luspatercept data were presented in a poster at the American Society of Hematology annual meeting being held in San Diego.

"The patient numbers are small but we're encouraged by these new luspatercept data because it suggests the drug could be superior to ESAs," said Acceleron Chief Operating Officer Steve Ertel.

There is no direct comparison of luspatercept and ESAs in this group of MDS patients, but Ertel points to previously presented study results from Amgen and J&J showing red blood cell response rates of 14% and 32%, respectively.

From this perspective, the luspatercept 60% response rate looks promising, although the small number of patients treated is a risk.

Based on these data, Acceleron and Celgene are moving ahead to further develop luspatercept a potential replacement for ESAs in low-risk, treatment-naive MDS patients. The companies are also exploring potential uses for luspatercept and a sister drug sotatercept in myelofibrosis, another blood disease.

Accleron and Celgene continue to enroll MDS and beta-thalassemia patients into two phase III studies but the companies are not providing guidance on when the studies will be fully enrolled or completed.

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.