**3.2 MSC: immunogenic effect and safety for transplantation**

One of the main and most important features of MSC is the low expression of HLA class I, with no expression of HLA class II. Also, MSCs do not appear to express the co-stimulatory molecules CD80 or CD86 required for effector T cell induction [55]. The absence of co-stimulatory molecules implies that any residual engagement of the T cell receptor on Th cells would result in absence of the normal immune response to a particular antigen and contribute to tolerance rather than allogeneic responses. This feature allows the cell to be characterized as hypoimmunogenic, since it does not stimulate the patient's immune system and can be used safely in transplants [113]. As well, MSCs have properties attributed to immune functions, indicating their ability to immunomodulatory activity. Studies indicated that MSCs can regulate immune responses during chronic inflammation through the innate and adaptive immune system, regulating the recruitment and their function [56, 57].
