High Prevalence of Activated Intraepithelial Cytotoxic T Lymphocytes and Increased Neoplastic Cell Apoptosis in Colorectal Carcinomas with Microsatellite Instability

Abstract

Microsatellite instability (MSI) characterizes colorectal carcinomas (CRCs) in hereditary nonpolyposis colorectal cancer (HNPCC) syndrome and a proportion of sporadic CRCs. These MSI+ CRCs share several clinicopathological features, including a reputation for better survival rates than MSI- cases and a pronounced stromal inflammatory reaction of still undefined nature. In the present study, the presence, spatial distribution, and activation status of infiltrating cytotoxic effectors were investigated comparatively in 18 MSI+ and 37 MSI- CRCs by immunohistochemistry. The frequency of apoptosis was also evaluated by morphology and in situ end-labeling. MSI+ cases carried significantly higher numbers of cytotoxic lymphocytes infiltrating within neoplastic epithelial structures, as shown by immunostaining for CD3 (15.1 +/- 6.2 versus 4.6 +/- 4.1, P < 0.001), CD8 (13 +/- 6.4 versus 3.7 +/- 3.8, P < 0.001), and TIA-1 (11.2 +/- 6.5 versus 1.9 +/- 1.7, P < 0.001). These cytotoxic effectors were globally more activated in MSI+ than in MSI- tumors, as revealed by the expression of granzyme B (5.3 +/- 4.5 versus 0.6 +/- 1.3, P < 0.001). In MSI+ CRCs, the number of intraepithelial activated cytotoxic lymphocytes was significantly correlated with the proximal location of the tumor, a poorly differentiated phenotype, and the presence of peritumor lymphoid nodules. Multivariate analysis revealed that MSI was the major determinant of the presence of activated cytotoxic intraepithelial lymphocytes. Moreover, MSI+ CRCs also showed a significantly higher percentage of tumor cells undergoing apoptotic cell death (4.1 +/- 2.1 versus 2.6 +/- 1.1, P < 0.0001, by the TUNEL method), often located in close proximity of activated cytotoxic lymphocytes. These results are consistent with the presence of anti-tumor cytotoxic immune responses in most of MSI+ CRCs, a phenomenon that may at least in part contribute to the survival advantage ascribed to these patients.

Immunoprofiles of colorectal cancer from Lynch syndrome

“…4,5,8,18,19 Gene expression profiling further linked Lynch syndrome with genes involved in antigen processing and presentation, T cell activation, natural killer cell-mediated cytotoxicity, and apoptosis. 8,20–22 Loss of B2M in 28% of the Lynch syndrome tumors was within previous reported range of 21–30% and are likely caused by frameshift mutations in microsatellite regions of the B2M gene (Figure 1). 13,15 The tumorigenic event of B2M loss is likely occurring in the middle of the adenoma-carcinoma sequence since B2M loss has not been found in metastasizing tumors or MMR deficient adenomas.…”

Strong HLA-DR expression in microsatellite stable carcinomas of the large bowel is associated with good prognosis

“…This hypothesis is supported by the fact that there is a significant increase of the pronounced inflammatory reaction in the MSI-H tumours. Recently, two studies have identified the majority of TIL in MSI-H tumours as CD8+ T-cells, the number being higher than in MSS tumours (Dolcetti et al, 1999;Michael-Robinson et al, 2001). The number and distribution of infiltrating CD4+ lymphocytes were similar in MSI and MSS tumours (Dolcetti et al, 1999).…”

“…High density of tumour infiltrating lymphocytes (TIL) are found in MSI-H colorectal cancers, whereas it is only infrequently observed in MSI-L and MSS tumours (Jass et al, 1998;Smyrk et al, 2001). Recently, two studies have identified significantly more cytotoxic lymphocytes (CD3, CD8 and TIA-1) and a higher rate of cells undergoing apoptosis in MSI-H colorectal carcinomas than in MSI-L and MSS (Dolcetti et al, 1999;Michael-Robinson et al, 2001). Furthermore, patients with MSI-H tumours and a high content of activated cytotoxic lymphocytes showed improved overall survival (Guidoboni et al, 2001).…”

Immune Cells in Colorectal Cancer: Prognostic Relevance and Role of MSI

“…For a better prognostic assessment, Dolcetti et al [71] suggested the combination of evaluation of local lymphocytosis and the MSI status. MSI in combination with a high content of intraepithelial lymphocytes was found to be related to an improved overall survival in a group of exclusively right-sided CRCs.…”

“…Guidoboni et al [72] showed a significantly higher prevalence of activated CD8 + IEL in MSI+ versus MSI-CRC, suggesting that the occurrence of a local cytotoxic immune response may be the major determinant of the good clinical course of these MSI+ CRC patients. Dolcetti et al [71] and Michael-Robinson et al [73] demonstrated that the increased frequency of TILs associated with MSI-H cancers are only weakly or moderately correlated with tumor apoptosis. However, while TILs might be expected to explain the increased apoptotic rate and improved prognosis of MSI-H cancers, it is likely that MSI-H cancers are intrinsically more prone to apoptosis, independently of T cell attack [73].…”