IL2 Targeted to CD8+ T Cells Promotes Robust Effector T-cell Responses and Potent Antitumor Immunity.

IL2 signals pleiotropically on diverse cell types, some of which contribute to therapeutic activity against tumors, whereas others drive undesired activity, such as immunosuppression or toxicity. We explored the theory that targeting of IL2 to CD8+ T cells, which are key antitumor effectors, could enhance its therapeutic index. To this aim, we developed AB248, a CD8 cis-targeted IL2 that demonstrates over 500-fold preference for CD8+ T cells over natural killer and regulatory T cells (Tregs), which may contribute to toxicity and immunosuppression, respectively. AB248 recapitulated IL2's effects on CD8+ T cells in vitro and induced selective expansion of CD8+T cells in primates. In mice, an AB248 surrogate demonstrated superior antitumor activity and enhanced tolerability as compared with an untargeted IL2Rßγ agonist. Efficacy was associated with the expansion and phenotypic enhancement of tumor-infiltrating CD8+ T cells, including the emergence of a "better effector" population. These data support the potential utility of AB248 in clinical settings. Significance: The full potential of IL2 therapy remains to be unlocked. We demonstrate that toxicity can be decoupled from antitumor activity in preclinical models by limiting IL2 signaling to CD8+ T cells, supporting the development of CD8+ T cell-selective IL2 for the treatment of cancer. See related article by Kaptein et al. p. 1226.

Targeting of the CD161 inhibitory receptor enhances T-cell-mediated immunity against hematological malignancies.

ABSTRACT: The CD161 inhibitory receptor is highly upregulated by tumor-infiltrating T cells in multiple human solid tumor types, and its ligand, CLEC2D, is expressed by both tumor cells and infiltrating myeloid cells. Here, we assessed the role of the CD161 receptor in hematological malignancies. Systematic analysis of CLEC2D expression using the Cancer Cell Line Encyclopedia revealed that CLEC2D messenger RNA was most abundant in hematological malignancies, including B-cell and T-cell lymphomas as well as lymphocytic and myelogenous leukemias. CLEC2D protein was detected by flow cytometry on a panel of cell lines representing a diverse set of hematological malignancies. We, therefore, used yeast display to generate a panel of high-affinity, fully human CD161 monoclonal antibodies (mAbs) that blocked CLEC2D binding. These mAbs were specific for CD161 and had a similar affinity for human and nonhuman primate CD161, a property relevant for clinical translation. A high-affinity CD161 mAb enhanced key aspects of T-cell function, including cytotoxicity, cytokine production, and proliferation, against B-cell lines originating from patients with acute lymphoblastic leukemia, diffuse large B-cell lymphoma, and Burkitt lymphoma. In humanized mouse models, this CD161 mAb enhanced T-cell-mediated immunity, resulting in a significant survival benefit. Single cell RNA-seq data demonstrated that CD161 mAb treatment enhanced expression of cytotoxicity genes by CD4 T cells as well as a tissue-residency program by CD4 and CD8 T cells that is associated with favorable survival outcomes in multiple human cancer types. These fully human mAbs, thus, represent potential immunotherapy agents for hematological malignancies.

Systematic Interrogation of Tumor Cell Resistance to Chimeric Antigen Receptor T-cell Therapy in Pancreatic Cancer.

