The present disclosure describes immunosuppressive mesenchymal stromal cells and exosomes secreted from immunosuppressive mesenchymal stromal cells, and methods for their preparation. The disclosure also describes methods for treating subjects or preventing subjects at risk for conditions by administering the immunosuppressive mesenchymal stromal cells or secreted exosomes. The present disclosure also describes kits for preparing immunosuppressive mesenchymal stromal cells and exosomes secreted from immunosuppressive mesenchymal stromal cells.