Diagonal Therapeutics Secures $125M in Series B Funding for Disease-Modifying Antibodies

Diagonal Therapeutics just closed an oversubscribed $125M Series B, and this is not one of those biotech headlines floating on vibes, deck aesthetics, and hope. This is what happens when computation, biology, and restraint stop posturing and start agreeing. Watertown, Massachusetts keeps proving that the loudest breakthroughs rarely raise their voice. They just show the data and wait.

Founded in 2022 by Alexey Lugovskoy, Ph.D., alongside Atlas Venture, Diagonal Therapeutics emerged from stealth in April 2024 with a $128M Series A and a very specific opinion about signaling. Most antibodies shut things down. Diagonal activates, clusters, and restores. Digital. Agonist. Antibody. Ligand. The name is not marketing, it is architecture, and the science follows the blueprint.

Alexey Lugovskoy, Ph.D. brings 25+ years across Dragonfly Therapeutics, Morphic Therapeutic, Merrimack Pharmaceuticals, and Biogen, plus co-inventor status on tovorafenib, now approved as Ojemda for pediatric low grade glioma. Over 100 patents and publications later, this company feels less like a startup and more like a long prepared argument finally getting airtime.

DIAG723 is the lead program, armed with Orphan Drug Designation from the FDA and a positive opinion from the EMA for hereditary hemorrhagic telangiectasia. Preclinical data shows prevention and reversal of arteriovenous malformations, correction of anemia, survival improvement from 25% to 100% in mouse models, and meaningful impact in pulmonary arterial hypertension models. Not incremental. Directional.

The DIAGONAL Product Engine is where the quiet flex lives. Roughly 200K antibody sequences, more than 10B theoretical combinations, reduced through computational clustering developed with Dima Kozakov, Ph.D. at Boston University into about 100 viable candidates in under 8 months. This is computation doing real work, not filling slides.

The Series B was co-led by Sanofi Ventures and Janus Henderson Investors, with new participation from Deep Track Capital, EcoR1 Capital, Logos Capital, Balyasny Asset Management, and Woodline Partners, alongside continued conviction from Atlas Venture, BVF Partners, Lightspeed Venture Partners, RA Capital Management, Frazier Life Sciences, Viking Global Investors, RV Invest, Velosity Capital, Biovision Ventures, and Checkpoint Capital. Paulina Hill, Ph.D. of Sanofi Ventures joins the board, adding another layer of signal discipline.

The leadership bench runs deep with John Lee, M.D., Ph.D. as Chief Medical Officer, Patrick Andre, Ph.D. as Chief Scientific Officer, and Sandra Teixeira, Ph.D. leading development, supported by a team that understands rare disease patients are not edge cases, they are waiting.

First in human trials for DIAG723 are expected in 1H 2026, informed by a natural history study with Cure HHT that shows how daily and relentless this disease really is. Roughly 150K people globally with HHT, nearly 200K with PAH, and zero approved disease modifying therapies addressing root cause. That gap is not theoretical. It is personal.