One such mechanism was subsequently studied, where third-generation HER2-CAR-T cells were used in combination with Programmed Cell Death Protein 1 (PD-1) inhibition to enhance the activation of CAR-T cells in vitro.35 Normally, PD-1 prevents the activation of cytotoxic T cells in tumors, which allows cancer cells to evade the immune system. The gene discussed is PDCD1; the disease is cancer.