SLAM family receptors and SAP adaptors in immunity

Mechanisms of organ transplant injury mediated by B cells and antibodies: Implications for antibody-mediated rejection

Recent adjustments to the histological diagnosis and the introduction of molecular classification are providing renewed support for the paradigm that antibody-mediated rejection (ABMR) is an important clinical problem for which there is an urgent need for better therapies. Acute ABMR is observed when the graft is exposed to rapid increases in high-titer donor-specific antibodies (DSA) that are most often generated as anamnestic responses in sensitized recipients or de novo responses in nonsensitized patients who are nonadherent. Chronic ABMR is associated with slower increases in DSA, which may be high or low titer and transient or persistent. These DSA elicit cycles of injury and repair that manifest as multilamination of the peritubular capillary basement membrane or arteriopathy manifesting as intimal fibrosis. Mitigating the problem of AMBR requires the anamnestic and de novo DSA responses to be prevented and established DSA responses to be reversed. To this end, a better understanding of the immunobiology of DSA production is necessary and also the development of assays capable of detecting early humoral immune responses.Recent advances in understanding the immunobiology of B cells and areas requiring further investigation that might lead to new therapies or better diagnosis are discussed in this review.

Diagnostic challenges for a novel SH2D1A mutation associated with X-linked lymphoproliferative disease

Mutations in SH2D1A, encoding the intracellular adaptor signaling lymphocyte activation molecule associated protein (SAP), are associated with X-linked lymphoproliferative disease type 1 (XLP1). We identified a novel hemizygous SH2D1A c.49G > A (p.E17K) variant in a 21-year-old patient with fatal Epstein-Barr virus infection-associated hemophagocytic lymphohistiocytosis. Cellular and biochemical assays revealed normal expression of the SAP variant protein, yet binding to phosphorylated CD244 receptor was reduced by >95%. Three healthy brothers carried the SH2D1A c.49G > A variant. Thus, data suggest that this variant represents a pathogenic mutation, but with variable expressivity. Importantly, our results highlight challenges in the clinical interpretation of SH2D1A variants and caution in using functional flow cytometry assays for the diagnosis of XLP1.

Infection and immune control of human oncogenic γ-herpesviruses in humanized mice

Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) comprise the oncogenic human γ-herpesvirus family and are responsible for 2-3% of all tumours in man. With their prominent growth-transforming abilities and high prevalence in the human population, these pathogens have probably shaped the human immune system throughout evolution for near perfect immune control of the respective chronic infections in the vast majority of healthy pathogen carriers. The exclusive tropism of EBV and KSHV for humans has, however, made it difficult in the past to study their infection, tumourigenesis and immune control in vivo. Mice with reconstituted human immune system components (humanized mice) support replication of both viruses with both persisting latent and productive lytic infection. Moreover, B-cell lymphomas can be induced by EBV alone and KSHV co-infection with gene expression hallmarks of human malignancies that are associated with both viruses. Furthermore, cell-mediated immune control by primarily cytotoxic lymphocytes is induced upon infection and can be probed for its functional characteristics as well as putative requirements for its priming. Insights that have been gained from this model and remaining questions will be discussed in this review. This article is part of the theme issue 'Silent cancer agents: multi-disciplinary modelling of human DNA oncoviruses'.

Critical Role for SLAM/SAP Signaling in the Thymic Developmental Programming of IL-17- and IFN-γ-Producing γδ T Cells

During thymic development, mouse γδ T cells commit to either an IFN-γ- or an IL-17-producing phenotype through mechanisms that remain unclear. In this study, we investigated the extent to which the SLAM/SAP signaling pathway regulates the functional programming of γδ T cells. Characterization of SLAM family receptor expression revealed that thymic γδ T cell subsets were each marked by distinct coexpression profiles of SLAMF1, SLAMF4, and SLAMF6. In the thymus, Vγ1 and Vγ4 T cells that exhibited an SLAMF1+SLAMF6+ double positive phenotype were largely contained within immature CD24+CD73- and CD24+CD73+ subsets, whereas SLAMF1 single positive, SLAMF6 single positive, or SLAMF1SLAMF6 double negative cells were found within mature CD24-CD73+ and CD24-CD73- subsets. In the periphery, SLAMF1 and SLAMF6 expression distinguished IL-17- and IFN-γ-producing γδ T cells, respectively. Disruption of SLAM family receptor signaling through deletion of SAP resulted in impaired thymic Vγ1 and Vγ4 T cell maturation at the CD24+CD73-SLAMF1+SLAMF6+ double positive stage that was associated with a decreased frequency of CD44+RORγt+ γδ T cells. Impaired development was in turn associated with decreased γδ T cell IL-17 and IFN-γ production in the thymus as well as in peripheral tissues. The role for SAP was subset-specific, as Vγ1Vδ6.3, Vγ4, Vγ5, but not Vγ6 subsets were SAP-dependent. Together, these data suggest that the SLAM/SAP signaling pathway plays a larger role in γδ T cell development than previously appreciated and represents a critical checkpoint in the functional programming of both IL-17- and IFN-γ-producing γδ T cell subsets.

Novel Agents in Multiple Myeloma

The therapeutic landscape of multiple myeloma (MM) has dramatically changed in the last 15 years with the advent of immunomodulatory drugs and proteasome inhibitors. However, majority of MM patients relapse, and new therapies are needed. Various agents with diverse mechanisms of action and distinct targets, including cellular therapies, monoclonal antibodies, and small molecules, are currently under investigation. In this review, we report novel drugs recently approved or under advanced investigation that will likely be incorporated in the future as new standard for MM treatment, focusing on their mechanisms of action, cellular targets, and stage of development.

Genetic susceptibility to EBV infection: insights from inborn errors of immunity

Epstein-Barr virus (EBV) is a ubiquitous human pathogen, infecting > 90% of the adult population. In the vast majority of healthy individuals, infection with EBV runs a relatively benign course. However, EBV is by no means a benign pathogen. Indeed, apart from being associated with at least seven different types of malignancies, EBV infection can cause severe and often fatal diseases-hemophagocytic lymphohistiocytosis, lymphoproliferative disease, B-cell lymphoma-in rare individuals with specific monogenic inborn errors of immunity. The discovery and detailed investigation of inborn errors of immunity characterized by heightened susceptibility to, or increased frequency of, EBV-induced disease have elegantly revealed cell types and signaling pathways that play critical and non-redundant roles in host-defense against EBV. These analyses have revealed not only mechanisms underlying EBV-induced disease in rare genetic conditions, but also identified molecules and pathways that could be targeted to treat severe EBV infection and pathological consequences in immunodeficient hosts, or even potentially enhance the efficacy of an EBV-specific vaccine.

Immunotherapy in Multiple Myeloma

Multiple myeloma is a complex disease and immune dysfunction has been known to play an important role in the disease pathogenesis, progression, and drug resistance. Recent efforts in drug development have been focused on immunotherapies to modify the MM disease process. Here, we summarize the emerging immunotherapies in the MM treatment landscape.

