Spatial Immunology in Liver Metastases from Colorectal Carcinoma according to the Histologic Growth Pattern

Simple Summary

In the era of immunotherapy, the tumor microenvironment (TME) has attracted special interest. However, colorectal liver metastases (CRC-LM) present histological peculiarities that could affect the interaction of immune and tumor cells such as fibrotic encapsulation and dense intratumoral stroma. We explored the spatial distribution of lymphocytic infiltrates in CRC-LM in the context of the histologic growth patterns using multispectral digital pathology providing data on three different scenarios, tumor periphery, invasive margin, and central tumoral areas. Our results illustrate a similar poor cell density of CD8⁺ cells between different metastases subtypes in intratumoral regions. However, in encapsulated metastases, cytotoxic cells reach the tumor cells while remaining retained in stromal areas in non-encapsulating metastases. Some aspects are still unresolved, such as understanding the reason why most lymphocytes are largely retained in the capsule.

Abstract

Colorectal cancer liver metastases (CRC-LM) present differential histologic growth patterns (HGP) that determine the interaction between immune and tumor cells. We explored the spatial distribution of lymphocytic infiltrates in CRC-LM in the context of the HGP using multispectral digital pathology. We did not find statistically significant differences of immune cell densities in the central regions of desmoplastic (_dHGP) and non-desmoplastic (_ndHGP) metastases. The spatial evaluation reported that _dHGP-metastases displayed higher infiltration by CD8⁺ and CD20⁺ cells in peripheral regions as well as CD4⁺ and CD45RO⁺ cells in _ndHGP-metastases. However, the reactive stroma regions at the invasive margin (IM) of _ndHGP-metastases displayed higher density of CD4⁺, CD20⁺, and CD45RO⁺ cells. The antitumor status of the TIL infiltrates measured as CD8/CD4 reported higher values in the IM of encapsulated metastases up to 400 μm towards the tumor center (p < 0.05). Remarkably, the IM of _dHGP-metastases was characterized by higher infiltration of CD8⁺ cells in the epithelial compartment parameter assessed with the ratio CD8^epithelial/CD8^stromal, suggesting anti-tumoral activity in the encapsulating lesions. Taking together, the amount of CD8⁺ cells is comparable in the IM of both HGP metastases types. However, in _dHGP-metastases some cytotoxic cells reach the tumor nests while remaining retained in the stromal areas in _ndHGP-metastases.

The Tumor Microenvironment in Liver Metastases from Colorectal Carcinoma in the Context of the Histologic Growth Patterns

Colorectal carcinoma (CRC) is the third most common cancer. Likewise, it is a disease that has a long survival if it is prematurely detected. However, more than 50% of patients will develop metastases, mainly in the liver (LM-CRC), throughout the evolution of their disease, which accounts for most CRC-related deaths. Treatment it is certainly a controversial issue, since it has not been shown to increase overall survival in the adjuvant setting, although it does improve disease free survival (DFS). Moreover, current chemotherapy combinations are administered based on data extrapolated from primary tumors (PT), not considering that LM-CRC present a very particular tumor microenvironment that can radically condition the effectiveness of treatments designed for a PT. The liver has a particular histology and microenvironment that can determine tumor growth and response to treatments: double blood supply, vascularization through fenestrated sinusoids and the presence of different mesenchymal cell types, among other particularities. Likewise, the liver presents a peculiar immune response against tumor cells, a fact that correlates with the poor response to immunotherapy. All these aspects will be addressed in this review, putting them in the context of the histological growth patterns of LM-CRC, a particular pathologic feature with both prognostic and predictive repercussions.

Noncanonical TGFβ Pathway Relieves the Blockade of IL1β/TGFβ-Mediated Crosstalk between Tumor and Stroma: TGFBR1 and TAK1 Inhibition in Colorectal Cancer

PURPOSE

The aim of the study is blocking the recruitment of a protective stroma by altering the crosstalk between normal stromal cells and tumor cells for stripping tumors of the protection conferred by the microenvironment.

