Functional magnetic resonance imaging in oncology: state of the art

In the investigation of tumors with conventional magnetic resonance imaging, both quantitative characteristics, such as size, edema, necrosis, and presence of metastases, and qualitative characteristics, such as contrast enhancement degree, are taken into consideration. However, changes in cell metabolism and tissue physiology which precede morphological changes cannot be detected by the conventional technique. The development of new magnetic resonance imaging techniques has enabled the functional assessment of the structures in order to obtain information on the different physiological processes of the tumor microenvironment, such as oxygenation levels, cellularity and vascularity. The detailed morphological study in association with the new functional imaging techniques allows for an appropriate approach to cancer patients, including the phases of diagnosis, staging, response evaluation and follow-up, with a positive impact on their quality of life and survival rate.

Characterization of local and systemic immune-modulation in melanoma patients

Le mélanome cutané est un des cancers les plus agressifs et dont l'incidence augmente le plus en Suisse. Une fois métastatique, le pronostic de survie moyenne avec les thérapies actuelles est d'environ huit mois, avec moins de 5% de survie à cinq ans. Les récents progrès effectués dans la compréhension de la biologie de la cellule tumorale mais surtout dans l'importance du système immunitaire dans le contrôle de ce cancer ont permis le développement de nouveaux traitements novateurs et prometteurs. Ces thérapies, appelées immunothérapies, reposent sur la stimulation et l'augmentation de la réponse immunitaire à la tumeur. Alors que les derniers essais cliniques ont démontré l'efficacité de ces traitements chez les patients avec des stades avancés de la maladie, le contrôle de la maladie à long- terme est seulement atteint chez une minorité des patients. La suppression locale et systémique de la réponse immunitaire spécifique anti-tumorale apparaitrait comme une des raisons expliquant la persistance d'un mauvais pronostic clinique chez ces patients. Des études sur les souris ont montré que les vaisseaux lymphatiques joueraient un rôle primordial dans ce processus en induisant une tolérance immune, ce qui permettrait à la tumeur d'échapper au contrôle du système immunitaire et métastatiser plus facilement. Ces excitantes découvertes n'ont pas encore été établi et prouvé chez l'homme. Dans cette thèse, nous montrons pour la première fois que les vaisseaux lymphatiques sont directement impliqués dans la modulation de la réponse immunitaire au niveau local et systémique dans le mélanome chez l'homme. Ces récentes découvertes montrent le potentiel de combiner des thérapies visant le système lymphatique avec les immunothérapies actuellement utilisées afin d'améliorer le pronostic des patients atteint du mélanome. -- Cutaneous melanoma is one of the most invasive and metastatic human cancers and causes 75% of skin cancer mortality. Current therapies such as surgery and chemotherapy fail to control metastatic disease, and relapse occurs frequently due to microscopic residual lesions. It is, thus, essential to develop and optimize novel therapeutic strategies to improve curative responses in these patients. In recent decades, tumor immunologists have revealed the development of spontaneous adaptive immune responses in melanoma patients, leading to the accumulation of highly differentiated tumor-specific T cells at the tumor site. This remains one of the most powerful prognostic markers to date. Immunotherapies that augment the natural function of these tumor-specific T cells have since emerged as highly attractive therapeutic approaches to eliminate melanoma cells. While recent clinical trials have demonstrated great progress in the treatment of advanced stage melanoma, long-term disease control is still only achieved in a minority of patients. Local and systemic immune suppression by the tumor appears to be responsible, in part, for this poor clinical evolution. These facts underscore the need for a better analysis and characterization of immune- related pathways within the tumor microenvironment (TME), as well as at the systemic level. The overall goal of this thesis is, thus, to obtain greater insight into the complexity and heterogeneity of the TME in human melanoma, as well as to investigate immune modulation beyond the TME, which ultimately influences the immune system throughout the whole body. To achieve this, we established two main objectives: to precisely characterize local and systemic immune modulation (i) in untreated melanoma patients and (ii) in patients undergoing peptide vaccination or checkpoint blockade therapy with anti-cytotoxic T- lymphocyte-asisctaed protein-4 (CTLA-4) antibody. In the first and main part of this thesis, we analyzed lymphatic vessels in relation to anti-tumor immune responses in tissues from vaccinated patients using a combination of immunohistochemistry (IHC) techniques, whole slide scanning/analysis, and an automatic quantification system. Strikingly, we found that increased lymphatic vessel density was associated with high expression of immune suppressive molecules, low functionality of tumor-infiltrating CD8+ T cells and decreased cytokine production by tumor-antigen specific CD8+ T cells in the blood. These data revealed a previously unappreciated local and systemic role of lymphangiogenesis in modulating T cell responses in human cancer and support the use of therapies that target lymphatic vessels combined with existing and future T cell based therapies. In the second objective, we describe a metastatic melanoma patient who developed pulmonary sarcoid-like granulomatosis following repetitive vaccination with peptides and CpG. We demonstrated that the onset of this pulmonary autoimmune adverse event was related to the development of a strong and long-lasting tumor-specific CD8+ T cell response. This constitutes the first demonstration that a new generation tumor vaccine can induce the development of autoimmune adverse events. In the third objective, we assessed the use of Fourier Transform Infrared (FTIR) imaging to identify melanoma cells and lymphocyte subpopulations in lymph node (LN) metastasis tissues, thanks to a fruitful collaboration with researchers in Brussels. We