MHC class I antigen processing pathway defects, ras mutations and disease stage in colorectal carcinoma

(R)Evolutionary therapy: the potential of immunotherapy to fulfill the promise of personalized cancer treatment

Since the millennium, personalized medicine has been at the forefront of therapeutic endeavors in medical oncology. The latest technology has given researchers the ability to define cancer at its molecular core. This has led to the development of "targeted therapies," designed to eliminate driver mutations while leaving healthy cells unscathed. Unfortunately, more than 10 years into the targeted molecular therapy era, successes have been infrequent, and toxicity remains largely unchanged compared with relatively indiscriminant, traditional chemotherapy. Emerging data suggests that the malignant clonal heterogeneity within solid tumors is so diverse that targeting one or even several mutations is likely to have minimal, transient impact. In recent years, new therapies have emerged that can effectively stimulate the immune system and improve survival in patients with metastatic disease. Through immune activation, there is the potential to target the cancer with a biologic diversity that can potentially rival the multiplicity of malignant mutations within tumors. Stimulating the immune system to become an evolving adversary against malignant cells may revolutionize cancer therapy in the years to come.

The prognostic impact of human leukocyte antigen (HLA) class I antigen abnormalities in salivary gland cancer. A clinicopathological study of 288 cases

AIMS

To study abnormalities of proteins of the major histocompatibility complex class I in a series of 288 salivary gland carcinomas, and to correlate findings with patients' overall survival (OS).

METHODS AND RESULTS

Protein expression of human leukocyte antigen (HLA)-A, heavy chain (HC)-10, β2 -microglobulin, low molecular weight polypeptides (LMP) 2 and 7, transporters associated with antigen processing (TAP) 1 and 2, calnexin, calreticulin, endoplasmic reticulum (ER) p57 and tapasin was evaluated by immunohistochemistry and semiquantitatively analyzed. As compared with normal salivary gland tissue, HLA-A, LMP7, TAP2 and HLA class I were significantly down-regulated in salivary gland carcinomas, whereas β2 -microglobulin, calnexin, LMP2, and TAP1 were upregulated. Expression of calreticulin, ERp57 and tapasin was unaltered. In univariate Kaplan-Meier analyses, low expression of LMP7 (P = 0.005) and high expression of β2 -microglobulin (P = 0.028), HLA-A (P < 0.001), TAP1 (P = 0.01), and tapasin (P < 0.001) were significantly associated with shorter OS. In multivariate analysis incorporating tumour stage, nodal/distant metastasis, and grade, HLA-A (P = 0.014), LMP7 (P = 0.033), and tapasin (P = 0.024), as well as distant metastasis (P = 0.012) and high tumour grade (P < 0.001), remained statistically significant.

CONCLUSION

The prognostic influence of up-regulated HLA-A and tapasin and down-regulated LMP7 may provide a rationale for targeting these specific components of the antigen processing and presentation pathway in salivary gland carcinomas.

Blocking oncogenic RAS enhances tumour cell surface MHC class I expression but does not alter susceptibility to cytotoxic lymphocytes

Mutations in the RAS family of oncogenes are highly prevalent in human cancer and, amongst its manifold effects, oncogenic RAS impairs the expression of components of the antigen presentation pathway. This allows evasion of cytotoxic T lymphocytes (CTL). CTL and natural killer (NK) cells are reciprocally regulated by MHC class I molecules and any gain in CTL recognition obtained by therapeutic inactivation of oncogenic RAS may be offset by reduced NK cell activation. We have investigated the consequences of targeted inactivation of oncogenic RAS on the recognition by both CTL and NK cells. Inactivation of oncogenic RAS, either by genetic deletion or inactivation with an inducible intracellular domain antibody (iDAb), increased MHC class I expression in human colorectal cell lines. The common RAS mutations, at codons 12, 13 and 61, all inhibited antigen presentation. Although MHC class I modulates the activity of both CTL and NK cells, the enhanced MHC class I expression resulting from inactivation of mutant KRAS did not significantly affect the in vitro recognition of these cell lines by either class of cytotoxic lymphocyte. These results show that oncogenic RAS and its downstream signalling pathways modulate the antigen presentation pathway and that this inhibition is reversible. However, the magnitude of these effects was not sufficient to alter the in vitro recognition of tumour cell lines by either CTL or NK cells.

Targeted re-sequencing identified rs3106189 at the 5' UTR of TAPBP and rs1052918 at the 3' UTR of TCF3 to be associated with the overall survival of colorectal cancer patients

Recent studies have demonstrated the power of deep re-sequencing of the whole genome or exome in understanding cancer genomes. However, targeted capture of selected genomic whole gene-body regions, rather than the whole exome, have several advantages: 1) the genes can be selected based on biology or a hypothesis; 2) mutations in promoter and intronic regions, which have important regulatory roles, can be investigated; and 3) less expensive than whole genome or whole exome sequencing. Therefore, we designed custom high-density oligonucleotide microarrays (NimbleGen Inc.) to capture approximately 1.7 Mb target regions comprising the genomic regions of 28 genes related to colorectal cancer including genes belonging to the WNT signaling pathway, as well as important transcription factors or colon-specific genes that are over expressed in colorectal cancer (CRC). The 1.7 Mb targeted regions were sequenced with a coverage ranged from 32× to 45× for the 28 genes. We identified a total of 2342 sequence variations in the CRC and corresponding adjacent normal tissues. Among them, 738 were novel sequence variations based on comparisons with the SNP database (dbSNP135). We validated 56 of 66 SNPs in a separate cohort of 30 CRC tissues using Sequenom MassARRAY iPLEX Platform, suggesting a validation rate of at least 85% (56/66). We found 15 missense mutations among the exonic variations, 21 synonymous SNPs that were predicted to change the exonic splicing motifs, 31 UTR SNPs that were predicted to occur at the transcription factor binding sites, 20 intronic SNPs located near the splicing sites, 43 SNPs in conserved transcription factor binding sites and 32 in CpG islands. Finally, we determined that rs3106189, localized to the 5′ UTR of antigen presenting tapasin binding protein (TAPBP), and rs1052918, localized to the 3′ UTR of transcription factor 3 (TCF3), were associated with overall survival of CRC patients.

MHC class I antigen processing and presenting machinery: organization, function, and defects in tumor cells

The surface presentation of peptides by major histocompatibility complex (MHC) class I molecules is critical to all CD8(+) T-cell adaptive immune responses, including those against tumors. The generation of peptides and their loading on MHC class I molecules is a multistep process involving multiple molecular species that constitute the so-called antigen processing and presenting machinery (APM). The majority of class I peptides begin as proteasome degradation products of cytosolic proteins. Once transported into the endoplasmic reticulum by TAP (transporter associated with antigen processing), peptides are not bound randomly by class I molecules but are chosen by length and sequence, with peptidases editing the raw peptide pool. Aberrations in APM genes and proteins have frequently been observed in human tumors and found to correlate with relevant clinical variables, including tumor grade, tumor stage, disease recurrence, and survival. These findings support the idea that APM defects are immune escape mechanisms that disrupt the tumor cells' ability to be recognized and killed by tumor antigen-specific cytotoxic CD8(+) T cells. Detailed knowledge of APM is crucial for the optimization of T cell-based immunotherapy protocols.

