y These authors contributed equally to this work.Mesenchymal stem cells (MSCs) are being investigated extensively due to their ability to dampen immune responses. Here, we tested the ability of MSCs from three distinct sources to prolong rat corneal allograft survival. A fully allogeneic rat cornea transplant model (DA to LEW) was used. Recipient rats received 1 Â 10 6 MSCs (syn [LEW], allo [DA] or third-party [Wistar Furth]) intravenously 7 days before transplantation and again on the day of transplantation (day 0). A high percentage of untreated and syn-MSC treated allografts were rejected (80% and 100%, respectively). Preactivation of syn-MSCs with interferon gamma also failed to prolong allograft survival. Conversely, corneal allograft survival was significantly prolonged in allo-MSC treated (90%) and third-party MSC treated (80%) allograft recipients. Flow cytometric analysis revealed less infiltrating natural killer T cells in corneas of both allo-and third-party MSC treated animals, coupled with a higher proportion of splenic CD4þFoxp3þ regulatory T cells, compared to controls. In the case of allo-and third-party MSCs, results from a delayed-type hypersensitivity assay clearly showed that hypo-responsiveness was specific for corneal donor-associated alloantigens. Thus, allo-and third-party MSC treatment prolongs corneal allograft survival by suppressing peripheral immune responses and promoting an intragraft immunoregulatory milieu.

Mesenchymal stromal cells (MSCs) have shown promise as a therapy for immune‐mediated disorders, including transplant rejection. Our group previously demonstrated the efficacy of pretransplant, systemic administration of allogeneic but not syngeneic MSCs in a rat cornea transplant model. The aim of this study was to enhance the immunomodulatory capacity of syngeneic MSCs. In vitro, MSCs licensed with TNF‐α/IL‐1β (MSCsTNF‐α/IL‐1β) suppress syngeneic lymphocyte proliferation via NO production. In vivo, when administered post‐transplantation, non‐licensed syngeneic MSCs improved graft survival from 0 to 50% and MSCsTNF‐α/IL‐1β, in an NO‐dependent manner, improved survival to 70%. Improved survival was associated with increased CD4+CD25+ forkhead box P3+ regulatory T (Treg) cells and decreased proinflammatory cytokine expression in the draining lymph node. MSCsTNF‐α/IL‐1β demonstrated a more potent immunomodulatory capacity compared with nonlicensed MSCs, promoting an immune‐regulatory CD11b+B220+ monocyte/macrophage population and significantly expanding Treg cells in the lungs and spleen. Ex vivo, we observed that lung‐derived myeloid cells act as intermediaries of MSC immunomodulatory function. MSC‐conditioned myeloid cells suppressed stimulated lymphocyte proliferation and promoted expansion of Treg cells from naive lymphocytes. This work illustrates how syngeneic MSC therapy can be enhanced by licensing and optimization of timing strategies and further highlights the important role of myeloid cells in mediating MSC immunomodulatory capacity.—Murphy, N., Treacy, O., Lynch, K., Morcos, M., Lohan, P., Howard, L., Fahy, G., Griffin, M. D., Ryan, A. E., Ritter, T. TNF‐α/IL‐1β—licensed mesenchymal stromal cells promote corneal allograft survival via myeloid cell—mediated induction of Foxp3+ regulatory T cells in the lung. FASEB J. 33, 9404–9421 (2019). http://www.fasebj.org

Corneal sutures are a risk factor for infective keratitis irrespective of their site. Suture-related keratitis may progress rapidly to endophthalmitis despite intensive topical antibiotics. Intravitreal antibiotics are indicated when endophthalmitis is present.