∙ Subjects must meet all the following criteria to be eligible to participate in the study:

• Signed informed consent

• Diagnosis with histologically proven epithelioid unresectable MPM (stage I-IV)

• Age ≥ 18 years at the time of signing informed consent

• World Health Organization (WHO) performance status 0-1

• Adequate hematologic and end-organ function, defined by the following laboratory test results, obtained at the time of screening:

‣ Absolute neutrophil count (ANC) ≥ 1.5 x 10\^9/L (1500/μL) without granulocyte colony- stimulating factor support

⁃ Lymphocyte count ≥ 0.5 x 10\^9/L (500/μL)

⁃ Platelet count ≥ 100 x 10\^9/L (100,000/μL) without transfusion

⁃ Hemoglobin ≥ 90 g/L (9 g/dL) Patients may be transfused to meet this criterion

⁃ Aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) ≤ 2.5 x upper limit of normal (ULN), with the following exceptions:

⁃ Patients with documented liver metastases: AST and ALT ≤ 5 x ULN

⁃ Patients with documented liver or bone metastases: ALP ≤ 5 x ULN

⁃ Total bilirubin ≤ 1.5 x ULN with the following exception:

⁃ Patients with known Gilbert disease: total bilirubin ≤ 3 x ULN

⁃ Creatinine ≤ 1.5 x ULN

⁃ Albumin ≥ 25 g/L (2.5 g/dL)

⁃ For patients not receiving therapeutic anticoagulation: prothrombin international normalized ration (PT-INR) and activated partial thromboplastin time (APTT) ≤ 1.5 x ULN

• Negative Human Immunodeficiency Virus (HIV) test at screening

• Negative hepatitis B surface antigen (HBsAg) test at screening

• Negative total hepatitis B core antibody (HBcAb) test at screening, or positive total HBcAb test followed by a negative hepatitis B virus (HBV) DNA test at screening

‣ The HBV DNA test will be performed only for patients who have a negative HBsAg test and a positive total HBcAb test.

• Negative hepatitis C virus (HCV) antibody test at screening, or positive HCV antibody test followed by a negative HCV RNA test at screening. The HCV RNA test must be performed for patients who have a positive HCV antibody test.

• Willing and able to comply with the study protocol, as judged by the treating physician

• Women of childbearing potential must have a negative serum or urine pregnancy test at the time of screening and agree to use effective contraception (\<1% failure rate per year) before, during and for at least five months after the last atezolizumab administration or at least hundred days after the last WT1/DC vaccine administration (whichever takes longer). Men must agree to use effective contraception before, during and for at least hundred days after the last study treatment administration.