Li, Nan

Background and Aims: Efficacy of chimeric antigen receptor (CAR) T cells for treating solid tumors, including HCC, remains a challenge. Nanobodies are emerging building blocks of CAR T cells due to their small size and high expression. Membrane proximal sites have been shown as attractive epitopes of CAR T cells. However, current CAR formats are not tailored toward nanobodies or targeting membrane distal epitopes. Approach and Results: Using hYP7 Fv (membrane proximal) and HN3 VH nanobody (membrane distal) as GPC3 targeting elements, we sought to determine how hinges and transmembrane portions of varying structures and sizes affect CAR T-cell function. We generated multiple permutations of CAR T cells containing CD8, CD28, IgG4, and Fc domains. We show that engineered HN3 CAR T cells can be improved by 2 independent, synergistic changes in the hinge and transmembrane domains. The T cells expressing the HN3 CAR which contains the hinge region of IgG4 and the CD28 transmembrane domain (HN3-IgG4H-CD28TM) exhibited high cytotoxic activity and caused complete HCC tumor eradication in immunodeficient mice. HN3-IgG4H-CD28TM CAR T cells were enriched for cytotoxic-memory CD8+ T cells and NFAT signals, and reduced β catenin levels in HCC cells. Conclusion: Our findings indicate that altering the hinge and transmembrane domains of a nanobody-based CAR targeting a distal GPC3 epitope, in contrast to a membrane proximal epitope, lead to robust T-cell signaling and induce swift and durable eradication of HCC tumors.

e14512 Background: Glypican 3 (GPC3), a cell surface protein associated with early development, is an established biomarker of hepatocellular carcinoma (HCC). In a vast compendium of work, HN3, a human GPC3 nanobody (VH) isolated from a phage library, was shown to abrogate HCC tumors and block the distally located Wnt binding domain of GPC3. To date, it remains challenging how to precisely engineer CAR T cells for improved efficacy in solid tumors. In the context of hepatocellular carcinoma, we determined how hinges and transmembrane portions of varying structures and sizes affect CAR T cell function. Here, we show how rationally designed, engineered Chimeric Antigen Receptor (CAR) T cells containing HN3, demonstrate enhanced CAR T activity in HCC. Methods: We generated and compared multiple permutations of GPC3 targeted CAR T cells containing HN3, CD8, CD28, IgG4 and Fc domains. Incorporation of HN3, into multiple CAR formats yielded nine constructs, which were screened for antigen-specific and antigen-independent signaling using a luciferase reporter system in Hep3B, Huh7 and HepG2 cell lines. For in vivo assessment, immunodeficient NSG mice were intraperitonially injected with Hep3B or Huh7 cells and treated with a single dose (5 or 15 million) of engineered HN3 CAR T cells. Blood was collected at 2, 4 and 5 weeks to assess proliferation, T cell subtypes and exhaustion. Results: In vitro, the HN3-IgG4H-CD28TM CAR T cells induced high specificity and cytotoxic activity. HN3-IgG4H-CD28TM CAR T cells markedly improved HN3 cell killing activity by 30-40% in low (1.6:1) and high (25:1) effector to target ratios. Similarly, in vivo, in a high antigen environment, two determinative changes in the hinge region and transmembrane domains led to complete tumor eradication in immunodeficient mice bearing HCC tumors within 7-10 days. Moreover, HN3-IgG4H-CD28TM CAR T cells maintained specific tumor killing and averted exhaustion by producing a clear T cell response signature of enriched cytotoxic-memory (Temra) CD8+ along with a subset of naïve T cells. Conclusions: Engineered nanobody based CAR T cells containing the appropriate hinge and transmembrane domains can lead to determinative T cell signaling capable of inducing swift and durable eradication of HCC tumors. Altogether, we show that engineered HN3 CAR T cell therapy demonstrates strong potential for treatment of aggressive HCCs enabled by Wnt dysregulation.