Less than three years after inking a potential $500 million cell therapy partnership with SQZ Biotechnologies Co., Roche Holding Co. is going back for seconds in an expanded deal that could more than triple the economics. SQZ is set to receive $125 million in up-front and near-term milestones and could earn up to $250 million in clinical, regulatory and sales milestones for each product that emerges from the expanded collaboration. In addition, the Watertown, Mass.-based company may receive development milestone payments exceeding $1 billion. Moreover, the five-year-old biotech could share commercial rights with Roche, of Basel, Switzerland, for certain approved products.