EXPERIMENTAL DESIGN

A transcriptomic analysis of cocultured normal colonic fibroblasts and colorectal tumor cells was performed. We focused on the study of molecules that mediate the communication between both compartments and that entail fibroblasts' activation and the alteration of the sensitivity to chemotherapy. We identified targets for the blocking of the tumor-stroma interaction. Finally, we tested, in vivo, the blockade of the tumor-stroma interaction in orthotopic models derived from patients and in models of acquired resistance to oxaliplatin.

RESULTS

IL1β/TGFβ1 are the triggers for fibroblasts' recruitment and conversion into carcinoma-associated fibroblasts (CAF) in colorectal cancer. CAFs then secrete proinflammatory factors that alter sensitivity in tumor cells, activating JAK/STAT and PI3KCA/AKT pathways. Blocking such crosstalk with a neutralizing IL1β antibody and a TGFBR1 inhibitor is relieved by the TAK1-mediated activation of the noncanonical TGFβ pathway, which induces a change in the cytokine/chemokine repertoire that maintains a sustained activation of AKT in tumor cells. TAK1 plus TGFBR1 inhibition blocks IL1β/TGFβ1-mediated fibroblast activation, decreasing the secretion of proinflammatory cytokines. In turn, tumor cells became more sensitive to chemotherapy. In vivo, the combination of a TAK1 inhibitor plus TGFBR1 inhibitor reduced the metastatic capacity of tumor cells and the recruitment of fibroblasts.

CONCLUSIONS

Our findings provide a translational rationale for the inhibition of TAK1 and TGFBR1 to remove the chemoprotection conferred by CAFs.

Prediction of pathological response to neoadjuvant treatment in rectal cancer with a two-protein immunohistochemical score derived from stromal gene-profiling

Background

Preoperative chemoradiotherapy followed by surgical mesorectal resection is the standard of care for locally advanced rectal carcinomas. Yet, predicting that patients will respond to treatment remains an unmet clinical challenge.

Experimental design

Using laser-capture microdissection we isolated RNA from stroma and tumour glands from prospective pre-treatment samples (n = 15). Transcriptomic profiles were obtained hybridising PrimeView Affymetrix arrays. We modelled a carcinoma-associated fibroblast-specific genes filtering data using GSE39396.

Results

The analysis of differentially expressed genes of stroma/tumour glands from responder and non-responder patients shows that most changes were associated with the stromal compartment; codifying mainly for extracellular matrix and ribosomal components. We built a carcinoma-associated fibroblast (CAF) specific classifier with genes showing changes in expression according to the tumour regression grade (FN1, COL3A1, COL1A1, MMP2 and IGFBP5). We assessed these five genes at the protein level by means of immunohistochemical staining in a patient's cohort (n = 38). For predictive purposes we used a leave-one-out cross-validated model with a positive predictive value (PPV) of 83.3%. Random Forest identified FN1 and COL3A1 as the best predictors. Rebuilding the leave-one-out cross-validated regression model improved the classification performance with a PPV of 93.3%. An independent cohort was used for classifier validation (n = 36), achieving a PPV of 88.2%. In a multivariate analysis, the two-protein classifier proved to be the only independent predictor of response.

Conclusion

We developed a two-protein immunohistochemical classifier that performs well at predicting the non-response to neoadjuvant treatment in rectal cancer.

Unsupervised analyses reveal molecular subtypes associated to prognosis and response to therapy in colorectal cancer

SUMMARY

Colorectal cancer (CRC) tumors are highly heterogeneous at a molecular level. Recent studies have proposed molecular classifications of intrinsic CRC molecular subtypes identified after applying unsupervised clustering methods to genome-wide data. Those subtypes, characterized by their distinct clinical and biological features, provide new insight about the complexity of CRC. A common finding shared by almost all analyses was the identification of microsatellite instable tumors as an independent cluster, which is associated to better prognosis. Clusters of tumors characterized by a high stromal component exhibited a poor outcome. Moreover, some of the clusters were associated with response to standard chemotherapy or targeted agents. Regarding biological functions underlying tumor subtypes, recurrent ones across different studies were WNT pathway activation, epithelial-to-mesenchymal transition or cancer stem cell-like phenotype. Now, the challenge is to translate these findings into a comprehensive CRC classification and characterization helpful for patients’ stratification and better clinical management.

