Lymphocytic Activation Molecule Family Receptors Research Articles

Signaling lymphocytic activation molecule family receptors as potential immune therapeutic targets in solid tumors.

Recently, cancer immunotherapy has revolutionized cancer treatment. Various forms of immunotherapy have a manageable safety profile and result in prolongation of overall survival in patients with solid tumors, but only in a proportion of patients. Various factors in the tumor microenvironment play critical roles and may be responsible for this lack of therapeutic response. Signaling lymphocytic activation molecule family (SLAMF) members are increasingly being studied as factors impacting the tumor immune microenvironment. SLAMF members consist of nine receptors mainly expressed in immune cells. However, SLAMF receptors have also been detected in cancer cells, and they may be involved in a spectrum of anti-tumor immune responses. Here, we review the current knowledge of the expression of SLAMF receptors in solid tumors and tumor-infiltrating immune cells and their association with patient outcomes. Furthermore, we discuss the therapeutic potential of targeting SLAMF receptors to improve outcomes of cancer therapy in solid tumors. We believe the research on SLAMF receptor-targeted strategies may enhance anti-cancer immunity in patients with solid tumors and improve clinical outcomes.

α-Tocopherol Attenuates Oxidative Phosphorylation of CD34+ Cells, Enhances Their G0 Phase Fraction and Promotes Hematopoietic Stem and Primitive Progenitor Cell Maintenance.

Alpha tocopherol acetate (αTOA) is an analogue of alpha tocopherol (αTOC) that exists in the form of an injectable drug. In the context of the metabolic hypothesis of stem cells, we studied the impact of αTOA on the metabolic energetic profile and functional properties of hematopoietic stem and progenitor cells. In ex vivo experiments performed on cord blood CD34+ cells, we found that αTOA effectively attenuates oxidative phosphorylation without affecting the glycolysis rate. This effect concerns complex I and complex II of the mitochondrial respiratory chain and is related to the relatively late increase (3 days) in ROS (Reactive Oxygen Species). The most interesting effect was the inhibition of Hypoxia-Inducible Factor (HIF)-2α (Hexpression, which is a determinant of the most pronounced biological effect—the accumulation of CD34+ cells in the G0 phase of the cell cycle. In parallel, better maintenance of the primitive stem cell activity was revealed by the expansion seen in secondary cultures (higher production of colony forming cells (CFC) and Severe Combined Immunodeficiency-mice (scid)-repopulating cells (SRC)). While the presence of αTOA enhanced the maintenance of Hematopoietic Stem Cells (HSC) and contained their proliferation ex vivo, whether it could play the same role in vivo remained unknown. Creating αTOC deficiency via a vitamin E-free diet in mice, we found an accelerated proliferation of CFC and an expanded compartment of LSK (lineagenegative Sca-1+cKit+) and SLAM (cells expressing Signaling Lymphocytic Activation Molecule family receptors) bone marrow cell populations whose in vivo repopulating capacity was decreased. These in vivo data are in favor of our hypothesis that αTOC may have a physiological role in the maintenance of stem cells. Taking into account that αTOC also exhibits an effect on proliferative capacity, it may also be relevant for the ex vivo manipulation of hematopoietic stem cells. For this purpose, low non-toxic doses of αTOA should be used.

Regulation of antiviral CD8 T cell immunity by CD352/SLAMF6: from patterns to pathways

Abstract A better understanding of CD8 memory T cell (TM) formation during acute and chronic viral infections is critical for both effective immunotherapy and vaccine design. Signaling lymphocytic activation molecule family receptors (SLAMF) including CD150, CD48, CD229, CD244, CD84, CD352, and CD319 were found to be involved in T cell activation and differentiation, but their contribution to the regulation of antigen-specific T cell immunity remains incompletely understood. Here, we analyzed the dynamics of SLAMF co-expression patterns by antiviral CD8 T cells in response to acute and chronic lymphocytic choriomeningitis virus (LCMV) infection. Our results demonstrate distinct SLAMF levels not only on LCMV-specific CD8 effector (TE) and TM cell subsets, but differential kinetics during acute vs. chronic infection. Importantly, we identified CD352 as a unique marker for long-term CD8 TM potential and capacity with significant upregulation on memory-precursor (MPEC) vs. short-lived effector (SLEC) as well as on central (TCM) vs. effector memory (TEM) CD8 T cells (MPEC>>TCM>TEM≥SLEC). Moreover, in the context of chronic viral infection, we found CD352+ CD8 T cells to be partially resistant to exhaustion as demonstrated by a memory-like phenotype, preserved CD8 T cell function, and better in vivo recall capacity upon adoptive transfer into naïve hosts. Conversely, chronically-infected CD352-deficient mice showed an impaired CD8 T cell response with reduced frequencies of LCMV-specific CD8 T cells, a more exhausted phenotype, lower expression of TM markers, and reduced functional properties. Collectively, our data reveal CD352 as a potential therapeutic target to modify CD8 T cell responses during acute and chronic viral infections.

