Len Walt, Vice President, Head of Medical Affairs, SOBI in North America, discusses his company’s activities in Hemophagocytic lymphohistiocytosis (HLH), a rare condition in which the body makes too many activated immune cells (macrophages and lymphocytes). People with HLH usually develop symptoms within the first months or years of life. Symptoms may include fever, enlarged liver or spleen, cytopenia (decreased number of blood cells), and neurological abnormalities.

HLH may be inherited in an autosomal recessive manner or it can have non-genetic causes in which case it is called acquired HLH. There are five subtypes of inherited HLH which are designated as familial HLH, types 1-5. Each subtype is caused by a change (mutation) in a different gene. The genetic cause of type 1 is currently unknown. Types 2-5 are caused by mutations in the PRF1 gene, the UNC13D gene, the STX11 gene and the STXBP2 gene, respectively. Treatment depends on a number of factors, including the severity of symptoms, the age of onset, and the underlying cause of the condition.

Primary HLH mainly occurs in infants and young children and the secondary form of the disease (sHLH) is acquired from or associated with infection, autoimmune diseases or malignancy. The estimated patient population in the United States, European Union, and Japan amounts to around 5,000 people across both primary and secondary HLH. There is currently no approved drug therapy for HLH, with a current treatment protocol consisting of immuno-chemotherapy being used to suppress the immune reaction.

SOBI has entered into a strategic partnership with Novimmune to develop and commercialize emapalumab, a late-stage experimental drug being developed to treat primary HLH. Emapalumab is an anti-interferon-gamma monoclonal antibody currently under U.S. Food and Drug Administration review for the treatment of primary HLH. In the United States, emapalumab has received Orphan Drug designation, Breakthrough Therapy designation and Rare Pediatric Disease designation from the FDA. Novimmune will be eligible to receive a Priority Review Voucher upon approval.

A regulatory decision in the United States is expected towards the end of 2018. In Europe, emapalumab has been granted Orphan Drug designation and PRIME (PRIority MEdicine) status by the EMA. The EMA filing is expected to be submitted later in 2018. Emapalumab has potential therapeutic value in other serious medical conditions, with studies in secondary HLH and hematopoietic stem cell transplant ongoing or being planned.