Cellular Uptake of siRNA-Loaded Nanocarriers to Knockdown PD-L1: Strategies to Improve T-cell Functions.

Raweewan Thiramanas,Volker Mailänder,Katharina Landfester,Shuai Jiang,Mengyi Li

doi:10.3390/cells9092043

Abstract

T-cells are a type of lymphocyte (a subtype of white blood cells) that play a central role in cell-mediated immunity. Currently, adoptive T-cell immunotherapy is being developed to destroy cancer cells. In this therapy, T-cells are harvested from a patient’s blood. After several weeks of growth in culture, tumor-specific T-cells can be reinfused into the same cancer patient. This technique has proved highly efficient in cancer treatment. However, there are several biological processes that can suppress the anti-cancer responses of T-cells, leading to a loss of their functionality and a reduction of their viability. Therefore, strategies are needed to improve T-cell survival and their functions. Here, a small interfering RNA (siRNA)-loaded nanocarrier was used to knockdown PD-L1, one of the most important proteins causing a loss in the functionality of T-cells. The biocompatibility and the cellular uptake of siRNA-loaded silica nanocapsules (SiNCs) were investigated in CD8+ T-cells. Then, the PD-L1 expression at protein and at mRNA levels of the treated cells were evaluated. Furthermore, the effect of the PD-L1 knockdown was observed in terms of cell proliferation and the expression of specific biomarkers CD25, CD69 and CD71, which are indicators of T-cell functions. The results suggest that this siRNA-loaded nanocarrier showed a significant potential in the delivery of siRNA into T-cells. This in turn resulted in enhanced T-cell survival by decreasing the expression of the inhibitory protein PD-L1. Such nanocarriers could, therefore, be applied in adoptive T-cell immunotherapy for the treatment of cancer.

Highlights

T-cells, or T-lymphocytes, are some of the most important cells in the immune system
A small interfering RNA-loaded nanocarrier was used to knockdown PD-L1, one of the most important proteins causing a loss in the functionality of T-cells
The transfected T-cells successfully increased the interferon-γ production and antigen-specific cytotoxicity. These findings suggest that small interfering RNA (siRNA)-mediated PD-L1 silencing is another possible approach towards inhibiting the immune checkpoint proteins, leading to an enhanced T-cell function

Summary

Introduction

T-cells, or T-lymphocytes, are some of the most important cells in the immune system. CD8+ T-cells (cytotoxic T-cells) play a major role in destroying virus-infected cells and tumor cells [1,2,3] Given this outstanding ability to kill cancer cells, adoptive T-cell immunotherapy for cancer treatment using CD8+ T-cells was employed and studied intensively for the past decade with promising results [4,5]. In the first step of this specific immunotherapy, CD8+ T-cells were collected from the patient’s blood. These were selected and activated while undergoing culture conditions, in order to enhance the number of specific T-cells and to make them strong enough to attack cancer cells before being reinfused into the patient’s body [6].

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