Tumour-infiltrating lymphocytes in colorectal cancer with microsatellite instability are activated and cytotoxic.
BACKGROUND
Patients with colorectal cancer that display high-level microsatellite instability (MSI-H) appear to have a better prognosis. This may be explained by the pronounced T cell infiltrate seen in MSI-H tumours that is related to a specific antigen-driven immune response. The nature of tumour-infiltrating lymphocytes in colorectal cancers was investigated using quantitative real-time polymerase chain reaction (PCR) and immunohistochemistry.


METHODS
Quantitative fluorescent hydrolysis probe-based reverse transcriptase-PCR assays were used to detect levels of mRNA specifying T cell markers in fresh frozen colorectal tissue from MSI-H tumours and those with little or no microsatellite instability (microsatellite stable (MSS) tumours). In addition, immunohistochemistry was performed on paraffin-embedded sections to compare expression of the same T cell markers and the activation markers granzyme B and interleukin 2 receptor alpha-subunit (IL-2Ralpha) in MSI-H and MSS tumours.


RESULTS
MSI-H tumours contained higher ratios of CD8/CD3 mRNA copy numbers than MSS tumours (P = 0.016), confirming the cytotoxic nature of lymphocyte infiltrates in this subset of colorectal cancers. Furthermore, immunohistochemistry confirmed that MSI-H tumours contained more infiltrating lymphocytes than MSS tumours, as shown by increased expression of CD3 (P = 0.003) and CD8 (P = 0.008). Consistent with other studies, the lymphocytes in MSI-H tumours were activated as indicated by significantly higher granzyme B counts (P = 0.020) and a significantly higher level of expression of IL-2Ralpha (P = 0.017).


CONCLUSIONS
The results support the hypothesis that MSI-H colorectal cancers may be more immunogenic than MSS tumours.
Phillips
S M
SM
Academic Department of Surgery, Royal London Hospital, London, UK.
Banerjea
A
A
Feakins
R
R
Li
S R
SR
Bustin
S A
SA
Dorudi
S
S
D000368:Aged; D017252:CD3 Complex / Q000276:immunology; D016827:CD8 Antigens / Q000276:immunology; D015179:Colorectal Neoplasms / Q000276:immunology*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology*; D008297:Male; D018895:Microsatellite Repeats / Q000276:immunology*; D011379:Prognosis; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods
D017252:CD3 Complex; D016827:CD8 Antigens