title: Tumour-infiltrating lymphocytes in colorectal cancer with microsatellite instability are activated and cytotoxic.
abstract: 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.
authors.affiliation: Academic Department of Surgery, Royal London Hospital, London, UK.
authors.forename: S M
authors.initials: SM
authors.lastname: Phillips
authors.forename: A
authors.initials: A
authors.lastname: Banerjea
authors.forename: R
authors.initials: R
authors.lastname: Feakins
authors.forename: S R
authors.initials: SR
authors.lastname: Li
authors.forename: S A
authors.initials: SA
authors.lastname: Bustin
authors.forename: S
authors.initials: S
authors.lastname: Dorudi
mesh_terms: 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
chemical_list: D017252:CD3 Complex; D016827:CD8 Antigens