X-Linked Lymphoproliferative Disease Type 1: A Clinical and Molecular Perspective

X-linked lymphoproliferative disease (XLP) was first described in the 1970s as a fatal lymphoproliferative syndrome associated with infection with Epstein–Barr virus (EBV). Features include hemophagocytic lymphohistiocytosis (HLH), lymphomas, and dysgammaglobulinemias. Molecular cloning of the causative gene, SH2D1A, has provided insight into the nature of disease, as well as helped characterize multiple features of normal immune cell function. Although XLP type 1 (XLP1) provides an example of a primary immunodeficiency in which patients have problems clearing primarily one infectious agent, it is clear that XLP1 is also a disease of severe immune dysregulation, even independent of EBV infection. Here, we describe clinical features of XLP1, how molecular and biological studies of the gene product, SAP, and the associated signaling lymphocyte activation molecule family receptors have provided insight into disease pathogenesis including specific immune cell defects, and current therapeutic approaches including the potential use of gene therapy. Together, these studies have helped change the outcome of this once almost uniformly fatal disease.

Targeting of Ly9 (CD229) Disrupts Marginal Zone and B1 B Cell Homeostasis and Antibody Responses.

Marginal zone (MZ) and B1 B cells have the capacity to respond to foreign Ags more rapidly than conventional B cells, providing early immune responses to blood-borne pathogens. Ly9 (CD229, SLAMF3), a member of the signaling lymphocytic activation molecule family receptors, has been implicated in the development and function of innate T lymphocytes. In this article, we provide evidence that in Ly9-deficient mice splenic transitional 1, MZ, and B1a B cells are markedly expanded, whereas development of B lymphocytes in bone marrow is unaltered. Consistent with an increased number of these B cell subsets, we detected elevated levels of IgG3 natural Abs and a striking increase of T-independent type II Abs after immunization with 2,4,6-trinitrophenyl-Ficoll in the serum of Ly9-deficient mice. The notion that Ly9 could be a negative regulator of innate-like B cell responses was supported by the observation that administering an mAb directed against Ly9 to wild-type mice selectively eliminated splenic MZ B cells and significantly reduced the numbers of B1 and transitional 1 B cells. In addition, Ly9 mAb dramatically diminished in vivo humoral responses and caused a selective downregulation of the CD19/CD21/CD81 complex on B cells and concomitantly an impaired B cell survival and activation in an Fc-independent manner. We conclude that altered signaling caused by the absence of Ly9 or induced by anti-Ly9 may negatively regulate development and function of innate-like B cells by modulating B cell activation thresholds. The results suggest that Ly9 could serve as a novel target for the treatment of B cell-related diseases.

Signaling Lymphocytic Activation Molecule Family Receptor Homologs in New World Monkey Cytomegaloviruses.

