Capstan Therapeutics Begins Phase 1 Trial of CAR-T Therapy CPTX2309 for Autoimmune Disease

SAN DIEGO, CA, USA I June 11, 2025 I Capstan Therapeutics, Inc., a biotechnology company at the forefront of clinical development, has initiated the first dosing of volunteers in its Phase 1 trial of CPTX2309. This represents Capstan's leading candidate for anti-CD19 in vivo CAR-T therapy aimed at addressing B cell-mediated autoimmune diseases. The trial will investigate various aspects, including the safety and tolerability of CPTX2309, as well as its pharmacokinetics and pharmacodynamics. The primary focus is to evaluate the extent of peripheral B cell depletion and recovery among healthy participants across different dosage levels.

Preclinical evaluations have already shown promising results, indicating rapid and substantial depletion of B cells in both blood and tissues. These findings have paved the way for the clinical assessment of CPTX2309, supporting the exploration of its effectiveness at specific doses and treatment plans.

Dr. Ramin Farzaneh-Far, Chief Medical Officer at Capstan, commented on the therapeutic objectives of CPTX2309, emphasizing the aim to achieve an "immune reset" through extensive B cell depletion. This is accomplished by leveraging transient and adjustable in vivo CAR-T technology that is ready for use without the need for lymphodepletion or permanent CAR integration into the genome. The Phase 1 trial's healthy volunteer focus allows for efficient dose escalation, highlighting potential safety benefits. The primary aim is to identify a pharmacologically active dose that can transition to Phase 2 studies, where the therapy will be tested on patients with autoimmune conditions.

Capstan Therapeutics, Inc. is committed to expanding the realm of therapeutic possibilities for patients through targeted in vivo RNA technologies. The company's proprietary CellSeeker™ platform utilizes innovative lipid nanoparticles (LNPs) conjugated with recombinant protein binders like monoclonal antibodies. These structures deliver RNA payloads capable of reprogramming cells within the body. Capstan is initially concentrating on developing in vivo CAR-T therapies, combining CAR-T therapy's potency with the convenience of an off-the-shelf product for autoimmune disease treatment.

CPTX2309, an investigational in vivo CAR-T therapy, is specifically designed to manage B cell-mediated autoimmune disorders via tunable and dose-dependent CAR expression. This therapy potentially offers a favorable safety profile based on preclinical data. Studies have shown that CPTX2309 effectively engineers CD8+ CAR T cells in vivo, leading to significant B cell depletion in both blood and tissues. Post-depletion, there is a repopulation predominantly with naive B cells, as observed in non-human primate models. Currently, Capstan is advancing the Phase 1 trial of CPTX2309 with healthy volunteers in Australia.

By employing cutting-edge technology and innovative methods, Capstan Therapeutics positions itself as a leader in the development of advanced therapies for autoimmune diseases. Through strategic clinical trials and ongoing research, the company aims to make significant strides in the field of RNA-based treatments, ultimately enhancing patient outcomes and offering new hope in the management of complex autoimmune conditions.