Memory immune response: a major challenge in vaccination

Abstract A crucial challenge for vaccine development is to design vaccines that induce a long-lasting protective immune response, i.e., immune memory. The persistence of antigen-specific antibody titers over a protective threshold, and the ability to exibit a 'recall response' to a subsequent encounter with an antigen have long been the only measurable correlates of vaccine take and immune memory development, suffering from the disadvantage of relying on long-term monitoring of the immune response. In the last few years, advances in the technologies for the identification and characterization of the cell subsets and molecular pathways involved in the immune response to vaccination have allowed innovative approaches to the identification of early correlates of immune memory. In this review, we discuss recent data and hypotheses on early correlates of the development of immune memory, with special emphasis on the gene expression signatures that underlie the self-renewal ability of some lymphocyte subsets, and their similarities with gene expression signatures in stem cells.

Alum and squalene-oil-in-water emulsion enhance the titer and avidity of anti-Aβ antibodies induced by multimeric protein antigen (1-11)E2, preserving the Igg1-skewed isotype distribution

The development of active immunotherapy for Alzheimer's disease (AD) requires the identification of immunogens that can ensure a high titer antibody response toward Aβ, while minimizing the risks of adverse reactions. Multimeric protein (1–11)E2 induces a robust and persistent antibody response to Aβ in mice, when formulated in Freund's adjuvant. The goal of this translational study was to evaluate the immunogenicity of (1–11)E2 formulated in alum (Alhydrogel 2%), or in a squalene oil-in-water emulsion (AddaVax), or without adjuvant. A IgG1-skewed isotype distribution was observed for the anti-Aβ antibodies generated in mice immunized with either the non-adjuvanted or the adjuvanted vaccine, indicating that (1–11)E2 induces a Th2-like response in all tested conditions. Both Alhydrogel 2% and AddaVax enhanced the titer and avidity of the anti-Aβ response elicited by (1–11)E2. We conclude that (1–11)E2 is a promising candidate for anti-Aβ immunization protocols that include alum or squalene-oil-in-water emulsion, or no adjuvant.

Filamentous bacteriophage fd as an antigen delivery system in vaccination

Peptides displayed on the surface of filamentous bacteriophage fd are able to induce humoral as well as cell-mediated immune responses, which makes phage particles an attractive antigen delivery system to design new vaccines. The immune response induced by phage-displayed peptides can be enhanced by targeting phage particles to the professional antigen presenting cells, utilizing a single-chain antibody fragment that binds dendritic cell receptor DEC-205. Here, we review recent advances in the use of filamentous phage fd as a platform for peptide vaccines, with a special focus on the use of phage fd as an antigen delivery platform for peptide vaccines in Alzheimer's Disease and cancer.

Conformation regulation of the X chromosome inactivation center: a model

X-Chromosome Inactivation (XCI) is the process whereby one, randomly chosen X becomes transcriptionally silenced in female cells. XCI is governed by the Xic, a locus on the X encompassing an array of genes which interact with each other and with key molecular factors. The mechanism, though, establishing the fate of the X's, and the corresponding alternative modifications of the Xic architecture, is still mysterious. In this study, by use of computer simulations, we explore the scenario where chromatin conformations emerge from its interaction with diffusing molecular factors. Our aim is to understand the physical mechanisms whereby stable, non-random conformations are established on the Xic's, how complex architectural changes are reliably regulated, and how they lead to opposite structures on the two alleles. In particular, comparison against current experimental data indicates that a few key cis-regulatory regions orchestrate the organization of the Xic, and that two major molecular regulators are involved.

In mammal female cells X-Chromosome Inactivation (XCI) is the vital process whereby one X, randomly chosen, is silenced to compensate dosage of X products with respect to males. XCI is governed by a region on the X, the X Inactivation Centre (Xic), which undergoes a sequence of conformational modifications during the process. The two Xic are exposed, though, to the same environment, and it is obscure how they attain different architectures. By use of computer simulations of a molecular model, here we individuate general physical mechanisms whereby random Brownian molecules can assemble chromatin stable architectures, reliably regulate conformational changes, and establish opposite transformations on identical alleles. In the case-study of the murine Xic, our analysis highlights the existence of a few key regulatory regions and molecular factors. It also predicts, e.g., the effects of genetic modifications in the locus, which are compared with current deletion/insertion experiments. The physical mechanisms we describe are rooted in thermodynamics and could be relevant well beyond XCI.

