Chimeric antigen receptor (CAR) T cell therapy is a remarkable achievement for fighting diseases using the body’s immune system, but there is a pressing need to make CAR T cells available for large patient groups. Most CAR T cell therapies, including all United States Food and Drug Administration-approved products, adopt an autologous approach. This means that clinicians take a patient’s own T cells, engineer them to express CARs, and infuse them back into the same patient. These autologous CAR T cells require a costly, lengthy, and individualized manufacturing process, often delaying and preventing patient access to treatments (1). 

To mitigate these issues, scientists are exploring the possibility of utilizing allogeneic T cells from healthy donors for CAR T cell generation. Unlike patient-derived T cells, which may have become dysfunctional due to exposure to malignant tumors or infections, T cells from healthy blood demonstrate greater proliferative capacity and antitumor effects (2). 

Using allogeneic T cells ensures CAR T cell product quality and facilitates the standardization of CAR T cell manufacturing. Researchers can select donors based on specific immune characteristics and produce batches of homogenous CAR T cells ahead of time, making treatments immediately available for patients. Since a single T cell collection can generate multiple therapeutic doses, the treatment may also cost less. 

However, like many tissue and organ transplants, allogeneic CAR T cell infusions can cause undesirable alloimmune responses, including graft-versus-host disease (GvHD), a life-threatening condition where donor-derived CAR T cells recognize the recipient’s cells as non-self via T cell αβ receptors (αβ TCRs) and attack the recipient’s cells. Researchers have developed strategies to reduce GvHD by using T cell subsets that comprise lower αβ TCR diversities, such as T cells differentiated from hematopoietic stem cells, virus specific memory T cells, and non-αβ T cells (2). 

Gene editing technologies have also emerged as effective tools for preventing GvHD. Scientists use engineered transcription activator-like effector nucleases (TALENs), restriction enzymes that recognize and cleave DNA at specific sites to eliminate αβ TCR expression. For example, researchers from the University College London used TALEN-edited allogeneic CAR T cells to treat two infants with leukemia. Using TALEN enzymes that target αβ TCR genes, they abolished αβ TCR expression on T cells. The two children achieved sustained remissions after the therapy and only showed mild skin GvHD, in contrast to typical multisystem and fulminant GvHD symptoms (3). 

In addition to TALENs, scientists from the Free University of Brussels recently established a CRISPR-Cas9-mediated approach for generating GvHD-free allogeneic CAR T cells (4). They knocked out αβ TCR genes in T cells derived from human peripheral blood using CRISPR-Cas9 and expressed a leukemia-specific CAR. The leukemia mice infused with modified T cells showed reduced tumor burden and prolonged survival without developing any GvHD symptoms. 

By employing various T cell sources, gene editing techniques, and cell delivery systems, researchers around the world keep improving the efficacy and safety of CAR T cell therapy and developing new strategies for large scale CAR T cell manufacturing. With a number of allogeneic CAR T cell therapies for blood cancer and solid tumors under preclinical and clinical investigation, a universal off-the-shelf immunotherapy accessible for many more patients may soon be a reality. 

Learn more about advances in immuno-oncology in this ebook.

References

1.  Köhl, U., Arsenieva, S., Holzinger, A. & Abken, H. CAR T Cells in Trials: Recent Achievements and Challenges that Remain in the Production of Modified T Cells for Clinical Applications. Hum Gene Ther  29, 559–568 (2018). 
2. Depil, S., Duchateau, P., Grupp, S. A., Mufti, G. & Poirot, L. ‘Off-the-shelf’ allogeneic CAR T cells: development and challenges. Nat Rev Drug Discov  19, 185–199 (2020). 
3. Qasim, W. et al. Molecular remission of infant B-ALL after infusion of universal TALEN geneedited CAR T cells. Sci Transl Med  9, eaaj2013 (2017). 
4. Tipanee, J., Samara-Kuko, E., Gevaert, T., Chuah, M. K. & VandenDriessche, T. Universal allogeneic CAR T cells engineered with Sleeping Beauty transposons and CRISPR-CAS9 for cancer immunotherapy. Mol Ther  30, 3155–3175 (2022).