New role of signal peptide peptidase to liberate C-terminal peptides for MHC class I presentation.

The signal peptide peptidase (SPP) is an intramembrane cleaving aspartyl protease involved in release of leader peptide remnants from the endoplasmic reticulum membrane, hence its name. We now found a new activity of SPP that mediates liberation of C-terminal peptides. In our search for novel proteolytic enzymes involved in MHC class I (MHC-I) presentation, we found that SPP generates the C-terminal peptide-epitope of a ceramide synthase. The display of this immunogenic peptide-MHC-I complex at the cell surface was independent of conventional processing components like proteasome and peptide transporter TAP. Absence of TAP activity even increased the MHC-I presentation of this Ag. Mutagenesis studies revealed the crucial role of the C-terminal location of the epitope and "helix-breaking" residues in the transmembrane region just upstream of the peptide, indicating that SPP directly liberated the minimal 9-mer peptide. Moreover, silencing of SPP and its family member SPPL2a led to a general reduction of surface peptide-MHC-I complexes, underlining the involvement of these enzymes in Ag processing and presentation.

Peptide transporter TAP mediates between competing antigen sources generating distinct surface MHC class I peptide repertoires.

We recently described a category of TAP-independent peptide-epitopes that are selectively presented by cells with processing defects in the classical MHC class I (MHC-I) pathway. Here, we studied the ER-resident ceramide synthase Trh4 as a prototypic example of these neo-antigens and found that moderate inhibition of TAP permits cell surface presentation of the Trh4 peptide. The absence of this peptide from WT cells was not related to the binding or stability of the Trh4/D(b) complexes, or to the availability of MHC-I heavy chains, but rather to the limited expression of the antigen. Strongly elevated antigen levels were needed to reach comparable peptide display on WT as on TAP-deficient cells. Our data suggest that the normal influx of TAP-transported peptides in the ER during routine processing creates an efficient barrier for peptides from alternative processing routes. Impairment of TAP function, as commonly found in cancers and virus-infected cells, lowers this resistance allowing for MHC-I presentation of other peptide sources.

A novel category of antigens enabling CTL immunity to tumor escape variants: Cinderella antigens.

Deficiencies in MHC class I antigen presentation are a common feature of tumors and allows escape from cytotoxic T lymphocyte (CTL)-mediated killing. It is crucial to take this capacity of tumors into account for the development of T-cell-based immunotherapy, as it may strongly impair their effectiveness. A variety of escape mechanisms has been described thus far, but progress in counteracting them is poor. Here we review a novel strategy to target malignancies with defects in the antigenic processing machinery (APM). The concept is based on a unique category of CD8+ T-cell epitopes that is associated with impaired peptide processing, which we named TEIPP. We characterized this alternative peptide repertoire emerging in MHC-I on tumors lacking classical antigen processing due to defects in the peptide transporter TAP (transporter associated with peptide processing). These TEIPPs exemplify interesting parallels with the folktale figure Cinderella: they are oppressed and neglected by a stepmother (like functional TAP prevents TEIPP presentation), until the suppression is released and Cinderella/TEIPP achieves unexpected recognition. TEIPP-specific CTLs and their cognate peptide-epitopes provide a new strategy to counteract immune evasion by APM defects and bear potential to targeting escape variants observed in a wide range of cancers.

Extracellular Vesicle-Based Therapeutics for Heart Repair.

Extracellular vesicles (EVs) are constituted by a group of heterogeneous membrane vesicles secreted by most cell types that play a crucial role in cell-cell communication. In recent years, EVs have been postulated as a relevant novel therapeutic option for cardiovascular diseases, including myocardial infarction (MI), partially outperforming cell therapy. EVs may present several desirable features, such as no tumorigenicity, low immunogenic potential, high stability, and fine cardiac reparative efficacy. Furthermore, the natural origin of EVs makes them exceptional vehicles for drug delivery. EVs may overcome many of the limitations associated with current drug delivery systems (DDS), as they can travel long distances in body fluids, cross biological barriers, and deliver their cargo to recipient cells, among others. Here, we provide an overview of the most recent discoveries regarding the therapeutic potential of EVs for addressing cardiac damage after MI. In addition, we review the use of bioengineered EVs for targeted cardiac delivery and present some recent advances for exploiting EVs as DDS. Finally, we also discuss some of the most crucial aspects that should be addressed before a widespread translation to the clinical arena.

