Ganglioside-exposed dendritic cells inhibit T-cell effector function by promoting regulatory cell activity

Tumour pathogenesis is characterized by an immunosuppressive microenvironment that limits the development of effective tumour‐specific immune responses. This is in part the result of tumour‐dependent recruitment and activation of regulatory cells, such as myeloid‐derived suppressor cells and regulatory T cells in the tumour microenvironment and draining lymph nodes. Shedding of gangliosides by tumour cells has immunomodulatory properties, suggesting that gangliosides may be a critical factor in initiating an immunosuppressive microenvironment. To better define the immunomodulatory properties of gangliosides on antigen‐specific T‐cell activation and development we have developed an in vitro system using ganglioside‐treated murine bone‐marrow‐derived dendritic cells to prime and activate antigen‐specific CD4⁺ T cells from AND T‐cell receptor transgenic mice. Using this system, ganglioside treatment promotes the development of a dendritic cell population characterized by decreased CD86 (B7‐2) expression, and decreased interleukin‐12 and interleukin‐6 production. When these cells are used as antigen‐presenting cells, CD4 T cells are primed to proliferate normally, but have a defect in T helper (Th) effector cell development. This defect in Th effector cell responses is associated with the development of regulatory T‐cell activity that can suppress the activation of previously primed Th effector cells in a contact‐dependent manner. In total, these data suggest that ganglioside‐exposed dendritic cells promote regulatory T‐cell activity that may have long‐lasting effects on the development of tumour‐specific immune responses.