Blocking TGF-β Signaling Is Necessary for iPSC-NK Cell Therapy of Liver Cancer

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and is a highly lethal malignancy with a 5-year survival rate of less than 20%. Although targeted drugs such as sorafenib and other kinase inhibitors have been used to treat HCC, these therapies are generally incurable. Immunotherapy (e.g., atezolizumab) combined with vascular endothelial growth factor (VEGF) inhibition (bevacizumab) is currently the first-line treatment for HCC, but the efficacy remains low.

Cell-based immunotherapy has been proposed as an option to address this unmet clinical need. However, the use of T cell and natural killer (NK) cell therapy to treat solid tumors remains challenging. These challenges include tumor heterogeneity, adequate trafficking of immune cells to tumors, and an immunosuppressive tumor microenvironment (TME). In the TME, immune effector cells can be inhibited by a variety of cell-binding and soluble factors that impair their survival, activation, proliferation, and effector function. Previous studies have also shown that CAR-T or CAR-NK cell therapy has limited clinical efficacy in the treatment of HCC.

In July 2024, researchers from the University of California, San Diego published a research paper titled "Disruption of TGF-β signaling pathway is required to mediate effective killing of hepatocellular carcinoma by human iPSC-derived NK cells" in Cell Stem Cell, a subsidiary of Cell. The study showed that blocking TGF-β signaling is necessary for induced pluripotent stem cell (iPSC)-derived natural killer cells (iPSC-NK) to effectively treat HCC.

Figure 1. TGF-β signaling blockade is required for effective NK cell function against HCC and potentially other malignancies that express high levels of TGF-β. (Thangaraj J L, et al., 2024)

NK cells are innate immune effector cells with the inherent ability to kill virus-infected cells and tumor cells without antigen sensitization. NK cell-mediated cytotoxicity is regulated by the expression of a series of activating and inhibitory receptors. Activated NK cells can release granzymes and perforins through granule-dependent pathways, and can also induce granule-independent cell death through death receptor pathways.

Multiple clinical trials have shown that allogeneic primary NK cells from peripheral blood, induced pluripotent stem cells, and umbilical cord blood, whether expressing chimeric antigen receptors (CARs) or not, are relatively safe and do not cause any significant toxicity, such as cytokine release syndrome (CRS), neurotoxicity, and graft-versus-host disease (GvHD).

The team pioneered the use of iPSC-NK cells as standardized "off-the-shelf" allogeneic cell therapy to treat various malignancies. iPSCs are also an excellent platform for designing CARs or other methods to enhance the anti-tumor activity of iPSC-derived NK cells. Currently, several iPSC-NK cell therapies are in clinical trials for the treatment of hematological malignancies and solid tumors, and early studies have shown their efficacy and safety. iPSC-NK cells provide an attractive approach for the treatment of malignancies such as HCC.

In this study, the research team engineered iPSC-derived NK cells to overcome TGF-β-mediated inhibition and combined the expression of CARs targeting HCC to improve their anti-tumor activity.

The research team applied two strategies to engineer iPSC-NK cells to overcome the inhibitory effects of TGF-β and then combined anti-GPC3 or anti-AFP-CARs to induce more specific tumor killing. The research team found that engineered NK cells with suppressed TGF-β showed significantly improved anti-tumor activity, while CAR-N cells without suppressed TGF-β did not lead to effective anti-tumor activity.

Specifically, the research team produced iPSC-NK cells, and then these cells were either knocked out TGF-β receptor 2 (TGFBR2-KO) or expressed a dominant negative form of TGF-β receptor 2 (TGFBR2-DN), combined with chimeric antigen receptors (CARs) targeting GPC3 or AFP. TGFBR2-KO iPSC-NK cells and TGFBR2-DN iPSC-NK cells showed enhanced anti-HCC activity. However, expressing anti-HCC CAR on iPSC-NK cells did not produce effective anti-HCC activity unless TGF-β activity was also inhibited.

These findings suggest that in HCC, inhibition of TGF-β signaling is required for effective NK cell antitumor activity, regardless of CAR expression, and may also be true for other tumors with high levels of TGF-β expression in the tumor microenvironment.

Reference

Thangaraj J L, et al. Disruption of TGF-β signaling pathway is required to mediate effective killing of hepatocellular carcinoma by human iPSC-derived NK cells. Cell Stem Cell, 2024.