Autologous antigen-presenting cells efficiently expand piggyBac transposon CAR-T cells with predominant memory phenotype

The quality of chimeric antigen receptor (CAR)-T cell products, including the expression of memory and exhaustion markers, has been shown to influence their long-term functionality. The manufacturing process of CAR-T cells should be optimized to prevent early T cell exhaustion during expansion. Activation of T cells by monoclonal antibodies is a critical step for T cell expansion, which may sometimes induce excess stimulation and exhaustion of T cells. Given that piggyBac transposon (PB)-based gene transfer could circumvent the conventional pre-activation of T cells, we established a manufacturing method of PB-mediated HER2-specific CAR-T cells (PB-HER2-CAR-T cells) that maintains their memory phenotype without early T cell exhaustion. Through stimulation of CAR-transduced T cells with autologous peripheral blood mononuclear cell-derived feeder cells expressing both truncated HER2, CD80, and 4-1BBL proteins, we could effectively propagate memory-rich, PD-1-negative PB-HER2-CAR-T cells. PB-HER2-CAR-T cells demonstrated sustained antitumor efficacy in vitro and debulked the HER2-positive tumors in vivo. Mice treated with PB-HER2-CAR-T cells rejected the second tumor establishment owing to the in vivo expansion of PB-HER2-CAR-T cells. Our simple and effective manufacturing process using PB system and genetically modified donor-derived feeder cells is a promising strategy for the use of PB-CAR-T cell therapy.