The study design has been amended after the decision to prematurely stop patient accrual due to enrollment challenges. As only 5 participants were enrolled, the study blinding will not be maintained, and placebo infusions will not be administered. Patients assigned to the MOXR0916 arm may continue study treatment with the combination of atezolizumab and MOXR0916 or with atezolizumab alone based on a discussion of benefit and risk with the treating investigator.