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This study explored the novel immune checkpoint poliovirus receptor- related immunoglobulin domain-containing (PVRIG) in acute myeloid leukemia (AML). We showed that AML patient blasts consistently expressed the PVRIG ligand (poliovirus receptor-related 2, PVRL2). Furthermore, PVRIG blockade significantly enhanced naural killer (NK)-cell killing of PVRL2+, poliovirus receptor (PVR)lo AML cell lines, and significantly increased NK-cell activation and degranulation in the context of patient primary AML blasts. However, in AML patient bone marrow, NK-cell PVRIG expression levels were not increased. In order to understand how PVRIG blockade might potentially be exploited therapeutically, we investigated the biology of PVRIG and revealed that NK-cell activation resulted in reduced PVRIG expression on the cell surface. This occurred whether NK cells were activated by tumor cell recognition, cytokines (interleukin 2 [IL-2] and IL-12) or activating receptor stimulation (CD16 and NKp46). PVRIG was present at higher levels in the cytoplasm than on the cell surface, particularly on CD56bright NK cells, which further increased cytoplasmic PVRIG levels following IL-2 and IL-12 activation. PVRIG was continually transported to the cell surface via the endoplasmic reticulum and Golgi in both unstimulated and activated NK cells. Taken together, our findings suggest that anti-PVRIG blocking antibody functions by binding to surface-bound PVRIG, which undergoes rapid turnover in both unstimulated and activated NK cells. We conclude that the PVRIG-PVRL2 immune checkpoint axis can feasibly be targeted with PVRIG blocking antibody for NK-mediated immunotherapy of PVRL2+ AML.

Patients with refractory relapsed multiple myeloma (RRMM) respond to Elotuzumab (Elo) and lenalidomide (Len) combination treatment. The mechanisms underlying this observation are not fully understood. Furthermore, predictive biomarkers of response have not been revealed to date. To address these issues, we used a humanized myeloma mouse model and adoptive transfer of human NK cells to show that Elo and Len treatment controlled myeloma growth, and this was mediated through CD16 on NK cells. In co-culture studies, we showed that PBMCs from a subset of RRMM patients were effective killers of OPM2 myeloma cells when treated with Elo and Len, and this was associated with significantly increased expression of CD54 expression on OPM2 cells. Furthermore, Elo and Len induced OPM2 cell killing and increased OPM2 CD54 expression was dependent on both monocytes and NK cells, and was not mediated by soluble factors alone. At the transcript level, Elo and Len treatment significantly increased OPM2 myeloma cell expression of genes for trafficking and adhesion molecules, NK cell activation ligands and antigen presentation molecules. In conclusion, our findings suggest that MM patients require Elo and Len-mediated upregulation of CD54 on the autologous myeloma cells, in combination with NK cells and monocytes to mediate an effective anti-tumour response. Further, our data suggest that increased myeloma cell CD54 expression levels could be a powerful predictive biomarker for response to Elo and Len treatment.

Simple Summary Breast implant-associated lymphoma is a unique entity that arises in the setting of breast prostheses due to a complex interplay of external and internal factors. Understanding of the mechanisms of pathogenesis is yet to be fully elucidated but recurrent mutations in signalling pathways, tumour suppressors and epigenetic regulators have been reported. This article summarises the key studies to date that have described these genetic aberrancies, which have provided an insight into potential pathways to lymphogenesis. Abstract Breast implant-associated lymphoma (BIA-ALCL) is a rare subtype of anaplastic large-cell lymphoma associated with breast prostheses. Most patients present with a localised periprosthetic effusion and are managed with removal of the implant and surrounding capsule. Less commonly, the lymphoma can form a mass associated with the capsule and rarely can present with disseminated disease. Recent series characterising the genomic landscape of BIA-ALCL have led to insights into the mechanisms of lymphomagenesis. Constitutive JAK/STAT pathway activation has emerged as a likely key component while, more recently, aberrancies in epigenetic regulators have been reported. This review describes the genomic characterisation reported to date and the insight these findings have provided into this rare entity.