SHP2 is overexpressed and inhibits pSTAT1-mediated APM component expression, T-cell attracting chemokine secretion, and CTL recognition in head and neck cancer cells

PURPOSE

Human leukocyte antigen (HLA) class I antigen processing machinery (APM) component downregulation permits escape of malignant cells from recognition by cytotoxic T lymphocytes (CTL) and correlates with poor prognosis in patients with head and neck cancer (HNC). Activated STAT1 (pSTAT1) is necessary for APM component expression in HNC cells. We investigated whether an overexpressed phosphatase was responsible for basal suppression of pSTAT1 and subsequent APM component-mediated immune escape in HNC cells.

EXPERIMENTAL DESIGN

Immunohistochemical staining and reverse transcription PCR of paired HNC tumors was performed for the phosphatases src homology domain-containing phosphatase (SHP)-1 and SHP2. Depletion of phosphatase activity in HNC and STAT1(-/-) tumor cells was achieved by siRNA knockdown. HLA class I-restricted, tumor antigen-specific CTL were used in IFN-γ ELISPOT assays against HNC cells. Chemokine secretion was measured after SHP2 depletion in HNC cells.

RESULTS

SHP2, but not SHP1, was significantly upregulated in HNC tissues. In HNC cells, SHP2 depletion significantly upregulated expression of pSTAT1 and HLA class I APM components. Overexpression of SHP2 in nonmalignant keratinocytes inhibited IFN-γ-mediated STAT1 phosphorylation, and SHP2 depletion in STAT1(-/-) tumor cells did not significantly induce IFN-γ-mediated APM component expression, verifying STAT1 dependence of SHP2 activity. SHP2 depletion induced recognition of HNC cells by HLA class I-restricted CTL and secretion of inflammatory, T-cell attracting chemokines, RANTES and IP10.

CONCLUSION

These findings suggest for the first time an important role for SHP2 in APM-mediated escape of HNC cells from CTL recognition. Targeting SHP2 could enhance T-cell-based cancer immunotherapy.

The role of classical and non-classical HLA class I antigens in human tumors

In human tumors alterations in the surface expression and/or function of the major histocompatibility complex (MHC) class I antigens are frequently found and equip neoplastic cells with mechanisms to escape immune control. The aberrant expression of HLA class I molecules can be caused by structural alterations or dysregulations of genes encoding the classical HLA class I antigens and/or components of the HLA class I antigen processing machinery (APM). The dysregulation of APM components could occur at the epigenetic, transcriptional or post-transcriptional level. In some malignancies these abnormalities are significantly associated with a higher tumor staging, grading, disease progression and a reduced survival of patients as well as a failure to CD8(+) T cell-based immunotherapies. In addition to HLA class I abnormalities, expression of the non-classical HLA-G antigen is often induced in tumors, which could be mediated by various microenvironmental factors. Interestingly, soluble HLA-G serum and plasma levels have been useful markers for the prediction of some malignancies. The biological consequence of HLA-G expression or sHLA-G is an escape from T and NK cell-mediated recognition. Thus, alterations of non-classical and classical HLA class I antigens and components of the antigen processing pathway provide tumor cells with different mechanisms to inactivate immune responses resulting in tumor growth and evasion from host immune surveillance.

Novel insights into the molecular mechanisms of HLA class I abnormalities

Alterations in the MHC class I surface antigens represent one mechanism of tumor cells to escape from natural or immunotherapy-induced antitumor immune responses. In order to restore MHC class I expression, knowledge about the underlying molecular mechanisms of MHC class I defects in different tumor types is required. In most cases, abnormalities of MHC class I expression are reversible by cytokines suggesting a deregulation rather than structural abnormalities of members of the antigen-processing and presentation machinery (APM). The impaired expression of APM components could be controlled at the epigenetic, transcriptional and/or posttranscriptional level. Furthermore, a direct link between altered transcription factor binding, interferon signal transduction and MHC class I APM component expression has been shown, which might be further associated with cell cycle progression. This information will not only give novel insights into the (patho) physiology of the antigen-processing and presenting pathway, but will help in the future to design effective T cell-based immunotherapies.

Proteasome inhibitors

In May 2003, the US Food and Drug Administration (FDA) granted accelerated approval for the use of the first-in-class proteasome inhibitor bortezomib as a third-line therapy in multiple myeloma, and the European Union followed suit a year later. Bortezomib has subsequently been approved for multiple myeloma as a second-line treatment on its own and as a first-line therapy in combination with an alkylating agent and a corticosteroid. Furthermore, bortezomib has also been approved as a second-line therapy for mantle cell lymphoma. In this chapter, the focus is on the current clinical research on bortezomib, its adverse effects, and the resistance of multiple myeloma patients to bortezomib-based therapy. The various applications of bortezomib in different diseases and recent advances in the development of a new generation of inhibitors that target the proteasome or other parts of the ubiquitin-proteasome system are also reviewed.

Expression of antigen processing and presenting molecules in brain metastasis of breast cancer

Defects in human leukocyte antigen class I antigen processing machinery (APM) component expression can have a negative impact on the clinical course of tumors and the response to T cell-based immunotherapy. Since brain metastases of breast cancer are of increasing clinical significance, the APM component expression levels and CD8(+) T cell infiltration patterns were analyzed in primary breast and metastatic brain lesions of breast cancer by immunohistochemistry. Comparison of unpaired 50 primary and 33 brain metastases showed lower expression of β2-microglobulin, transporter associated with antigen processing (TAP) 1, TAP2 and calnexin in the brain lesions. Although no significant differences were found in APM component scores between primary breast and brain lesions in 15 paired cases, primary breast lesions of which patients eventually developed brain metastases showed lower levels of β2-microglobulin, TAP1 and calnexin compared with breast lesions without known brain metastases. The extent of CD8(+) T cell infiltration was significantly higher in the lesions without metastasis compared with the ones with brain metastases, and was positively associated with the expression of TAP1 and calnexin. Furthermore, mouse tumor cells stably transfected with silencing hairpin (sh)RNA for TAP1 demonstrated a decreased susceptibility to cytotoxic T lymphocytes in vitro and enhanced spontaneous brain metastasis in vivo. These data support the functional significance of TAP1 expression in tumor cells. Taken together, our data suggest that patients with low or defective TAP1 or calnexin in primary breast cancers may be at higher risks for developing brain metastasis due to the defects in T cell-based immunosurveillance.

