Seven CAR T-cell products have won FDA approval since 2017. All of them treat blood cancers: B-cell acute lymphoblastic leukemia, several lymphomas, chronic lymphocytic leukemia and multiple myeloma. A recent review in Frontiers in Oncology lays out what researchers are building next, and why.
In plain terms, a CAR T-cell is a patient’s T cell that has been genetically modified to carry a synthetic receptor, one that locks onto a marker on tumor cells. In large B-cell lymphoma the approach has improved overall survival. In multiple myeloma it has extended the time before the disease progresses, and patients with follicular and mantle cell lymphoma have had long remissions.
Solid tumors are another story. Early studies of conventional CAR T-cells there were disappointing, the review says. The target marker shows up unevenly on cancer cells, and some cancer clones simply stop displaying it. The tissue around a tumor also wears the T cells down.
Tuning the receptor
A CAR has three parts: a binding domain outside the cell, a transmembrane section, and a signaling domain inside. Researchers are now reworking each. Lower-affinity binding domains, for instance, may help the cells engage a target repeatedly and last longer.
The choice of co-stimulatory signal matters too. Think of it like choosing between a sprinter and a distance runner. CD28 produces a highly potent but short-lived effector cell. 4-1BB helps the cells multiply and persist in the body and makes them less prone to exhaustion. Other options, including ICOS, CD27 and OX40, each shift memory formation and survival in their own way.
Logic gates and safety switches
The review also covers logic-gated designs: synNotch receptors, inducible ON-switch CARs, inhibitory CARs and modular adaptor systems. The aim is for a cell to act only in the right context, which should reduce damage to healthy tissue. Other work targets T-cell dysfunction directly, through checkpoint rewiring, cytokine armoring and epigenetic reprogramming.
Off-the-shelf cells
The practical upshot for patients may come from allogeneic products, made from healthy donors rather than from the patient. The review also lists induced pluripotent stem cells, natural killer cells, gamma-delta T cells and macrophages as starting material. The central problems are graft-versus-host disease and rejection by the host’s immune system. Success would allow manufacturing at scale.
The authors name immunogenicity, regulatory complexity and production logistics as the remaining bottlenecks, and point to Boolean logic circuits, safety switches and automated GMP-compliant manufacturing as the direction of travel. Five generations of CAR designs have been developed so far.