demonstrated that the different cell types in metastatic LNs have different infrared spectral features allowing automated identification of these cells. This technic is therefore capable of distinguishing known and novel biological features in human tissues and has, therefore, significant potential as a tool for histopathological diagnosis and biomarker assessment. Finally, in the fourth objective, we investigated the role of colony- stimulating factor-1 (CSF-1) in modulating the anti-tumor response in ipilimumab-treated patients using IHC and in vitro co-cultures, revealing that melanoma cells produce CSF-1 via CTL-derived cytokines when attacked by cytotoxic T lymphocytes (CTLs), resulting in the recruitment of immunosuppressive monocytes. These findings support the combined use of CSF-1R blockade with T cell based immunotherapy for melanoma patients. Taken together, our results reveal the existence of novel mechanisms of immune modulation and thus promote the optimization of combination immunotherapies against melanoma. -- Le mélanome cutané est un des cancers humains les plus invasifs et métastatiques et est responsable de 75% de la mortalité liée aux cancers de la peau. Les thérapies comme la chirurgie et la chimiothérapie ont échoué à contrôler le mélanome métastatique, par ailleurs les rechutes sous ces traitements ont été montrées fréquentes. Il est donc essentiel de développer et d'optimiser de nouvelles stratégies thérapeutiques pour améliorer les réponses thérapeutiques de ces patients. Durant les dernières décennies, les immunologistes spécialisés dans les tumeurs ont démontré qu'un patient atteint du mélanome pouvait développer spontanément une réponse immune adaptative à sa tumeur et que l'accumulation de cellules T spécifiques tumorales au sein même de la tumeur était un des plus puissants facteurs pronostiques. Les immunothérapies qui ont pour but d'augmenter les fonctions naturelles de ces cellules T spécifiques tumorales ont donc émergé comme des approches thérapeutiques très attractives pour éliminer les cellules du mélanome. Alors que les derniers essais cliniques ont démontré un progrès important dans le traitement des formes avancées du mélanome, le contrôle de la maladie à long-terme est seulement atteint chez une minorité des patients. La suppression immune locale et systémique apparaitrait comme une des raisons expliquant la persistance d'un mauvais pronostic clinique chez ces patients. Ces considérations soulignent la nécessité de mieux analyser et caractériser les voies immunitaires non seulement au niveau local dans le microenvironement tumoral mais aussi au niveau systémique dans le sang des patients. Le but de cette thèse est d'obtenir une plus grande connaissance de la complexité et de l'hétérogénéité du microenvironement tumoral dans les mélanomes mais aussi d'investiguer la modulation immunitaire au delà du microenvironement tumoral au niveau systémique. Afin d'atteindre ce but, nous avons établi deux objectifs principaux : caractériser précisément la modulation locale et systémique du système immunitaire (i) chez les patients atteints du mélanome qui n'ont pas reçu de traitement et (ii) chez les patients qui ont été traités soit par des vaccins soit par des thérapies qui bloquent les points de contrôles. Dans la première et majeure partie de cette thèse, nous avons analysé les vaisseaux lymphatiques en relation avec la réponse immunitaire anti-tumorale dans les tissus des patients vaccinés grâce à des techniques d'immunohistochimie et de quantification informatisé et automatique des marquages. Nous avons trouvé qu'une densité élevée de vaisseaux lymphatiques dans la tumeur était associée à une plus grande expression de molécules immunosuppressives ainsi qu'à une diminution de la fonctionnalité des cellules T spécifiques tumoral dans la tumeur et dans le sang des patients. Ces résultats révèlent un rôle jusqu'à là inconnu des vaisseaux lymphatiques dans la modulation directe du système immunitaire au niveau local et systémique dans les cancers de l'homme. Cette recherche apporte finalement des preuves du potentiel de combiner des thérapies visant le système lymphatique avec des autres immunothérapies déjà utilisées en clinique. Dans le second objectif, nous rapportons le cas d'un patient atteint d'un mélanome avec de multiples métastases qui a développé à la suite de plusieurs vaccinations répétées et consécutives avec des peptides et du CpG, un évènement indésirable sous la forme d'une granulomatose pulmonaire sarcoid-like. Nous avons démontré que l'apparition de cet évènement était intimement liée au développement d'une réponse immunitaire durable et spécifique contre les antigènes de la tumeur. Par là- même, nous prouvons pour la première fois que la nouvelle génération de vaccins est aussi capable d'induire des effets indésirables auto-immuns. Pour le troisième objectif, nous avons voulu savoir si l'utilisation de la spectroscopie infrarouge à transformée de Fourier (IRTF) était capable d'identifier les cellules du mélanome ainsi que les différents sous-types cellulaires dans les ganglions métastatiques. Grâce à nos collaborateurs de Bruxelles, nous avons pu établir que les diverses composantes cellulaires des ganglions atteints par des métastases du mélanome présentaient des spectres infrarouges différents et qu'elles pouvaient être identifiées d'une façon automatique. Cette nouvelle technique permettrait donc de distinguer des caractéristiques biologiques connues ou nouvelles dans les tissus humains qui auraient des retombées pratiques importantes dans le diagnostic histopathologique et dans l'évaluation des biomarqueurs. Finalement dans le dernier objectif, nous avons investigué le rôle du facteur de stimulation des colonies (CSF-1) dans la modulation de la réponse immunitaire anti-tumorale chez les patients qui ont été traités par l'Ipilimumab. Nos expériences in vivo au niveau des tissus tumoraux et nos co-cultures in vitro nous ont permis de démontrer que les cytokines secrétées par les cellules T spécifiques anti-tumorales induisaient la sécrétion de CSF-1 dans les cellules du mélanome ce qui résultait en un recrutement de monocytes immunosuppresseurs. Dans son ensemble, cette thèse révèle donc l'existence de nouveaux mécanismes de modulation de la réponse immunitaire anti-tumorale et propose de nouvelles optimisations de combinaison d'immunothérapies contre le mélanome.

