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Defects of DNA mismatch repair (MMR) cause the high level microsatellite instability (MSI-H) phenotype. MSI-H cancers may develop either sporadically or in the context of the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome that is caused by germline mutations of MMR genes. In colorectal cancer (CRC), MSI-H is characterized by a dense lymphocytic infiltration, reflecting a high immunogenicity of these cancers. As a consequence of immunoselection, MSI-H CRCs frequently display a loss of human leukocyte antigen (HLA) class I antigen presentation caused by mutations of the b2-microglobulin (b2m) gene. To examine the implications of b2m mutations during MSI-H colorectal tumor development, we analyzed the prevalence of b2m mutations in MSI-H colorectal adenomas (n 5 38) and carcinomas (n 5 104) of different stages. Mutations were observed in 6/38 (15.8%) MSI-H adenomas and 29/104 (27.9%) MSI-H CRCs. A higher frequency of b2m mutations was observed in MSI-H CRC patients with germline mutations of MMR genes MLH1 or MSH2 (36.4%) compared with patients without germline mutations (15.4%). The high frequency of b2m mutations in HNPCC-associated MSI-H CRCs is in line with the hypothesis that immunoselection may be particularly pronounced in HNPCC patients with inherited predisposition to develop MSI-H cancers. b2m mutations were positively related to stage in tumors without distant metastases (UICC I-III), suggesting that loss of b2m expression may promote local progression of colorectal MSI-H tumors. However, no b2m mutations were observed in metastasized CRCs (UICC stage IV, p 5 0.04). These results suggest that functional b2m may be necessary for distant metastasis formation in CRC patients. ' 2007 Wiley-Liss, Inc.

High-level microsatellite instability (MSI-H) in colorectal cancer accounts for about 12% of colorectal cancers and is typically associated with a dense infiltration with cytotoxic CD8-positive lymphocytes. The role of regulatory T cells that may interfere with the host's antitumoural immune response in MSI-H colorectal cancers has not been analysed yet. Using an antibody directed against the regulatory T-cell marker transcription factor forkhead box P3 (FOXP3), regulatory T cells were examined in 70 colorectal cancers with known MSI status (MSI-H, n ¼ 37; microsatellite stable, n ¼ 33). In MSI-H colorectal cancers, we found a significantly higher intraepithelial infiltration with FOXP3-positive cells (median: 8.5 cells per 0.25 mm 2 vs 3.1 cells per 0.25 mm 2 in microsatellite stable, Po0.001), and a significantly elevated ratio of intraepithelial to stromal infiltration (0.05 vs 0.01 in microsatellite stable, Po0.001). CD8-positive cell counts were related positively to the number of FOXP3-positive cells (Spearman's r ¼ 0.56 and 0.55, respectively). Our results show that the elevated number of CD8-positive lymphocytes found in MSI-H colorectal cancers is paralleled by an enhanced infiltration with CD8-negative FOXP3-positive cells. These data suggest that FOXP3-positive cells may play a role in the regulation of the immune response directed against MSI-H colorectal cancers at the primary tumour site.

Purpose: DNA mismatch repair (MMR) deficiency is a hallmark of Lynch syndrome, the most common inherited cancer syndrome. MMR-deficient cancer cells accumulate numerous insertion/deletion mutations at microsatellites. Mutations of coding microsatellites (cMS) lead to the generation of immunogenic frameshift peptide (FSP) neoantigens. As the evolution of MMR-deficient cancers is triggered by mutations inactivating defined cMS-containing tumor suppressor genes, distinct FSP neoantigens are shared by most MMRdeficient cancers. To evaluate safety and immunogenicity of an FSP-based vaccine, we performed a clinical phase I/IIa trial (Micoryx).Patients and Methods: The trial comprised three cycles of four subcutaneous vaccinations (FSP neoantigens derived from mutant AIM2, HT001, TAF1B genes) mixed with Montanide ISA-51 VG over 6 months. Inclusion criteria were history of MMR-deficient colorectal cancer (UICC stage III or IV) and completion of chemotherapy. Phase I evaluated safety and toxicity as primary endpoint (six patients), phase IIa addressed cellular and humoral immune responses (16 patients).Results: Vaccine-induced humoral and cellular immune responses were observed in all patients vaccinated per protocol. Three patients developed grade 2 local injection site reactions. No vaccination-induced severe adverse events occurred. One heavily pretreated patient with bulky metastases showed stable disease and stable CEA levels over 7 months.Conclusions: FSP neoantigen vaccination is systemically well tolerated and consistently induces humoral and cellular immune responses, thus representing a promising novel approach for treatment and even prevention of MMR-deficient cancer.