The ubiquitin-like protein, ISG15, is a novel tumor-associated antigen for cancer immunotherapy

The recent announcement of the first FDA-approved therapeutic vaccine for prostate cancer, Sipuleucel-T, is a watershed moment for the field of tumor immunotherapy. However, while Sipuleucel-T provides a powerful tool to clinicians for the most prevalent form of cancer in men, there remains an unmet need for a similar therapeutic strategy against breast cancer, the most prevalent cancer in women. While current breast cancer vaccines in development target several antigens, the most prevalent is the tumor-associated antigen, HER2. Initial results with HER2 vaccines appear promising in terms of efficacy; however, the lack of HER2 overexpression by a majority of breast tumors and the safety concerns associated with current HER2-targeted immunotherapy suggest that additional therapeutic strategies would be beneficial. Recently, several studies have identified ISG15 as a molecule highly expressed in numerous malignancies. ISG15 is a small ubiquitin-like protein regulated by type-I interferon and classically associated with viral defense. Elevated ISG15 expression in breast cancer is especially well documented and is independent of HER2, progesterone receptor, and estrogen receptor status. Additionally, high ISG15 expression in breast cancer correlates with an unfavorable prognosis and poor responses to traditional treatment strategies such as chemotherapy and radiation. To overcome these challenges, we employ a novel strategy to specifically target tumor-associated ISG15 expression with immunotherapy. We demonstrate that vaccination against ISG15 results in significant CD8-mediated reductions in both primary and metastatic mammary tumor burden. These results validate ISG15 as a tumor-associated antigen for cancer immunotherapy.

Camouflage and sabotage: tumor escape from the immune system

The field of tumor immunology has made great progress in understanding tumor immune interactions. As a consequence a number of immuno-therapeutic approaches have been successfully introduced into the clinic and a large number of promising therapeutic strategies are investigated in ongoing clinical trials. Evaluation of anti-tumor immunity in such trials as well as in animal models has shown that tumor escape from immune recognition and tumor-mediated suppression of anti-tumor immunity can pose a significant obstacle to successful cancer therapy. Here, we review mechanisms of tumor immune escape and immune-subversion with a focus on the research interests in our laboratory: loss of MHC class I on tumor cells, increased oxidative stress, recruitment of myeloid-derived suppressor cells, and regulatory T cells.

The cell biology of major histocompatibility complex class I assembly: towards a molecular understanding

Major histocompatibility complex class I (MHC I) proteins protect the host from intracellular pathogens and cellular abnormalities through the binding of peptide fragments derived primarily from intracellular proteins. These peptide-MHC complexes are displayed at the cell surface for inspection by cytotoxic T lymphocytes. Here we reveal how MHC I molecules achieve this feat in the face of numerous levels of quality control. Among these is the chaperone tapasin, which governs peptide selection in the endoplasmic reticulum as part of the peptide-loading complex, and we propose key amino acid interactions central to the peptide selection mechanism. We discuss how the aminopeptidase ERAAP fine-tunes the peptide repertoire available to assembling MHC I molecules, before focusing on the journey of MHC I molecules through the secretory pathway, where calreticulin provides additional regulation of MHC I expression. Lastly we discuss how these processes culminate to influence immune responses.

Role of gene methylation in antitumor immune response: implication for tumor progression

Cancer immunosurveillance theory has emphasized the role of escape mechanisms in tumor growth. In this respect, a very important factor is the molecular characterization of the mechanisms by which tumor cells evade immune recognition and destruction. Among the many escape mechanisms identified, alterations in classical and non-classical HLA (Human Leucocyte Antigens) class I and class II expression by tumor cells are of particular interest. In addition to the importance of HLA molecules, tumor-associated antigens and accessory/co-stimulatory molecules are also involved in immune recognition. The loss of HLA class I antigen expression and of co-stimulatory molecules can occur at genetic, transcriptional and post-transcriptional levels. Epigenetic defects are involved in at least some mechanisms that preclude mounting a successful host-antitumor response involving the HLA system, tumor-associated antigens, and accessory/co-stimulatory molecules. This review summarizes our current understanding of the role of methylation in the regulation of molecules involved in the tumor immune response.

Tumor infiltrating regulatory T cells: tractable targets for immunotherapy

Several studies have linked tumor-infiltration by regulatory T cells with poor patient outcome. Targeting the mechanisms by which regulatory T cells traffic to and persist in the tumor may circumvent tumor immune-escape by de-restricting T cell-mediated cytotoxicity. In this review, we describe the principle axes that govern regulatory T cell migration and the mechanisms that underpin their immunosuppressive activity in cancer. Inhibiting either the migration or function of regulatory T cells may enhance host-anti-cancer immune responses and as such are attractive and tractable targets for therapeutic intervention.

T cell recognition of HLA-A2 restricted tumor antigens is impaired by the oncogene HER2

The HER2 oncogene is frequently over-expressed in human cancers and a promising target for immune therapy. Previous studies have shown that over-expression of mouse or rat HER2 leads to markedly reduced levels of major histocompatibility complex (MHC) class I and molecules of the antigen processing and presentation machinery (APM), thus resulting in a phenotype promoting tumor escape from the immune system. Our study focuses on analyzing the effect of HER2 on MHC class I antigen presentation and sensitivity to tumor-antigen specific cytotoxic T lymphocytes (CTLs) in HLA-A2.1(+) melanoma cell lines. We demonstrate significant inverse correlations both between the expression of HER2 and total MHC class I surface expression as well as between HER2 and HLA-A2. A significant reduction of HLA-A2 levels was found when melanoma and carcinoma cell lines were transfected with a human HER2 gene. A signaling-competent HER2 molecule was crucial for the observed HLA-A2 down-regulation, as transfectants expressing high levels of HER2 mutated in the tyrosine signaling domain did not show altered HLA-A2 expression. Importantly, the human melanoma cell line EST049 demonstrated reduced HER2 and melanoma antigen-specific recognition by CTLs upon HER2 transfection. In addition, high expression of HER2 prevented both IFN-γ mediated HLA-A2 up-regulation and improved recognition by HLA-A2-restricted CTLs in treated cells. Moreover, key APM molecules were down-regulated by HER2. These findings implicate that HER2 over-expressing tumors may be more prone to escape from HLA-A2 restricted CTLs suggesting that immunotherapy approaches inducing an integrated humoral, cellular and innate immune response would be most effective.

Identification of E2F1 as an important transcription factor for the regulation of tapasin expression

HER-2/neu overexpression in tumor cells caused abnormalities of MHC class I surface expression due to impaired expression of components of the antigen-processing machinery (APM) including the low molecular weight proteins, the transporter associated with antigen processing (TAP), and the chaperone tapasin, whereas the expression of MHC class I heavy chain as well as β(2)-microglobulin was only marginally affected. This oncogene-mediated deficient APM component expression could be reverted by interferon-γ treatment, suggesting a deregulation rather than structural alterations as underlying molecular mechanisms. To determine the level of regulation, the transcriptional activity of APM components was analyzed in HER-2/neu(-) and HER-2/neu(+) cells. All major APM components were transcriptionally down-regulated in HER-2/neu(+) when compared with HER-2/neu(-) cells, which was accompanied by a reduced binding of RNA polymerase II to the APM promoters. Site-directed mutagenesis of the p300- and E2F-binding sites in the APM promoters did not reconstitute the oncogene-mediated decreased transcription rate with the exception of tapasin, which was restored in HER-2/neu(+) cells to levels of wild type tapasin promoter activity in HER-2/neu(-) fibroblasts. The E2F-directed control of tapasin expression was further confirmed by chromatin immunoprecipitation analyses showing that E2F1 and p300 bind to the tapasin and APM promoters in both cell lines. Moreover, siRNA-mediated silencing of E2F1 was associated with an increased tapasin expression, whereas transient overexpression of E2F1 launch a reduced tapasin transcription, suggesting that E2F1 is an essential transcription factor for tapasin.

