Using spontaneous, slow-growing, transgenic tg(Grm1)EPv melanoma tumor model, Prokopi et al. showed upregulation of immunosuppressive molecules (PD-L1 and Galectin-9) and downregulation of the cDC2 (conventional dendritic cell) population during melanoma progression. A DC boost therapy (Flt3L plus polyI:C/agonist-CD40) increased activated cDC1 and cDC2 populations in tumors and lymph nodes, and increased recruitment and priming of gp100-specific CD8+ T cells in tumor-draining lymph nodes. In combination with anti-PD-1 and anti-TIM3 mAbs, DC boost therapy increased T cell cytotoxicity, delayed tumor growth, and extended survival.
Contributed by Shishir Pant
BACKGROUND: Immunotherapy with checkpoint inhibitors has shown impressive results in patients with melanoma, but still many do not benefit from this line of treatment. A lack of tumor-infiltrating T cells is a common reason for therapy failure but also a loss of intratumoral dendritic cells (DCs) has been described.
Methods: We used the transgenic tg(Grm1)EPv melanoma mouse strain that develops spontaneous, slow-growing tumors to perform immunological analysis during tumor progression. With flow cytometry, the frequencies of DCs and T cells at different tumor stages and the expression of the inhibitory molecules programmed cell death protein-1 (PD-1) and T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) on T cells were analyzed. This was complemented with RNA-sequencing (RNA-seq) and real-time quantitative PCR (RT-qPCR) analysis to investigate the immune status of the tumors. To boost DC numbers and function, we administered Fms-related tyrosine 3 ligand (Flt3L) plus an adjuvant mix of polyI:C and anti-CD40. To enhance T cell function, we tested several checkpoint blockade antibodies. Immunological alterations were characterized in tumor and tumor-draining lymph nodes (LNs) by flow cytometry, CyTOF, microarray and RT-qPCR to understand how immune cells can control tumor growth. The specific role of migratory skin DCs was investigated by coculture of sorted DC subsets with melanoma-specific CD8+ T cells.
Results: Our study revealed that tumor progression is characterized by upregulation of checkpoint molecules and a gradual loss of the dermal conventional DC (cDC) 2 subset. Monotherapy with checkpoint blockade could not restore antitumor immunity, whereas boosting DC numbers and activation increased tumor immunogenicity. This was reflected by higher numbers of activated cDC1 and cDC2 as well as CD4+ and CD8+ T cells in treated tumors. At the same time, the DC boost approach reinforced migratory dermal DC subsets to prime gp100-specific CD8+ T cells in tumor-draining LNs that expressed PD-1/TIM-3 and produced interferon γ (IFNγ)/tumor necrosis factor α (TNFα). As a consequence, the combination of the DC boost with antibodies against PD-1 and TIM-3 released the brake from T cells, leading to improved function within the tumors and delayed tumor growth.
Conclusions: Our results set forth the importance of skin DC in cancer immunotherapy, and demonstrates that restoring DC function is key to enhancing tumor immunogenicity and subsequently responsiveness to checkpoint blockade therapy.
Author Info: (1) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (2) Department of Dermatology, Venereology & Allergology, Medical Uni
Author Info: (1) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (2) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (3) Department of Immunology, St. Jude Children's Research Hospital, Memphis, Tennessee, USA. (4) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (5) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (6) Department of Immunology, St. Jude Children's Research Hospital, Memphis, Tennessee, USA. (7) Department of Micobiology & Immunology, Stanford University School of Medicine, Stanford, California, USA. (8) Institute of Bioinformatics, Medical University of Innsbruck, Innsbruck, Austria. (9) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (10) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (11) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (12) Center of Integrated Protein Science Munich (CIPS-M) and Division of Clinical Pharmacology, Department of Medicine IV, Klinikum der Universitt Mnchen, LMU Munich, Germany. Member of the German Center for Lung Research (DZL), Munich, Germany. (13) Center of Integrated Protein Science Munich (CIPS-M) and Division of Clinical Pharmacology, Department of Medicine IV, Klinikum der Universitt Mnchen, LMU Munich, Germany. Member of the German Center for Lung Research (DZL), Munich, Germany. German Center for Translational Cancer Research (DKTK), partner site Munich, Munich, Germany. (14) Bioceros BV, Utrecht, The Netherlands. (15) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria. (16) Institute of Bioinformatics, Medical University of Innsbruck, Innsbruck, Austria. (17) Ernest Mario School of Pharmacy and Rutgers Cancer Institute, Rutgers University, New Brunswick, New Jersey, USA. (18) Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, Amsterdam, The Netherlands. (19) Department of Micobiology & Immunology, Stanford University School of Medicine, Stanford, California, USA. (20) Department of Immunology, St. Jude Children's Research Hospital, Memphis, Tennessee, USA. (21) Department of Dermatology, Venereology & Allergology, Medical University of Innsbruck, Innsbruck, Austria patrizia.stoitzner@i-med.ac.at.