Sexual dimorphism in cancer.

The incidence of many types of cancer arising in organs with non-reproductive functions is significantly higher in male populations than in female populations, with associated differences in survival. Occupational and/or behavioural factors are well-known underlying determinants. However, cellular and molecular differences between the two sexes are also likely to be important. In this Opinion article, we focus on the complex interplay that sex hormones and sex chromosomes can have in intrinsic control of cancer-initiating cell populations, the tumour microenvironment and systemic determinants of cancer development, such as the immune system and metabolism. A better appreciation of these differences between the two sexes could be of substantial value for cancer prevention as well as treatment.

Most of the Abundant Protein Fractions of Embryonic Cerebrospinal Fluid are Produced Out of the Brain Anlagen

The microenvironment of the central nervous system is important for neuronal function and development. During the early stages of embryo development the cephalic vesicles are filled by embryonic cerebrospinal fluid, a complex fluid containing different protein fractions, which contributes to the regulation of the survival, proliferation and neurogenesis of neuroectodermal stem cells. The protein content of embryonic cerebrospinal fluid from chick and rat embryos at the start of neurogenesis has already been determined. Most of the identified gene products are thought to be involved in the regulation of developmental processes during embryogenesis. However, due to the crucial roles played by embryonic cerebrospinal fluid during brain development, the embryological origin of the gene products it contains remains an intriguing question. According to the literature most of these products are synthesised in embryonic tissues other than the neuroepithelium. In this study we examined the embryological origin of the most abundant embryonic cerebrospinal fluid protein fractions by means of slot-blot analysis and by using several different embryonic and extraembryonic protein extracts, immunodetected with polyclonal antibodies. This first attempt to elucidate their origin is not based on the proteins identified by proteomic methods, but rather on crude protein fractions detected by SDS-PAGE analysis and to which polyclonal antibodies were specifically generated. Despite some of the limitations of this study, i.e. that one protein fraction may contain more than one gene product, and that a specific gene product may be contained in different protein fractions depending on post-translational modifications, our results show that most of the analysed protein fractions are not produced by the cephalic neuroectoderm but are rather stored in the egg reservoir; furthermore, few are produced by embryo tissues, thus indicating that they must be transported from their production or storage sites to the cephalic cavities, most probably via embryonic serum. These results raise the question as to whether the transfer of proteins from these two embryo compartments is regulated at this early developmental stage.