Dendritic cell/tumor hybrids enhances therapeutic efficacy against colorectal cancer liver metastasis in SCID mice

OBJECTIVE

Colorectal cancer (CRC) is one of the most common malignancies in the western world. More than 60% among patients will develop liver metastases. Although surgical resection is the first choice worldwide, at this point an effective approach for the treatment of patients with liver metastasis and cancer recurrence postoperation has not yet been found. The aim of this study is to investigate the role of the allogeneic dendritomas from fusion of DCs and metastatic colon cancer cells in the activation of anti-tumor immunity against colorectal cancer liver metastases.

MATERIAL AND METHODS

Hybrids were generated by fused allogeneic human peripheral blood dendritic cells with metastatic colon cancer SW620 cells using 50% polyethylene glycol (PEG). Induction of immune responses was assessed by ex vivo ELISPOT assays. A murine model of CRC liver metastasis was used by intrasplenic injection. The validity of the vaccine was observed by Vaccination CRC liver metastasis murine model with DC/tumor hybrids.

RESULTS

The hybrids highly express the major molecules of DCs and tumor cells. The number of hybrids pulsed CTL secreting IFN-gamma was significantly higher when compared to the DC controls (p < 0.01). In a therapeutic setting mice vaccinated with in vitro cultured hybrids produced strong cellular immune responses and significant inhibition of tumor growth, compared to sham vaccinated controls.

CONCLUSIONS

Vaccination with hybrids can induces strong cellular responses and significant protection from challenge in SCID mouse metastatic CRC model.

Down-regulation of HLA class I antigen-processing machinery components in esophageal squamous cell carcinomas: association with disease progression

OBJECTIVE

Lack of human leukocyte antigen (HLA) presentation has been proposed to contribute to the immune evasion of cancer cells in some cancers including esophageal cancer. The aim of this study was to examine the expression of HLA class I antigen and the antigen-processing machinery (APM) components in esophageal squamous cell carcinoma (ESCC) lesions and to assess their association with histopathological characteristics.

MATERIAL AND METHODS

A total of 143 formalin-fixed, paraffin-embedded ESCC lesions collected in two hospitals in Shandong Province of China were studied. The expression levels were determined by immunohistochemistry.

RESULTS

TAP1, TAP2, LMP2, LMP7, beta2m, and HLA class I antigen were lost or down-regulated in 30.8%, 35.0%, 45.0%, 48.0%, 56.0%, and 60.8% of the ESCC lesions tested, respectively. The loss of or down-regulated expressions of HLA class I, beta2m, TAP1, LMP2, and LMP7 in tumor lesions were all significantly correlated to tumor grade and lymph node status. Expression of HLA class I antigens was strongly correlated to the expression levels of beta2m, TAP1, TAP2, LMP2, and LMP7, suggesting APM component defects as a mechanism underlying HLA class I antigen down-regulation in ESCC lesions. Expression of APM components and HLA class I antigens was significantly associated with the extent of intratumoral T-cell infiltration.

CONCLUSIONS

Our results indicate that lack or reduction of HLA class I antigens and expression of APM components in ESCC may render some tumor cells to escape the immunosurveillance mediated by CD8(+) T cells and contribute to the clinical course of ESCC.

The prognostic role of classical and nonclassical MHC class I expression in endometrial cancer

The aim of this study was to investigate classical MHC class I and nonclassical MHC (human leukocyte antigen-G [HLA-G]) expression in a large cohort of patients with endometrial cancer, to determine the prognostic value of these cell surface markers and their relation with clinicopathological variables. Tissue microarrays containing epithelial endometrial carcinoma tissue from 554 patients were stained for classical and nonclassical MHC class I using the following monoclonal antibodies: 4H84 (anti-HLA-G), beta2-m (anti-beta-2-microglobulin) and HC-10 (MHC class I antigen heavy chain). Expression data were linked to known clinicopathological characteristics and survival. HLA-G upregulation and MHC class I downregulation in neoplastic cells was observed in 40% and 48%, respectively. Nonendometrioid tumor type, advanced stage disease (FIGO stage > or = II) and poorly or undifferentiated tumors were associated with MHC class I downregulation. Absence of HLA-G expression was independently associated with MHC class I downregulation. In univariate analysis, MHC class I downregulation was a predictor of worse disease-specific survival. Prognostic unfavorable tumor characteristics were correlated with downregulation of MHC class I expression in endometrial cancer cells. Furthermore, downregulated MHC class I has a negative impact on disease-specific survival, observed in a large cohort of patients with endometrial cancer. As there seems to be a relation between classical and nonclassical MHC class I molecules (HLA-G), further research is warranted to unravel this regulatory mechanism.

Absence of tapasin alters immunodominance against a lymphocytic choriomeningitis virus polytope

Tapasin edits the peptide repertoire presented to CD8(+) T cells by favoring loading of slow off-rate peptides on MHC I molecules. To investigate the role of tapasin on T cell immunodominance we used poxvirus viral vectors expressing a polytope of lymphocytic choriomeningitis virus epitopes with different off-rates. In tapasin-deficient mice, responses to subdominant fast off-rate peptides were clearly favored. This alteration of the CD8(+) T cell hierarchy was a consequence of tapasin editing and not a consequence of the alteration of the T cell repertoire in tapasin-deficient mice, because bone marrow chimeric mice (wild-type recipients reconstituted with tapasin knockout bone marrow) showed the same hierarchy as the tapasin knockout mice. Tapasin editing is therefore a contributing factor to the phenomenon of immunodominance. Although tapasin knockout cells have low MHC I surface expression, Ag presentation was efficient and resulted in strong T cell responses involving T cells with increased functional avidity. Therefore, in this model, tapasin-deficient mice do not have a reduced but rather have an altered immune response.

Down-regulation of HLA Class I and NKG2D ligands through a concerted action of MAPK and DNA methyltransferases in colorectal cancer cells

Most malignant features of cancer cells are triggered by activated oncogenes and the loss of tumor suppressors due to mutation or epigenetic inactivation. It is still unclear, to what extend the escape of emerging cancer cells from recognition and elimination by the immune system is determined by similar mechanisms. We compared the transcriptomes of HCT116 colorectal cancer cells deficient in DNA methyltransferases (DNMTs) and of cells, in which the RAS pathway as the major growth-promoting signaling system is blocked by inhibition of MAPK. We identified the MHC Class I genes HLA-A1/A2 and the ULBP2 gene encoding 1 of the 8 known ligands of the activating NK receptor NKG2D among a cluster of immune genes up-regulated under the conditions of both DNMT-deficiency and MEK-inhibition. Bisulphite sequencing analyses of HCT116 with DNMT deficiency or after MEK-inhibition showed that de-methylation of the ULPB2 promoter correlated with its enhanced surface expression. The HLA-A promoters were not methylated indicating that components of the HLA assembly machinery were also suppressed in DNMT-deficient and MEK-inhibited cells. Increased HLA-A2 surface expression was correlated with enhanced recognition and lysis by A2-specific CTL. On the contrary, elevated ULBP2 expression was not reflected by enhanced recognition and lysis by NK cells. Cosuppression of HLA Class I and NKG2D ligands and genes encoding peptide transporters or proteasomal genes mediates a strong functional link between RAS activation, DNMT activity and disruption of the antigen presenting system controlling immune recognition in colorectal cancer cells.

