Cloverleaf Bio, a Yale University spinout founded in 2023, has closed a $33 million seed round for its unconventional approach to cancer treatment using engineered transfer RNA, the company announced September 8. The financing, led by 4BIO Capital and joined by the venture arms of AbbVie, Eli Lilly, and Boehringer Ingelheim, stands out in a biotech fundraising landscape where seed rounds for similar companies typically hovered around $6 million to $9 million in 2025, according to PitchBook data from that year's second quarter.
The sheer size of the raise and the presence of three Big Pharma investors at such an early stage signal unusual confidence in a technology that remains largely unproven in humans. Transfer RNA therapies have generated buzz in recent years as a potential new frontier in genetic medicine, but the field has yet to produce clinical validation. The most advanced player, Flagship-backed Alltrna, plans to start its first human trial later this year, while at least one well-funded competitor has already folded.
Austin Draycott and Cole Lewis, both Yale-trained scientists who founded Cloverleaf in 2023, are betting they can engineer tRNA molecules to selectively shut down RNA-modifying enzymes that cancer cells depend on. Their technology emerged from work in the lab of Wendy Gilbert, now chair of the company's scientific advisory board and a professor at Yale who previously trained under CRISPR pioneer Jennifer Doudna.
The New Haven–based startup intends to push its lead compound, CLB-001, into early-stage clinical trials for liver cancer, with a secondary program targeting colorectal cancer using an antibody-tRNA hybrid. According to the company, preclinical studies showed the lead asset killed cancer cells more effectively than healthy ones and retained potency against tumors resistant to standard chemotherapy. Animal toxicity screens came back clean, though those assurances carry limited weight before human testing begins.
"To attract major strategic investors, including AbbVie Ventures, Lilly, and Boehringer Ingelheim Venture Fund at this stage reflects the level of scientific interest in this approach," Draycott said in a statement. Perhaps more than the founders anticipated when they first spun out of Yale.
Dima Kuzmin, co-founder and managing partner at 4BIO Capital, framed the investment as a bet on "transformative frontier science" that could establish an entirely new drug class. Christina Vorvis, a director at AbbVie Ventures, noted her firm has backed Cloverleaf since its Yale origins, suggesting the pharma giant sees strategic value beyond a typical seed check.
Before this round, Cloverleaf scraped together early validation the hard way: a $100,000 non-dilutive grant from a Nucleate and Eli Lilly challenge in 2024, $50,000 from placing second in a pitch competition, and support from a National Cancer Institute small business program. Lewis earned a spot on the Forbes 30 Under 30 Healthcare list last year while still finishing his PhD.
The tRNA field carries both promise and risk. Alltrna is preparing what would be the first-in-human trial of an engineered tRNA therapy, but hC Bioscience, which had backing from ARCH Venture Partners and Takeda Ventures, shut down in March after early preclinical work revealed delivery obstacles that proved insurmountable, according to Fierce Biotech. Getting large, complex RNA molecules into the right cells without triggering immune responses or off-target effects remains a fundamental challenge.
Cloverleaf operates out of New Haven and is expanding into Boston, according to job postings. The company's LinkedIn profile lists fewer than ten employees, a skeleton crew typical of seed-stage biotechs racing to generate the data needed for a Series A. Whether the $33 million runway proves sufficient to reach that milestone will depend on how quickly the science translates from mice to humans.
Additional investors in the round included Draper Associates, Mission BioCapital, and American Cancer Society BrightEdge. The company's advisory board includes Albert Lai of AbbVie Ventures, Luisa Escobar-Hoyos of Yale, and Michael McCaman, former head of chemistry, manufacturing, and controls at Intellia Therapeutics, a CRISPR company that has navigated the transition from preclinical promise to approved therapy.
