Ikaros imposes a barrier to CD8+ T cell differentiation by restricting autocrine IL-2 production

Foxp3 depends on Ikaros for control of regulatory T cell gene expression and function

Ikaros is a transcriptional factor required for conventional T cell development, differentiation, and anergy. While the related factors Helios and Eos have defined roles in regulatory T cells (Treg), a role for Ikaros has not been established. To determine the function of Ikaros in the Treg lineage, we generated mice with Treg-specific deletion of the Ikaros gene (Ikzf1). We find that Ikaros cooperates with Foxp3 to establish a major portion of the Treg epigenome and transcriptome. Ikaros-deficient Treg exhibit Th1-like gene expression with abnormal production of IL-2, IFNg, TNFa, and factors involved in Wnt and Notch signaling. While Ikzf1-Treg-cko mice do not develop spontaneous autoimmunity, Ikaros-deficient Treg are unable to control conventional T cell-mediated immune pathology in response to TCR and inflammatory stimuli in models of IBD and organ transplantation. These studies establish Ikaros as a core factor required in Treg for tolerance and the control of inflammatory immune responses.

TIM-3, LAG-3, or 2B4 gene disruptions increase the anti-tumor response of engineered T cells

Background

In adoptive T cell therapy, the long term therapeutic benefits in patients treated with engineered tumor specific T cells are limited by the lack of long term persistence of the infused cellular products and by the immunosuppressive mechanisms active in the tumor microenvironment. Exhausted T cells infiltrating the tumor are characterized by loss of effector functions triggered by multiple inhibitory receptors (IRs). In patients, IR blockade reverts T cell exhaustion but has low selectivity, potentially unleashing autoreactive clones and resulting in clinical autoimmune side effects. Furthermore, loss of long term protective immunity in cell therapy has been ascribed to the effector memory phenotype of the infused cells.

Methods

We simultaneously redirected T cell specificity towards the NY-ESO-1 antigen via TCR gene editing (TCRED) and permanently disrupted LAG3, TIM-3 or 2B4 genes (IRKO) via CRISPR/Cas9 in a protocol to expand early differentiated long-living memory stem T cells. The effector functions of the TCRED-IRKO and IR competent (TCRED-IRCOMP) cells were tested in short-term co-culture assays and under a chronic stimulation setting in vitro. Finally, the therapeutic efficacy of the developed cellular products were evaluated in multiple myeloma xenograft models.

Results

We show that upon chronic stimulation, TCRED-IRKO cells are superior to TCRED-IRCOMP cells in resisting functional exhaustion through different mechanisms and efficiently eliminate cancer cells upon tumor re-challenge in vivo. Our data indicate that TIM-3 and 2B4-disruption preserve T-cell degranulation capacity, while LAG-3 disruption prevents the upregulation of additional inhibitory receptors in T cells.

Conclusion

These results highlight that TIM-3, LAG-3, and 2B4 disruptions increase the therapeutic benefit of tumor specific cellular products and suggest distinct, non-redundant roles for IRs in anti-tumor responses.

Optimal CD8+ T cell effector function requires costimulation-induced RNA-binding proteins that reprogram the transcript isoform landscape

Boosting T cell activation through costimulation directs defense against cancer and viral infections. Despite multiple studies targeting costimulation in clinical trials, the increased potency and reprogramming of T cells endowed by costimulation is poorly understood. Canonical dogma states that transcription mediates T cell activation. Here, we show that the spliceosome, controlling post-transcriptional alternative splicing and alternative polyadenylation, is the most enriched pathway in T cells after CD134/CD137 costimulation. Costimulation of CD8+ T cells significantly increases expression of 29 RNA-binding proteins while RNA-seq uncovers over 1000 differential alternative splicing and polyadenylation events. Using in vivo mouse and in vitro human models, we demonstrate that RNA-binding protein Tardbp is required for effector cytokine production, CD8+ T cell clonal expansion, and isoform regulation after costimulation. The prospect of immune response optimization through reprogramming of mRNA isoform production offered herein opens new avenues for experimentally and therapeutically tuning the activities of T cells.

Gain-of-function IKZF1 variants in humans cause immune dysregulation associated with abnormal T/B cell late differentiation

IKZF1/IKAROS is a key transcription factor of lymphocyte development expressed throughout hematopoiesis. Heterozygous germline IKZF1 haploinsufficient (IKZF1^HI) and dominant-negative (IKZF1^DN) variants in humans cause B cell immune deficiency and combined immunodeficiency. Here, we identified previously unidentified heterozygous IKZF1 variants (R183C/H) located in the DNA binding domain in eight individuals with inflammatory, autoimmune, allergic symptoms, and abnormal plasma cell (PC) proliferation. Leukocytes of patients exhibited specific defects including impaired IL-2 production by T cells, T helper (T_H) skewing toward T_H2, low numbers of regulatory T cells (T_reg), eosinophilia, and abnormal PC proliferation. In contrast to IKZF1^HI and IKZF1^DN, IKZF1^R183H/C proteins showed increased DNA binding associated with increased gene expression of T_H2 and PC differentiation, thus demonstrating that IKZF1^R183H/C behave as gain-of-function (GOF) alleles. In vitro treatment with lenalidomide, known to degrade IKZF1, corrected T_H2 and PC abnormalities caused by IKZF1^R183H/C. These data extend the spectrum of pathological mechanisms associated with IKZF1 deficiencies and highlight the role of IKZF1 in late lymphoid differentiation stages.

