Targeting TNFR2 with antagonistic antibodies inhibits proliferation of ovarian cancer cells and tumor-associated T _regs

Abstract

Major barriers to cancer therapy include the lack of selective inhibitors of regulatory T cells (T) and the lack of broadly applicable ways to directly target tumors through frequently expressed surface oncogenes. Tumor necrosis factor receptor 2 (TNFR2) is an attractive target protein because of its restricted abundance to highly immunosuppressive T and oncogenic presence on human tumors. We characterized the effect of TNFR2 inhibition using antagonistic antibodies. In culture-based assays, we found that two TNFR2 antagonists inhibited T proliferation, reduced soluble TNFR2 secretion from normal cells, and enabled T effector cell expansion. The antagonistic activity occurred in the presence of added TNF, a natural TNFR2 agonist. These TNFR2 antibodies killed T isolated from ovarian cancer ascites more potently than it killed T from healthy donor samples, suggesting that these antibodies may have specificity for the tumor microenvironment. The TNFR2 antagonists also killed OVCAR3 ovarian cancer cells, which have abundant surface TNFR2. The antibodies stabilized antiparallel dimers in cell surface TNFR2 that rendered the receptor unable to activate the nuclear factor κB pathway and trigger cell proliferation. Our data suggest that, by targeting tumor cells and immunosuppressive tumor-associated T, antagonistic TNFR2 antibodies may be an effective treatment for cancers positive for TNFR2.

Structural principles of tumor necrosis factor superfamily signaling

“…The antiparallel dimers on the other hand bury part of the ligand-binding region and therefore are unable to bind the ligand. It has been proposed that the antiparallel dimers may represent the resting or "nonsignaling" state of the receptor (41), which, when locked in this conformation by an antibody, can efficiently block ligand binding and receptor activation (43). There is further experimental evidence to support the formation of antiparallel dimers as a structure to inhibit receptor signaling.…”

“…The dimer is formed by receptor monomers from two different signaling units that occlude the ligand-binding site, maintaining a resting state. This state can most effectively be stabilized by the recently characterized dominant antagonist antibodies that firmly lock in the antiparallel dimer (43). If TNFR2 antagonist antibodies stabilized the antiparallel dimer, this would explain the requirement for at least F(ab′) 2 structures but failure of a single Fab antibody fragment to confer antagonism (43).…”

“…Because of the high structural homology, this model may be applicable to all TNFSF ligands and receptors. As an example, TNFR2 agonism also shows synergistic activation when both TNF and a crosslinking TNFR2 agonist antibody are coadministered (43).…”

“…It has been recognized as a potent oncoprotein and a bidirectional switch for expansion of the immunosuppressive T reg population (7,43). These dual roles make TNFR2 agonism an attractive approach for autoimmunity and regenerative medicine (72), and TNFR2 antagonism an emerging novel approach for cancer immunotherapy (43). Recessive and dominant antagonists raised against TNFR2 can block TNF binding (43).…”

“…These dual roles make TNFR2 agonism an attractive approach for autoimmunity and regenerative medicine (72), and TNFR2 antagonism an emerging novel approach for cancer immunotherapy (43). Recessive and dominant antagonists raised against TNFR2 can block TNF binding (43). In this context, we define recessive or dominant antagonists based on how well they can compete with TNF.…”