CD27 costimulation enhances T-cell viability. (A) In coimmunoprecipitation experiments, only full-length CD27-ζ associated with TRAF2. (B) T cells expressing CD70-CAR or ΔCD70-CAR showed equivalent killing of CD70⁺ LCL and U266 cells, but did not kill CD70⁻ K562 cells in ⁵¹Cr-release assays. (C) Microscopic evaluation (10×) of T cells expressing CD70-CAR or ΔCD70-CAR activated with autologous fibroblasts genetically modified to express CD70 revealed larger “T-cell clumps” of T cells expressing CD70-CAR; however, CFSE dilution analysis showed no significant differences in proliferation between groups. (D) The viability of ΔCD70-CAR T cells was 35% ± 16% that of T cells expressing CD70-CAR (n = 5). (E) Intracellular staining for Bcl-xl was performed on T cells 3 days after stimulation with CD70-transgenic autologous fibroblasts. Bcl-xl expression was consistently increased in CD70-CAR T cells compared with ΔCD70-CAR T cells (n = 3). One representative FACS analysis is shown.