Capsida Clinical Trial - Information for Families

Updates as of February 2025

Capsida Biotherapeutics (Capsida) is a gene therapy company that utilizes proprietary technology to engineer AAV-based gene therapy products. One such product, CAP-002, is a potential  investigational, next-generation IV-administered gene therapy designed to enable replacement  of  STXBP1 protein throughout the brain following a single IV infusion.

At this time, Capsida is completing IND-enabling studies. If these are successful,  a clinical trial for CAP-002 would potentially start enrolling in the latter half of 2025. The Foundation understands the excitement that this news has generated in the STXBP1 community, and we share this excitement. The Foundation also understands that many of you may have questions concerning this gene therapy product or the upcoming clinical trial, and we would like to address some of these questions in the following points:  

  • CAP-002 is a potential investigational AAV gene therapy product that is intended to deliver a healthy copy of the STXBP1 gene throughout the brain with a single IV infusion. This aims to boost the STXBP1 protein levels, which are low in people with a faulty STXBP1 gene.  

  • According to Capsida, CAP-002 has been engineered to better target the brain, compared to other AAV vectors, while also de-targeting other organs like the liver.  

  • Capsida is still planning the clinical trial and isn't recruiting participants yet. When the trial begins, they will handle the recruitment process.  

  • The clinical trial will likely test different doses of CAP-002 to see how safe they are. This type of trial usually involves a small number of participants (around 12 or fewer) and can take up to a year or more to enroll.  

  • It is likely that Capsida will restrict participation in this first trial to children of certain ages . Later trials may include a wider range of people with STXBP1. There will likely be other enrollment criteria as well, including screening for existing antibodies to the gene therapy due to past viral exposures.  

  • Since this is a gene therapy study, each participant is typically followed for at least five years during the course of the study.  

  • Although the treatment is given in a single dose, all patients are followed closely for two years with periodic assessments for safety and effectiveness, with additional follow-up for a total of at least five years.  

  • We don't know yet where the trial will take place. It could be in the U.S., another country, or multiple countries.  

  • Being part of the STARR natural history study doesn’t affect your child's chances of being selected for the CAP-002 trial.  

  • There isn’t a sign-up list for the CAP-002 trial. However, the Foundation encourages you sign up on our Parent/Caregiver contact list so you can receive regular updates on research and clinical trials for STXBP1: https://www.stxbp1disorders.org/contact-list.  

  • When Capsida has finalized their plans for the CAP-002 trial the Foundation will share this information with the community.