T Cells Engaging the Conserved MHC Class Ib Molecule Qa-1b with TAP-Independent Peptides Are Semi-Invariant Lymphocytes.

The HLA-E homolog in the mouse (Qa-1b) is a conserved MHC class Ib molecule presenting monomorphic peptides to germline-encoded natural killer receptor CD94/NKG2A. Previously, we demonstrated the replacement of this canonical peptide by a diverse peptidome upon deficiency of the TAP peptide transporter. Analysis of this Qa-1b-restricted T cell repertoire against these non-mutated neoantigens revealed characteristics of conventional hypervariable CD8+ T cells, but also of invariant T cell receptor (TCR)αß T cells. A shared TCR Vα chain was used by this subset in combination with a variety of Vß chains. The TCRs target peptide ligands that are conserved between mouse and man, like the identified peptide derived from the transcriptional cofactor Med15. The thymus selection was studied in a TCR-transgenic mouse and emerging naïve CD8+ T cells displayed a slightly activated phenotype, as witnessed by higher CD122 and Ly6C expression. Moreover, the Qa-1b protein was dispensable for thymus selection. Importantly, no self-reactivity was observed as reported for other MHC class Ib-restricted subsets. Naïve Qa-1b restricted T cells expanded, contracted, and formed memory cells in vivo upon peptide vaccination in a similar manner as conventional CD8+ T cells. Based on these data, the Qa-1b restricted T cell subset might be positioned closest to conventional CD8+ T cells of all MHC class Ib populations.

TAP-independent self-peptides enhance T cell recognition of immune-escaped tumors.

Tumor cells frequently escape from CD8+ T cell recognition by abrogating MHC-I antigen presentation. Deficiency in processing components, like the transporter associated with antigen processing (TAP), results in strongly decreased surface display of peptide/MHC-I complexes. We previously identified a class of hidden self-antigens known as T cell epitopes associated with impaired peptide processing (TEIPP), which emerge on tumor cells with such processing defects. In the present study, we analyzed thymus selection and peripheral behavior of T cells with specificity for the prototypic TEIPP antigen, the "self" TRH4 peptide/Db complex. TEIPP T cells were efficiently selected in the thymus, egressed with a naive phenotype, and could be exploited for immunotherapy against immune-escaped, TAP-deficient tumor cells expressing low levels of MHC-I (MHC-Ilo). In contrast, overt thymus deletion and functionally impaired TEIPP T cells were observed in mice deficient for TAP1 due to TEIPP antigen presentation on all body cells in these mice. Our results strongly support the concept that TEIPPs derive from ubiquitous, nonmutated self-antigens and constitute a class of immunogenic neoantigens that are unmasked during tumor immune evasion. These data suggest that TEIPP-specific CD8+ T cells are promising candidates in the treatment of tumors that have escaped from conventional immunotherapies.

Alternative Antigen Processing for MHC Class I: Multiple Roads Lead to Rome.

