The NMR structure of the Orf63 lytic developmental protein from lambda bacteriophage

The orf63 gene resides in a region of the lambda bacteriophage genome between the exo and xis genes and is among the earliest genes transcribed during infection. In lambda phage and Shiga toxin (Stx) producing phages found in enterohemorrhagic Escherichia coli (EHEC) associated with food poisoning, Orf63 expression reduces the host survival and hastens the period between infection and lysis thereby giving it pro-lytic qualities. The NMR structure of dimeric Orf63 reveals a fold consisting of two helices and one strand that all make extensive intermolecular contacts. Structure-based data mining failed to identify any Orf63 homolog beyond the family of temperate bacteriophages. A machine learning approach was used to design an amphipathic helical ligand that bound a hydrophobic cleft on Orf63 with micromolar affinity. This approach may open a new path towards designing therapeutics that antagonize the contributions of Stx phages in EHEC outbreaks.

MHC class I-related molecule, MR1, and mucosal-associated invariant T cells

The MHC-related 1, MR1, molecule presents a new class of microbial antigens (derivatives of the riboflavin [Vitamin B2] biosynthesis pathway) to mucosal-associated invariant T (MAIT) cells. This raises many questions regarding antigens loading and intracellular trafficking of the MR1/ligand complexes. The MR1/MAIT field is also important because MAIT cells are very abundant in humans and their frequency is modified in many infectious and non-infectious diseases. Both MR1 and the invariant TCRα chain expressed by MAIT cells are strikingly conserved among species, indicating important functions. Riboflavin is synthesized by plants and most bacteria and yeasts but not animals, and its precursor derivatives activating MAIT cells are short-lived unless bound to MR1. The recognition of MR1 loaded with these compounds is therefore an exquisite manner to detect invasive bacteria. Herein, we provide an historical perspective of the field before describing the main characteristics of MR1, its ligands, and the few available data regarding its cellular biology. We then summarize the current knowledge of MAIT cell differentiation and discuss the definition of MAIT cells in comparison to related subsets. Finally, we describe the phenotype and effector activities of MAIT cells.

Mucosal-associated invariant T cell-rich congenic mouse strain allows functional evaluation

Mucosal-associated invariant T cells (MAITs) have potent antimicrobial activity and are abundant in humans (5%-10% in blood). Despite strong evolutionary conservation of the invariant TCR-α chain and restricting molecule MR1, this population is rare in laboratory mouse strains (≈0.1% in lymphoid organs), and lack of an appropriate mouse model has hampered the study of MAIT biology. Herein, we show that MAITs are 20 times more frequent in clean wild-derived inbred CAST/EiJ mice than in C57BL/6J mice. Increased MAIT frequency was linked to one CAST genetic trait that mapped to the TCR-α locus and led to higher usage of the distal Vα segments, including Vα19. We generated a MAIThi congenic strain that was then crossed to a transgenic Rorcgt-GFP reporter strain. Using this tool, we characterized polyclonal mouse MAITs as memory (CD44+) CD4-CD8lo/neg T cells with tissue-homing properties (CCR6+CCR7-). Similar to human MAITs, mouse MAITs expressed the cytokine receptors IL-7R, IL-18Rα, and IL-12Rβ and the transcription factors promyelocytic leukemia zinc finger (PLZF) and RAR-related orphan receptor γ (RORγt). Mouse MAITs produced Th1/2/17 cytokines upon TCR stimulation and recognized a bacterial compound in an MR1-dependent manner. During experimental urinary tract infection, MAITs migrated to the bladder and decreased bacterial load. Our study demonstrates that the MAIThi congenic strain allows phenotypic and functional characterization of naturally occurring mouse MAITs in health and disease.

Synaptic release of CCL5 storage vesicles triggers CXCR4 surface expression promoting CTL migration in response to CXCL12

The lytic function of CTL relies on the polarized release of cytotoxic granules (CG) at the immune synapse (IS) with target cells. CTL also contain CCL5 in cytoplasmic storage vesicles (CCL5V) distinct from CG, the role of which, in regulating T cell effector functions, is not understood. Using human CD8(+) T cells specific to a lung tumor-associated Ag, we show in this article that CTL release both secretory compartments into the immune synapse with autologous tumor cells. Moreover, we demonstrate that disorganization of the T cell microtubule cytoskeleton and defects in hMunc13-4 or Rab27a abrogate CG exocytosis and synaptic secretion of the chemokine. Mechanistically, synaptic release of CCL5 cytoplasmic storage vesicles likely occurs upon their coalescence with the Rab27a-hMunc13-4 compartment and results in autocrine, CCR5-dependent induction of CXCR4 cell surface expression, thereby promoting T cell migration in response to CXCL12. We propose that CCL5 polarized delivery represents a mechanism by which CTL control immune synapse duration.