Combination Immune Checkpoint Blockade Enhances IL-2 and CD107a Production from HIV-Specific T Cells Ex Vivo in People Living with HIV on Antiretroviral Therapy

In people with HIV (PWH) on antiretroviral therapy (ART), immune dysfunction persists, including elevated expression of immune checkpoint (IC) proteins on total and HIV-specific T cells. Reversing immune exhaustion is one strategy to enhance the elimination of HIV-infected cells that persist in PWH on ART. We aimed to evaluate whether blocking CTL-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), T cell Ig domain and mucin domain 3 (TIM-3), T cell Ig and ITIM domain (TIGIT) and lymphocyte activation gene-3 (LAG-3) alone or in combination would enhance HIV-specific CD4⁺ and CD8⁺ T cell function ex vivo. Intracellular cytokine staining was performed using human PBMCs from PWH on ART (n = 11) and expression of CD107a, IFN-γ, TNF-α, and IL-2 was quantified with HIV peptides and Abs to IC. We found the following: 1) IC blockade enhanced the induction of CD107a and IL-2 but not IFN-γ and TNF-α in response to Gag and Nef peptides; 2) the induction of CD107a and IL-2 was greatest with multiple combinations of two Abs; and 3) Abs to LAG-3, CTLA-4, and TIGIT in combinations showed synergistic induction of IL-2 in HIV-specific CD8⁺ and CD107a and IL-2 production in HIV-specific CD4⁺ and CD8⁺ T cells. These results demonstrate that the combination of Abs to LAG-3, CTLA-4, or TIGIT can increase the frequency of cells expressing CD107a and IL-2 that associated with cytotoxicity and survival of HIV-specific CD4⁺ and CD8⁺ T cells in PWH on ART. These combinations should be further explored for an HIV cure.

Keeping Myeloma in Check: The Past, Present and Future of Immunotherapy in Multiple Myeloma

Multiple myeloma is an incurable disease of malignant plasma cells and an ideal target for modern immune therapy. The unique plasma cell biology maintained in multiple myeloma, coupled with its hematological nature and unique bone marrow microenvironment, provide an opportunity to design specifically targeted immunotherapies that selectively kill transformed cells with limited on-target off-tumor effects. Broadly defined, immune therapy is the utilization of the immune system and immune agents to treat a disease. In the context of multiple myeloma, immune therapy can be subdivided into four main categories: immune modulatory imide drugs, targeted antibodies, adoptive cell transfer therapies, and vaccines. In recent years, advances in all four of these categories have led to improved therapies with enhanced antitumor activity and specificity. In IMiDs, modified chemical structures have been developed that improve drug potency while reducing dose limiting side effects. Targeted antibody therapies have resulted from the development of new selectively expressed targets as well as the development of antibody drug conjugates and bispecific antibodies. Adoptive cell therapies, particularly CAR-T therapies, have been enhanced through improvements in the manufacturing process, as well as through the development of CAR constructs that enhance CAR-T activation and provide protection from a suppressive immune microenvironment. This review will first cover in-class breakthrough therapies for each of these categories, as well as therapies currently utilized in the clinic. Additionally, this review will explore up and coming therapeutics in the preclinical and clinical trial stage.

Biological and Translational Considerations regarding the Recent Therapeutic Successes and Upcoming Challenges for Multiple Myeloma

Even though multiple myeloma (MM) is still considered incurable, the therapeutic management of this disease has undergone a major transformation over the last two decades, with several new classes of therapeutics and diverse options for their combined use in many different regimens that have contributed to major improvement in overall survival of patients. This review discusses key themes underlying the pharmacological and immune-based therapies that represent the cornerstones of this progress. A major part of the clinical progress achieved by these classes' therapeutics has depended on the targeting of molecular pathways with distinct or preferential roles for the biology of plasma cells-normal or malignant-and the ability of many of these agents to be incorporated into combination regimens that exhibit enhanced antimyeloma responses, without precipitating acceptable levels of toxicity. This review also discusses why these advances have not yet translated into curative outcomes and how these remaining barriers could be overcome.

Cereblon harnesses Myc-dependent bioenergetics and activity of CD8+ T lymphocytes

Immunomodulatory drugs, such as thalidomide and related compounds, potentiate T-cell effector functions. Cereblon (CRBN), a substrate receptor of the DDB1-cullin-RING E3 ubiquitin ligase complex, is the only molecular target for this drug class, where drug-induced, ubiquitin-dependent degradation of known "neosubstrates," such as IKAROS, AIOLOS, and CK1α, accounts for their biological activity. Far less clear is whether these CRBN E3 ligase-modulating compounds disrupt the endogenous functions of CRBN. We report that CRBN functions in a feedback loop that harnesses antigen-specific CD8+ T-cell effector responses. Specifically, Crbn deficiency in murine CD8+ T cells augments their central metabolism manifested as elevated bioenergetics, with supraphysiological levels of polyamines, secondary to enhanced glucose and amino acid transport, and with increased expression of metabolic enzymes, including the polyamine biosynthetic enzyme ornithine decarboxylase. Treatment with CRBN-modulating compounds similarly augments central metabolism of human CD8+ T cells. Notably, the metabolic control of CD8+ T cells by modulating compounds or Crbn deficiency is linked to increased and sustained expression of the master metabolic regulator MYC. Finally, Crbn-deficient T cells have augmented antigen-specific cytolytic activity vs melanoma tumor cells, ex vivo and in vivo, and drive accelerated and highly aggressive graft-versus-host disease. Therefore, CRBN functions to harness the activation of CD8+ T cells, and this phenotype can be exploited by treatment with drugs.

