A drug for acute lymphoblastic leukemia called tisagenlecleucel is one of the FDA-approved CAR-T therapies that has produced long-lasting remissions in patients whose cancer resisted other treatment. A review in Frontiers in Immunology now looks at where the technology is headed, and the answer goes well beyond blood cancers.
CAR-T therapy takes a patient’s own T cells and engineers them to carry a chimeric antigen receptor. The receptor has an outer piece, usually taken from an antibody, that latches onto a target on another cell. That piece is joined to internal signaling domains, including CD3ζ along with the co-stimulatory molecules CD28 and 4-1BB, which switch the T cell on, help it multiply and keep it alive.
Where it works, and where it struggles
Blood cancers have been the success story. Part of the reason, the authors explain, is that circulating tumor cells are easy to reach and often share a uniform marker such as CD19.
Solid tumors are harder. Efficacy there is held back by immunosuppressive surroundings, by antigens that vary from one part of a tumor to another, and by a shortage of targets found only on tumor cells.
The review also describes growing interest in diseases outside cancer. Researchers are testing CAR-T cells in multiple sclerosis, systemic lupus erythematosus and myasthenia gravis, and in chronic viral infections such as HIV and hepatitis B. Traditional treatment for autoimmune disease relies on broad immunosuppressants. CAR-T cells could instead be built to remove only the faulty immune cells, which might make treatment more targeted and less toxic.
Those conditions bring their own difficulty. According to the authors, effective therapy there needs precise control of how long the cells persist and how the immune system rebuilds itself, not just strong killing power.
Off-the-shelf cells
Today most CAR-T products are autologous, made from the patient’s own cells, and that process is complex and resource-intensive. Allogeneic products come from healthy donors and could be ready sooner, made to a standard recipe and at lower cost. The risk is graft-versus-host disease, along with rejection by the recipient’s immune system.
“Universal” CAR-T cells try to solve this through gene editing. Tools such as TALENs, CRISPR/Cas9 and base editing can knock out the T-cell receptor gene TRAC and alter HLA molecules. A second route uses switchable platforms, UNICAR among them, that allow outside control of the cells. A product called CYAD-101 takes a different path, limiting alloreactivity without editing the genome. Not every allogeneic product counts as universal, the review notes.
Another approach swaps T cells for natural killer cells. CAR-NK cells carry minimal risk of graft-versus-host disease and tend to produce less of the inflammatory signal IL-6, which was linked to milder cytokine release syndrome and neurotoxicity in early studies. Their drawback is shorter persistence in the body.
Open questions
The authors also cover in vivo gene delivery, which aims to bypass manufacturing cells outside the body, and safety switches such as logic-gated and inducible designs. They list unresolved issues: which universal approaches can truly scale, whether in vivo engineering can replace conventional manufacturing, and how to add safety controls without weakening the treatment.
The encouraging part is how much is being tried. Patients curious about whether CAR-T therapy could apply to their condition should talk to their doctor.
