Integrated Single-Cell (Phospho-)Protein and RNA Detection Uncovers Phenotypic Characteristics and Active Signal Transduction of Human Antibody-Secreting Cells.

Single-cell technologies are currently widely applied to obtain a deeper understanding of the phenotype of single-cells in heterogenous mixtures. However, integrated multilayer approaches including simultaneous detection of mRNA, protein expression, and intracellular phospho-proteins are still challenging. Here, we combined an adapted method to in vitro-differentiate peripheral B-cells into antibody-secreting cells (ASCs) (i.e., plasmablasts and plasma cells) with integrated multi-omic single-cell sequencing technologies to detect and quantify immunoglobulin subclass-specific surface markers, transcriptional profiles, and signaling transduction pathway components. Using a common set of surface proteins, we integrated two multimodal datasets to combine mRNA, protein expression, and phospho-protein detection in one integrated dataset. Next, we tested whether ASCs that only seem to differ in its ability to secrete different IgM, IgA, or IgG antibodies exhibit other differences that characterize these different ASCs. Our approach detected differential expression of plasmablast and plasma cell markers, homing receptors, and TNF receptors. In addition, differential sensitivity was observed for the different cytokine stimulations that were applied during in vitro differentiation. For example, IgM ASCs were more sensitive to IL-15, while IgG ASC responded more to IL-6 and IFN addition. Furthermore, tonic BCR activity was detected in IgA and IgM ASCs, while IgG ASC exhibited active BCR-independent SYK activity and NF-κB and mTOR signaling. We confirmed these findings using flow cytometry and small molecules inhibitors, demonstrating the importance of SYK, NF-κB, and mTOR activity for plasmablast/plasma cell differentiation/survival and/or IgG secretion. Taken together, our integrated multi-omics approach allowed high-resolution phenotypic characterization of single cells in a heterogenous sample of in vitro-differentiated human ASCs. Our strategy is expected to further our understanding of human ASCs in healthy and diseased samples and provide a valuable tool to identify novel biomarkers and potential drug targets.

Determinants of Ligand-Functionalized DNA Nanostructure-Cell Interactions.

Synthesis of ligand-functionalized nanomaterials with control over size, shape, and ligand orientation facilitates the design of targeted nanomedicines for therapeutic purposes. DNA nanotechnology has emerged as a powerful tool to rationally construct two- and three-dimensional nanostructures, enabling site-specific incorporation of protein ligands with control over stoichiometry and orientation. To efficiently target cell surface receptors, exploration of the parameters that modulate cellular accessibility of these nanostructures is essential. In this study, we systematically investigate tunable design parameters of antibody-functionalized DNA nanostructures binding to therapeutically relevant receptors, including the programmed cell death protein 1, the epidermal growth factor receptor, and the human epidermal growth factor receptor 2. We show that, although the native affinity of antibody-functionalized DNA nanostructures remains unaltered, the absolute number of bound surface receptors is lower compared to soluble antibodies due to receptor accessibility by the nanostructure. We explore structural determinants of this phenomenon to improve efficiency, revealing that receptor binding is mainly governed by nanostructure size and DNA handle location. The obtained results provide key insights in the ability of ligand-functionalized DNA nanostructures to bind surface receptors and yields design rules for optimal cellular targeting.

APRIL and BCMA promote human multiple myeloma growth and immunosuppression in the bone marrow microenvironment.

