Successful anti-tumor immunotherapeutic approaches are improving survival in many malignancies but not all patients respond to these interventions, and several also relapse. This may result from an immunosuppressive tumor microenvironment (TME) that contributes towards tumor growth and metastasis. Besides tumor cells, the TME is comprised of immune cells such as dendritic cells (DCs) and T cells, as well as non-immune cells like the cells of the extra-cellular matrix (ECM) and stromal cells that provide an anchor for the tumor. Factors that can modulate the TME to help promote tumors are a primary impediment to all anti-cancer treatments. One such protein, the matrixmetalloproteinase-2 (MMP-2) is of particular importance as it is produced by the multiple constituents of the TME including the tumor cells. Furthermore, the increased MMP-2 presence on tumor cells is thought to cause faster tumor growth and poorer survival rates in patients. Clinical trials using drugs that directly targeted MMPs have yielded disappointing results suggesting that a more global understanding of the TME is required.
Our lab has recently identified two mechanisms by which MMP-2 subverts DC function, resulting in the skewing of adaptive immune response towards a pro-tumorigenic TH2 phenotype by inducing OX40L on DCs and limiting IL-12 production. Activated DCs produce IL-12p35 through IFNAR1 and STAT1 signaling. DCs secrete high levels of IL-12p70 necessary for priming naïve CD4+ T cells into TH1 cells. We found that in the context of melanoma, tumor and stroma produce and activate MMP-2. Active MMP-2 degrades IFNAR1 on DCs, leading to low levels of STAT1 phosphorylation preventing transcription of IL-12p35. Furthermore, MMP-2 induces OX40L over-expression on the surface of DCs through triggering of TLR2 and possibly TLR4 (in mice). Both lack of IL-12p70 and OX40L overexpression by MMP- 2-exposed DCs are responsible for priming naïve CD4+ T cells into inflammatory TH2 cells .
The importance of endogenous alarmins as key drivers of tumorigenisis is becoming increasingly evident. Our preliminary data indicates that melanoma cells express functionally responsive TLR-2 and secrete active MMP-2 which could impact tumor growth through cis and trans mechanisms. Mansi’s project aims at further characterizing the MMP-2-TLR-2 signaling axis on human DCs and human melanoma cells to test the hypothesis that MMP-2 driven TLR-2 stimulation alters the cellular transcription machinery in DCs and melanoma cells to promote a TH2 skewed TME that supports melanoma progression. These studies will lead to a greater appreciation of TME immunoregulatory mechanisms and identify targets for inhibition.
Luciana’s project focuses on studying the TME in the context of melanoma. We are particularly curious about the cross talk between immune cells and tumor cells and how matrix metalloproteinase 2 (MMP-2) that we have described to be produced within the TME, signals via Toll-like receptors (TLRs) to impact the TME and skew T cells towards a pro-tumorigenic T helper 2 (TH2) phenotype. We combine in vitro approaches with mouse models of melanoma to dissect the signaling mechanisms by which MMP-2 promotes tumor establishment and growth. Specifically, we have been characterizing MMP-2’s TH2 skewing role in vivo and ex vivo and also the effects of intra-tumor injections of MMP-2 in the establishment and growth of melanomas in WT and TLR deficient mice. Luciana is further dissecting the role of tumor versus stromal cell derived MMP-2 in melanoma in vivo.