On August 8, 2022, Mersana Therapeutics, a clinical-stage biopharmaceutical company focused on discovering and developing antibody-drug conjugates, announced that it had entered into a global collaboration agreement with GSK. The agreement provides GSK with an exclusive option to co-develop and commercialize XMT-2056, a proprietary Mersana antibody-drug conjugate that targets a novel epitope of HER2 by activating the innate immune system through STING signaling. Mersana expects to initiate a Phase 1 clinical trial of XMT-2056 to investigate its potential in a range of HER2-expressing tumors such as breast, gastric and non-small-cell lung cancers.

Under the terms of the agreement, Mersana will receive an upfront option purchase fee of $100 million, and is eligible to receive up to $1.36 billion in the form of an option exercise payment and development, regulatory and commercial milestone payments if GSK exercises its option. Mersana also retains options to share in profits and to co-promote XMT-2056 in the United States and will be eligible to receive royalties on net product sales either worldwide (if it does not exercise its US profit-sharing option) or outside the US (if it does exercise its US profit-sharing option).

The WilmerHale team advising Mersana Therapeutics was led by Steven Barrett and Mat Trachok.