APC, T cells, and the immune synapse

From Bench to Field: A Guide to Formulating and Evaluating Anti-Tick Vaccines Delving beyond Efficacy to Effectiveness

Ticks are ubiquitous blood-sucking ectoparasites capable of transmitting a wide range of pathogens such as bacteria, viruses, protozoa, and fungi to animals and humans. Although the use of chemicals (acaricides) is the predominant method of tick-control, there are increasing incidents of acaricide tick resistance. Furthermore, there are concerns over accumulation of acaricide residues in meat, milk and in the environment. Therefore, alternative methods of tick-control have been proposed, of which anti-tick cattle vaccination is regarded as sustainable and user-friendly. Over the years, tremendous progress has been made in identifying and evaluating novel candidate tick vaccines, yet none of them have reached the global market. Until now, Bm86-based vaccines (Gavac™ in Cuba and TickGARD^PLUS™ Australia-ceased in 2010) are still the only globally commercialized anti-tick vaccines. In contrast to Bm86, often, the novel candidate anti-tick vaccines show a lower protection efficacy. Why is this so? In response, herein, the potential bottlenecks to formulating efficacious anti-tick vaccines are examined. Aside from Bm86, the effectiveness of other anti-tick vaccines is rarely assessed. So, how can the researchers assess anti-tick vaccine effectiveness before field application? The approaches that are currently used to determine anti-tick vaccine efficacy are re-examined in this review. In addition, a model is proposed to aid in assessing anti-tick vaccine effectiveness. Finally, based on the principles for the development of general veterinary vaccines, a pipeline is proposed to guide in the development of anti-tick vaccines.

T Cells in Chronic Lymphocytic Leukemia: A Two-Edged Sword

Chronic lymphocytic leukemia (CLL) is a malignancy of mature, antigen-experienced B lymphocytes. Despite great progress recently achieved in the management of CLL, the disease remains incurable, underscoring the need for further investigation into the underlying pathophysiology. Microenvironmental crosstalk has an established role in CLL pathogenesis and progression. Indeed, the malignant CLL cells are strongly dependent on interactions with other immune and non-immune cell populations that shape a highly orchestrated network, the tumor microenvironment (TME). The composition of the TME, as well as the bidirectional interactions between the malignant clone and the microenvironmental elements have been linked to disease heterogeneity. Mounting evidence implicates T cells present in the TME in the natural history of the CLL as well as in the establishment of certain CLL hallmarks e.g. tumor evasion and immune suppression. CLL is characterized by restrictions in the T cell receptor gene repertoire, T cell oligoclonal expansions, as well as shared T cell receptor clonotypes amongst patients, strongly alluding to selection by restricted antigenic elements of as yet undisclosed identity. Further, the T cells in CLL exhibit a distinctive phenotype with features of “exhaustion” likely as a result of chronic antigenic stimulation. This might be relevant to the fact that, despite increased numbers of oligoclonal T cells in the periphery, these cells are incapable of mounting effective anti-tumor immune responses, a feature perhaps also linked with the elevated numbers of T regulatory subpopulations. Alterations of T cell gene expression profile are associated with defects in both the cytoskeleton and immune synapse formation, and are generally induced by direct contact with the malignant clone. That said, these abnormalities appear to be reversible, which is why therapies targeting the T cell compartment represent a reasonable therapeutic option in CLL. Indeed, novel strategies, including CAR T cell immunotherapy, immune checkpoint blockade and immunomodulation, have come to the spotlight in an attempt to restore the functionality of T cells and enhance targeted cytotoxic activity against the malignant clone.

