The Role of CAR-NK Cells in Cancer Cellular Immunotherapy

Unique Advantages of CAR-Engineered NK Cells

Cellular immunotherapy, is an innovative treatment approach that aims to harness body's immune system to eliminate cancer. The unique biological features of NK cells make them a more attractive source for genetically modified immune cell-based immunotherapy.

First，allogeneic CAR-NK cell infusions have reduced risk for graft versus host disease (GVHD). Cytokine release syndrome (CRS) and neurotoxicity are less likely to occur in CAR-NK immunotherapy partly due to a different spectrum of the secreted cytokines: activated NK cells usually produce IFN-γ and GM-CSF, whereas CAR-T cells predominantly induce cytokines, such as IL-1a, IL-1Ra, IL-2, IL-2Ra, IL-6, TNF-α, MCP-1, IL-8, IL-10, and IL-15, that are highly associated with CRS and severe neurotoxicity. Second, besides killing tumour target cells in the CAR-dependent manner, CAR-NK cells can potentially eliminate cancer cells in a CAR-independent manner. Third, the reduced risk for alloreactivity and thus GVHD even with allogeneic NK cells potentially allows CAR-NK cells to be generated from multiple sources, including NK92 cell lines, peripheral blood mononuclear cells (PBMCs), umbilical cord blood (UCB), and induced pluripotent stem cells (iPSCs).

Generation of CAR-NK Cells

Sources of NK cells

Currently, clinical-grade NK cells can be manufactured in a large scale from multiple sources including NK92 cell line, PBMCs, UBC, CD34 hematopoietic progenitor cells (HPCs), and iPSCs.

Fig. 1 Sources and manufacturing of CAR-NK cell products.

CAR constructs

So far, most CAR-NK cell studies use CAR constructs designed for CAR-T cells. Recently, novel CAR constructs have been designed for NK cells specifically. However, these different CAR constructs exhibited varying effects on cytotoxicity and cytokine production in NK cells.

CAR-gene transfer in NK cells

One of the major barriers for NK cell-based immunotherapy approaches has been the lack of an efficient gene transfer method in the primary NK cells. Retrovirus has been extensively used to generate CAR-NK cells in recent preclinical and clinical studies. Compared to retroviral vectors, lentivirus-based transduction represents a safer option because of a lower genotoxicity and insertional mutagenesis. But the efficiency of lentiviral transduction in primary NK cells is low, often requiring multiple rounds of transduction. Transfection methods such as electroporation and lipofection have also been used to deliver exogenous genes into NK cells. In addition , in NK cells, CRISPR/Cas9 system could be used to augment NK cell anti-tumour functions by targeted CAR insertion and stably knock-outing or integrating genes of interest involved in NK cell exhaustion, activation, tolerance, or memory.

Expansion of CAR-NK cells in vitro

Several cytokines, such as IL-2, IL-15, IL-12, IL-21, and IL-18, have been used to expand primary NK cells in vitro. Nevertheless, NK proliferation in vitro induced by these cytokines is generally limited. Co-culturing with stimulatory cells, such as a Wilms tumour-derived cell line, autologous PBMCs, Epstein-Barr virus-transformed lymphoblastoid cells, and chronic myelogenous leukaemia-derived cell line K562 cells, can induce rapid and sustained proliferation in NK cells.

Application of CAR-NK Cell Therapy

Unlike CAR-T cells, CAR-NK cells can mediate cytotoxic activity against cancer cells in both CAR-dependent and CAR-independent manner. NK cells express CD16 and exert ADCC-mediated tumour killing. Promising results have been obtained in patients with neuroblastoma or refractory NHL receiving allogeneic NK cells following administration of anti-GD2 or anti-CD20 antibody. CAR-NK cells have a great promise as a novel cellular immunotherapy platform against cancer and with a potential for generating “off-the-shelf” products that could be readily available and safe for clinical use.

Future Prospective

With the increasing safety and promising activity in preclinical studies and clinical trials, combined with advanced efforts addressing the remaining challenges, it is expected that CAR-NK cell therapy will continue to evolve and lead to major improvement in the survival of cancer patients with otherwise very limited treatment options.

Reference:

Xie, G. et al. CAR-NK cells: A promising cellular immunotherapy for cancer. EBioMedicine, 2020, 59: 102975.

* For research use only. Not intended for any clinical use.

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The Role of CAR-NK Cells in Cancer Cellular Immunotherapy

Unique Advantages of CAR-Engineered NK Cells

Generation of CAR-NK Cells

Application of CAR-NK Cell Therapy

Future Prospective

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