Modified live vaccine strains of porcine reproductive and respiratory syndrome virus cause immune system dysregulation similar to wild strains

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) emerged about 30 years ago and continues to cause major economic losses in the pork industry. The lack of effective modified live vaccines (MLV) allows the pandemic to continue.

Background and objective

We have previously shown that wild strains of PRRSV affect the nascent T cell repertoire in the thymus, deplete T cell clones recognizing viral epitopes essential for neutralization, while triggering a chronic, robust, but ineffective antibody response. Therefore, we hypothesized that the current MLV are inappropriate because they cause similar damage and fail to prevent viral-induced dysregulation of adaptive immunity.

Methods

We tested three MLV strains to demonstrate that all have a comparable negative effect on thymocytes in vitro. Further in vivo studies compared the development of T cells in the thymus, peripheral lymphocytes, and antibody production in young piglets. These three MLV strains were used in a mixture to determine whether at least some of them behave similarly to the wild virus type 1 or type 2.

Results

Both the wild and MLV strains cause the same immune dysregulations. These include depletion of T-cell precursors, alteration of the TCR repertoire, necrobiosis at corticomedullary junctions, low body weight gain, decreased thymic cellularity, lack of virus-neutralizing antibodies, and production of non-neutralizing anti-PRRSV antibodies of different isotypes.

Discussion and conclusion

The results may explain why the use of current MLV in young animals may be ineffective and why their use may be potentially dangerous. Therefore, alternative vaccines, such as subunit or mRNA vaccines or improved MLV, are needed to control the PRRSV pandemic.

Spontaneous Regression of Swine Melanoma: The Role of Tumour-infiltrating T and NK Cells

BACKGROUND/AIM

Melanoma is a skin cancer without effective therapy, showing high immunogenicity and mostly partial spontaneous regression (SR). The exact mechanisms of SR are still not well understood; therefore, the use of animal melanoma models is necessary to unravel the immunological processes during SR.

MATERIALS AND METHODS

Skin melanoma samples (n=57) and peripheral blood samples (n=57) from the same animals were collected. Melanoma-bearing Libechov Minipigs (MeLiM) aged 3, 4, 6, 8, 10, 12, 20, and 32 weeks were used, and samples were analysed by flow cytometry for detection of immune cell subpopulations.

RESULTS

The proportion of CD3-CD8+ (NK) cells in melanoma samples was found to be higher compared to blood samples at 6-8 weeks of age and then at 12 weeks of age. The population of CD4+CD8+ (effector/memory T helper) cells and CD4-CD8+ (cytotoxic T and NK) cells was also increased in melanoma compared to blood samples in 10-32-week-old pigs. The proportion of CD4-CD8+ cells in melanoma samples, then augmented until the 32^nd week. On the contrary, the proportion of CD4+CD8- (naive T helper) cells was lower in melanoma samples versus blood samples in 6-32-week-old animals.

CONCLUSION

Cytotoxic T cells were the most abundant population of tumour infiltrating immune cells found in MeLiM melanomas of animals aged 10-32 weeks, probably causing the destruction of melanoma cells. Furthermore, the development of specific (adaptive) immune response represented mainly by cytotoxic T cells seems to be crucial for the successful SR of porcine melanoma.

Dysbiosis of skin microbiome and gut microbiome in melanoma progression

Background

The microbiome alterations are associated with cancer growth and may influence the immune system and response to therapy. Particularly, the gut microbiome has been recently shown to modulate response to melanoma immunotherapy. However, the role of the skin microbiome has not been well explored in the skin tumour microenvironment and the link between the gut microbiome and skin microbiome has not been investigated in melanoma progression. Therefore, the aim of the present study was to examine associations between dysbiosis in the skin and gut microbiome and the melanoma growth using MeLiM porcine model of melanoma progression and spontaneous regression.