Successful endoscopic treatment of Bouveret's syndrome by mechanical lithotripsy

Gastric outlet obstruction secondary to the impaction of large biliary stones into the duodenum (Bouveret's syndrome) is a well-known complication of biliary lithiasis, most often requiring surgical intervention. We report a case of successful endoscopic removal of a large stone impacted in the duodenal bulb by means of mechanical lithotripsy.

Endocytoscopy can identify dysplasia in aberrant crypt foci of the colorectum: a prospective in vivo study

BACKGROUND AND STUDY AIM

A catheter-type endocytoscope has recently been developed that is able to provide in vivo cellular images of gastrointestinal mucosa. Aberrant crypt foci (ACF) represent the earliest precursor of colorectal cancer featuring the dysplasia-carcinoma sequence. The aim of the current study was to assess the potential of the endocytoscopy system (ECS) in the "in vivo" detection of dysplasia in colorectal ACF.

PATIENTS AND METHODS

Consecutive patients with colorectal ACF were studied with endocytoscopy. Blinded endoscopic and histological assessments were obtained. Lesions were excised en bloc for histology.

RESULTS

A total of 48 colorectal lesions were examined in 41 patients. The mean duration of the ECS procedure was 44 +/- 12 minutes (range 31 - 62 minutes). The quality of ECS images was rated as good in 39/48, medium in six, and poor in three (6.2 %). It was possible to observe lesions at the cellular level and evaluate both cellular and structural atypia in vivo. In normal mucosa, crypts had preserved individuality and round-shaped contours. Nuclei were located at the basal third of the crypt in a single line, and the lumen was circular. In dysplastic ACF, crypt contours were polygonal, cell nuclei were elongated with pseudostratification toward the luminal half of the crypt and irregularly arranged, and the lumen was linear. In all, 23 endocytoscopic images were labeled as dysplastic and 25 as nondysplastic. Histology confirmed low-grade dysplasia in 21/23 cases (91.4 % sensitivity). Absence of dysplasia was confirmed in the remaining 25 cases (100 % specificity). Interobserver agreement between trained endoscopist and pathologist was good (wK 0.68; 95 % CI 0.59 - 0.78).

CONCLUSIONS

Endocytoscopy provides real-time histological images in vivo, with clear visualization of cellular details and features of dysplasia in colorectal ACF.

The colocalization transition of homologous chromosomes at meiosis

Meiosis is the specialized cell division required in sexual reproduction. During its early stages, in the mother cell nucleus, homologous chromosomes recognize each other and colocalize in a crucial step that remains one of the most mysterious of meiosis. Starting from recent discoveries on the system molecular components and interactions, we discuss a statistical mechanics model of chromosome early pairing. Binding molecules mediate long-distance interaction of special DNA recognition sequences and, if their concentration exceeds a critical threshold, they induce a spontaneous colocalization transition of chromosomes, otherwise independently diffusing.

Immunogenicity and therapeutic efficacy of phage-displayed beta-amyloid epitopes

In vitro and in vivo studies indicate that Alzheimer's Disease (AD) could be prevented or treated by active immunization against self-peptide beta-amyloid. In this study, we compared the immunogenicity of different regions of beta-amyloid, displayed on filamentous phages. We established that a filamentous phage displaying epitope 2-6 (AEFRH) of beta-amyloid at the N-terminus of Major Capside Protein (phage fdAD(2-6)) is more immunogenic than a phage displaying epitope 1-7 (DAEFRHD) that differs only in flanking residues. Monthly injections of fdAD(2-6) trigger a robust anti-beta-amyloid antibody response, and afford a significant reduction of plaque pathology in a mouse model of AD, whereas the same treatment, performed with phage fdAD(1-7), induces a lower anti-beta-amyloid titer and does not protect from amyloid deposition. "Memory" anti-amyloid antibodies induced by a single prime-boost cycle with vaccine fdAD(2-6), that have a lower titer compared to antibodies induced by monthly restimulations, do not prevent plaque pathology. Our data show that optimization of epitope display is essential in vaccine design, and suggest that the titer of the anti-amyloid response is the crucial parameter to obtain therapeutic efficacy in vivo.

