The infiltration, and prognostic importance, of Th1 lymphocytes vary in molecular subgroups of colorectal cancer

Abstract

Giving strong prognostic information, T‐cell infiltration is on the verge of becoming an additional component in the routine clinical setting for classification of colorectal cancer (CRC). With a view to further improving the tools for prognostic evaluation, we have studied how Th1 lymphocyte infiltration correlates with prognosis not only by quantity, but also by subsite, within CRCs with different molecular characteristics (microsatellite instability, CpG island methylator phenotype status, and BRAF and KRAS mutational status). We evaluated the Th1 marker T‐bet by immunohistochemistry in 418 archival tumour tissue samples from patients who underwent surgical resection for CRC. We found that a high number of infiltrating Th1 lymphocytes is strongly associated with an improved prognosis in patients with CRC, irrespective of intratumoural subsite, and that both extent of infiltration and patient outcome differ according to molecular subgroup. In brief, microsatellite instability, CpG island methylator phenotype‐high and BRAF mutated tumours showed increased infiltration of Th1 lymphocytes, and the most pronounced prognostic effect of Th1 infiltration was found in these tumours. Interestingly, BRAF mutated tumours were found to be more highly infiltrated by Th1 lymphocytes than BRAF wild‐type tumours whereas the opposite was seen for KRAS mutated tumours. These differences could be explained at least partly by our finding that BRAF mutated, in contrast to KRAS mutated, CRC cell lines and tumour specimens expressed higher levels of the Th1‐attracting chemokine CXCL10, and reduced levels of CCL22 and TGFB1, stimulating Th2/Treg recruitment and polarisation. In conclusion, the strong prognostic importance of Th1 lymphocyte infiltration in CRC was found at all subsites evaluated, and it remained significant in multivariable analyses, indicating that T‐bet may be a valuable marker in the clinical setting. Our results also indicate that T‐bet is of value when analysed in molecular subgroups of CRC, allowing identification of patients with especially poor prognosis who are in need of extended treatment.

The density of Tbet+ tumor-infiltrating T lymphocytes reflects an effective and druggable preexisting adaptive antitumor immune response in colorectal cancer, irrespective of the microsatellite status

“…Furthermore, Ling et al reported the favorable prognostic impact of Tbet+ TILs in MSI CRC, and observed the same trend (not statistically significant however) in MSS CRC. 40 Thus, our results demonstrate that quantification of Tbet+ can recapitulate the favorable ongoing IFNγ response induced by Th1/Tc1 TILs, more frequent in MSI but also in some "inflamed" MSS CRC. To further characterize these "inflamed" MSS CRC, especially the potential immunogenicity of BRAF or RAS mutations in those tumors, we correlated the Tbet/CD3 ratio with the tumor BRAF or RAS mutational status but did not find any significant difference between mutated or wild-type MSS CRC.…”

“…The identification of Tbet+ TILs by immunohistochemistry was previously reported in CRC in only few studies, with a higher density in MSI than in MSS CRC in line with our results. 39,40 However, these studies did not precise the heterogeneous expression of this biomarker, especially among MSS CRC between inflammatory versus noninflammatory tumors, a major issue in this therapeutic and prognostic context. Furthermore, Ling et al reported the favorable prognostic impact of Tbet+ TILs in MSI CRC, and observed the same trend (not statistically significant however) in MSS CRC.…”

“…The average count per field was calculated and recorded, without analyzing separately the center and the invasive front of the tumor since the clinical impact of Tbet+ TILs seems to be independent of the intratumoral subsite. 40 Two pathologists (EO and CB) independently scored all cases and discrepant cases were reviewed on a multiheaded microscope.…”

TAP1 down-regulation elicits immune escape and poor prognosis in colorectal cancer

“…6,41 Lymphovascular invasion was recorded as present or absent (yes or no). Tumor budding at the invasive front was quantified on pancytokeratin-stained slides according to Prall et al 42 and scored as low grade (0-9 buds per microscopic field) or high grade (10 or more), adapted from Ueno et al 43 Infiltration of different subsets of lymphocytes and macrophages has also previously been assessed in the CRUMS cohort, 5,6,41,44 along with infiltration of neutrophils (CD66b C ) (unpublished evaluation). After exclusions due to unavailable or insufficient tumor sample, and/or lack of clinical information, 436 patients were included in the study.…”

“…Several studies, by us and others, have focused on the tumor immune response which has proven critical to prognosis in CRC. [2][3][4][5][6][7] Findings in this area have driven the design of the Immunoscore system, 8 which is to be implemented in clinic as a complement to the TNM staging system.…”