Designation recognizes ISP-002, an engineered B cell therapy designed for sustained enzyme delivery

SAN FRANCISCO, Jan. 26, 2026 /PRNewswire/ — Immusoft of CA, a clinical-stage biotechnology company pioneering engineered B cell therapies, today announced that the U.S. Food and Drug Administration (FDA) has granted Rare Pediatric Disease (RPD) designation to ISP-002, the company’s investigational therapy for the treatment of mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome.

The FDA grants RPD designation for serious or life-threatening diseases that primarily affect children 18 years old or younger and affect fewer than 200,000 people nationwide. RPD designation allows recipient companies, upon approval of their designated treatment, to be eligible for a Priority Review Voucher (PRV¹), which may be used for priority review of a future submission of a New Drug Application or Biologics License Application. Priority review can reduce FDA review time by several months. Priority review vouchers may be sold to a third party and recent prices paid for PRVs have been as much as $200 million.

MPS II is a rare, inherited lysosomal storage disorder caused by a deficiency of the enzyme iduronate-2-sulfatase (IDS), which leads to the accumulation of glycosaminoglycans in tissues and organs throughout the body. The disease primarily affects pediatric patients and is associated with progressive, multisystem involvement, including neurocognitive impairment, cardiopulmonary complications, skeletal abnormalities, and reduced life expectancy. The current standard of care is enzyme replacement therapy, which requires frequent lifelong infusions and may not achieve consistent enzyme exposure across all affected tissues.

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