Here we show that overexpression or activation of B-cell maturation antigen (BCMA) by its ligand, a proliferation-inducing ligand (APRIL), promotes human multiple myeloma (MM) progression in vivo. BCMA downregulation strongly decreases viability and MM colony formation; conversely, BCMA overexpression augments MM cell growth and survival via induction of protein kinase B (AKT), MAPK, and nuclear factor (NF)-κB signaling cascades. Importantly, BCMA promotes in vivo growth of xenografted MM cells harboring p53 mutation in mice. BCMA-overexpressing tumors exhibit significantly increased CD31/microvessel density and vascular endothelial growth factor compared with paired control tumors. These tumors also express increased transcripts crucial for osteoclast activation, adhesion, and angiogenesis/metastasis, as well as genes mediating immune inhibition including programmed death ligand 1, transforming growth factor ß, and interleukin 10. These target genes are consistently induced by paracrine APRIL binding to BCMA on MM cells, which is blocked by an antagonistic anti-APRIL monoclonal antibody hAPRIL01A (01A). 01A is cytotoxic against MM cells even in the presence of protective bone marrow (BM) myeloid cells including osteoclasts, macrophages, and plasmacytoid dendritic cells. 01A further decreases APRIL-induced adhesion and migration of MM cells via blockade of canonical and noncanonical NF-κB pathways. Moreover, 01A prevents in vivo MM cell growth within implanted human bone chips in SCID mice. Finally, the effect of 01A on MM cell viability is enhanced by lenalidomide and bortezomib. Taken together, these data delineate new molecular mechanisms of in vivo MM growth and immunosuppression critically dependent on BCMA and APRIL in the BM microenvironment, further supporting targeting this prominent pathway in MM.

Human TLR10 is an anti-inflammatory pattern-recognition receptor.

Toll-like receptor (TLR)10 is the only pattern-recognition receptor without known ligand specificity and biological function. We demonstrate that TLR10 is a modulatory receptor with mainly inhibitory effects. Blocking TLR10 by antagonistic antibodies enhanced proinflammatory cytokine production, including IL-1ß, specifically after exposure to TLR2 ligands. Blocking TLR10 after stimulation of peripheral blood mononuclear cells with pam3CSK4 (Pam3Cys) led to production of 2,065 ± 106 pg/mL IL-1ß (mean ± SEM) in comparison with 1,043 ± 51 pg/mL IL-1ß after addition of nonspecific IgG antibodies. Several mechanisms mediate the modulatory effects of TLR10: on the one hand, cotransfection in human cell lines showed that TLR10 acts as an inhibitory receptor when forming heterodimers with TLR2; on the other hand, cross-linking experiments showed specific induction of the anti-inflammatory cytokine IL-1 receptor antagonist (IL-1Ra, 16 ± 1.7 ng/mL, mean ± SEM). After cross-linking anti-TLR10 antibody, no production of IL-1ß and other proinflammatory cytokines could be found. Furthermore, individuals bearing TLR10 polymorphisms displayed an increased capacity to produce IL-1ß, TNF-α, and IL-6 upon ligation of TLR2, in a gene-dose-dependent manner. The modulatory effects of TLR10 are complex, involving at least several mechanisms: there is competition for ligands or for the formation of heterodimer receptors with TLR2, as well as PI3K/Akt-mediated induction of the anti-inflammatory cytokine IL-1Ra. Finally, transgenic mice expressing human TLR10 produced fewer cytokines when challenged with a TLR2 agonist. In conclusion, to our knowledge we demonstrate for the first time that TLR10 is a modulatory pattern-recognition receptor with mainly inhibitory properties.

CD4+ T cells produce IFN-I to license cDC1s for induction of cytotoxic T-cell activity in human tumors.

CD4+ T cells can "help" or "license" conventional type 1 dendritic cells (cDC1s) to induce CD8+ cytotoxic T lymphocyte (CTL) anticancer responses, as proven in mouse models. We recently identified cDC1s with a transcriptomic imprint of CD4+ T-cell help, specifically in T-cell-infiltrated human cancers, and these cells were associated with a good prognosis and response to PD-1-targeting immunotherapy. Here, we delineate the mechanism of cDC1 licensing by CD4+ T cells in humans. Activated CD4+ T cells produce IFNß via the STING pathway, which promotes MHC-I antigen (cross-)presentation by cDC1s and thereby improves their ability to induce CTL anticancer responses. In cooperation with CD40 ligand (L), IFNß also optimizes the costimulatory and other functions of cDC1s required for CTL response induction. IFN-I-producing CD4+ T cells are present in diverse T-cell-infiltrated cancers and likely deliver "help" signals to CTLs locally, according to their transcriptomic profile and colocalization with "helped/licensed" cDCs and tumor-reactive CD8+ T cells. In agreement with this scenario, the presence of IFN-I-producing CD4+ T cells in the TME is associated with overall survival and the response to PD-1 checkpoint blockade in cancer patients.