The well described conventional antigen-processing pathway is accountable for most peptides that end up in MHC class I molecules at the cell surface. These peptides experienced liberation by the proteasome and transport by the peptide transporter TAP. However, there are multiple roads that lead to Rome, illustrated by the increasing number of alternative processing pathways that have been reported during last years. Interestingly, TAP-deficient individuals do not succumb to viral infections, suggesting that CD8 T cell immunity is sufficiently supported by alternative TAP-independent processing pathways. To date, a diversity of viral and endogenous TAP-independent peptides have been identified in the grooves of different MHC class I alleles. Some of these peptides are not displayed by normal TAP-positive cells and we therefore called them TEIPP, for "T-cell epitopes associated with impaired peptide processing." TEIPPs are hidden self-antigens, are derived from normal housekeeping proteins, and are processed via unconventional processing pathways. Per definition, TEIPPs are presented via TAP-independent pathways, but recent data suggest that part of this repertoire still depend on proteasome and metalloprotease activity. An exception is the C-terminal peptide of the endoplasmic reticulum (ER)-membrane-spanning ceramide synthase Trh4 that is surprisingly liberated by the signal peptide peptidase (SPP), the proteolytic enzyme involved in cleaving leader sequences. The intramembrane cleaving SPP is thereby an important contributor of TAP-independent peptides. Its family members, like the Alzheimer's related presenilins, might contribute as well, according to our preliminary data. Finally, alternative peptide routing is an emerging field and includes processes like the unfolded protein response, the ER-associated degradation, and autophagy-associated vesicular pathways. These data convince us that there is a world to be discovered in the field of unconventional antigen processing.

Dominant contribution of the proteasome and metalloproteinases to TAP-independent MHC-I peptide repertoire.

Tumors frequently display defects in the MHC-I antigen processing machinery, such as deficiency of the peptide transporter TAP. Interestingly, the residual peptide repertoire contains neo-antigens which are not presented by processing-proficient cells. We termed these immunogenic peptides TEIPP ('T-cell epitopes associated with impaired peptide processing') and were interested to unravel their TAP-independent processing pathways. With an array of chemical inhibitors we assessed the participation of numerous proteases to TAP-independent peptides and found that the previously described catalytic enzymes signal peptidase and furin contributed in a cell-type and MHC-I allele-specific way. In addition, a dominant role for the proteasome and metallopeptidases was observed. These findings raised the question how these proteasome products get access to MHC-I molecules. A novel TEIPP peptide-epitope that represented this intracellular route revealed that the lysosomal peptide transporter ABCB9 ('TAP-like') was dispensable for its presentation. Interestingly, prevention of endolysosomal vesicle acidification by bafilomycin enhanced the surface display of this TEIPP peptide, suggesting that this proteasome-dependent pathway intersects endolysosomes and that these antigens are merely destroyed there. In conclusion, the proteasome has a surprisingly dominant role in shaping the TAP-independent MHC-I peptide repertoire and some of these antigens might be targeted to the endocytic vesicular pathway.

Importance of TAP-independent processing pathways.

The majority of peptides presented in MHC class I at the cell surface originate from the conventional antigen processing pathway, involving the proteasome and TAP peptide transporter. Alternative pathways, however, certainly contribute to the diversity of the total peptide repertoire. The importance of such TAP-independent processing pathways is nicely illustrated by the finding that individuals with an inherited deficiency in this peptide transporter still sufficiently mount T cell responses against viruses. Although defects in TAP do result in strongly decreased surface display of MHC class I molecules, the residual levels are capable to educate and elicit T cell immunity. In our work, we have shown that a broad repertoire of peptides is presented on processing-deficient cells. The characterization of these peptides, which we called TEIPP - "T-cell epitopes associated with impaired peptide processing", showed that they derive from housekeeping proteins, are diverse in length and amino-acid composition, and are not presented on normal cells. So, TAP-deficiency promotes the emergence of neo-antigens. These TAP-independent peptides might be processed via the two already known pathways, signal sequence liberation or furin-mediated cleavage in the Golgi, or via yet other routes. Our study on TEIPP antigens reveals that there is a world to be discovered in the alternative antigen processing field. Autophagy, vesicular routing, membrane-associated proteolysis, invariant chain involvement and recycling of MHC class I molecules all might come to the stage in this interesting research area.

The other Janus face of Qa-1 and HLA-E: diverse peptide repertoires in times of stress.

