Therapeutic antibodies have transformed cancer therapy, unlocking mechanisms of action by engaging the immune system. Unfortunately, cures rarely occur and patients display intrinsic or acquired resistance. Here, we demonstrate the therapeutic potential of targeting human (h) FcγRIIB (CD32B), a receptor implicated in immune cell desensitization and tumor cell resistance. FcγRIIB-blocking antibodies prevented internalization of the CD20-specific antibody rituximab, thereby maximizing cell surface accessibility and immune effector cell mediated antitumor activity. In hFcγRIIB-transgenic (Tg) mice, FcγRIIB-blocking antibodies effectively deleted target cells in combination with rituximab, and other therapeutic antibodies, from resistance-prone stromal compartments. Similar efficacy was seen in primary human tumor xenografts, including with cells from patients with relapsed/refractory disease. These data support the further development of hFcγRIIB antibodies for clinical assessment.

We isolated a tumor B-cell-targeting antibody, BI-505, from a highly diversified human phage-antibody library, using a pioneering "function-first" approach involving screening for (1) specificity for a tumor B cell surface receptor, (2) induction of tumor programmed cell death, and (3) enhanced in vivo antitumor activity compared to currently used treatments. BI-505 bound to intercellular adhesion molecule-1, identifying a previously unrecognized role for this receptor as a therapeutic target in cancer. The BI-505 epitope was strongly expressed on the surface of multiple myeloma cells from both newly diagnosed and relapsed patients. BI-505 had potent macrophage-dependent antimyeloma activity and conferred enhanced survival compared to currently used treatments in advanced experimental models of multiple myeloma.

Development of antibody drugs against novel targets and pathways offers great opportunities to improve current cancer treatment. We here describe a phenotypic discovery platform enabling efficient identification of therapeutic antibody-target combinations. The platform utilizes primary patient cells throughout the discovery process and includes methods for differential phage display cell panning, high-throughput cell-based specificity screening, phenotypic in vitro screening, target deconvolution, and confirmatory in vivo screening. In this study the platform was applied on cancer cells from patients with Chronic Lymphocytic Leukemia resulting in discovery of antibodies with improved cytotoxicity in vitro compared to the standard of care, the CD20-specific monoclonal antibody rituximab. Isolated antibodies were found to target six different receptors on Chronic Lymphocytic Leukemia cells; CD21, CD23, CD32, CD72, CD200, and HLA-DR of which CD32, CD200, and HLA-DR appeared as the most potent targets for antibody-based cytotoxicity treatment. Enhanced antibody efficacy was confirmed in vivo using a patient-derived xenograft model.

The pleiotropic TNF-α:TNFR axis plays a central role in the immune system. While the cellular expression of TNFR1 is broad, TNFR2 expression is mainly restricted to immune cells and especially high on T regs. The therapeutic potential of targeting TNFR2 for cancer treatment has been previously indicated but the mechanism-of-action (MoA) of these reagents remains unclear, with conflicting data reported by different investigators. To gain further insight, we identified and characterized a wide panel of human and mouse TNFR2-specific antibodies, generated from the n-CoDeR F.I.R.S.T™ phage display platform. Based on their ability to block TNF-α:TNFR2 binding and to agonize or antagonize TNFR2 signaling, we identified parallel human and mouse TNFR2-specific antibodies with activities ranging from agonist to antagonist, and from complete ligand blocking to non-blocking. Two antibody variants with distinctly opposing in vitro activities (complete ligand-blocking antagonist versus non-blocking agonist), were expressed in various IgG formats preferentially engaging activating FcγR (mIgG2a), inhibitory FcγR (mIgG1), or no FcγR (N297A Fc-mutated) and screened for in vivo antitumor activity. Both anti-TNFR2 antibody clones displayed anti-tumor efficacy but showed strikingly different FcγR-dependence for optimal antitumor activity. Further characterization demonstrated potent anti-tumor efficacy across several syngeneic in vivo cancer models (CT26, MC38 and B16), both as single agents, and when combined with anti-PD-1. In vivo mode-of-action studies indicated different initial events are evoked by the two antibodies but that they ultimately converge to elicit a similar immune modulation within the tumor that is associated with anti-tumor efficacy. The antagonist antibody caused early intra-tumoral T reg depletion, while the agonist caused dramatic CD8+ T cell increases. Over time, both antibodies induce an increase in effector T cells at the tumor site, improved CD8/T reg ratios, and tumor regression. In addition, the two antibodies similarly modulated the tumor myeloid content. Based on careful MoA-characterization, two human lead candidate anti-TNFR2 antibodies are being developed for treatment of solid cancer; BI-1808, a ligand-blocking T reg depleting antibody and BI-1910, a TNFR2 agonist. Citation Format: Linda Mårtensson, Kirstie Cleary, Monika Semmrich, Mathilda Kovacek, Petra Holmkvist, Caroline Svensson, Mimoza Demiri, Therese Blidberg, Ulla-Carin Thornberg, Vincentiu Pitic, Osman Dadas, Sean H. Lim, Stephen A. Beers, Mark S. Cragg, Björn Frendéus, Ingrid Teige. Targeting TNFR2 for cancer immunotherapy: Ligand blocking depletors versus receptor agonists [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 936.

Inevitable relapses remain as the major therapeutic challenge in patients with mantle cell lymphoma (MCL) despite FDA approval of multiple targeted therapies and immunotherapies. Fc gamma receptors (FcγRs) play important roles in regulating antibody-mediated immunity. FcγRIIB, the unique immune-checkpoint inhibitory member of the FcγR family, has been implicated in immune cell desensitization and tumor cell resistance to the anti-CD20 antibody rituximab and other antibody-mediated immunotherapies; however, little is known about its expression and its immune-modulatory function in patients with aggressive MCL, especially those with multi-resistance. In this study, we found that FcγRIIB was ubiquitously expressed in both MCL cell lines and primary patient samples. FcγRIIB expression is significantly higher in CAR T-relapsed patient samples (p < 0.0001) compared to ibrutinib/rituximab-naïve, sensitive or resistant samples. Rituximab-induced CD20 internalization in JeKo-1 cells was completely blocked by concurrent treatment with BI-1206, a recombinant human monoclonal antibody targeting FcγRIIB. Combinational therapies with rituximab-ibrutinib, rituximab-venetoclax and rituximab-CHOP also induced CD20 internalization which was again effectively blocked by BI-1206. BI-1206 significantly enhanced the in vivo anti-MCL efficacy of rituximab-ibrutinib (p = 0.05) and rituximab-venetoclax (p = 0.02), but not the rituximab-CHOP combination in JeKo-1 cell line-derived xenograft models. In patient-derived xenograft (PDX) models, BI-1206, as a single agent, showed high potency (p < 0.0001, compared to vehicle control) in one aggressive PDX model that is resistant to both ibrutinib and venetoclax but sensitive to the combination of rituximab and lenalidomide (the preclinical mimetic of R2 therapy). BI-1206 sensitized the efficacy of rituximab monotherapy in a PDX model with triple resistance to rituximab, ibrutinib and CAR T-therapies (p = 0.030). Moreover, BI-1206 significantly enhanced the efficacy of the rituximab-venetoclax combination (p < 0.05), which led to long-term tumor remission in 25% of mice. Altogether, these data support that targeting this new immune-checkpoint blockade enhances the therapeutic activity of rituximab-based regimens in aggressive MCL models with multi-resistance. Graphical Abstract