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


RESULTS
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).


CONCLUSIONS
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.
Surgical Oncology Unit, Veneto Institute of Oncology IOV-IRCCS, Padova, Italy.
Marco
M
Scarpa
General Surgery Unit (IV), "Ca' Foncello" Hospital, Treviso, Italy.
Cesare
C
Ruffolo
Pathology Unit, "Ca' Foncello" Hospital, Treviso, Italy.
Fabio
F
Canal
Surgical Oncology Unit, Veneto Institute of Oncology IOV-IRCCS, Padova, Italy.
Melania
M
Scarpa
Department of Surgical, Oncological and Gastroenterological Sciences, University of Padova, Padova, Italy.
Silvia
S
Basato
Department of Surgical, Oncological and Gastroenterological Sciences, University of Padova, Padova, Italy.
Francesca
F
Erroi
General Surgery Unit (IV), "Ca' Foncello" Hospital, Treviso, Italy.
Alain
A
Fiorot
Department of Surgical, Oncological and Gastroenterological Sciences, University of Padova, Padova, Italy.
Lucia
L
Dall'Agnese
Department of Surgical, Oncological and Gastroenterological Sciences, University of Padova, Padova, Italy.
Anna
A
Pozza
Department of Molecular Medicine, University of Padova, Padova, Italy.
Andrea
A
Porzionato
Department of Molecular Medicine, University of Padova, Padova, Italy.
Ignazio
I
Castagliuolo
Pathology Unit, "Ca' Foncello" Hospital, Treviso, Italy.
Angelo P
AP
Dei Tos
General Surgery Unit (IV), "Ca' Foncello" Hospital, Treviso, Italy.
Nicolò
N
Bassi
Surgical Oncology Unit, Veneto Institute of Oncology IOV-IRCCS, Padova, Italy.
Carlo
C
Castoro
D000368:Aged; D000369:Aged, 80 and over; D018122:B7-1 Antigen / Q000032:analysis / Q000096:biosynthesis; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000276:immunology* / Q000401:mortality; D053843:DNA Mismatch Repair / Q000235:genetics*; D005260:Female; D005434:Flow Cytometry; D019073:HT29 Cells; D006801:Humans; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology*; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D012189:Retrospective Studies; D046888:Tissue Array Analysis
D018122:B7-1 Antigen
CD80; colorectal cancer; immune surveillance; mismatch repair