CTLA4 and neoplasm: Surprisingly, we found for the first time an enhanced expression of PD-1 receptor when the tumor cells were treated with anti-PD1, anti-PD-L1 or anti-CTLA-4 mAbs (Figure 2B), whereas a decreased phosphorylation of Erk (Figure 3A), that could partially explain the reduction of cell viability, was found after treatment with all of them.