Different regulation of MHC class I antigen processing components in human tumors

In recent years, progress has been made in understanding how peptides presented by MHC Class I molecules were generated, in particular which proteases are involved in this process and how intracellular pathways influence antigen presentation in professional antigen-presenting cells and various types of tumor cells. This review will give an overview of MHC Class I abnormalities in malignancies and their underlying molecular mechanisms. Dependent on the tumor types structural alterations in particular of the MHC Class I heavy chain, beta(2)-m and the TAP1 subunit have been found at a low frequency, whereas dysregulation of MHC Class I antigen processing components appears to be the major mechanism of MHC Class I down-regulation in tumors of distinct origin. This could occur at the epigenetic, transcriptional and/or post-transcriptional level. The lack or suppression of MHC Class I surface expression due to antigen-processing deficiencies are accompanied by reduced recognition and lysis by antigen-specific cytotoxic T-lymphocytes, which is further often associated with disease progression.

Down-regulation of proteasomal subunit MB1 is an independent predictor of improved survival in ovarian cancer

OBJECTIVE

To investigate the expression and to determine the prognostic impact of components of the antigen processing and presentation pathway (APPP) in ovarian cancer.

METHODS

Expression of MB1, LMP7, TAP1, TAP2, ERp57, ERAP1, beta(2)-microglobulin and the alpha-chains, HLA-B/C and HLA-A, of the MHC class I molecules was evaluated on tissue microarrays containing primary tumor samples from 232 FIGO stages I-IV ovarian cancer patients. Expression levels were correlated to clinicopathological data and disease specific (DSS) survival.

RESULTS

Patients with expression of all components of the MHC class I complex, i.e. HLA-A(+)-beta(2)-m(+) and HLA-B/C(+)-beta(2)-m(+) patients, more often had expression of LMP7, a component of the immunoproteasome than patients with other phenotypes (p<0.001). These patients were also more prone to loss of MB1, part of the constitutive multicatalytic proteasome (p<0.05). Nuclear MB1 expression was an independent predictor of worse DSS (HR 1.94, 95% CI 1.16-3.26, p=0.012). The HLA-B/C(+)-beta(2)-m(+) phenotype was an independent predictor of a better prognosis (HR 0.63, 95% CI 0.40-0.99, p=0.047). Median DSS was longer for patients with normal nuclear expression of LMP7 (57.4 vs. 31.0 months, p=0.029).

CONCLUSIONS

The prognostic influence of the proteasomal subunit MB1 and the MHC class I complex in ovarian cancer provides a rationale for targeting these specific APPP components in ovarian cancer.

ProtEx technology for the generation of novel therapeutic cancer vaccines

Therapeutic vaccines present an attractive alternative to conventional treatments for cancer. However, tumors have evolved various immune evasion mechanisms to modulate innate, adaptive, and regulatory immunity for survival. Therefore, successful vaccine formulations may require a non-toxic immunomodulator or adjuvant that not only induces/stimulates innate and adaptive tumor-specific immune responses, but also overcomes immune evasion mechanisms. Given the paramount role costimulation plays in modulating innate, adaptive, and regulatory immune responses, costimulatory ligands may serve as effective immunomodulating components of therapeutic cancer vaccines. Our laboratory has developed a novel technology designated as ProtEx that allows for the generation of recombinant costimulatory ligands with potent immunomodulatory activities and the display of these molecules on the cell surface in a rapid and efficient manner as a practical and safe alternative to gene therapy for immunomodulation. Importantly, the costimulatory ligands not only function when displayed on tumor cells, but also as soluble proteins that can be used as immunomodulatory components of conventional vaccine formulations containing tumor-associated antigens (TAAs). We herein discuss the application of the ProtEx technology to the development of effective cell-based as well as cell-free conventional therapeutic cancer vaccines.

HLA class I antigen processing machinery component expression and intratumoral T-Cell infiltrate as independent prognostic markers in ovarian carcinoma

PURPOSE

Defects in the antigen processing machinery (APM) may provide tumor cells with a mechanism to escape immune recognition. The purpose of this study is to determine the clinical significance of APM component down-regulation and tumor-infiltrating T cells in ovarian carcinoma.

EXPERIMENTAL DESIGN

After institutional review board approval, tumor samples from 150 patients with invasive epithelial ovarian cancers were examined for TAP1, TAP2, tapasin, HLA class I heavy chain (HLA-HC), beta 2 microglobulin, and T-cell (CD3+ and CD8+) tumor infiltration using immunohistochemistry.

RESULTS

The majority of tumors had either heterogeneous or positive expression of TAP1, TAP2, HLA-HC, and beta 2 microglobulin (66.7%, 73.3%, 70.7%, and 63.3%, respectively), except tapasin for which 58% of the tumors lacked expression. Furthermore, 67% and 88% of the lesions possessed intratumoral and peritumoral CD3+ or CD8+ cells, respectively. The majority of APM component expression examined was significantly associated with both intratumoral and peritumoral T-cell infiltration (P < 0.05). The expression of APM components and the presence of intratumoral T-cell infiltrates were significantly associated with improved survival (all P < or = 0.01); however, peritumoral T-cell infiltrates did not significantly affect survival (P = 0.33). APM component down-regulation (P < 0.001), lack of intratumoral T-cell infiltrates (P = 0.03), and suboptimal cytoreduction (P < 0.001) were independent prognostic markers for death from ovarian carcinoma.

CONCLUSION

The negative effect of APM component down-regulation by itself and in combination with absent intratumoral T-cell infiltration on the survival of patients with ovarian carcinoma implies a role for immune escape in addition to immunosurveillance in the clinical course of disease.

Ten recently identified associations between nsSNPs and colorectal cancer could not be replicated in German families

Ten non-synonymous single nucleotide polymorphisms (nsSNPs), which were recently associated with colorectal cancer risk in a comprehensive, array based study (AKAP9 M463I, DKK3 G335R, AMPD1 Q12X, LIPC L356F, PSMB9 V32I, THBS1 N700S, CA6 S90G, ASCC3 C1995S, DHX36 S416C and CPA4 G303C) were re-evaluated in the present study based on 626 German familial non-HNPCC colorectal cancer patients and 736 healthy controls. No associations of any of the 10 nsSNPs with colorectal cancer could be replicated. The combined analyses indicated that further research based on additional independent samples is required.

Survival of ovarian cancer patients overexpressing the tumour antigen p53 is diminished in case of MHC class I down-regulation

OBJECTIVES

The adaptive immune system seems to play an essential role in the natural course of ovarian cancer. Aim of this study was to establish whether disease-specific survival for patients expressing the tumour antigen p53 is influenced by MHC class I expression or the presence of p53 autoantibodies (p53-Aab).

METHODS

P53 and MHC class I expression were analysed in ovarian cancer tissue of 329 patients by immunohistochemistry using tissue microarrays. For 233 patients, pre-treatment serum samples were available to study the presence of p53 autoantibodies by ELISA. Data were linked to clinicopathological parameters and disease-specific survival.

