Gilead Sciences and Arcus Biosciences have expanded their collaboration agreement, with Gilead making an additional equity investment of $320 million and raising its ownership stake in Arcus to 33%.   Gilead’s separate equity investment of $320 million will be in Arcus common stock at $21 per share. The deal will also see Gilead Chief Commercial Officer Johanna Mercier join Arcus’ board, marking a third Gilead member.   According to the announcement, the amendment to the companies’ partnersh...