SLAMF6​ deficiency augments tumor killing and skews toward an effector phenotype revealing it as a novel T cell checkpoint

SLAMF6 is a homotypic receptor of the Ig-superfamily whose exact role in immune modulation has remained elusive. Its constitutive expression on resting and activated T cells precludes it from being a bona fide exhaustion marker. By breeding Pmel-1 mice with SLAMF6 -/- mice, we generated donors for T cells lacking SLAMF6 and expressing a transgenic TCR for gp100-melanoma antigen. Activated Pmel-1xSLAMF6 -/- CD8+ T cells displayed improved polyfunctionality and strong tumor cytolysis. T-bet was the dominant transcription factor in Pmel-1 x SLAMF6 -/- cells, and upon activation, they acquired an effector-memory phenotype. Adoptive transfer of Pmel-1 x SLAMF6 -/- T cells to melanoma-bearing mice resulted in lasting tumor regression in contrast to temporary responses achieved with Pmel-1 T cells. LAG-3 expression was elevated in the SLAMF6 -/- cells, and the addition of the LAG-3-blocking antibody to the adoptive transfer protocol improved the SLAMF6 -/- T cells and expedited the antitumor response even further. The results from this study support the notion that SLAMF6 is an inhibitory immune receptor whose absence enables powerful CD8+ T cells to eradicate tumors.

T and B-cell signaling in activated PI3K delta syndrome: From immunodeficiency to autoimmunity

Phosphatidylinositol 3 kinases (PI3K) are a family of lipid kinases that are activated by a variety of cell-surface receptors, and regulate a wide range of downstream readouts affecting cellular metabolism, growth, survival, differentiation, adhesion, and migration. The importance of these lipid kinases in lymphocyte signaling has recently been highlighted by genetic analyses, including the recognition that both activating and inactivating mutations of the catalytic subunit of PI3Kδ, p110δ, lead to human primary immunodeficiencies. In this article, we discuss how studies on the human genetic disorder "Activated PI3K-delta syndrome" and mouse models of this disease (Pik3cd^E1020K/+ mice) have provided fundamental insight into pathways regulated by PI3Kδ in T and B cells and their contribution to lymphocyte function and disease, including responses to commensal bacteria and the development of autoimmunity and tumors. We highlight critical roles of PI3Kδ in T follicular helper cells and the orchestration of the germinal center reaction, as well as in CD8⁺ T-cell function. We further  present data demonstrating the ability of the AKT-resistant FOXO1^AAA mutant to rescue IgG1 class switching defects in Pik3cd^E1020K/+ B cells, as well as data supporting a role for PI3Kδ in promoting multiple T-helper effector cell lineages.

Signalling lymphocyte activation molecule family member 9 is found on select subsets of antigen-presenting cells and promotes resistance to Salmonella infection

Signalling lymphocyte activation molecule family member 9 (SLAMF9) is an orphan receptor of the CD2/SLAM family of leucocyte surface proteins. Examination of SLAMF9 expression and function indicates that SLAMF9 promotes inflammation by specialized subsets of antigen‐presenting cells. Within healthy liver and circulating mouse peripheral blood mononuclear cells, SLAMF9 is expressed on CD11b⁺, Ly6C⁻, CD11c^low, F4/80^low, MHC‐II⁺, CX₃CR1⁺ mononuclear phagocytes as well as plasmacytoid dendritic cells. In addition, SLAMF9 can be found on peritoneal B1 cells and small (F4/80^low), but not large (F4/80^high), peritoneal macrophages. Upon systemic challenge with Salmonella enterica Typhimurium, Slamf9^−/− mice were impaired in their ability to clear the infection from the liver. In humans, SLAMF9 is up‐regulated upon differentiation of monocytes into macrophages, and lipopolysaccharide stimulation of PMA‐differentiated, SLAMF9 knockdown THP‐1 cells showed an essential role of SLAMF9 in production of granulocyte–macrophage colony‐stimulating factor, tumour necrosis factor‐α, and interleukin‐1β. Taken together, these data implicate SLAMF9 in the initiation of inflammation and clearance of bacterial infection.

T cell interactions with B cells during germinal center formation, a three-step model

Establishment of effective immunity against invading microbes depends on continuous generation of antibodies that facilitate pathogen clearance. Long-lived plasma cells with the capacity to produce high affinity antibodies evolve in germinal centers (GCs), where B cells undergo somatic hypermutation and are subjected to affinity-based selection. Here, we focus on the cellular interactions that take place early in the antibody immune response during GC colonization. Clones bearing B-cell receptors with different affinities and specificities compete for entry to the GC, at the boundary between the B-cell and T-cell zones in lymphoid organs. During this process, B cells compete for interactions with T follicular helper cells, which provide selection signals required for differentiation into GC cells and antibody secreting cells. These cellular engagements are long-lasting and depend on activation of adhesion molecules that support persistent interactions and promote transmission of signals between the cells. Here, we discuss how interactions between cognate T and B cells are primarily maintained by three types of molecular interactions: homophilic signaling lymphocytic activation molecule (SLAM) interactions, T-cell receptor: peptide-loaded major histocompatibility class II (pMHCII), and LFA-1:ICAMs. These essential components support a three-step process that controls clonal selection for entry into the antibody affinity maturation response in the GC, and establishment of long-lasting antibody-mediated immunity.

Regulation of MHC class I-independent NK cell education by SLAM family receptors

Seven members of signaling lymphocytic activation molecule (SLAM) family receptors (SFRs) are ubiquitously expressed on hematopoietic cells and they play critical roles in immune cell differentiation and activation. The engagement of these receptors transmits intracellular signaling mainly by recruiting SLAM-associated protein (SAP) and its related adaptors, EWS-FLI1-activated transcript-2 (EAT-2) and EAT-2-related transducer (ERT). The critical roles of SFRs and SAP-family adaptors are highlighted by the discovery that SAP is mutated in human X-linked lymphoproliferative (XLP1) disease in which the contact between T and B cells in germinal center and cytotoxic lymphocytes (NK cells and CD8⁺ T cells) function are severely compromised. These immune defects are closely associated with the defective antibody production and the high incidence of lymphoma in the patients with XLP1. In addition to these well-known functions, SLAM-SAP family is involved in NK cell education, a process describing NK cell functional competence. In this chapter, we will mainly discuss these unappreciated roles of SAP-dependent and SAP-independent SFR signaling in regulating MHC-I-independent NK cell education.

Concomitant deletion of SLAM-family receptors, NKG2D and DNAM-1 reveals gene redundancy of NK cell activating receptors in NK cell development and education

NK cells recognize "unwanted" cells using a variety of germline-encoded activating receptors, such as the seven members of signaling lymphocyte activating molecule (SLAM)-family receptors (SFRs), natural killer cell group 2D (NKG2D), and DNAX accessory molecule-1(DNAM-1). Whether these receptors redundantly or synergistically regulate NK cell development and effector function remains poorly understood. By generating mice lacking SFRs, NKG2D, and DNAM-1, separately or in combination, we found that SLAMF6, one of the SFR members, was associated with NK cell differentiation, but its absence had no severe effect on NK cell differentiation and function, likely due to SFR redundancy. Moreover, we revealed that SFRs might work with other NK cell activating receptors in regulating NK cell development and function. We found that SFR deficiency caused an increase in immature NK cell subsets (CD27⁺ CD11b^- ), and this effect was further augmented by the additional deficiency of NKG2D but not DNAM-1. However, SFR-deficient NK cells exhibited elevated responsiveness against "missing-self" hematopoietic targets, whereas the deletion of either NKG2D or DNAM-1 could partially abrogate the elevated effect of SFR deficiency on NK cell activation. Therefore, our results reveal the complexity of activating receptors in regulating NK cell differentiation and activation, extending our insights into the gene redundancy and compensatory effect of NK cell activating receptors.

