Optimized gene engineering of murine CAR-T cells reveals the beneficial effects of IL-15 coexpression

Limited clinical benefit has been demonstrated for chimeric antigen receptor (CAR) therapy of solid tumors, but coengineering strategies to generate so-called fourth-generation (4G) CAR-T cells are advancing toward overcoming barriers in the tumor microenvironment (TME) for improved responses. In large part due to technical challenges, there are relatively few preclinical CAR therapy studies in immunocompetent, syngeneic tumor-bearing mice. Here, we describe optimized methods for the efficient retroviral transduction and expansion of murine T lymphocytes of a predominantly central memory T cell (T-CM cell) phenotype. We present a bicistronic retroviral vector encoding both a tumor vasculature-targeted CAR and murine interleukin-15 (mIL-15), conferring enhanced effector functions, engraftment, tumor control, and TME reprogramming, including NK cell activation and reduced presence of M2 macrophages. The 4G-CAR-T cells coexpressing mIL-15 were further characterized by up-regulation of the antiapoptotic marker Bcl-2 and lower cell-surface expression of the inhibitory receptor PD-1. Overall, this work introduces robust tools for the development and evaluation of 4G-CAR-T cells in immunocompetent mice, an important step toward the acceleration of effective therapies reaching the clinic.

Automated summary

Limited clinical benefit has been shown for CAR therapy in solid tumors, but fourth-generation CAR-T cells coengineered with mIL-15 are being developed to enhance responses. Technical challenges have limited preclinical studies using immunocompetent mice, but optimized methods for efficient transduction and expansion of T lymphocytes in murine models have been described. The bicistronic retroviral vector encoding a tumor vasculature-targeted CAR and mIL-15 shows enhanced effector functions and potential for TME reprogramming, with upregulation of antiapoptotic markers and downregulation of inhibitory receptors.