Established and emergent roles for Ikaros transcription factors in lymphoid cell development and function

Ikaros zinc finger transcription factors are important regulators of the gene programs underlying the development of hematopoietic cell lineages. The family consists of five members: Ikaros, Helios, Aiolos, Eos, and Pegasus, which engage in both homo- and heterotypic intrafamilial interactions to exert diverse functional effects. Pioneering studies focused on the role of these factors in early lymphoid development, as their absence resulted in severe defects in lymphocyte populations. More recent work has now begun to define nuanced, stage-specific roles for Ikaros family members in the differentiation and function of mature T, B, and innate lymphoid cell populations including natural killer (NK) cells. The precise transcriptional mechanisms by which these factors function, both independently and collaboratively, is an area of active investigation. However, several key themes appear to be emerging regarding the pathways influenced by Ikaros family members, including the end-to-end regulation of cytokine signaling. Here, we review roles for Ikaros factors in lymphoid cell development, differentiation, and function, including a discussion of the current understanding of the transcriptional mechanisms they employ and considerations for the future study of this important transcription factor family.

First-in-Human, Single- and Multiple-Ascending-Dose Studies in Healthy Subjects to Assess Pharmacokinetics, Pharmacodynamics, and Safety/Tolerability of Iberdomide, a Novel Cereblon E3 Ligase Modulator

Pharmacokinetics, pharmacodynamics, and safety/tolerability of iberdomide (CC‐220), a highly potent oral cereblon E3 ligase modulator (CELMoD), were evaluated in escalating single‐dose (0.03, 0.1, 0.3, 1, 2, 4, 6 mg) and multiple‐dose (0.3 mg once daily for 14 days, 1 mg once daily for 28 days, 0.3 mg once daily for 28 days, or 1 mg once daily for 7 days with a 7‐day washout, then once daily for 7 more days) studies in healthy subjects (n = 99). Iberdomide exposure increased in a dose‐proportional manner. Terminal half‐life was 9‐13 hours after a single dose. Iberdomide decreased peripheral CD19+ B lymphocytes (E_max, 92.4%; EC₅₀, 0.718 ng/mL), with modest reductions in CD3+ T lymphocytes (E_max, 34.8%; EC₅₀, 0.932 ng/mL). Lipopolysaccharide‐stimulated proinflammatory cytokines (IL‐1α, IL‐1β) were reduced, but anti‐CD3‐stimulated IL‐2 and interferon‐γ were increased. Iberdomide 1 mg once daily partially decreased T‐cell‐independent antibody responses to PPV23 but did not change tetanus toxoid recall response. Pharmacodynamic data suggest dose‐dependent, differential immunomodulatory effects on B and T lymphocytes. Iberdomide was tolerated up to 6 mg as a single dose and at 0.3 mg once daily for 4 weeks. Grade 3 asymptomatic neutropenia was observed following 1 mg once daily for 21 days; a 7‐day drug holiday alleviated neutropenia. Further investigation of iberdomide in autoimmune and hematological diseases is warranted.

Revving the CAR - Combination strategies to enhance CAR T cell effectiveness

Chimeric antigen receptor (CAR) T cell therapy is currently approved for treatment of refractory B-cell malignancies. Response rates in these diseases are impressive by historical standards, but most patients do not have a durable response and there remains room for improvement. To date, CAR T cell activity has been even more limited in solid malignancies. These limitations are thought to be due to several pathways of resistance to CAR T cells, including cell-intrinsic mechanisms and the immunosuppressive tumor microenvironment. In this review, we discuss current experimental strategies that combine small molecules and monoclonal antibodies with CAR T cells to overcome these resistance mechanisms. We describe the biological rationale, pre-clinical data and clinical trials in progress that test the efficacy and safety of these combinations.

Coexpression of FOXP3 and a Helios isoform enhances the effectiveness of human engineered regulatory T cells

Regulatory T cells (Tregs) are a subset of immune cells that suppress the immune response. Treg therapy for inflammatory diseases is being tested in the clinic, with moderate success. However, it is difficult to isolate and expand Tregs to sufficient numbers. Engineered Tregs (eTregs) can be generated in larger quantities by genetically manipulating conventional T cells to express FOXP3. These eTregs can suppress in vitro and in vivo but not as effectively as endogenous Tregs. We hypothesized that ectopic expression of the transcription factor Helios along with FOXP3 is required for optimal eTreg immunosuppression. To test this theory, we generated eTregs by retrovirally transducing total human T cells (CD4+ and CD8+) with FOXP3 alone or with each of the 2 predominant isoforms of Helios. Expression of both FOXP3 and the full-length isoform of Helios was required for eTreg-mediated disease delay in a xenogeneic graft-versus-host disease model. In vitro, this corresponded with superior suppressive function of FOXP3 and full-length Helios-expressing CD4+ and CD8+ eTregs. RNA sequencing showed that the addition of full-length Helios changed gene expression in cellular pathways and the Treg signature compared with FOXP3 alone or the other major Helios isoform. Together, these results show that functional human CD4+ and CD8+ eTregs can be generated from total human T cells by coexpressing FOXP3 and full-length Helios.

