Harnessing the cytotoxic granule exocytosis to augment the efficacy of T-cell-engaging bispecific antibody therapy.

T-cell-engaging bispecific antibody (T-BsAb, also known as BiTE) therapy has emerged as a powerful therapeutic modality against multiple myeloma. Given that T-BsAb therapy redirects endogenous T cells to eliminate tumor cells, reinvigorating dysfunctional T cells may be a potential approach to improve the efficacy of T-BsAb. While various immunostimulatory cytokines can potentiate effector T-cell functions, the optimal cytokine treatment for T-BsAb therapy is yet to be established, partly due to a concern of cytokine release syndrome driven by aberrant interferon (IFN)-γ production. Here, we functionally screen immunostimulatory cytokines to determine an ideal combination partner for T-BsAb therapy. This approach reveals IL-21 as a potential immunostimulatory cytokine with the ability to augment T-BsAb-mediated release of granzyme B and perforin, without increasing IFN-γ release. Transcriptome profiling and functional characterization strongly support that IL-21 selectively targets the cytotoxic granule exocytosis pathway, but not pro-inflammatory responses. Notably, IL-21 modulates multiple steps of cytotoxic effector functions including upregulation of co-activating CD226 receptor, increasing cytotoxic granules, and promoting cytotoxic granule delivery at the immunological synapse. Indeed, T-BsAb-mediated myeloma-killing is cytotoxic granule-dependent, and IL-21 priming significantly augments cytotoxic activities. Furthermore, in vivo IL-21 treatment induces cytotoxic effector reprogramming in bone marrow T cells, showing synergistic anti-myeloma effects in combination with T-BsAb therapy. Together, harnessing the cytotoxic granule exocytosis pathway by IL-21 may be a potential approach to achieve better responses by T-BsAb therapy.

Regulatory T cells hamper the efficacy of T-cell-engaging bispecific antibody therapy.

T-cell-engaging bispecific antibodies (T-BsAb) have produced impressive clinical responses in patients with relapsed/refractory B-cell malignancies, although treatment failure remains a major clinical challenge. Growing evidence suggests that a complex interplay between immune cells and tumor cells is implicated in the mechanism of action and therefore, understanding immune regulatory mechanisms might provide a clue for how to improve the efficacy of T-BsAb therapy. Here, we investigated the functional impact of regulatory T (Treg) cells on anti-tumor immunity elicited by T-BsAb therapy. In a preclinical model of myeloma, the activation and expansion of Treg cells in the bone marrow were observed in response to anti-B-cell maturation antigen (BCMA) T-BsAb therapy. T-BsAb triggered the generation of induced Treg cells from human conventional CD4 cells after co-culture with tumor cells. Moreover, T-BsAb directly activated freshly isolated circulating Treg cells, leading to the production of interleukin-10 and inhibition of T-BsAb-mediated CD8 T-cell responses. The activation of Treg cells was also seen in bone marrow samples from myeloma patients after ex vivo treatment with T-BsAb, further supporting that T-BsAb have an impact on Treg homeostasis. Importantly, transient ablation of Treg cells in combination with T-BsAb therapy dramatically improved effector lymphocyte activities and disease control in the preclinical myeloma model, leading to prolonged survival. Together, this information suggests that therapy-induced activation of Treg cells critically regulates anti-tumor immunity elicited by T-BsAb therapy, with important implications for improving the efficacy of such treatment.

Inhibition of CD39 unleashes macrophage antibody-dependent cellular phagocytosis against B-cell lymphoma.

Redirection of tumor-associated macrophages to eliminate tumor cells holds great promise for overcoming therapeutic resistance to rituximab and other antibody drugs. Here, we determined the expression of ectonucleotidases CD39 and CD73 in diffuse large B-cell lymphoma (DLBCL), and examined the impact of extracellular ATP (eATP) metabolism on macrophage-mediated anti-lymphoma immunity. Immunostaining of tissue microarray samples showed that CD39 (the ecto-enzyme for eATP hydrolysis) was highly expressed in tumors with the non-germinal center B-cell-like (non-GCB) subtype, and to a lesser extent tumors with the GCB subtype. By contrast, the expression of CD73 (the ecto-enzyme for adenosine generation) was undetectable in tumor cells. Pharmacological blockade of CD39 prevented eATP degradation and enhanced engulfment of antibody-coated lymphoma cells by macrophages in a P2X7 receptor-dependent manner, indicating that eATP fueled antibody-dependent cellular phagocytosis (ADCP) activity. Importantly, inhibition of CD39 augmented in vivo anti-lymphoma effects by therapeutic antibodies including rituximab and daratumumab. Furthermore, the addition of a CD39 inhibitor to anti-CD20 and anti-CD47 combination therapy significantly improved survival in a disseminated model of aggressive B-cell lymphoma, supporting the benefit of dual targeting CD39-mediated eATP hydrolysis and CD47-mediated "don't eat me" signal. Together, preventing eATP degradation may be a potential approach to unleash macrophage-mediated anti-lymphoma immunity.