Development and characterization of APRIL antagonistic monoclonal antibodies for treatment of B-cell lymphomas.

APRIL (A proliferation-inducing ligand) is a TNF family member that binds two TNF receptor family members, TACI and BCMA. It shares these receptors with the closely related TNF family member, B-cell activating factor (BAFF). Contrary to BAFF, APRIL binds heparan sulfate proteoglycans (HSPGs), which regulates cross-linking of APRIL and efficient signaling. APRIL was originally identified as a growth promoter of solid tumors, and more recent evidence defines APRIL also as an important survival factor in several human B-cell malignancies, such as chronic lymphocytic leukemia (CLL). To target APRIL therapeutically, we developed two anti-human APRIL antibodies (hAPRIL.01A and hAPRIL.03A) that block APRIL binding to BCMA and TACI. Their antagonistic properties are unique when compared with a series of commercially available monoclonal anti-human APRIL antibodies as they prevent in vitro proliferation and IgA production of APRIL-reactive B cells. In addition, they effectively impair the CLL-like phenotype of aging APRIL transgenic mice and, more importantly, block APRIL binding to human B-cell lymphomas and prevent the survival effect induced by APRIL. We therefore conclude that these antibodies have potential for further development as therapeutics to target APRIL-dependent survival in B-cell malignancies.

CD4+ helper T cells endow cDC1 with cancer-impeding functions in the human tumor micro-environment.

Despite their low abundance in the tumor microenvironment (TME), classical type 1 dendritic cells (cDC1) play a pivotal role in anti-cancer immunity, and their abundance positively correlates with patient survival. However, their interaction with CD4+ T-cells to potentially enable the cytotoxic T lymphocyte (CTL) response has not been elucidated. Here we show that contact with activated CD4+ T-cells enables human ex vivo cDC1, but no other DC types, to induce a CTL response to cell-associated tumor antigens. Single cell transcriptomics reveals that CD4+ T-cell help uniquely optimizes cDC1 in many functions that support antigen cross-presentation and T-cell priming, while these changes don't apply to other DC types. We robustly identify "helped" cDC1 in the TME of a multitude of human cancer types by the overlap in their transcriptomic signature with that of recently defined, tumor-infiltrating DC states that prove to be positively prognostic. As predicted from the functional effects of CD4+ T-cell help, the transcriptomic signature of "helped" cDC1 correlates with tumor infiltration by CTLs and Thelper(h)-1 cells, overall survival and response to PD-1-targeting immunotherapy. These findings reveal a critical role for CD4+ T-cell help in enabling cDC1 function in the TME and may establish the helped cDC1 transcriptomic signature as diagnostic marker in cancer.

Development of [89Zr]Zr-hCD103.Fab01A and [68Ga]Ga-hCD103.Fab01A for PET imaging to noninvasively assess cancer reactive T cell infiltration: Fab-based CD103 immunoPET.

BACKGROUND: CD103 is an integrin specifically expressed on the surface of cancer-reactive T cells. The number of CD103+ T cells significantly increases during successful immunotherapy and might therefore be an attractive biomarker for noninvasive PET imaging of immunotherapy response. Since the long half-life of antibodies preclude repeat imaging of CD103+ T cell dynamics early in therapy, we therefore here explored PET imaging with CD103 Fab fragments radiolabeled with a longer (89Zr) and shorter-lived radionuclide (68Ga). METHODS: Antihuman CD103 Fab fragment Fab01A was radiolabeled with 89Zr or 68Ga, generating [89Zr]Zr-hCD103.Fab01A and [68Ga]Ga-hCD103.Fab01A, respectively. In vivo evaluation of these tracers was performed in male nude mice (BALB/cOlaHsd-Foxn1nu) with established CD103-expressing CHO (CHO.CD103) or CHO-wildtype (CHO.K1) xenografts, followed by serial PET imaging and ex vivo bio-distribution. RESULTS: [89Zr]Zr-hCD103.Fab01A showed high tracer uptake in CD103+ xenografts as early as 3 h post-injection. However, the background signal remained high in the 3- and 6-h scans. The background was relatively low at 24 h after injection with sufficient tumor uptake. [68Ga]Ga-hCD103.Fab01Ashowed acceptable uptake and signal-to-noise ratio in CD103+ xenografts after 3 h, which decreased at subsequent time points. CONCLUSION: [89Zr]Zr-hCD103.Fab01A demonstrated a relatively low background and high xenograft uptake in scans as early as 6 h post-injection and could be explored for repeat imaging during immunotherapy in clinical trials. 18F or 64Cu could be explored as alternative to 68Ga in optimizing half-life and radiation burden of the tracer.

