Another study comparing 4-1BB and CD28 signaling in a PSCA CAR to treat patient derived prostate cancer xenografts found 4-1BB to be superior to CD28, with 4-1BBζ CARs leading to less exhaustion and better antigen selectivity (however, in vitro killing was equal between the two CARs) (179). The gene discussed is CD28; the disease is prostate cancer.