A monotonic and prognostic genomic signature from fibroblasts for colorectal cancer initiation, progression, and metastasis

The differential gene expression patterns between normal colonic fibroblasts (NCF), carcinoma-associated fibroblasts from primary tumors (CAF-PT), and CAFs from hepatic metastasis (CAF-LM) are hypothesized to be useful for predicting relapse in primary tumors. A transcriptomic profile of NCF (n = 9), CAF-PT (n = 14), and CAF-LM (n = 11) was derived. Prediction Analysis of Microarrays (PAM) was used to obtain molecular details for each fibroblast class, and differentially expressed transcripts were used to classify patients according to recurrence status. A number of transcripts (n = 277) were common to all three types of fibroblasts and whose expression level was sequentially deregulated according to the transition: NCF→CAF-PT→CAF-LM. Importantly, the gene signature was able to accurately classify patients with primary tumors according to their prognosis. This capacity was exploited to obtain a refined 19-gene classifier that predicted recurrence with high accuracy in two independent datasets of patients with colorectal cancer and correlates with fibroblast migratory potential. The prognostic power of this genomic signature is strong evidence of the link between the tumor-stroma microenvironment and cancer progression. Furthermore, the 19-gene classifier was able to identify low-risk patients very accurately, which is of particular importance for stage II patients, who would benefit from the omission of chemotherapy, especially T4N0 patients, who are clinically classified as being at high risk.

IMPLICATIONS

A defined stromal gene expression signature predicts relapse in patients with colorectal cancer.

Differences between CAFs and their paired NCF from adjacent colonic mucosa reveal functional heterogeneity of CAFs, providing prognostic information

Little is known about the difference in gene expression between carcinoma-associated fibroblasts (CAFs) and paired normal colonic fibroblasts (NCFs) in colorectal cancer. Paired CAFs and NCFs were isolated from eight primary human colorectal carcinoma specimens. In culture conditions, soluble factors secreted by CAFs in the conditioned media increased clonogenicity and migration of epithelial cancer cells lines to a greater extent than did NCF. In vivo, CAFs were more competent as tumour growth enhancers than paired NCFs when co-inoculated with colorectal cell lines. Gene expression analysis of microarrays of CAF and paired NCF populations enabled us to identify 108 deregulated genes (38 upregulated and 70 downregulated genes). Most of those genes are fibroblast-specific. This has been validated in silico in dataset GSE39396 and by qPCR in selected genes. GSEA analysis revealed a differential transcriptomic profile of CAFs, mainly involving the Wnt signallingsignalling pathway, focal adhesion and cell cycle. Both deregulated genes and biological processes involved depicted a considerable degree of overlap with deregulated genes reported in breast, lung, oesophagus and prostate CAFs. These observations suggest that similar transcriptomic programs may be active in the transition from normal fibroblast in adjacent tissues to CAFs, independently of their anatomic demarcation. Additionally NCF already depicted an activated pattern associated with inflammation. The deregulated genes signature score seemed to correlate with CAF tumour promoter abilities in vitro, suggesting a high degree of heterogeneity between CAFs, and it has also prognostic value in two independent datasets. Further characterization of the roles these biomarkers play in cancer will reveal how CAFs provide cancer cells with a suitable microenvironment and may help in the development of new therapeutic targets for cancer treatment.

Aberrant gene expression in mucosa adjacent to tumor reveals a molecular crosstalk in colon cancer

Background

A colorectal tumor is not an isolated entity growing in a restricted location of the body. The patient’s gut environment constitutes the framework where the tumor evolves and this relationship promotes and includes a complex and tight correlation of the tumor with inflammation, blood vessels formation, nutrition, and gut microbiome composition. The tumor influence in the environment could both promote an anti-tumor or a pro-tumor response.

