Background Immunotherapy has significantly improved the outcome of patients with metastatic melanoma. However, there is still an unmet need to develop rational combination therapies for patients who develop resistance after immunotherapy or cross-resistance after prior targeted therapy. In solid tumors, the tumor microenvironment (TME) is a major determinant of anti-tumor immunity and is strongly influenced by the cancer cells.

Methods To investigate the mechanisms of immune evasion and the requirements for a functional T cell response, we performed transcriptomic and metabolomic profiling of previously published murine cross-resistant melanoma models.¹ Detailed characterization of the TME was performed using flow cytometry, single-cell RNA sequencing, and spatial profiling by volumetric immunofluorescence microscopy. Genetic ablation and over-expression experiments were used to assess the contribution of cancer cell-derived factors in remodeling the TME. In addition, our findings were further explored in human immunotherapy datasets.

Results We found that immunotherapy-resistant tumors produce high levels of prostaglandin E2 (PGE2), a bioactive lipid previously implicated in immune evasion.^{2 3} Genetic ablation of PGE2 synthesis increased T cell infiltration and re-sensitized resistant tumors to immunotherapy, leading to long-term tumor control. In these tumors, inflammatory hubs consisting of dendritic cells and other antigen-presenting cells with high antigen presentation capacity and chemokine production were re-established and facilitated local T cell expansion required for anti-tumor immunity. Pharmacological modulation with COX2 inhibitors resulted in partial repolarization of the TME, increased T-cell infiltration, and led to transient tumor control. The rational combination of COX2 inhibitors with DC-enhancing agents achieved long-term tumor control.

Conclusions Our work provides a mechanistic understanding of how cancer cells orchestrate an immune-evasive TME that lacks inflammatory hubs required for T cell expansion at the tumor and offers clinically relevant combination therapies to extend the durable benefit of immunotherapy to a larger number of patients.

References

1. Haas L, Elewaut A, Gerard CL. Acquired resistance to anti-MAPK targeted therapy confers an immune-evasive tumor microenvironment and cross-resistance to immunotherapy in melanoma. Nat Cancer. 2021;2:693–708.

2. Böttcher JP, Bonavita E, Chakravarty P. NK cells stimulate recruitment of cDC1 into the tumor microenvironment promoting cancer immune control. Cell. 2018;172:1022–37.

3. Zelenay S, van der Veen AG, Böttcher JP. Cyclooxygenase-dependent tumor growth through evasion of immunity. Cell. 2015;162:1257–70.

Ethics Approval All experiments using animals were performed in accordance with our protocol approved by the Austrian Ministry, protocol number: GZ:MA58–2260492-2022–22.