Results

Parallel analysis of cutaneous microbiota and faecal microbiota of the same individuals was performed in 8 to 12 weeks old MeLiM piglets. The bacterial composition of samples was analysed by high throughput sequencing of the V4-V5 region of the 16S rRNA gene. A significant difference in microbiome diversity and richness between melanoma tissue and healthy skin and between the faecal microbiome of MeLiM piglets and control piglets were observed. Both Principal Coordinate Analysis and Non-metric multidimensional scaling revealed dissimilarities between different bacterial communities. Linear discriminant analysis effect size at the genus level determined different potential biomarkers in multiple bacterial communities. Lactobacillus, Clostridium sensu stricto 1 and Corynebacterium 1 were the most discriminately higher genera in the healthy skin microbiome, while Fusobacterium, Trueperella, Staphylococcus, Streptococcus and Bacteroides were discriminately abundant in melanoma tissue microbiome. Bacteroides, Fusobacterium and Escherichia-Shigella were associated with the faecal microbiota of MeLiM piglets. Potential functional pathways analysis based on the KEGG database indicated significant differences in the predicted profile metabolisms between the healthy skin microbiome and melanoma tissue microbiome. The faecal microbiome of MeLiM piglets was enriched by genes related to membrane transports pathways allowing for the increase of intestinal permeability and alteration of the intestinal mucosal barrier.

Conclusion

The associations between melanoma progression and dysbiosis in the skin microbiome as well as dysbiosis in the gut microbiome were identified. Results provide promising information for further studies on the local skin and gut microbiome involvement in melanoma progression and may support the development of new therapeutic approaches.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02458-5.

Melanoma-Bearing Libechov Minipig (MeLiM): The Unique Swine Model of Hereditary Metastatic Melanoma

National cancer databases document that melanoma is the most aggressive and deadly cutaneous malignancy with worldwide increasing incidence in the Caucasian population. Around 10% of melanomas occur in families. Several germline mutations were identified that might help to indicate individuals at risk for preventive interventions and early disease detection. More than 50% of sporadic melanomas carry mutations in Ras/Raf/mitogen-activated protein kinase (MAPK/MEK) pathway, which may represent aims of novel targeted therapies. Despite advances in targeted therapies and immunotherapies, the outcomes in metastatic tumor are still unsatisfactory. Here, we review animal models that help our understanding of melanoma development and treatment, including non-vertebrate, mouse, swine, and other mammal models, with an emphasis on those with spontaneously developing melanoma. Special attention is paid to the melanoma-bearing Libechov minipig (MeLiM). This original swine model of hereditary metastatic melanoma enables studying biological processes underlying melanoma progression, as well as spontaneous regression. Current histological, immunohistochemical, biochemical, genetic, hematological, immunological, and skin microbiome findings in the MeLiM model are summarized, together with development of new therapeutic approaches based on tumor devitalization. The ongoing study of molecular and immunological base of spontaneous regression in MeLiM model has potential to bring new knowledge of clinical importance.

Immunohistochemical Evidence of the Involvement of Natural Killer (CD161+) Cells in Spontaneous Regression of Lewis Rat Sarcoma

BACKGROUND/AIM

Spontaneous regression (SR) of tumours is a rare phenomenon not yet fully understood. The aim of this study was to investigate immune cells infiltrating progressive and SR tumours in a Lewis rat sarcoma model.

MATERIALS AND METHODS

Rats were subcutaneously inoculated with rat sarcoma R5-28 (clone C4) cells. Developing tumours were obtained on day 42 and cryosections were immunohistochemically processed for detection of immune cells.

RESULTS

A high density of granulocytes was found in the necrotic areas of both progressive and SR tumours. CD4⁺ cells and CD8⁺ cells were rare and sparsely dispersed in the tumour tissue without clear difference between the two types of tumours. On the contrary, CD161⁺ cells were abundant and evenly distributed in SR tumours, but these cells were very rare in progressive tumours.

CONCLUSION

Based on the differences in number and distribution of the immune cell subpopulations, we believe that natural killer (CD161⁺) cells play a major role in the destruction of cancer cells during SR of tumours in this Lewis rat model.

The role of αβ T-cells in spontaneous regression of melanoma tumors in swine

Using a porcine model, we describe Melanoma-Associated CD4⁺CD8^hi T-lymphocytes (MATL) in peripheral blood that increase during melanoma regression. These MATL possess the CD4⁺CD8^hi phenotype and they have their direct counterparts in Tumor Infiltrating Lymphocytes (TIL) isolated from melanoma loci. Both MATL and CD4⁺CD8^hi TIL have a similar expression of selected markers indicating that they represent effector/memory αβ T-cell subset. Moreover, although TIL also contain CD4^-CD8⁺ T-cells, only CD4⁺CD8^hi TIL expand during melanoma regression. Importantly, TIL isolated from different pigs and different melanoma loci among the same pig have similar composition of CD4/CD8 subsets, indicating that the composition of the MATL and TIL compartment is identical. Analysis of sorted cells from regressing pigs revealed a unique MATL subpopulation with mono-specific T-cell receptor that was further analyzed by sequencing. These results indicate that pigs regressing melanomas possess a characteristic population of recirculating T-cells playing a role in tumor control and regression.

