Background CAR T cell therapy has demonstrated clinical efficacy against hematological malignancies, while prominent barriers including poor T cell effector function, lack of proliferation, and limited CAR T cell persistence have prevented CAR T cell therapies from reaching their full curative potential, especially in solid tumors. For example, CAR T cell therapies targeting GPC3, whose overexpression is associated with various malignancies such as hepatocellular carcinoma (HCC), have demonstrated modest depths of response.
Interleukin-2 (IL-2) is a potent stimulator of T cell proliferation, survival, and cytotoxic function. However, therapeutic use of IL-2 is limited by systemic toxicity due its promiscuous activation of undesired immune cell populations. To facilitate selective ex vivo and in vivo expansion/activation of engineered T cells, we developed a human orthogonal ligand/receptor system consisting of a half-life extended IL-2 mutein (STK-009) that does not significantly stimulate cells expressing wild type IL-2 receptor and a mutated IL-2 Receptor Beta (hoRb) that responds to STK-009 but not wild type IL-2. This system enables selective in vivo IL-2 signaling in engineered cells that express the hoRb while avoiding stimulation of native IL-2 responsive cells. Previously, we demonstrated the ability of the STK-009/hoRb pair to selectively enhance the anti-tumor efficacy of hoRb expressing CD19 CAR T cells (SYNCAR-001) in preclinical lymphoma mouse models.1 SYNCAR-001 is currently being tested in a clinical trial targeting CD19+ B-cell malignancies (NCT05665062).
Methods We incorporated the hoRb downstream of a second generation anti-GPC3 CAR via a T2A cleavage peptide to allow for bicistronic expression from one lentiviral construct in transduced T cells (SYNCAR-002). SYNCAR-002 was tested in combination with or without STK-009 in various subcutaneous and intraperitoneal mouse models of HCC for anti-tumor response with transcriptomic and immunophenotyping analyses.
Results In vitro, SYNCAR-002 transduced cells could be selectively enriched with STK-009 with a less exhaustive phenotype compared to WT IL-2. In vivo, STK-009 administration enabled tumor rejections of highly aggressive HCC models by SYNCAR-002 and durability of response against tumor rechallenges (figures 1 and 2). Additionally, STK-009 treatment resulted in significant expansion of SYNCAR-002 in the peripheral blood and intratumorally. Importantly, STK-009 induced the expression of cytotoxic machinery, pro-survival, and proliferative genes in tumor-infiltrating SYNCAR-002 (figure 3).
Conclusions These findings validate that the orthogonal IL-2 platform has the potential to improve the efficacy and durability of CAR T therapy for solid tumor targets such as GPC3 by selectively expanding CAR-T cells in vivo and activating CAR-T cells in a hostile tumor microenvironment.
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