Abstract 5232: Placental circulating T cells expressing CD16 in combination with trastuzumab demonstrate robust anti-tumor antibody-dependent cellular cytotoxicity (ADCC) against gastric cancer
Authors: Karasiewicz-Mendez Kathy , Gleason Joseph , Tess Kristina , Djedaini Mansour , Lin Shengchen , Huang Chenfei , He Shuyang , Hariri Robert , Kilcoyne Adrian 
Published: March 2024

Introduction: Celularity is developing PT-CD16VS as a novel platform for use in combination with approved monoclonal antibodies for the potential treatment of multiple cancers. PT-CD16VS is an allogeneic cell therapy derived from human postpartum placental circulating T (P-T) cells that are genetically modified to express a proprietary CD16 variant and endogenous T cell receptor (TCR) knockout. Here we report the characterization and preclinical evaluation of PT-CD16VS against HER2+ gastric cancer cells in combination with Trastuzumab. In vitro safety studies evaluating the potential for on-target/off-tumor activity of PT-CD16VS against HER2 low expressing lung epithelial cells (LEC) and human dermal fibroblasts (HDF) are also highlighted.

Methods: P-T cells were activated and transduced with a lentiviral vector containing a CD16 construct expressing a high affinity CD16 variant, CD16VS. Following transduction, P-T cells were transfected to knock out the TCR. In vitro, the functional activity of PT-CD16VS cells in combination with Trastuzumab was assessed against the HER2+ gastric cancer NCI-N87 cell line in cytotoxicity, cytokine release, and proliferation assays. For on-target/off-tumor studies, similar assays were utilized to assess activity against the HER2 low expressing LEC and HDF cell lines. In vivo, PT-CD16VS with Trastuzumab was evaluated in a subcutaneous NCI-N87 xenograft model in NSG mice. Tumor volume was measured and tumor samples were evaluated for PT-CD16VS infiltration.

Results: High CD16 transduction efficiency (&gt;60%) was achieved across donors. In vitro, PT-CD16VS plus Trastuzumab demonstrated potent cytotoxicity against NCI-N87 cells at low E:T ratios (0.625:1) and at 12 hours of co-culture with moderate cytokine secretion at 24-hour of co-culture. PT-CD16VS proliferated following 48-hour incubation with NCI-N87 cells and Trastuzumab, as compared to an IgG1 control. PT-CD16VS in combination with Trastuzumab did not elicit on-target/off-tumor cytotoxicity or cytokine release in response to low HER2 expression on normal LEC or HDF cells. In vivo, PT-CD16VS with Trastuzumab demonstrated significant reduction in tumor volume compared to vehicle, Trastuzumab alone, and the positive control Enhertu groups. In addition, PT-CD16VS infiltration into the tumor was shown to be Trastuzumab dependent, with infiltrating cells expressing high levels of CD16 and Ki67.

Conclusions: Our results show that PT-CD16VS has robust in vitro and in vivo ADCC activity against gastric cancer tumor cells when combined with Trastuzumab. Furthermore, PT-CD16VS activity is specific to tumor HER2 antigen expression and does not target low HER2 expression on normal healthy cells. PT-CD16VS is being developed in combination with various monoclonal antibodies for the treatment of multiple cancers.

Citation Format: Kathy Karasiewicz-Mendez, Joseph Gleason, Kristina Tess, Mansour Djedaini, Shengchen Lin, Chenfei Huang, Shuyang He, Robert Hariri, Adrian Kilcoyne. Placental circulating T cells expressing CD16 in combination with trastuzumab demonstrate robust anti-tumor antibody-dependent cellular cytotoxicity (ADCC) against gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5232.