Trüb et al. showed that FAP-4-1BBL (a non-FcγR binding IgG1 heterodimer comprising TNF superfamily 4-1BB ligand and a Fab specific for the fibroblast activation protein [FAP]), enhanced activation, proliferation, cytokine secretion and tumor killing by human peripheral blood 4-1BBlo T cells stimulated in the presence of FAP+ fibroblasts with anti-CD3 or bispecific antibodies specific for tumor antigen and CD3. FAP-4-1BBL revitalized PD-1hi TIGIThi TIM-3hi CD160hi BTLAhi Lag-3hi 4-1BBlo T cells from primary tumor digests to upregulate Bcl2 and secrete IFNγ, IL-2, TNFα and IL-13. IL-13 upregulated the apoptotic marker active caspase 3 in IL-13R+ tumor cells.
Contributed by Paula Hochman
BACKGROUND: The costimulatory receptor 4-1BB (CD137, TNFRSF9) plays an important role in sustaining effective T cell immune responses and is investigated as target for cancer therapy. Systemic 4-1BB directed therapies elicit toxicity or low efficacy, which significantly hampered advancement of 4-1BB-based immunotherapy. Therefore, targeted delivery of 4-1BB agonist to the tumor side is needed for eliciting antitumor efficacy while avoiding systemic toxicity. METHODS: We analyzed the immunostimulatory properties of a fibroblast activation protein (FAP)-targeted 4-1BB agonist (FAP-4-1BBL) by assessing tumor-infiltrating lymphocytes' (TIL) activity from patients with non-small cell lung cancer and epithelial ovarian cancer. RESULTS: Combination treatment with FAP-4-1BBL and T cell receptor stimulation by either anti-CD3 or T cell bispecific antibodies significantly enhanced TIL activation and effector functions, including T cell proliferation, secretion of proinflammatory cytokines and cytotoxicity. Notably, costimulation with FAP-4-1BBL led to de novo secretion of interleukin (IL)-13. This was associated with cytokine-mediated tumor cell apoptosis, which was partially dependent on IL-13 alpha 1/2 receptors and STAT6 phosphorylation. CONCLUSIONS: Our study provides mechanistic insights into T cell stimulation induced by FAP-4-1BBL in primary human tumors and supports the investigation of FAP-4-1BBL compound in early clinical trials.