Invariant NKT cells dictate antitumor immunity elicited by a bispecific antibody cotargeting CD3 and BCMA.

CD3-engaging bispecific antibodies (BsAbs) have emerged as powerful therapeutic approaches by their ability to redirect T cells to eliminate tumor cells in a major histocompatibility complex-independent manner. However, how we can potentiate the efficacy of BsAbs remains largely unknown. To address this question, we investigated immunological mechanisms of action of a BsAb cotargeting CD3 and B-cell maturation antigen (BCMA) in syngeneic preclinical myeloma models. Treatment with the CD3/BCMA BsAb stimulated multiple CD3-expressing T-cell subsets and natural killer (NK) cells in the myeloma bone marrow (BM), highlighting its broad immunostimulatory effect. Notably, the BsAb-mediated immunostimulatory and antitumor effects were abrogated in mice lacking invariant NKT (iNKT) cells. Mechanistically, activation of iNKT cells and interleukin-12 production from dendritic cells (DCs) were crucial upstream events for triggering effective antitumor immunity by the BsAb. Myeloma progression was associated with a reduced number of BM iNKT cells. Importantly, the therapeutic efficacy of a single dose of CD3/BCMA BsAb was remarkably augmented by restoring iNKT cell activity, using adoptive transfer of α-galactosylceramide-loaded DCs. Together, these results reveal iNKT cells as critical players in the antitumor activity of CD3 engaging BsAbs and have important translational implications.

A simple organic solvent precipitation method to improve detection of low molecular weight proteins.

Mass spectrometry-based proteomics revolutionized global proteomic profiling. Although high molecular weight abundant proteins are readily sampled in global proteomics studies, less abundant low molecular weight proteins are often underrepresented. This includes biologically important classes of low molecular weight proteins including ligands, growth factors, peptide hormones and cytokines. Although extensive fractionation can facilitate achieving better coverage of proteome, it requires additional infrastructure, mass spectrometry time and labour. There is need for a simple method that can selectively deplete high molecular weight abundant proteins and enrich for low molecular weight less abundant proteins to improve their coverage in proteomics studies. We present a simple organic-solvent based protein precipitation method that selectively depletes high molecular weight proteins and enriches low molecular weight proteins in the soluble fraction. Using this strategy, we demonstrate identification of low molecular weight proteins that are generally underrepresented in proteomics datasets. In addition, we show the utility of this approach in identifying functional cleavage products from precursor proteins and low molecular weight short open reading frame proteins encoded by non-coding regions such as lncRNAs and UTRs. As the method does not require additional infrastructure, it can complement existing proteomics workflows to increase detection and coverage of low molecular weight proteins that are less abundant.

The Cancer-Immunity Cycle in Multiple Myeloma.

Multiple myeloma is a plasma cell malignancy that primarily affects the elderly. The global burden of multiple myeloma is increasing in many countries due to an aging population. Despite recent advances in therapy, myeloma remains an incurable disease, highlighting the pressing need for new therapies. Accumulating evidence supports that triggering the host immune system is a critical therapeutic mechanism of action by various anti-myeloma therapies. These anti-myeloma therapies include proteasome inhibitors, immunomodulatory drugs, monoclonal antibody drugs, and autologous stem cell transplantation. More recently, T cell-based immunotherapeutics (including chimeric antigen receptor T-cell therapies and bispecific T-cell engagers) have shown dramatic clinical benefits in patients with relapsed or refractory multiple myeloma. While immune-based therapeutic approaches are recognized as key modalities for improved clinical outcomes in myeloma patients, understanding the immune system in multiple myeloma patients remains elusive. The cancer-immunity cycle is a conceptual framework illustrating how immune cells recognize and eliminate tumor cells. Based on this framework, this review will provide an overview of the immune system in multiple myeloma patients and discuss potential therapeutic approaches to stimulate anti-tumor immunity.

