RiboX announced that the FDA has cleared it to begin a phase 1 trial of RXIM002, a therapy designed to equip immune T-cells with synthetic receptors inside the body

RiboX announced that the FDA has cleared it to begin a phase 1 trial of RXIM002, a therapy designed to equip immune T-cells with synthetic receptors inside the body

On August 8, the company announced that RXIM002 would be tested in autoimmune cytopenias, a group of diseases in which the immune system destroys blood cells. The therapy is intended to deliver circular RNA to T-cells, providing instructions for making a synthetic receptor. The trial is called POPULUS-1.

In conventional CAR-T therapy, T-cells are collected from the patient and modified in a laboratory to express a CAR, a synthetic receptor that recognizes a selected target. The cells are then expanded and returned to the patient. This process must be performed separately for each dose.

For RXIM002, RiboX describes a different approach. A lipid nanoparticle, which is a tiny container made from fat-like molecules, is intended to deliver circular RNA into a T-cell. The cell would read the instructions and produce the CAR itself.

The CAR targets CD19, a protein found on B-cells, which produce antibodies. In autoimmune cytopenias, some of these antibodies may target blood cells. The receptor is intended to recognize CD19 and direct T-cells toward B-cells.

Circular RNA is an instructional molecule whose ends are joined. In a 2025 study, researchers compared it with linear mRNA, another type of instructional molecule, in human T-cells. The circular version produced more CAR protein and maintained its level for longer. The researchers then packaged the instructions in nanoparticles targeted to immune cells and generated CAR-expressing immune cells in mice. That study used a different construct. It shows that the combination of circular RNA and targeted delivery to immune cells has already been tested in cells and mice.

A separate early trial of RXIM002 has already been registered in China. According to the international ClinicalTrials.gov registry, Ruijin Hospital plans to enroll 27 adults with autoimmune diseases in which B-cells play a central role. RiboX is listed as a partner. The protocol includes assessments of safety, nanoparticle and RNA concentrations in the blood, and the number of CAR-expressing T-cells.