Fig. 6

CAF-derived IL-6 attenuated FRα-CAR T cell cytotoxicity in 3D cancer cell culture. A The representative of spheroids of mWasabi-luciferase expressing target cells (T) after pre-treating with CM and coculturing with effector FRα-CAR T cells (E) at E:T ratios of 2.5:1, 5:1, and 10:1 for 4 days (scale bars = 100 μm). The target-only condition (T-only) indicates target cells without effector cells. B Bar graphs show the killing ability of FRα-CAR-T cells from two donors (means ± SD of three independent experiments of each donor). ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 compared to the T-only condition using one-way ANOVA. C The proposed mechanism of CAF-derived IL-6 in promoting resistance to chemo- and immunotherapy. CAFs secrete high IL-6 which can bind to IL-6R on BCA cells. CAF-derived IL-6 induces Dox resistance by promoting cancer cell survival and promoting PD-L1 production through STAT3 and AKT signaling pathways. This PD-L1 induction by CAF-derived IL-6 can be attenuated by STAT3 and AKT inhibitors. The high PD-L1 expressing cancer cells suppress FRα-CAR-T cell killing ability. UT, untreated cells; BNF, breast normal fibroblast; CAFs, cancer-associated fibroblasts; CM, conditioned medium; IL-6R KD, IL-6R knocked down; rhIL-6, recombinant human IL-6; NS, no significance. BCA; breast cancer, FRα; folate receptor alpha, PD-L1; programmed death ligand 1, PD-1; programmed death 1, CAR T cell; chimeric antigen receptor T cell