CD155 on Tumor Cells Drives Resistance to Immunotherapy by Inducing the Degradation of the Activating Receptor CD226 in CD8+ T Cells.

The activating receptor CD226 is expressed on lymphocytes, monocytes, and platelets and promotes anti-tumor immunity in pre-clinical models. Here, we examined the role of CD226 in the function of tumor-infiltrating lymphocytes (TILs) and resistance to immunotherapy. In murine tumors, a large proportion of CD8+ TILs had decreased surface expression of CD226 and exhibited features of dysfunction, whereas CD226hi TILs were highly functional. This correlation was seen also in TILs isolated from HNSCC patients. Mutation of CD226 at tyrosine 319 (Y319) led to increased CD226 surface expression, enhanced anti-tumor immunity and improved efficacy of immune checkpoint blockade (ICB). Mechanistically, tumor-derived CD155, the ligand for CD226, initiated phosphorylation of Y319 by Src kinases, thereby enabling ubiquitination of CD226 by CBL-B, internalization, and proteasomal degradation. In pre-treatment samples from melanoma patients, CD226+CD8+ T cells correlated with improved progression-free survival following ICB. Our findings argue for the development of therapies aimed at maintaining the expression of CD226.

The NK cell granule protein NKG7 regulates cytotoxic granule exocytosis and inflammation.

Immune-modulating therapies have revolutionized the treatment of chronic diseases, particularly cancer. However, their success is restricted and there is a need to identify new therapeutic targets. Here, we show that natural killer cell granule protein 7 (NKG7) is a regulator of lymphocyte granule exocytosis and downstream inflammation in a broad range of diseases. NKG7 expressed by CD4+ and CD8+ T cells played key roles in promoting inflammation during visceral leishmaniasis and malaria-two important parasitic diseases. Additionally, NKG7 expressed by natural killer cells was critical for controlling cancer initiation, growth and metastasis. NKG7 function in natural killer and CD8+ T cells was linked with their ability to regulate the translocation of CD107a to the cell surface and kill cellular targets, while NKG7 also had a major impact on CD4+ T cell activation following infection. Thus, we report a novel therapeutic target expressed on a range of immune cells with functions in different immune responses.

Targeting an adenosine-mediated "don't eat me signal" augments anti-lymphoma immunity by anti-CD20 monoclonal antibody.

A growing body of evidence suggests that macrophage immune checkpoint molecules are potential targets in the era of cancer immunotherapy. Here we showed that extracellular adenosine, an abundant metabolite in the tumor microenvironment, critically impedes the therapeutic efficacy of anti-CD20 monoclonal antibodies (mAbs) against B-cell lymphoma. Using a syngeneic B-cell lymphoma model, we showed that host deficiency of adenosine 2A receptor (A2AR), but not A2BR, remarkably improved lymphoma control by anti-CD20 mAb therapy. Conditional deletion of A2AR in myeloid cells, and to a lesser extent in NK cells, augmented therapeutic efficacy of anti-CD20 mAb. Indeed, adenosine signaling impaired antibody-mediated cellular phagocytosis (ADCP) by macrophages and limited the generation of anti-lymphoma CD8+ T cells. Pharmacological inhibition of A2AR overcame the adenosine-mediated negative regulation of ADCP by rituximab in a xeno-transplanted lymphoma model. Moreover, aberrant overexpression of CD39, an apical ecto-enzyme for adenosine generation, showed a negative impact on prognosis in patients with diffuse large B-cell lymphoma, as well as on preclinical efficacy of rituximab. Together, adenosine acts as a "don't eat me signal", and may be a potential target to harness anti-lymphoma immunity.

Anticancer activity of a Gold(I) phosphine thioredoxin reductase inhibitor in multiple myeloma.

Multiple myeloma (MM), the second most common haematological malignancy, is a clonal plasma B-cell neoplasm that forms within the bone marrow. Despite recent advancements in treatment, MM remains an incurable disease. Auranofin, a linear gold(I) phosphine compound, has previously been shown to exert a significant anti-myeloma activity by inhibiting thioredoxin reductase (TrxR) activity. A bis-chelated tetrahedral gold(I) phosphine complex [Au(d2pype)2]Cl (where d2pype is 1,2-bis(di-2-pyridylphosphino)ethane) was previously designed to improve the gold(I) compound selectivity towards selenol- and thiol-containing proteins, such as TrxR. In this study, we show that [Au(d2pype)2]Cl significantly inhibited TrxR activity in both bortezomib-sensitive and resistant myeloma cells, which led to a significant reduction in cell proliferation and induction of apoptosis, both of which were dependent on ROS. In clonogenic assays, treatment with [Au(d2pype)2]Cl completely abrogated the tumourigenic capacity of MM cells, whereas auranofin was less effective. We also show that [Au(d2pype)2]Cl exerted a significant anti-myeloma activity in vivo in human RPMI8226 xenograft model in immunocompromised NOD/SCID mice. The MYC oncogene, known to drive myeloma progression, was downregulated in both in vitro and in vivo models when treated with [Au(d2pype)2]Cl. This study highlights the "proof of concept" that improved gold(I)-based compounds could potentially be used to not only treat MM but as an alternative tool to understand the role of the Trx system in the pathogenesis of this blood disease.

