Cytotoxic tumour-infiltrating T lymphocytes influence outcome in resected pancreatic ductal adenocarcinoma

Highlights

• The prognostic effects of lymphocyte subpopulations were studied in patients with pancreatic carcinoma (PDAC).

• A high number of CD8-positive lymphocytes are associated with longer in PDAC.

• The ratio of intraepithelial to total CD103-positive lymphocytes is associated with longer DFS and OS in PDAC.

Abstract

Background

We studied the prognostic effect of CD3-, CD8- and CD103-positive T lymphocytes in a cohort of 165 patients with resected pancreatic ductal adenocarcinomas (PDACs) of the treatment group (adjuvant gemcitabine) and the untreated control group of the CONKO-001 study.

Methods

Immunohistochemical stainings on tissue microarrays (TMAs) against CD3, CD8 and CD103 were performed according to standard procedures.

Results

A high number of CD8-positive lymphocytes were significantly and independently associated with longer disease-free survival (DFS) and overall survival (OS) in the overall study population. Median DFS/OS were 7.4/18.1 months for patients with a low number of CD8-positive intratumoural lymphocytes ($\le$42 per 1 mm tissue core) and 12.7/25.2 months for patients with high numbers (>42 per 1-mm tissue core; p = 0.008/0.020; HR 0.62/0.65). The ratio of intraepithelial to total CD103-positive lymphocytes, but not total numbers of CD103-positive lymphocytes or CD103-positive intraepithelial lymphocytes, was associated with significantly improved DFS and OS in the overall study population (p = 0.022/0.009). Median DFS/OS was 5.9/15.7 for patients with a ratio of intraepithelial to total CD103-positive intratumoural lymphocytes higher than 0.3 and 11.6/24.7 for patients with a lower ratio.

Conclusion

T-lymphocyte subpopulations might be prognostic in resectable PDAC but need standardization and verification by further studies.

Introduction

Over the past decades it has been recognised that the complex tumour microenvironment with its multiple different cell types like cancer-associated fibroblasts, endothelial cells, pericytes and different immune cells has an important impact on the development [1] and behaviour of different solid tumours. The host immune reaction to the tumour might be one of the most important factors of the tumour microenvironment and subsequent immune escape mechanisms have been recognised as an emerging hallmark of cancer [2]. The host immune reaction to the tumour is highly complex and comprises cells with tumour-promoting capabilities and those with capabilities directed against cancer cells. T lymphocytes as part of the adaptive immune response are frequently found in the tumour microenvironment. Studies on large cohorts of breast cancer [3], [4] or colon carcinoma [5], [6] have shed light on the prognostic and predictive impacts of tumour-infiltrating T lymphocytes.

Despite the fact that lymphocytic infiltrations are regularly seen in pancreatic ductal adenocarcinoma (PDAC), studies on the prognostic impact of lymphocytes are still sparse. In the here-presented translational study, the prognostic effect of CD3- and CD8-expressing T lymphocytes was studied in a cohort of 165 pancreatic adenocarcinomas from the prospective clinical multicenter CONKO-001 trial. Furthermore, we studied the prognostic effect of CD103-expressing lymphocytes. The only known ligand to the alpha_E/beta₇ integrin adhesion molecule subunit CD103 is E-cadherin [7], [8], [9], which is typically expressed by epithelial cells. Therefore, CD103 is thought to demarcate specifically intraepithelial tumour-infiltrating lymphocytes (TILs) in some cancer entities, like different types of ovarian epithelial cancer [10] and might play a role in the host response against pancreatic cancer. CONKO-001 is a prospective phase III trial, investigating the role of adjuvant gemcitabine in pancreatic cancer patients [11]. It disposes prospectively collected clinical data and a follow-up of more than 5 years, as well as two randomised groups of patients: one treated for 6 months postoperatively with gemcitabine compared with the one that was only observed.

In this study, we evaluated the hypothesis that increased numbers of CD3, CD8 and CD103 tumour-associated lymphocytes are linked to better prognosis. Gemcitabine is known to influence the immune reaction to antigens and has been administered in clinical studies to boost the immune reaction to vaccinated peptides [12], [13]. Therefore, we evaluated if the prognostic effect of CD8- and CD103-expressing cytotoxic T lymphocytes in formalin-fixed paraffin-embedded (FFPE) tumour specimen was different in patients with or without adjuvant chemotherapy in the two treatment arms of the CONKO-001 trial. We additionally correlated the number of CD103-positive T lymphocytes with the expression of the CD103-ligand E-cadherin in tumour cells.