ICOS and central nervous system cancer: We have previously shown that splenocytes isolated from tumor-bearing mice treated with Delta24-RGD are able to recognize both tumor and virus antigens.28 To test the efficacy of antibody immunotherapy, splenocytes derived from glioma-bearing mice treated with Delta24-RGD were co-cultured with GL261 cells in the presence of anti-PD-1 (blocking) and anti-ICOS (agonist) antibodies.