Boston-based Strand Therapeutics has raised $153 million in a Series B round to accelerate development of its programmable, self-replicating mRNA platform and pipeline of solid tumour immunotherapies.

The raise — co-led by Redmile Group and FPV Ventures — brings in Regeneron, Lilly Asia Ventures, Amgen Ventures, Playground Global, and Kinnevik. The funding will support ongoing clinical trials and platform expansion, as the company sharpens its focus on precision immunotherapy for solid tumours, a space where checkpoint inhibitors have seen limited success.

Strand’s lead candidate, STX-001, encodes interleukin-12 (IL-12) and is delivered via intratumoural injection. In early data presented at ASCO 2025, the therapy showed initial anti-tumour activity, durable disease control, and favourable tolerability in a heavily pre-treated population — suggesting the platform’s promise in modulating the tumour microenvironment without triggering systemic toxicity.

Unlike conventional mRNA therapies, Strand’s platform uses synthetic biology logic gates and payload control systems to regulate gene expression only in tumour tissue. The company says its next wave of candidates will be systemically administered but will selectively activate within tumours, opening the door to repeat dosing and combination approaches.

“Patients with solid tumours have largely been left behind by current immunotherapies,” said CEO Jake Becraft. “This financing positions us to change that.”

The funding also marks a broader vote of confidence in mRNA’s post-COVID future — beyond vaccines — as programmable, persistent, and precise gene therapies gain traction in oncology and rare disease.