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Blockade of surface bound TGF-β abrogates Treg suppression of effector T cell function within the tumor microenvironment
  1. Sadna Budhu1,
  2. David Schaer2,
  3. Yongbiao Li3,
  4. Alan Houghton1,
  5. Samuel Silverstein4,
  6. Taha Merghoub1 and
  7. Jedd D Wolchok1
  1. Aff1 grid.51462.340000000121719952ImmunologyMemorial Sloan Kettering Cancer Center New York NY USA
  2. Aff2 grid.417540.30000 0000 2220 2544Cancer ImmunobiologyImClone Systems New York NY USA
  3. Aff3 grid.51462.340000000121719952Research EngineeringMemorial Sloan Kettering Cancer Center New York NY USA
  4. Aff4 grid.239585.00000000122852675Physiology and Cellular BiophysicsColumbia University Medical Center New York NY USA

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Meeting abstracts

Regulatory T cells (Treg) play a role in suppression of anti-melanoma immunity; however, the exact mechanism is poorly understood. Through intravital two photon microcopy, we found that tumor-specific Pmel-1 effectors engage in cell-cell interactions with tumor resident Tregs. To determine if contact between Tregs and Teff hinders killing of tumor cells in vivo, we utilized ex-vivo three-dimensional collagen-fibrin gel cultures of B16 melanoma cells. Collagen-fibrin gel cultures recapitulated the in vivo suppression, rendering the dissociated tumor resistant to killing by in vitro activated antigen specific T cells. In vivo depletion of Tregs in Foxp3-DTR mice prior to tumor excision reversed the suppression. In vivo modulation of Tregs by GITR ligation had a similar effect, reducing the number of intra-tumor Tregs leading to ex-vivo tumor killing. Using neutralizing antibodies, we found that blocking TGF-β reversed the suppression. In addition, soluble factors from collagen-fibrin gel tumors do not inhibit killing suggesting that suppression is contact or proximity dependent. The CD8 T cells recovered from these gels exhibit a decrease in Granzyme B expression and an increase in expression of T cell exhaustion marker PD-1. These findings support the conclusion that intra-tumor contact with Tregs during the effector phase of the immune response is responsible for inhibiting anti-melanoma immunity in a TGF-β dependent manner shedding light into novel ways to inhibit intratumoral Tregs.

This study was supported by Swim Across America; NIH grants R01CA56821, P01CA33049, and P01CA59350 (to J.W. and A.H.); D.S. and S.B. received support from the NIH/NCI Immunology Training GrantT32 CA09149-30.