Chimeric antigen receptor (CAR) T-cell therapy can lead to dramatic clinical responses in B-cell malignancies. However, early clinical trials with CAR T-cell therapy in non-B-cell malignancies have been disappointing to date, suggesting that tumor-intrinsic features contribute to resistance. To investigate tumor-intrinsic modes of resistance, we performed genome scale CRISPR-Cas9 screens in mesothelin (MSLN)-expressing pancreatic cancer cells. Co-culture with MSLN-targeting CAR T cells identified both antigen-dependent and antigen-independent modes of resistance. In particular, loss of the majority of the genes involved in the pathway responsible for GPI-anchor biosynthesis and attachment abrogated the ability of CAR T cells to target pancreatic cancer cells, suggesting that disruption of this pathway may permit MSLN CAR T-cell evasion in the clinic. Antigen-independent mediators of CAR T-cell response included members of the death receptor pathway as well as genes that regulate tumor transcriptional responses, including TFAP4 and INTS12. TFAP4-mediated CAR T resistance depended on the NFκB transcription factor p65, indicating that tumor resistance to CAR T-cell therapy likely involves alterations in tumor-intrinsic states. Overall, this study uncovers multiple antigen-dependent and -independent mechanisms of CAR T-cell evasion by pancreatic cancer, paving the way for overcoming resistance in this disease that is notoriously refractory to immunotherapy. SIGNIFICANCE: The identification and validation of key determinants of CAR T-cell response in pancreatic cancer provide insights into the landscape of tumor cell intrinsic resistance mechanisms and into approaches to improve therapeutic efficacy.

BAF Complex Maintains Glioma Stem Cells in Pediatric H3K27M Glioma.

Diffuse midline gliomas are uniformly fatal pediatric central nervous system cancers that are refractory to standard-of-care therapeutic modalities. The primary genetic drivers are a set of recurrent amino acid substitutions in genes encoding histone H3 (H3K27M), which are currently undruggable. These H3K27M oncohistones perturb normal chromatin architecture, resulting in an aberrant epigenetic landscape. To interrogate for epigenetic dependencies, we performed a CRISPR screen and show that patient-derived H3K27M-glioma neurospheres are dependent on core components of the mammalian BAF (SWI/SNF) chromatin remodeling complex. The BAF complex maintains glioma stem cells in a cycling, oligodendrocyte precursor cell-like state, in which genetic perturbation of the BAF catalytic subunit SMARCA4 (BRG1), as well as pharmacologic suppression, opposes proliferation, promotes progression of differentiation along the astrocytic lineage, and improves overall survival of patient-derived xenograft models. In summary, we demonstrate that therapeutic inhibition of the BAF complex has translational potential for children with H3K27M gliomas. SIGNIFICANCE: Epigenetic dysregulation is at the core of H3K27M-glioma tumorigenesis. Here, we identify the BRG1-BAF complex as a critical regulator of enhancer and transcription factor landscapes, which maintain H3K27M glioma in their progenitor state, precluding glial differentiation, and establish pharmacologic targeting of the BAF complex as a novel treatment strategy for pediatric H3K27M glioma. See related commentary by Beytagh and Weiss, p. 2730. See related article by Mo et al., p. 2906.

Interactions between cancer cells and immune cells drive transitions to mesenchymal-like states in glioblastoma.

The mesenchymal subtype of glioblastoma is thought to be determined by both cancer cell-intrinsic alterations and extrinsic cellular interactions, but remains poorly understood. Here, we dissect glioblastoma-to-microenvironment interactions by single-cell RNA sequencing analysis of human tumors and model systems, combined with functional experiments. We demonstrate that macrophages induce a transition of glioblastoma cells into mesenchymal-like (MES-like) states. This effect is mediated, both in vitro and in vivo, by macrophage-derived oncostatin M (OSM) that interacts with its receptors (OSMR or LIFR) in complex with GP130 on glioblastoma cells and activates STAT3. We show that MES-like glioblastoma states are also associated with increased expression of a mesenchymal program in macrophages and with increased cytotoxicity of T cells, highlighting extensive alterations of the immune microenvironment with potential therapeutic implications.

CARM1 Inhibition Enables Immunotherapy of Resistant Tumors by Dual Action on Tumor Cells and T Cells.