Preparation and properties of perichromic dye: an undergraduate laboratory

An undergraduate experiment that illustrates the phenomenon of perichromism-the sensitivity of a dye to its microenvironment, as assessed by color changes of its solutions-is described. An easily prepared perichromic imine is synthesized and characterized, and its solvatochromism, thermochromism, halochromism, and preferential solvation in binary solvent mixtures are demonstrated by visual inspection of its solutions. The results are rationalized by invoking solute - solvent interactions in the various media.

Ascite quilosa traumática

Chylous ascites is a rare clinical entity. In infancy it is less commom still. The etiology of most of them is usually congenital or idiopathic; trauma is a less frequent cause. It has been implicated in about 10% of all cases 1-5. There have been less than one hundred cases published in the English literature, including 12 in children. We report a pediatric case of chylous ascites as a result of blunt abdominal trauma managed by ligation of the lymphatic leak.

Perfuração espontânea da via biliar principal na infância

The authors report a case of spontaneous perforation of the biliary tract (S.P.B.T) in a three-month-old infant. The diagnosis was suspected before the operation by clinical signs and diagnostic tests. The importance of paracentesis and scintigraphy is stressed. A surgical approach was chosen and drainage procedure of the area around the perforation and a cholecystostomy were done. S.P.B.T. is rare and its etiology is controversial, but cannot be forgotten in association between biliary ascites and cholestatic jaundice during the first months of life.

Senecio spp. POISONING OF HORSES IN SOUTHERN BRAZIL

Cases of seneciosis in horses occurring in four farms in the state of Santa Catarina and in another in the state of Rio Grande do Sul, southern Brazil, are reported. S. brasiliensis or S. oxyphyllus or both were detected in four of the five properties. Five horses (one on each property) were necropsied, and tissues for histopathological examination were collected from four horses. Neurological signs, such as depression, ataxia, aimeless walking, circling, head pressing, faulty prehension of food, dysphagia and blindness were consistently observed. Other signs included inappetence, loss of weight, colic, subcutaneous edema, icterus and photodermatitis. At necropsy the livers were firmer and darker than normal and had accentuation of lobular pattern. Edema of the mesentery and ascites were observed in one horse. Main histopathological changes consisted of hepatic chiefly periportal fibrosis, hepatomegalocytosis and biliary hyperplasia. Marked cholestasis and morphological evidence of hepatic encephalopathy were seen respectively in the liver and brain of one of the horses.

Postweaning multisystemic wasting syndrome in farmed wild boars (Sus scrofa) in Rio Grande do Sul

This report concerns an outbreak of postweaning multisystemic wasting syndrome in wild boars from commercial herds in Rio Grande do Sul, Brazil. The main clinical signs were progressive wasting, respiratory distress, diarrhea, and ocular discharges. Enhanced lymph nodes and spleens, ascites, hydrothorax, and non collapsed lungs were the principal gross lesions. Varying degrees of lymphohistiocytic infiltrates in lymph nodes, spleen, and intestines were the most significant microscopic changes. Although a total of 26 animals had showed clinical and pathological findings consistent with the disease, only in 11 of them it was possible to confirm a PMWS diagnosis through the association of specific lesions in lymphoid tissues with the presence of the viral antigen detected by immunohistochemistry. These findings were similar to those reported in the swine disease.

