CAR-T cells beyond CD19, UnCAR-Ted territory

CD19/CD20 dual-targeted chimeric antigen receptor-engineered natural killer cells exhibit improved cytotoxicity against acute lymphoblastic leukemia

BACKGROUND

Chimeric antigen receptor natural killer (CAR-NK) cells represent a promising advancement in CAR cell therapy, addressing limitations observed in CAR-T cell therapy. However, our prior study revealed challenges in CAR-NK cells targeting CD19 antigens, as they failed to eliminate CD19+ Raji cells in NSG tumor-bearing mice, noting down-regulation or loss of CD19 antigen expression in some Raji cells. In response, this study aims to enhance CD19 CAR-NK cell efficacy and mitigate the risk of tumor recurrence due to target antigen escape by developing CD19 and CD20 (CD19/CD20) dual-targeted CAR-NK cells.

METHODS

Initially, mRNA encoding anti-CD19 CARs (FMC63 scFv-CD8α-4-1BB-CD3ζ) and anti-CD20 CARs (LEU16 scFv-CD8α-4-1BB-CD3ζ) was constructed via in vitro transcription. Subsequently, CD19/CD20 dual-targeted CAR-NK cells were generated through simultaneous electrotransfection of CD19/CD20 CAR mRNA into umbilical cord blood-derived NK cells (UCB-NK).

RESULTS

Following co-electroporation, the percentage of dual-CAR expression on NK cells was 86.4% ± 1.83%, as determined by flow cytometry. CAR expression was detectable at 8 h post-electric transfer, peaked at 24 h, and remained detectable at 96 h. CD19/CD20 dual-targeted CAR-NK cells exhibited increased specific cytotoxicity against acute lymphoblastic leukemia (ALL) cell lines (BALL-1: CD19+CD20+, REH: CD19+CD20-, Jurkat: CD19-CD20-) compared to UCB-NK, CD19 CAR-NK, and CD20 CAR-NK cells. Moreover, CD19/CD20 dual-targeted CAR-NK cells released elevated levels of perforin, IFN-γ, and IL-15. Multiple activation markers such as CD69 and cytotoxic substances were highly expressed.

CONCLUSIONS

The creation of CD19/CD20 dual-targeted CAR-NK cells addressed the risk of tumor escape due to antigen heterogeneity in ALL, offering efficient and safe 'off-the-shelf' cell products. These cells demonstrate efficacy in targeting CD20 and/or CD19 antigens in ALL, laying an experimental foundation for their application in ALL treatment.

Recent advances in the production, reprogramming, and application of CAR-T cells for treating hematological malignancies

As genetically engineered cells, chimeric antigen receptor (CAR)-T cells express specific receptors on their surface to target and eliminate malignant cells. CAR proteins are equipped with elements that enhance the activity and survival of T cells. Once injected, CAR-T cells act as a "living drug" against tumor cells in the body. Up to now, CAR-T cell therapy has been demonstrated as a robust adoptive cell transfer (ACT) immunotherapeutic modality for eliminating tumor cells in refractory hematological malignancies. CAR-T cell therapy modality involves several steps, including the collecting of the blood from patients, the isolation of peripheral blood mononuclear cells (PBMCs), the enrichment of CD4⁺/CD8⁺ T cell, the genetic reprogramming, the expansion of modified T cells, and the injection of genetically engineered T cells. The production of CAR-T cells is a multi-step procedure, which needs precise and safety management systems, including good manufacturing practice (GMP), and in-line quality control and assurance. The current study describes the structure of CARs and concentrates on the next generations of CARs that are engaged in enhancing the anti-tumor responses and safety of the engineered T cells. This paper also highlights the important concerns in quality control and nonclinical research of CAR-T cells, as well as general insights into the manufacture, reprogramming, and application of CAR-T cells based on new and enhanced techniques for treating hematological malignancies. Besides, the application of the CRISPR-Cas9 genome editing technology and nanocarrier-based delivery systems containing CAR coding sequences to overcome the limitations of CAR-T cell therapy has also been explained.

Mechanisms of response and resistance to CAR T cell therapies

Chimeric antigen receptor (CAR) T cell therapy is successful for some B cell malignancies but remains limited for a wider range of patients and cancers. Recent advances have shown that patients with more naïve and early memory-like T cells have better response rates due to increased expansion and persistence of the CAR T cells. The costimulatory domain used in the CAR is also important for their persistence and anti-tumor activity. Modifying these domains can improve CAR T cell efficacy. Tumors escape CAR T cell targeting through loss of the target antigen or other genetic characteristics and suppressive microenvironments. Using combinations treatments or further genetically modifying CAR T cells to overcome these limitations is the focus of current research.

Chimeric Antigen Receptor-T Cells for Targeting Solid Tumors: Current Challenges and Existing Strategies

Chimeric antigen receptor-T cells (CAR-Ts) are an exciting new cancer treatment modality exemplified by the recent regulatory approval of two CD19-targeted CAR-T therapies for certain B cell malignancies. However, this success in the hematological setting has yet to translate to a significant level of objective clinical responses in the solid tumor setting. The reason for this lack of translation undoubtedly lies in the substantial challenges raised by solid tumors to all therapies, including CAR-T, that differ from B cell malignancies. For instance, intravenously infused CAR-Ts are likely to make rapid contact with cancerous B cells since both tend to reside in the same vascular compartments within the body. By contrast, solid cancers tend to form discrete tumor masses with an immune-suppressive tumor microenvironment composed of tumor cells and non-tumor stromal cells served by abnormal vasculature that restricts lymphocyte infiltration and suppresses immune function, expansion, and persistence. Moreover, the paucity of uniquely and homogeneously expressed tumor antigens and inherent plasticity of cancer cells provide major challenges to the specificity, potency, and overall effectiveness of CAR-T therapies. This review focuses on the major preclinical and clinical strategies currently being pursued to tackle these challenges in order to drive the success of CAR-T therapy against solid tumors.