T-lymphocyte coactivator molecules

Paroxysmal Nocturnal Hemoglobinuria: Biology and Treatment

Paroxysmal nocturnal hemoglobinuria (PNH) is a nonmalignant clonal hematopoietic disorder characterized by the lack of glycosylphosphatidylinositol-anchored proteins (GPI-APs) as a consequence of somatic mutations in the phosphatidylinositol glycan anchor biosynthesis class A (PIGA) gene. Clinical manifestations of PNH are intravascular hemolysis, thrombophilia, and bone marrow failure. Treatment of PNH mainly relies on the use of complement-targeted therapy (C5 inhibitors), with the newest agents being explored against other factors involved in the complement cascade to alleviate unresolved intravascular hemolysis and extravascular hemolysis. This review summarizes the biology and current treatment strategies for PNH with the aim of reaching a general audience with an interest in hematologic disorders.

Tumor and Systemic Immunomodulatory Effects of MEK Inhibition

PURPOSE OF REVIEW

Mitogen-activated protein kinase (MAPK) kinase (MEK) is an integral component of the RAS signaling pathway, one of the most frequently mutated pathways in cancer biology. MEK inhibitors were initially developed to directly target oncogenic signaling, but are recognized to have pleiotropic effects on both tumor cells and lymphocytes. Here, we review the preclinical and clinical evidence that MEK inhibition is immunomodulatory and discuss the potential rationale for combining MEK inhibitors with systemic immunotherapies.

RECENT FINDINGS

MEK inhibition may modulate the tumor microenvironment (TME) through direct effects on both tumor cells and immune cells. Despite encouraging evidence that MEK inhibition can reprogram the tumor microenvironment (TME) and augment anti-tumor immunity regardless of KRAS/BRAF status, recent clinical outcome studies combining MEK inhibition with systemic immunotherapy have yielded mixed results. The combination of MEK inhibitors plus systemic immunotherapies has been tolerable, but has thus far failed to demonstrate clear evidence of synergistic clinical activity. These results underscore the need to understand the appropriate therapeutic context for this combination. MEK inhibitors have the potential to inhibit oncogenic signaling and reprogram the tumor immune microenvironment, representing an attractive therapy to combine with systemic immunotherapies. Ongoing preclinical and clinical studies will further clarify the immunomodulatory effects of MEK inhibitors to inform the design of rational therapeutic combinations.

T Cell Adaptive Immunity Proceeds through Environment-Induced Adaptation from the Exposure of Cryptic Genetic Variation

Evolution is often characterized as a process involving incremental genetic changes that are slowly discovered and fixed in a population through genetic drift and selection. However, a growing body of evidence is finding that changes in the environment frequently induce adaptations that are much too rapid to occur by an incremental genetic search process. Rapid evolution is hypothesized to be facilitated by mutations present within the population that are silent or “cryptic” within the first environment but are co-opted or “exapted” to the new environment, providing a selective advantage once revealed. Although cryptic mutations have recently been shown to facilitate evolution in RNA enzymes, their role in the evolution of complex phenotypes has not been proven. In support of this wider role, this paper describes an unambiguous relationship between cryptic genetic variation and complex phenotypic responses within the immune system. By reviewing the biology of the adaptive immune system through the lens of evolution, we show that T cell adaptive immunity constitutes an exemplary model system where cryptic alleles drive rapid adaptation of complex traits. In naive T cells, normally cryptic differences in T cell receptor reveal diversity in activation responses when the cellular population is presented with a novel environment during infection. We summarize how the adaptive immune response presents a well studied and appropriate experimental system that can be used to confirm and expand upon theoretical evolutionary models describing how seemingly small and innocuous mutations can drive rapid cellular evolution.

Kinetics of Th1/Th2 cytokines and lymphocyte subsets to predict chronic GVHD after allo-SCT: results of a prospective study

