Comparison of CD4ζ - and bNAb-based CARs, and modulation of CAR T cell activation and potency. CD4ζ -based CARs possess lower affinity (strength of the binding between epitope and binding site) but higher avidity (cumulative strength of an interaction, factoring in multiple epitopes/binding sites), potentially leading to more potent T cell activation relative to bNAb-based CARs. The proper combination of affinity, avidity, and accessibility of the targeted epitope(s), among other parameters, are likely key in determining CAR-T cell potency.