Tissue Rebuilding During Spontaneous Regression of Melanoma in the Melanoma-bearing Libechov Minipig

BACKGROUND/AIM

Melanoma is a cancer disease with increasing incidence in the Caucasian population. It is often accompanied by spontaneous regression (SR), probably due to high immunogenicity. Understanding of this phenomenon could allow its induction in clinical practice, but detailed study in humans is impossible for ethical reasons. The aim of this study was to determine the role of fibronectin, tenascin C, and MMP-2 in the process of SR.

MATERIALS AND METHODS

Time-lapse study of SR was performed in the MeLiM (Melanoma-bearing Libechov Minipig) model. Skin melanomas were taken from 3 weeks to 8 months of age and immunohistochemically processed for fibronectin, tenascin C and matrix metalloproteinase-2 (MMP-2).

RESULTS

Expression of all studied proteins increased up to the 10th week of age. Two structurally different areas were distinguishable from the 3rd month of age. MPP-2 expression predominated in areas with melanoma cells, whereas fibronectin and tenascin-C prevailed in the forming fibrous tissue.

CONCLUSION

Rebuilding of melanoma into the fibrous tissue during SR was connected with a general rise in fibronectin and tenascin C expression.

MALDI MSI of MeLiM melanoma: Searching for differences in protein profiles

Background

Treatment of advanced cutaneous melanoma remains challenging, and new data on melanoma biology are required. The most widely accepted criteria for the prognostic evaluation of melanoma are histopathological and clinical parameters, and the identification of additional tumor markers is thus of paramount importance. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI), an important tool in cancer research, is useful for unraveling the molecular profile of melanoma.

Methodology/Principal findings

In this report, we used the melanoma-bearing Libechov minipig (MeLiM), a unique animal model that allows observation of the complete spontaneous regression of invasive cutaneous melanoma, to investigate i) the differences between melanoma and healthy skin protein profiles and ii) the proteins potentially involved in spontaneous regression. The MeLiM tissues were cryosected, histologically characterized, analyzed by MALDI MSI, and immunohistologically stained. Multivariate statistical analyses of the MALDI MSI data revealed ten relevant m/z ions, of which the expression levels varied significantly among the studied MeLiM tissues. These ion peaks were used to create mass ion images/maps and visualize the differences between tumor and healthy skin specimens, as well as among histologically characterized tissue regions.

Conclusions/Significance

Protein profiles comprising ten statistically significant mass ion peaks useful for differentiating cutaneous melanoma and healthy skin tissues were determined. Peaks at m/z 3044, 6011, 6140 and 10180 were overexpressed in melanoma compared with healthy skin tissue. More specifically, m/z 6140 was expressed at significantly (p < 0.05) higher levels in normally growing melanoma regions than in regions with early and late spontaneous regression. This study demonstrates the clinical utility of MALDI MSI for the analysis of tissue cryosections at a molecular level.

Immunohistochemical Analysis of Collagen IV and Laminin Expression in Spontaneous Melanoma Regression in the Melanoma-Bearing Libechov Minipig

Spontaneous regression (SR) of human melanoma is a rare, well-documented phenomenon that is not still fully understood. Its detailed study cannot be performed in patients due to ethical reasons. Using the Melanoma-bearing Libechov Minipig (MeLiM) animals of various ages (from 3 weeks to 8 months) we implemented a long-term monitoring of melanoma growth and SR. We focused on immunohistochemical detection of two important extracellular matrix proteins, collagen IV and laminin, which are associated with cancer. We showed that SR of melanoma is a highly dynamic process. The expression of collagen IV and laminin correlated with changes in population of melanoma cells. Tumours of 3-week-old animals consisted primarily of melanoma cells with a granular expression of collagen IV and laminin around them. Thereafter, melanoma cells were gradually destroyed and tumour tissue was rebuilt into the connective tissue. Collagen IV expression slightly increased in tumours of 10-week-old pigs showing extracellular fibrous appearance. In tumours of older animals, areas lacking melanoma cells demonstrated a low expression and areas still containing melanoma cells a high expression of both proteins. We considered the age of 10 weeks as a turning point in the transition between tumour growth and SR of the MeLiM melanoma.