SLAM Family Receptor Signaling in Viral Infections: HIV and Beyond

The signaling lymphocytic activation molecule (SLAM) family of receptors are expressed on the majority of immune cells. These receptors often serve as self-ligands, and play important roles in cellular communication and adhesion, thus modulating immune responses. SLAM family receptor signaling is differentially regulated in various immune cell types, with responses generally being determined by the presence or absence of two SLAM family adaptor proteins-Ewing's sarcoma-associated transcript 2 (EAT-2) and SLAM-associated adaptor protein (SAP). In addition to serving as direct regulators of the immune system, certain SLAM family members have also been identified as direct targets for specific microbes and viruses. Here, we will discuss the known roles for these receptors in the setting of viral infection, with special emphasis placed on HIV infection. Because HIV causes such complex dysregulation of the immune system, studies of the roles for SLAM family receptors in this context are particularly exciting.

Signaling Lymphocytic Activation Molecule Family Member 1 Engagement Inhibits T Cell-B Cell Interaction and Diminishes Interleukin-6 Production and Plasmablast Differentiation in Systemic Lupus Erythematosus

OBJECTIVE

Signaling lymphocytic activation molecule family member 1 (SLAMF1) homophilic interactions promote immunoglobulin production and T cell-B cell cross-talk. SLAMF1 is overexpressed on T and B cells in patients with systemic lupus erythematosus (SLE). This study was undertaken to determine the role of SLAMF1 monoclonal antibody (mAb) in modulating T cell-B cell interaction and B cell activation.

METHODS

Anti-IgM-prestimulated naive or total B cells from either healthy donors or patients with SLE were cocultured with autologous T cells under CD3/CD28 stimulation, in the presence or absence of the SLAMF1 mAb. Naive B cells were stimulated with anti-IgM and CD40L in the presence of the SLAMF1 antibody. Cytokine production by CD4+ T cells and B cells was examined by flow cytometry and/or quantitative polymerase chain reaction. Plasmablast formation and T cell and B cell conjugates were assessed by flow cytometry. IgG and antinuclear antibody production was determined by enzyme-linked immunosorbent assay.

RESULTS

SLAMF1 ligation in a human peripheral blood T cell-B cell culture system reduced the following in both healthy controls and patients with SLE: conjugate formation, interleukin-6 (IL-6) production by B cells, IL-21 and IL-17A production by T cells, and Ig and autoantibody production. Whereas the SLAMF1 mAb directly affected the function of isolated peripheral B cells by decreasing IL-6 and Ig production in vitro, it did not affect cytokine production by isolated T cells stimulated in vitro.

CONCLUSION

The SLAMF1 antibody inhibits T cell-B cell interaction and suppresses B cell cytokine production and differentiation, thereby acting as a potential therapeutic tool in the treatment of patients with SLE.

SLAM-SAP-Fyn: Old Players with New Roles in iNKT Cell Development and Function

Invariant natural killer T (iNKT) cells are a unique T cell lineage that develop in the thymus and emerge with a memory-like phenotype. Accordingly, following antigenic stimulation, they can rapidly produce copious amounts of Th1 and Th2 cytokines and mediate activation of several immune cells. Thus, it is not surprising that iNKT cells play diverse roles in a broad range of diseases. Given their pivotal roles in host immunity, it is crucial that we understand the mechanisms that govern iNKT cell development and effector functions. Over the last two decades, several studies have contributed to the current knowledge of iNKT cell biology and activity. Collectively, these studies reveal that the thymic development of iNKT cells, their lineage expansion, and functional properties are tightly regulated by a complex network of transcription factors and signaling molecules. While prior studies have clearly established the importance of the SLAM-SAP-Fyn signaling axis in iNKT cell ontogenesis, recent studies provide exciting mechanistic insights into the role of this signaling cascade in iNKT cell development, lineage fate decisions, and functions. Here we summarize the previous literature and discuss the more recent studies that guide our understanding of iNKT cell development and functional responses.

Management of IgG4-related disease

IgG4-related disease was unrecognised as a unified disease entity until this century, yet in a short period of time the disease has been appreciated to have a worldwide distribution, and its clinical, pathological, and radiological features have been described in considerable detail. The disease has strong organ predilections, and many of the clinical presentations of disease are increasingly familiar to both generalists and specialists. Early recognition of IgG4-related disease is crucial because although the disease is highly treatable, it can lead to serious organ damage and even death if undiagnosed until advanced stages. Its indolent nature often makes diagnosis challenging, and IgG4-related disease is one of the great mimickers of other diseases in the current era. Glucocorticoids are an effective treatment for IgG4-related disease, but their long-term use is problematic in a disease that frequently affects middle-aged to elderly individuals and often leads to pancreatic dysfunction. Our understanding of the pathophysiology of the disease is surprisingly advanced given the relatively recent recognition of this condition. Insights into disease pathophysiology offer the possibility of a variety of targeted treatment approaches. Looking ahead, biological therapies could profoundly alter the way in which IgG4-related disease is managed, permitting the use of specific therapies that are tailored to patients' clinical phenotypes.

Enhanced SLAMF7 Homotypic Interactions by Elotuzumab Improves NK Cell Killing of Multiple Myeloma

Elotuzumab (Elo) is an IgG₁ monoclonal antibody targeting SLAMF7 (CS1, CRACC, and CD319), which is highly expressed on multiple myeloma (MM) cells, natural killer (NK) cells, and subsets of other leukocytes. By engaging with FcγRIIIA (CD16), Elo promotes potent NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC) and macrophage-mediated antibody-dependent cellular phagocytosis (ADCP) toward SLAMF7⁺ MM tumor cells. Relapsed/refractory MM patients treated with the combination of Elo, lenalidomide, and dexamethasone have improved progression-free survival. We previously showed that Elo enhances NK cell activity via a costimulation mechanism, independent of CD16 binding. Here, we further studied the effect of Elo on cytotoxicity of CD16-negative NK-92 cells. Elo, but not other SLAMF7 antibodies, uniquely enhanced cytotoxicity mediated by CD16-negative NK-92 cells toward SLAMF7⁺ target cells. Furthermore, this CD16-independent enhancement of cytotoxicity required expression of SLAMF7 containing the full cytoplasmic domain in the NK cells, implicating costimulatory signaling. The CD16-independent costimulation by Elo was associated with increased expression of NKG2D, ICAM-1, and activated LFA-1 on NK cells, and enhanced cytotoxicity was partially reduced by NKG2D blocking antibodies. In addition, an Fc mutant form of Elo that cannot bind CD16 promoted cytotoxicity of SLAMF7⁺ target cells by NK cells from most healthy donors, especially if previously cultured in IL2. We conclude that in addition to promoting NK cell-mediated ADCC (CD16-dependent) responses, Elo promoted SLAMF7-SLAMF7 interactions in a CD16-independent manner to enhance NK cytotoxicity toward MM cells.

