CD137/OX40 Bispecific Antibody Induces Potent Antitumor Activity that Is Dependent on Target Coengagement.

Following the success of immune checkpoint blockade therapy against cancer, agonistic antibodies targeting T-cell costimulatory pathways are in clinical trials. The TNF superfamily of receptors (TNFRSF) members CD137 and OX40 are costimulatory receptors that stimulate T-cell proliferation and activation upon interaction with their cognate ligands. Activating CD137 and OX40 with agonistic mAbs stimulates the immune system due to their broad expression on CD4+ and CD8+ T cells and natural killer cells and has antitumor effects in preclinical models. Most TNFRSF agonist antibodies require crosslinking via Fcγ receptors (FcγR), which can limit their clinical activity. FS120 mAb2, a dual agonist bispecific antibody targeting CD137 and OX40, activated both CD4+ and CD8+ T cells in an FcγR-independent mechanism, dependent on concurrent binding. A mouse surrogate version of the bispecific antibody displayed antitumor activity in syngeneic tumor models, independent of T regulatory cell depletion and of FcγR interaction, but associated with peripheral T-cell activation and proliferation. When compared with a crosslink-independent CD137 agonist mAb, the FS120 surrogate induced lower liver T-cell infiltration. These data support initiation of clinical development of FS120, a first-in-class dual agonist bispecific antibody for the treatment of human cancer.

FS222, a CD137/PD-L1 Tetravalent Bispecific Antibody, Exhibits Low Toxicity and Antitumor Activity in Colorectal Cancer Models.

PURPOSE: With the increased prevalence in checkpoint therapy resistance, there remains a significant unmet need for additional therapies for patients with relapsing or refractory cancer. We have developed FS222, a bispecific tetravalent antibody targeting CD137 and PD-L1, to induce T-cell activation to eradicate tumors without the current toxicity and efficacy limitations seen in the clinic. EXPERIMENTAL DESIGN: A bispecific antibody (FS222) was developed by engineering CD137 antigen-binding sites into the Fc region of a PD-L1 IgG1 mAb. T-cell activation by FS222 was investigated using multiple in vitro assays. The antitumor efficacy, survival benefit, pharmacodynamics, and liver pharmacology of a murine surrogate molecule were assessed in syngeneic mouse tumor models. Toxicology and the pharmacokinetic/pharmacodynamic profile of FS222 were investigated in a non-human primate dose-range finding study. RESULTS: We demonstrated simultaneous binding of CD137 and PD-L1 and showed potent T-cell activation across CD8+ T-cell activation assays in a PD-L1-dependent manner with a CD137/PD-L1 bispecific antibody, FS222. FS222 also activated T cells in a human primary mixed lymphocyte reaction assay, with greater potency than the monospecific mAb combination. FS222 showed no signs of liver toxicity up to 30 mg/kg in a non-human primate dose-range finding study. A surrogate molecule caused significant tumor growth inhibition and survival benefit, concomitant with CD8+ T-cell activation, in CT26 and MC38 syngeneic mouse tumor models. CONCLUSIONS: By targeting CD137 agonism to areas of PD-L1 expression, predominantly found in the tumor microenvironment, FS222 has the potential to leverage a focused, potent, and safe immune response augmenting the PD-(L)1 axis blockade.

Generation of Fcabs targeting human and murine LAG-3 as building blocks for novel bispecific antibody therapeutics.

The immunoglobulin superfamily protein lymphocyte-activation gene 3 (LAG-3) participates in immune suppression and has been identified as a suitable target for cancer therapies. In order to generate bispecific antibodies targeting LAG-3, Fcabs (Fc-region with antigen binding) targeting human and murine LAG-3 were generated from phage libraries. These Fcabs bind to LAG-3, inhibiting its interaction with MHC class II, and induce IL-2 production in a T cell assay. Bispecific antibodies, known as mAb2, were produced by replacing the Fc region of a monoclonal antibody with Fcab sequences in the CH3 domain. mAb2 containing anti-LAG-3 Fcabs have mAb-like biophysical characteristics and retain LAG-3 binding and functional activity. mAb2 can thus be generated using multiple Fabs to investigate bispecific parings and develop novel therapeutics.