Self-assembly and DNA binding of the blocking factor in x chromosome inactivation

X chromosome inactivation (XCI) is the phenomenon occurring in female mammals whereby dosage compensation of X-linked genes is obtained by transcriptional silencing of one of their two X chromosomes, randomly chosen during early embryo development. The earliest steps of random X-inactivation, involving counting of the X chromosomes and choice of the active and inactive X, are still not understood. To explain “counting and choice,” the longstanding hypothesis is that a molecular complex, a “blocking factor” (BF), exists. The BF is present in a single copy and can randomly bind to just one X per cell which is protected from inactivation, as the second X is inactivated by default. In such a picture, the missing crucial step is to explain how the molecular complex is self-assembled, why only one is formed, and how it binds only one X. We answer these questions within the framework of a schematic Statistical Physics model, investigated by Monte Carlo computer simulations. We show that a single complex is assembled as a result of a thermodynamic process relying on a phase transition occurring in the system which spontaneously breaks the symmetry between the X's. We discuss, then, the BF interaction with X chromosomes. The thermodynamics of the mechanism that directs the two chromosomes to opposite fates could be, thus, clarified. The insights on the self-assembling and X binding properties of the BF are used to derive a quantitative scenario of biological implications describing current experimental evidences on “counting and choice.”

In mammals, female cells silence one of their two X chromosomes to equalize X products with respect to males. The mechanism whereby cells count their X's and randomly choose the one to inactivate is, though, one of the most mysterious aspects of X chromosome inactivation (XCI). The longstanding hypothesis is that a molecular complex, a “blocking factor” (BF), exists: the BF is present in a single copy and can randomly bind to just one X per cell which is protected from inactivation, as the second X is inactivated by default. We add here a missing crucial step to such a picture: we explain, on a thermodynamic ground, why only one complex is formed in the cell, how it is self-assembled and how it selectively binds DNA recognition sequences. Such a process, leading to the spontaneous breaking of the binding symmetry of two equivalent targets, results from collective behavior at a molecular level whose general features are independent from the ultimate biochemical molecular details. It embodies, thus, a new general stochastic regulatory mechanism which could be relevant to a broad class of cell processes involving a random switch.

Symmetry-breaking model for X-chromosome inactivation

In mammals, dosage compensation of X linked genes in female cells is achieved by inactivation of one of their two X chromosomes which is randomly chosen. The earliest steps in X-chromosome inactivation (XCI), namely, the mechanism whereby cells count their X chromosomes and choose between two equivalent X chromosomes, remain mysterious. Starting from the recent discovery of X chromosome colocalization at the onset of X-chromosome inactivation, we propose a statistical mechanics model of XCI, which is investigated by computer simulations and checked against experimental data. Our model describes how a "blocking factor" complex is self-assembled and why only one is formed out of many diffusible molecules, resulting in a spontaneous symmetry breaking in the binding to two identical chromosomes. These results are used to derive a scenario of biological implications.

Management of gastro-oesophageal reflux disease: role of proton pump inhibitor test and upper gastro-intestinal endoscopy

Authors report the available scientific evidence on the role of proton pump inhibitors and upper gastro-intestinal endoscopy in the management of patients with gastro-oesophageal reflux disease. Relative indications, advantages and pitfalls of various diagnostic and therapeutic strategies for cost-effective management of this condition are discussed. The most recent evidence-based guidelines are outlined.

Lineage-Specific Requirement for the PH Domain of Vav1 in the Activation of CD4+ but Not CD8+ T Cells

Vav1 is a guanine nucleotide exchange factor (GEF) for Rho-family GTPases, which is activated by tyrosine phosphorylation following TCR stimulation. Vav1-deficient mice have defects in positive and negative selection of thymocytes as well as TCR-induced proliferation in mature T cells, demonstrating a critical role for Vav1 in transducing TCR signals. Binding of phospholipids to the PH domain of Vav1 has been proposed to regulate its GEF activity in vitro. To test this model in vivo, we have generated mice carrying a point mutation in the PH domain of Vav1, and we show that they have defects in T cell development and activation. We demonstrate that the mutation affects the function of Vav1 as a GEF and perturbs PI3K-dependent pathways downstream of Vav1. Unexpectedly, the mutation selectively affects TCR-induced proliferation of CD4(+) but not CD8(+) T cells, demonstrating differences in the wiring of TCR signaling pathways between the two lineages.