A Thpok-Directed Transcriptional Circuitry Promotes Bcl6 and Maf Expression to Orchestrate T Follicular Helper Differentiation

The generation of high-affinity neutralizing antibodies, the objective of most vaccine strategies, occurs in B cells within germinal centers (GCs) and requires rate-limiting "help" from follicular helper CD4⁺ T (Tfh) cells. Although Tfh differentiation is an attribute of MHC II-restricted CD4⁺ T cells, the transcription factors driving Tfh differentiation, notably Bcl6, are not restricted to CD4⁺ T cells. Here, we identified a requirement for the CD4⁺-specific transcription factor Thpok during Tfh cell differentiation, GC formation, and antibody maturation. Thpok promoted Bcl6 expression and bound to a Thpok-responsive region in the first intron of Bcl6. Thpok also promoted the expression of Bcl6-independent genes, including the transcription factor Maf, which cooperated with Bcl6 to mediate the effect of Thpok on Tfh cell differentiation. Our findings identify a transcriptional program that links the CD4⁺ lineage with Tfh differentiation, a limiting factor for efficient B cell responses, and suggest avenues to optimize vaccine generation.

SLAMF9 regulates pDC homeostasis and function in health and disease

SLAMF9 belongs to the conserved lymphocytic activation molecule family (SLAMF). Unlike other SLAMs, which have been extensively studied, the role of SLAMF9 in the immune system remained mostly unexplored. By generating CRISPR/Cas9 SLAMF9 knockout mice, we analyzed the role of this receptor in plasmacytoid dendritic cells (pDCs), which preferentially express the SLAMF9 transcript and protein. These cells display a unique capacity to produce type I IFN and bridge between innate and adaptive immune response. Analysis of pDCs in SLAMF9^-/- mice revealed an increase of immature pDCs in the bone marrow and enhanced accumulation of pDCs in the lymph nodes. In the periphery, SLAMF9 deficiency resulted in lower levels of the transcription factor SpiB, elevation of pDC survival, and attenuated IFN-α and TNF-α production. To define the role of SLAMF9 during inflammation, pDCs lacking SLAMF9 were followed during induced experimental autoimmune encephalomyelitis. SLAMF9^-/- mice demonstrated attenuated disease and delayed onset, accompanied by a prominent increase of immature pDCs in the lymph node, with a reduced costimulatory potential and enhanced infiltration of pDCs into the central nervous system. These results suggest the crucial role of SLAMF9 in pDC differentiation, homeostasis, and function in the steady state and during experimental autoimmune encephalomyelitis.

Chimeric Antigen Receptor-Modified T Cell Therapy in Multiple Myeloma: Beyond B Cell Maturation Antigen

Chimeric antigen receptor (CAR)-modified T cell therapy is a rapidly emerging immunotherapeutic approach that is revolutionizing cancer treatment. The impressive clinical results obtained with CAR-T cell therapy in patients with acute lymphoblastic leukemia and lymphoma have fueled the development of CAR-T cells targeting other malignancies, including multiple myeloma (MM). The field of CAR-T cell therapy for MM is still in its infancy, but remains promising. To date, most studies have been performed with B cell maturation antigen (BCMA)-targeted CARs, for which high response rates have been obtained in early-phase clinical trials. However, responses are usually temporary, and relapses have frequently been observed. One of the major reasons for relapse is the loss or downregulation of BCMA expression following CAR-T therapy. This has fostered a search for alternative target antigens that are expressed on the MM cell surface. In this review, we provide an overview of myeloma target antigens other than BCMA that are currently being evaluated in pre-clinical and clinical studies.

Increased SLAMF7high monocytes in myelofibrosis patients harboring JAK2V617F provide a therapeutic target of elotuzumab

Monocyte-derived fibrocytes recently garnered attention because the novel pathogenesis of myelofibrosis (MF), and suppression of fibrocyte differentiation by serum amyloid P remarkably improved MF. We previously revealed that human fibrocytes highly expressed signaling lymphocytic activation molecule F7 (SLAMF7) compared with macrophages and that SLAMF7^high monocytes in the peripheral blood (PB) of MF patients were significantly elevated relative to those in healthy controls (HCs). In this study, we evaluated SLAMF7^high monocyte percentage in the PB of HCs, myeloproliferative neoplasm (MPN) patients with MF, and MPN patients without MF by using a cross-sectional approach. We found that MPN patients with MF who harbored JAK2V617F had a significantly elevated SLAMF7^high monocyte percentage, which correlated positively with the JAK2V617F allele burden. In addition, the serum concentration of interleukin-1ra (IL-1ra) was significantly correlated with the SLAMF7^high monocyte percentage and JAK2V617F allele burden. These findings suggest that both SLAMF7^high monocytes and IL-1ra could be useful noninvasive markers of MF onset. Furthermore, the JAK2V617F allele burden of SLAMF7^high monocytes was significantly higher than that of SLAMF7^low monocytes and could be a potential target of elotuzumab (Elo), an anti-SLAMF7 antibody used for treating multiple myeloma. Elo independently inhibited differentiation of fibrocytes derived not only from HCs but also from MF patients in vitro. Elo also ameliorated MF and splenomegaly induced by romiplostim administration in humanized NOG mice. In conclusion, an increase of SLAMF7^high monocytes with higher JAK2V617F allele burden was associated with the onset of MF in MPN patients harboring JAK2V617F, and Elo could be a therapeutic agent for MPN patients with MF who harbor JAK2V617F.

The Role of Adaptor Proteins in the Biology of Natural Killer T (NKT) Cells

Adaptor proteins contribute to the selection, differentiation and activation of natural killer T (NKT) cells, an innate(-like) lymphocyte population endowed with powerful immunomodulatory properties. Distinct from conventional T lymphocytes NKT cells preferentially home to the liver, undergo a thymic maturation and differentiation process and recognize glycolipid antigens presented by the MHC class I-like molecule CD1d on antigen presenting cells. NKT cells express a semi-invariant T cell receptor (TCR), which combines the Vα14-Jα18 chain with a Vβ2, Vβ7, or Vβ8 chain in mice and the Vα24 chain with the Vβ11 chain in humans. The avidity of interactions between their TCR, the presented glycolipid antigen and CD1d govern the selection and differentiation of NKT cells. Compared to TCR ligation on conventional T cells engagement of the NKT cell TCR delivers substantially stronger signals, which trigger the unique NKT cell developmental program. Furthermore, NKT cells express a panoply of primarily inhibitory NK cell receptors (NKRs) that control their self-reactivity and avoid autoimmune activation. Adaptor proteins influence NKT cell biology through the integration of TCR, NKR and/or SLAM (signaling lymphocyte-activation molecule) receptor signals or the variation of CD1d-restricted antigen presentation. TCR and NKR ligation engage the SH2 domain-containing leukocyte protein of 76kDa slp-76 whereas the SLAM associated protein SAP serves as adaptor for the SLAM receptor family. Indeed, the selection and differentiation of NKT cells selectively requires co-stimulation via SLAM receptors. Furthermore, SAP deficiency causes X-linked lymphoproliferative disease with multiple immune defects including a lack of circulating NKT cells. While a deletion of slp-76 leads to a complete loss of all peripheral T cell populations, mutations in the SH2 domain of slp-76 selectively affect NKT cell biology. Furthermore, adaptor proteins influence the expression and trafficking of CD1d in antigen presenting cells and subsequently selection and activation of NKT cells. Adaptor protein complex 3 (AP-3), for example, is required for the efficient presentation of glycolipid antigens which require internalization and processing. Thus, our review will focus on the complex contribution of adaptor proteins to the delivery of TCR, NKR and SLAM receptor signals in the unique biology of NKT cells and CD1d-restricted antigen presentation.