Spontaneous poisoning by larvae of Perreyia flavipes (Pergidae) in sheep

From a flock of 175 Texel sheep 25 animals died after consumption of a sawfly larvae subsequently identified as Perreyia flavipes. The disease occurred in June-July 2006 on a farm located in the county of Encruzilhada do Sul, Rio Grande do Sul, Brazil. Although there were 11 cattle in the same paddock, none of them was affected. High numbers of compact masses containing up to 150 larvae were scattered in the paddock where the animals were grazing. Most affected sheep showed severe apathy during 24-36 h before death, but weakness, muscular tremors and depression were also observed. Necropsy was performed on six sheep and the main macroscopic lesions were hemorrhages in the subcutaneous tissues, endocardium, gallbladder wall, and abomasal mucosa. In all animals was found hydrothorax, hydropericardium, ascites, and mild jaundice. Edema in the abomasal folds, mesentery, perirenal tissues, and gallbladder wall were also seen. The livers were yellowish with disseminated pinpoint hemorrhages in the parenchyma and had an enhanced lobular pattern. Perreyia flavipes larval body fragments and heads were found in the forestomach contents of the six sheep. Feces were scant, dry and formed balls coated by mucus and streaks of blood. Similar contents were also present at the end of the cecum. Prominent microscopic lesions included severe and diffuse periacinar or massive necrosis of hepatocytes associated with multifocal random hemorrhages. Diffuse necrosis of lymphoid follicles in lymph nodes and Peyer's patches, lymphoid depletion and necrosis in germinative centers of the spleen, and diffuse vacuolization in the renal tubular epithelia were also seen.

Sawfly larval poisoning in cattle: Report on new outbreaks and brief review of the literature

Sawfly larval poisoning (SLP) is an acute hepatotoxicosis documented in livestock in Australia, Denmark and in countries of South America. It is caused by the ingestion of the larval stage of insects of the suborder Symphyta, order Hymenoptera, commonly known as "sawfly". Three species of sawfly are reportedly involved in the toxicosis. The insect involved in Australian SLP is Lophyrotoma interrupta (Pergidae), in Denmark the cause of SLP is the ingestion of the larvae Arge pullata (Argidae), and in South American countries documented outbreaks of SLP were caused by the ingestion of yet another sawfly, Perreyia flavipes (Pergidae). In all geographical areas where it occurred, SLP causes important livestock losses. In cattle, as well as in other affected species, the disease has a short clinical course and in many outbreaks affected cattle can be found dead. When observed, clinical signs include apathy, recumbence, tremors, paddling movements and death in 24-48 hours. Neurological signs such aggressiveness attributable to hepatic encephalopathy are also observed. In cases with a more protracted course icterus and photodermatitis may develop. Gross findings included ascites, petechiae and ecchymosis over serosal surfaces of thoracic and abdominal cavities, and an enlarged liver that displays accentuation of the lobular pattern and edema of the gall bladder wall. Sawfly larval body fragments and heads are consistently found in the fore stomachs and occasionally abomasum of affected cattle. Main microscopic lesions are restricted to the liver and consist of centrolobular (periacinar) to massive hepatocellular necrosis. In most lobules necrotic areas extended up to the portal triads where only a few viable hepatocytes remain. Mild to moderate lymphocyte necrosis is seen in lymphatic tissues. Cases occur in the winter months when the larval stages of the sawfly are developing. D-amino acid-containing peptides have been found to be the toxic principle in each sawfly involved in SLP. The octapeptide lophyrotomin is the major toxin in the in the larvae of Australian and Danish sawflies and is present in small amounts in the larvae of South American sawfly. The heptadecapeptide pergidin is the main toxin in the South American sawfly while small amounts of pergidin have been found in the other two species of toxic sawfly. During the winter of 2011 (July-August) four outbreaks of SLP were diagnosed in the State of Rio Grande do Sul, Brazil. The findings in those outbreaks are reported here and a brief review of the literature regarding SLP around the world is provided.

Clinical and pathological aspects of chronic Senecio spp. poisoning in sheep

This paper describes an outbreak of chronic Senecio spp. poisoning in grazing sheep in Rio Grande do Sul, Brazil, causing the death of 10 out of 860 adult sheep. Eight sick ewes were euthanized and necropsied. Cattle from this farm were also affected. Clinical signs included progressive weight loss, apathy and photosensitization. Four out of seven tested sheep had increased gamma-glutamyl transferase serum activity and two of them presented serum elevation of alkaline phosphatase. At necropsy, three out of eight ewes presented slightly irregular toughened livers with multifocal nodules, two out of eight ewes had a whitish liver with thickened fibrotic Glisson's capsule partially adhered to the diaphragm, and three out of eight ewes had smooth and grossly normal livers. Necropsy findings attributed to liver failure included hydropericardium (7/8), ascites (5/8), icterus (2/8), hydrothorax (1/8), and edema of mesentery (1/8). The main hepatic histological findings that allowed the establishment of the diagnosis were megalocytosis, proliferation of bile ducts and fibrosis. Spongy degeneration was observed in the brains of all eight necropsied sheep and was more severe at the cerebellar peduncles, mesencephalon, thalamus, and pons. These are suggested as the portions of election to investigate microscopic lesions of hepatic encephalopathy in sheep with chronic seneciosis. The diagnosis of Senecio spp. poisoning was based on epidemiology, clinical signs, laboratory data, necropsy and histological findings.