The role of different cytokines and cells of immune system in the pathogenesis of chronic GVHD (cGVHD) is still controversial. Earlier studies, which were either retrospective or analysed one or a few factors, did not show unequivocal results. We prospectively evaluated cytokine levels and lymphocyte subsets in 30 patients who underwent Allo-SCT to investigate their possible correlation with cGVHD. Levels of IL-4, IL-6, IL-10, IFN-gamma, tumour necrosis factor-alpha (TNF-alpha) and its soluble receptors were assessed by ELISA in 30 patients at different times after SCT. Lymphocyte subsets were evaluated by flow cytometry in peripheral blood at the same times as cytokines. A multivariate analysis was performed using principal component analysis and multi-factor ANOVA (analysis of variance). Eighteen patients developed cGVHD at a median time of 6 months (range, 5-9) after SCT. In multivariate analysis, we observed a correlation between cGVHD and clusters of cytokines and lymphocyte subsets from the third to the sixth month after SCT. These clusters changed their composition over time, but they constantly included natural killer (NK) and CD152+ T cells as negative predictors of cGVHD. TNF-alpha prevailed among other cytokines before the onset of cGVHD. This prevalence could be related partly to the defect of immunoregulatory cells.

Refinement of molecular approaches to improve the chance of identification of hematopoietic-restricted minor histocompatibility antigens

Minor histocompatibility antigens (mHAgs) constitute the target antigens of the T cell-mediated graft-versus-leukemia response after HLA-identical allogeneic stem cell transplantation (SCT). Several human mHAgs have been identified, but only a few are selectively expressed by hematopoietic cells representing potential targets for specific immunotherapy. Molecular approaches including cDNA library screening and genetic linkage analysis have been successfully applied to identify T cell-defined mHAgs, but each approach has its drawbacks which may lead to mis-identification of the mHAg of interest. We improved both molecular strategies to facilitate more robust identification of hematopoietic-restricted mHAgs. First, we adapted cDNA library cloning by using 293T cells with stable expression of the relevant MHC class I allele, CD80 and CD54. We demonstrated that cDNA library screening using this 293T expression system results in strong activation of cytotoxic T lymphocytes, which significantly contributes to improvement of the assay sensitivity. Second, we refined genetic linkage analysis using single nucleotide polymorphism (SNP) genotyping to narrow down the defined genetic region that holds the mHAg-encoding gene. We showed that SNP marker analysis provides additional information about the genetic position of the antigen-encoding gene. Application of these optimized molecular approaches will lead to more rapid and reliable molecular identification of hematopoietic-restricted mHAgs.

Antigen recognition and T-cell biology

Despite the wealth of information that has been acquired regarding the way T cells recognize their targets, we are left with far more questions than answers regarding how to manipulate the immune response to better treat cancer patients. Clearly, most patients have a broad repertoire of T cells capable of recognizing their tumor cells. Despite the presence of these tumor reactive T cells and our ability to increase their frequency though vaccination or adoptive transfer, patients still progress. From the T cell side, defects in T cell signaling may account for much of our failure to achieve significant numbers of objective clinical responses. In spite of these negatives, the horizon does remain bright for T cell based immune therapy of cancer. The periodic objective clinical response tells us that immune therapy can work. Now that we know that cancer patients have the capacity to mount immune responses against their tumors, current and future investigations with agents which alter T cell function combined with vaccination or adoptive T cell transfer may help tip the balance towards effective immune therapies.

T cell avidity and tumor recognition: implications and therapeutic strategies

In the last two decades, great advances have been made studying the immune response to human tumors. The identification of protein antigens from cancer cells and better techniques for eliciting antigen specific T cell responses in vitro and in vivo have led to improved understanding of tumor recognition by T cells. Yet, much remains to be learned about the intricate details of T cell – tumor cell interactions. Though the strength of interaction between T cell and target is thought to be a key factor influencing the T cell response, investigations of T cell avidity, T cell receptor (TCR) affinity for peptide-MHC complex, and the recognition of peptide on antigen presenting targets or tumor cells reveal complex relationships. Coincident with these investigations, therapeutic strategies have been developed to enhance tumor recognition using antigens with altered peptide structures and T cells modified by the introduction of new antigen binding receptor molecules. The profound effects of these strategies on T cell – tumor interactions and the clinical implications of these effects are of interest to both scientists and clinicians. In recent years, the focus of much of our work has been the avidity and effector characteristics of tumor reactive T cells. Here we review concepts and current results in the field, and the implications of therapeutic strategies using altered antigens and altered effector T cells.

