Objective:To investigate the effects of autophagy-mediated crizotinib resistance on cancer stem-like cell subsets in anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALK + ALCL). Methods:The preliminary research of our group divided ALK + ALCL Karpas299 cell line into two subgroups: reporter unresponsive (RU) and reporter responsive (RR) cells through the implantation of Sox2 reporter genes, among which the RR cells had the characteristics of stem cells. Fluorescent labeled LC3 overexpressing RR and RU cells (RR-LC3 and RU-LC3) were constructed by lentiviral transfection technique, and the transfection efficiency was verified by using Western blotting and flow cytometry. RU-LC3 and RR-LC3 were treated with crizotinib at different concentrations (0, 250, 500, 1 000 nmol/L). The RED and GEN signals were detected by using double-signal flow cytometry to observe autophagy flux (RED represents the red signal B695 of the next generation of far-red fluorescent protein TagFP635 mKate; GEN represents the green signal from pH-sensitive GFP variant pHluorin B530), and the RED to GEV ratio represents autophagy flux. Real-time quantitative polymerase chain reaction (qRT-PCR) was used to detect autophagy related genes ULK1, WIPI1 and LC3B mRNA expression levels in cells. The effects of different concentrations of crizotinib (250, 500, 1 000 nmol/L) combined with chloroquine (5, 10 μmol/L) on the cell survival were detected by using MTS assay. Results:RU-LC3 and RR-LC3 cells with overexpression of LC3 were successfully constructed. After induction of 250, 500 and 1 000 nmol/L crizotinib, the RED to GEN ratio in RU-LC3 cells was 1.135±0.017, 1.453±0.017 and 1.755±0.021, respectively; the RED to GEN ratio in RR-LC3 cells was 1.193±0.018, 2.116±0.013 and 3.307±0.189, respectively; the RED to GEN ratio in RU-LC3 cells and RR-LC3 cells showed a dose-dependent manner. The RED to GEN ratio in RR-LC3 cells was higher than that in RU-LC3 cells when treated with same concentrations of crizotinib, and the differences were statistically significant (all P < 0.01). The autophagy flux of RR-LC3 cells was larger than that of RU-LC3 cells. When treated without crizotinib, mRNA relative expression levels of ULK1, WIPI1 and LC3B in RR cells were higher than those in RU cells (1.69±0.05 vs.1.01±0.02, t = -1.62, P < 0.01; 1.24±0.04 vs. 1.03±0.05, t = -2.11, P < 0.01; 1.70±0.22 vs. 1.02±0.05, t = -1.74, P = 0.033). In the absence of chloroquine, the half-inhibitory concentration ( IC50) of crizotinib in RR cells was higher than that of RU cells (950 nmol/L vs. 709 nmol/L). After treated with chloroquine, IC50 of RU cells did not change, while IC50 of RR cells was decreased with the increase of chloroquine concentration. Conclusions:Compared with RU cells, autophagy reaction of cancer stem-like RR cells is more rapid and intense, which is considered to be one of the important reasons for their resistance to crizotinib.