Rallybio down shifts to $81M IPO to fuel rare disease programs

After filing to raise up to $100 million in its Wall Street debut, Rallybio is reeling in a smaller sum of $80.6 million. The funds will bankroll several clinical trials, including a phase 1/2 study of its lead asset in a rare fetal bleeding disorder.

The $100 million IPO has become somewhat of a formality in biotech, with companies such as Caribou Biosciences, Erasca and Centessa Pharma all inking that number when they filed to go public. But unlike those companies, which outraised that initial figure by two- or even threefold, Rallybio changed its goal to $80.5 million late last week, according to a securities filing.

The bulk of the proceeds along with the cash Rallybio already has in the bank will bring a pair of treatments for fetal and neonatal alloimmune thrombocytopenia (FNAIT) through the clinic. The company will use between $75 million and $83 million to get its lead program, RLYB211 through a phase 1/2 study and put a second program, RLYB212, through a phase 1 and 1b study, according to the filing. It expects to start its first human trial for the latter in Germany in the first quarter of 2022.

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FNAIT is a rare disease that causes a mother’s immune system to attack her fetus or newborn child’s platelets, the blood cells involved in clotting. It happens when the fetus and mother express different proteins on their platelets. When the mother’s and fetus’s blood mixes, the mother’s immune system develops antibodies against the fetus’s platelets. These antibodies can then cross into the fetus, where they attack the fetus’s platelets.

There is no treatment for FNAIT, which can lead to miscarriage, death of the newborn baby or neurological disability due to bleeding in the fetus’s brain.

The IPO comes weeks after Rallybio established proof of concept for RLYB211, a polyclonal antibody treatment made by purifying antibodies from donated plasma. It is designed to clear fetal platelets from the mother’s circulation, preventing the immune attack against them. In early data reported earlier this month, the treatment cleared the troublesome platelets in a small group of adult men who received it after being injected with the platelets.

Rallybio tagged another $35 million to $41 million to push two programs for complement-driven diseases, which are caused by an overactive part of the immune system. The complement system helps—or complements—antibodies and white blood cells that fend off invading pathogens, but, when it is overactivated, it can turn against a body’s healthy tissues.

The company aims to file a Clinical Trial Application for RLB116, the more advanced of the two, by the end of the year, according to the filing. It is developing the treatment for paroxysmal nocturnal hemoglobinuria (PNH), a rare disorder where red blood cells break apart prematurely, and myasthenia gravis, an autoimmune and neuromuscular disease. It blocks the complement protein C5, the same target as Alexion’s Soliris and Ultomiris.

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Rallybio is developing a second C5 inhibitor, RLYB114, for complement-driven eye disease. It expects to apply to start a clinical trial for RLYB114 in the first half of 2023, it said in the filing.

Finally another $10 million to $14 million will support the company’s joint venture with Exscientia, struck in Kuly 2019. The partners have two discovery-stage programs focused on identifying new treatments for patients with rare metabolic diseases, according to the filing. The proceeds will push an ENPP1 inhibitor into phase 1.