Simple Summary Chimeric antigen receptors (CAR) are engineered molecules expressed on the cell surface that can recognise specific proteins and deliver an activation signal to the cells. Human T lymphocytes equipped with CAR, also called CAR-T cells, can target and kill tumour cells. This technology has been successfully used in treating some of the blood cancers in the last decade. Although the majority of research interest in CAR technology has been focused on CAR-T cells to date, the CAR design has also been used in other types of immune cells to fight against cancers. In this review, we discuss recent advances in CAR design beyond that used in conventional CAR-T cells and their novel indications to develop more potent CAR-based therapy for cancers. Abstract Chimeric antigen receptors (CAR) are genetically engineered receptors that can recognise specific antigens and subsequently activate downstream signalling. Human T cells engineered to express a CAR, also known as CAR-T cells, can target a specific tumour antigen on the cell surface to mediate a cytotoxic response against the tumour. CAR-T cell therapy has achieved remarkable success in treating hematologic malignancies, but not in solid tumours. Currently, extensive research is being carried out to make CAR-T cells a therapy for solid tumours. To date, most of the research interest in the field has focused on cytotoxic T lymphocytes as the carrier of CAR products. However, in addition to T cells, the CAR design can be introduced in other immune cells, such as natural killer (NK)/NKT cells, γδ T cells, mucosal-associated invariant T (MAIT) cells, dendritic cells (DC), macrophages, regulatory T cells (Treg), B cells, etc. Some of the CAR-engineered immune cells, such as CAR- γδ T and CAR-NK/NK-T cells, are directly involved in the anti-tumour response, demonstrated in preclinical studies and/or clinical trials. CAR-Tregs showed promising therapeutic potential in treating autoimmune diseases. In particular, B cells engineered with chimeric receptors can be used as a platform for long-term delivery of therapeutic proteins, such as recombinant antibodies or protein replacement, in an antigen-specific manner. CAR technology is one of the most powerful engineering platforms in immunotherapy, especially for the treatment of cancers. In this review, we will discuss the recent application of the CAR design in non-CAR-T cells and future opportunities in immunotherapy.

Immunomodulatory drugs (IMiDs) are effective treatments for patients with multiple myeloma. IMiDs have pleotropic effects including targeting the myeloma cells directly, and improving the anti-myeloma immune response. In the absence of myeloma cells, lenalidomide and pomalidomide induce CD4+ T cell secretion of IL-2 and indirect activation of Natural Killer (NK) cells. In the context of T cell receptor ligation, IMiDs enhance T cell proliferation, cytokine release and Th1 responses, both in vivo and in vitro. Furthermore, combination treatment of IMiDs and myeloma-targeting monoclonal antibodies eg. daratumumab (anti-CD38) and elotuzumab (anti-SLAMF7), checkpoint inhibitors, or bispecific T cell engagers showed synergistic effects, mainly via enhanced T and NK cell dependent cellular toxicity and T cell proliferation. Conversely, the corticosteroid dexamethasone can impair the immune modulatory effects of IMiDs, indicating that careful choice of myeloma drugs in combination with IMiDs is key for the best anti-myeloma therapeutic efficacy. This review presents an overview of the role for T cells in the overall anti-myeloma effects of immunomodulatory drugs.

Mucosal-associated invariant T (MAIT) cells produce inflammatory cytokines and cytotoxic granzymes in response to by-products of microbial riboflavin synthesis. Although MAIT cells are protective against some pathogens, we reasoned that they might contribute to pathology in chronic bacterial infection. We observed MAIT cells in proximity to Helicobacter pylori bacteria in human gastric tissue, and so, using MR1-tetramers, we examined whether MAIT cells contribute to chronic gastritis in a mouse H. pylori SS1 infection model. Following infection, MAIT cells accumulated to high numbers in the gastric mucosa of wild-type C57BL/6 mice, and this was even more pronounced in MAIT TCR transgenic mice or in C57BL/6 mice where MAIT cells were preprimed by Ag exposure or prior infection. Gastric MAIT cells possessed an effector memory Tc1/Tc17 phenotype, and were associated with accelerated gastritis characterized by augmented recruitment of neutrophils, macrophages, dendritic cells, eosinophils, and non-MAIT T cells and by marked gastric atrophy. Similarly treated MR1−/− mice, which lack MAIT cells, showed significantly less gastric pathology. Thus, we demonstrate the pathogenic potential of MAIT cells in Helicobacter-associated immunopathology, with implications for other chronic bacterial infections.

Despite recent breakthroughs in identifying mucosal-associated invariant T (MAIT) cell antigens (Ags), the precise requirements for in vivo MAIT cell responses to infection remain unclear. Using major histocompatibility complex-related protein 1 (MR1) tetramers, the MAIT cell response was investigated in a model of bacterial lung infection employing riboflavin gene-competent and -deficient bacteria. MAIT cells were rapidly enriched in the lungs of C57BL/6 mice infected with Salmonella Typhimurium, comprising up to 50% of αβ-T cells after 1 week. MAIT cell accumulation was MR1-dependent, required Ag derived from the microbial riboflavin synthesis pathway, and did not occur in response to synthetic Ag, unless accompanied by a Toll-like receptor agonist or by co-infection with riboflavin pathway-deficient S. Typhimurium. The MAIT cell response was associated with their long-term accumulation in the lungs, draining lymph nodes and spleen. Lung MAIT cells from infected mice displayed an activated/memory phenotype, and most expressed the transcription factor retinoic acid-related orphan receptor γt. T-bet expression increased following infection. The majority produced interleukin-17 while smaller subsets produced interferon-γ or tumor necrosis factor, detected directly ex vivo. Thus the activation and expansion of MAIT cells coupled with their pro-inflammatory cytokine production occurred in response to Ags derived from microbial riboflavin synthesis and was augmented by co-stimulatory signals.