Throughout evolution, large DNA viruses have been usurping genes from their hosts to equip themselves with proteins that restrain host immune defenses. Signaling lymphocytic activation molecule (SLAM) family (SLAMF) receptors are involved in the regulation of both innate and adaptive immunity, which occurs upon engagement with their ligands via homotypic or heterotypic interactions. Here we report a total of seven SLAMF genes encoded by the genomes of two cytomegalovirus (CMV) species, squirrel monkey CMV (SMCMV) and owl monkey CMV (OMCMV), that infect New World monkeys. Our results indicate that host genes were captured by retrotranscription at different stages of the CMV-host coevolution. The most recent acquisition led to S1 in SMCMV. S1 is a SLAMF6 homolog with an amino acid sequence identity of 97% to SLAMF6 in its ligand-binding N-terminal Ig domain. We demonstrate that S1 is a cell surface glycoprotein capable of binding to host SLAMF6. Furthermore, the OMCMV genome encodes A33, an LY9 (SLAMF3) homolog, and A43, a CD48 (SLAMF2) homolog, two soluble glycoproteins which recognize their respective cellular counterreceptors and thus are likely to be viral SLAMF decoy receptors. In addition, distinct copies of further divergent CD48 homologs were found to be encoded by both CMV genomes. Remarkably, all these molecules display a number of unique features, including cytoplasmic tails lacking characteristic SLAMF signaling motifs. Taken together, our findings indicate a novel immune evasion mechanism in which incorporation of host SLAMF receptors that retain their ligand-binding properties enables viruses to interfere with SLAMF functions and to supply themselves with convenient structural molds for expanding their immunomodulatory repertoires. The way in which viruses shape their genomes under the continual selective pressure exerted by the host immune system is central for their survival. Here, we report that New World monkey cytomegaloviruses have broadly captured and duplicated immune cell receptors of the signaling lymphocyte activation molecule (SLAM) family during host-virus coevolution. Notably, we demonstrate that several of these viral SLAMs exhibit exceptional preservation of their N-terminal immunoglobulin domains, which results in maintenance of their ligand-binding capacities. At the same time, these molecules present distinctive structural properties which include soluble forms and the absence of typical SLAM signaling motifs in their cytoplasmic domains, likely reflecting the evolutionary adaptation undergone to efficiently interfere with host SLAM family activities. The observation that the genomes of other large DNA viruses might bear SLAM family homologs further underscores the importance of these molecules as a novel class of immune regulators and as convenient scaffolds for viral evolution.

SLAMF4 Is a Negative Regulator of Expansion of Cytotoxic Intraepithelial CD8+ T Cells That Maintains Homeostasis in the Small Intestine

Intraepithelial T lymphocyte cells (IEL) are the first immune cells to respond to pathogens; they help maintain the integrity of the epithelial barrier. We studied the function of the mouse glycoprotein Signaling Lymphocyte Activation Molecule Family receptor (SLAMF) 4 (encoded by Slamf4) on the surface of CD8αβ αβ T-cell receptor (TCR)(+) IELs, and the roles of these cells in homeostasis of the small intestine in mice. SLAMF4(-) CD8(+) αβTCR(+) cells isolated from spleens of OT-I Rag1(-/-) mice were induced to express gut-homing receptors and transferred to C57BL/6J mice; levels of SLAMF4(+) cells were measured in small intestine tissues. After administration of anti-CD3 or antigen, with or without anti-SLAM4, to C57BL/6J and Slamf4(-/-) mice, CD8αβ αβTCR(+) IELs were collected; cytokine production and cytotoxicity were measured. Depletion of CX3CR1(+) phagocytes was assessed in mice by live-cell confocal imaging or by cytofluorometry; small intestine tissues were analyzed by histology and inflammation was quantified. Splenic CD8(+) αβTCR(+) cells began to express SLAMF4 only after migrating to the small intestine. Injection of C57BL/6J mice with anti-SLAMF4 and anti-CD3 increased levels of interleukin 10 and interferon gamma secretion by IEL, compared with injection of anti-CD3 only. Similarly, the number of granzyme B(+) cytotoxic CD8(+) αβTCR(+) IELs increased in Slamf4(-/-) mice after injection of anti-CD3 and anti-SLAMF4, administration of antigen, or injection of anti-CD3. Surprisingly, invivo activation of CD8αβ(+) IELs with anti-CD3 or antigen caused transient depletion of CX3CR1(+) phagocytes, which was prolonged by co-injection with anti-SLAMF4 or in Slamf4(-/-) mice. Anti-CD3 aggravated inflammation in the small intestines of Slamf4(-/-) mice and Eat2a(-/-)Eat2b(-/-) mice, indicated by flattened villi and crypt hyperplasia. In mice, the intestinal environment induces SLAMF4 expression and localization to the surface of CD8(+) αβTCR(+) IELs. Signaling via SLAMF4 controls expansion of cytotoxic CD8αβ(+) IELs, which regulate the reversible depletion of lamina propria phagocytes and inflammation in the small intestine.

A Role for Ly108 in the Induction of Promyelocytic Zinc Finger Transcription Factor in Developing Thymocytes

The promyelocytic zinc finger transcription factor (PLZF) is required for the development of activated phenotypes in NKT and other innate T lymphocytes. Although strong TCR stimulation has been implicated in the induction of PLZF, the factors regulating PLZF expression are incompletely understood. We show in this study that costimulation of preselection double-positive thymocytes through the signaling lymphocyte activation molecule family receptor Ly108 markedly enhanced PLZF expression compared with that induced by TCR stimulation alone. Costimulation with Ly108 increased expression of early growth response protein (Egr)-2 and binding of Egr-2 to the promoter of Zbtb16, which encodes PLZF, and resulted in PLZF levels similar to those seen in NKT cells. In contrast, costimulation with anti-CD28 failed to enhance Egr-2 binding and Zbtb16 expression. Moreover, mice lacking Ly108 showed decreased numbers of PLZF-expressing CD4(+) T cells. Together, these results support a potential role for Ly108 in the induction of PLZF.

