MADRID (FRONTLINE MEDICAL NEWS) – A single injection of allogeneic mesenchymal precursor cells was apparently both safe and effective for relieving some symptoms of rheumatoid arthritis in biological-refractory patients in a phase II randomized trial with 48 patients.

Most of the efficacy measures ran out to 12 weeks, but researchers followed one measure, the American College of Rheumatology N ( ACR-N ) index of improvement, out to 39 weeks after a single infusion, and this measure showed a statistically significant, durable benefit from the higher tested dose of mesenchymal precursor cells (MPC) when compared with placebo, Suzanne Kafaja, MD , said while presenting a poster at the European Congress of Rheumatology.

For safety, follow-up observations found no infusion reaction and similar rates of treatment-related adverse effects, compared with placebo, throughout follow-up, said Dr. Kafaja, a rheumatologist at the University of California, Los Angeles.

“The trial met its primary endpoints, and so far the data look pretty encouraging, but it’s still pretty early,” she said.

“I was surprised by the durability” of the anti-inflammatory effect of the MPC at 39 weeks, Dr. Kafaja added in an interview.

The study , run at 16 U.S. centers and 2 sites in Australia, enrolled 48 patients with rheumatoid arthritis and on a stable methotrexate regimen for at least 4 months who had a history of failing to adequately respond to at least one biological disease-modifying drug, most commonly a tumor necrosis factor inhibitor. The average age of the enrolled patients was 55 years; nearly three-quarters were women. The patients had been diagnosed with rheumatoid arthritis for an average of 13 years, and more than one-third of the patients had a history of inadequate response to three or more biological agents.

Thirty-six of the patients received a single infusion of a preparation of MPC taken from the bone marrow of healthy donors and isolated and expanded ex vivo. Half the patients in the active-treatment group received 1 million MPC per kg, and the other half received 2 million MPC per kg. An additional 16 patients received placebo. The researchers obtained the MPC from Mesoblast Limited, an Australia-based company that sponsored the study and uses a proprietary method for MPC processing to produce an “off-the-shelf” product.

The allogeneic MPC used in the study is a homogeneous population of cells that respond to pro-inflammatory cytokines by releasing cytokines of their own that induce monocytes and T-cells into an anti-inflammatory state.

The treatment groups showed no difference, compared with the placebo group, for the ACR20, ACR50, and ACR70 measurements, but for two other measures, the Health Assessment Questionnaire and the 28-joint Disease Activity Score, the results showed trends toward dose-related improvements following MPC treatment. The results showed statistically significant improvements after 12 and 39 weeks in average ACR-N in the patients who received 2 million MPC per kg. After 39 weeks, the average ACR-N improvement rate was about 35% among patients who had received 2 million MPC per kg, about 10% among those who received 1 million cells per kg, and about 8% among placebo patients, Dr. Kafaja reported .

Mesoblast funded the study. Dr. Kafaja had no other disclosures.

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