Despite the dramatic benefit achieved by these strategies, it has to be noted that in one hand, sustained expansion of PD-1-expressing CTLs by the stimulation of tumor antigens in vitro and in vivo may require continuous treatment with anti-PD-1 antibody which is costly, on the other hand, the long term systematic administration of the blocking antibody carries the risk of breaking immune tolerance may cause immune attack of normal tissues. Here, PDCD1 is linked to neoplasm.