Tumor progression is associated with increasing CD11b+ cells and CCL2 in Lewis rat sarcoma

Tumor models are essential for basic anticancer research and development of novel therapies. In this study, we used a rat sarcoma model in which subcutaneous tumor develops after D6 cell inoculation. The aim of the current study was to analyze changes in haematological parameters, immune cell sub-populations and cytokine profiling during tumor growth, after tumor excision and after second inoculation of D6 cells. Tumor progression was found to be associated with an increased number of leukocytes and increased proportion of CD11b+ cells in peripheral blood. Serum concentration of chemokine (c-c motif) ligand 2, L-selectin and intra cellular adhesion molecule-1 also increased with growing tumor. However, the proportion of CD4+, CD8+ and MHC II+ cells decreased with growth of tumors. After tumor excision, all these parameters returned to pre-inoculation levels and did not change even after a second inoculation of D6 cells. Moreover, absence of secondary tumors after second inoculation of D6 cells gives an insight into development of antitumor immunity stimulated by primary tumor.

Immunostimulatory properties and antitumor activities of glucans (Review)

New foods and natural biological modulators have recently become of scientific interest in the investigation of the value of traditional medical therapeutics. Glucans have an important part in this renewed interest. These fungal wall components are claimed to be useful for various medical purposes and they are obtained from medicinal mushrooms commonly used in traditional Oriental medicine. The immunotherapeutic properties of fungi extracts have been reported, including the enhancement of anticancer immunity responses. These properties are principally related to the stimulation of cells of the innate immune system. The discovery of specific receptors for glucans on dendritic cells (dectin-1), as well as interactions with other receptors, mainly expressed by innate immune cells (e.g., Toll-like receptors, complement receptor-3), have raised new attention toward these products as suitable therapeutic agents. We briefly review the characteristics of the glucans from mycelial walls as modulators of the immunity and their possible use as antitumor treatments.

Characterization of three newly established rat sarcoma cell clones

Establishment of new animal models using selected cell lines with different behaviour is very important for cancer investigations. In this study, we describe three morphologically distinct rat sarcoma clones-C4, C7 and D6-isolated from the R5-28 cell line. Cells of all clones expressed vimentin, fibronectin, laminin, collagen IV and matrix metalloproteinases 2 and 9. However, desmin, cytokeratins 8 and 18, ZO-1 and desmoplakins I and II were not detected. Significant proliferative capacity was documented by proliferating cell nuclear antigen expression and BrdU positivity. Karyotype of the C4, C7 and D6 cells greatly differed from diploid chromosome number of normal rat somatic cells. High expression of three cytokines-monocyte chemoattractant protein 1, tissue inhibitor of metalloproteinases 1 and vascular endothelial growth factor-was observed in all three clones. However, they varied in concentration of chemokines associated with neutrophil migration and activation-cytokine induced neutrophil chemoattractant 2 and lipopolysaccharide induced CXC chemokine. The C4 clone showed spontaneous tumour regression in vivo that was associated with significant changes in lymphocyte subpopulations.

Identification of differentially expressed genes in spontaneously regressing melanoma using the MeLiM swine model

Partial and some few cases of complete spontaneous regression have been observed in cutaneous melanoma patients but little is known about the molecular mechanisms involved. The Melanoblastoma-bearing Libechov Minipig (MeLiM) is a suitable animal model to study the phenomenon of spontaneous regression because MeLiM pigs exhibit naturally occurring melanomas which regress completely 6 months after birth. In this study, we used suppression subtractive hybridization (SSH) to identify molecular determinants of melanoma regression within swine melanoma tissues and melanoma cell cultures. Several markers involved in cell-adhesion, -communication, -motility, signal transduction, negative regulation of cell proliferation, transport and immune response were identified that correlated with melanoma regression whereas the main genes involved in melanin synthesis showed a strong downregulation. For the most differentially expressed genes, we validated the results obtained by SSH with qRT-PCR and with immunohistochemistry for some of them (CD9, MITF, RARRES1). Most notable, for the first time in melanoma, we identified the retinoic acid responder 1 gene (RARRES1) as a main actor of the regression process in melanoma. This first gene expression study in swine melanoma regression, may contribute to the finding of new therapeutic targets for human melanoma treatment.