RESULTS

P53 overexpression, MHC class I down-regulation in neoplastic cells and serum p53 autoantibodies were observed in 49.4, 38.9 and 15.9% of patients, respectively. MHC class I down-regulation in p53-overexpressing tumours correlated with a 10-month reduced disease-specific survival in univariate analysis (log-rank 4.10; p=0.043). p53-Aab were strongly correlated with p53 overexpression (p<0.001), but did not influence disease-specific survival.

CONCLUSIONS

As the prognosis of patients with p53-overexpressing ovarian cancer is affected by the MHC class I status of tumour cells and ovarian cancer patients can generate immune responses to the p53 tumour antigen, the further development of immunotherapy should evaluate strategies to improve MHC class I expression by tumour cells to facilitate antigen presentation in an attempt to increase clinical responses.

Combining the antigen processing components TAP and Tapasin elicits enhanced tumor-free survival

PURPOSE

Tpn is a member of the MHC class I loading complex and functions to bridge the TAP peptide transporter to MHC class I molecules. Metastatic human carcinomas often express low levels of the antigen-processing components Tapasin and TAP and display few functional surface MHC class I molecules. As a result, carcinomas are unrecognizable by effector CTLs. The aim of this study is to examine if Tapasin (Tpn) plays a critical role in the escape of tumors from immunologic recognition.

EXPERIMENTAL DESIGN

To test our hypothesis, a nonreplicating adenovirus vector encoding human Tpn (AdhTpn) was constructed to restore Tpn expression in vitro and in vivo in a murine lung carcinoma cell line (CMT.64) that is characterized by down-regulation of surface MHC class I due to deficiency in antigen-processing components.

RESULTS

Ex vivo, Tpn expression increased surface MHC class I and restored susceptibility of tumor cells to antigen-specific CTL killing, and AdhTpn infection of dendritic cells also significantly increased cross-presentation and cross-priming. Furthermore, tumor-bearing animals inoculated with AdhTpn demonstrated a significant increase in CD8(+) and CD4(+) T cells and CD11c(+) dendritic cells infiltrating the tumors. Provocatively, whereas syngeneic mice bearing tumors that were inoculated with AdhTpn a significant reduction in tumor growth and increased survival compared with vector controls, combining AdhTpn inoculation with AdhTAP1 resulted in a significant augmentation of protection from tumor-induced death than either component alone.

CONCLUSIONS

This is the first demonstration that Tpn alone can enhance survival and immunity against tumors but additionally suggests that Tpn and TAP should be used together as components of immunotherapeutic vaccine protocols to eradicate tumors.

Enhanced expression of interferon-gamma-induced antigen-processing machinery components in a spontaneously occurring cancer

In human tumors, changes in the surface expression and/or function of major histocompatibility complex (MHC) class I antigens are frequently found and may provide malignant cells with a mechanism to escape control of the immune system. This altered human lymphocyte antigen (HLA) class I phenotype can be caused by either structural alterations or dysregulation of genes encoding subunits of HLA class I antigens and/or components of the MHC class I antigen-processing machinery (APM). Herein we analyze the expression of several proteins involved in the generation of MHC class I epitopes in feline injection site sarcoma, a spontaneously occurring tumor in cats that is an informative model for the study of tumor biology in other species, including humans. Eighteen surgically removed primary fibrosarcoma lesions were analyzed, and an enhanced expression of two catalytic subunits of immunoproteasomes, PA28 and leucine aminopeptidase, was found in tumors compared to matched normal tissues. As a functional counterpart of these changes in protein levels, proteasomal activities were increased in tissue extracts from fibrosarcomas. Taken together, these results suggest that alterations in the APM system may account for reduced processing of selected tumor antigens and may potentially provide neoplastic fibroblasts with a mechanism for escape from T-cell recognition and destruction.

Association of immunoescape mechanisms with Epstein-Barr virus infection in nasopharyngeal carcinoma

We have investigated the association of immunoescape mechanisms in nasopharyngeal carcinoma (NPC) lesions with Epstein-Barr virus (EBV) infection and clinical course of the disease. Tumor biopsy specimens obtained from 36 Japanese NPC patients were examined for antigen processing machinery component and HLA class I antigen expression, CD8(+) T cell infiltration, and Fas, Fas ligand (FasL) and IL-10 expression using immunohistochemical staining. The results were correlated with the histopathological characteristics of the lesions, the clinical course of the disease and EBV infection. LMP2, TAP1, tapasin and HLA class I antigens were downregulated in more than 65% of the lesions tested, while FasL, Fas and IL-10 were expressed in at least 60% of the lesions. Statistical analysis showed that (i) HLA class I antigen expression was significantly correlated with LMP2 and tapasin expression (r = 0.39 and 0.45, respectively); (ii) CD8(+) T cell infiltration into tumor lesions was significantly correlated with HLA class I antigen, LMP2 and Fas expression (r = 0.34, 0.49 and 0.44, respectively); (iii) LMP2 and FasL expression was significantly correlated with IL-10 expression (r = 0.49 and 0.52, respectively); (iv) IL-10 expression was significantly associated with EBERs and EBV oncoprotein LMP1 expression (p = 0.00078 and 0.015, respectively) and (v) FasL overexpression was significantly associated with reduced patients' survival (p = 0.033). Multivariate analysis identified FasL overexpression as an independent unfavorable prognostic marker. These results suggest that NPC cells may utilize multiple immunoescape mechanisms, including dysfunction of HLA class I antigens and Fas/FasL apoptosis pathways. Furthermore, FasL expression appears to be associated with IL-10 upregulation in EBV positive NPC cells.

Enhanced intestinal expression of the proteasome subunit low molecular mass polypeptide 2 in patients with inflammatory bowel disease

PURPOSE

Low molecular mass polypeptide 2 is an inducible immunoproteasome subunit. The expression of low molecular mass polypeptide 2 has not been examined in the intestine of patients with inflammatory bowel disease. This study was designed to determine whether the intestinal expression of low molecular mass polypeptide 2 was enhanced in a group of patients with inflammatory bowel disease compared with a group of control patients without inflammatory bowel disease. Moreover, we examined the association between low molecular mass polypeptide 2 expression and histologic pathology in these patients.

METHODS

Twenty-one patients participated in the study. These included six control subjects without inflammatory bowel disease, eight patients with ulcerative colitis, and seven patients with Crohn's disease. Intestinal low molecular mass polypeptide 2 expression was evaluated by immunohistochemistry, as well as by Western blot. Histology scores (0-40 severity scale) were determined on the same sections of intestine as those used for low molecular mass polypeptide 2 histochemistry.

RESULTS

By immunohistochemistry, low molecular mass polypeptide 2 expression was significantly enhanced (P < 0.05 vs. control subjects) throughout visibly diseased areas of colon, rectum, and ileum from patients with inflammatory bowel disease. Low molecular mass polypeptide 2 expression also was increased in macroscopically normal intestine from patients with inflammatory bowel disease compared with normal tissue from control subjects. There was a significant correlation (P < 0.0001) between low molecular mass polypeptide 2 expression and histologic pathology in our patients. Western blot results confirmed that low molecular mass polypeptide 2 expression was enhanced in patients with ulcerative colitis (3.1-fold) and in patients with Crohn's disease (3.5-fold).