Methods

A set of 98 paired adjacent mucosa and tumor tissues from colorectal cancer (CRC) patients and 50 colon mucosa from healthy donors (246 samples in total) were included in this work. RNA extracted from each sample was hybridized in Affymetrix chips Human Genome U219. Functional relationships between genes were inferred by means of systems biology using both transcriptional regulation networks (ARACNe algorithm) and protein-protein interaction networks (BIANA software).

Results

Here we report a transcriptomic analysis revealing a number of genes activated in adjacent mucosa from CRC patients, not activated in mucosa from healthy donors. A functional analysis of these genes suggested that this active reaction of the adjacent mucosa was related to the presence of the tumor. Transcriptional and protein-interaction networks were used to further elucidate this response of normal gut in front of the tumor, revealing a crosstalk between proteins secreted by the tumor and receptors activated in the adjacent colon tissue; and vice versa. Remarkably, Slit family of proteins activated ROBO receptors in tumor whereas tumor-secreted proteins transduced a cellular signal finally activating AP-1 in adjacent tissue.

Conclusions

The systems-level approach provides new insights into the micro-ecology of colorectal tumorogenesis. Disrupting this intricate molecular network of cell-cell communication and pro-inflammatory microenvironment could be a therapeutic target in CRC patients.

Lurbinectedin (PM01183), a new DNA minor groove binder, inhibits growth of orthotopic primary graft of cisplatin-resistant epithelial ovarian cancer

PURPOSE

Epithelial ovarian cancer (EOC) is the fifth leading cause of death in women diagnosed with gynecologic malignancies. The low survival rate is because of its advanced-stage diagnosis and either intrinsic or acquired resistance to standard platinum-based chemotherapy. So, the development of effective innovative therapeutic strategies to overcome cisplatin resistance remains a high priority.

EXPERIMENTAL DESIGN

To investigate new treatments in in vivo models reproducing EOCs tumor growth, we generated a preclinical model of ovarian cancer after orthotopic implantation of a primary serous tumor in nude mice. Further, matched model of acquired cisplatin-resistant tumor version was successfully derived in mice. Effectiveness of lurbinectedin (PM01183) treatment, a novel marine-derived DNA minor groove covalent binder, was assessed in both preclinical models as a single and a combined-cisplatin agent.

RESULTS

Orthotopically perpetuated tumor grafts mimic the histopathological characteristics of primary patients' tumors and they also recapitulate in mice characteristic features of tumor response to cisplatin treatments. We showed that single lurbinectedin or cisplatin-combined therapies were effective in treating cisplatin-sensitive and cisplatin-resistant preclinical ovarian tumor models. Furthermore, the strongest in vivo synergistic effect was observed for combined treatments, especially in cisplatin-resistant tumors. Lurbinectedin tumor growth inhibition was associated with reduced proliferation, increased rate of aberrant mitosis, and subsequent induced apoptosis.

CONCLUSIONS

Taken together, preclinical orthotopic ovarian tumor grafts are useful tools for drug development, providing hard evidence that lurbinectedin might be a useful therapy in the treatment of EOC by overcoming cisplatin resistance.

Stromal interaction molecule 2 (STIM2) is frequently overexpressed in colorectal tumors and confers a tumor cell growth suppressor phenotype

Allelic imbalances at chromosome 4p have been largely documented in many different tumor types. In colorectal cancer, loss of heterozygosity (LOH) at 4p15 has been associated with tumor aggressiveness and poor patient outcome, however no target genes in the region have been identified to date. Since stromal interaction molecule 2 (STIM2) is located at 4p15.2 and has been proposed as a candidate gene for this region in glioblastoma multiforme, we aimed at investigating the role of STIM2 in colorectal cancer. We studied STIM2 transcript expression levels in a collection of xenografted primary colorectal tumors (n = 20) and a well-annotated tumor series of colorectal cancer (n = 140). We observed an overexpression of STIM2 in 63.5% of the cases that was associated with a less invasive phenotype. In vitro and in vivo functional studies with colon cancer cell lines revealed that overexpression of STIM2 reduced cell proliferation and tumor growth, respectively. Our work presents several lines of evidence indicating that STIM2 overexpression is a frequent trait in colorectal cancer that results in cell growth suppression, certifying that even in the absence of somatic genetic or epigenetic alterations, recurrent regions of LOH should still be considered a hallmark for the presence of relevant genes for tumorigenesis.

