ERBB2 and neoplasm: The better performance of RB-340-1ss_2M compared with conventional HER2 CAR, cRB-340-1 or RB-340-1ss_1M combined with the observation that the former displayed lower PD-1 levels in tumor at necropsy (Fig. 7B) suggests that the active component of RB-340-1, LdCK is quantitatively responsible for the enhanced anti-tumor effectiveness rather than the higher number of transduced cells alone.