Co-administration of Cyclo(-Leu-DTrp-Pro-Thr-Asp-Leu-DPheLys(Dde)-Val-Arg (40 mg/kg) by intraperitoneally injection (ip) with anti-CD8 antibody suppressed the tumor volume (54.8%) and tumor weight (64.9%) in a B16F10 tumor bearing animal model. Here, CD8A is linked to neoplasm.