Stress immunity in lymphomas: mesenchymal cells as a target of therapy.

The role of lymphocytes in eliminating lymphoma cells is based on the interaction between activating receptors on lymphocytes and target surface ligands on lymphoma cells. Stress-related immunity can be triggered both in Hodgkin's (HL) and non-Hodgkin lymphomas (NHL), through the activation of the NKG2D receptor on CD8+ T and gammadelta T lymphocytes, by NKG2D-ligands (NKG2D-L), as the MHC class-I related molecules MIC-A/B and the UL16-binding proteins 1-4 (ULBPs), expressed on lymphoma cells. Furthermore, NKG2D-L can be shed and interact with NKG2D on effector lymphocytes affecting the recognition of lymphoma cells. Proteolytic cleavage of MIC-A is known to depend on the thiol isomerase ERp5 and the disintegrins and metalloproteinases ADAM10 and ADAM17, which also cleave ULPBs. Mesenchymal stromal cells (MSC) are relevant in regulating effector T lymphocytes-mediated lymphoma surveillance. Indeed, MSC can be seen as targets of potential new therapeutic schemes acting on lymphoma microenvironment, to redirect the stress immune response and avoid escape strategies, by inducing stress molecules, inhibiting sheddase activity, shifting cytokine production to Th1 pattern and blocking Treg differentiation.