CpG is required for therapeutic effect of anti-OX40 + anti-CTLA4 combination. Mice bearing tumors at 2 sites received either no treatment, CpG intratumorally alone at one site, anti-OX40 + anti-CTLA4 intraperitoneally (without CpG), or the combination of both (CpG + anti-OX40 + anti-CTLA4), according to the schedule described previously. Growth curves represent the size of the left (non-CpG–injected) tumor.