Rheumatoid Arthritis New Major Clinical Target After Mesoblast Obtains Positive Results In Inflammatory Arthritis

Severe joint synovial inflammation with cartilage loss and bony erosions, characteristic of human RA, occurs in sheep injected with collagen. In a pilot study, significant numbers of allogeneic MPCs were detected in involved joints or lymph nodes of arthritic sheep at 24 hours after a single intravenous injection, but not in normal sheep, indicating that MPCs selectively migrate to sites of immune-mediated inflammation.

A randomized, placebo-controlled study was next performed in 30 sheep with established collagen-induced arthritis, comparing a single intravenous injection of allogeneic MPCs at one of three doses (0.3, 1 and 2 million MPCs/kg) to saline. Thirty days later, joint synovial tissues from arthritic sheep were examined. In comparison with saline treated controls, synovial tissue from arthritic sheep receiving a single intravenous injection of 2 million MPCs/kg showed 88% mean reduction in IL-6 levels (p=0.029), 83% mean reduction in TNF-alpha levels (p=0.049), 53% mean reduction in IL-17 levels (p=0.005), and 52% mean reduction in infiltrating monocytes/macrophages (p=0.009). MPC-treated animals had a 31% mean reduction in histopathology severity scores compared with controls (p=0.025). Intermediate effects were seen with 1 million MPCs/kg, and the lowest MPC dose was least effective.

These findings demonstrate that MPCs are immunoregulatory and concomitantly suppress the activation and proliferation of T-cells, monocytes, and synoviocytes seen in active Rheumatoid Arthritis. Mechanistically, the data suggest that MPCs inhibit the Th17 CD4 T cell subset, with the subsequent simultaneous reduction in the key cytokines, IL-17, IL-6, and TNF-alpha. Mesoblast has an upcoming scheduled meeting with the United States Food and Drug Administration (FDA) to discuss its Phase 2 clinical program in patients with RA. Subject to FDA clearance, the Company intends to commence a randomized, placebo-controlled Phase 2 trial in the fourth quarter of 2012. "Rheumatoid Arthritis represents the second indication, after Type 2 diabetes, in a growing list of major market segments that will be targeted by Mesoblast's intravenous product formulation," Professor Itescu added.

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