Stem cell secretome attenuates acute rejection in rat lung allotransplant

OBJECTIVES Stem cells secrete significant amounts of bioactive factors in their secretome that can be immunosuppressive. We studied the effect of the secretome obtained from bone marrow-derived mesenchymal stem cells (BMSC-sec) in combination with cyclosporine A following acute rejection of lung allografts in the rat. METHODS Lung allotransplants were performed from male Brown Norway donor rats to recipient male Fisher 344 rats. Rat BMSC-sec was introduced intratracheally in the recipient every day after the transplant until the day the animal was sacrificed. Group A (n = 5) received control medium and cyclosporine A (2.5 mg/kg body weight intraperitoneally) for 5 days post-transplant and group B (n = 5) received BMSC-sec and cyclosporine A. Blood gas analysis was performed to assess graft function at day 5 only from the graft, and the tissue was sampled for measurement of the wet/dry ratio and histological grading of rejection. RESULTS All control animals (group A) showed severe signs of rejection. At day 5 grafts in group B showed improved gas exchange (i.e. mean PaO2 mmHg 237.9 ± 130 mmHg vs 24.9 ± 7.8 mmHg in group A). Histological examination according to the International Society of Heart and Lung Transplantation (ISHLT) revealed moderate to severe rejection in all animals in group A (III B) and a significant improvement in group B (I-IIA). The wet/dry ratio was also reduced in group B to 6.19 ± 0.6 compared to 9.36 ± 2 in group A. Furthermore, in vitro T-cell proliferation was reduced after treatment with BMSC-sec for CD 3 cells (69.55 ± 07 vs 73 ± 0.84), for CD 4 (24.95 ± 1.2 vs 27.75 ± 0.21) and for CD 8 cells (3.75 ± 0.2 vs 5.68 ± 0.02). CONCLUSIONS The BMSC-sec is a promising novel cell-based therapeutic option for acute rejection in a rat lung allograft model.