Lack of patent liver autoimmunity after breakage of tolerance in a mouse model

We report in this work that a cellular and humoral autoreactive response can be induced against liver-specific self-determinants by repeated immunization with a chimeric tissue-specific self-antigen carrying a heterologous T(h) epitope. Epitope spreading rendering the autoimmune reaction independent of the presence of the cognate heterologous help is also demonstrated. Although neutrophil infiltrates can be demonstrated in the livers of treated mice, no clinical sign of organ damage is observed. These findings suggest that breakage of tolerance by this means leads the process only up to the next checkpoint in the progression of autoimmune disease and that further events are required to precipitate functional organ impairment.

Vav1: a key signal transducer downstream of the TCR

Vav1 is a 95-kDa protein expressed in all hemopoietic cells that becomes rapidly tyrosine phosphorylated following T cell antigen receptor (TCR) stimulation. Vav1 contains multiple domains characteristic of signal transducing proteins, including a Dbl homology domain, a hallmark of a guanine nucleotide exchange factor (GEF) for Rho-family GTPases. Indeed Vav1 is a GEF for Rac1, Rac2 and RhoG, and it is activated following tyrosine phosphorylation. Generation of mice deficient in Vav1 has shown that it plays an important role in selection events within the thymus, including both positive and negative selection, consistent with Vav1 transducing TCR signals required to drive these processes. Furthermore, Vav1-deficient T cells are defective in TCR-induced proliferation and cytokine synthesis. Analysis of TCR signaling pathways in Vav1-deficient T cells and thymocytes has shown that Vav1 is required to transduce signals to the activation of a calcium flux, extracellular signal-regulated kinase (ERK) and the nuclear factor kappaB (NF-kappaB) transcription factor. Vav1 has also been shown to control the activation of phospholipase Cgamma1 (PLCgamma1) via both phosphoinositide-3-kinase (PI3K)-dependent and -independent pathways. Finally, Vav1 has been shown to transduce TCR signals to some but not all cytoskeleton-dependent pathways. In particular, Vav1 is required for efficient TCR-induced conjugate formation with antigen presenting cells (APCs), activation of the integrin leukocyte function-associated antigen-1 (LFA-1) and cell polarization.

Design of cassette vectors permitting cloning of all types of human TCR variable alpha and beta regions

T cell clones are an irreplaceable asset for the study of immune responses relevant to human pathologies. Such cells, however, cannot always be maintained in long-term culture. In order to reconstitute functional human T cell receptors (TCRs) into stable and fast growing hybridoma T cells, we developed a general approach based on a versatile cassette system, which allows cloning of all types of human T cell receptor variable alpha and beta region genes fused to murine constant regions. These chimeric constructs are easily excised and transferred into expression vectors that can be used to transfect a human CD4-expressing murine T cell hybridoma recipient. The resulting transfectants are highly stable both in terms of T cell receptor-CD3 expression and IL-2 response to the specific antigenic stimulus. Using these cassette vectors, we reconstituted the original HLA-restricted antigen specificity for two human T cell clones, one recognizing an immunodominant epitope of HIV-1 gp120, and the other recognizing an immunodominant epitope of HIV-1 reverse transcriptase. We found that the reconstituted hybridomas maintain the ability of the original T cell clones to recognize the appropriate epitope in the context of the relevant MHC either as a synthetic peptide or after processing. Their unlimited growth capacity makes them particularly suited for in vitro studies.

Unbalanced expression of HLA-A and -B antigens: a specific feature of cutaneous melanoma and other non-hemopoietic malignancies reverted by IFN-gamma

Conflicting evidences suggested that levels of HLA-A and -B antigens expressed on normal and neoplastic cells of given individuals are genetically predetermined, or, on the other hand, regulated by molecular mechanisms generating the down-regulated expression of HLA-B antigens frequently observed on melanoma cells. In our study, we quantitated, both at the protein and mRNA level, the amounts of HLA-A and -B antigens constitutively expressed on 23 primary cultures of metastatic melanomas and on autologous peripheral blood mononuclear cells (PBMC). Flow cytometric analyses identified a significantly (p < 0.01) lower expression of HLA-B antigens on melanoma cell cultures but not on autologous PBMC. Consistently, lower amounts of HLA-B antigens mRNA were detected by RNase protection assay exclusively in neoplastic cells. This unbalanced expression of HLA-A and -B antigens was readily reverted by interferon (IFN)-gamma but not by the DNA hypomethylating agent 5-aza-2'-deoxycytidine in 4 melanoma cell cultures investigated. Significantly (p < 0.05) lower levels of HLA-B antigens were also detected on cells from solid malignancies of different histotypes but not on neoplastic cells from hemopoietic neoplasms; levels of HLA-B antigens were rapidly up-regulated by IFN-gamma exclusively on non-hemopoietic transformed cells. Together, these data strongly argue against a genetic predetermination of the amounts of HLA-A and -B antigens expressed on normal and neoplastic cells of distinct melanoma patients and suggest that constitutively low levels of HLA-B antigens are a specific feature of non-hemopoietic transformed cells that is controlled by common regulatory mechanism(s) and that is possibly shared by non-hemopoietic normal cells.