Integrins and chemokine receptors control maturation and duration of the cytotoxic immune synapse between CTL and tumor cells (P2171)

Cytotoxic T lymphocytes (CTL) exert their lytic activity through the polarized release of cytotoxic granules at the immune synapse (IS) formed with specific target cells. Integrins and their cognate ligands on target cells play a major role in T-cell receptor (TCR)-mediated functions. We show here that cytotoxicity towards epithelial cancer cells requires, along with TCR engagement, the interaction of either CD103 with E-cadherin or LFA-1 with ICAM-1 thereby enhancing the strength of the T-cell/target cell adhesion. Integrin-dependent mature cytotoxic IS (mcIS) displays a cohesive ultrastructure characterized by polarized degranulation and chemokine release associated with target cell killing and chemokine receptor induction on effector cells. Our results provide new insights into molecular mechanisms regulating antitumor CTL responses and the role of integrins and chemokine receptors on the formation and duration of the cIS.

Role of chemokines and chemokine receptors in shaping the effector phase of the antitumor immune response

Immune system-mediated eradication of neoplastic cells requires induction of a strong long-lasting antitumor T-cell response. However, generation of tumor-specific effector T cells does not necessarily result in tumor clearance. CTL must first be able to migrate to the tumor site, infiltrate the tumor tissue, and interact with the target to finally trigger effector functions indispensable for tumor destruction. Chemokines are involved in circulation, homing, retention, and activation of immunocompetent cells. Although some of them are known to contribute to tumor growth and metastasis, others are responsible for changes in the tumor microenvironment that lead to extensive infiltration of lymphocytes, resulting in tumor eradication. Given their chemoattractive and activating properties, a role for chemokines in the development of the effector phase of the antitumor immune response has been suggested. Here, we emphasize the role of the chemokine-chemokine receptor network at multiple levels of the T-cell-mediated antitumor immune response. The identification of chemokine-dependent molecular mechanisms implicated in tumor-specific CTL trafficking, retention, and regulation of their in situ effector functions may offer new perspectives for development of innovative immunotherapeutic approaches to cancer treatment.

CD103 or LFA-1 engagement at the immune synapse between cytotoxic T cells and tumor cells promotes maturation and regulates T-cell effector functions

T-cell adhesion/costimulatory molecules and their cognate receptors on target cells play a major role in T-cell receptor (TCR)-mediated activities. Here, we compared the involvement of CD103 and LFA-1, and their respective ligands, in the maturation of the cytotoxic immune synapse (cIS) and in the activation of CTL effector functions. Our results indicate that cytotoxicity toward cancer cells and, to a lesser extent, cytokine production by specific CTL require, together with TCR engagement, the interaction of either CD103 with E-cadherin or LFA-1 with ICAM-1. Flow-based adhesion assay showed that engagement of CD103 or LFA-1, together with TCR, enhances the strength of the T-cell/target cell interaction. Moreover, electron microscopic analyses showed that integrin-dependent mature cIS (mcIS) displays a cohesive ultrastructure, with tight membrane contacts separated by extensive clefts. In contrast, immature cIS (icIS), which is unable to trigger target cell lysis, is loose, with multiple protrusions in the effector cell membrane. Experiments using confocal microscopy revealed polarized cytokine release and degranulation at the mcIS associated with target cell killing, whereas icIS is characterized by failure of IFN-γ and granzyme B relocalization. Thus, interactive forces between CTL and epithelial tumor cells, mainly regulated by integrin engagement, correlate with maturity and the ultrastructure of the cIS and influence CTL effector functions. These results provide new insights into molecular mechanisms regulating antitumor CTL responses and may lead to the development of more efficient cancer immunotherapy strategies.

Matrix architecture defines the preferential localization and migration of T cells into the stroma of human lung tumors

Appropriate localization and migration of T cells is a prerequisite for antitumor immune surveillance. Studies using fixed tumor samples from human patients have shown that T cells accumulate more efficiently in the stroma than in tumor islets, but the mechanisms by which this occurs are unknown. By combining immunostaining and real-time imaging in viable slices of human lung tumors, we revealed that the density and the orientation of the stromal extracellular matrix likely play key roles in controlling the migration of T cells. Active T cell motility, dependent on chemokines but not on β1 or β2 integrins, was observed in loose fibronectin and collagen regions, whereas T cells migrated poorly in dense matrix areas. Aligned fibers in perivascular regions and around tumor epithelial cell regions dictated the migratory trajectory of T cells and restricted them from entering tumor islets. Consistently, matrix reduction with collagenase increased the ability of T cells to contact cancer cells. Thus, the stromal extracellular matrix influences antitumor immunity by controlling the positioning and migration of T cells. Understanding the mechanisms by which this collagen network is generated has the potential to aid in the development of new therapeutics.

