High-Throughput Image Cytometry Detection Method for CAR-T Transduction, Cell Proliferation, and Cytotoxicity Assays

Affinity fine-tuning anti-CAIX CAR-T cells mitigate on-target off-tumor side effects

One of the major hurdles that has hindered the success of chimeric antigen receptor (CAR) T cell therapies against solid tumors is on-target off-tumor (OTOT) toxicity due to sharing of the same epitopes on normal tissues. To elevate the safety profile of CAR-T cells, an affinity/avidity fine-tuned CAR was designed enabling CAR-T cell activation only in the presence of a highly expressed tumor associated antigen (TAA) but not when recognizing the same antigen at a physiological level on healthy cells. Using direct stochastic optical reconstruction microscopy (dSTORM) which provides single-molecule resolution, and flow cytometry, we identified high carbonic anhydrase IX (CAIX) density on clear cell renal cell carcinoma (ccRCC) patient samples and low-density expression on healthy bile duct tissues. A Tet-On doxycycline-inducible CAIX expressing cell line was established to mimic various CAIX densities, providing coverage from CAIX-high skrc-59 tumor cells to CAIX-low MMNK-1 cholangiocytes. Assessing the killing of CAR-T cells, we demonstrated that low-affinity/high-avidity fine-tuned G9 CAR-T has a wider therapeutic window compared to high-affinity/high-avidity G250 that was used in the first anti-CAIX CAR-T clinical trial but displayed serious OTOT effects. To assess the therapeutic effect of G9 on patient samples, we generated ccRCC patient derived organotypic tumor spheroid (PDOTS) ex vivo cultures and demonstrated that G9 CAR-T cells exhibited superior efficacy, migration and cytokine release in these miniature tumors. Moreover, in an RCC orthotopic mouse model, G9 CAR-T cells showed enhanced tumor control compared to G250. In summary, G9 has successfully mitigated OTOT side effects and in doing so has made CAIX a druggable immunotherapeutic target.

Immune-restoring CAR-T cells display antitumor activity and reverse immunosuppressive TME in a humanized ccRCC mouse model

One of the major barriers that have restricted successful use of chimeric antigen receptor (CAR) T cells in the treatment of solid tumors is an unfavorable tumor microenvironment (TME). We engineered CAR-T cells targeting carbonic anhydrase IX (CAIX) to secrete anti-PD-L1 monoclonal antibody (mAb), termed immune-restoring (IR) CAR G36-PDL1. We tested CAR-T cells in a humanized clear cell renal cell carcinoma (ccRCC) orthotopic mouse model with reconstituted human leukocyte antigen (HLA) partially matched human leukocytes derived from fetal CD34+ hematopoietic stem cells (HSCs) and bearing human ccRCC skrc-59 cells under the kidney capsule. G36-PDL1 CAR-T cells, haploidentical to the tumor cells, had a potent antitumor effect compared to those without immune-restoring effect. Analysis of the TME revealed that G36-PDL1 CAR-T cells restored active antitumor immunity by promoting tumor-killing cytotoxicity, reducing immunosuppressive cell components such as M2 macrophages and exhausted CD8+ T cells, and enhancing T follicular helper (Tfh)-B cell crosstalk.

Development of optimized cytotoxicity assays for assessing the antitumor potential of CAR-T cells

CAR-T cells are T cells expressing a chimeric antigen receptor (CAR) rendering them capable of killing tumor cells after recognition of a target antigen. CD19 CAR-T cells have revolutionized the treatment of hematological malignancies. Their function is typically assessed by cytotoxicity assays using human allogeneic cell lines expressing the target antigen CD19 such as Nalm-6. However, an alloreactive reaction is observed with these cells, leading to a CD19-independent killing. To address this issue, we developed a fluorescence microscopy-based potency assay using murine target cells to provide an optimized cytotoxicity assay with enhanced specificity towards CD19. Murine NIH/3T3 (3T3) fibroblast-derived cell line and EL4 T-cell lymphoma-derived cell line were used as targets (no xenoreactivity was observed after coculture with human T cells). 3T3 and EL4 cells were engineered to express eGFP (enhanced Green Fluorescent Protein) and CD19 or CD22 using retroviral vectors. CD19 CAR-T cells and non-transduced (NT) control T cells were produced from several donors. After 4 h or 24 h, alloreactive cytotoxicity against CD19+ Nalm-6-GFP cells and CD19- Jurkat-GFP cells was observed with NT or CAR-T cells. In the same conditions, CAR-T but not NT cells specifically killed CD19+ but not CD19- 3T3-GFP or EL4-GFP cells. Both microscope- and flow cytometry-based assays revealed as sensitive as impedance-based assay. Using flow cytometry, we could further determine that CAR-T cells had mostly a stem cell-like memory phenotype after contact with EL4 target cells. Therefore, CD19+ 3T3-GFP or EL4-GFP cells and fluorescence microscopy- or flow cytometry-based assays provide convenient, sensitive and specific tools to evaluate CAR-T cell function with no alloreactivity.