Biological Therapy of Hematologic Malignancies: Toward a Chemotherapy- free Era

Less than 70 years ago, the vast majority of hematologic malignancies were untreatable diseases with fatal prognoses. The development of modern chemotherapy agents, which had begun after the Second World War, was markedly accelerated by the discovery of the structure of DNA and its role in cancer biology and tumor cell division. The path travelled from the first temporary remissions observed in children with acute lymphoblastic leukemia treated with single-agent antimetabolites until the first cures achieved by multi-agent chemotherapy regimens was incredibly short. Despite great successes, however, conventional genotoxic cytostatics suffered from an inherently narrow therapeutic index and extensive toxicity, which in many instances limited their clinical utilization. In the last decade of the 20th century, increasing knowledge on the biology of certain malignancies resulted in the conception and development of first molecularly targeted agents designed to inhibit specific druggable molecules involved in the survival of cancer cells. Advances in technology and genetic engineering enabled the production of structurally complex anticancer macromolecules called biologicals, including therapeutic monoclonal antibodies, antibody-drug conjugates and antibody fragments. The development of drug delivery systems (DDSs), in which conventional drugs were attached to various types of carriers including nanoparticles, liposomes or biodegradable polymers, represented an alternative approach to the development of new anticancer agents. Despite the fact that the antitumor activity of drugs attached to DDSs was not fundamentally different, the improved pharmacokinetic profiles, decreased toxic side effects and significantly increased therapeutic indexes resulted in their enhanced antitumor efficacy compared to conventional (unbound) drugs. Approval of the first immune checkpoint inhibitor for the treatment of cancer in 2011 initiated the era of cancer immunotherapy. Checkpoint inhibitors, bispecific T-cell engagers, adoptive T-cell approaches and cancer vaccines have joined the platform so far, represented mainly by recombinant cytokines, therapeutic monoclonal antibodies and immunomodulatory agents. In specific clinical indications, conventional drugs have already been supplanted by multi-agent, chemotherapy-free regimens comprising diverse immunotherapy and/or targeted agents. The very distinct mechanisms of the anticancer activity of new immunotherapy approaches not only call for novel response criteria, but might also change fundamental treatment paradigms of certain types of hematologic malignancies in the near future.

SLAMF6 clustering is required to augment T cell activation

The signaling lymphocytic activation molecule (SLAM) family is comprised of nine distinct receptors that are expressed exclusively on hematopoietic cells. Most of these transmembrane receptors are homotypic by nature and downstream signaling occurs when cells that express the same SLAM receptor interact. Previous studies have determined that anti-SLAMF6 antibodies can have a therapeutic effect in autoimmunity and cancer. However, little is known about the role of SLAMF6 in the adaptive immune responses and in order to utilize SLAMF6 interventional approaches, a better understanding of the biology of this receptor in T cell is warranted. Accordingly, the objective of our study was to investigate both functionally and structurally the role of SLAMF6 in T cell receptor (TCR) mediated responses. Biochemical and genetic experiments revealed that SLAMF6 was required for productive TCR downstream signaling. Interestingly, SLAMF6 ectodomain was required for its function, but not for its recruitment to the immunological synapse. Flow-cytometry analysis demonstrated that tyrosine 308 of the tail of SLAMF6 was crucial for its ability to enhance T cell function. Imaging studies revealed that SLAMF6 clustering, specifically with the TCR, resulted in dramatic increase in downstream signaling. Mechanistically, we showed that SLAMF6 enhanced T cell function by increasing T cell adhesiveness through activation of the small GTPase Rap1. Taken together SLAMF6 is an important regulator of T cell activation where both its ectodomain and its endodomain contribute differentially to T cell functions. Additional studies are underway to better evaluate the role of anti-SLAMF6 approaches in specific human diseases.

Expression analysis of two SLAM family receptors, SLAMF2 and SLAMF7, in patients with multiple myeloma

Monoclonal antibodies against surface antigens on MM cells, such as anti-SLAMF7 and anti-CD38 antibodies, represent an attractive therapeutic modality for the eradication of multiple myeloma (MM) cells. However, further exploration of target molecules is urgently needed for the development of more effective therapies. In the present study, we studied the expression of CD48 in a total of 74 primary MM samples derived from patients to evaluate SLAMF2 (CD48) as a candidate in mAb therapy for MM. Of 74 samples, 39 were subjected to SLAMF7 analysis. Most of the MM cells, defined as CD38 and CD138 double-positive cells, showed strong expression of CD48 or SLAMF7 independent of disease stage or treatment history. In these 39 samples, most MM cells showed expression of both SLAMF7 and CD48; however, several samples showed expression of either only CD48 or only SLAMF7, including seven cases that were only highly positive for SLAMF7, and five that were only highly positive for CD48. Our study demonstrates that the immune receptor CD48 is overexpressed on MM cells together with SLAMF7, and that CD48 may be considered as an alternative target for treatment of MM in cases showing weak expression of SLAMF7.

Compartmentalization of dendritic cell and T-cell interactions in the lymph node: Anatomy of T-cell fate decisions

Upon receiving cognate and co-stimulatory priming signals from antigen (Ag)-presenting dendritic cells (DCs) in secondary lymphoid tissues, naïve CD4+ T cells differentiate into distinct effector and memory populations. These alternate cell fate decisions, which ultimately control the T-cell functional attributes, are dictated by programming signals provided by Ag-bearing DCs and by other cells that are present in the microenvironment in which T-cell priming occurs. We know that DCs can be subdivided into multiple populations and that the various DC subsets exhibit differential capacities to initiate development of the different CD4+ T-helper populations. What is less well understood is why different subanatomic regions of secondary lymphoid tissues are colonized by distinct populations of Ag-presenting DCs and how the location of these DCs influences the type of T-cell response that will be generated. Here we review how chemokine receptors and their ligands, which position allergen and nematode-activated DCs within different microdomains of secondary lymphoid tissues, contribute to the establishment of IL-4 committed follicular helper T and type 2 helper cell responses.