A number of cancer drugs activate innate immune pathways in tumor cells but unfortunately also compromise antitumor immune function. We discovered that inhibition of CARM1, an epigenetic enzyme and cotranscriptional activator, elicited beneficial antitumor activity in both cytotoxic T cells and tumor cells. In T cells, Carm1 inactivation substantially enhanced their antitumor function and preserved memory-like populations required for sustained antitumor immunity. In tumor cells, Carm1 inactivation induced a potent type 1 interferon response that sensitized resistant tumors to cytotoxic T cells. Substantially increased numbers of dendritic cells, CD8 T cells, and natural killer cells were present in Carm1-deficient tumors, and infiltrating CD8 T cells expressed low levels of exhaustion markers. Targeting of CARM1 with a small molecule elicited potent antitumor immunity and sensitized resistant tumors to checkpoint blockade. Targeting of this cotranscriptional regulator thus offers an opportunity to enhance immune function while simultaneously sensitizing resistant tumor cells to immune attack. SIGNIFICANCE: Resistance to cancer immunotherapy remains a major challenge. Targeting of CARM1 enables immunotherapy of resistant tumors by enhancing T-cell functionality and preserving memory-like T-cell populations within tumors. CARM1 inhibition also sensitizes resistant tumor cells to immune attack by inducing a tumor cell-intrinsic type 1 interferon response.This article is highlighted in the In This Issue feature, p. 1861.

Inhibitory CD161 receptor identified in glioma-infiltrating T cells by single-cell analysis.

T cells are critical effectors of cancer immunotherapies, but little is known about their gene expression programs in diffuse gliomas. Here, we leverage single-cell RNA sequencing (RNA-seq) to chart the gene expression and clonal landscape of tumor-infiltrating T cells across 31 patients with isocitrate dehydrogenase (IDH) wild-type glioblastoma and IDH mutant glioma. We identify potential effectors of anti-tumor immunity in subsets of T cells that co-express cytotoxic programs and several natural killer (NK) cell genes. Analysis of clonally expanded tumor-infiltrating T cells further identifies the NK gene KLRB1 (encoding CD161) as a candidate inhibitory receptor. Accordingly, genetic inactivation of KLRB1 or antibody-mediated CD161 blockade enhances T cell-mediated killing of glioma cells in vitro and their anti-tumor function in vivo. KLRB1 and its associated transcriptional program are also expressed by substantial T cell populations in other human cancers. Our work provides an atlas of T cells in gliomas and highlights CD161 and other NK cell receptors as immunotherapy targets.

Opposing immune and genetic mechanisms shape oncogenic programs in synovial sarcoma.

Synovial sarcoma (SyS) is an aggressive neoplasm driven by the SS18-SSX fusion, and is characterized by low T cell infiltration. Here, we studied the cancer-immune interplay in SyS using an integrative approach that combines single-cell RNA sequencing (scRNA-seq), spatial profiling and genetic and pharmacological perturbations. scRNA-seq of 16,872 cells from 12 human SyS tumors uncovered a malignant subpopulation that marks immune-deprived niches in situ and is predictive of poor clinical outcomes in two independent cohorts. Functional analyses revealed that this malignant cell state is controlled by the SS18-SSX fusion, is repressed by cytokines secreted by macrophages and T cells, and can be synergistically targeted with a combination of HDAC and CDK4/CDK6 inhibitors. This drug combination enhanced malignant-cell immunogenicity in SyS models, leading to induced T cell reactivity and T cell-mediated killing. Our study provides a blueprint for investigating heterogeneity in fusion-driven malignancies and demonstrates an interplay between immune evasion and oncogenic processes that can be co-targeted in SyS and potentially in other malignancies.

Integrin αvß6-TGFß-SOX4 Pathway Drives Immune Evasion in Triple-Negative Breast Cancer.

