title: Agonist anti-GITR monoclonal antibody induces melanoma tumor immunity in mice by altering regulatory T cell stability and intra-tumor accumulation.
abstract: In vivo GITR ligation has previously been shown to augment T-cell-mediated anti-tumor immunity, yet the underlying mechanisms of this activity, particularly its in vivo effects on CD4+ foxp3+ regulatory T cells (Tregs), have not been fully elucidated. In order to translate this immunotherapeutic approach to the clinic it is important gain better understanding of its mechanism(s) of action. Utilizing the agonist anti-GITR monoclonal antibody DTA-1, we found that in vivo GITR ligation modulates regulatory T cells (Tregs) directly during induction of melanoma tumor immunity. As a monotherapy, DTA-1 induced regression of small established B16 melanoma tumors. Although DTA-1 did not alter systemic Treg frequencies nor abrogate the intrinsic suppressive activity of Tregs within the tumor-draining lymph node, intra-tumor Treg accumulation was significantly impaired. This resulted in a greater Teff:Treg ratio and enhanced tumor-specific CD8+ T-cell activity. The decreased intra-tumor Treg accumulation was due both to impaired infiltration, coupled with DTA-1-induced loss of foxp3 expression in intra-tumor Tregs. Histological analysis of B16 tumors grown in Foxp3-GFP mice showed that the majority of GFP+ cells had lost Foxp3 expression. These "unstable" Tregs were absent in IgG-treated tumors and in DTA-1 treated TDLN, demonstrating a tumor-specific effect. Impairment of Treg infiltration was lost if Tregs were GITR(-/-), and the protective effects of DTA-1 were reduced in reconstituted RAG1(-/-) mice if either the Treg or Teff subset were GITR-negative and absent if both were negative. Our results demonstrate that DTA-1 modulates both Teffs and Tregs during effective tumor treatment. The data suggest that DTA-1 prevents intra-tumor Treg accumulation by altering their stability, and as a result of the loss of foxp3 expression, may modify their intra-tumor suppressive capacity. These findings provide further support for the continued development of agonist anti-GITR mAbs as an immunotherapeutic strategy for cancer.
authors.affiliation: Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors.forename: Adam D
authors.initials: AD
authors.lastname: Cohen
authors.forename: David A
authors.initials: DA
authors.lastname: Schaer
authors.forename: Cailian
authors.initials: C
authors.lastname: Liu
authors.forename: Yanyun
authors.initials: Y
authors.lastname: Li
authors.forename: Daniel
authors.initials: D
authors.lastname: Hirschhorn-Cymmerman
authors.forename: Soo Chong
authors.initials: SC
authors.lastname: Kim
authors.forename: Adi
authors.initials: A
authors.lastname: Diab
authors.forename: Gabrielle
authors.initials: G
authors.lastname: Rizzuto
authors.forename: Fei
authors.initials: F
authors.lastname: Duan
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Perales
authors.forename: Taha
authors.initials: T
authors.lastname: Merghoub
authors.forename: Alan N
authors.initials: AN
authors.lastname: Houghton
authors.forename: Jedd D
authors.initials: JD
authors.lastname: Wolchok
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D051858:Forkhead Transcription Factors / Q000378:metabolism; D053450:Glucocorticoid-Induced TNFR-Related Protein; D007109:Immunity / Q000276:immunology*; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology; D008545:Melanoma / Q000276:immunology* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D017475:Receptors, Nerve Growth Factor / Q000819:agonists* / Q000276:immunology*; D018124:Receptors, Tumor Necrosis Factor / Q000819:agonists* / Q000276:immunology*; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D015854:Up-Regulation / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; D053450:Glucocorticoid-Induced TNFR-Related Protein; D017475:Receptors, Nerve Growth Factor; D018124:Receptors, Tumor Necrosis Factor; C106544:Tnfrsf18 protein, mouse
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