CRISPR knock out of programmed cell death protein 1 enhances anti-tumor activity of cytotoxic T lymphocytes.

Zhilong Zhao,Zexian Fu,Wei Zhang,Jianhui Cai,Jinsheng Han,Long Shi,Shaohui Zhang

doi:10.18632/oncotarget.23730

Zhilong Zhao, Zexian Fu + Show 5 more

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https://doi.org/10.18632/oncotarget.23730

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Programmed cell death protein 1 (PD-1) is an immune checkpoint receptor that functions to attenuate T cell activation. In this study, we knocked out (KO) PD-1 in cytotoxic T lymphocytes (CTLs) using CRISPR-Cas9 system to evaluate its effect on the anti-tumor activity of the CTLs against multiple myeloma (MM). Results show that PD-1 KO CTLs facilitate apoptosis and caspase activation of the co-cultured MM cells and enhanced MM cell death by 36% compared with the control. PD-1 KO also increased TNF-α and IFN-γ secretion of the CTLs by 2.4 and 1.9-fold respectively. The effectiveness of PD-1 KO in enhancing anti-tumor activity of the CTLs was verified in vivo using mouse xenograft model. The xenografted mice treated with PD-1 KO CTLs demonstrated repressed MM tumor growth and prolonged survival compared with the control group. We conclude that CRISPR-Cas9 is an efficient system to knock out PD-1 from CTLs and PD-1 KO could significantly enhance the anti-tumor activity of CTLs.

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The immune system plays a critical role in cancer development
Flow cytometry analysis demonstrated a reduction of tumor cells in the PD-1 knocked out (KO) co-culture: the MM.1S cells accounted for 46.1% in the control co-culture but only 21.9% in the PD-1 KO co-culture (Figure 2B)
Compared to the control cytotoxic T lymphocytes (CTLs), PD-1 KO CTLs were found to be more efficient at killing tumor cells

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Introduction

The immune system plays a critical role in cancer development. Under normal circumstances, the immune system can recognize, control, and even eliminate tumors [1]. Cytotoxic T lymphocytes (CTLs, known as CD8+ T cells or killer T cells) are the primary immune cells responsible for killing tumor cells. PD-L1 is expressed by most types of cells [4]; the PD-1/PD-L1 pathway plays a crucial role in the immune system to keep the self-tolerance and physiological immune responses in balance [5]. Many tumor cells express PD-L1; tumor cells can utilize the PD-1/PD-L1 pathway to attenuate T cell activity and escape the recognizing and killing capacity of CTLs [5]. In this situation, the PD-1/PD-L1 checkpoint functions to interrupt cancer immunity cycle [6]

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