Rallybio Lands $145M to Alter Course of FNAIT and More Rare Diseases

Xconomy New York — 

One of the risks to a newborn’s life comes from the mother’s immune system. It attacks the platelets of the fetus, depleting these blood-clotting cells and risking uncontrollable bleeding in the baby. Rallybio aims to develop the first FDA-approved treatment for this rare condition and the startup has raised $145 million to bring that drug, and others in its pipeline, into clinical testing.

The Series B round of financing announced Tuesday was led by Pivotal bioVenture Partners.

New Haven, CT-based Rallybio is first targeting a disease called fetal and neonatal alloimmune thrombocytopenia, often shortened to FNAIT or NAIT. It’s caused when the platelets of a pregnant woman have a surface protein, human platelet antigen 1 (HPA1), that is incompatible with the platelets of her fetus. That mismatch causes the the mother’s immune system to see the fetus’s platelets as foreign, sparking the production of antibodies in response.

NAIT is rare, occurring once in every 1,200 live births, according to data cited by the National Institutes of Health’s Genetic and Rare Diseases Information Center (GARD). The center says the disorder is typically triggered during birth, when the mother is exposed to the baby’s blood. While some cases are mild, in some instances NAIT leads to severe bleeding in a newborn’s brain. GARD says treatment for the infant includes platelet transfusions and intravenously delivered immunoglobulin, which is an infusion of antibodies. But in severe cases, the bleeding is fatal to the newborn.

The platelet incompatability can be detected before childbirth by testing for fetal DNA in the mother’s blood, says Steve Uden, a co-founder of Rallybio. No new diagnostic is needed, as blood tests that are already available can be used to also test for HPA1, he added. The company’s experimental treatment, RLYB211, is intended to provide what’s called antibody-mediated immune suppression. The drug, an antibody derived from plasma, is designed to bind to and remove fetal platelets from circulation in the mother’s blood (see Rallybio graphic above). Consequently, the mother’s immune system does not produce antibodies that target the fetus’s platelets. Once the mother is treated with the drug, FNAIT no longer poses a risk, Uden says. Of course, Rallybio still has to show that in clinical trials.

Martin Mackay, Rallybios chairman and CEO, says the company plans to start a Phase 1/2 study in Germany in the second half of this year. Enrolling pregnant women in clinical trials under ordinary circumstances is risky to the fetus and the mother, and the risk is higher now given the ongoing COVID-19 pandemic. When that study starts, it will test the drug’s effect in men, Uden says. There’s precedent for first testing in men drugs meant for pregnant women: Uden points to Rhesus disease, a blood disorder caused by a specific mix of blood types between a pregnant mother and her unborn baby  that stems from an  incompatability of a different protein, Rhesus factor, on red blood cells. Pregnant women are screened for Rhesus disease as part of the blood tests they routinely receive.

“We’re confident that men are the right place to test before testing in women who are pregnant,” he says.

RLYB211 was initially developed by Norwegian company Prophylix, which had advanced it to preclinical development. Rallybio acquired the program last June for an undisclosed upfront sum. The Connecticut company will owe royalties from sales if it is successful in bringing the therapy to the market.

The Rallybio pipeline has another preclinical compound, RLYB212, which is in development for an undisclosed rare blood disorder, and preclinical compounds for rare inflammatory disesaes, also undisclosed. Like its lead drug, those programs were acquired in deals financed by the cash raised from Rallybio’s $37 million Series A round of funding in 2018, says Jeff Fryer, chief financial officer of the company. Mackay says that the new capital will fund clinical development of the pipeline and support the company’s efforts to scout for more rare disease drugs.

Mackay, Uden, and Fryer are all veterans of Alexion Pharmaceuticals (NASDAQ: ALXN), a rare disease drug developer once based in New Haven that relocated to Boston in 2018. As executive vice president and global head of R&D at Alexion, Mackay played a role in the development of eculizumab (Soliris), a treatment for a different rare blood disorder that has become a blockbuster seller.

Rallybio’s latest round of funding brings aboard new financial backers Viking Global Investors, TPG’s The Rise Fund, F-Prime Capital, funds managed by Tekla Capital Management, Solasta Ventures, Fairview Capital, and Mitsui & Co. Global Investment. The company’s earlier investors—5AM Ventures, Canaan Partners, and New Leaf Venture Partners, and Connecticut Innovations—also participated in the new financing.

Image by Rallybio