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Chimeric antigen receptor (CAR) T cell therapies have demonstrated significant successes in treating cancer. Currently, there are six approved CAR T cell products available on the market that target different malignancies of the B cell lineage. However, to overcome the limitations of CAR T cell therapies, other immune cells are being investigated for CAR-based cell therapies. CAR natural killer (NK) cells can be applied as allogeneic cell therapy, providing an economical, safe, and efficient alternative to autologous CAR T cells. To improve CAR research and future in-patient monitoring of cell therapeutics, a simple, reliable, and versatile CAR detection reagent is crucial. As most existing CARs contain a single-chain variable fragment (scFv) with either a Whitlow or a G4S linker site, linker-specific monoclonal antibodies (mAbs) can detect a broad range of CARs. This study demonstrates that these linker-specific mAbs can detect different CAR NK cells in vitro, spiked in whole blood, and within patient-derived tumor spheroids with high specificity and sensitivity, providing an effective and almost universal alternative for scFv-based CAR detection. Additionally, we confirm that linker-specific antibodies can be used for functional testing and enrichment of CAR NK cells, thereby providing a useful research tool to fast-track the development of novel CAR-based therapies.

Adoptive cell therapy using chimeric antigen receptor (CAR) technology has become mainstream by employing advanced engineering platforms to promote cancer immunotherapy. CAR T cells have shown remarkable efficacy in the treatment of hematological malignancies; however, the value of this therapy remains inconclusive in the context of solid tumors. Immunotherapy of solid tumors is restrained by several obstacles including the presence of an immunosuppressive tumor microenvironment (TME), limited tumor trafficking, inhibited immune cell infiltration, absence of tumor-specific antigens, and off-target toxicity and adverse events associated with these therapies. Despite recent advances in CAR T cell construction, including the integration of co-stimulatory domains and the creation of armed CAR T cells, with promising outcomes in the treatment of some solid tumors, there are still many unresolved obstacles that need to be overcome. To surmount these impediments to effective CAR T cell therapies, other immune cells, such as natural killer cells and macrophages, have been engineered to serve as appealing alternatives for successful cancer immunotherapy of solid tumors. CAR NK cells demonstrate significant clinical advantages due to their ready availability and minimal toxicity. CAR macrophage (M) cells provide considerable therapeutic potential due to their ability to penetrate the TME of solid tumors. In this review, we comprehensively examine the latest developments and prospects of engineered immune cell-based cancer immunotherapies specifically designed for treating solid tumors. In addition, we provide a concise overview of current clinical trials that are examining the safety and effectiveness of modified immune cells, such as CAR T, CAR NK, and CAR M, in their ability to specifically target solid tumors and promote improved therapeutic outcomes in patients with diverse solid cancers., (Copyright © 2024. Published by Elsevier Inc.)

Natural killer (NK) cells are a family of lymphocytes with a natural ability to kill infected, harmed, or malignantly transformed cells. As these cells are part of the innate immunity, the cytotoxic mechanisms are activated upon recognizing specific patterns without prior antigen sensitization. This recognition is crucial for NK cell function in the maintenance of homeostasis and immunosurveillance. NK cells not only act directly toward malignant cells but also participate in the complex immune response by producing cytokines or cross-talk with other immune cells. Cancer may be seen as a break of all immune defenses when malignant cells escape the immunity and invade surrounding tissues creating a microenvironment supporting tumor progression. This process may be reverted by intervening immune response with immunotherapy, which may restore immune recognition. NK cells are important effector cells for immunotherapy. They may be used for adoptive cell transfer, genetically modified with chimeric antigen receptors, or triggered with appropriate antibodies and other antibody-fragment-based recombinant therapeutic proteins tailored specifically for NK cell engagement. NK cell receptors, responsible for target recognition and activation of cytotoxic response, could also be targeted in immunotherapy, for example, by various bi-, tri-, or multi-specific fusion proteins designed to bridge the gap between tumor markers present on target cells and activation receptors expressed on NK cells. However, this kind of immunoactive therapeutics may be developed only with a deep functional and structural knowledge of NK cell receptor: ligand interactions. This review describes the recent developments in the fascinating protein-engineering field of NK cell immunotherapeutics., (Copyright © 2022 Elsevier Inc. All rights reserved.)