Rescue of tumor-infiltrating lymphocytes from activation-induced cell death enhances the antitumor CTL response in CD5-deficient mice

The CD5 coreceptor is expressed on all T cells and on the B1a B cell subset. It is associated with TCR and BCR, and modulates intracellular signals initiated by both Ag receptor complexes. Human CD5 contributes to regulation of the antitumor immune response and susceptibility of specific CTL to activation-induced cell death (AICD) triggered by the tumor. In this study, we compared the T cell response to the B16F10 melanoma engrafted into CD5-deficient and wild-type C57BL/6 mice. Compared with wild-type mice, CD5 knockout animals displayed delayed tumor growth, associated with tumor infiltration by T cell populations exhibiting a more activated phenotype and enhanced antitumor effector functions. However, control of tumor progression in CD5(-/-) mice was transient due to increased AICD of CD8(+) tumor-infiltrating T lymphocytes. Remarkably, in vivo protection of T cells from TCR-mediated apoptosis by an adenovirus engineered to produce soluble Fas resulted in a dramatic reduction in tumor growth. Our data suggest that recruitment of tumor-specific T cells in the tumor microenvironment occurs at early stages of cancer development and that tumor-mediated AICD of tumor-infiltrating T lymphocytes is most likely involved in tumor escape from the immune system.

Abstract LB-150: Influence of CD103-E-cadherin interaction in stimulatory versus cytotoxic immune synapse formed between CTL and specific tumor cell

We have previously reported that interaction of integrin αE(CD103)β7, often expressed by tumor-infiltrating lymphocytes (TIL), with E-cadherin on epithelial tumor cells is required for polarized exocytosis of cytotoxic granules resulting in target cell lysis. Our results also indicated that binding of CD103 on tumor-specific cytotoxic T lymphocytes (CTL) to a recombinant E-cadherin-Fc molecule is sufficient to induce polarization of cytolytic granules in a phospholipase Cγ-dependent pathway, whereas degranulation also requires co-engagement of the T-cell receptor (TCR). In the present study, we compared the ultrastructure of the immune synapses formed between CD103+ or CD103- CTL and specific lung cancer cells, and analyzed the involvement of adhesion/costimulatory molecules in the activation of cytotoxicity versus stimulatory functions. Our results indicated that stimulatory and lytic synapses display differential activation threshold and intercellular molecular requirements.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-150. doi:10.1158/1538-7445.AM2011-LB-150

CD5 knock out mice display a strong antitumor immune response associated with tumor infiltration by hyperactivated tumor-reactive CD8+ T lymphocytes (101.21)

We have previously reported the TCR inhibitory molecule CD5 impairs reactivity of tumor-specific PBL-derived T-cell clones against the cognate target and controls their susceptibility to activation-induced cell death (AICD) triggered by tumor cells. In this report, we compared the antitumor T-cell response developed against the B16F10 melanoma engrafted in CD5-deficient and wild-type (wt) C57BL/6 mice. Our results indicate that CD5 knock out mice elicit a delayed tumor growth as compared to wt mice, which is associated with tumor infiltration by more activated tumor-reactive T lymphocytes. Our data also indicate that tumor suppression in CD5-deficient mice is transient and that tumor flare up correlates with increase in AICD of tumor-infiltrating CD8+ T cells. Our data suggest that tumor T lymphocyte infiltration occurs at early stages of cancer development and that tumor-mediated AICD is most likely involved in the induction of T-cell tolerance to malignant cells.

Interaction of CD103 with E-cadherin triggers CCR5 recruitment at the immunological synapse resulting in intratumoral retention of tumor-specific CTL (40.37)

We previously characterized two tumor-specific T-cell clones from PBL and tumor-infiltrating lymphocytes (TIL) of a lung cancer patient with identical TCR and similar lytic potential, but with different anti-tumor reactivity. We demonstrated that the interaction of alphaE(CD103)beta7 integrin, expressed on the TIL clone but not on the PBL counterpart, with the epithelial marker E-cadherin on human lung tumor cells, plays a crucial role in TCR-mediated cytotoxicity. In the present study we show that both TIL and PBL clones are able to migrate towards autologous tumor cells and that chemokine receptor CCR5 is involved in this process. Interestingly, adoptive transfer of the PBL clone in the cognate tumor engrafted in SCID-NOD mice and subsequent TCR engagement and TGF-β1 secretion triggers CD103 expression on T-cell surface and thus potentiation of anti-tumor cytotoxic activity. Furthermore, confocal microscopy analyses indicated that the interaction of αEβ7 integrin with E-cadherin, but not LFA-1 with ICAM-1, promotes CCR5 recruitment at the immunological synapse formed between TIL and tumor cells, leading to inhibition of T-cell sensitivity to CCL5 chemotactic gradient. Our results provide evidence for a role of tumor microenvironment in regulating anti-tumor CTL function and suggest a role of CD103 in intratumoral retention of tumor-specific T cells by a mechanism involving CCR5.

