Souffle Therapeutics, the Boston RNA medicines company co founded by Robert Langer, has closed an oversubscribed $135 million Series B. Juvia Group led the round, joined by new investors including TCG Crossover Management, BB Biotech, Fidelity Management and Research, Balyasny Asset Management and an unnamed sovereign wealth fund, with existing backers such as Amgen Ventures, ARCH Venture Partners, Leaps by Bayer, Temasek and Vida Ventures also participating.
The money funds the step from platform to clinic. Souffle’s three lead programs, in facioscapulohumeral muscular dystrophy, heart failure with reduced ejection fraction, and muscle and metabolic disorders, will move into first clinical studies, while the balance supports earlier pipeline work in other tissues. The company emerged from stealth in October 2025 with a $200 million Series A, according to Fierce Biotech’s fundraising tracker, so the Series B arrives roughly a year later and at a larger syndicate.
The scientific claim is delivery. Oligonucleotide drugs work well in the liver and poorly almost everywhere else. Souffle’s REMEDY engine identifies receptors that internalize into specific cell types and builds binders, including monoclonal antibodies, to carry oligonucleotides into striated muscle and heart muscle cells. Whether that selectivity survives human dosing is the question the Series B is paying to answer.
Chief executive Amir Nashat said the syndicate’s breadth reflects confidence in the science and in the path to innovative therapies. For the sector, the round is one more data point that crossover investors are still funding platform risk in RNA, provided the platform is aimed at a named clinical program rather than discovery alone.