Immunodetection of myeloid and plasmacytoid dendritic cells in mammary carcinomas of female dogs

ABSTRACT: Dendritic cells have attracted great interest from researchers as they may be used as targets of tumor immune evasion mechanisms. The main objective of this study was to evaluate the relationship between the dendritic cells (DCs) subpopulation in simple type mammary carcinomas in female dogs. Two groups of samples were used: the control group consisted of 18 samples of mammary tissue without changes and the tumor group with 26 simple type mammary carcinomas. In these groups, we evaluated the immunodetection of immature and mature myeloid DCs, plasmacytoid DCs and MHC-II. In mammary tumor, mature myeloid DCs predominated in the peritumoral region, while immature myeloid DCs and plasmacytoid DCs were evident in the intratumoral region. Immunostaining of MHC-II was visualized in mammary acini (control group), in tumor cells and inflammatory infiltration associated with tumors. The comparison between the control and tumor groups showed a statistically significant difference between immature myeloid DCs, mature myeloid DCs and plasmacytoid DCs. The immunodetection of MHC-II was not significant when comparing the groups. The predominance of immature DCs in the tumor group is possibly related to an inefficient immune response, promoting the development and survival of tumor cells. The presence of plasmacytoid DCs in the same group suggests a worse prognosis for female dogs with mammary tumors. Therefore, the ability of differentiation of canine dendritic cells could be influenced by neoplastic cells and by the tumor microenvironment.

Fibronectin in the ascitic fluid of cirrhotic patients: correlation with biochemical risk factors for the development of spontaneous bacterial peritonitis

Cirrhotic patients (23 with alcoholic cirrhosis, 5 with posthepatitic cirrhosis and 2 with cryptogenic cirrhosis) with ascites and portal hypertension were studied and divided into two groups corresponding to high or low risk to develop spontaneous bacterial peritonitis (SBP) related to the concentration of total protein in the ascitic fluid (A-TP): group I (high risk): A-TP£1.5 g/dl and group II (low risk): A-TP>1.5 g/dl. Fibronectin (FN), C3 and C4 concentrations were measured by radial immunodiffusion while total protein was measured by the biuret method. The mean values (group I vs group II) of C3 (12.59 ± 4.72 vs 24.53 ± 15.58 mg/dl), C4 (4.26 ± 3.87 vs 7.26 ± 4.14 mg/dl) and FN (50.47 ± 12.49 vs 75.89 ± 24.70 mg/dl) in the ascitic fluid were significantly lower (P<0.05) in the group considered to be at high risk for SBP. No significant difference was observed in the plasma/ascites fibronectin ratio (3.91 ± 1.21 vs 3.80 ± 1.26) or gradient (131.46 ± 64.01 vs 196.96 ± 57.38) between groups. Fibronectin in ascites was significantly correlated to C3 (r = 0.76), C4 (r = 0.58), total protein (r = 0.73) and plasma FN (r = 0.58) (P<0.05). The data suggest that the FN concentration in ascites is related to the opsonic capacity of this fluid, and that its concentration in the ascitic fluid may be a biochemical risk factor indicator for the development of spontaneous bacterial peritonitis

The conveyor belt hypothesis for thymocyte migration: participation of adhesion and de-adhesion molecules

Thymocyte differentiation is the process by which bone marrow-derived precursors enter the thymus, proliferate, rearrange the genes and express the corresponding T cell receptors, and undergo positive and/or negative selection, ultimately yielding mature T cells that will represent the so-called T cell repertoire. This process occurs in the context of cell migration, whose cellular and molecular basis is still poorly understood. Kinetic studies favor the idea that these cells leave the organ in an ordered pattern, as if they were moving on a conveyor belt. We have recently proposed that extracellular matrix glycoproteins, such as fibronectin, laminin and type IV collagen, among others, produced by non-lymphoid cells both in the cortex and in the medulla, would constitute a macromolecular arrangement allowing differentiating thymocytes to migrate. Here we discuss the participation of both molecules with adhesive and de-adhesive properties in the intrathymic T cell migration. Functional experiments demonstrated that galectin-3, a soluble ß-galactoside-binding lectin secreted by thymic microenvironmental cells, is a likely candidate for de-adhesion proteins by decreasing thymocyte interaction with the thymic microenvironment.