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Supplementary information on cell maintenance, and antibody selection and characterization

FAP-drozitumab antibody-mediated apoptosis does not correlate with DR5.

Characterization and optimization of RG7386 dosing in vivo.

Dysregulated cellular apoptosis and resistance to cell death are hallmarks of neoplastic initiation and disease progression. Therefore, the development of agents that overcome apoptosis dysregulation in tumor cells is an attractive therapeutic approach. Activation of the extrinsic apoptotic pathway is strongly dependent on death receptor (DR) hyperclustering on the cell surface. However, strategies to activate DR5 or DR4 through agonistic antibodies have had only limited clinical success. To pursue an alternative approach for tumor-targeted induction of apoptosis, we engineered a bispecific antibody (BsAb), which simultaneously targets fibroblast-activation protein (FAP) on cancer-associated fibroblasts in tumor stroma and DR5 on tumor cells. We hypothesized that bivalent binding to both FAP and DR5 leads to avidity-driven hyperclustering of DR5 and subsequently strong induction of apoptosis in tumor cells but not in normal cells. Here, we show that RG7386, an optimized FAP-DR5 BsAb, triggers potent tumor cell apoptosis in vitro and in vivo in preclinical tumor models with FAP-positive stroma. RG7386 antitumor efficacy was strictly FAP dependent, was independent of FcR cross-linking, and was superior to conventional DR5 antibodies. In combination with irinotecan or doxorubicin, FAP-DR5 treatment resulted in substantial tumor regression in patient-derived xenograft models. FAP-DR5 also demonstrated single-agent activity against FAP-expressing malignant cells, due to cross-binding of FAP and DR5 across tumor cells. Taken together, these data demonstrate that RG7386, a novel and potent antitumor agent in both mono- and combination therapies, overcomes limitations of previous DR5 antibodies and represents a promising approach to conquer tumor-associated resistance to apoptosis. Mol Cancer Ther; 15(5); 946–57. ©2016 AACR.

Figure S2. Related to Figure 3. In vitro characterization of the FAP-DR5 BsAb RG7386; Table S4. Characterization of RG7386 binding avidities.

Figure S1. Related to Figure 1. Characterization of FAP-drozitumab BsAbs and antitumor efficacy in the presence of FAP-expressing fibroblasts in in vitro co-culture models; Table S1. BsAb binding to DR5 and FAP antigens; Table S2. Anti-tumor efficacy of FAP-drozitumab bispecific molecules is FAPdependent.

Pharmacokinetic profiles of CEA TCB in mice, additional information on CD3 signaling, T cell activation, tumor cell lysis and cytokine release upon CEA TCB and untargeted control TCB treatment.

Purpose: CEA TCB is a novel IgG-based T-cell bispecific (TCB) antibody for the treatment of CEA-expressing solid tumors currently in phase I clinical trials (NCT02324257). Its format incorporates bivalent binding to CEA, a head-to-tail fusion of CEA- and CD3e-binding Fab domains and an engineered Fc region with completely abolished binding to FcγRs and C1q. The study provides novel mechanistic insights into the activity and mode of action of CEA TCB.Experimental Design: CEA TCB activity was characterized on 110 cell lines in vitro and in xenograft tumor models in vivo using NOG mice engrafted with human peripheral blood mononuclear cells.Results: Simultaneous binding of CEA TCB to tumor and T cells leads to formation of immunologic synapses, T-cell activation, secretion of cytotoxic granules, and tumor cell lysis. CEA TCB activity strongly correlates with CEA expression, with higher potency observed in highly CEA-expressing tumor cells and a threshold of approximately 10,000 CEA-binding sites/cell, which allows distinguishing between high- and low-CEA–expressing tumor and primary epithelial cells, respectively. Genetic factors do not affect CEA TCB activity confirming that CEA expression level is the strongest predictor of CEA TCB activity. In vivo, CEA TCB induces regression of CEA-expressing xenograft tumors with variable amounts of immune cell infiltrate, leads to increased frequency of activated T cells, and converts PD-L1 negative into PD-L1–positive tumors.Conclusions: CEA TCB is a novel generation TCB displaying potent antitumor activity; it is efficacious in poorly infiltrated tumors where it increases T-cell infiltration and generates a highly inflamed tumor microenvironment. Clin Cancer Res; 22(13); 3286–97. ©2016 AACR.

Representative videos of intravital two-photon (2P) microscopy of tumors treated with CEA TCB. Tumor cells red, T cells green.

Representative videos of intravital two-photon (2P) microscopy of tumors treated with untargeted TCB. Tumor cells red, T cells green.