B Cell Responses: Cell Interaction Dynamics and Decisions

B cells and the antibodies they produce have a deeply penetrating influence on human physiology. Here, we review current understanding of how B cell responses are initiated; the different paths to generate short- and long-lived plasma cells, germinal center cells, and memory cells; and how each path impacts antibody diversity, selectivity, and affinity. We discuss how basic research is informing efforts to generate vaccines that induce broadly neutralizing antibodies against viral pathogens, revealing the special features associated with allergen-reactive IgE responses and uncovering the antibody-independent mechanisms by which B cells contribute to health and disease.

SLE-Associated Defects Promote Altered T Cell Function

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease linked to profound defects in the function and phenotype of T lymphocytes. Here, we describe abnormal signaling pathways that have been documented in T cells from patients with SLE and discuss how they impact gene expression and immune function, in order to understand how they contribute to disease development and progression.

NK cell recognition of hematopoietic cells by SLAM-SAP families

The signaling lymphocyte activation molecule (SLAM) family of receptors (SFRs) are ubiquitously expressed on immune cells, and they regulate multiple immune events by recruiting SH2 (Src homology 2) domain-containing SAP family adapters, including SAP and its homologs, Ewing's sarcoma-associated transcript 2 (EAT-2) and EAT-2 related transducer (ERT). In human patients with X-linked lymphoproliferative (XLP) disease, which is caused by SAP mutations, SFRs alternatively bind other inhibitory SH2 domain-containing molecules to suppress immune cell activation and development. NK cells express multiple SFRs and all SAP family adapters. In recent decades, SFRs have been found to be critical for enhancing NK cell activation in response to abnormal hematopoietic cells in SAP-family-intact NK cells; however, SFRs might suppress NK cell activation in SAP-family-deficient mice or patients with XLP1. In this paper, we review how these two distinct SFR signaling pathways orchestrate NK cell activation and inhibition and highlight the importance of SFR regulation of NK cell biology and their physiological status and pathological relevance in patients with XLP1.

Clinical assessment and identification of immuno-oncology markers concerning the 19-gene based risk classifier in stage IV colorectal cancer

BACKGROUND

Genomic profiling of tumors has contributed to the understanding of colorectal cancer (CRC), facilitating diagnosis, prognosis and selection of treatments, including targeted regimens. A report suggested that a 19-gene-based risk classifier (TCA19) was a prognostic tool for patients with stage III CRC. The survival outcomes in patients with stage IV CRC are still poor and appropriate selection of targeted therapies and immunotherapies is challenging.

AIM

To assess clinical implication of TCA19 in patients with stage IV CRC, and to identify TCA19 with involvement in immune-oncology.

METHODS

A retrospective review of the medical records of 60 patients with stage IV CRC was conducted, assessing clinicopathological variables and progression-free survival (PFS). TCA19 gene expression was determined by quantitative polymerase chain reaction (qPCR) in matched normal and tumor tissues taken from the study cohort. Expression of potential immune-oncology regulatory proteins and targets was examined by immunohistochemistry (IHC), western blot, immunofluorescence staining in tissues from a validation cohort of 10 patients, and in CRC cell lines co-cultured with monocyte in vitro.

RESULTS

In the patients with TCA19 score higher than the median, the PFS rates of eight patients who received the targeted regimens were significantly higher than the PFS rates of four patients who received 5-fluorouracil-based regimen (P = 0.041). In multivariate analysis, expression of signaling lymphocytic activation molecule family, member 7 (SLAMF7) and triggering receptor expressed on myeloid cells 1 (TREM1) was associated with PFS in the 60-patient cohort. After checking another 10 validate set, the expression of the IHC, the level of real-time qPCR, and the level of western blot were lower for SLAMF7 and higher for TREM7 in primary and metastatic tumors than in normal tissues. In CRC cells expressing SLAMF7 that were co-cultured with a monocytic cell line, levels of CD 68 and CD 73 were significantly lower at day 5 of co-culture than at day 0.

CONCLUSION

The TCA19 score might be prognostic for target-regimen-specific PFS in stage IV CRC. Down-regulation of SLAMF7 and up-regulation of TREM1 occur in primary and metastatic tumor tissues.

Viral CD229 (Ly9) homologs as new manipulators of host immunity

The signaling lymphocytic activation molecule family (SLAMF) of receptors plays crucial roles during innate and adaptive immune responses. The SLAMF member CD229 (Ly9, SLAMF3) is a homophilic receptor predominantly expressed on the surface of B and T cells. CD229 acts as a cosignaling molecule, regulating lymphocyte homoeostasis and activation. To promote viral replication and survival in their hosts, viruses have developed sophisticated mechanisms to combat and avoid immune surveillance. Many of these strategies rely on host defense genes captured during the process of virus-host coevolution. In particular, large DNA viruses devote a wide range of proteins to interfere with almost every host immune pathway. Given that CD229 is critically involved in regulating immune responses, it is not surprising that viruses have designed tactics to mimic or interfere with this receptor. The discovery, in recent years, that some viruses have hijacked CD229 genes from their hosts, incorporating them as an integral part of their genomes, or have evolved proteins to directly target CD229, indicates that this is the case. While it is still an emerging area of research, the present review discusses these viral molecules and their potential in immune modulation. A more detailed understanding of the mechanisms of action and the functional implications of these new viral CD229 mimics may not only provide seminal information on viral immune evasion mechanisms but also, unveil unrecognized aspects of CD229 immune functions.

Complementary Role of CD4+ T Cells in Response to Pneumococcal Polysaccharide Vaccines in Humans

Bacterial pathogens expressing capsular polysaccharides are common causes of mucosal infections (pneumonia, intestinal), as well as often fatal, invasive infections (meningitis, bloodstream infections) in children and adults worldwide. These chemically simple but structurally complex carbohydrate structures on the bacterial surface confer resistance to recognition and clearance by the immune system through a range of mechanisms. Such recognition of capsular polysaccharides may be reduced by their limited ability to directly stimulate B cells and the T cells that may facilitate these humoral responses. The capsules may promote the evasion of complement deposition and activation and may sterically shield the recognition of other subjacent protein antigens by innate factors. Antibodies to capsular polysaccharides, elicited by infection and vaccines, may overcome these obstacles and facilitate bacterial agglutination at mucosal surfaces, as well as the opsonization and clearance of these organisms in tissues and the systemic compartment. However, the immunogenicity of these antigens may be limited by their lack of direct recognition by T cells (“T-independent” antigens) and their restricted ability to generate effective memory responses. In this review, we consider the mechanisms by which polysaccharides may initiate B cell responses and specific antibody responses and the role of T cells, particularly CD4+ follicular helper (TFH) cells to support this process. In addition, we also consider more recent counterintuitive data that capsular polysaccharides themselves may bind major histocompatibility antigen HLA class II to provide a more physiologic mechanism of T cell enhancement of B cell responses to capsular polysaccharides. Defining the contributions of T cells in the generation of effective humoral responses to the capsular polysaccharides will have important implications for understanding and translating this immunobiology for the development of more effective vaccines, to prevent the morbidity and mortality associated with these common mucosal and invasive pathogens in populations at risk.