Toward high-throughput engineering techniques for improving CAR intracellular signaling domains

Chimeric antigen receptors (CAR) are generated by linking extracellular antigen recognition domains with one or more intracellular signaling domains derived from the T-cell receptor complex or various co-stimulatory receptors. The choice and relative positioning of signaling domains help to determine chimeric antigen receptors T-cell activity and fate in vivo. While prior studies have focused on optimizing signaling power through combinatorial investigation of native intracellular signaling domains in modular fashion, few have investigated the prospect of sequence engineering within domains. Here, we sought to develop a novel in situ screening method that could permit deployment of directed evolution approaches to identify intracellular domain variants that drive selective induction of transcription factors. To accomplish this goal, we evaluated a screening approach based on the activation of a human NF-κB and NFAT reporter T-cell line for the isolation of mutations that directly impact T cell activation in vitro. As a proof-of-concept, a model library of chimeric antigen receptors signaling domain variants was constructed and used to demonstrate the ability to discern amongst chimeric antigen receptors containing different co-stimulatory domains. A rare, higher-signaling variant with frequency as low as 1 in 1000 could be identified in a high throughput setting. Collectively, this work highlights both prospects and limitations of novel mammalian display methods for chimeric antigen receptors signaling domain discovery and points to potential strategies for future chimeric antigen receptors development.

Comparison of chimeric antigen receptor-T cell-mediated cytotoxicity assays with suspension tumor cells using plate-based image cytometry method

In the recent decade, chimeric antigen receptor (CAR)-T cell therapy has revolutionized strategies for cancer treatments due to its highly effective clinical efficacy and response for B cell malignancies. The success of CAR-T cell therapy has stimulated the increase in the research and development of various CAR constructs to target different tumor types. Therefore, a robust and efficient in vitro potency assay is needed to quickly identify potential CAR gene design from a library of construct candidates. Image cytometry methodologies have been utilized for various CAR-T cell-mediated cytotoxicity assay using different fluorescent labeling methods, mainly due to their ease-of-use, ability to capture cell images for verification, and higher throughput performance. In this work, we employed the Celigo Image Cytometer to evaluate and compare two CAR-T cell-mediated cytotoxicity assays using GFP-expressing or fluorescent dye-labeled myeloma and plasmacytoma cells. The GFP-based method demonstrated higher sensitivity in detecting CAR-T cell-mediated cytotoxicity when compared to the CMFDA/DAPI viability method. We have established the criteria and considerations for the selection of cytotoxicity assays that are fit-for-purpose to ensure the results produced are meaningful for the specific testing conditions.

Anti-CAIX BBζ CAR4/8 T cells exhibit superior efficacy in a ccRCC mouse model

Improving CAR-T cell therapy for solid tumors requires a better understanding of CAR design and cellular composition. Here, we compared second-generation (BBζ and 28ζ) with third-generation (28BBζ) carbonic anhydrase IX (CAIX)-targeted CAR constructs and investigated the antitumor effect of CAR-T cells with different CD4/CD8 proportions in vitro and in vivo. The results demonstrated that BBζ exhibited superior efficacy compared with 28ζ and 28BBζ CAR-T cells in a clear-cell renal cell carcinoma (ccRCC) skrc-59 cell bearing NSG-SGM3 mouse model. The mice treated with a single dose of BBζ CD4/CD8 mixture (CAR4/8) showed complete tumor remission and remained tumor-free 72 days after CAR-T cells infusion. In the other CAR-T and control groups, tumor-infiltrating T cells were recovered and profiled. We found that BBζ CAR8 cells upregulated expression of major histocompatibility complex (MHC) class II and cytotoxicity-associated genes, while downregulating inhibitory immune checkpoint receptor genes and diminishing differentiation of regulatory T cells (Treg cells), leading to excellent therapeutic efficacy in vivo. Increased memory phenotype, elevated tumor infiltration, and decreased exhaustion genes were observed in the CD4/8 untransduced T (UNT) cells compared with CD8 alone, indicating that CD4/8 would be the favored cellular composition for CAR-T cell therapy with long-term persistence. In summary, these findings support that BBζ CAR4/8 cells are a highly potent, clinically translatable cell therapy for ccRCC.

Kinetic, imaging based assay to measure NK cell cytotoxicity against adherent cells

Natural Killer cells (NK cells) are a key component of the innate immune system and are key effectors of immunosurveillance. NK cells not only have the inherent ability to directly kill malignant, compromised, or virally infected cells, but also recruit and coordinate responses by other immune cells to prime the adaptive immune response. Given this potent anti-tumor response and good safety profile, adoptive NK cell therapy is an emerging cancer treatment modality. Direct killing of tumor cells is major mode of action for NK cell anti-tumor activity and measuring changes in NK cell cytotoxic response in vitro is a critical step in pre-clinical evaluation of novel NK cellular products. Here, we provide a detailed protocol for a live-cell imaging assay for testing NK cell cytotoxicity against a broad range of adherent and 3D in vitro tumor models. Compared to other methods for measuring in vitro cytotoxicity, this method offers real-time dynamic tracking of and provides a multiparameter readout for more robust understanding of NK cell tumor killing.

Formulation Considerations for Autologous T Cell Drug Products

Genetically modified autologous T cells have become an established immunotherapy in the fight against cancer. The manufacture of chimeric antigen receptor (CAR) and αβ-T cell receptor (TCR) transduced T cells poses unique challenges, including the formulation, cryopreservation and fill-finish steps, which are the focus of this review. With an increasing number of marketing approvals for CAR-T cell therapies, comparison of their formulation design and presentation for administration can be made. These differences will be discussed alongside the emergence of automated formulation and fill-finish processes, the formulation design space, Monte Carlo simulation applied to risk analysis, primary container selection, freezing profiles and thaw and the use of dimethyl sulfoxide and alternative solvents/excipients as cryopreservation agents. The review will conclude with a discussion of the pharmaceutical solutions required to meet the simplification of manufacture and flexibility in dosage form for clinical treatment.