Abstract 2657: PD-L1 blockade enhances T cell cytotoxicity against primary mediastinal B cell lymphoma

Abstract

Abstract Background: Primary Mediastinal B cell Lymphoma (PMBL) represents 2-4% of Non-Hodgkin Lymphomas (NHL) in adolescents and young adults (AYA) (Gerrard/Cairo et al., Blood, 2013). Disease progression, relapse and long-term toxicity remain a concern for patients treated on current chemo-immunotherapy and mediastinal radiotherapy. Alternative therapeutic regimens are urgently needed, especially in patients without an early response to therapy. Programmed Death 1 (PD-1) is a negative co-stimulatory receptor critical for suppression of T-cell activation, with binding of PD-1 and Programmed Death Ligand 1 (PD-L1) resulting in T cell exhaustion (Postow/Wolchok et al., J Clin Oncol, 2015). Gain in 9p associated with amplification of PD-L1 has been reported in up to 60% of PMBL specimens, leading to overexpression of PD-L1 and potential immune cell evasion of PMBL (Rosenwald/Staudt et al., J Exp Med, 2003; Twa/Steidl et al., Blood, 2014). Blockade of PD-1/PD-L1 interaction, therefore, constitute a potentially promising alternative for treatment of resistant PMBL. Objective: In the current study, we sought to investigate whether PD-L1 blockade enhances T cell responses in PD-L1 expressing PMBL. Methods: PD-L1 expression on Karpas 1106p PMBL treated with or without IFN γ was investigated by western blotting and flow cytometry analyses. T cells were isolated from human PBMC followed by activation and expansion using anti-CD2, anti-CD3 and anti-CD28 Biotinylated MACSiBead particles. T cell activation was confirmed by CD25 and CD69 expression using flow cytometry. Activated T cells were incubated with or without anti-PD-L1 (Clone 6E11, Genentech) at a dose of 10 ug/ml together with Karpas 1106p cells treated with or without IFN γ. Cell proliferation was assessed with MTS assays after incubation for 24 hours. Results: We demonstrated that Karpas 1106p cells express a low level of PD-L1. However, following IFN γ treatment (48 hours) there was a significant increase in PD-L1 expression. Anti-PD-L1 had no significant effect on T cell mediated inhibition of cell proliferation in Karpas 1106p cells with low PD-L1 expression. However, anti-PD-L1 and T cell treatment significantly inhibited cell proliferation in IFN γ treated Karpas 1106p cells when compared to T cell treatment alone (32±18% vs. 3±3% at E:T=5:1, p=0.048). Conclusion: PD-L1 blockade enhances T cell cytotoxicity against PMBL, which is dependent on PD-L1 expression level on PMBL cells. Future in-vivo NSG xenograft studies are ongoing. Citation Format: Tishi Shah, Wen Luo, Aradhana Awasthi, Janet Ayello, Jessica Hochberg, Mitchell Cairo. PD-L1 blockade enhances T cell cytotoxicity against primary mediastinal B cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2657. doi:10.1158/1538-7445.AM2017-2657