The expression and the regulatory role of OX40 and 4-1BB heterodimer in activated human T cells

OX40 and 4-1BB are members of the tumor necrosis factor (TNF) family of costimulatory receptors whose signaling is important for differential immune responses mediated by CD4+ or CD8+ T cells. Although activated T cells may acquire OX40/4-1BB double-positive phenotype and signaling from each receptor is expected to influence cell functions, the relevance between OX40 and 4-1BB has never been investigated before. While we were investigating the expression of OX40 and 4-1BB on activated human T cells, we found that they colocalize. The study of receptor gene–transfected cells showed that both receptors coendocytose and the complex of OX40 and 4-1BB was detected by specific ligands or antibodies (Abs). The heterodimer of OX40 and 4-1BB was identified by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) under nonreduced conditions and was associated with the tumor receptor–associated factor (TRAF) family proteins in a unique manner. Furthermore, the stimulation of OX40/4-1BB rendered cells sensitive to apoptosis induced by TNF-α that accompanied reduced activation of nuclear factor-κB (NF-κB). Finally, the OX40/4-1BB stimulation repressed the mitogen response in activated CD25+CD4+ T cells and preactivated CD8+ T cells. Thus, the OX40/4-1BB heterodimer appears to represent a unique regulatory receptor in activated T cells.

Activation of Resting Human Primary T Cells with Chimeric Receptors: Costimulation from CD28, Inducible Costimulator, CD134, and CD137 in Series with Signals from the TCRζ Chain

Chimeric receptors that include CD28 signaling in series with TCRzeta in the same receptor have been demonstrated to activate prestimulated human primary T cells more efficiently than a receptor providing TCRzeta signaling alone. We examined whether this type of receptor can also activate resting human primary T cells, and whether molecules other than CD28 could be included in a single chimeric receptor in series with TCRzeta to mediate the activation of resting human primary T cells. Human CD33-specific chimeric receptors were generated with CD28, inducible costimulator, CD134, or CD137 signaling regions in series with TCRzeta signaling region and transfected by electroporation into resting human primary T cells. Their ability to mediate Ag-specific activation was analyzed in comparison with a receptor providing TCRzeta signaling alone. Inclusion of any of the costimulatory signaling regions in series with TCRzeta enhanced the level of specific Ag-induced IL-2, IFN-gamma, TNF-alpha, and GM-CSF cytokine production and enabled resting primary T cells to survive and proliferate in response to Ag in the absence of any exogenous factors. Inclusion of CD28, inducible costimulator, or CD134 enhanced TCRzeta-mediated, Ag-specific target cell lysis. Chimeric receptors providing B7 and TNFR family costimulatory signals in series with TCRzeta in the same receptor can confer self-sufficient clonal expansion and enhanced effector function to resting human T cells. This type of chimeric receptor may now be used to discover the most potent combination of costimulatory signals that will improve current immunotherapeutic strategies.

Coarse(PM(2.5-10)), fine(PM(2.5)), and ultrafine air pollution particles induce/increase immune costimulatory receptors on human blood-derived monocytes but not on alveolar macrophages

Diesel particles have been shown to possess adjuvant activity and influence the development of allergic sensitization. Also, more heterogeneous mixtures of pollution particles have been shown to affect host defenses and development of immunity in animal models. In the present study it was determined whether freshly collected particulate matter (PM(10)) in the size ranges 2.5-10 micro m (PM(2.5-10), coarse), 0.1-2.5 micro m (PM(2.5), fine), and </=0.1 micro m (ultrafine) in diameter affected the development of antigen presenting cells by evaluating the expression of surface receptors involved in T-cell interaction on both human alveolar macrophages (AM) and blood-derived monocytes (Mo). A Mo-AM coculture was exposed to 50 micro g/ml of particles and expression of HLA-DR, CD40, CD80, and CD86 on each cell type was assessed by flow cytometry. Mo upregulated the expression of all four receptors in response to each of the particle fractions, while expression was unaffected in AM. The cells were also exposed to two model air pollution particles, diesel dust and volcanic ash, neither of which affected receptor expression. Furthermore, Mo and AM were separately exposed to the three PM size fractions and supernatants assessed for the T-helper (CD4(+)) lymphocyte chemoattractant interleukin-16 (IL-16). AM, but not Mo, produced IL-16, and this chemoattractant was released only in response to PM(2.5-10). These data suggest that a wide size range of pollution particles contain materials that may promote antigen presentation by Mo, while the capability to specifically recruit CD4(+) lymphocytes is contained in AM stimulated with the coarse PM fraction.