PRL-3 overexpression in epithelial cells is induced by surrounding stromal fibroblasts

We isolate and culture carcinoma-associated fibroblasts (CAFs) from primary tumour (CAFpt), CAFs from corresponding synchronous liver metastasis (CAFlm) as well as normal colonic fibroblasts (NCF) from the same patient. From these cultures, conditioned media (CM) was obtained. Culture of a wide panel of colorectal and pancreatic cell lines in CM from CAFlm resulted in overexpression of mRNA PRL-3 and higher overexpression in CAFs than in non-activated fibroblasts. Moreover PRL-3 mRNA expression correlates with expression of alpha-SMA and deposition of collagen fibrils in the stroma. We demonstrate that products secreted by CAFs trigger PRL-3 overexpression in cancer cells. Identification of these factors may contribute to new stroma-targeted therapies for desmoplastic tumours.

Bioselection of a gain of function mutation that enhances adenovirus 5 release and improves its antitumoral potency

Genetic bioselection of a mutagenized Ad5wt stock in human tumor xenografts led us to isolate AdT1, a mutant displaying a large-plaque phenotype in vitro and an enhanced systemic antitumor activity in vivo. AdT1 phenotype correlates with an increased progeny release without affecting total viral yield in different human tumors and cancer-associated fibroblasts. An approach combining hybrid Ad5/AdT1 recombinants and sequencing identified a truncating insertion in the endoplasmic reticulum retention domain of the E3/19K protein (445A mutation) which relocates the protein to the plasma membrane and is responsible for AdT1's enhanced release. E3/19K-445A phenotype does not correlate with the protein's ability to interact with MHC-I or induce apoptosis. Intracellular calcium measurement revealed that the 445A mutation induces extracellular Ca(2+) influx, deregulating intracellular Ca(2+) homeostasis and inducing membrane permeabilization, a viroporin-like function. E3/19K-445A mutants also display enhanced antitumoral activity when injected both intratumorally and systemically in different models in vivo. Our results indicate that the inclusion of mutation 445A in tumor-selective adenoviruses would be a very powerful tool to enhance their antitumor efficacy.

Mutations in TP53 are a prognostic factor in colorectal hepatic metastases undergoing surgical resection

The aim of this study was to analyze the prognostic value of TP53 mutations in a consecutive series of patients with hepatic metastases (HMs) from colorectal cancer undergoing surgical resection. Ninety-one patients with liver metastases from colorectal carcinoma were included. Mutational analysis of TP53, exons 4-10, was performed by single-strand conformation polymorphism and sequencing. P53 and P21 protein immunostaining was assessed. Multivariate Cox models were adjusted for gender, number of metastasis, resection margin, presence of TP53 mutations and chemotherapy treatment. Forty-six of 91 (50.05%) metastases showed mutations in TP53, observed mainly in exons 5-8, although 14.3% (n = 13) were located in exons 9 and 10. Forty percent (n = 22) were protein-truncating mutations. TP53 status associated with multiple (> or =3) metastases (65.6%, P = 0.033), advanced primary tumor Dukes' stage (P = 0.011) and younger age (<57 years old, P = 0.03). Presence of mutation associated with poor prognosis in univariate (P = 0.017) and multivariate Cox model [hazard ratio (HR) = 1.80, 95% confidence interval (CI) = 1.07-3.06, P = 0.028]. Prognostic value was maintained in patients undergoing radical resection (R0 series, n = 79, P = 0.014). Mutation associated with a worse outcome in chemotherapy-treated patients (HR = 2.54, 95% CI = 1.12-5.75, P = 0.026). The combination of > or =3 metastases and TP53 mutation identified a subset of patients with very poor prognosis (P = 0.009). P53 and P21 protein immunostaining did not show correlation with survival. TP53 mutational status seems to be an important prognostic factor in patients undergoing surgical resection of colorectal cancer HMs.

