FDA Grants Orphan Drug Designation to Immusoft’s Engineered B Cell Therapy for the Treatment of MPS II

SAN FRANCISCO, Dec. 15, 2025 — Immusoft, a clinical-stage biotechnology company, announced today that the U.S. Food and Drug Administration (FDA) has granted Orphan Drug Designation to ISP-002, an investigational cell therapy for Mucopolysaccharidosis type II (MPS II), or Hunter syndrome. This designation marks a significant expansion of the company’s proprietary platform, which uses a patient’s own immune cells as “bio-factories” for therapeutic enzymes.

MPS II is a life-threatening rare genetic disease caused by a deficiency in the enzyme iduronate-2-sulfatase (IDS). Without this enzyme, toxic sugars accumulate in the body, leading to skeletal deformities, heart complications, and reduced life expectancy.

A Paradigm Shift in Cell Therapy

Immusoft’s approach utilizes an engineered B cell platform. This cell therapy programs a patient’s B cells to continuously produce and secrete the missing IDS enzyme from within the body.

This method offers several potential advantages over standard treatments:

• Sustained Production: Provides continuous enzyme exposure, unlike the “peaks and valleys” associated with weekly enzyme replacement infusions.

• Redosability: Clinical data from the company’s MPS I trial (ISP-001) suggests these cells can be redosed without the need for toxic pre-conditioning, lymphodepletion, or immunosuppression—a common hurdle for many AAV and cell therapy protocols.

• Durability: The platform aims to provide long-term disease control, addressing the high unmet needs of the Hunter syndrome community.

Building on Clinical Success

The move into MPS II follows the successful foundational work of ISP-001, the first-ever engineered B cell cell therapy tested in humans. Early Phase 1/2 clinical results for MPS I have demonstrated a favorable safety profile, paving the way for the expansion of this platform into other lysosomal storage disorders. “Orphan Drug Designation for ISP-002 is an important milestone… and underscores our commitment to developing durable, redosable therapies,” said Sean Ainsworth, CEO of Immusoft.

The preclinical development of this platform received support from the California Institute for Regenerative Medicine (CIRM). With the new FDA designation, Immusoft intends to accelerate the advancement of ISP-002 toward human clinical trials while exploring the application of its B cell technology in additional rare disease indications.