List, Source and CEA binding sites of Cell Lines used in the study

Assessment of binding of CEA TCB to human and cynomolgus monkey CEA- and CD3-expressing cells, internalization and ADCC, CDC activity.

Detection of tumor targeting by in vivo imaging (fluorescent intensity, FLI)of CEA TCB formats having bivalent or monovalent binding to CEA and directly labeled with Alexa647.

Supplemental Material and Methods describing CEA TCB production and purification process, determination of affinity and avidity, genetic characterization of cell lines, determination of CEA binding sites, assessment of T cell proliferation and activation, Jurkat NFAT assay, confocal microscopy, FRET, SDPK, in vivo efficacy and imaging studies. Supplemental Video Legends are also within the file.

Blockade of CD28 costimulation with CTLA-4-Ig/Abatacept is used to dampen effector T cell responses in autoimmune and transplantation settings. However, a significant drawback of this approach is impaired regulatory T cell homeostasis that requires CD28 signaling. Therefore, strategies that restrict the effects of costimulation blockade to effector T cells would be advantageous. Here we probe the relative roles of CD28 and IL-2 in maintaining Treg. We find provision of IL-2 counteracts the regulatory T cell loss induced by costimulation blockade while minimally affecting the conventional T cell compartment. These data suggest that combining costimulation blockade with IL-2 treatment may selectively impair effector T cell responses while maintaining regulatory T cells. Using a mouse model of autoimmune diabetes, we show combined therapy supports regulatory T cell homeostasis and protects from disease. These findings are recapitulated in humanised mice using clinically relevant reagents and provide an exemplar for rational use of a second immunotherapy to offset known limitations of the first.

Engineered antibodies have become an invaluable source of biopharmaceuticals against a wide range of diseases. About 200 antibody-based biologicals have been tested in clinical trials. Single chain variable fragments of antibodies (scFvs) provide binding specificity and offer an increased ease of in vitro display selection. Here, we present the generation of a human scFv library from peripheral blood lymphocyte RNA of a patient with relapsed T-cell non-Hodgkin lymphoma (T-NHL) who experienced a rare case of "spontaneous" remission. Antibodies against human T-cell antigen CD28, a co-stimulatory protein that influences the immune response by amplification of the transcriptional effects of T-cell receptors, might have contributed to the patient's remission. The scFv library was panned against CD28 using ribosome display and further subjected to affinity maturation. Isolated scFv were assessed for binding specificity and affinity and may provide the basis for the development of novel immunotherapeutic strategies. This work demonstrates the selection of a fully human antibody fragment from a patient-derived gene pool by in vitro ribosome display technology.

Engineered antibodies and their fragments are invaluable tools for a vast range of biotechnological and pharmaceutical applications. However, they are facing increasing competition from a new generation of protein display scaffolds, specifically selected for binding virtually any target. Some of them have already entered clinical trials. Most of these nonimmunoglobulin proteins are involved in natural binding events and have amazingly diverse origins, frameworks, and functions, including even intrinsic enzyme activity. In many respects, they are superior over antibody-derived affinity molecules and offer an ever-extending arsenal of tools for, e.g., affinity purification, protein microarray technology, bioimaging, enzyme inhibition, and potential drug delivery. As excellent supporting frameworks for the presentation of polypeptide libraries, they can be subjected to powerful in vitro or in vivo selection and evolution strategies, enabling the isolation of high-affinity binding reagents. This article reviews the generation of these novel binding reagents, describing validated and advanced alternative scaffolds as well as the most recent nonimmunoglobulin libraries. Characteristics of these protein scaffolds in terms of structural stability, tolerance to multiple substitutions, ease of expression, and subsequent applications as specific targeting molecules are discussed. Furthermore, this review shows the close linkage between these novel protein tools and the constantly developing display, selection, and evolution strategies using phage display, ribosome display, mRNA display, cell surface display, or IVC (in vitro compartmentalization). Here, we predict the important role of these novel binding reagents as a toolkit for biotechnological and biomedical applications.

Novel in vitro methods for screening of antibody libraries against disease-related antigens have led to the development of powerful protein-based biotherapeutics. Ribosome display represents an emerging and innovative in vitro technology for the rapid isolation and evolution of high-affinity peptides or proteins. Eukaryotic ternary ribosome complexes can be used to display human single chain antibodies (scFvs) in order to isolate specific binding reagents. Here we present the isolation of human scFv against the validated immunotherapeutic target antigen CD22 from a leukaemia patient-derived human scFv library using ribosome display technology. The ribosome-displayed scFv were enriched against the human CD22 conjugated to magnetic beads. Isolated constructs were further affinity-matured and specific target recognition was demonstrated by surface plasmon resonance and validated using in vitro cell assays.