Abstract 4467: Bim and CX3CR1/granzyme B in circulating CD8+ T cells are predictive biomarkers for PD-1 blockade therapy
Authors: Zhu Mojun , Zhang Henan , Foster Nathan R. , Dong Haidong , Bekaii-Saab Tanios S. , Jaszewski Brandy L. , Boland Patrick M. , Overman Michael J. , Pedersen Katrina , McWilliams Robert R. ,   Academic and Community Cancer Research United (AACRU)
Published: September 2020

Abstract
Immunotherapy targeting immune checkpoints has become a common approach for many types of cancer but currently there are no reliable biomarkers to predict and monitor treatment response. Immunohistochemical staining of PD-L1, which was initially developed as a companion diagnostic, is problematic due to tumor heterogeneity, variations in specimen preparation and multiple scoring schemes. There is, therefore, a critical need for a better biomarker to guide the use of immunotherapy to improve clinical outcomes. We previously reported that higher levels of Bim and CX3CR1/granzyme B in CD8+ T cells were associated with increased response to PD-1 blockade therapy in patients with melanoma; high levels of Bim were also prognostic of poor survival in melanoma patients. In this study, we investigated the roles of Bim and CX3CR1/granzyme B in patients receiving PD-1 blockade therapy (i.e. pembrolizumab) for small bowel adenocarcinoma as part of planned correlative analysis of the ACCRU clinical trial, NCT02949219. Patients with unresectable or metastatic biopsy-proven small bowel adenocarcinoma (excluding ampulla of Vater and appendix) who had at least one prior line of systemic chemotherapy were eligible for the trial. Pembrolizumab (200 mg) was administered over 30 minutes intravenously every 3 weeks until unacceptable toxicity, disease progression, or patient refusal. All patients underwent peripheral blood collection at baseline prior to initiation of treatment and then after 3 cycles of treatment. Levels of Bim and CX3CR1/granzyme B in circulating T cells were quantified by flow cytometry using patients' peripheral blood mononuclear cells. Data was analyzed via Cox proportional hazards model, Wilcoxon Rank-Sum test, and Kaplan Meier curves using SAS 9.4. A total of 35 eligible patients were included in the analysis. Three patients had confirmed response (all partial responses) and 10 had stable disease as their best overall response. Seven patients had disease progression around the second blood draw. The median time from baseline to the second blood draw was 9 weeks. Lower levels of Bim in CD8+CD11ahi T cells at baseline on the percentage scale were associated with treatment response (median 54.5% vs. 79.5%; p=0.0087) and disease control (partial response plus stable disease; median 71.2% vs. 81.3%; p=0.0104) but higher levels led to worse progression-free survival (hazard ratio=1.05, 95% confidence interval 1.01-1.08; p=0.0051). In addition, positive changes in CX3CR1/granzyme B in CD8+CD11ahi T cells from baseline were associated with better overall survival (median 20.2 months vs. 3.7 months, p=0.0086). The levels of PD-1 and Ki-67 in CD8+CD11ahi T cells were not associated with treatment response or survival. In conclusion, Bim and CX3CR1/granzyme B are biomarkers that associate with response and survival benefits respectively of PD-1 blockade therapy. This preliminary data calls for a larger-scale, prospective study to validate their predictive and prognostic utilities.
Citation Format: Mojun Zhu, Henan Zhang, Nathan R. Foster, Haidong Dong, Tanios S. Bekaii-Saab, Brandy L. Jaszewski, Patrick M. Boland, Michael J. Overman, Katrina Pedersen, Robert R. McWilliams, Academic and Community Cancer Research United (AACRU). Bim and CX3CR1/granzyme B in circulating CD8+ T cells are predictive biomarkers for PD-1 blockade therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4467.