Cancer immunotherapy shows limited efficacy against many solid tumors that originate from epithelial tissues, including triple-negative breast cancer (TNBC). We identify the SOX4 transcription factor as an important resistance mechanism to T cell-mediated cytotoxicity for TNBC cells. Mechanistic studies demonstrate that inactivation of SOX4 in tumor cells increases the expression of genes in a number of innate and adaptive immune pathways important for protective tumor immunity. Expression of SOX4 is regulated by the integrin αvß6 receptor on the surface of tumor cells, which activates TGFß from a latent precursor. An integrin αvß6/8-blocking monoclonal antibody (mAb) inhibits SOX4 expression and sensitizes TNBC cells to cytotoxic T cells. This integrin mAb induces a substantial survival benefit in highly metastatic murine TNBC models poorly responsive to PD-1 blockade. Targeting of the integrin αvß6-TGFß-SOX4 pathway therefore provides therapeutic opportunities for TNBC and other highly aggressive human cancers of epithelial origin.

Distinct evolutionary paths in chronic lymphocytic leukemia during resistance to the graft-versus-leukemia effect.

Leukemic relapse remains a major barrier to successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) for aggressive hematologic malignancies. The basis for relapse of advanced lymphoid malignancies remains incompletely understood and may involve escape from the graft-versus-leukemia (GvL) effect. We hypothesized that for patients with chronic lymphocytic leukemia (CLL) treated with allo-HSCT, leukemic cell-intrinsic features influence transplant outcomes by directing the evolutionary trajectories of CLL cells. Integrated genetic, transcriptomic, and epigenetic analyses of CLL cells from 10 patients revealed that the clinical kinetics of post-HSCT relapse are shaped by distinct molecular dynamics. Early relapses after allo-HSCT exhibited notable genetic stability; single CLL cell transcriptional analysis demonstrated a cellular heterogeneity that was static over time. In contrast, CLL cells relapsing late after allo-HSCT displayed notable genetic evolution and evidence of neoantigen depletion, consistent with marked single-cell transcriptional shifts that were unique to each patient. We observed a greater rate of epigenetic change for late relapses not seen in early relapses or relapses after chemotherapy alone, suggesting that the selection pressures of the GvL bottleneck are unlike those imposed by chemotherapy. No selective advantage for human leukocyte antigen (HLA) loss was observed, even when present in pretransplant subpopulations. Gain of stem cell modules was a common signature associated with leukemia relapse regardless of posttransplant relapse kinetics. These data elucidate the biological pathways that underlie GvL resistance and posttransplant relapse.

Single-Cell RNA-Seq Reveals Cellular Hierarchies and Impaired Developmental Trajectories in Pediatric Ependymoma.

Ependymoma is a heterogeneous entity of central nervous system tumors with well-established molecular groups. Here, we apply single-cell RNA sequencing to analyze ependymomas across molecular groups and anatomic locations to investigate their intratumoral heterogeneity and developmental origins. Ependymomas are composed of a cellular hierarchy initiating from undifferentiated populations, which undergo impaired differentiation toward three lineages of neuronal-glial fate specification. While prognostically favorable groups of ependymoma predominantly harbor differentiated cells, aggressive groups are enriched for undifferentiated cell populations. The delineated transcriptomic signatures correlate with patient survival and define molecular dependencies for targeted treatment approaches. Taken together, our analyses reveal a developmental hierarchy underlying ependymomas relevant to biological and clinical behavior.

Neoantigen vaccine generates intratumoral T cell responses in phase Ib glioblastoma trial.

Neoantigens, which are derived from tumour-specific protein-coding mutations, are exempt from central tolerance, can generate robust immune responses1,2 and can function as bona fide antigens that facilitate tumour rejection3. Here we demonstrate that a strategy that uses multi-epitope, personalized neoantigen vaccination, which has previously been tested in patients with high-risk melanoma4-6, is feasible for tumours such as glioblastoma, which typically have a relatively low mutation load1,7 and an immunologically 'cold' tumour microenvironment8. We used personalized neoantigen-targeting vaccines to immunize patients newly diagnosed with glioblastoma following surgical resection and conventional radiotherapy in a phase I/Ib study. Patients who did not receive dexamethasone-a highly potent corticosteroid that is frequently prescribed to treat cerebral oedema in patients with glioblastoma-generated circulating polyfunctional neoantigen-specific CD4+ and CD8+ T cell responses that were enriched in a memory phenotype and showed an increase in the number of tumour-infiltrating T cells. Using single-cell T cell receptor analysis, we provide evidence that neoantigen-specific T cells from the peripheral blood can migrate into an intracranial glioblastoma tumour. Neoantigen-targeting vaccines thus have the potential to favourably alter the immune milieu of glioblastoma.