PI3K Orchestrates T Follicular Helper Cell Differentiation in a Context Dependent Manner: Implications for Autoimmunity

T follicular helper (Tfh) cells are a specialized population of CD4⁺ T cells that provide help to B cells for the formation and maintenance germinal centers, and the production of high affinity class-switched antibodies, long-lived plasma cells, and memory B cells. As such, Tfh cells are essential for the generation of successful long-term humoral immunity and memory responses to vaccination and infection. Conversely, overproduction of Tfh cells has been associated with the generation of autoantibodies and autoimmunity. Data from gene-targeted mice, pharmacological inhibitors, as well as studies of human and mice expressing activating mutants have revealed that PI3Kδ is a key regulator of Tfh cell differentiation, acting downstream of ICOS to facilitate inactivation of FOXO1, repression of Klf2 and induction of Bcl6. Nonetheless, here we show that after acute LCMV infection, WT and activated-PI3Kδ mice (Pik3cd^E1020K/+) show comparable ratios of Tfh:Th1 viral specific CD4⁺ T cells, despite higher polyclonal Tfh cells in Pik3cd^E1020K/+ mice. Thus, the idea that PI3K activity primarily drives Tfh cell differentiation may be an oversimplification and PI3K-mediated pathways are likely to integrate multiple signals to promote distinct effector T cell lineages. The consequences of dysregulated Tfh cell generation will be discussed in the context of the human primary immunodeficiency “Activated PI3K-delta Syndrome” (APDS), also known as “p110 delta-activating mutation causing senescent T cells, lymphadenopathy and immunodeficiency” (PASLI). Overall, these data underscore a major role for PI3K signaling in the orchestration of T lymphocyte responses.

Epstein-Barr Virus-Associated T and NK-Cell Lymphoproliferative Diseases

EBV-associated T and NK-cell lymphoproliferative diseases (EBV-T/NK LPDs) are characterized by the transformation and proliferation of EBV-infected T or NK cells. The 2016 revised World Health Organization classification recognizes the following EBV-positive lymphoproliferative disorders (LPD): chronic active EBV infection (CAEBV) of T- and NK-cell type (cutaneous and systemic forms), systemic EBV-positive T-cell lymphoma of childhood, aggressive NK-cell leukemia, extranodal NK/T-cell lymphoma, nasal type, and the new provisional entity primary EBV-positive nodal T/NK-cell lymphoma. EBV-associated hemophagocytic lymphohistiocytosis (HLH), although not included in the WHO classification because it is a reactive, inflammatory disease, is included in this review because it can be life-threatening and may have overlapping features with other EBV+ T/NK LPDs. EBV+ T/NK LPDs are rare diseases difficult to diagnose and manage properly, because some LPDs have unusual presentations, and discrepancies between clinical and histological findings might be encountered. Furthermore, EBV+ T/NK disorders share some clinico-pathological features, and may evolve into other categories during the clinical course, including malignant transformation of CAEBV. Here, we review the EBV+ T/NK LPDs in terms of their definitions, clinical features, histology, immunophenotype, molecular findings, and pathogenesis. This review aims to increase our understanding and awareness of the differential diagnosis among the different EBV+ T/NK LPDs. New insights into the genetic characteristics of these disorders will also be discussed.

Management of XLP-1 and ITK deficiency: The challenges posed by PID with an unpredictable spectrum of disease manifestations

The incorporation of next generation sequencing into routine immunological practice has enabled the identification of novel inborn errors of disease, helped define new categories of immune deficiency and extended the clinical spectrum associated with many long-recognised diseases. The family of EBV (Epstein Barr Virus)-sensitive primary immune deficiencies is one such group and in this paper we describe three families: two with X-linked lymphoproliferative disease type-1 (XLP-1) and one with deficiency of Interleukin-2 Inducible T-cell Kinase (ITK). Both diseases have a wide range of clinical manifestations and are united by an exquisite predisposition to EBV, dysgammaglobulinemia, hemophagocytic lymphohistiocytosis, and lymphoma. We detail our approach to diagnosis, treatment, and risk stratification in these diseases where both clinicians and patients must grapple with constant uncertainty.

Combined deficiency of SLAMF8 and SLAMF9 prevents endotoxin-induced liver inflammation by downregulating TLR4 expression on macrophages

Classical signaling lymphocyte activating molecule (SLAM) family receptors are abundant within many types of immune cells, whereas the nonclassical SLAM family receptors SLAMF8 and SLAMF9, which uniquely lack cytoplasmic signaling motifs, are highly expressed by myeloid cells. Due to the potential redundancy, whether these two receptors regulate macrophage function remains largely unknown. Here, we show that SLAMF8 and SLAMF9 co-regulate macrophage-mediated liver inflammation. To overcome the redundancy, we generated mice that simultaneously lacked SLAMF8 and SLAMF9 using CRISPR-Cas9 technology. Although macrophage differentiation was not altered by the combined deficiency of SLAMF8 and SLAMF9, the loss of these two receptors significantly protected against lipopolysaccharide (LPS)-induced liver injury. SLAMF8 and SLAMF9 double-deficient mice had a prolonged survival rate and less infiltration of inflammatory cells. The depletion of macrophages using clodronate liposomes abolished the effects of SLAMF8 and SLAMF9 deficiencies on LPS-induced liver injury, which demonstrates that these receptors are required for macrophage activation following LPS challenge. Moreover, the deficiency of SLAMF8 and SLAMF9 suppressed the secretion of inflammatory cytokines by downregulating the expression of Toll-like receptor-4 (TLR4), a receptor that specifically binds LPS, which led to decreased mitogen-activated protein kinases (MAPK) signaling activation. Notably, combined injections of truncated extracellular SLAMF8 and SLAMF9 proteins significantly alleviated LPS-induced liver injury. Thus, our findings provide insights into the role of SLAMF8 and SLAMF9 in endotoxin-induced liver injury and suggest that SLAMF8 and SLAMF9 are potential therapeutic targets for acute hepatic injury.

SLAMF7 Is a Critical Negative Regulator of IFN-α-Mediated CXCL10 Production in Chronic HIV Infection

Current advances in combined antiretroviral therapy have rendered HIV infection a chronic, manageable disease; however, the problem of persistent immune activation still remains despite treatment. The immune cell receptor SLAMF7 has been shown to be upregulated in diseases characterized by chronic immune activation. In this study, we studied the function of the SLAMF7 receptor in immune cells of HIV patients and the impacts of SLAMF7 signaling on peripheral immune activation. We observed increased frequencies of SLAMF7⁺ PBMCs in HIV⁺ individuals in a clinical phenotype-dependent manner, with discordant and long-term nonprogressor patients showing elevated SLAMF7 levels, and elite controllers showing levels comparable to healthy controls. We also noted that SLAMF7 was sensitive to IFN-⍺ stimulation, a factor elevated during HIV infection. Further studies revealed SLAMF7 to be a potent inhibitor of the monocyte-derived proinflammatory chemokine CXCL10 (IP-10) and other CXCR3 ligands, except in a subset of HIV⁺ patients termed SLAMF7 silent (SF7S). Studies utilizing small molecule inhibitors revealed that the mechanism of CXCL10 inhibition is independent of known SLAMF7 binding partners. Furthermore, we determined that SLAMF7 activation on monocytes is able to decrease their susceptibility to HIV-1 infection in vitro via downregulation of CCR5 and upregulation of the CCL3L1 chemokine. Finally, we discovered that neutrophils do not express SLAMF7, are CXCL10⁺ at baseline, are able to secrete CXCL10 in response to IFN-⍺ and LPS, and are nonresponsive to SLAMF7 signaling. These findings implicate the SLAMF7 receptor as an important regulator of IFN-⍺-driven innate immune responses during HIV infection.