Hemostatic status in long-term surviving xenografts

BACKGROUND

Liver xenotransplantation presents, apart from immunologic problems, metabolic incompatibilities between species. The liver plays a key role in blood coagulation. The aim of this study is to describe the hemostatic status of long-term surviving xenografts in a hamster-to-rat liver xenotransplantation model.

METHODS

Orthotopic liver transplantation with Tacrolimus and MMF was carried out with Golden Syrian hamsters, Brown Norway, or Dark Agouti rats as donors and Lewis rats as recipients. Prothrombine time (PT), activated partial thromboplastin time (APTT), antithrombin, protein-C, free protein-S, TAT-complexes, and factors V and VIII were assessed using standard methods.

RESULTS

Protein-C was absent in rats, but values in xenotransplanted animals increased progressively toward those recorded in hamsters. Xenotransplanted animals also acquired PT, APTT, free protein-S, and antithrombin levels similar to those of donors and we observed a substantial activation of coagulation especially 7 days post-transplantation. Despite TAT high levels, we did not find thrombotic alterations in the histologic analysis of grafts.

CONCLUSIONS

These results reflect a destabilization of the thrombotic-hemostatic balance, not associated with consumption coagulopathy, which gradually disappears. This deregulation is a general imbalance resulting from the replacement of all the components of hepatic synthesis. After 100 days of xenotransplantation, the absence of symptoms of thrombosis or hemorrhage suggests that the change of hemostatic status takes place under conditions of relative equilibrium.

Tumor thymidylate synthase 1494del6 genotype as a prognostic factor in colorectal cancer patients receiving fluorouracil-based adjuvant treatment

PURPOSE

The purpose of this study was to analyze the value of germline and tumor thymidylate synthase (TS) genotyping as a prognostic marker in a series of colorectal cancer patients receiving adjuvant fluorouracil (FU) -based treatment.

PATIENTS AND METHODS

One hundred twenty-nine colorectal cancer patients homogeneously treated with FU plus levamisole or leucovorin in the adjuvant setting were included. TS enhancer region, 3R G > C single nucleotide polymorphism (SNP), and TS 1494del6 polymorphisms were assessed in both fresh-frozen normal mucosa and tumor. Mutational analyses of TS and allelic imbalances were studied in all primary tumors and in 18 additional metachronic metastases. TS protein immunostaining was assessed in an expanded series of 214 tumors. Multivariate Cox models were adjusted for stage, differentiation, and location.

RESULTS

Tumor genotyping (frequency of allelic loss, 26%) showed that the 3R/3R genotype was associated with a better outcome (hazard ratio [HR] = 0.38; 95% CI, 0.16 to 0.93; P = .020 for the recessive model). 3R G > C SNP genotyping did not add prognostic information. Tumor TS 1494del6 allele (frequency of allelic loss, 36%) was protective (for each allele with the deletion, based on an additive model, HR = 0.42; 95% CI, 0.22 to 0.82; P = .0034). Both polymorphisms were in strong linkage disequilibrium (D' = 0.71, P < .001), and the 3R/-6 base pair (bp) haplotype showed a significant overall survival benefit compared with the most prevalent haplotype 2R/+6bp (HR = 0.42; 95% CI, 0.20 to 0.85; P = .017). No TS point mutation was detected in primary tumors or metastases. TS protein immunostaining was not associated with survival or any of the genotypes analyzed.

CONCLUSION

Tumor TS 1494del6 genotype may be a prognostic factor in FU-based adjuvant treatment of colorectal cancer patients.

Lymphocyte populations in Parkinson's disease and in rat models of parkinsonism

To assess the involvement of the immune system in Parkinson's disease we studied the phenotype of circulating lymphocytes in 30 untreated and 34 treated patients. We found a numeric decrease in helper T cells (higher in CD4(+)CD45RA(+) than in CD4(+)CD29(+)) and B cells, and a rise in activated, CD4(+)CD25(+) lymphocytes that was correlated with lymphocyte depletion. All these alterations were independent of levodopa treatment. In addition, we performed striatal dopamine depletion in rats with either MPP(+) or 6-OHDA, showing that MPP(+) but not 6-OHDA can increase CD4(+)CD25(+) lymphocytes. Thus, mechanisms other than dopamine deficit may explain the immune activation in Parkinson's disease.