Epitope mapping of monoclonal antibodies: a comprehensive comparison of different technologies.

Monoclonal antibodies have become an important class of therapeutics in the last 30 years. Because the mechanism of action of therapeutic antibodies is intimately linked to their binding epitopes, identification of the epitope of an antibody to the antigen plays a central role during antibody drug development. The gold standard of epitope mapping, X-ray crystallography, requires a high degree of proficiency with no guarantee of success. Here, we evaluated six widely used alternative methods for epitope identification (peptide array, alanine scan, domain exchange, hydrogen-deuterium exchange, chemical cross-linking, and hydroxyl radical footprinting) in five antibody-antigen combinations (pembrolizumab+PD1, nivolumab+PD1, ipilimumab+CTLA4, tremelimumab+CTLA4, and MK-5890+CD27). The advantages and disadvantages of each technique are demonstrated by our data and practical advice on when and how to apply specific epitope mapping techniques during the drug development process is provided. Our results suggest chemical cross-linking most accurately identifies the epitope as defined by crystallography.

Functional transformation of the chromatoid body in mouse spermatids requires testis-specific serine/threonine kinases.

The cytoplasmic chromatoid body (CB) organizes mRNA metabolism and small regulatory RNA pathways, in relation to haploid gene expression, in mammalian round spermatids. However, little is known about functions and fate of the CB at later steps of spermatogenesis, when elongating spermatids undergo chromatin compaction and transcriptional silencing. In mouse elongating spermatids, we detected accumulation of the testis-specific serine/threonine kinases TSSK1 and TSSK2, and the substrate TSKS, in a ring-shaped structure around the base of the flagellum and in a cytoplasmic satellite, both corresponding to structures described to originate from the CB. At later steps of spermatid differentiation, the ring is found at the caudal end of the newly formed mitochondrial sheath. Targeted deletion of the tandemly arranged genes Tssk1 and Tssk2 in mouse resulted in male infertility, with loss of the CB-derived ring structure, and with elongating spermatids possessing a collapsed mitochondrial sheath. These results reveal TSSK1- and TSSK2-dependent functions of a transformed CB in post-meiotic cytodifferentiation of spermatids.

Development of 89Zr-anti-CD103 PET imaging for non-invasive assessment of cancer reactive T cell infiltration.

PURPOSE: CD103, an integrin specifically expressed on the surface of cancer-reactive T cells, is significantly increased during successful immunotherapy across human malignancies. In this study, we describe the generation and zirconium-89 (89Zr) radiolabeling of monoclonal antibody (mAb) clones that specifically recognize human CD103 for non-invasive immune positron-emission tomography (PET) imaging of T cell infiltration as potential biomarker for effective anticancer immune responses. EXPERIMENTAL DESIGN: First, to determine the feasibility of anti-CD103 immuno-PET to visualize CD103-positive cells at physiologically and clinically relevant target densities, we developed an 89Zr-anti-murine CD103 PET tracer. Healthy, non-tumor bearing C57BL/6 mice underwent serial PET imaging after intravenous injection, followed by ex vivo biodistribution. Tracer specificity and macroscopic tissue distribution were studied using autoradiography combined with CD103 immunohistochemistry. Next, we generated and screened six unique mAbs that specifically target human CD103 positive cells. Optimal candidates were selected for 89Zr-anti-human CD103 PET development. Nude mice (BALB/cOlaHsd-Foxn1nu) with established CD103 expressing Chinese hamster ovary (CHO) or CHO wild-type xenografts were injected with 89Zr-anti-human CD103 mAbs and underwent serial PET imaging, followed by ex vivo biodistribution. RESULTS: 89Zr-anti-murine CD103 PET imaging identified CD103-positive tissues at clinically relevant target densities. For human anti-human CD103 PET development two clones were selected based on strong binding to the CD103+ CD8+ T cell subpopulation in ovarian cancer tumor digests, non-overlapping binding epitopes and differential CD103 blocking properties. In vivo, both 89Zr-anti-human CD103 tracers showed high target-to-background ratios, high target site selectivity and a high sensitivity in human CD103 positive xenografts. CONCLUSION: CD103 immuno-PET tracers visualize CD103 T cells at relevant densities and are suitable for future non-invasive assessment of cancer reactive T cell infiltration.

