PDCD1 and lymphoma: However, PD-1-Fc in combination with herpes simplex virus thymidine kinase (HSVtk) enzyme expression under the control of the cytomegalovirus (CMV) promoter and a trans-splicing ribozyme targeting human telomerase reverse transcriptase significantly enhanced the regression of not only subcutaneous CT26 tumors in BALB/c mice, but also subcutaneous E.G7-OVA (a derivative of lymphoma EL4 cells stably expressing ovalbumin) tumors in C57/BL6 mice compared with Ad5 encoding the HSVtk enzyme alone [60].