Mismatch repair gene defects in sporadic colorectal cancer enhance immune surveillance.

Marco Scarpa,Ignazio Castagliuolo,Alain Fiorot,Francesca Erroi,Carlo Castoro,Lucia Dall’Agnese,Andrea Porzionato,Anna Pozza,Fabio Canal,Melania Scarpa,Angelo P Dei Tos,Nicolò Bassi,Silvia Basato,Cesare Ruffolo

doi:10.18632/oncotarget.6179

Abstract

There is evidence that colorectal cancers (CRC) with DNA mismatch repair deficiency (MMR-D) are associated with a better prognosis than the generality of large bowel malignancies. Since an active immune surveillance process has been demonstrated to influence CRC outcome, we investigated whether MMR-D can enhance the immune response in CRC. A group of 113 consecutive patients operated for CRC (42 stage I or II and 71 with stage III or IV) was retrospectively analyzed. The expression of MMR genes (MSH2, MLH1, MSH6 and PSM2) and co-stimulatory molecule CD80 was assessed by tissue microarray immunohistochemistry. In addition, tumor infiltrating mononuclear cells (TIMC) and T cell subpopulations (CD4, CD8, T-bet and FoxP-3) were quantified. The effect of specific siRNA (siMSH2, siMLH1, siMSH6 and siPSM2) transfection in HT29 on CD80 expression was quantified by flow cytometry. Non parametric statistics and survival analysis were used. Patients with MMR-D showed a higher T-bet/CD4 ratio (p = 0.02), a higher rate of CD80 expression and CD8 lymphocyte infiltration compared to those with no MMR-D. Moreover, in the MMR-D group, the Treg marker FoxP-3 was not expressed (p = 0.05). MMR-D patients with stage I or II and T-bet expression had a significant better survival (p = 0.009). Silencing of MSH2, MLH1 and MSH6, but not PSM2, significantly increased the rate of CD80+ HT29 cells (p = 0.007, p = 0.023 and p = 0.015, respectively). CRC with MMR-D showed a higher CD80 expression, and CD8+ and Th1 T-cell infiltration. In vitro silencing of MSH2, MLH1 and MSH6 significantly increased CD80+ cell rate. These results suggest an enhanced immune surveillance mechanism in presence of MMR-D.

Highlights

5% of colorectal cancers (CRC) occur in the setting of a heritable syndrome, such as hereditary non polyposis colon cancer (HNPCC) syndrome [1]
In vitro silencing of MSH2, MLH1 and MSH6 significantly increased CD80+ cell rate. These results suggest an enhanced immune surveillance mechanism in presence of MMR-D
We demonstrated that CD80-CD28 signalling controls the progression of inflammatory colorectal carcinogenesis [2628]

Summary

Introduction

5% of colorectal cancers (CRC) occur in the setting of a heritable syndrome, such as hereditary non polyposis colon cancer (HNPCC) syndrome [1]. Highfrequency MSI occurs in approximately 15% of sporadic colon and other tumours [3], wherein the MMR defect develops because of epigenetic inactivation of the MLH1 gene by DNA methylation [4,5,6]. The underlying mechanisms responsible for the better outcome of MMR-deficient CRC are poorly understood. Sinicrope et al observed that a higher density of tumor infiltrating lymphocytes (TILs), most of which were CD3+T lymphocytes [16], was associated with better disease free survival in cases with defective versus intact MMR [17]. There is evidence that colorectal cancers (CRC) with DNA mismatch repair deficiency (MMR-D) are associated with a better prognosis than the generality of large bowel malignancies. Since an active immune surveillance process has been demonstrated to influence CRC outcome, we investigated whether MMR-D can enhance the immune response in CRC

Methods

Results

Conclusion