Cutting Edge: Ly9 (CD229), a SLAM Family Receptor, Negatively Regulates the Development of Thymic Innate Memory-like CD8+ T and Invariant NKT Cells

Signaling lymphocytic activation molecule family receptors and the specific adapter signaling lymphocytic activation molecule-associated protein modulate the development of innate-like lymphocytes. In this study, we show that the thymus of Ly9-deficient mice contains an expanded population of CD8 single-positive cells with the characteristic phenotype of innate memory-like CD8(+) T cells. Moreover, the proportion of these innate CD8(+) T cells increased dramatically postinfection with mouse CMV. Gene expression profiling of Ly9-deficient mice thymi showed a significant upregulation of IL-4 and promyelocytic leukemia zinc finger. Analyses of Ly9(-/-)IL4ra(-/-) double-deficient mice revealed that IL-4 was needed to generate the thymic innate CD8(+) T cell subset. Furthermore, increased numbers of invariant NKT cells were detected in Ly9-deficient thymi. In wild-type mice, IL-4 levels induced by α-galactosylceramide injection could be inhibited by a mAb against Ly9. Thus, Ly9 plays a unique role as an inhibitory cell surface receptor regulating the size of the thymic innate CD8(+) T cell pool and the development of invariant NKT cells.

Cutting Edge: The Adapters EAT-2A and -2B Are Positive Regulators of CD244- and CD84-Dependent NK Cell Functions in the C57BL/6 Mouse

EWS/FLI1-activated transcript 2 (EAT-2)A and EAT-2B are single SH2-domain proteins, which bind to phosphorylated tyrosines of signaling lymphocyte activation molecule family receptors in murine NK cells. While EAT-2 is a positive regulator in human cells, a negative regulatory role was attributed to the adapter in NK cells derived from EAT-2A-deficient 129Sv mice. To evaluate whether the genetic background or the presence of a selection marker in the mutant mice could influence the regulatory mode of these adapters, we generated EAT-2A-, EAT-2B-, and EAT-2A/B-deficient mice using C57BL/6 embryonic stem cells. We found that NK cells from EAT-2A- and EAT-2A/B-deficient mice were unable to kill tumor cells in a CD244- or CD84-dependent manner. Furthermore, EAT-2A/B positively regulate phosphorylation of Vav-1, which is known to be implicated in NK cell killing. Thus, as in humans, the EAT-2 adapters act as positive regulators of signaling lymphocyte activation molecule family receptor-specific NK cell functions in C57BL/6 mice.

Slam Haplotypes Modulate the Response to Lipopolysaccharide In Vivo through Control of NKT Cell Number and Function

CD1d-restricted NKT cells make up an innate-like T cell subset that plays a role in amplifying the response of innate immune leukocytes to TLR ligands. The Slam locus contains genes that have been implicated in innate and adaptive immune responses. In this study, we demonstrate that divergent Slam locus haplotypes modulate the response of macrophages to the TLR4 ligand LPS through their control of NKT cell number and function. In response to LPS challenge in vivo, macrophage TNF production in Slam haplotype-2(+) 129S1/SvImJ and 129X1/SvJ mice was significantly impaired in comparison with macrophage TNF production in Slam haplotype-1(+) C57BL/6J mice. Although no cell-intrinsic differences in macrophage responses to LPS were observed between strains, 129 mice were found to be deficient in liver NKT cell number, in NKT cell cytokine production in response to the CD1d ligand alpha-galactosylceramide, and in NKT cell IFN-gamma production after LPS challenge in vivo. Using B6.129c1 congenic mice and adoptive transfer, we found that divergent Slam haplotypes controlled the response to LPS in vivo, as well as the diminished NKT cell number and function, and that these phenotypes were associated with differential expression of signaling lymphocytic activation molecule family receptors on NKT cells. These data suggest that the polymorphisms that distinguish two Slam haplotypes significantly modulate the innate immune response in vivo through their effect on NKT cells.