Regeneron struck a major research collaboration with Parabilis Medicines to develop antibody–peptide conjugates built around Parabilis’ Helicon platform. The pact centers on five undisclosed targets, with the potential to expand through additional options. Financial terms include a $125 million upfront payment plus Regeneron’s commitment to invest $75 million in Parabilis’ next equity financing, along with development, regulatory, and commercial milestones that could total about $2.2 billion and tiered royalties on any resulting medicines. The companies framed Helicons as a way to modulate intracellular proteins, including historically undruggable targets, by combining targeted delivery with Helicon “payload” activity. Investors appeared to weigh the strategic upside against near-term portfolio noise: Regeneron shares fell nearly 10% around the announcement, following earlier melanoma trial disappointment tied to fianlimab.