Mesenchymal stromal cells promote B-cell lymphoma in lacrimal glands by inducing immunosuppressive microenvironment

Mesenchymal stromal cells (MSCs) have therapeutic potential for various diseases because of their anti-inflammatory and immunosuppressive properties. However, the immunosuppressive microenvironment allows tumor cells to evade immune surveillance, whereas maintenance of inflammation is required for tumor development and progression. Hence, MSCs may promote or suppress tumors in a context-dependent manner. We here investigated the effects of bone marrow-derived MSCs in a murine model of lacrimal gland B-cell lymphoma. Co-injection of MSCs with B lymphoma cells enhanced tumor growth in lacrimal glands without long-term engraftment. Of note, MSCs induced greater infiltration of immune and immune-regulatory cells near tumor: CD4⁺ cells, CD11b⁺ cells, CD4⁺Foxp3⁺ regulatory T cells and CD11b⁺Ly6C⁺Ly6G^- myeloid-derived suppressor cells. Concurrently, there was up-regulation of immune-related molecules including TNF-α, IL-1β, TGF-β1, and arginase in glands treated with MSCs. Apoptosis in tumor was less severe in mice treated with MSCs compared to those without MSCs; however, MSCs did not directly inhibit apoptosis of B lymphoma cells in an in vitro co-culture. Together, data demonstrate that MSCs create immunosuppressive milieu by recruiting regulatory immune cells and promote B-cell lymphoma growth in lacrimal glands.