NKG2D-CAR-transduced Natural Killer Cells Efficiently Target Multiple Myeloma

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Summary

CAR therapy is an attractive strategy for cancer treatment. CAR-NK cells are promising immunotherapy for multiple myeloma patients due to strong cytotoxicity to tumor cells and weak side effects to normal cells. NKG2D ligands show an increased expression in a large proportion of cancers and can be targeted by NKG2D expressed in NK cells and most T cells. In this article, researchers developed autologous NKG2D-CAR-NK cells for MM patients. This CAR-NK cell performed greater cytotoxicity to myeloma cells in vitro and efficiently repressed tumor growth in mouse models. This activated CAR-NK cell therapy demonstrates superior anti-tumor efficacy than cognate CAR-T cell, which supports that this strategy is a functional approach for MM patients.

Brief Description

Multiple myeloma is malignant plasma cell-induced cell aberrant expansion in the bone marrow and extramedullary locations. Though novel therapeutics have been developed to improve the survival rate of patients, relapse often occurs as a challenge. While CAR-T cell therapy is highly efficient in leukemia, the associated side effects are threatening. NK cells are short-lived, and the cytotoxicity is balanced by the stimulatory and inhibitory receptors, indicating that CAR-engineered NK cells are safer and more efficient than CAR-T therapy.

Inspired by the good clinical response of the adoptive transferred activated and expanded NK cells and broad expression of NKG2D ligand on B cells of MM patients, scientists try to transduce NKG2D-CAR to NK cells to enhance their anti-tumor efficacy. The NKG2D-based CAR construct is introduced to activated NK cells and memory T cells by a lentiviral vector, and 20.65% CAR+ NK cells and 52% CAR-T cells are detected. CAR-NK and CAR-T cells both present an activated phenotype and retain the genomics features of corresponding origin cells.

Fig.1 NKG2D CAR expression levels on T cells and NK cells.¹

Fig.2 Phenotype of T and NK cells before and after CAR transduction.¹

CAR-NK cells are verified to exhibit greater cytotoxicity over parent NK cells and show 100% killing efficiency at a low effector-to-target ratio. The effect of CAR-NK cells is dependent on the expression level of NKG2D ligands on cancer cells.

Fig.3 Cytotoxicity of NKG2D CAR-T and CAR-NK cells against myeloma cells.¹

With advanced transcriptome analysis, researchers find that CAR-NK and CAR-T cells have the same cytokine secretion spectrum, including IFNg, TNFa, granzyme A, granzyme B, perforin, granulysin, sFas, and sFasL. The cytokines expression and cell activation are significantly higher in CAR-T cells. Gene expression assay also elucidates the anti-tumor mechanism of action on CAR-NK cells is related to improved cell activation, migration, and effector process, which is relatively lower in CAR-T cells.

Fig.4 Mechanism of action on NKG2D CAR-T and CAR-NK cells.¹

Luciferase transduced U-266 cell line is used to develop a myeloma mouse model. CAR-NK cells display a strong in vivo anti-tumor efficacy against myeloma cells and prolong the survival time of tumor-loaded mice two times longer than the control and CAR-T group. The CAR+ cells are detected 20 days after infusion with a lower proportion in peripheral blood and much lower in bone marrow with high NKG2D and effector process-related proteins expression.

Fig.5 NKG2D CAR-NK cells show robust anti-myeloma activity in vivo.¹

Though NK and CAR-NK cells have similar toxicity to lung, colon, and PBMC in vitro, they did not show significant GvHD against multiple organs in mice, indicating that they are much safer than CAR-T cells.

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Reference

Leivas, A.; et al. NKG2D-CAR-transduced natural killer cells efficiently target multiple myeloma. Blood Cancer J. 2021, 11, 146.