Original ResearchPD-L1 is upregulated by radiochemotherapy in rectal adenocarcinoma patients and associated with a favourable prognosis
Introduction
The programmed cell death protein 1 (PD-1) pathway, functioning as an ‘immune checkpoint’, is a promising target for immunotherapy of cancer. PD-1 negatively regulates T-cell response. An inhibition of PD-1 is suspected to promote anti-tumour immunity by re-activating suppressed T-lymphocytes. Recently, the immune checkpoint inhibitors nivolumab and pembrolizumab, which inhibit the PD-1 pathway, dramatically improved the treatment of metastatic melanoma and lung cancer in large phase III trials [1], [2]. In a phase II trial, pembrolizumab was also highly effective in mismatch repair-deficient colorectal cancer [3]. Programmed death-ligand 1 (PD-L1) (synonym: B7-H1) and PD-L2 (synonym: B7-DC) are the ligands of PD-1 and are physiologically found on inflammatory cells. It is suspected that cancer cells express PD-1 ligands as a mean of immune evasion. Recently, PD-L1 expression was identified to be predictive of a successful PD-1 inhibitor therapy [4].
Radiotherapy is generally regarded as a cell death-inducing technique. It is less appreciated that radiation can induce inflammatory or anti-inflammatory reactions depending on dose and fractionation [5], [6]. Radiotherapeutic treatment schemes against cancer induce tumour cell death and inflammation in the tumour microenvironment [6]. This leads to a local immune response with upregulation of PD-L1 in vitro [7], [8]. Pre-clinical studies propose a synergism of local radiotherapy and PD-1/PD-L1 pathway inhibition by the induction of systemic anti-cancer immune responses. This combination improved both local and systemic tumour control in mice [7], [8], [9]. In a small oesophageal cancer patient cohort with paired tissue samples of 12 patients before and after radiochemotherapy (RCT), an upregulation of PD-L1 was detected [10].
Thus, one aim of this study was to evaluate the influence of RCT on PD-L1 expression in a representative number of cancer patients, as an upregulation of PD-L1 in vivo, would strongly support the initiation of clinical trials combining RCT and PD-1 blockade.
Both systemic inflammation and local immune markers in tumour tissue can be used as prognostic markers [11], [12]. In colorectal cancer, the prognostic value of PD-L1 is discussed contradictorily [13], [14], [15]. To our knowledge, no analysis exists in advanced rectal adenocarcinoma patients homogenously treated with neoadjuvant RCT. Furthermore, the prognostic value of PD-L1 expression on inflammatory cells has only been studied marginally. So another aim of this analysis was to evaluate the PD-L1 expression on cancer cells and inflammatory cells as possible prognostic markers in rectal adenocarcinoma treated with neoadjuvant RCT.
Section snippets
Patients
Formalin-fixed paraffin-embedded tissue of 199 patients with rectal adenocarcinoma treated with neoadjuvant RCT at the University Hospital Erlangen between 2006 and 2013 was collected. Clinical characteristics of the study group are given in Table 1. In more than 80% of the patients, the neoadjuvant RCT was performed with 5-fluorouracil (5-FU)/oxaliplatin or 5-FU concomitantly. Radiotherapy consisted of 50.4 Gy radiation in 28 fractions delivered to the primary tumour and the mesorectal,
PD-L1 expression before and after neoadjuvant radiochemotherapy
PD-L1 in rectal adenocarcinoma cells and inflammatory cells was evaluated in a patient cohort treated homogenously with neoadjuvant RCT (Table 1). One hundred and three pre-RCT biopsies and 159 post-RCT surgical specimens were available. All samples were included in the analysis. PD-L1 expression was studied both in pre-RCT biopsies and post-RCT surgical specimens in the central tumour, invasive front and adjacent normal mucosa. Both the maximum staining intensity and the proportion of
Discussion
In pre-clinical models, the combination of PD-1 inhibitors and ionizing radiation synergistically inhibited tumour growth. In mouse models with different tumour types, an excellent local tumour control was achieved with PD-1/PD-L1 pathway blockade combined with radiotherapy [7], [8], [9]. Furthermore, anti-tumour immunity was promoted by this approach, which also improved tumour control of contralateral not-irradiated second tumours in mice. The suspected mechanism is a local radiation-induced
Conclusion
Neoadjuvant RCT is associated with an increase of the proportion of PD-L1+ tumour cells in rectal adenocarcinoma patients. This finding confirms pre-clinical experiments and supports the initiation of clinical trials investigating a combination of radiochemotherapy and PD-1/PD-L1 pathway blockade. To determine whether there exists a cause-and-effect relation of RCT and upregulation of PD-L1 will require further investigation. High PD-L1 on inflammatory cells, but not on tumour cells, is
Conflict of interest statement
None declared.
Funding
The study was funded by the Department of Radiation Oncology and the Department of Pathology of the Universitätsklinikum Erlangen of the Friedrich-Alexander-Universität Erlangen-Nürnberg.
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These authors contributed equally to this work.