The non-polymorphic MHC molecule Qa-1 and its human counterpart HLA-E present monomorphic signal peptides to innate receptors and thereby regulate lymphocyte activity. Under stress, this peptide content is replaced with a surprisingly diverse repertoire of novel peptides that are associated with heat-shock proteins, infectious agents or antigen processing defects.

The nonpolymorphic MHC Qa-1b mediates CD8+ T cell surveillance of antigen-processing defects.

The nonclassical major histocompatibility complex (MHC) Qa-1b accommodates monomorphic leader peptides and functions as a ligand for germ line receptors CD94/NKG2, which are expressed by natural killer cells and CD8+ T cells. We here describe that the conserved peptides are replaced by a novel peptide repertoire of surprising diversity as a result of impairments in the antigen-processing pathway. This novel peptide repertoire represents immunogenic neoantigens for CD8+ T cells, as we found that these Qa-1b-restricted T cells dominantly participated in the response to tumors with processing deficiencies. A surprisingly wide spectrum of target cells, irrespective of transformation status, MHC background, or type of processing deficiency, was recognized by this T cell subset, complying with the conserved nature of Qa-1b. Target cell recognition depended on T cell receptor and Qa-1b interaction, and immunization with identified peptide epitopes demonstrated in vivo priming of CD8+ T cells. Our data reveal that Qa-1b, and most likely its human homologue human leukocyte antigen-E, is important for the defense against processing-deficient cells by displacing the monomorphic leader peptides, which relieves the inhibition through CD94/NKG2A on lymphocytes, and by presenting a novel repertoire of immunogenic peptides, which recruits a subset of cytotoxic CD8+ T cells.

Fluorimetric determination of cyclofenil using photochemical derivatization.

In this work, a fluorimetric approach for the determination of cyclofenil, 4-4'-(cyclohexylidenemethylene)bis(phenylacetate), is presented. The method was based on the intense fluorescence (250/410 nm) observed after a UV photochemical treatment of cyclofenil. The influence of the pH and solvent system and UV exposure time on the fluorescence magnitude was studied. Optimization of parameters was made using experimental design (factorial design and central composite design). Limit of detection (3S(b)/m) were estimated to be 1.1 x 10(-8)mol L(-1) with the linear dynamic range extending up to 8 x 10(-5)mol L(-1). This analytical approach was tested through the analysis of a commercial pharmaceutical formulation. In this case, tests enabled an average recovery of 98.3+/-3.9% (for n=9) using the analytical curve. The identification of the fluorescent derivative is proposed based on results achieved from GC-MS.

Anestesia no cirrótico / Anesthesia of cirrhotic patients

A perda progressiva do parênquima hepático, que é substituído por tecido fibroso e nódulos de regeneraçäo, determina a destruiçäo da arquitetura normal que modifica as características da irrigaçäo sanguínea e entäo ocorre a rápida deterioraçäo do estado geral do paciente que passa a apresentar distúrbios de vários órgäos e sistemas, que säo extremamente graves e que compöem o estágio terminal do acometimento hepático - cirrose. Existem várias situaçöes nas quais pacientes portadores de cirrose hepática säo submetidos a intervençöes cirúrgicas e, para tanto é necessário o conhecimento e rápida atuaçäo da equipe médica pois o sofrimento hepático resultante da combinaçäo do binômio cirurgia-anestesia tem várias razöes e graus e é dever do médico que assiste o paciente na qualidade de anestesiologista näo somente administrar drogas capazes de abolir a consciência, drogas que promovam analgesia e relaxamento muscular como também propiciar condiçöes hemodinâmicas, ventilatórias e renais suficientes para a manutençäo da homeostase interna bem como corrigir os distúrbios da coagulaçäo de modo a diminuir as perdas sanguíneas, baseando-se em profundos conhecimentos da farmacocinética e farmacodinâmica dos anestésicos na vigência de distúrbios hepáticos e, com único objetivo em mente que é prevenir prejuízo adicional da funçäo hepática ainda remanescente nesses pacientes