Helper T-cell-regulated B-cell immunity

Helper T-cell-regulated B-cell responses constitute a major component of the immune response to many pathogens. Spatially and temporally organized cognate intercellular communication within secondary lymphoid organs is the critical regulating event in this complex adaptive response to antigen. Here, we discuss what is known of these molecular exchanges and their cellular consequences in a serial synapsis model of adaptive immunity.

Differential chemokine expression profiles in human peripheral blood T lymphocytes: dependence on T-cell coreceptor and calcineurin signaling

The chemokine superfamily consists of small (8-10 kDa) molecules that function to attract, selectively, different subsets of leukocytes. Binding of chemokines to their appropriate G-protein-coupled receptors is necessary for primary immune responses and for homing of leukocytes to lymphoid tissues. Here, we have characterized the signaling pathways in primary T lymphocytes that regulate chemokine gene induction using an RNase protection assay. Dependence on stimulation through the coreceptor CD28 and sensitivity to the calcineurin inhibitors cyclosporine and tacrolimus were studied using purified human peripheral blood lymphocytes. Lymphotactin (Ltn), macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta were all rapidly induced and sensitive to cyclosporine treatment. At later time points, the expression of MIP-1alpha and MIP-1beta, but not of Ltn, was restored despite the inhibition of calcineurin activity. By contrast, the induction of interleukin-8 was delayed and was found to be cyclosporine insensitive. Calcineurin activity of IP-10 mRNA induction was contingent on the specific T-cell stimulation conditions, suggesting that IP-10 expression is modulated by calcineurin-dependent and -independent signaling pathways. Differential chemokine expression profiles result from the engagement of T-cell coreceptors and the requirement for, and the dependence on, calcineurin phosphatase activity.

It's all Rel-ative: NF-kappaB and CD28 costimulation of T-cell activation

Costimulatory signals complement or modify the signals provided to a lymphocyte through antigen receptors. For productive T-cell activation, the CD28 molecule is apparently the most important, although not the only, costimulatory receptor. CD28 can provide a signal that is at least partially distinct from that delivered by the T cell receptor (TCR)-CD3 complex. Several lines of evidence indicate that the nuclear factor (NF)-kappaB pathway is perhaps the most relevant biochemical or transcriptional target for the costimulatory activity of CD28. Although many questions remain, recent years have witnessed significant progress in understanding the signal transduction pathways leading from the TCR and CD28 to Rel/NF-kappaB-dependent transcription.

CD28 costimulation induces delta opioid receptor expression during anti-CD3 activation of T cells

Previous studies have demonstrated that naive splenic mouse T cells express no or only very low levels of the delta-type opioid receptor (delta OR), but stimulation of mouse splenocytes with Con A results in induction of delta OR mRNA and protein. In this report we have shown that stimulation of highly purified populations of naive mouse T cells with anti-CD3 mAb alone results in T cell activation, as evidenced by sustained IL-2 secretion and cell proliferation, but fails to elicit delta OR expression. However, delta OR expression is induced by costimulation of these very pure T cells with anti-CD3 and anti-CD28 mAbs. The delta OR induction by anti-CD3 and anti-CD28 costimulation was completely blocked by inhibition of phosphatidylinositol 3-kinase with wortmannin. Because phosphatidylinositol 3-kinase activation in T cells is linked to costimulation, these results suggest that induction of delta OR expression during T cell activation is strictly dependent on costimulation. It also appears that costimulatory receptors other than CD28 can provide the signaling required for delta OR expression because delta OR mRNA was induced by Con A stimulation of splenocytes from CD28-deficient mice.

CD8+CD28- T cells: certainties and uncertainties of a prevalent human T-cell subset

Human peripheral blood CD8+ T cells comprise cells that are in different states of differentiation and under the control of complex homeostatic processes. In a number of situations ranging from chronic inflammatory conditions and infectious diseases to ageing, immunodeficiency, iron overload and heavy alcohol intake, major phenotypic changes, usually associated with an increase in CD8+ T cells lacking CD28 expression, take place. CD8+CD28- T cells are characterized by a low proliferative capacity to conventional stimulation in vitro and by morphological and functional features of activated/memory T cells. Although the nature of the signals that give origin to this T-cell subset is uncertain, growing evidence argues for the existence of an interplay between epithelial cells, molecules with the MHC-class I fold and CD8+ T cells. The possibility that the generation of CD8+CD28- T cells is the combination of TCR/CD3zeta- and regulatory factor-mediated signals as a result of the sensing of modifications of the internal environment is discussed.