SAG/RBX2 E3 Ubiquitin Ligase Differentially Regulates Inflammatory Responses of Myeloid Cell Subsets.

Macrophages form an important component of the innate immune system and serve as first responders against invading pathogens. While pathways critical for initiation of inflammatory responses between macrophages and other LysM+ myeloid cells are largely similar, it remains unknown whether a specific pathway has differential effects on inflammatory responses mediated between these cells. Recent studies demonstrated that depletion of SAG (Sensitive to Apoptosis Gene), an E3 ubiquitin ligase, blocked inflammatory responses generated by macrophages and dendritic cells in response to LPS in cell culture settings. However, the in vivo role of Sag on modulation of macrophages and neutrophil is not known. Here we generated LysM-Cre/Sagfl/fl mice with selective Sag deletion in myeloid lineage, and found that in contrast to in vitro observations, LysM-Cre/Sagfl/fl mice showed increased serum levels of proinflammatory cytokines and enhanced mortality in response to LPS. Interestingly, while Sag-/- macrophages released less proinflammatory cytokines, Sag-/- neutrophils released more. Mechanistically, expression of a list of genes response to LPS was significantly altered in bone marrow cells from LysM-Cre+/Sagfl/fl mice after LPS challenge. Specifically, induction by LPS of myeloperoxidase (Mpo), a key neutrophil enzyme, and Elane, neutrophil expressed elastase, was significantly decreased upon Sag depletion. Collectively, our study revealed that Sag plays a differential role in the activation of macrophages and neutrophils.

Developmental and oncogenic programs in H3K27M gliomas dissected by single-cell RNA-seq.

Gliomas with histone H3 lysine27-to-methionine mutations (H3K27M-glioma) arise primarily in the midline of the central nervous system of young children, suggesting a cooperation between genetics and cellular context in tumorigenesis. Although the genetics of H3K27M-glioma are well characterized, their cellular architecture remains uncharted. We performed single-cell RNA sequencing in 3321 cells from six primary H3K27M-glioma and matched models. We found that H3K27M-glioma primarily contain cells that resemble oligodendrocyte precursor cells (OPC-like), whereas more differentiated malignant cells are a minority. OPC-like cells exhibit greater proliferation and tumor-propagating potential than their more differentiated counterparts and are at least in part sustained by PDGFRA signaling. Our study characterizes oncogenic and developmental programs in H3K27M-glioma at single-cell resolution and across genetic subclones, suggesting potential therapeutic targets in this disease.

A Critical Analysis of the Role of SNARE Protein SEC22B in Antigen Cross-Presentation.

Cross-presentation initiates immune responses against tumors and viral infections by presenting extracellular antigen on MHC I to activate CD8+ T cell-mediated cytotoxicity. In vitro studies in dendritic cells (DCs) established SNARE protein SEC22B as a specific regulator of cross-presentation. However, the in vivo contribution of SEC22B to cross-presentation has not been tested. To address this, we generated DC-specific Sec22b knockout (CD11c-Cre Sec22bfl/fl) mice. Contrary to the paradigm, SEC22B-deficient DCs efficiently cross-present both in vivo and in vitro. Although in vitro small hairpin RNA (shRNA)-mediated Sec22b silencing in bone-marrow-derived dendritic cells (BMDCs) reduced cross-presentation, treatment of SEC22B-deficient BMDCs with the same shRNA produced a similar defect, suggesting the Sec22b shRNA modulates cross-presentation through off-target effects. RNA sequencing of Sec22b shRNA-treated SEC22B-deficient BMDCs demonstrated several changes in the transcriptome. Our data demonstrate that contrary to the accepted model, SEC22B is not necessary for cross-presentation, cautioning against extrapolating phenotypes from knockdown studies alone.

