 I. Assess the safety and toxicity of atezolizumab in combination with immunogenic chemotherapy gemcitabine plus oxaliplatin with rituximab R-GEMOX-ATEZO in patients with relapsed or refractory relref transformed diffuse large B-cell lymphoma DLBCL, including determination of the maximum tolerated dose MTD and the recommended phase II dose RP2D of R-GEMOX-ATEZO. 