Heart and liver xenotransplantation under low-dose tacrolimus: graft survival after withdrawal of immunosuppression

BACKGROUND

The hamster-to-rat xenotransplantation model is a useful model to investigate the features of extended host response to long-surviving xenografts. Early xenoantibody responses are T-cell independent and resistant to tacrolimus. Treatment with the combination of mofetil mycophenolate plus FK506 avoids acute xenograft rejection completely, but after withdrawal of immunosuppression hamster grafts are rejected by a process called late xenograft rejection (LXR).

METHODS

Hamster hearts and livers were transplanted into Lewis rats. Grafted rats were treated with mofetil mycophenolate (25 mg/kg/day) for 8 days and FK506 (0.2 mg/kg/day) for 31 days. Serum IgM and IgG levels were determined by flow cytometry and interferon-gamma levels by ELISA. IgM, IgG, and C3 deposits were measured in tissue by immunofluorescence, and leukocyte infiltration was measured by immunoperoxidase staining. Results. Survival of heart and liver xenografts in the rats was 48+/-4 days and 63+/-8 days, respectively. After cessation of all immunosuppression, hearts were rejected in 18+/-4 days and livers in 33+/-8 days. Production sequences of xenoantibodies in the two organs differed substantially, especially 7 days after transplantation and at the moment of rejection. Quantification of interferon-gamma levels indicated that there were no significant changes after transplantation. Histological and immunohistochemical studies showed signs of humoral mechanism of LXR in rats undergoing heart transplantation and cellular mechanism of LXR in those that received a liver transplant. Conclusions. These observations suggest that rejection in the hamster-to-rat heart xenotransplantation model is mediated by a T cell-independent B-cell response to which a T cell-dependent B-cell response is added in LXR. In the liver xenotransplantation model, our hypothesis is that LXR is mediated by a mixed cell mechanism, involving lymphocytes CD4+ CD45RC+, macrophages, and cytotoxic T lymphocytes. In summary, we have demonstrated and compared the peculiar features of LXR in two different organs.

Liver xenotransplantation: changes in lipid and lipoprotein concentration after long-term graft survival

BACKGROUND/AIMS

Today, scientists devote considerable effort to the study of mechanisms of xenograft rejection, but with liver xenotransplantation (XTx) researchers face the added problem of metabolic incompatibility between species. To date, there have been few studies of molecular xenogeneic interactions, perhaps because little progress has been made in solving immunological problems. This study is an initial analysis of lipoprotein metabolism in a hamster-to-rat hepatic xenotransplantation model.

METHODS

There were 6 experimental groups (n=8): (1) male Sprague-Dawley (S.D.) rats (220-280 g); (2) male Golden Syrian hamsters (100-150 g); (3) S.D. rats, "sham" operation with immunosuppression; (4) S.D. rat-to-S.D. rat alloTx; (5) S.D. rat-to-S.D. rat alloTx with immunosuppression; (6) XTx hamster G.S-to-S.D. rat with immunosuppression. Mofetil mycophenolate (25 mg/kg/d) was administered for 14 days and FK506 (0.2 mg/kg/d) for 45 days (groups 3, 5 and 6). After 24 h fasting, animals were sacrificed (day +50 postransplantation) and a complete lipoprotein profile was determined. Serum lipoproteins were subfractioned by ultracentrifugation in density gradient.

RESULTS

There was a large increase in serum lipid levels in xenografted rats compared with control rats and allografted rats. Xenografted rats presented a severely altered lipoprotein profile compared with normal rats. Surprisingly, the characterisation of lipoproteins in xenografted rats displayed the same composition as donor animals. Histological study did not show signs of alteration of the hepatic architecture.

CONCLUSIONS

Since the liver is the main solid organ co-ordinator of metabolic pathways, such as lipid metabolism, hepatic xenotransplantation makes changes in lipid concentrations in the recipient and also changes in lipid compositions of lipoproteins. Hepatic xenotransplantation is not a feasible solution given the organ's metabolic complexity.