“off-the-shelf” (Allogeneic) CAR-T cell therapy expands horizons
CAR-T cell therapy offers immense potential to revolutionize the treatment of cancer and other diseases, but a significant hurdle has been the lengthy process of manufacturing these therapies. The current approach, involving the collection of a patient's T cells, their genetic engineering in a laboratory, expansion, and subsequent reinfusion into the patient, is time-consuming and expensive. Unlike traditional CAR-T cell therapy (autologous) which requires a patient's own T cells, allogeneic (off-the shelf) T cells from healthy donors can be utilized to manufacture CAR-T cell therapies in advance and stored, making them readily available for treatment in multiple patients. This approach significantly reduces the time it takes to produce the therapy, with a potential for broader applications including those who may not be eligible for traditional CAR-T cell therapy due to age or other factors. Several off-the-shelf allogeneic CAR-T products are currently under clinical evaluation in Phase I or Phase I/II studies by therapeutic companies.
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Two major challenges in developing allogeneic CAR-T cell therapy are "graft-versus-host disease" (GvHD) and "host-versus-graft disease" (HvG). GvHD is triggered by recognition of the patient's healthy tissues by the T-Cell receptor (TCR) on the surface of allogeneic CAR-T cells. On the other hand, HvG disease is triggered by the host immune system recognizing CAR-T cells as foreign, that affects the persistence of CAR-T cells. Other challenges include streamlining manufacturing, enhancing safety and efficacy and expanding applications beyond blood cancers.
Most T cells have a T-cell receptor (TCR) made of alpha and beta protein chains. These TCRs can recognize HLA-peptide complexes on target cells via the direct pathway of allorecognition, which can cause GvHD. Source of T cells for CAR-T manufacturing is crucial for minimizing GvHD. The most frequently used sources are PBMCs (peripheral blood mononuclear cells), others include iPSCs (pluripotent stem cells) and UCB (umbilical cord blood) from healthy donors. Stem memory T cells offer a promising approach to overcome GvHD due to their unique properties. Being less differentiated, they can self-renew and differentiate into various T cell types. CAR-T cells derived from stem memory T cells have shown reduced cytokine release syndrome (CRS) and neurotoxicity, along with long-term persistence. A key advantage is that a single clone of stem memory T cells can be used to generate CAR-T cells, enabling clonal expansion into a homogenous, genetically identical final cell population. Studies have demonstrated Cytokine-induced killer (CIK) cells as promising alternative, as they target tumor cells independent of HLA matching, have significantly lower alloreactivity, thereby reducing the risk of GvHD.
HvG can be overcome by engineering donor T cells to become invisible to the recipient's immune defenses. Cutting-edge gene editing tools, such as CRISPR-Cas9, Base Editing and TALEN, are being increasingly used to precisely target and disable genes responsible for immune rejection—like those coding for T-cell receptors (TCRs) and beta-2 microglobulin. Furthermore, ingenious viral vectors, naturally evolved to slip past immune surveillance, are being harnessed to deliver therapeutic CAR constructs. This approach promises to generate CAR T cells that are far less likely to trigger a harmful immune response. Groundbreaking research at Memorial Sloan Kettering Cancer Center (MSK) has even revealed the potential of HIV-derived Nef protein that help CAR T cells evade immune attack by reducing a protein on the surface of CAR T cells that signals them as foreign, offering a powerful new strategy for safer, more effective cell therapies. Non-gene editing approaches overcome the complexity of editing multiple genes. Two strategies are being explored to eliminate TCR expression in CAR T-cells: One approach uses a TCR inhibitory molecule (TIM) to compete with TCR elements, while the other employs an miRNA scaffold to completely abolish CD3ζ, a crucial component of the TCR complex. Both methods aim to create safer, allogeneic CAR T-cell therapies.
CAR-T cell therapy for solid tumors struggles with identifying truly specific tumor antigens, leading to challenges like antigen escape and off-target effects. Researchers are developing strategies like optimized CAR constructs and combination therapies to enhance CAR-T cell specificity, efficacy, and ability to overcome the hostile tumor microenvironment, all while focusing on better targeting of relevant tumor antigens. A key challenge in CAR-T cell therapy is finding tumor-specific antigens to avoid harming healthy tissues. To combat antigen loss and tumor heterogeneity, researchers are exploring CARs that target multiple antigens, including bispecific CAR-T cells designed to engage two targets simultaneously.
Recent advances in the field show CAR-NK (Natural Killer) cells as a safer, off-the-shelf approach, bypassing HLA compatibility issues and reducing toxicity. Meanwhile, CAR-M (macrophage) cells leverage their potent phagocytic abilities and tumor-antigen presentation to attack solid tumors with broad infiltration. These emerging immunotherapies offer new hope in the fight against solid tumors.
In 2022 FDA approved clinical trial for allogeneic NK cells, derived from induced pluripotent stem cells, engineered against dual targets of MHC class-I-related proteins-A and -B (MICA and MICB). This trial showed safety and scalability of NK cell therapy offering a promising alternative towards solid malignancies. Further research is ongoing to optimize CAR-NK therapy in order to enhance its efficacy.
The future of CAR-T therapy hinges on logistics and costs, in streamlining the manufacturing process to make Allogeneic CAR-T therapy more efficient and affordable. Crucially, advancements in cryopreservation are enabling the creation of true "off-the-shelf" therapies, where CAR-T cells can be stored frozen and ready to deploy at short notice.