The thymus and the science of self

The conventional perception asserts that immunology is the science of ‘discrimination’ between self and non-self. This concept is however no longer tenable as effector cells of the adaptive immune system are first conditioned to be tolerant to the body’s own antigens, collectively known as self until now. Only then attain these effectors the responsiveness to non-self. The acquisition of this essential state of tolerance to self occurs for T cells in the thymus, the last major organ of our body that revealed its intricate function in health and disease. The ‘thymus’ as an anatomical notion was first notably documented in Ancient Greece although our present understanding of the organ’s functions was only deciphered commencing in the 1960s. In the late 1980s, the thymus was identified as the site where clones of cells reactive to self, termed ‘forbidden’ thymocytes, are physically depleted as the result of a process now known as negative selection. The recognition of this mechanism further contributed to the belief that the central rationale of immunology as a science lies in the distinction between self and non-self. This review will discuss the evidence that the thymus serves as a unique lymphoid organ able to instruct T cells to recognize and be tolerant to harmless self before adopting the capacity to defend the body against potentially injurious non-self-antigens presented in the context of different challenges from infections to exposure to malignant cells. The emerging insight into the thymus’ cardinal functions now also provides an opportunity to exploit this knowledge to develop novel strategies that specifically prevent or even treat organ-specific autoimmune diseases.

Dendritic cells loaded with the lysate of tumor cells infected with Newcastle Disease Virus trigger potent anti-tumor immunity by promoting the secretion of IFN-γ and IL-2 from T cells

Dendritic cells (DCs) are professional antigen-presenting cells that are pivotal in the generation and sustainability of antitumor immune responses. Whole tumor cell lysates (TCLs) have been used as sources of tumor antigens for the development of DC vaccines. However, the clinical outcomes of the use of TCL-based DC vaccines have so far been unsatisfactory because of the weak immunogenicity of tumor cells. To improve the efficacy of TCL-based DC vaccines, viruses have been used to enhance the immunity of TCLs and to further enhance the antigen delivery and antigen-presenting ability of DCs. The aim of the present study was to improve the antigen-presenting ability of DCs and to use them to effectively activate T lymphocytes. The present study demonstrated that DCs loaded with the lysate of Newcastle Disease Virus (NDV)-infected tumor cells (NDV-TCL) have increased levels of cluster of differentiation 80 (CD80), CD86, CD83 and human leukocyte antigen-antigen D-associated expression, compared with those loaded with TCL alone. The DCs loaded with the NDV-TCL promoted T-cell proliferation and antitumor cytokine secretion from T cells. These results indicated that loading DCs with NDV-TCL could enhance the antigen-presenting ability of the DCs. On the basis of the results of the present study, we hypothesize that this method of loading DCs with NDV-TCL can be used to develop novel DC vaccines for tumor immunotherapy in the future.

An in vitro system of autologous lymphocytes culture that allows the study of homeostatic proliferation mechanisms in human naive CD4 T-cells

The size of peripheral T-cell pool is kept constant throughout life. However, a decline in lymphocyte numbers is a feature of several human disorders, in which fast and slow homeostatic proliferation play a crucial role. Several in vitro and in vivo models have been developed to study such processes. Nevertheless, self- and commensal- antigens, well-known triggers of homeostatic proliferation, have not been examined in these models. We have designed an in vitro culture of human T-cells exposed to rIL7 and autologous antigen-presenting cells (aAPC) that allows the simultaneous characterization of the different types of homeostatic proliferation. Using our model, we first confirmed that both rIL7 and aAPC are survival signals ultimately leading to homeostatic proliferation. In addition, we explored the modulation of different anti-apoptotic, proliferative, activation and homing markers during fast and slow homeostatic proliferation. Finally, different subsets of Treg were generated during homeostatic proliferation in our model. In summary, our in vitro system is able to simultaneously reproduce both types of homeostatic proliferation of human naive CD4 T-cells, and allows the characterization of these processes. Our in vitro system is a useful tool to explore specific features of human homeostatic proliferation in different human lymphopenia-related disorders and could be used as a cell therapy approach.