Utilizing of Adsorptive Transfer Stripping Technique Brdicka Reaction for Determination of Metallothioneins Level in Melanoma Cells, Blood Serum and Tissues

In the paper we utilized the adsorptive transfer stripping differential pulse voltammetry Brdicka reaction for the determination of metallothioneins (MT) in melanoma cells, animal melanoma tissues (MeLiM miniature pig) and blood serum of patients with malignant melanoma. Primarily we attempted to investigate the influence of dilution of real sample on MT electrochemical response. Dilution of samples of 1 000 times was chosen the most suitable for determination of MT level in biological samples. Then we quantified the MT level in the melanoma cells, the animal melanoma tissues and the blood serum samples. The MT content in the cells varied within the range from 4.2 to 11.2 μM. At animal melanoma tissues (melanomas localized on abdomen, back limb and dorsum) the highest content of MT was determined in the tumour sampled on the back of the animal and was nearly 500 μg of MTs per gram of a tissue. We also quantified content of MT in metastases, which was found in liver, spleen and lymph nodes. Moreover the average MT level in the blood serum samples from patients with melanoma was 3.0 ± 0.8 μM. MT levels determined at melanoma samples were significantly (p < 0.05) higher compared to control ones at cells, tissues and blood serum.

Transcription analysis in the MeLiM swine model identifies RACK1 as a potential marker of malignancy for human melanocytic proliferation

BACKGROUND

Metastatic melanoma is a severe disease. Few experimental animal models of metastatic melanoma exist. MeLiM minipigs exhibit spontaneous melanoma. Cutaneous and metastatic lesions are histologically similar to human's. However, most of them eventually spontaneously regress. Our purpose was to investigate whether the MeLiM model could reveal markers of malignancy in human melanocytic proliferations.

RESULTS

We compared the serial analysis of gene expression (SAGE) between normal pig skin melanocytes and melanoma cells from an early pulmonary metastasis of MeLiM minipigs. Tag identification revealed 55 regulated genes, including GNB2L1 which was found upregulated in the melanoma library. In situ hybridisation confirmed GNB2L1 overexpression in MeLiM melanocytic lesions. GNB2L1 encodes the adaptor protein RACK1, recently shown to influence melanoma cell lines tumorigenicity. We studied the expression of RACK1 by immunofluorescence and confocal microscopy in tissues specimens of normal skin, in cutaneous and metastatic melanoma developped in MeLiM minipigs and in human patients. In pig and human samples, the results were similar. RACK1 protein was not detected in normal epidermal melanocytes. By contrast, RACK1 signal was highly increased in the cytoplasm of all melanocytic cells of superficial spreading melanoma, recurrent dermal lesions and metastatic melanoma. RACK1 partially colocalised with activated PKCalphabeta. In pig metastases, additional nuclear RACK1 did not associate to BDNF expression. In human nevi, the RACK1 signal was low.

CONCLUSION

RACK1 overexpression detected in situ in human melanoma specimens characterized cutaneous and metastatic melanoma raising the possibility that RACK1 can be a potential marker of malignancy in human melanoma. The MeLiM strain provides a relevant model for exploring mechanisms of melanocytic malignant transformation in humans. This study may contribute to a better understanding of melanoma pathophysiology and to progress in diagnosis.

Treatment of recalcitrant venous leg ulcers with autologous keratinocytes in fibrin sealant: a multinational randomized controlled clinical trial

In a multicenter trial, the effect of a commercially available combination of autologous keratinocytes (3-6 x 10(6)/mL) with fibrin sealant (Tissucol Duo S Immuno, Baxter Hyland Immuno) on the healing of recalcitrant venous leg ulcers (duration >3 months) was compared with standard care. The primary endpoint was time to healing, and the secondary endpoint was number of healed ulcers in both groups. Both groups received compression therapy with short-stretch bandages. Forty-four (38.3%) of the 116 patients who had BioSeed-S treatment achieved complete healing of the target ulcer compared with 24 (22.4%) of 109 patients who received standard treatment. The advantage for treatment with BioSeed-S over standard treatment was statistically significant (chi-square test: p=0.0106). Time to complete healing of ulcers: the log-rank test for equality over strata revealed a superiority of treatment with BioSeed-S+compression (median: 176 days) over compression+standard care (median >201 days) (p<0.0001). This study, to date the largest multicenter study with autologous keratinocytes, provides evidence for its efficacy in the treatment of patients with therapy-resistant chronic venous leg ulcers.

