Cytokine Induced Killer cells are effective against sarcoma cancer stem cells spared by chemotherapy and target therapy

Metastatic bone and soft tissue sarcomas often relapse after chemotherapy (CHT) and molecular targeted therapy (mTT), maintaining a severe prognosis. A subset of sarcoma cancer stem cells (sCSC) is hypothesized to resist conventional drugs and sustain disease relapses. We investigated the immunotherapy activity of cytokine induced killer cells (CIK) against autologous sCSC that survived CHT and mTT. The experimental platform included two aggressive bone and soft tissue sarcoma models: osteosarcoma (OS) and undifferentiated-pleomorphic sarcoma (UPS). To visualize putative sCSC we engineered patient-derived sarcoma cultures (2 OS and 3 UPS) with a lentiviral sCSC-detector wherein the promoter of stem-gene Oct4 controls the expression of eGFP. We visualized a fraction of sCSC (mean 24.2 +/- 5.2%) and confirmed their tumorigenicity in vivo. sCSC resulted relatively resistant to both CHT and mTT in vitro. Therapeutic doses of doxorubicin significantly enriched viable eGFP(+)sCSC in both OS (2.6 fold, n = 16) and UPS (2.3 fold, n = 29) compared to untreated controls. Treatment with sorafenib (for OS) and pazopanib (for UPS) also determined enrichment (1.3 fold) of viable eGFP(+)sCSC, even if less intense than what observed after CHT. Sarcoma cells surviving CHT and mTT were efficiently killed in vitro by autologous CIK even at minimal effector/target ratios (40:1 = 82%, 1:4 = 29%, n = 13). CIK immunotherapy did not spare sCSC that were killed as efficiently as whole sarcoma cell population. The relative chemo-resistance of sCSC and sensitivity to CIK immunotherapy was confirmed in vivo. Our findings support CIK as an innovative, clinically explorable, approach to eradicate chemo-resistant sCSC implicated in tumor relapse.