PRF1 and neoplasm: Finally, Karpas 1718 was resistant to all CD20 antibodies tested, both monospecific and bispecific, despite significant CD20 expression and effector cell engagement, suggesting a tumour‐intrinsic mechanism of resistance, which may relate to the quality of the immune synapse, resistance to cytotoxic mediators including perforin, granzymes, TNFα, IFNγ, FasL and TRAIL, or alternatively impairment of CD20 downstream signalling.