The Molecular Architecture of Cell Adhesion: Dynamic Remodeling Revealed by Videonanoscopy

The plasma membrane delimits the cell, which is the basic unit of living organisms, and is also a privileged site for cell communication with the environment. Cell adhesion can occur through cell-cell and cell-matrix contacts. Adhesion proteins such as integrins and cadherins also constitute receptors for inside-out and outside-in signaling within proteolipidic platforms. Adhesion molecule targeting and stabilization relies on specific features such as preferential segregation by the sub-membrane cytoskeleton meshwork and within membrane proteolipidic microdomains. This review presents an overview of the recent insights brought by the latest developments in microscopy, to unravel the molecular remodeling occurring at cell contacts. The dynamic aspect of cell adhesion was recently highlighted by super-resolution videomicroscopy, also named videonanoscopy. By circumventing the diffraction limit of light, nanoscopy has allowed the monitoring of molecular localization and behavior at the single-molecule level, on fixed and living cells. Accessing molecular-resolution details such as quantitatively monitoring components entering and leaving cell contacts by lateral diffusion and reversible association has revealed an unexpected plasticity. Adhesion structures can be highly specialized, such as focal adhesion in motile cells, as well as immune and neuronal synapses. Spatiotemporal reorganization of adhesion molecules, receptors, and adaptors directly relates to structure/function modulation. Assembly of these supramolecular complexes is continuously balanced by dynamic events, remodeling adhesions on various timescales, notably by molecular conformation switches, lateral diffusion within the membrane and endo/exocytosis. Pathological alterations in cell adhesion are involved in cancer evolution, through cancer stem cell interaction with stromal niches, growth, extravasation, and metastasis.

Dendritic cell-based vaccine efficacy: aiming for hot spots

Many approaches for cancer immunotherapy have targeted dendritic cells (DCs), directly or indirectly, for the induction of antitumor immune responses. DC-based vaccines have been developed using a wide variety of ex vivo DC culture conditions, antigen (Ag) source and loading strategies, maturation agents, and routes of vaccination. Adjuvants are used to activate innate immune cells at the vaccine injection site, to promote Ag transport to the draining lymph nodes (LNs) and to model adaptive immune responses. Despite years of effort, the effective induction of strong and durable antitumor T-cell responses in vaccinated patients remains a challenge. The study of vaccine interactions with other immune cells in the LNs and, more recently, in the injection site has opened new doors for understanding antitumor effector T-cell licensing and function. In this review, we will briefly discuss the relevant sites and up-to-date facts regarding possible targets for antitumor vaccine refinement. We will focus on the processes taking place at the injection site, adjuvant combinations and their role in DC-based vaccines, LN homing, and modeling vaccine-induced immune responses capable of controlling tumor growth and generating immune memory.

Affinity proteomics led identification of vimentin as a potential biomarker in colon cancers: insights from serological screening and computational modelling

Proteomic analysis using multiplex affinity reagents is perhaps the most reliable strategy to capture differentially expressed proteins that are slightly or immensely modified. In addition to expressional variation, it is comprehensively evident that the immunogenicity of a protein can be a deciding factor for instigating an inflammation afflicted-carcinogenesis. Considering both these factors, a simple and systematic strategy was designed to capture the immunogenic cancer biomarkers from sera of colorectal cancer patients. The affinity reagent, in the form of an antibody repertoire against the secretome of the HT29 cell line was used to grade the sera samples on the basis of the degree of immuno-reactivity and to capture differentially expressed antigens from the patient sera. Following affinity based 2DE-MALDI-TOF; the proteins were identified as (1) soluble vimentin; and (2) TGF-beta-inhibited membrane-associated protein (PP16B), in colon cancer sera and (3) keratin, type II cytoskeletal protein in rectal cancer sera. Pathway reconstruction and protein-protein networking of identified proteins predicted only Vimentin to be physically and genetically engaged in close proximity with the most established colorectal cancer associated tumorigenic pathways. Furthermore, our findings suggest that a possible surface stoichiometric shift in the structure of protein could be due to mutations in the coding sequence of Vimentin that may elicit its enhanced secretion possibly due to protein-hyperphosphorylation. Of the three proteins identified, only Vimentin showed higher expression in sera of colon cancer patients alone. Thus, it could be argued that vimentin might help in predicting individuals at higher risk of developing colon cancers. Our data are therefore suggestive of using vimentin as an antigen for tumor vaccination in an autologous set-up for colon cancers.

