Redirected Primary Human Chimeric Antigen Receptor Natural Killer Cells As an “Off-the-Shelf Immunotherapy” for Improvement in Cancer Treatment

Abstract

Primary human natural killer (NK) cells recognize and subsequently eliminate virus infected cells, tumor cells, or other aberrant cells. However, cancer cells are able to develop tumor immune escape mechanisms to undermine this immune control. To overcome this obstacle, NK cells can be genetically modified to express chimeric antigen receptors (CARs) in order to improve specific recognition of cancer surface markers (e.g., CD19, CD20, and ErbB2). After target recognition, intracellular CAR domain signaling (CD3ζ, CD28, 4-1BB, and 2B4) leads to activation of PI3K or DNAX proteins (DAP10, DAP12) and finally to enhanced cytotoxicity, proliferation, and/or interferon γ release. This mini-review summarizes both the first preclinical trials with CAR-engineered primary human NK cells and the translational implications for “off-the-shelf immunotherapy” in cancer treatment. Signal transduction in NK cells as well as optimization of CAR signaling will be described, becoming more and more a focal point of interest in addition to redirected T cells. Finally, strategies to overcome off-target effects will be discussed in order to improve future clinical trials and to avoid attacking healthy tissues.

CAR-Expressing Natural Killer Cells for Cancer Retargeting

“…In contrast to CAR-T cells, CAR-NK cells have the advantage of “off-the-shelf” manufacturing, but still face several challenges. This includes the improvement in cell numbers, making the intracellular signalling more specific for NK cells, as reviewed by Oberschmidt et al [9], and finally, finding the best source of NK cells. Also, the question of whether long-living immature or short-living mature CAR-NK cells are more suitable as therapeutic products has not been answered yet.…”

“…Other than NK-92 cells, which can be expanded in cell culture, limiting amounts of primary NK cells challenged the development of NK cell-based therapeutic approaches. To solve this problem, a dose escalation phase I/II study with umbilical CB-derived CAR-engineered NK cells was authorised for patients with relapsed and refractory B-lymphoid malignancies (NCT03056339; Table 1) [4, 9]. In addition, the first clinical CAR-NK cell trials targeting antigens such as human epidermal growth factor receptor 2 (HER2), CD33, Mucin-1 (MUC1), CD7, and NK group 2, member D (NKG2D) ligands have been initiated (Table 1).…”

The Advances and Challenges of CAR-NK Cells for Tumor Immunotherapy

“…This costimulator is incorporated into the cytoplasmic portion of CAR to increase the signaling from the activation domain. 2B4 contains immunoreceptor tyrosine-based switch motifs (ITSMs) that are responsible for NK cells stimulatory pathway activation [26], and its combination with CD3ζ enhance IFN-γ and TNF-α production [27]. Similar results were obtained using 4-1BB-CD3ζ CAR construct in NK cells.…”

You Have Got a Fast CAR: Chimeric Antigen Receptor NK Cells in Cancer Therapy

“…The feasibility of manufacturing an off-the-shelf CAR-NK cell product to universally treat patients would significantly increase the speed of administration, effectively reducing the lag time from the decision to treat and first dosing to 1 day ( Figure 2). As no severe toxicities are observed or expected with CAR-NK cells, treatment can be administered with 'out-patient' follow-up monitoring, significantly reducing the huge indirect costs associated with CAR-T cell therapy due to lengthy post-treatment hospitalization [61]. While an induced pluripotent stem cell (iPSC)-derived CAR-T cell product can also be manufactured as an off-the-shelf product, extra genetic modification is required to remove the endogenous TCR in order to produce a universal product without the need for HLA-matching.…”

“…Implementation of the CAR technology in NK cells is often performed with constructs optimized for inducing T cell activation. Although some of the signaling is conserved between T cells and NK cells, namely CD3ζ and 4-1BB, other co-stimulatory domains commonly used in CAR-T cells, as well as TM domains and hinges, are completely absent in NK cells, namely CD8α and CD28 [61,143]. Furthermore, differences in activating signaling, leading to immune synapse formation and subsequent cytolysis of the target cell, are cell type-specific.…”