CD274 and cancer: It will be critical to evaluate levels of PD-L1 expression on tumor associated CD45 + and CD45- cells upon p19Arf/IFNβ gene therapy, which besides revealing if cancer cells or immune host cells are actually mediating immune resistance, may also provide rational for associating PD-1 checkpoint blockade, an immunotherapy proposed as the cornerstone for most combinatorial immunotherapeutic strategies36, especially for those that rely on promoting strong inflammatory immune responses.