MMP-2: A novel target for antitumor immune therapy

Abstract

3053 Background: Over the last two decades, a large array of antigens expressed by melanoma cells (MAA) has been identified and used in various immunization strategies to treat cancer patients. However, the therapeutic efficacy of these approaches remains limited. Because MMP-2 (matrix metalloproteinase-2) activity is critical for melanoma progression, this protein represents a unique antigen for vaccine therapy. Methods: Antigen-specific T cell clones were obtained from healthy donors. CD4+ cells were stimulated with overlapping MMP-2 peptides pulsed with irradiated autologous CD4- fraction. After 12 days, MMP-2-specific responses were determined by intracellular staining for cytokines. Specific T cells from positive samples were enriched, using the IFNγ-capture assay (Miltenyi), followed by cloning using limiting dilution. Cytokine production was assessed by ELISA, intracellular staining, or cytometric bead array method. Results: We identified 11 novel CD4 MMP-2-derived epitopes, and showed that the corresponding T cells displayed an inflammatory TH2 profile, i.e., mainly secreting TNF, IL-4 and IL-13 and expressing the TH2-specific transcription factor GATA-3. In contrast, CD4+ T cells that recognize other associated MAAs were typically TH1. MMP-2-specific responses were detected in the CD45RO+/CD62L- T cell memory fraction. Interestingly, naïve T cells primed with active MMP-2 gave rise to TH2 specific cells, while naïve T cells primed with peptides generated IFNγ-secreting specific cells, consistent with a TH1 profile. Accordingly, we showed that the enzymatic activity of MMP-2 inhibited IL-12 secretion by mature DCs, possibly explaining the TH2 skewing of MMP-2-specific T cells. Furthermore, MMP-2 specific TH2 cells were found in at least 18 tumor-infiltrating lymphocyte populations out of the 31 melanoma patients tested. Conclusions: The protease activity of MMP-2 blocks DC maturation, more precisely IL-12 production, which could be responsible for the observed TH2 lineage commitment of MMP-2-specific T cells. These findings open the way to therapeutic strategies skewing these already frequent and diverse MMP-2-specific responses towards a more efficient antitumor TH1 phenotype to treat melanoma patients. No significant financial relationships to disclose.