Detection of novel quantitative trait loci for cutaneous melanoma by genome-wide scan in the MeLiM swine model

Human cutaneous melanoma is a complex trait inherited in about 10% of cases. Although 2 high-risk genes, CDKN2A and CDK4, and 1 low risk gene, MC1R, have been identified, susceptibility genes remain to be discovered. Here, we attempted to determine new genomic regions linked to melanoma using the pig MeLiM strain, which develops hereditary cutaneous melanomas. We applied quantitative trait loci (QTL) mapping method to a significant genome-wide scan performed on 331 backcross pigs derived from this strain. QTLs were detected at chromosome-wide level for a melanoma synthetic trait corresponding to the development of melanoma. The peak positions on Sus scrofa chromosomes (SSC) were at 49.4 and 88.0 cM (SSC1), 56.0 cM (SSC13), 86.5 cM (SSC15) and 39.8 cM (SSC17), and, on SSC2, at 16.9 cM, in families derived from F1 males only (p < 0.05, except for SSC13, p < 0.01). Analysis of 7 precise specific traits revealed highly significant QTLs on SSC10 (ulceration), on SSC12 (presence of melanoma at birth), on SSC13 (lesion type), and on SSC16 and SSC17 (number of aggressive melanomas) at the respective positions 42.0, 95.6, 81.0, 45.3 and 44.8 cM (p < 0.001 and p < 0.05 respectively at the chromosome- and genome-wide levels). We also showed that MeLiM MC1R*2 allele, which determines black coat colour in pigs, predisposes significantly to melanoma. Interactions were observed between MC1R and markers located on SSC1 (p < 0.05). Taken together, these results indicate that MeLiM swine is a model for human multigenic diseases. Comparative mapping revealed human regions of interest to search for new melanoma susceptibility candidates.

Clinical and histopathological characterization of cutaneous melanomas in the melanoblastoma-bearing Libechov minipig model

Spontaneous animal tumors appear to be highly suitable models to study human oncology and cancer therapy. The aim of this study was to characterize the clinical and histological features of hereditary melanocytic lesions found in the French herd of melanoblastoma-bearing Libechov minipigs (MeLiM) and their Duroc crossbreeds. Clinically, we discriminated between three types of melanocytic skin lesions, which offer a lesion continuum from lentigo to metastatic melanomas. More than 70% of these lesions appear on piglets before they are 3 months old and preferentially on homogeneous black coat piglets. The incidence of melanoma reaches 50% in MeLiM. Most of the highly invasive melanomas regressed spontaneously in the first year of the piglet's life and the regression was followed by hair, skin and iris depigmentation. A histopathological study was conducted according to the human melanoma classification. Except for lentigo maligna, we observed the three main types of human melanoma in swine [superficial spreading melanoma (SSM), nodular or unclassified melanoma] with an excess of SSM (59-67%). The histological events leading to total spontaneous regression are chronologically described. The genetic predisposition, the high incidence of melanoma, the clinical and histopathological features similar to the human disease and the high rate of spontaneous regression offer an opportunity to use this model for studying genetic events controlling melanoma development and regression and the biological mechanisms involved in oncogenesis and anti-cancerous self-defense.

Identification of five chromosomal regions involved in predisposition to melanoma by genome-wide scan in the MeLiM swine model

In human familial melanoma, 3 risk susceptibility genes are already known, CDKN2A, CDK4 and MC1R. However, various observations suggest that other melanoma susceptibility genes have not yet been identified. To search for new susceptibility loci, we used the MeLiM swine as an animal model of hereditary melanoma to perform a genome scan for linkage to melanoma. Founders of the affected MeLiM stock were crossed with each other and with healthy Duroc pigs, generating MeLiM, F1 and backcross families. As we had previously excluded the MeLiM CDKN2A gene, we paid special attention to CDK4 and MC1R, as well as to other candidates such as BRAF and the SLA complex, mapping them on the swine radiation hybrid map and/or isolating close microsatellite markers to introduce them into the genome scan. The results revealed, first, that swine melanoma was inherited as an autosomal dominant trait with incomplete penetrance, preferably in black animals. Second, 4 chromosomal regions potentially involved in melanoma susceptibility were identified on Sus Scrofa chromosomes (SSC) 1, 2, 7 and 8, respectively, in intervals 44-103, 1.9-18, 59-73 and 47-62 cM. A fifth region close to MC1R was revealed on SSC 6 by analyzing an individual marker located at position 7.5 cM. Lastly, CDK4 and BRAF were unlikely to be melanoma susceptibility genes in the MeLiM swine model. The 3 regions on SSC 1, 6 and 7, respectively, have counterparts on human chromosomes (HSA) 9p, 16q and 6p, harboring melanoma candidate loci. The 2 others, on SSC 2 and 8, have counterparts on HSA 11 and 4, which might therefore be of interest for human studies.

