Supplementary Figure 2: T cell populations in the spleen and tumor of FS120m treated mice. (A) Percentages of indicated T cell populations in the tumors of mice treated with FS120m or control antibodies. (B) Percentages of indicated T cell populations in the spleens of mice treated with FS120m or control antibodies. (C) Absolute counts of exTreg cells and Foxp3+ RFP+ Treg cells per gram of tumors (left) and in whole spleens (right) of FS120m treated animals. (D) Absolute counts of IFN-γ producing exTreg cells and Foxp3+ RFP+ Treg cells per gram of tumors (left) and in whole spleens (right) of FS120m-treated animals. (E) Absolute counts of TNF producing exTreg cells and Foxp3+ RFP+ Treg cells per gram of tumors (left) and in whole spleens (right) of FS120m-treated animals. * P ≤ 0.05, ** P ≤ 0.01. Student’s t test. Bars and error are mean and s.e.m.
ARTICLE ABSTRACT
Regulatory T cells (Treg) are highly enriched within many tumors and suppress immune responses to cancer. There is intense interest in reprogramming Tregs to contribute to antitumor immunity. OX40 and CD137 are expressed highly on Tregs, activated and memory T cells, and NK cells. In this study, using a novel bispecific antibody targeting mouse OX40 and CD137 (FS120m), we show that OX40/CD137 bispecific agonism induces potent antitumor immunity partially dependent upon IFNγ production by functionally reprogrammed Tregs. Treatment of tumor-bearing animals with OX40/CD137 bispecific agonists reprograms Tregs into both fragile Foxp3+ IFNγ+ Tregs with decreased suppressive function and lineage-instable Foxp3− IFNγ+ ex-Tregs. Treg fragility is partially driven by IFNγ signaling, whereas Treg instability is associated with reduced IL2 responsiveness upon treatment with OX40/CD137 bispecific agonists. Importantly, conditional deletion of Ifng in Foxp3+ Tregs and their progeny partially reverses the antitumor efficacy of OX40/CD137 bispecific agonist therapy, revealing that reprogramming of Tregs into IFNγ-producing cells contributes to the anti-tumor efficacy of OX40/CD137 bispecific agonists. These findings provide insights into mechanisms by which bispecific agonist therapies targeting costimulatory receptors highly expressed by Tregs potentiate antitumor immunity in mouse models.
The bispecific antibody FS120, an immunotherapy currently being tested in the clinic, partially functions by inducing anti-tumor activity of Tregs, which results in tumor rejection.