Danger Signals and Graft-versus-host Disease: Current Understanding and Future Perspectives.

Graft-versus-host response after allogeneic hematopoietic stem cell transplantation (allo-HCT) represents one of the most intense inflammatory responses observed in humans. Host conditioning facilitates engraftment of donor cells, but the tissue injury caused from it primes the critical first steps in the development of acute graft-versus-host disease (GVHD). Tissue injuries release pro-inflammatory cytokines (such as TNF-α, IL-1ß, and IL-6) through widespread stimulation of pattern recognition receptors (PRRs) by the release of danger stimuli, such as damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs). DAMPs and PAMPs function as potent stimulators for host and donor-derived antigen presenting cells (APCs) that in turn activate and amplify the responses of alloreactive donor T cells. Emerging data also point towards a role for suppression of DAMP induced inflammation by the APCs and donor T cells in mitigating GVHD severity. In this review, we summarize the current understanding on the role of danger stimuli, such as the DAMPs and PAMPs, in GVHD.

SAG/Rbx2-Dependent Neddylation Regulates T-Cell Responses.

Neddylation is a crucial post-translational modification that depends on the E3 cullin ring ligase (CRL). The E2-adapter component of the CRL, sensitive to apoptosis gene (SAG), is critical for the function of CRL-mediated ubiquitination; thus, the deletion of SAG regulates neddylation. We examined the role of SAG-dependent neddylation in T-cell-mediated immunity using multiple approaches: a novel T-cell-specific, SAG genetic knockout (KO) and chemical inhibition with small-molecule MLN4924. The KO animals were viable and showed phenotypically normal mature T-cell development. However, in vitro stimulation of KO T cells revealed significantly decreased activation, proliferation, and T-effector cytokine release, compared with WT. Using in vivo clinically relevant models of allogeneic bone marrow transplantation also demonstrated reduced proliferation and effector cytokine secretion associated with markedly reduced graft-versus-host disease. Similar in vitro and in vivo results were observed with the small-molecule inhibitor of neddylation, MLN4924. Mechanistic studies demonstrated that SAG-mediated effects in T cells were concomitant with an increase in suppressor of cytokine signaling, but not NF-κB translocation. Our studies suggest that SAG is a novel molecular target that regulates T-cell responses and that inhibiting neddylation with the clinically available small-molecule MLN4924 may represent a novel strategy to mitigate T-cell-mediated immunopathologies, such as graft-versus-host disease.

Gut microbiome-derived metabolites modulate intestinal epithelial cell damage and mitigate graft-versus-host disease.

The effect of alterations in intestinal microbiota on microbial metabolites and on disease processes such as graft-versus-host disease (GVHD) is not known. Here we carried out an unbiased analysis to identify previously unidentified alterations in gastrointestinal microbiota-derived short-chain fatty acids (SCFAs) after allogeneic bone marrow transplant (allo-BMT). Alterations in the amount of only one SCFA, butyrate, were observed only in the intestinal tissue. The reduced butyrate in CD326(+) intestinal epithelial cells (IECs) after allo-BMT resulted in decreased histone acetylation, which was restored after local administration of exogenous butyrate. Butyrate restoration improved IEC junctional integrity, decreased apoptosis and mitigated GVHD. Furthermore, alteration of the indigenous microbiota with 17 rationally selected strains of high butyrate-producing Clostridia also decreased GVHD. These data demonstrate a heretofore unrecognized role of microbial metabolites and suggest that local and specific alteration of microbial metabolites has direct salutary effects on GVHD target tissues and can mitigate disease severity.