The Untold Story of TIMP-1 and How it Relays Immunogenicity in Melanoma

How do dendritic cells (DCs) communicate and coordinate antigen presentation and activation across a heterogeneous tumor microenvironment (TME), particularly when some tumor regions are heavily immunosuppressed? Given the complex landscape of tumors, where different areas can either inhibit or enable immune responses, understanding this coordination is crucial for overcoming localized immunosuppression and ensuring effective immune activation. This question led us to a groundbreaking discovery about the role of TIMP-1 in providing tumor "immunogenicity relay", a term we coined to describe one of the mechanisms by which dendritic cells (DCs) sustain cross-presentation. This finding could open a new research field, potentially enhancing our understanding of cancer immunity.

The Beginning of Our Journey

The story began with our literature reviews on new molecules that could impact melanoma immunity, bringing attention to TIMP-1 and its role in melanoma. Traditionally known as a metalloproteinase inhibitor, TIMP-1 has been shown to inhibit tumorigenesis and metastasis by blocking the matrix-degrading properties of endopeptidases. However, contradictory evidence suggested its overexpression was linked to tumor progression, anti-apoptosis, and pro-angiogenesis. This paradox led us to hypothesize that TIMP-1 might play a role in antitumor immunity, particularly for more advanced tumors that are the ones harnessing higher antitumor immune responses.

Initial Hypotheses and Explorations

To test this hypothesis, our group, the Medical Immuno-Oncology Research Group (MIORG), implements the reverse translational approach by analyzing existing public and internal human cancer datasets. We began by examining the GDC-TCGA cutaneous melanoma study to investigate the relationship between TIMP1 mRNA levels, patient survival, and immune infiltrating markers. Our findings revealed that higher TIMP1 transcript levels were associated with better survival outcomes and more immunogenic tumors, as evidenced by increased intratumoral CD8A levels. Notably, these associations were even stronger with HLA family molecules, which are involved in antigen presentation. These preliminary results suggested a potential link between TIMP-1 and tumor immunogenicity. However, we questioned whether these associations were merely coincidental with inflamed tumors or if TIMP-1 might specifically play a role in antigen presentation, leading to higher CD8 T cell infiltrations.

From Hypothesis to Research Project

Though not initially a primary focus of MIORG projects, the intriguing potential of TIMP-1 in melanoma's immunogenicity inspired us to incorporate this study into our research pipeline. We hypothesized that TIMP-1, primarily expressed as a secreted protein, could play a role in activating tumor immunity through autocrine and paracrine mechanisms within the TME, potentially interfering with targets and pathways being investigated in our ongoing projects.

Through cellular databases, we observed that TIMP1 is expressed in immune cells, particularly myeloid dendritic cells (DCs) and CD4 T cells. We further observed that at the protein level, TIMP-1 is also secreted by both DCs and T cells, with increasing levels under stimulatory conditions, suggesting a role in immune activation. This led us to test the potential role of TIMP-1 in activating immune cells using well-established functional studies.

In parallel, our ongoing study using state-of-the-art spatial transcriptomics of a new national melanoma cohort not only validated the GDC-TCGA findings but revealed that higher TIMP1 expression correlating with increased CD8A levels happens only when TIMP1 is highly expressed in the immune segments of tumor biopsies. This validation in combination with the knowledge that TIMP-1 is secreted by myeloid DCs suggested that TIMP-1 might have a role in the generation and/or activation of CD8 T cells.

Cross-Tissue Analysis and Mechanistic Insights

Using our national melanoma cohort, we conducted cross-tissue analyses comparing melanoma and skin biopsies with matched lymph node samples. The results showed that high TIMP-1 levels in the skin were associated with upregulated antigen presentation pathways in the lymph nodes, particularly those linked with peptide loading to MHC class I (MHC-I).

Coincidently, our wet lab functional screening was already pointing out that soluble TIMP-1 does not have a significant effect on tumor cell biology, nor on the activation of macrophages, CD4 or CD8 T cells, but it significantly upregulates the expression of MHC surface molecules on myeloid DCs. Later, functional studies demonstrated that MHC-I surface upregulation on primary myeloid DCs in response to TIMP-1 enhances T cell clonal expansion and activation. Preliminary mechanistic studies indicated that TIMP-1 might improve antigen processing through the immunoproteasome.

Conclusion and Future Directions

Our research highlights the significance of TIMP-1 as a potential player in a mechanism by which myeloid dendritic cells seek for auto sufficiency in antigen presentation (autocrine function) but also with the potential to support and amplify antigen presentation in neighboring DCs (paracrine functions), creating an "immunogenicity relay" in the TME. We regard this mechanism as a new perspective on how DCs maintain antigen presentation and T cell activation despite the tumor's attempt to suppress these processes in the TME. This study opens a new field of research focusing on tumor factors that potentially suppress molecules like TIMP-1, impairing the intrinsic ability of DCs to autocrinely and paracrinely activate surrounding myeloid DCs.

Uncovering the regulation of immunogenicity relay processes in cancer, not only involving TIMP-1 but potentially other molecular partners, will open a new field for immuno-oncology . Developing therapies that inhibit regulators of immunogenicity relay displayed by TIMP-1, or strategies that upregulate its functions can significantly enhance the efficacy of immune checkpoint therapies, which depend on increased levels of antitumor CD8 T cells in the TME.

This research not only advances our understanding of TIMP-1 in tumor immunity but also sets new grounds for innovative approaches to cancer immunotherapy, potentially improving outcomes for patients with cold tumor features.

Reference: Langguth M# and Maranou E# et al. TIMP-1 is an activator of MHC-I expression in myeloid dendritic cells with implications for tumor immunogenicity. Genes Immun. 2024 May 22. doi: 10.1038/s41435-024-00274-7.