Sanofi SA is paying about $1 billion up front and pledging as much as $225 million in development milestone payments to acquire Amunix Pharmaceuticals Inc. in an arrangement that brings aboard several immuno-oncology platforms. South San Francisco-based Amunix’s lead candidate is the clinic-bound, masked T-cell engager (TCE) AMX-818, which targets HER2-expressing solid tumors. The candidate emerged from the company’s XPAT technology, designed with the longstanding XTEN and centered on a protein polymer in a strategy similar to pegylation, except with a polypeptide. XPAT stands for XTENylated, protease-activated TCEs.