Preclinical characterization and clinical translation of pharmacodynamic markers for MK-5890: a human CD27 activating antibody for cancer immunotherapy.

BACKGROUND: Immune checkpoint inhibitors (ICI) have radically changed cancer therapy, but most patients with cancer are unresponsive or relapse after treatment. MK-5890 is a CD27 agonist antibody intended to complement ICI therapy. CD27 is a member of the tumor necrosis factor receptor superfamily that plays a critical role in promoting responses of T cells, B cells and NK cells. METHODS: Anti-CD27 antibodies were generated and selected for agonist activity using NF-кB luciferase reporter assays. Antibodies were humanized and characterized for agonism using in vitro T-cell proliferation assays. The epitope recognized on CD27 by MK-5890 was established by X-ray crystallography. Anti-tumor activity was evaluated in a human CD27 knock-in mouse. Preclinical safety was tested in rhesus monkeys. Pharmacodynamic properties were examined in mouse, rhesus monkeys and a phase 1 dose escalation clinical study in patients with cancer. RESULTS: Humanized anti-CD27 antibody MK-5890 (hIgG1) was shown to bind human CD27 on the cell surface with sub-nanomolar potency and to partially block binding to its ligand, CD70. Crystallization studies revealed that MK-5890 binds to a unique epitope in the cysteine-rich domain 1 (CRD1). MK-5890 activated CD27 expressed on 293T NF-κB luciferase reporter cells and, conditional on CD3 stimulation, in purified CD8+ T cells without the requirement of crosslinking. Functional Fc-receptor interaction was required to activate CD8+ T cells in an ex vivo tumor explant system and to induce antitumor efficacy in syngeneic murine subcutaneous tumor models. MK-5890 had monotherapy efficacy in these models and enhanced efficacy of PD-1 blockade. MK-5890 reduced in an isotype-dependent and dose-dependent manner circulating, but not tumor-infiltrating T-cell numbers in these mouse models. In rhesus monkey and human patients, reduction in circulating T cells was transient and less pronounced than in mouse. MK-5890 induced transient elevation of chemokines MCP-1, MIP-1α, and MIP-1ß in the serum of mice, rhesus monkeys and patients with cancer. MK-5890 was well tolerated in rhesus monkeys and systemic exposure to MK-5890 was associated with CD27 occupancy at all doses. CONCLUSIONS: MK-5890 is a novel CD27 agonistic antibody with the potential to complement the activity of PD-1 checkpoint inhibition in cancer immunotherapy and is currently undergoing clinical evaluation.

Therapeutic antibody targeting of CD97 in experimental arthritis: the role of antigen expression, shedding, and internalization on the pharmacokinetics of anti-CD97 monoclonal antibody 1B2.