Microglia-derived TGF-β as an important regulator of glioblastoma invasion—an inhibition of TGF-β-dependent effects by shRNA against human TGF-β type II receptor

The invasion of tumor cells into brain tissue is a pathologic hallmark of malignant gliomas and contributes to treatment failures. Diffuse glioblastomas contain numerous microglial cells, which enhance the progression of gliomas; however, factors responsible for invasion-promoting role of microglia are unknown. Transforming growth factor-beta (TGF-beta) can enhance tumor growth, invasion, angiogenesis and immunosuppression. Antagonizing TGF-beta activity has been shown to inhibit tumor invasion in vitro and tumorigenicity, but a systemic inhibition or lack of TGF-beta signaling results in acute inflammation and disruption of immune system homeostasis. We developed plasmid-transcribed small hairpin RNAs (shRNAs) to downregulate the TGF-beta type II receptor (TbetaIIR) expression, which effectively inhibited cytokine-induced signaling pathways and transcriptional responses in transiently transfected human glioblastoma cells. Silencing of TbetaIIR abolished TGF-beta-induced glioblastoma invasiveness and migratory responses in vitro. Moreover, tumorigenicity of glioblastoma cells stably expressing TbetaIIR shRNAs in nude mice was reduced by 50%. Microglia strongly enhanced glioma invasiveness in the co-culture system, but this invasion-promoting activity was lost in glioma cells stably expressing shTbetaRII, indicating a crucial role of microglia-derived TGF-beta in tumor-host interactions. Our results demonstrate a successful targeting of TGF-beta-dependent invasiveness and tumorigenicity of glioblastoma cells by RNAi-mediated gene silencing.

Distribution of two HIV-1-resistant polymorphisms (SDF1-3'A and CCR2-64I alleles) in the Polish population

Chemokine receptors (CCR2 and CXCR4) are used as coreceptors for entry of human immunodeficiency virus (HIV) into the target cells. Mutations in CCR2 (CCR2-64I) and stromal-derived factor SDF1 (SDF1-3'A), the primary ligand for CXCR4, exhibited a protective effect against the onset of acquired immune deficiency syndrome (AIDS). The frequency of the SDF1-3'A and CCR2-64I alleles were determined in blood donors from 16 provinces, covering the entire territory of Poland. Of 1063 individuals, 274 (25.8%) were carriers of the SDF1-3'A allele; 36 of them (3.4%) were homozygotes (SDF-3'A/A) while 238 (22.4%) were heterozygotes (SDF-3'G/A), resulting in a 14.6% frequency of the SDF1-3'A allele. Moreover, in the same group of individuals, 234 (22.0%) carried the CCR2-64I allele; 6 of them (0.6%) were homozygotes (CCR2-64I/I), and 228 (21.4%) were heterozygotes (CCR2-64V/I), resulting in an 11.3% frequency of the CCR2-64I allele. The highest frequencies of the SDF1-3'A allele were found in the northeastern provinces and in one of the western provinces of Poland. In contrast, allelic frequencies of CCR2-64I varied slightly among different provinces. The different pattern of prevalence of the SDF1-3'A and CCR2-64I alleles in Poland might suggest that the CCR2-64I allele was spread much earlier than the SDF1-3'A allele in the population of Poland.

The effect of high molecular weight dextran sulfate on the production of interleukin-8 in monocyte cell culture

It has been demonstrated that high molecular weight dextran sulfate (HMDS) is involved in the activation of immune cells. We have shown that HMDS increases the concentration of interleukin (IL)-8 in the medium of monocyte cell culture, in a dose-dependent fashion, whereas under the same conditions, low molecular weight dextran sulfate (LMDS) does not exhibit any effect on IL-8 biosynthesis. The effect of HMDS on IL-8 production is additive to that of IL-1beta and tumor necrosis factor-a (TNFalpha). Flow cytometric analysis revealed the biosynthesis of IL-8 in monocytes incubated in the presence of the HMDS. We hereby postulate that HMDS induces IL-8 biosynthesis in monocyte cell culture.