Harbour BioMed forms ‘new co.’ Solstice Onco focused on CTLA-4 antibody

Edited by Robert McTiernan··2 min read

China-based Harbour BioMed signed an exclusive licensing and equity partnership deal with US-based Solstice Oncology for the development and commercialization of HBM4003, a fully human anti-CTLA-4 monoclonal antibody, outside Greater China, according to an official company statement. Under the deal, Solstice takes responsibility for advancing the clinical-stage immune checkpoint inhibitor across global markets excluding Greater China, where Harbour BioMed retains rights.

Harbour BioMed will receive upfront consideration valued at over USD 105 million, including USD 50 million in upfront payments, USD 5 million in near-term cash payments, and more than USD 50 million in equity in Solstice Oncology. Harbour is also eligible for up to approximately USD 1.1 billion in development, regulatory, and commercial milestone payments, in addition to tiered royalties on net sales outside Greater China.

Deal context

HBM4003 is a next-generation cytotoxic T-lymphocyte-associated protein 4 (CTLA-4)-targeting antibody engineered using Harbour BioMed’s Harbour Mice platform to enhance regulatory T cell depletion within the tumor microenvironment while reducing systemic toxicity associated with earlier CTLA-4 inhibitors. The molecule is currently undergoing Phase I clinical evaluation in solid tumors, including assessment as both a monotherapy and in combination with PD-1 inhibitors.

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Solstice Oncology is the latest example of the “New Co.” model, referring to the trend for China-based biotechs to establish an overseas entity or joint venture to develop licensed assets, partnering with investors while retaining an equity stake in the new company. Harbour BioMed is thereby able to participate in the global development of HBM4003 beyond its core geographic focus.

The agreement comes amid continued interest in next-generation CTLA-4-targeted therapies. CTLA‑4 is a validated but toxicity‑limited checkpoint target, with the field’s innovation focus now aiming to improve on the first-in-class Yervoy (ipilimumab) by re‑engineering CTLA‑4 biology to improve the therapeutic index. These efforts include tumor‑selective activation (masked/prodrug antibodies); Fc engineering to preferentially deplete intratumoral Tregs via ADCC/ADCP; and bispecific formats that condition CTLA‑4 blockade on a second marker (often PD‑1/PD‑L1) to bias activity toward the tumor microenvironment (TME).

In 2023, BioNTech signed with OncoC4 for global rights to the next-generation anti-CTLA-4 monoclonal antibody candidate, ONC-392, a molecule currently at the Phase III stage. Another CTLA-4-targeting molecule in active clinical development is Agenus’s AGEN1181 (Agenus), currently Phase I (NCT03860272).