CD97 is a member of the EGF-TM7 family of adhesion class receptors, with a proposed role in inflammatory cell recruitment. Neutralization of murine CD97 with the anti-mCD97 mAb 1B2 was efficacious in prevention of murine collagen-induced arthritis, a model with features resembling rheumatoid arthritis. Here, the therapeutic potential of neutralizing CD97 in arthritis was studied with emphasis on the 1B2 pharmacokinetics. Mice with established arthritis were treated with anti-mCD97 or anti-TNF-alpha serum. Ab pharmacokinetics and biodistribution were studied in diseased and nondiseased mice using labeled 1B2. The impact of CD97 expression on Ab pharmacokinetics was studied using CD97 knockout mice. Treatment with 1B2 showed an efficacy comparable to anti-TNF-alpha treatment. Pharmacokinetic analysis of 1B2 in wild-type and CD97 knockout mice indicated a dose-dependent Ab clearance, due to specific interaction with CD97. Biodistribution studies showed accumulation of 1B2 in spleen and lung. In vitro studies using murine splenocytes revealed that CD97 when bound to Ab was internalized. Moreover, soluble CD97 was detected in the supernatant, suggesting Ag shedding. Finally, in arthritic mice, higher levels of soluble CD97 were found and 1B2 treatment led to specific targeting of inflamed paws, resulting in a higher clearance rate of 1B2 in arthritic mice than in wild-type mice. In conclusion, our data support a therapeutic value of CD97 neutralization in experimental arthritis. The pharmacokinetic profile of the 1B2 Ab illustrates the complexity of Ab elimination from an organism and stresses the importance of understanding Ag-Ab interactions when developing therapeutic mAbs.

Single-cell intracellular epitope and transcript detection reveals signal transduction dynamics.

To further our understanding of how biochemical information flows through cells upon external stimulation, we require single-cell multi-omics methods that concurrently map changes in (phospho)protein levels across signaling networks and the associated gene expression profiles. Here, we present quantification of RNA and intracellular epitopes by sequencing (QuRIE-seq), a droplet-based platform for single-cell RNA and intra- and extracellular (phospho)protein quantification through sequencing. We applied QuRIE-seq to quantify cell-state changes at both the signaling and the transcriptome level after 2-, 4-, 6-, 60-, and 180-min stimulation of the B cell receptor pathway in Burkitt lymphoma cells. Using the multi-omics factor analysis (MOFA+) framework, we delineated changes in single-cell (phospho)protein and gene expression patterns over multiple timescales and revealed the effect of an inhibitory drug (ibrutinib) on signaling and gene expression landscapes.

CD97 in leukocyte trafficking.

CD97 is a member of the EGF-TM7 family of adhesion G protein-coupled receptors (GPCRs) broadly expressed on leukocytes. CD97 interacts with several cellular ligands via its N-terminal epidermal growth factor (EGF)-like domains. To understand the biological function of CD97, monoclonal antibodies (mAbs) specific for individual EGF domains have been applied in a variety of in vivo models in mice, which represent different aspects of innate and adaptive immunity. Targeting CD97 by mAbs inhibited the accumulation of neutrophilic granulocytes at sites of inflammation thereby affecting antibacterial host defense, inflammatory disorders and stem cell mobilization from bone marrow. Interestingly, targeting CD97 did not impact antigen-specific (adaptive response) models such as delayed type hypersensitivity (DTH) or experimental autoimmune encephalomyelitis (EAE). However, collagen-induced arthritis (CIA), a model for rheumatoid arthritis, was significantly ameliorated suggesting therapeutic value of CD97 targeting. CD97-deficient mice are essentially normal at steady state except for a mild granulocytosis, which increases under inflammatory conditions. Comparison of the consequences of antibody treatment and gene targeting implies that CD97 mAbs actively inhibit the innate response presumably at the level of granulocyte or macrophage recruitment to sites of inflammation. Based on the collected data, we propose that the CD97 mAbs either activate CD97-mediated signal transduction via a yet unknown mechanism or act by inducing CD97 internalization, making CD97 unavailable for binding to its ligands and thereby blocking recruitment of neutrophils and possibly macrophages.

Helpless Priming Sends CD8+ T Cells on the Road to Exhaustion.