Endoclip-assisted resection of large pedunculated colon polyps

BACKGROUND

Large pedunculated colorectal polyps are often difficult to remove endoscopically.

METHODS

Four patients with giant pedunculated polyps (>3 cm) underwent an endoscopic procedure in which the polyp stalk was ligated with multiple clips and resected with a needle-knife papillotome.

RESULTS

No complications occurred either during or immediately after the procedure. Mean size of the resected polyps was 4.8 +/- 1.2 cm (range 3 to 6 cm). Mean time for the entire procedure was 31 +/- 5 minutes (range 25 to 45). No bleeding was found after a mean follow-up period of 4.3 +/- 1.1 months (range 3 to 6 months).

CONCLUSIONS

Although technical refinements are necessary to make the procedure easier and faster, this approach might represent the only option for selected patients who would otherwise need surgical resection of large pedunculated colonic polyps.

In vitro immunization with a recombinant antigen carrying the HIV-1 RT248-262 determinant inserted at different locations results in altered TCRVB region usage

Immunodominance or cripticity of a peptide-borne determinant may be influenced by the protein context in which the epitope is embedded. In this frame, we previously showed that certain human T cell clones, derived from different donors, may differentially recognize the RT248-262 helper determinant depending on whether it is provided to the presenting cells as a synthetic peptide or as a recombinant carrier protein to which the sequence of interest is fused. We now report that, upon in vitro immunization of human PBL with autologous APC, the epitope-specific TCRVB repertoire obtained when selection is applied by pulsing the APC with the cognate synthetic peptide is different from that found when a recombinant protein is used in which the antigenic sequence is placed at either a N-terminal or C-terminal location of the GST carrier. As the TCRVB distribution is not a function of the APC used, we propose that processing of different recombinant molecules containing the same epitope may generate MHC/peptide complexes which, being antigenically diverse, may recruit distinct TCR specificities. These findings may be relevant for evaluating and predicting the immunogenic potential of subunit vaccines based on synthetic peptides or on recombinant proteins as compared to the native antigen.

Recognition of HIV-derived B and T cell epitopes displayed on filamentous phages

The amino acid sequence of HIV reverse transcriptase (RT) from residue 248 to residue 262 was expressed on the surface of filamentous phage fd, fused to the major coat protein gVIIIp. The chimeric phage was used to assess the ability of anti-RT (248-262) human T cell lines and clones to become activated by the phage-displayed peptide. The RT peptide displayed on phage was recognized by the T-cells and induced production of Abs. However, not all T cells raised against the synthetic RT (248-262) peptide could respond. Lack of recognition did not depend on differences in the ability of different APCs to present the phage, but was apparently determined by the TCR specificity. The results presented here may be relevant to the design of recombinant protein-based subunit vaccines.

The Rho-family GTP exchange factor Vav is a critical transducer of T cell receptor signals to the calcium, ERK, and NF-kappaB pathways

Vav is a GTP/GDP exchange factor (GEF) for members of the Rho-family of GTPases that is rapidly tyrosine-phosphorylated after engagement of the T cell receptor (TCR), suggesting that it may transduce signals from the receptor. T cells from mice made Vav-deficient by gene targeting (Vav-/-) fail to proliferate in response to TCR stimulation because they fail to secrete IL-2. We now show that this is due at least in part to the failure to initiate IL-2 gene transcription. Furthermore, we analyze TCR-proximal signaling pathways in Vav-/- T cells and show that despite normal activation of the Lck and ZAP-70 tyrosine kinases, the mutant cells have specific defects in TCR-induced intracellular calcium fluxes, in the activation of extracellular signal-regulated mitogen-activated protein kinases and in the activation of the NF-kappaB transcription factor. Finally, we show that the greatly reduced TCR-induced calcium flux of Vav-deficient T cells is an important cause of their proliferative defect, because restoration of the calcium flux with a calcium ionophore reverses the phenotype.