Background/Purpose:

Use of mesenchymal/multipotent stem cells (MSCs/MAPCs) is an emerging immune modulatory therapeutic strategy promising for a number of human diseases. Multipotent adult progenitor cells (MAPC) are adherent cells isolated from adult bone marrow and have strong anti-inflammatory and immunomodulatory properties. MultiStem®, a cGMP manufactured MAPC product, is in Phase II clinical use for treatment of ischemic strokeand ulcerative colitis. We are interested in treating new onset Rheumatoid Arthritis (RA) patients with MAPC to induce immune regulation and tolerance. In the present study our goal was to demonstrate the potential for of MAPC-based therapy in new onset RA. To that end, we characterized the effect of MAPC conditioned media on RA effector T-cell (Teff) and T-regulatory (Treg) function ex vivo. We hypothesized that Treg function and number might improve following treatment with MAPC conditioned media. We evaluated RA Teff function in the presence of cytokine stimulated conditioned media (CCM) that was generated following co-culture with MAPC.

 Methods:

Active sero-positive RA subjects (RF+ or CCP+) with DAS28 scores varying from 4.5-5.8 were recruited. Teff and Treg were obtained (flow sorted) from seropositive RA patients off therapy, and 6 weeks after start of therapy with methotrexate. Treg were CD4+CD25^hi cells and Teff were CD4+CD25 ^low.  To measure the effect of conditioned MAPC media and Treg on Teff responses, suppression assays were performed; RA and healthy donor (HD) Teff were incubated with CCM with or without Treg and proliferation was measured at 5- 6 days by dye dilution method and flow cytometry.  The dilution of CCM to growth media (GM) ranged from a high of 7/8 to a low of 1/8 (GM is media prior to addition of cytokines or culture with MAPC).

 Results:

Cytokine stimulated MAPC conditioned media (CCM) alone suppressed Teff proliferation in a dose dependent fashion. Maximal suppression by CCM was observed with 7/8 CCM/GM and ranged from 48 to 80% (median 57%) suppression. Treg also suppressed Teff in a dose dependent fashion; 50% suppression of Teff proliferation was observed with Treg (no CCM) at a Treg:Teff ratio of 1:1. Combining Tregs (1:1 Treg:Teff) and CCM (CCM:GM 1:1) led to 86% suppression of Teff.  Dose dependent suppression was observed with varying Treg numbers and/or CCM dilution. The possibility that Treg proliferation occurred was excluded by stimulating Treg alone with beads, and measuring proliferation as described for Teff.

 Conclusion:

Potent suppression of RA Teff by combining MAPC conditioned media and Treg is demonstrated. This strongly suggests that MAPC will offer therapeutic value in RA and may act in synergy with Treg. To what extent MAPC therapeutic effects in vivoare mediated by increases in Treg number and/or function is an open question. Studies testing MAPC therapeutically in RA should be accompanied by studies to understand mechanism.

 This publication was made possible by the Clinical and Translational Science Collaborative of Cleveland, UL1TR000439 from the National Center for Advancing Translational Sciences (NCATS) component of the National Institutes of Health and NIH roadmap for Medical Research.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ex-vivo-suppression-of-ra-effector-t-cells-teff-by-mapc-media-is-synergistic-with-treg/