Persistent antigen exposure in chronic infection and cancer has been proposed to lead to cytotoxic T lymphocyte (CTL) "exhaustion", i.e., loss of effector function and disease control. Recent work identifies a population of poorly differentiated TCF-1+PD-1+ CD8+ T cells as precursors of the terminally exhausted CTL pool. These "predysfunctional" CTLs are suggested to respond to PD-1 targeted therapy by giving rise to a pool of functional CTLs. Supported by gene expression analyses, we present a model in which lack of CD4+ T cell help during CD8+ T cell priming results in the formation of predysfunctional CTLs. Our model implies that predysfunctional CTLs are formed during priming and that the remedy for CTL dysfunction is to provide "help" signals for generation of optimal CTL effectors. We substantiate that this may be achieved by engaging CD4+ T cells in new CD8+ T cell priming, or by combined PD-1 blocking and CD27 agonism with available immunotherapeutic antibodies.

Biophysical and Immunological Characterization and In Vivo Pharmacokinetics and Toxicology in Nonhuman Primates of the Anti-PD-1 Antibody Pembrolizumab.

The programmed cell death 1 (PD-1) pathway represents a major immune checkpoint, which may be engaged by cells in the tumor microenvironment to overcome active T-cell immune surveillance. Pembrolizumab (Keytruda®, MK-3475) is a potent and highly selective humanized mAb of the IgG4/kappa isotype designed to directly block the interaction between PD-1 and its ligands, PD-L1 and PD-L2. This blockade enhances the functional activity of T cells to facilitate tumor regression and ultimately immune rejection. Pembrolizumab binds to human and cynomolgus monkey PD-1 with picomolar affinity and blocks the binding of human and cynomolgus monkey PD-1 to PD-L1 and PD-L2 with comparable potency. Pembrolizumab binds both the C'D and FG loops of PD-1. Pembrolizumab overcomes human and cynomolgus monkey PD-L1-mediated immune suppression in T-cell cultures by enhancing IL2 production following staphylococcal enterotoxin B stimulation of healthy donor and cancer patient cells, and IFNγ production in human primary tumor histoculture. Ex vivo and in vitro studies with human and primate T cells show that pembrolizumab enhances antigen-specific T-cell IFNγ and IL2 production. Pembrolizumab does not mediate FcR or complement-driven effector function against PD-1-expressing cells. Pembrolizumab displays dose-dependent clearance and half-life in cynomolgus monkey pharmacokinetic and toxicokinetic studies typical for human IgG4 antibodies. In nonhuman primate toxicology studies, no findings of toxicologic significance were observed. The preclinical data for pembrolizumab are consistent with the clinical anticancer activity and safety that has been demonstrated in human clinical trials.

Blockade of ErbB2 and PD-L1 using a bispecific antibody to improve targeted anti-ErbB2 therapy.

A significant proportion of human epidermal growth factor receptor 2 (Her2/ErbB2)-positive metastatic breast cancer patients are refractory to Her2-targeted trastuzumab-like therapy. Some of this resistance has been attributed to the upregulation of immune checkpoints such as programmed cell death-1 (PD-1) and its ligand, PD-L1 in Her2-positive breast cancer patients. Therefore, therapies targeting both the PD-1/PD-L1 interaction and oncogenic Her2 signaling are of significant clinical interest. Here, we constructed a mouse bispecific antibody targeting PD-L1 and rat Her2 (referred to as BsPD-L1xrErbB2) aiming to redirect the anti-PD-L1 response toward Her2-expressing tumor cells. BsPD-L1xrErbB2 demonstrated additive binding to interferon (IFN)-γ treated Her2+ TUBO tumor cells, but it did not affect the proliferation of tumor cells in-vitro. BsPD-L1xrErbB2 also blocked the PD-1/PD-L1 interaction. This bispecific antibody was constructed with a mouse IgG2a Fc backbone and interacted with Fcγ receptors and resulted in complement deposition (C3). ADCC and complement action could be potential mechanisms of action of this molecule. BsPD-L1xrErbB2 successfully reduced TUBO tumor growth and increased tumor rejection rate compared to the monovalent anti-PD-L1, monovalent anti-ErbB2 or the combination of anti-PD-L1 and anti-ErbB2 monotherapies. The enhanced anti-tumor effect of BsPD-L1xrErbB2 was dependent on CD8+ T lymphocytes and IFN-γ, as depletion of CD8+ T lymphocytes and neutralization of IFN-γ completely abolished the antitumor activity of the bispecific antibody. Consistently, BsPD-L1xrErbB2 treatment also increased the frequency of intratumor CD8+ T lymphocytes. Taken together, our data support a bispecific antibody approach to enhance the anti-tumor efficacy of PD-1/PD-L1 checkpoint blockade in Her2-positive metastatic breast cancers.