Downregulation of inhibitory SRC homology 2 domain-containing phosphatase-1 (SHP-1) leads to recovery of T cell responses in elderly

BACKGROUND

Immune responses are generally impaired in aged mammals. T cells have been extensively studied in this context due to the initial discovery of their reduced proliferative capacity with aging. The decreased responses involve altered signaling events associated with the early steps of T cell activation. The underlying causes of these changes are not fully understood but point to alterations in assembly of the machinery for T cell activation. Here, we have tested the hypothesis that the T cell pool in elderly subjects displayed reduced functional capacities due to altered negative feedback mechanisms that participate in the regulation of the early steps of T cell activation. Such conditions tip the immune balance in favor of altered T cell activation and a related decreased response in aging.

RESULTS

We present evidence that the tyrosine phosphatase SHP-1, a key regulator of T cell signal transduction machinery is, at least in part, responsible for the impaired T cell activation in aging. We used tyrosine-specific mAbs and Western blot analysis to show that a deregulation of the Csk/PAG loop in activated T cells from elderly individuals favored the inactive form of tyrosine-phosphorylated Lck (Y505). Confocal microscopy analysis revealed that the dynamic movements of these regulatory proteins in lipid raft microdomains was altered in T cells of aged individuals. Enzymic assays showed that SHP-1 activity was upregulated in T cells of aged donors, in contrast to young subjects. Pharmacological inhibition of SHP-1 resulted in recovery of TCR/CD28-dependent lymphocyte proliferation and IL-2 production of aged individuals to levels approaching those of young donors. Significant differences in the active (Y394) and inactive (Y505) phosphorylation sites of Lck in response to T cell activation were observed in elderly donors as compared to young subjects, independently of CD45 isoform expression.

CONCLUSIONS

Our data suggest that the role of SHP-1 in T cell activation extends to its increased effect in negative feedback in aging. Modulation of SHP-1 activity could be a target to restore altered T cell functions in aging. These observations could have far reaching consequences for improvement of immunosenescence and its clinical consequences such as infections, altered response to vaccination.

CD4⁺ but not CD8⁺ T cells revert the impaired emotional behavior of immunocompromised RAG-1-deficient mice

An imbalanced immune system has long been known to influence a variety of mood disorders including anxiety, obsessive-compulsive disorders and depression. In this study, we sought to model the impact of an immunocompromised state on these emotional behaviors using RAG-1⁻/⁻ mice, which lack T and B cells. We also investigated the relative contribution of CD4⁺ or CD8⁺ T cells to these manifestations using RAG-1⁻/⁻/OT-II and RAG-1⁻/⁻/OT-I transgenic mice, respectively. Our results show that RAG-1⁻/⁻ mice present a significant increase in digging and marble-burying activities compared with wild-type mice. Surprisingly, these anxiety-like behaviors were significantly reverted in RAG-1⁻/⁻/OT-II but not RAG-1⁻/⁻/OT-I transgenic mice. Immunodepletion experiments with anti-CD4 or anti-CD8 in C57/BL6 mice or repopulation studies in RAG-1⁻/⁻ mice did not reproduce these findings. Microarray analysis of the brain of RAG-1⁻/⁻ and RAG-1⁻/⁻/OT-II mice revealed a significantly different gene fingerprint, with the latter being more similar to wild-type mice than the former. Further analysis revealed nine main signaling pathways as being significantly modulated in RAG-1⁻/⁻ compared with wild-type mice. Taken together, these results suggest that life-long rather than transient immunodeficient conditions influence the emotional behaviors in mice. Most interestingly, these effects seem to correlate with a specific absence of CD4⁺ rather than CD8⁺ T cells. Validation of these findings in man might provide new clues on the mechanism by which early life immune modulation might impact mood response in adults and provide a further link between immune and emotional well-being.