Lynch syndrome is caused by germline mutations of DNA mismatch repair (MMR) genes, most frequently MLH1 and MSH2. Recently, MMR-deficient crypt foci (MMR-DCF) have been identified as a novel lesion which occurs at high frequency in the intestinal mucosa from Lynch syndrome mutation carriers, but very rarely progress to cancer. To shed light on molecular alterations and clinical associations of MMR-DCF, we systematically searched the intestinal mucosa from Lynch syndrome patients for MMR-DCF by immunohistochemistry. The identified lesions were characterised for alterations in microsatellite-bearing genes with proven or suspected role in malignant transformation. We demonstrate that the prevalence of MMR-DCF (mean 0.84 MMR-DCF per 1 cm2 mucosa in the colorectum of Lynch syndrome patients) was significantly associated with patients’ age, but not with patients’ gender. No MMR-DCF were detectable in the mucosa of patients with sporadic MSI-H colorectal cancer (n = 12). Microsatellite instability of at least one tested marker was detected in 89% of the MMR-DCF examined, indicating an immediate onset of microsatellite instability after MMR gene inactivation. Coding microsatellite mutations were most frequent in the genes HT001 (ASTE1) with 33%, followed by AIM2 (17%) and BAX (10%). Though MMR deficiency alone appears to be insufficient for malignant transformation, it leads to measurable microsatellite instability even in single MMR-deficient crypts. Our data indicate for the first time that the frequency of MMR-DCF increases with patients’ age. Similar patterns of coding microsatellite instability in MMR-DCF and MMR-deficient cancers suggest that certain combinations of coding microsatellite mutations, including mutations of the HT001, AIM2 and BAX gene, may contribute to the progression of MMR-deficient lesions into MMR-deficient cancers.

Germline deletions affecting the Epithelial cell adhesion molecule (EPCAM) gene lead to silencing of MSH2 and cause Lynch syndrome. We have recently reported that lack of EPCAM expression occurs in many, but not all tumors from Lynch syndrome patients with EPCAM germline deletions. The differences in EPCAM expression were not related to the localization of EPCAM germline deletions. We therefore hypothesized that the type of the second somatic hit, which leads to MSH2 inactivation during tumor development, determines EPCAM expression in the tumor cells. To test this hypothesis and to evaluate whether lack of EPCAM expression can already be detected in Lynch syndrome-associated adenomas, we analyzed four carcinomas and two adenomas from EPCAM germline deletion carriers for EPCAM protein expression and allelic deletion status of the EPCAM gene region by multiplex ligation-dependent probe amplification. In four out of six tumors we observed lack of EPCAM expression accompanied by biallelic deletions affecting the EPCAM gene. In contrast, monoallelic retention of the EPCAM gene was observed in the remaining two tumors with retained EPCAM protein expression. These results demonstrate that EPCAM expression in tumors from EPCAM deletion carriers depends on the localization of the second somatic hit that inactivates MSH2. Moreover, we report lack of EPCAM protein expression in a colorectal adenoma, suggesting that EPCAM immunohistochemistry may detect EPCAM germline deletions already at a precancerous stage. Modern Pathology (2012) 25, 911-916;

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QOL and functional results of patients with UC 10 years or more after IPAA were acceptable; however, those were reduced when compared to a healthy population. Pouch failure rate still increases up to 15.5% 15 years after IPAA. This result represents an important issue in providing patients with comprehensive preoperative information.