Functional characterization of the selective pan-allele anti-SIRPα antibody ADU-1805 that blocks the SIRPα-CD47 innate immune checkpoint.

BACKGROUND: Accumulating preclinical data indicate that targeting the SIRPα/CD47 axis alone or in combination with existing targeted therapies or immune checkpoint inhibitors enhances tumor rejection. Although several CD47-targeting agents are currently in phase I clinical trials and demonstrate activity in combination therapy, high and frequent dosing was required and safety signals (acute anemia, thrombocytopenia) were recorded frequently as adverse events. Based on the restricted expression pattern of SIRPα we hypothesized that antibodies targeting SIRPα might avoid some of the concerns noted for CD47-targeting agents. METHODS: SIRPα-targeting antibodies were generated and characterized for binding to human SIRPα alleles and blockade of the interaction with CD47. Functional activity was established in vitro using human macrophages or neutrophils co-cultured with human Burkitt's lymphoma cell lines. The effect of SIRPα versus CD47 targeting on human T-cell activation was studied using an allogeneic mixed lymphocyte reaction and a Staphylococcus enterotoxin B-induced T-cell proliferation assay. Potential safety concerns of the selected SIRPα-targeting antibody were addressed in vitro using a hemagglutination assay and a whole blood cytokine release assay, and in vivo in a single-dose toxicity study in cynomolgus monkeys. RESULTS: The humanized monoclonal IgG2 antibody ADU-1805 binds to all known human SIRPα alleles, showing minimal binding to SIRPß1, while cross-reacting with SIRPγ, and potently blocking the interaction of SIRPα with CD47. Reduced FcγR binding proved critical to retaining its function towards phagocyte activation. In vitro characterization demonstrated that ADU-1805 promotes macrophage phagocytosis, with similar potency to anti-CD47 antibodies, and enhances neutrophil trogocytosis. Unlike CD47-targeting agents, ADU-1805 does not interfere with T-cell activation and is not expected to require frequent and extensive dosing due to the restricted expression of SIRPα to cells of the myeloid lineage. ADU-1805 is cross-reactive to cynomolgus monkey SIRPα and upon single-dose intravenous administration in these non-human primates (NHPs) did not show any signs of anemia, thrombocytopenia or other toxicities. CONCLUSIONS: Blocking the SIRPα-CD47 interaction via SIRPα, while similarly efficacious in vitro, differentiates ADU-1805 from CD47-targeting agents with respect to safety and absence of inhibition of T-cell activation. The data presented herein support further advancement of ADU-1805 towards clinical development.

Basic helix-loop-helix transcription factor Tcfl5 interacts with the Calmegin gene promoter in mouse spermatogenesis.

In mouse spermatogenesis, differentiating germ line cells initiate expression of specific genes at subsequent developmental steps. The Calmegin (Clgn) gene is first expressed in meiotic prophase, in primary spermatocytes, and encodes a protein that acts as a chaperone. To identify testis-specific transcription factors that control expression of the Clgn gene in spermatogenesis, we performed a yeast one-hybrid screening with a Clgn promoter sequence as bait DNA. This screening resulted in the identification of mouse Tcfl5 as a candidate Clgn promoter-binding protein. Tcfl5 is a member of the basic helix-loop-helix (bHLH) family of transcription factors, and mouse Tcfl5 shows 83% amino acid sequence identity with human TCFL5. Gel-shift and yeast one-hybrid experiments showed that Tcfl5 interacts with a non-canonical CACGCG site that is present in the Clgn promoter. By using northern blot, RT-PCR and in situ hybridization, mouse Tcfl5 mRNA was detected only in testis, with the highest expression level in primary spermatocytes and round spermatids. The highest level of Tcfl5 protein was found in primary spermatocytes at the diplotene stage of meiotic prophase, where the protein colocalizes with transcriptionally active chromatin.