Preclinical efficacy and safety evaluation of interleukin-6-knockdown CAR-T cells targeting at CD19

Background: ssCART-19 cells with shRNA-IL-6 gene knockdown were subjected to a comprehensive safety evaluation, including efficacy, toxicity and biodistribution studies in NSG (Prkdc^scidIL2rg^tm1 /Bcgen) mice.

Methods: NSG mice were administered Raji-Luc and then singly dosed with ssCART-19 cells via intravenous infusion. ssCART-19 DNA fragments were quantified in different tissues by qPCR, and the optical intensity of Raji-Luc was determined for evaluate the efficacy of regular CAR-T and ssCART-19 cells. In toxicity study, clinical symptoms observation, body weight measurements, serum biochemical analysis, human cytokine detection, lymphocytes subsets quantification, necropsy and histopathological examination were performed.

Results: The ssCART-19 DNA was mainly concentrated in the liver within 3 hours, and was widely distributed in most of the organs/tissues for 4 weeks after administration. Chimeric antigen receptor gene modified T cells (CAR-Ts) were detected in the peripheral blood with a significant increase in number beginning at approximately 3 weeks. ssCART-19 administration resulted in increased of interferon-gamma (IFN-γ), tumor necrosis factor (TNF), interleukin-2 (IL-2), and IL-17A and decreased IL-10 and IL-6 levels. ssCART-19 inhibited the proliferation of Raji-Luc cells in tumor-bearing NSG mice, and reduced the incidence of lymphomas in the liver, kidneys and spleen. It alleviated clinical symptoms caused by tumor cell proliferation in treated animals.

Conclusions: ssCART-19 prolongs the survival time of tumor-bearing mice without obvious risks of immunotoxicity and tumorigenicity. ssCART-19 DNA was found in the brains of treated animals, however no significant central nervous system toxicity was observed. These data were used to support an investigational new drug (IND) application of ssCART-19 for clinical trial in China.