A comprehensive review on the role of co-signaling receptors and Treg homeostasis in autoimmunity and tumor immunity

The immune system ensures optimum T-effector (Teff) immune responses against invading microbes and tumor antigens while preventing inappropriate autoimmune responses against self-antigens with the help of T-regulatory (Treg) cells. Thus, Treg and Teff cells help maintain immune homeostasis through mutual regulation. While Tregs can contribute to tumor immune evasion by suppressing anti-tumor Teff response, loss of Treg function can result in Teff responses against self-antigens leading to autoimmune disease. Thus, loss of homeostatic balance between Teff/Treg cells is often associated with both cancer and autoimmunity. Co-stimulatory and co-inhibitory receptors, collectively known as co-signaling receptors, play an indispensable role in the regulation of Teff and Treg cell expansion and function and thus play critical roles in modulating autoimmune and anti-tumor immune responses. Over the past three decades, considerable efforts have been made to understand the biology of co-signaling receptors and their role in immune homeostasis. Mutations in co-inhibitory receptors such as CTLA4 and PD1 are associated with Treg dysfunction, and autoimmune diseases in mice and humans. On the other hand, growing tumors evade immune surveillance by exploiting co-inhibitory signaling through expression of CTLA4, PD1 and PDL-1. Immune checkpoint blockade (ICB) using anti-CTLA4 and anti-PD1 has drawn considerable attention towards co-signaling receptors in tumor immunology and created renewed interest in studying other co-signaling receptors, which until recently have not been as well studied. In addition to co-inhibitory receptors, co-stimulatory receptors like OX40, GITR and 4-1BB have also been widely implicated in immune homeostasis and T-cell stimulation, and use of agonistic antibodies against OX40, GITR and 4-1BB has been effective in causing tumor regression. Although ICB has seen unprecedented success in cancer treatment, autoimmune adverse events arising from ICB due to loss of Treg homeostasis poses a major obstacle. Herein, we comprehensively review the role of various co-stimulatory and co-inhibitory receptors in Treg biology and immune homeostasis, autoimmunity, and anti-tumor immunity. Furthermore, we discuss the autoimmune adverse events arising upon targeting these co-signaling receptors to augment anti-tumor immune responses.

SLAMF receptors on normal and malignant B cells

The Signaling Lymphocyte Activation Molecule family (SLAMF) is a collection of nine surface receptors expressed mainly on hematopoietic cells, and was found to modulate the behavior of immune cells. SLAMF receptors are expressed on B cells in health and disease. Each SLAM receptor has a unique differential expression pattern during the development and activation of B cells. Furthermore, recent findings have revealed a principal role for this family of receptors in B cell malignancies, emphasizing their importance in the control of malignant cell survival, cell to cell communication within the tumor microenvironment, retention in the supporting niches and regulation of T cell anti-tumor response. This review summarizes the latest studies regarding SLAMF expression and behavior in B cells and in B cell pathologies, and discusses the therapeutic potential of these receptors.

[A preliminary study on SLAMF6 expression in patients with severe aplastic anemia]

Objective: To explore the expression of SLAMF6 on CD8(+) T cells in patients with severe aplastic anemia (SAA) and its correlation with disease immune status. Methods: By flow cytometry (FCM), SLAMF6 expression level in peripheral blood CD8(+) T cells was detected in 21 patients with SAA and 15 normal controls respectively from February 2017 to April 2018. The correlation between SLAMF6 expression level and hematopoietic functions, including HGB, PLT, the neutrophil granulocyte and reticulocyte absolute value in peripheral blood, hyperplasia degree (percentage of granulocytes, erythrocytes, lymphocytes and megakaryocytes in bone marrow) and perforin, granzyme B, IFN-γ expression level in CD8(+) T cells were evaluated. To further confirm the effect of SLAMF6 on CD8(+) T cells, anti-SLAMF6 Ab was used to block SLAMF6 pathway (IgG as control), and FCM was used to detect the perforin, granzyme B, and IFN-γ production of CD8(+) T cells. Results: The expression of SLAMF6 on CD8(+) T cells in untreated SAA patients[(56.29±12.97)%]was significantly lower than that of normal controls[(80.96±7.36)%](t=-7.672, P<0.001). The expression of SLAMF6 on CD8(+) T cells in SAA patients were positively correlated with the HGB, PLT, the neutrophil granulocyte and reticulocyte absolute value in peripheral blood, percentage of granulocytes, erythrocytes in bone marrow (all P<0.05), but they were negatively correlated with the percentage of lymphocytes in bone marrow, and the expression of perforin, granzyme B, and IFN-γ of CD8(+) T cells (all P<0.05). After blocking SLAMF6 pathway by anti-SLAMF6 Ab, the expression levels of perforin, granzyme B and IFN-γ in SAA patients were significantly higher than those in the untreated group, and the differences were statistically significant (all P<0.05). Conclusions: SLAMF6 is significantly down-regulated on CD8(+) T cells in SAA patients, which may act as a negative immunoregulatory molecule participating in the mechanism of SAA by affecting the functional molecules secretion on CD8(+) T cells.

Signaling lymphocyte activation molecule family in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disease characterized by a breakdown in immune tolerance leading to the development of auto-reactive lymphocytes and autoantibodies. Recent findings have provided new insight on the role of the signaling lymphocytic activation molecule family (SLAMF) receptors, a group of nine co-regulatory molecules involved in the activation of hematopoietic cells, and their downstream protein SLAM-associated protein (SAP), into the pathogenesis of SLE. This review summarizes the current knowledge on SLAMF in human SLE immunopathogenesis, and the importance of SLAMF molecules as new therapeutic targets.

2B4 dysfunction in XLP1 NK cells: More than inability to control EBV infection

X-linked lymphoproliferative disease 1 (XLP1) is a monogenic disorder caused by mutations in SH2D1A, resulting in the absence/dysfunction of the signaling lymphocyte activation molecule (SLAM)-associated protein (SAP). Consequently, SLAM receptors as 2B4 (CD244) and NTB-A (SLAMF6), upon ligand engagement, exert inhibitory instead of activating function. This causes an immune dysfunction that is worsened by the selective inability of NK and T cells to kill EBV-infected B cells with dramatic clinical sequelae (e.g. fulminant mononucleosis, hyperinflammation, lymphoma). Here we outline recent findings on the interplay between inhibitory 2B4 and the various activating receptors in NK cells. 2B4 engagement selectively blocks ITAM-dependent activating receptors as NCR and CD16, while it does not affect NKG2D and DNAM-1. Furthermore, inhibitory 2B4 participates to NK cell education, as highlighted by the existence in XLP1 patients of a large subset of fully functional NK cells that lack self-HLA specific inhibitory receptors and exert autoreactivity against mature dendritic cells.