CXCR3 Identifies Human Naive CD8+ T Cells with Enhanced Effector Differentiation Potential

In mice, the ability of naive T (TN) cells to mount an effector response correlates with TCR sensitivity for self-derived Ags, which can be quantified indirectly by measuring surface expression levels of CD5. Equivalent findings have not been reported previously in humans. We identified two discrete subsets of human CD8+ TN cells, defined by the absence or presence of the chemokine receptor CXCR3. The more abundant CXCR3+ TN cell subset displayed an effector-like transcriptional profile and expressed TCRs with physicochemical characteristics indicative of enhanced interactions with peptide-HLA class I Ags. Moreover, CXCR3+ TN cells frequently produced IL-2 and TNF in response to nonspecific activation directly ex vivo and differentiated readily into Ag-specific effector cells in vitro. Comparative analyses further revealed that human CXCR3+ TN cells were transcriptionally equivalent to murine CXCR3+ TN cells, which expressed high levels of CD5. These findings provide support for the notion that effector differentiation is shaped by heterogeneity in the preimmune repertoire of human CD8+ T cells.

Phenotypic and functional analysis of malignant mesothelioma tumor-infiltrating lymphocytes

Given the growing interest and promising preliminary results of immunotherapy in malignant pleural mesothelioma (MPM), it has become important to more fully understand the immune landscape in this tumor. This may be especially relevant in deciding who might benefit most from checkpoint blockade or agonist antibody therapy. Since the phenotype of tumor infiltrating lymphocytes (TILs) in MPM has not been fully described and their function has not been carefully assessed, we collected fresh tumor and blood from 22 patients undergoing surgical resection and analysed single cell suspensions by flow cytometry. The functionality of TILs was assessed by measurement of cytokine expression (IFN-γ) following overnight stimulation ex vivo. Results showed low numbers of CD8+ TILs whose function was either moderately or severely suppressed. The degree of TIL hypofunction did not correlate with the presence of co-existing macrophages or neutrophils, nor with expression of the inhibitory receptors PD-1, CD39 and CTLA-4. Hypofunction was associated with higher numbers of CD4 regulatory T cells (Tregs) and with expression of the inhibitory receptor TIGIT. On the other hand, presence of tissue-resident memory (Trm) cells and expression of TIM-3 on CD8+ cells were positively associated with cytokine production. However, Trm function was partially suppressed when the transcription factor Eomesodermin (Eomes) was co-expressed. Understanding the function of TILs in malignant mesothelioma may have clinical implications for immunotherapy, especially in choosing the best immunotherapy targets. Our data suggests that Treg cell blocking agents or TIGIT inhibitor antibodies might be especially valuable in these patients.

Function of Human Tumor-Infiltrating Lymphocytes in Early-Stage Non-Small Cell Lung Cancer

Cancer progression is marked by dysfunctional tumor-infiltrating lymphocytes (TIL) with high inhibitory receptor (IR) expression. Because IR blockade has led to clinical responses in some patients with non-small cell lung cancer (NSCLC), we investigated how IRs influenced CD8⁺ TIL function from freshly digested early-stage NSCLC tissues using a killing assay and intracellular cytokine staining after in vitro T-cell restimulation. Early-stage lung cancer TIL function was heterogeneous with only about one third of patients showing decrements in cytokine production and lytic function. TIL hypofunction did not correlate with clinical factors, coexisting immune cells (macrophages, neutrophils, or CD4⁺ T regulatory cells), nor with PD-1, TIGIT, TIM-3, CD39, or CTLA-4 expression. Instead, we found that the presence of the integrin α_eβ₇ (CD103), characteristic of tissue-resident memory cells (T_RM), was positively associated with cytokine production, whereas expression of the transcription factor Eomesodermin (Eomes) was negatively associated with TIL function. These data suggest that the functionality of CD8⁺ TILs from early-stage NSCLCs may be influenced by competition between an antitumor CD103⁺ T_RM program and an exhaustion program marked by Eomes expression. Understanding the mechanisms of T-cell function in the progression of lung cancer may have clinical implications for immunotherapy.