CONCLUSIONS

Intestinal low molecular mass polypeptide 2 expression is significantly increased in inflammatory bowel disease. The association between intestinal low molecular mass polypeptide 2 expression and histologic pathology suggests that this proteasome subunit plays a role in the pathogenesis of inflammatory bowel disease.

Immune selective pressure and HLA class I antigen defects in malignant lesions

The revived cancer immune surveillance theory has emphasized the active role the immune system plays in eliminating tumor cells and in facilitating the emergence of their immunoresistant variants. MHC class I molecule abnormalities represent, at least in part, the molecular phenotype of these escape variants, given the crucial role of MHC class I molecules in eliciting tumor antigen-specific T cell responses, the high frequency of HLA class I antigen abnormalities in malignant lesions and their association with a poor clinical course of the disease. Here, we present evidence for this possibility and review the potential mechanisms by which T cell selective pressure participates in the generation of tumor cells with MHC class I molecule defects. Furthermore, we discuss the strategies to counteract tumor cell immune evasion.

HLA class I antigen down-regulation in primary laryngeal squamous cell carcinoma lesions as a poor prognostic marker

We have investigated the role of antigen-processing machinery (APM) component defects in HLA class I antigen down-regulation in laryngeal squamous cell carcinoma (SCC) lesions and assessed the clinical significance of these defects. To this end, 63 formalin-fixed, paraffin-embedded tumor lesions were examined for APM component and HLA class I antigen expression by immunohistochemistry. Calnexin, calreticulin, and ERp57 were down-regulated in approximately 25% of the lesions tested, whereas LMP2, TAP1, tapasin, and HLA class I antigens were down-regulated in at least 70% of the lesions tested. LMP2 and tapasin expression was significantly correlated with HLA class I antigen expression suggesting APM component defects as a mechanism underlying HLA class I antigen down-regulation in laryngeal SCC lesions. The expression of most APM components and HLA class I antigens was correlated with the extent of CD8+ T cell infiltration into tumor lesions. Furthermore, LMP2 and HLA class I antigen down-regulation and low CD8+ T cell infiltration were significantly associated with reduced patients' survival. Multivariate analysis identified HLA class I antigen down-regulation as an independent unfavorable prognostic marker. This association is likely to reflect the reduction in the extent of CD8+ T cell infiltration in laryngeal SCC lesions.

Cancer despite immunosurveillance: immunoselection and immunosubversion

Numerous innate and adaptive immune effector cells and molecules participate in the recognition and destruction of cancer cells, a process that is known as cancer immunosurveillance. But cancer cells avoid such immunosurveillance through the outgrowth of poorly immunogenic tumour-cell variants (immunoselection) and through subversion of the immune system (immunosubversion). At the early stages of carcinogenesis, cell-intrinsic barriers to tumour development seem to be associated with stimulation of an active antitumour immune response, whereas overt tumour development seems to correlate with changes in the immunogenic properties of tumour cells. The permanent success of treatments for cancer might depend on using immunogenic chemotherapy to re-establish antitumour immune responses.

Gene expression profiling of ATP-binding cassette (ABC) transporters as a predictor of the pathologic response to neoadjuvant chemotherapy in breast cancer patients

Drug resistance is a major obstacle to the successful chemotherapy. Several ATP-binding cassette (ABC) transporters including ABCB1, ABCC1 and ABCG2 have been known to be important mediators of chemoresistance. Using oligonucleotide microarrays (HG-U133 Plus 2.0; Affymetrix), we analyzed the ABC transporter gene expression profiles in breast cancer patients who underwent sequential weekly paclitaxel/FEC (5-fluorouracil, epirubicin and cyclophosphamide) neoadjuvant chemotherapy. We compared the ABC transporter expression profile between two classes of pretreatment tumor samples divided by the patients' pathological response to neoadjuvant chemotherapy (residual disease [RD] versus pathologic complete response [pCR]) ABCB3, ABCC7 and ABCF2 showed significantly high expression in the pCR. Several ABC transporters including ABCC5, ABCA12, ABCA1 ABCC13, ABCB6 and ABCC11 showed significantly increased expression in the RD (p<0.05). We evaluated the feasibility of developing a multigene predictor model of pathologic response to neoadjuvant chemotherapy using gene expression profiles of ABC transporters. The prediction error was evaluated by leave-one-out cross-validation (LOOCV). A multigene predictor model with the ABC transporters differentially expressed between the two classes (p<or=0.003) showed an average 92.8% of predictive accuracy (95% CI, 88.0-97.4%) with a 93.2% (95% CI, 85.2-100%) positive predictive value for pCR, a 93.6% (95% CI, 87.8-99.4%) negative predictive value, a sensitivity of 88.1%(95% CI, 76.8-99.4%), and a specificity of 95.9% (91.1% CI, 87.8-100%). Our results suggest that several ABC transporters in human breast cancer cells may affect the clinical response to neoadjuvant chemotherapy, and transcriptional profiling of these genes may be useful to predict the pathologic response to sequential weekly paclitaxel/FEC in breast cancer patients.

The mutation in the ATP-binding region of JAK1, identified in human uterine leiomyosarcomas, results in defective interferon-gamma inducibility of TAP1 and LMP2

The presentation of human leukocyte antigens (HLA) class I requires the coordinated expression of numerous components involved in antigen presentation. Tumor cells may alter the antigen presentation by HLA class I, allowing them to evade antitumor immunity. In many cases, the lack of antigen presentation can be attributed to the downregulation of genes needed for antigen processing, such as the transporters associated with antigen processing (TAP) 1, and the proteasomal component, low molecular weight proteins (LMP) 2. The TAP1 and LMP2 genes are transcribed from a shared bidirectional promoter containing an interferon (IFN)-gamma-response factor element; thus, the IFN-gamma-signal strongly induces both TAP1 and LMP2 expression. Low molecular weight proteins2-deficient mice exhibited the development of uterine leiomyosarcomas. Here, the differential responsiveness to IFN-gamma of the SKN human uterine leiomyosarcomas cell line was investigated. We now identify the G871E mutation in the ATP-binding region of Janus kinases 1, suggesting that the loss of TAP1 and LMP2 induction is a defect in the earliest steps of the IFN-gamma-signal pathway, resulting in the inability of SKN cells to upregulate the antigen-processing pathway. Understanding the mechanisms by which these tumors circumvent cytokine signalling, thereby evading antitumor-specific immunity, would greatly aid the efficacy of immunotherapy for treating uterine leiomyosarcomas.

Control of colorectal metastasis formation by K-Ras

Mutational activation of the K-Ras proto-oncogene is frequently observed during the very early stages of colorectal cancer (CRC) development. The mutant alleles are preserved during the progression from pre-malignant lesions to invasive carcinomas and distant metastases. Activated K-Ras may therefore not only promote tumor initiation, but also tumor progression and metastasis formation. Metastasis formation is a very complex and inefficient process: Tumor cells have to disseminate from the primary tumor, invade the local stroma to gain access to the vasculature (intravasation), survive in the hostile environment of the circulation and the distant microvascular beds, gain access to the distant parenchyma (extravasation) and survive and grow out in this new environment. In this review, we discuss the potential influence of mutant K-Ras on each of these phases. Furthermore, we have evaluated the clinical evidence that suggests a role for K-Ras in the formation of colorectal metastases.