Targeting CD39 in Cancer Reveals an Extracellular ATP- and Inflammasome-Driven Tumor Immunity.

We explored the mechanism of action of CD39 antibodies that inhibit ectoenzyme CD39 conversion of extracellular ATP (eATP) to AMP and thus potentially augment eATP-P2-mediated proinflammatory responses. Using syngeneic and humanized tumor models, we contrast the potency and mechanism of anti-CD39 mAbs with other agents targeting the adenosinergic pathway. We demonstrate the critical importance of an eATP-P2X7-ASC-NALP3-inflammasome-IL18 pathway in the antitumor activity mediated by CD39 enzyme blockade, rather than simply reducing adenosine as mechanism of action. Efficacy of anti-CD39 activity was underpinned by CD39 and P2X7 coexpression on intratumor myeloid subsets, an early signature of macrophage depletion, and active IL18 release that facilitated the significant expansion of intratumor effector T cells. More importantly, anti-CD39 facilitated infiltration into T cell-poor tumors and rescued anti-PD-1 resistance. Anti-human CD39 enhanced human T-cell proliferation and Th1 cytokine production and suppressed human B-cell lymphoma in the context of autologous Epstein-Barr virus-specific T-cell transfer. SIGNIFICANCE: Overall, these data describe a potent and novel mechanism of action of antibodies that block mouse or human CD39, triggering an eATP-P2X7-inflammasome-IL18 axis that reduces intratumor macrophage number, enhances intratumor T-cell effector function, overcomes anti-PD-1 resistance, and potentially enhances the efficacy of adoptive T-cell transfer.This article is highlighted in the In This Issue feature, p. 1631.

Chemotherapy followed by anti-CD137 mAb immunotherapy improves disease control in a mouse myeloma model.

Immunotherapy holds promise for multiple myeloma (MM) patients but little is known about how MM-induced immunosuppression influences response to therapy. Here, we investigated the impact of disease progression on immunotherapy efficacy in the Vk*MYC mouse model. Treatment with agonistic anti-CD137 (4-1BB) mAbs efficiently protected mice when administered early but failed to contain MM growth when delayed more than three weeks after Vk*MYC tumor cell challenge. The quality of CD8+ T cell response to CD137 stimulation was not altered by the presence of MM, but CD8+ T cell numbers were profoundly reduced at the time of treatment. Our data suggest that an insufficient ratio of CD8+ T cells over MM cells (CD8/MM) accounts for the loss of anti-CD137 mAb efficacy. We established serum M-protein levels prior to therapy as a predictive factor of response. Moreover, we developed an in silico model to capture the dynamic interactions between CD8+ T cells and MM cells. Finally, we explored two methods to improve the CD8/MM ratio: anti-CD137 mAb immunotherapy combined with Treg-depletion or administered after chemotherapy treatment with cyclophosphamide or melphalan efficiently reduced MM burden and prolonged survival. Altogether, our data indicate that consolidation treatment with anti-CD137 mAbs might prevent MM relapse.

Comparison of agar dilution and broth microdilution methods for Clostridium difficile antimicrobial susceptibility testing.

In this study, the performance of the broth microdilution (BMD) method for testing the antimicrobial susceptibility of Clostridium difficile in comparison with the agar dilution (AD) method used by the Clinical and Laboratory Standards Institute (CLSI) was evaluated. In total, 70 non-duplicate C. difficile clinical isolates were used in this study. The minimum inhibitory concentrations (MICs) of clindamycin, moxifloxacin, metronidazole and vancomycin were examined using AD and BMD. The results showed that BMD is acceptable for routine antimicrobial susceptibility testing of C. difficile as its performance was comparable with that of the AD method. In addition, it was noted that metronidazole- and vancomycin-resistant isolates are extremely rare in Japan.