Colorectal cancers with microsatellite instability display mRNA expression signatures characteristic of increased immunogenicity.
BACKGROUND
Colorectal cancers displaying high-degree microsatellite instability (MSI-H) have an improved prognosis compared to microsatellite stable (MSS) cancers. The observation of pronounced lymphocytic infiltrates suggests that MSI-H cancers are inherently more immunogenic. We aimed to compare the gene expression profiles of MSI-H and MSS cancers to provide evidence for an activated immune response in the former.


RESULTS
We analysed tissue from 133 colorectal cancer patients with full consent and Local Ethics Committee approval. Genomic DNA was analysed for microsatellite instability in BAT-26. High-quality RNA was used for microarray analysis on the Affymetrix HG-U133A chip. Data was analysed on GeneSpring software version 6.0. Confirmatory real-time RT-PCR was performed on 28 MSI-H and 26 MSS cancers. A comparison of 29 MSI-H and 104 MSS cancers identified 2070 genes that were differentially expressed between the two groups [P < 0.005]. Significantly, many key immunomodulatory genes were up-regulated in MSI-H cancers. These included antigen chaperone molecules (HSP-70, HSP-110, Calreticulin, gp96), pro-inflammatory cytokines (Interleukin (IL)-18, IL-15, IL-8, IL-24, IL-7) and cytotoxic mediators (Granulysin, Granzyme A). Quantitative RT-PCR confirmed up-regulation of HSP-70 [P = 0.016], HSP-110 [P = 0.002], IL-18 [P = 0.004], IL-8 [0.002] and Granulysin [P < 0.0001].


CONCLUSIONS
The upregulation of a large number of genes implicated in immune response supports the theory that MSI-H cancers are immunogenic. The novel observation of Heat Shock Protein up-regulation in MSI-H cancer is highly significant in light of the recognised roles of these proteins in innate and antigen-specific immunogenicity. Increased mRNA levels of pro-inflammatory cytokines and cytotoxic mediators also indicate an activated anti-tumour immune response.
Banerjea
Ayan
A
Centre for Academic Surgery, Barts and The London Queen Mary School of Medicine and Dentistry, The Royal London Hospital, Whitechapel, London, E1 1BB, UK. a.banerjea@qmul.ac.uk
Ahmed
Shafi
S
Hands
Rebecca E
RE
Huang
Fei
F
Han
Xia
X
Shaw
Peter M
PM
Feakins
Roger
R
Bustin
Stephen A
SA
Dorudi
Sina
S
D015179:Colorectal Neoplasms / Q000235:genetics* / Q000276:immunology*; D020869:Gene Expression Profiling; D006801:Humans; D018895:Microsatellite Repeats / Q000235:genetics / Q000276:immunology*; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation / Q000276:immunology
D012333:RNA, Messenger