Multimolecular analysis of stable immunological synapses reveals sustained recruitment and sequential assembly of signaling clusters

The formation of the immunological synapse between T cells and antigen-presenting cells (APC) begins within minutes of contact and can take hours for full T-cell activation. Although early phases of the synapse have been extensively studied for a select number of proteins, later phases have not yet been examined in detail. We studied the signaling network in stable synapses by measuring the simultaneous localization of 25 signaling and structural molecules over 2 h at the level of individual synapses using multi-epitope ligand cartography (MELC). Signaling proteins including phospho(p)ZAP70, pSLP76, pCD3ζ, and pLAT, along with proteins that influence synapse structure such as F-actin, tubulin, CD45, and ICAM-1, were localized in images of synapses and revealed the multidimensional construction of a mature synapse. The construction of the stable synapse included intense early TCR signaling, a phase of recruitment of structural proteins, and a sustained increase in signaling molecules and colocalization of TCR and pLAT signaling clusters in the center of the synapse. Consolidation of TCR and associated proteins resulted in formation of a small number of discrete synaptic microclusters. Development of synapses and cSMAC composition was greatly affected by the absence of Vav1, with an associated loss in PLCγ1 recruitment, pSLP76, and increased CXCR4. Together, these data demonstrate the use of multi-epitope ligand cartography to quantitatively analyze synapse formation and reveal successive recruitment of structural and signaling proteins and sustained phosphorylation at the mature synapse.

Aging, immunosenescence and membrane rafts: the lipid connection

The decreased efficiency of immune responses in older people is partly a consequence of alterations in T lymphocyte functions caused by modifications in the early events of signal transduction. Several alterations in the signaling pathways of T lymphocytes have been described in older humans and animals. A unifying cause could be modifications in the physicochemical properties of the plasma membrane resulting from changes in its lipid composition and the distribution and function of lipid rafts (LR). The latter serve to assemble the initial components of the signaling cascade. Accumulating data suggest that the function of plasma membrane LR is altered with aging; we hypothesize that this would significantly contribute to immune dysregulation. The role of aging and cholesterol in LR functions in T lymphocytes is reviewed and discussed here.

Logical development of the cell ontology

Background

The Cell Ontology (CL) is an ontology for the representation of in vivo cell types. As biological ontologies such as the CL grow in complexity, they become increasingly difficult to use and maintain. By making the information in the ontology computable, we can use automated reasoners to detect errors and assist with classification. Here we report on the generation of computable definitions for the hematopoietic cell types in the CL.

Results

Computable definitions for over 340 CL classes have been created using a genus-differentia approach. These define cell types according to multiple axes of classification such as the protein complexes found on the surface of a cell type, the biological processes participated in by a cell type, or the phenotypic characteristics associated with a cell type. We employed automated reasoners to verify the ontology and to reveal mistakes in manual curation. The implementation of this process exposed areas in the ontology where new cell type classes were needed to accommodate species-specific expression of cellular markers. Our use of reasoners also inferred new relationships within the CL, and between the CL and the contributing ontologies. This restructured ontology can be used to identify immune cells by flow cytometry, supports sophisticated biological queries involving cells, and helps generate new hypotheses about cell function based on similarities to other cell types.

Conclusion

Use of computable definitions enhances the development of the CL and supports the interoperability of OBO ontologies.

Find-me and eat-me signals in apoptotic cell clearance: progress and conundrums

Everyday we turnover billions of cells. The quick, efficient, and immunologically silent disposal of the dying cells requires a coordinated orchestration of multiple steps, through which phagocytes selectively recognize and engulf apoptotic cells. Recent studies have suggested an important role for soluble mediators released by apoptotic cells that attract phagocytes ("find-me" signals). New information has also emerged on multiple receptors that can recognize phosphatidylserine, the key "eat-me" signal exposed on the surface of apoptotic cells. This perspective discusses recent exciting progress, gaps in our understanding, and the conflicting issues that arise from the newly acquired knowledge.