This unit describes the utility of various mouse models of infection and immunization for studying mucosal-associated invariant T (MAIT) cell immunity: MAIT cells can be isolated from the lungs (or from other tissues/organs) and then identified and characterized by flow cytometry using MR1 tetramers in combination with a range of antibodies. The response kinetics, cytokine profiles, and functional differentiation of lung MAIT cells are studied following infection with the bacterial pathogen Legionella longbeachae or Salmonella enterica Typhimurium or immunization with synthetic MAIT cell antigen plus Toll-like receptor agonist. MAIT cells enriched or expanded during the process can be used for further studies. A step-by-step protocol is provided for MAIT cell sorting and adoptive transfer. Mice can then be challenged and MAIT cells tracked and further examined. © 2019 by John Wiley & Sons, Inc.

Background: Mucosal associated invariant T (MAIT) cells are evolutionarily-conserved, innate-like lymphocytes which are abundant in human lungs and can contribute to protection against pulmonary bacterial infection. However, whilst they are also activated during human viral infections, it is unknown whether MAIT cells play a significant protective or even detrimental role during viral infections in vivo. Aims and objectives: To determine whether MAIT cells play a significant role – either protective or detrimental – during influenza A infection in vivo. Methods: We used major histocompatibility complex–related protein 1 (MR1) tetramers and intracellular cytokine staining to track MAIT cell frequencies and activation during in vivo murine experimental challenge with two strains of influenza A virus in immunocompetent (C57BL/6), MAIT-cell deficient (MR1-/-) and immunodeficient (Rag2-/-γC-/-) mice. Results: MAIT cells accumulated and were activated early in infection, with upregulation of CD25, CD69 and Granzyme B peaking at 5 days post infection. Activation was modulated via cytokines interleukin (IL)-12, -15, -18 and type I interferon, independent of MR1. MR1-/- mice, which lack MAIT cells, showed enhanced body weight loss and mortality to severe (H1N1) influenza. This was ameliorated by prior adoptive transfer of pulmonary MAIT cells in both immunocompetent and immunodeficient Rag2-/-γC-/- mice which lack T, B and NK cells. Conclusions: MAIT cells contribute to protection during respiratory viral infections, and constitute a potential target for therapeutic manipulation.

Mucosal associated invariant T (MAIT) cells are evolutionarily-conserved, innate-like lymphocytes which are abundant in human lungs and can contribute to protection against pulmonary bacterial infection. MAIT cells are also activated during human viral infections, yet it remains unknown whether MAIT cells play a significant protective or even detrimental role during viral infectionsin vivo. Using murine experimental challenge with two strains of influenza A virus, we show that MAIT cells accumulated and were activated early in infection, with upregulation of CD25, CD69 and Granzyme B, peaking at 5 days post infection. Activation was modulated via cytokines independently of MR1. MAIT cell-deficient MR1−/−mice showed enhanced weight loss and mortality to severe (H1N1) influenza. This was ameliorated by prior adoptive transfer of pulmonary MAIT cells in both immunocompetent and immunodeficient RAG2−/−γC−/−mice. Thus, MAIT cells contribute to protection during respiratory viral infections, and constitute a potential target for therapeutic manipulation.

Mucosal associated invariant T (MAIT) cells recognize conserved microbial metabolites from riboflavin synthesis. Striking evolutionary conservation and pulmonary abundance implicate them in antibacterial host defense, yet their roles in protection against clinically significant pathogens are unknown. Murine Legionella infection induced MR1-dependent MAIT cell activation and rapid pulmonary accumulation of MAIT cells associated with immune protection detectable in fully immunocompetent host animals. MAIT cell protection was more evident in mice lacking CD4+ cells, whilst profoundly immunodeficient RAG2−/−γC−/− mice were substantially rescued from uniformly lethal Legionella infection by adoptively-transferred MAIT cells. This protection was dependent on MR1, IFN-γ and GM-CSF, but not IL-17, TNF-α or perforin. Protection was enhanced and observed earlier post-infection in mice that were Ag-primed to boost MAIT cells before infection. Our findings define a significant role for MAIT cells in protection against a major human pathogen and indicate a potential role for vaccination to enhance MAIT cell immunity.

The major-histocompatibility-complex-(MHC)-class-I-related molecule MR1 can present activating and non-activating vitamin-B-based ligands to mucosal-associated invariant T cells (MAIT cells). Whether MR1 binds other ligands is unknown. Here we identified a range of small organic molecules, drugs, drug metabolites and drug-like molecules, including salicylates and diclofenac, as MR1-binding ligands. Some of these ligands inhibited MAIT cells ex vivo and in vivo, while others, including diclofenac metabolites, were agonists. Crystal structures of a T cell antigen receptor (TCR) from a MAIT cell in complex with MR1 bound to the non-stimulatory and stimulatory compounds showed distinct ligand orientations and contacts within MR1, which highlighted the versatility of the MR1 binding pocket. The findings demonstrated that MR1 was able to capture chemically diverse structures, spanning mono- and bicyclic compounds, that either inhibited or activated MAIT cells. This indicated that drugs and drug-like molecules can modulate MAIT cell function in mammals.