Assessing the Functional Relevance of Variants in the IKAROS Family Zinc Finger Protein 1 (IKZF1) in a Cohort of Patients With Primary Immunodeficiency

Common variable immunodeficiency (CVID) is the most frequent symptomatic primary immunodeficiency. Patients with CVID are prone to recurrent bacterial infection due to the failure of adequate immunoglobulin production. Monogenetic defects have been identified in ~25% of CVID patients. Recently, mutations in IKZF1, encoding the zinc-finger transcription factor IKAROS which is broadly expressed in hematopoietic cells, have been associated with a CVID-like phenotype. Herein we describe 11 patients with heterozygous IKZF1 variants from eight different families with autosomal dominant CVID and two siblings with an IKZF1 variant presenting with inflammatory bowel disease (IBD). This study shows that mutations affecting the DNA binding domain of IKAROS can impair the interaction with the target DNA sequence thereby preventing heterochromatin and pericentromeric localization (HC-PC) of the protein. Our results also indicate an impairment of pericentromeric localization of IKAROS by overexpression of a truncated variant, caused by an immature stop codon in IKZF1. We also describe an additional variant in TNFSF10, encoding Tumor Necrosis Factor Related Apoptosis Inducing Ligand (TRAIL), additionally presented in individuals of Family A. Our results indicate that this variant may impair the TRAIL-induced apoptosis in target cell lines and prohibit the NFκB activation by TRAIL and may act as a modifier in Family A.

Paracrine costimulation of IFN-γ signaling by integrins modulates CD8 T cell differentiation

The cytokine IFN-γ is a critical regulator of immune system development and function. Almost all leukocytes express the receptor for IFN-γ, yet each cell type elicits a different response to this cytokine. Cell type-specific effects of IFN-γ make it difficult to predict the outcomes of the systemic IFN-γ blockade and limit its clinical application, despite many years of research. To better understand the cell-cell interactions and cofactors that specify IFN-γ functions, we focused on the function of IFN-γ on CD8 T cell differentiation. We demonstrated that during bacterial infection, IFN-γ is a dominant paracrine trigger that skews CD8 T cell differentiation toward memory. This skewing is preferentially driven by contact-dependent T cell-T cell (T-T) interactions and the localized IFN-γ secretion among activated CD8 T cells in a unique splenic microenvironment, and is less sensitive to concurrent IFN-γ production by other immune cell populations such as natural killer (NK) cells. Modulation of CD8 T cell differentiation by IFN-γ relies on a nonconventional IFN-γ outcome that occurs specifically within 24 hours following infection. This is driven by IFN-γ costimulation by integrins at T-T synapses, and leads to synergistic phosphorylation of the proximal STAT1 molecule and accelerated IL-2 receptor down-regulation. This study provides evidence of the importance of context-dependent cytokine signaling and gives another example of how cell clusters and the microenvironment drive unique biology.

Lenalidomide combined with low-dose cyclophosphamide and prednisone modulates Ikaros and Aiolos in lymphocytes, resulting in immunostimulatory effects in lenalidomide-refractory multiple myeloma patients

We recently showed that the outcome of multiple myeloma (MM) patients treated in the REPEAT study (evaluation of lenalidomide combined with low-dose cyclophosphamide and prednisone (REP) in lenalidomide-refractory MM) was markedly better than what has been described with cyclophosphamide-prednisone alone. The outcome with REP was not associated with plasma cell Cereblon expression levels, suggesting that the effect of REP treatment may involve mechanisms independent of plasma cell Cereblon-mediated direct anti-tumor activity. We therefore hypothesized that immunomodulatory effects contribute to the anti-MM activity of REP treatment, rather than plasma cell Cereblon-mediated effects. Consequently, we now characterized the effect of REP treatment on immune cell subsets in peripheral blood samples collected on day 1 and 14 of cycle 1, as well as on day 1 of cycle 2. We observed a significant mid-cycle decrease in the Cereblon substrate proteins Ikaros and Aiolos in diverse lymphocyte subsets, which was paralleled by an increase in T-cell activation. These effects were restored to baseline at day one of the second cycle, one week after lenalidomide interruption. In vitro, lenalidomide enhanced peripheral blood mononuclear cell-mediated killing of both lenalidomide-sensitive and lenalidomide-resistant MM cells in a co-culture system. These results indicate that the Cereblon-mediated immunomodulatory properties of lenalidomide are maintained in lenalidomide-refractory MM patients and may contribute to immune-mediated killing of MM cells. Therefore, combining lenalidomide with other drugs can have potent effects through immunomodulation, even in patients considered to be lenalidomide-refractory.

Mechanisms regulating T-cell infiltration and activity in solid tumors

T-lymphocytes play a critical role in cancer immunity as evidenced by their presence in resected tumor samples derived from long-surviving patients, and impressive clinical responses to various immunotherapies that reinvigorate them. Indeed, tumors can upregulate a wide array of defense mechanisms, both direct and indirect, to suppress the ability of Tcells to reach the tumor bed and mount curative responses upon infiltration. In addition, patient and tumor genetics, previous antigenic experience, and the microbiome, are all important factors in shaping the T-cell repertoire and sensitivity to immunotherapy. Here, we review the mechanisms that regulate T-cell homing, infiltration, and activity within the solid tumor bed. Finally, we summarize different immunotherapies and combinatorial treatment strategies that enable the immune system to overcome barriers for enhanced tumor control and improved patient outcome.

