 INDUCTION PHASE: Patients receive rituximab intravenously IV, gemcitabine IV, and oxaliplatin IV every 2 weeks. Starting course 2, patients also receive atezolizumab IV over 30-60 minutes every 2 weeks. Treatment repeats every 14 days of course 1 and every 28 days for up to 4 courses in the absence of disease progression or unaccepted toxicity. 