Targeted integration of EpCAM-specific CAR in human induced pluripotent stem cells and their differentiation into NK cells

Background

Redirection of natural killer (NK) cells with chimeric antigen receptors (CAR) is attractive in developing off-the-shelf CAR therapeutics for cancer treatment. However, the site-specific integration of a CAR gene into NK cells remains challenging.

Methods

In the present study, we genetically modified human induced pluripotent stem cells (iPSCs) with a zinc finger nuclease (ZFN) technology to introduce a cDNA encoding an anti-EpCAM CAR into the adeno-associated virus integration site 1, a “safe harbour” for transgene insertion into human genome, and next differentiated the modified iPSCs into CAR-expressing iNK cells.

Results

We detected the targeted integration in 4 out of 5 selected iPSC clones, 3 of which were biallelically modified. Southern blotting analysis revealed no random integration events. iNK cells were successfully derived from the modified iPSCs with a 47-day protocol, which were morphologically similar to peripheral blood NK cells, displayed NK phenotype (CD56+CD3-), and expressed NK receptors. The CAR expression of the iPSC-derived NK cells was confirmed with RT-PCR and flow cytometry analysis. In vitro cytotoxicity assay further confirmed their lytic activity against NK cell-resistant, EpCAM-positive cancer cells, but not to EpCAM-positive normal cells, demonstrating the retained tolerability of the CAR-iNK cells towards normal cells.

Conclusion

Looking ahead, the modified iPSCs generated in the current study hold a great potential as a practically unlimited source to generate anti-EpCAM CAR iNK cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02648-4.

Analysis of CAR-Mediated Tonic Signaling

CARs are synthetic receptors designed to drive antigen-specific activation upon binding of the scFv to its cognate antigen. However, CARs can also elicit different levels of ligand-independent constitutive signaling, also known as tonic signaling. Chronic T cell activation is observed in certain combinations of scFv, hinge, and costimulatory domains and may be increased due to high levels of CAR expression. Tonic signaling can be identified during primary T cell expansion due to differences in the phenotype and growth of CAR-T cells compared to control T cells. CARs displaying tonic signaling are associated with accelerated T cell differentiation and exhaustion and impaired antitumor effects. Selecting CARs which configuration does not induce tonic signaling is important to enhance antigen-specific T cell responses. In this chapter, we describe in detail different protocols to identify tonic signaling driven by CARs during primary T cell ex vivo expansion.

Analysis of Antitumor Effects of CAR-T Cells in Mice with Solid Tumors

Animal models provide an essential tool to study the efficacy of CAR-T cell treatments. Most of the current works test human CAR-T cells in immunodeficient animals, typically NOD Scid Gamma (NSG) mice transplanted with human tumors. Despite the limitations of this model, including the difficulty to study the interaction between CAR-T cells and the human innate system and to assess the toxicity of this therapy, NSG are extensively used for adoptive T cell transfer studies. In this chapter, we will describe the protocols to test CAR-T cells in NSG animals with solid tumors. We first describe the implantation of human xenograft tumors in NSG animals, followed by CAR-T cell administration and assessment of antitumor responses. We will also review the protocols to analyze T cell persistence in the blood of treated animals. Finally, we will focus on the analysis of the tumors at the end point of the experiment, including the percentage, phenotype, and function of tumor infiltrating T cells, and loss of antigen expression.

Gene therapy: Myth or reality?

Gene therapy has become a reality, although still a fragile one. Clinical benefit has been achieved over the last 17years in a limited number of medical conditions for which pathophysiological studies determined that they were favorable settings. They include inherited disorders of the immune system, leukodystrophies, possibly hemoglobinopathies, hemophilia B, and retinal dystrophies. Advances in the treatment of B-cell leukemias and lymphomas have also been achieved. Advances in vector development and possible usage of gene editing may lead to significant advances over the next years.