Cross-Tissue Transcriptomic Analysis of Human Secondary Lymphoid Organ-Residing ILC3s Reveals a Quiescent State in the Absence of Inflammation

A substantial number of human and mouse group 3 innate lymphoid cells (ILC3s) reside in secondary lymphoid organs, yet the phenotype and function of these ILC3s is incompletely understood. Here, we employed an unbiased cross-tissue transcriptomic approach to compare human ILC3s from non-inflamed lymph nodes and spleen to their phenotypic counterparts in inflamed tonsils and from circulation. These analyses revealed that, in the absence of inflammation, lymphoid organ-residing ILC3s lack transcription of cytokines associated with classical ILC3 functions. This was independent of expression of the natural cytotoxicity receptor NKp44. However, and in contrast to ILC3s from peripheral blood, lymphoid organ-residing ILC3s express activating cytokine receptors and have acquired the ability to be recruited into immune responses by inflammatory cytokines. This comprehensive cross-tissue dataset will allow for identification of functional changes in human lymphoid organ ILC3s associated with human disease.

The function and dysfunction of memory CD8+ T cells in tumor immunity

The generation and maintenance of CD8+ T cell memory is crucial to long-term host survival, yet the basic tenets of CD8+ T cell immunity are still being established. Recent work has led to the discovery of tissue-resident memory cells and refined our understanding of the transcriptional and epigenetic basis of CD8+ T cell differentiation and dysregulation. In parallel, the unprecedented clinical success of immunotherapy has galvanized an intense, global research effort to decipher and de-repress the anti-tumor response. However, the progress of immunotherapy is at a critical juncture, since the efficacy of immuno-oncology agents remains confined to a fraction of patients and often fails to provide durable benefit. Unlocking the potential of immunotherapy requires the design of strategies that both induce a potent effector response and reliably forge stable, functional memory T cell pools capable of protecting from recurrence or relapse. It is therefore essential that basic and emerging concepts of memory T cell biology are rapidly and faithfully transposed to advance therapeutic development in cancer immunotherapy. This review highlights seminal and recent reports in CD8+ T cell memory and tumor immunology, and evaluates recent data from solid cancer specimens in the context of the key paradigms from preclinical models. We elucidate the potential significance of circulating effector cells poised downstream of neoantigen recognition and upstream of T cell dysfunction and propose that cells in this immunological 'sweet spot' may be key anti-tumor effectors.

Ligand-mediated protein degradation reveals functional conservation among sequence variants of the CUL4-type E3 ligase substrate receptor cereblon

Upon binding to thalidomide and other immunomodulatory drugs, the E3 ligase substrate receptor cereblon (CRBN) promotes proteosomal destruction by engaging the DDB1-CUL4A-Roc1-RBX1 E3 ubiquitin ligase in human cells but not in mouse cells, suggesting that sequence variations in CRBN may cause its inactivation. Therapeutically, CRBN engagers have the potential for broad applications in cancer and immune therapy by specifically reducing protein expression through targeted ubiquitin-mediated degradation. To examine the effects of defined sequence changes on CRBN's activity, we performed a comprehensive study using complementary theoretical, biophysical, and biological assays aimed at understanding CRBN's nonprimate sequence variations. With a series of recombinant thalidomide-binding domain (TBD) proteins, we show that CRBN sequence variants retain their drug-binding properties to both classical immunomodulatory drugs and dBET1, a chemical compound and targeting ligand designed to degrade bromodomain-containing 4 (BRD4) via a CRBN-dependent mechanism. We further show that dBET1 stimulates CRBN's E3 ubiquitin-conjugating function and degrades BRD4 in both mouse and human cells. This insight paves the way for studies of CRBN-dependent proteasome-targeting molecules in nonprimate models and provides a new understanding of CRBN's substrate-recruiting function.

IKAROS expression in distinct bone marrow cell populations as a candidate biomarker for outcome with lenalidomide-dexamethasone therapy in multiple myeloma

Immunomodulatory drugs (IMiDs) are a cornerstone in the treatment of multiple myeloma (MM), but specific markers to predict outcome are still missing. Recent work pointed to a prognostic role for IMiD target genes (e.g. CRBN). Moreover, indirect activity of IMiDs on immune cells correlated with outcome, raising the possibility that cell populations in the bone marrow (BM) microenvironment could serve as biomarkers. We therefore analysed gene expression levels of six IMiD target genes in whole BM samples of 44 myeloma patients treated with lenalidomide-dexamethasone. Expression of CRBN (R = 0.30, P = .05), IKZF1 (R = 0.31, P = .04), IRF4 (R = 0.38, P = .01), MCT-1 (R = 0.30, P = .05), and CD147 (R = 0.38, P = .01), but not IKZF3 (R = -0.15, P = .34), was significantly associated with response. Interestingly, IKZF1 expression was elevated in BM environmental cells and thus selected for further investigation by multicolor flow cytometry. High IKAROS protein levels in total BM mononuclear cells (median OS 83.4 vs. 32.2 months, P = .02), CD19⁺ B cells (median OS 71.1 vs. 32.2 months, P = .05), CD3⁺ CD8⁺ T cells (median OS 83.4 vs 19.0 months, P = .008) as well as monocytes (median OS 53.9 vs 18.0 months, P = .009) were associated with superior overall survival (OS). In contrast, IKAROS protein expression in MM cells was not predictive for OS. Our data therefore corroborate the central role of immune cells for the clinical activity of IMiDs and built the groundwork for prospective analysis of IKAROS protein levels in distinct cell populations as a potential biomarker for IMiD based therapies.

