Dendritic cells (DCs) represent important mediators at the interface of innate and adaptive immunity. Our research focuses on the immune regulatory phenotype of DCs, which can be induced following stimulation via toll-like receptor ligands such as lipopolysaccharide (LPS). We identified the p38 substrate MAPK-activated protein kinase 2 (MK2) as a potential candidate molecule involved in directing DCs into the regulatory phenotype. As we are interested in enhancing effector T cell functions in the context of DC-based cancer immunotherapy, we investigated the role of MK2 in inflammation and immune regulation mediated by DCs using both conditional MK2 knock-out mice (CD11cCre-MK2fl/fl) and the MK2-specific small molecule kinase inhibitor MK2-I3.

Bone marrow- and tissue-derived murine DCs lacking MK2 activity exhibit an enhanced potential to differentiate TH1 effector cells upon LPS stimulation. MK2-deficient DCs show an altered cytokine profile leading to significantly increased IL-12 along with reduced IL-10 secretion. These observations correlate with higher levels of phosphorylated p38 and a down-modulation of JAK/STAT3 signaling. Accordingly, numbers of IFN-γ producing CD4+ T cells, as well as proliferation and cytotoxicity of CD8+ T cells are elevated as demonstrated in vitro and in vivo using ovalbumin as a model antigen. In a murine experimental autoimmune encephalomyelitis (EAE) model, we saw severely enhanced disease progression in CD11cCre-MK2fl/fl mice compared to wildtype littermate controls. We found clinical EAE manifestation to be mediated via IFN-γ producing cells, as symptoms are abrogated upon administration of an IFN-γ blocking antibody. Finally, we studied effects of MK2 deficiency in DCs on tumor growth in murine transplantable B16 and MC-38 models, showing significantly reduced tumor growth in CD11cCre-MK2fl/fl mice upon DC activation by administration of LPS together with whole tumor cell lysate as compared to wildtype littermate controls. Furthermore, in a model of DC-based immunotherapy, LPS-activated MK2-I3-treated DCs exhibit enhanced capacity to reduce tumor burden after injection into wildtype tumor bearing mice.

Our data contrast the previously described role of MK2 in pro-inflammatory mechanisms of the p38 signaling route and suggest an additional anti-inflammatory feedback function, which might be important in preventing DCs from prolonging excessive inflammation. Taken together, these findings provide novel strategies for the improvement of current DC-based tumor immunotherapy approaches by enhancing TH1-priming capacities of DCs.

Citation Format: Klara Soukup, Angela Halfmann, Fiona Poyer, Thomas Felzmann, Alexander Michael Dohnal. MAPK-activated protein kinase MK2 attenuates TH1 differentiation mediated by dendritic cells – implications for autoimmunity and cancer immunotherapy. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B46.