Overcoming CAR T-Cell Therapy Limitations

Autologous CAR T therapies are part of the standard of care for multiple hematological malignancies. While revolutionary in cancer treatment, they face several key limitations, mainly related to the fact that the product has to be generated from the patient’s T cells through a leukapheresis process.

First, the limited numbers of leukapheresis chairs across hospital centers limit the number of patients that can receive autologous CAR-T therapies. Many community hospital centers also do not have leukapheresis chairs, a bottleneck that is only expected to increase as CAR T-cell therapies show promise across higher-incidence indications, such as solid tumors or autoimmune disorders.

Second, for many cancer patients, their T cells have been severely affected by both previous lines of treatment (such as chemotherapy) and by cancer itself. This can limit the effectiveness of CAR T-cell therapies generated from patients’ cells.

Third, the personalized nature of autologous CAR T-cells limits scalability: each patient's cells constitute a separate batch, requiring dedicated equipment and processing suites. This leads to very high cost-of-goods-sold (CoGS) and significantly reduced (if not negative) gross margins compared to traditional pharmaceuticals.

Early on, Cellectis’ researchers realized that gene editing could be employed to transform CAR T therapies into off-the-shelf pharmaceuticals, and invented the allogeneic approach to CAR T.

Our process involves several key steps:

• T cells are obtained from healthy donors through leukapheresis.
• The T cells from healthy donors are then engineered using a CAR and TALEN gene-editing technology to eliminate other genes to prevent graft-vs-host disease and host immune rejection.
• The cells are then purified, and the final product is cryopreserved for off-the-shelf availability.
• Rigorous testing is performed to ensure product safety and efficacy before the final product is shipped to hospital centers as needed.

This approach solves the key limitations of autologous CAR T-cell therapies. The T-cells come from healthy donors, so leukapheresis chairs are no longer required, and the cells have not been affected by previous treatments or by cancer. Furthermore, the off-the-shelf approach allows for batch manufacturing and economies of scale, bringing the cost of goods significantly down.

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The allogeneic approach allows for a streamlined manufacturing process, creating a readily available supply of CAR T cells that can be quickly administered to patients. Using T cells from healthy donors facilitates large-scale production, as these cells can be collected, modified, expanded in advance and stored, unlike autologous CAR T cells.

In 2019, Cellectis made the critical decision to fully internalize its manufacturing. We are one of the few end-to-end gene editing, allogeneic CAR T-cell companies that control its gene and cell therapy process from start to finish. All the starting materials (mRNAs, plasmids and lentiviral vectors) are produced in our manufacturing facility in Paris, and our GMP manufacturing in Raleigh (NC) includes our clinical and commercial UCART manufacturing operations. 

With such internal operations, we can quickly iterate on our CAR T-cell designs, testing new versions and optimizing performance internally, ultimately accelerating the path to improved treatments for patients.

Immune rejection can be a challenge in optimizing allogeneic CAR T-cell approaches. Cellectis has developed several approaches to successfully address this topic:

1. A drug resistance approach, where allogeneic CART cells are genetically modified using TALEN gene-editing technology to inactivate the CD52 gene, while an anti-CD52 antibody is administered as part of the patient’s preconditioning regimen. This opens a window for CAR T-cell expansion while protecting CAR T cells from the effects of preconditioning.

2. A hypo immunity approach, where allogeneic CAR T cells are genetically modified to become “stealth”, i.e., shielded from the patient’s immune system. Strategies include using TALEN gene-editing technology to inactivate the B2M gene and insert the HLA-E gene to prevent NK-cell-mediated rejection.

Gene editing is therefore a potent solution to address the challenge of immune rejection when developing allogeneic therapies.

The CAR T approach has shown the potential to address autoimmune disorders by creating an immune system “reset”, thereby stopping the production of autoantibodies and potentially offering a one-off therapy allowing patients to go off immunosuppressive treatments.

Allogeneic therapy can be a viable and promising option for treating autoimmune disease over autologous approaches, mainly due to the use of healthy donor T cells and the removal of the leukapheresis step. Indeed, for these higher incidence indications, being able to produce cells with increased scalability and accessibility, without relying on the patient’s own T cells, may prove a critical factor.

Expansion to solid tumors is indeed an active area of active CAR T research thanks to sophisticated gene editing and cellular engineering. It is clear that the challenges posed by solid tumors, such as the sparse number of tumor-specific antigens, large tumor heterogeneity, a highly immuno-inhibitory tumor microenvironment, ineffective T cell trafficking and tumor infiltration, render first-generation CAR T therapies ineffective.

Gene-editing platforms, such as Cellectis’ TALEN technology, allow for sophisticated gene editing (including gene insertion, deletion, repair and replacement in T cells) to address such challenges. This is yet another advantage of the allogeneic approach, which allows for several steps of cellular engineering prior to T cell expansion.

By way of example, Cellectis’ UCARTMUC1 candidate product targets the MUC1 antigen, which is overexpressed in about 67% of triple-negative breast cancer (TNBC) cases. Multiple genetic modifications are incorporated to enhance UCARTMUC1 efficacy and safety and address the tumor microenvironment challenges of TNBC:

• Four TALEN knockouts: TCR (to prevent graft-versus-host disease), B2M (to create hypo-immunity), TGFBRII (to prevent the immunosuppressive effects of circulating TGFB) and PD-1 (to remove the inhibitory effects of the PD-1/PDL-1 pathway.
• Two knock-ins: B2M deletion is replaced by HLA-E insertion to protect against host NK cell detection and increase CAR T persistence, and PD-1 deletion is replaced by IL-12 insertion to enhance tumor cell destruction and attract pro-inflammatory cells by local secretion of IL-12.

With such approaches, UCARTMUC1 has already demonstrated potent anti-tumor activity in various in vivo models of TNBC. It is an example of the role that allogeneic CAR T with sophisticated armoring could play in solid tumors.