IL-2 Modulates the TCR Signaling Threshold for CD8 but Not CD4 T Cell Proliferation on a Single-Cell Level

Lymphocytes integrate Ag and cytokine receptor signals to make cell fate decisions. Using a specific reporter of TCR signaling that is insensitive to cytokine signaling, Nur77-eGFP, we identify a sharp, minimal threshold of cumulative TCR signaling required for proliferation in CD4 and CD8 T cells that is independent of both Ag concentration and affinity. Unexpectedly, IL-2 reduces this threshold in CD8 but not CD4 T cells, suggesting that integration of multiple mitogenic inputs may alter the minimal requirement for TCR signaling in CD8 T cells. Neither naive CD4 nor naive CD8 T cells are responsive to low doses of IL-2. We show that activated CD8 T cells become responsive to low doses of IL-2 more quickly than CD4 T cells, and propose that this relative delay in turn accounts for the differential effects of IL-2 on the minimal TCR signaling threshold for proliferation in these populations. In contrast to Nur77-eGFP, c-Myc protein expression integrates mitogenic signals downstream of both IL-2 and the TCR, yet marks an invariant minimal threshold of cumulative mitogenic stimulation required for cell division. Our work provides a conceptual framework for understanding the regulation of clonal expansion of CD8 T cells by subthreshold TCR signaling in the context of mitogenic IL-2 signals, thereby rendering CD8 T cells exquisitely dependent upon environmental cues. Conversely, CD4 T cell proliferation requires an invariant minimal intensity of TCR signaling that is not modulated by IL-2, thereby restricting responses to low-affinity or low-abundance self-antigens even in the context of an inflammatory milieu.

Rabex-5 is a lenalidomide target molecule that negatively regulates TLR-induced type 1 IFN production

Immunomodulatory drugs (IMiDs) are a family of compounds derived from thalidomide. Binding of the IMiD molecule to the Lon protease Cereblon initiates the degradation of substrates via the ubiquitin proteasome pathway. Here, we show that Cereblon forms a complex with Rabex-5, a regulator of immune homeostasis. Treatment with lenalidomide prevented the association of Cereblon with Rabex-5. Conversely, mutation of the IMiD binding site increased Cereblon-Rabex-5 coimmunoprecipitation. The thalidomide binding region of Cereblon therefore regulates the formation of this complex. Knockdown of Rabex-5 in the THP-1 macrophage cell line up-regulated Toll-like receptor (TLR)-induced cytokine and type 1 IFN production via a STAT1/IRF activating pathway. Thus, we identify Rabex-5 as a IMiD target molecule that functions to restrain TLR activated auto-immune promoting pathways. We propose that release of Rabex-5 from complex with Cereblon enables the suppression of immune responses, contributing to the antiinflammatory properties of IMiDs.

Origin and Role of a Subset of Tumor-Associated Neutrophils with Antigen-Presenting Cell Features in Early-Stage Human Lung Cancer

Based on studies in mouse tumor models, granulocytes appear to play a tumor-promoting role. However, there are limited data about the phenotype and function of tumor-associated neutrophils (TANs) in humans. Here, we identify a subset of TANs that exhibited characteristics of both neutrophils and antigen-presenting cells (APCs) in early-stage human lung cancer. These APC-like "hybrid neutrophils," which originate from CD11b(+)CD15(hi)CD10(-)CD16(low) immature progenitors, are able to cross-present antigens, as well as trigger and augment anti-tumor T cell responses. Interferon-γ and granulocyte-macrophage colony-stimulating factor are requisite factors in the tumor that, working through the Ikaros transcription factor, synergistically exert their APC-promoting effects on the progenitors. Overall, these data demonstrate the existence of a specialized TAN subset with anti-tumor capabilities in human cancer.

Fine-Tuning of CD8(+) T Cell Mitochondrial Metabolism by the Respiratory Chain Repressor MCJ Dictates Protection to Influenza Virus

Mitochondrial respiration is regulated in CD8(+) T cells during the transition from naive to effector and memory cells, but mechanisms controlling this process have not been defined. Here we show that MCJ (methylation-controlled J protein) acted as an endogenous break for mitochondrial respiration in CD8(+) T cells by interfering with the formation of electron transport chain respiratory supercomplexes. Metabolic profiling revealed enhanced mitochondrial metabolism in MCJ-deficient CD8(+) T cells. Increased oxidative phosphorylation and subcellular ATP accumulation caused by MCJ deficiency selectively increased the secretion, but not expression, of interferon-γ. MCJ also adapted effector CD8(+) T cell metabolism during the contraction phase. Consequently, memory CD8(+) T cells lacking MCJ provided superior protection against influenza virus infection. Thus, MCJ offers a mechanism for fine-tuning CD8(+) T cell mitochondrial metabolism as an alternative to modulating mitochondrial mass, an energetically expensive process. MCJ could be a therapeutic target to enhance CD8(+) T cell responses.

