Solstice Oncology will gain an exclusive worldwide license to Harbour BioMed’s porustobrt, an anti-CTLA-4 antibody currently being studied for melanoma, colorectal cancer and other malignancies in China.
Chinese biotech Harbour BioMed is taking part in the formation of Solstice Oncology alongside a group of unnamed venture capital investors, giving the startup exclusive global access to its lead asset HBM4003.
Under the terms of Tuesday’s deal, Harbour will receive $105 million upfront, a sum that covers a $50 million immediate cash payment, $5 million in near-term commitments and a $50 million equity stake in Solstice. The startup will also be on the hook for up to approximately $1.1 billion in development and commercialization milestones, according to the company’s news release.
HBM4003, also called porustobart, is a fully human monoclonal heavy chain-only antibody designed to target the CTLA-4 protein, according to Harbour’s website. Via this mechanism, the molecule boosts the immune system’s cancer-killing activity while also limiting toxic side effects.
For its investment, Solstice will receive the exclusive right to develop and market HBM4003 outside the Greater China region.
It is unclear which particular disease Solstice will be targeting, but under Harbour’s wing, the asset is being developed for melanoma, colorectal cancer (CRC), hepatocellular cancer and neuroendocrine neoplasms, all running in China. Phase II data released in October 2025 demonstrated a 34.8% objective response rate in heavily pretreated patients with metastatic CRC, resulting in a median progression-free survival of 4.2 months.
“By co-founding a company along with others and becoming a shareholder, we are participating in the building of a global biotechnology company,” Harbour CEO Jingsong Wang said in a statement.
Headquartered in Shanghai, Harbour has established a strong presence in Western markets. The biotech has one office in Natick, Massachusetts and another in Rotterdam, Netherlands.
In December 2025, Bristol Myers Squibb paid $90 million upfront for access to the biotech’s Harbour Mice platform, aiming to advance multispecific antibodies for undisclosed indications. The agreement also includes up to $1.035 billion in development and commercial milestones.
A few months earlier, in March 2025, Harbour signed a similar deal with AstraZeneca. For $175 million upfront, the pharma gained the option to license two preclinical immunology programs, as well as the ability to nominate additional targets. The agreement, also centered on multispecific antibodies, could yield a $4.4 billion prize for Harbour.
