In response to the TME’s weak acidity (pH 6.5), aPD-1-siRNA@NP delivered to the tumor tissue by either recruiting nanodrug-bound PD-1 + T cells triggers the first-stage drug release in TME to provide aPD-1 for blocking the PD-1-PD-L1 axis to activate the tumor-killing cytotoxic T cells [27]. The gene discussed is PDCD1; the disease is neoplasm.