A new animal model for the imaging of melanoma: correlation of FDG PET with clinical outcome, macroscopic aspect and histological classification in Melanoblastoma-bearing Libechov Minipigs

The aim of this study was to evaluate the Melanoblastoma-bearing Libechov Minipigs (MeLiM) as an animal model of melanoma for in vivo imaging. Serial whole-body 2-deoxy-2-[(18)F]fluoro- d-glucose positron emission tomography (FDG PET) scans were conducted on five MeLiM. In order to explore different clinical stages of the tumoural lesions, each animal was scanned two to four times, at intervals of 30-155 days. PET images were analysed by a semiquantitative method based on the tumour to muscle metabolic ratio. Histology was performed on biopsies taken between or after the scans and the histological grading of the tumours was compared with the FDG uptake. The overall sensitivity of FDG PET for the detection of cutaneous melanoma was 75%; 62.5% of involved lymph nodes were positive. Sensitivity was better for tumours with vertical growth than for flat lesions. FDG PET did not detect tumours with epidermal involvement only, nor did it detect small metastatic foci. The metabolic ratio was correlated with the evolution of the melanoma. FDG PET is effective in the staging of cutaneous melanoma and the follow-up of tumoural extension and regression in Melanoblastoma-bearing Libechov Minipigs. The results obtained in this animal model correlate well with those described in human melanoma. Accordingly, this model may be useful in testing new tracers specific for melanoma and in helping to detect molecules expressed early during tumoural regression.

CDKN2A region polymorphism and genetic susceptibility to melanoma in the melim swine model of familial melanoma

Some herds of miniature swine are genetically predisposed to cutaneous melanoma. To test if swine melanoma susceptibility could be linked to the CDKN2A gene, which is involved in a proportion of 9p21-linked human familial melanoma, we performed a genetic analysis of miniature pigs of the MeLiM strain. F(1) and backcross animals were generated by crossing 1 MeLiM boar with healthy Duroc sows. We isolated the swine CDKN2A gene and characterized a linked informative microsatellite marker, the S0644 marker. Using this marker and 2 flanking markers, we analyzed the segregation of the CDKN2A gene in a 3-generation pedigree. Allelic association, linkage analysis and haplotype analysis of these data led to exclusion of the CDKN2A gene as a candidate for melanoma susceptibility. Nonetheless, this analysis suggests an association with the swine 1q25 chromosomal region, which is homologous to the human 9p21 region.

Opposite regulation of tenascin-C and tenascin-X in MeLiM swine heritable cutaneous malignant melanoma

Interactions between tumour cells and surrounding extracellular matrix (ECM) influence the growth of tumour cells and their ability to metastasise. It is thus interesting to compare ECM composition in tumours and healthy tissues. Using the recently described MeLiM miniature pig model of heritable cutaneous malignant melanoma, we studied the expression of two ECM glycoproteins, the tenascin-C (TN-C) and tenascin-X (TN-X), in normal skin and melanoma. Using semiquantitative RT-PCR, we observed a 3.6-fold mean increase of TN-C RNAs in melanoma compared to normal skin. Both stromal and tumour cells synthesise TN-C. On the contrary, TN-X RNAs decreased 30-fold on average in melanoma. This opposite regulation of TN-C and TN-X RNAs was confirmed at the protein level by indirect immunofluorescence. Whereas pig normal skin displayed a discrete TN-C signal at the dermo-epidermal junction, around blood vessels and hair bulbs, the swine tumour showed enhanced expression of TN-C in these areas and around stromal and tumour cells. In contrast, normal skin showed a strong TN-X staining at the dermo-epidermal junction and in the dermis, whereas this signal almost completely disappeared in the tumour. The results presented here describe a dramatic alteration of the ECM composition in swine malignant melanoma which might have a large influence on tumourigenesis or invasion and metastasis of melanoma cells.