Patients with relapsed refractory subtypes of DLBCL who fulfill the inclusion / exclusion criteria will be recruited to this trial and treated in this open label, phase 2 trial with the PDL1 inhibitor Durvalumab and Lenalidomide. The combination treatment will be given from the time of recruitment for 6 months when Lenalidomide will be stopped but Durvalumab will continue for a total of 2 years. Response will be assessed by PET / CT scans as per standard lugano criteria.