Glutathione S -transferase T1 polymorphisms are associated with outcome in colorectal cancer

Colorectal cancer (CRC) remains a significant cause of mortality accounting for approximately 10% of all deaths from malignancy in the western world. Polymorphism in the glutathione S-transferase GSTT1 gene has been associated with CRC risk in some but not all studies. In this study, we examined associations between GSTT1 genotypes and CRC risk, and prognosis in 361 cases and 881 unrelated controls. GSTT1 null was associated with a small but significant increase in risk (P = 0.0006, odds ratio (OR) = 1.65, 95% confidence interval (CI) = 1.22-2.24). GSTT1 null was also associated with a significantly younger age at diagnosis (mean 65.2 years) compared with GSTT1 A (mean 67.6 years, P = 0.031). There were no significant associations between GSTT1 genotypes and clinical factors (e.g. Dukes stage, differentiation and tumour node metastasis classification) in the total case group. However, following stratification by age (<70 versus > or =70 years at diagnosis), in the patients diagnosed <70 years of age, GSTT1 null was more common in Dukes grade A/B tumours (P = 0.046), stage T1/T2 tumours (P = 0.053) and those with a pushing margin (P = 0.066). We also identified associations between GSTT1 null and increased prevalence of host lymphocyte response, particularly in the younger patients (P = 0.036). Furthermore, GSTT1 null was associated with improved survival in younger patients (P = 0.017, hazards ratio (HR) = 0.52, 95% CI = 0.31-0.89) but poorer survival in older patients (P = 0.017, HR = 1.89, 95% CI = 1.12-3.20). We proposed a model based on the dual functionality of GSTT1 to explain these contrasting results. We suggest that the null genotype is associated with improved immune response in younger patients, but poorer detoxification in older patients. These findings may also provide an explanation for the contrasting finding of other studies on the role of this gene in CRC.

Classical and nonclassical HLA class I antigen and NK Cell-activating ligand changes in malignant cells: current challenges and future directions

Changes in classical and nonclassical HLA class I antigen and NK cell-activating ligand expression have been identified in malignant lesions. These changes, which are described in this chapter, are believed to play a major role in the clinical course of the disease since both HLA class I antigens and NK cell-activating ligands are critical to the interaction between tumor cells and components of both innate and adaptive immune systems. Nevertheless, there is still debate in the literature about the biologic and functional significance of HLA class I antigen and NK cell-activating ligand abnormalities in malignant lesions. The reasons for this debate are reviewed. They include (i) the incomplete association between classical HLA class I antigen changes and the clinical course of the disease; (ii) the relatively limited number of malignant lesions that have been analyzed for nonclassical HLA class I antigen and NK cell-activating ligand expression; and (iii) the conflicting data regarding the role of immunoselection in the generation of malignant cells with HLA antigen and NK cell-activating ligand abnormalities. The technical limitations associated with the assessment of HLA antigen and NK cell-activating ligand expression in malignant lesions as well as the immunological and nonimmunological variables that may confound the impact of HLA antigen and NK cell-activating ligand changes on the clinical course of the disease are also discussed. Future studies aimed at overcoming these limitations and characterizing these variables are expected to provide a solution to the current debate regarding the significance of HLA class I antigen and NK cell-activating ligand abnormalities in malignant lesions.

Coordinated downregulation of the antigen presentation machinery and HLA class I/beta2-microglobulin complex is responsible for HLA-ABC loss in bladder cancer

Downregulation of MHC class I expression is a widespread phenomenon used by tumor cells to escape antitumor T-cell-mediated immune responses. These alterations may play a role in the clinical course of the disease. The aim of our study was to investigate the molecular mechanism underlying the absence of HLA-class I molecule expression in bladder cancer cells. Microdissected tumor tissues were characterized by real-time quantitative PCR for the expression of HLA-ABC, beta2-microglobulin and the members of the antigen processing machinery (APM) of HLA class I molecules (LMP2, LMP7, TAP1, TAP2 and tapasin). Our results showed that irreversible HLA loss by mutations in the beta2-microglobulin gene was not the cause of low HLA class I expression in bladder cancers. In contrast, we observed a coordinated transcription downregulation of HLA-ABC and beta2-microglobulin and APM genes in microdissected tumor tissue derived from bladder carcinomas. This mechanism may represent a major factor for the downregulation of HLA class I expression and in the subsequent direct recognition of cancer cells by cytolytic T lymphocytes. Because this regulatory mechanism is frequently reversible by IFN-gamma treatment, we conclude that HLA class I expression should be a major consideration for immunotherapeutic purposes in patients with bladder cancer.

TAP genes and immunity

The transporter associated with antigen processing (TAP) is a member of the ATP-binding cassette transporter family that specializes in delivering cytosolic peptides to class I molecules in the endoplasmic reticulum. The TAP is a major target of genetic alteration in tumours and disruption by viral inhibitors. In some species, TAP genes have co-evolved with MHC class I molecules to deliver peptides that are customised for particular alleles. In humans, MHC class I polymorphism determines the level of tapasin-mediated association with TAP and subsequent peptide optimisation within the peptide-loading complex (PLC). MHC class I molecules that still load peptides without complexing to the TAP might be more resistant to viral interference of the PLC and less sensitive to competition for TAP by other class I allotypes.

HLA class I antigen expression in malignant cells: why does it not always correlate with CTL-mediated lysis?

HLA class I antigen defects are frequently found in malignant cells. They appear to play a role in the clinical course of the disease, probably because they provide tumor cells with a mechanism to escape cytotoxic T lymphocyte (CTL) recognition and destruction. Expression of HLA class I antigens, however, is not always associated with the susceptibility of tumor cells to CTL lysis. Many mechanisms may underlie this finding, including the lack of tumor antigen (TA)-derived peptide presentation by a given HLA class I allospecificity, and/or the expression of immunosuppressive molecules such as HLA-G. These findings emphasize the need to develop probes to measure HLA class I allospecificity-TA peptide complex expression in malignant cells. Furthermore, the evaluation of the role of HLA class I antigens in the interaction of malignant cells with host immune cells should take into account the potential interference of tumor-derived immunomodulators.

Very long chain fatty acid beta-oxidation by rat liver mitochondria and peroxisomes

Crude mitochondrial fractions were isolated by differential centrifugation of rat liver homogenates. Subfractionation of these fractions on self-generating continuous Percoll gradients resulted in clearcut separation of peroxisomes from mitochondria. Hexacosanoic acid beta-oxidation was present mainly in peroxisomal fractions whereas hexacosanoyl CoA oxidation was present in the mitochondrial as well as in the peroxisomal fractions. The presence of much greater hexacosanoyl CoA synthetase activity in the purified preparations of microsomes and peroxisomes compared to mitochondria, suggests that the synthesis of coenzyme A derivatives of very long chain fatty acids (VLCFA) is limited in mitochondria. We postulate that a specific VLCFA CoA synthetase may be required to effectively convert VLCFA to VLCFA CoA in the cell. This specific synthetase activity is absent from the mitochondrial membrane, but present in the peroxisomal and the microsomal membranes. We postulate that substrate specificity and the subcellular localization of the specific VLCFA CoA synthetase directs and regulates VLCFA oxidation in the cell.