The oncolytic adenovirus XVir-N-31 represents a promising therapeutic agent to treat glioblastoma. Former preclinical studies showed that XVir-N-31 effectively lysed glioma cells and prolonged the survival of GBM bearing mice. We now examined immunostimulatory effects of XVir-N-31 and compared it to wild-type adenovirus (Ad-WT), using an immuno-humanized mouse model. Additionally, XVir-N-31 in combination with the immune checkpoint inhibitor Nivolumab, or XVir-N-31-anti-PD-L1 that codes for a PD-L1 blocking single chain antibody, were included. Although in vitro oncolysis of GBM cells was higher for Ad-WT, XVir-N-31 induced a stronger immunogenic cell death phenotype. In PD-L1 expressing glioblastomas XVir-N-31 increased the amount of CD4⁺ and CD8⁺ tumor infiltrating lymphocytes even more than Ad-WT, this not only in injected, but also in untreated tumors located in the contralateral hemisphere. XVir-N-31 in combination with Nivolumab, or XVir-N-31-anti-PD-L1 further induced lymphocyte infiltration. Whereas Ad-WT and XVir-N-31 showed massive growth reduction of virus-injected tumors, significant growth reduction in contralateral tumors was only detected after treatment with XVir-N-31 plus Nivolumab, or with XVir-N-31-anti-PD-L1. Our data provide strong evidence that for an effective treatment of glioblastomas with oncolytic adenoviruses the induction of immunogenic cell death is of greater importance than the cell killing capacity of the virus. However, an additional immune checkpoint blockade is necessary to achieve abscopal effects.