Effector, Memory, and Dysfunctional CD8(+) T Cell Fates in the Antitumor Immune Response

The adaptive immune system plays a pivotal role in the host's ability to mount an effective, antigen-specific immune response against tumors. CD8(+) tumor-infiltrating lymphocytes (TILs) mediate tumor rejection through recognition of tumor antigens and direct killing of transformed cells. In growing tumors, TILs are often functionally impaired as a result of interaction with, or signals from, transformed cells and the tumor microenvironment. These interactions and signals can lead to transcriptional, functional, and phenotypic changes in TILs that diminish the host's ability to eradicate the tumor. In addition to effector and memory CD8(+) T cells, populations described as exhausted, anergic, senescent, and regulatory CD8(+) T cells have been observed in clinical and basic studies of antitumor immune responses. In the context of antitumor immunity, these CD8(+) T cell subsets remain poorly characterized in terms of fate-specific biomarkers and transcription factor profiles. Here we discuss the current characterization of CD8(+) T cell fates in antitumor immune responses and discuss recent insights into how signals in the tumor microenvironment influence TIL transcriptional networks to promote CD8(+) T cell dysfunction.

Loss of B Cells in Patients with Heterozygous Mutations in IKAROS

BACKGROUND

Common variable immunodeficiency (CVID) is characterized by late-onset hypogammaglobulinemia in the absence of predisposing factors. The genetic cause is unknown in the majority of cases, and less than 10% of patients have a family history of the disease. Most patients have normal numbers of B cells but lack plasma cells.

METHODS

We used whole-exome sequencing and array-based comparative genomic hybridization to evaluate a subset of patients with CVID and low B-cell numbers. Mutant proteins were analyzed for DNA binding with the use of an electrophoretic mobility-shift assay (EMSA) and confocal microscopy. Flow cytometry was used to analyze peripheral-blood lymphocytes and bone marrow aspirates.

RESULTS

Six different heterozygous mutations in IKZF1, the gene encoding the transcription factor IKAROS, were identified in 29 persons from six families. In two families, the mutation was a de novo event in the proband. All the mutations, four amino acid substitutions, an intragenic deletion, and a 4.7-Mb multigene deletion involved the DNA-binding domain of IKAROS. The proteins bearing missense mutations failed to bind target DNA sequences on EMSA and confocal microscopy; however, they did not inhibit the binding of wild-type IKAROS. Studies in family members showed progressive loss of B cells and serum immunoglobulins. Bone marrow aspirates in two patients had markedly decreased early B-cell precursors, but plasma cells were present. Acute lymphoblastic leukemia developed in 2 of the 29 patients.

CONCLUSIONS

Heterozygous mutations in the transcription factor IKAROS caused an autosomal dominant form of CVID that is associated with a striking decrease in B-cell numbers. (Funded by the National Institutes of Health and others.).

Immune Cells and Inflammation in Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes. At its core, DN is a metabolic disorder which can also manifest itself in terms of local inflammation in the kidneys. Such inflammation can then drive the classical markers of fibrosis and structural remodeling. As a result, resolution of immune-mediated inflammation is critical towards achieving a cure for DN. Many immune cells play a part in DN, including key members of both the innate and adaptive immune systems. While these cells were classically understood to primarily function against pathogen insult, it has also become increasingly clear that they also serve a major role as internal sensors of damage. In fact, damage sensing may serve as the impetus for much of the inflammation that occurs in DN, in a vicious positive feedback cycle. Although direct targeting of these proinflammatory cells may be difficult, new approaches that focus on their metabolic profiles may be able to alleviate DN significantly, especially since dysregulation of the local metabolic environment may well be responsible for triggering inflammation to begin with. In this review, the authors consider the metabolic profile of several relevant immune types and discuss their respective roles.

Targeting Transcriptional Regulators of CD8+ T Cell Dysfunction to Boost Anti-Tumor Immunity

Transcription is a dynamic process influenced by the cellular environment: healthy, transformed, and otherwise. Genome-wide mRNA expression profiles reflect the collective impact of pathways modulating cell function under different conditions. In this review we focus on the transcriptional pathways that control tumor infiltrating CD8+ T cell (TIL) function. Simultaneous restraint of overlapping inhibitory pathways may confer TIL resistance to multiple mechanisms of suppression traditionally referred to as exhaustion, tolerance, or anergy. Although decades of work have laid a solid foundation of altered transcriptional networks underlying various subsets of hypofunctional or “dysfunctional” CD8+ T cells, an understanding of the relevance in TIL has just begun. With recent technological advances, it is now feasible to further elucidate and utilize these pathways in immunotherapy platforms that seek to increase TIL function.

Role of Ets Proteins in Development, Differentiation, and Function of T-Cell Subsets

Through positive selection, double-positive cells in the thymus differentiate into CD4(+) or CD8(+) T single-positive cells that subsequently develop into different types of effective T cells, such as T-helper and cytotoxic T lymphocyte cells, that play distinctive roles in the immune system. Development, differentiation, and function of thymocytes and CD4(+) and CD8(+) T cells are controlled by a multitude of secreted and intracellular factors, ranging from cytokine signaling modules to transcription factors and epigenetic modifiers. Members of the E26 transformation specific (Ets) family of transcription factors, in particular, are potent regulators of these CD4(+) or CD8(+) T-cell processes. In this review, we summarize and discuss the functions and underlying mechanisms of the Ets family members that have been characterized as involved in these processes. Ongoing research of these factors is expected to identify practical applications for the Ets family members as novel therapeutic targets for inflammation-related diseases.

Patent Highlights

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