Abstract 5230: A modified FcγRI expressing T cell (SolidT) exhibits profound anti-tumor activity followed by maturation into effector memory t cells that can be reactivated to kill a secondary tumor
Authors: Dotan Shahar , Pilpel Noam , Rider Peleg , Shpilt Hana , Rasoulouniriana Diana , Carmi Yaron , Wooldridge James E. 
Published: March 2024

Abstract
We previously described a subset of cytotoxic FcγRI (CD64)-expressing T cells in tumors and inflamed tissues (PMID 31449054). We subsequently expressed an engineered modified CD64 into T cells (“SolidT”) and demonstrated that these cells possessed greater specificity for tumor over normal tissues, reduced exhaustion, and attenuated cytokine secretion compared to other engineered cell therapies. SolidT activation correlates with surface tumor antigen density enabling the differentiation between tumor cells and normal cells by use of a specific antibody targeting tumor antigens. We previously showed that SolidT + mAb has anti-tumor activity in vitro and in vivo in several tumor models, including immunodeficient HER2 xenografts and an immunocompetent syngeneic B16-TYRP1 model (PMID 37070661). In this study, we further assessed the effect of SolidT on HER2+ tumors in a rechallenge model and extended the platform to CD20+ lymphoma models by combining SolidT with rituximab. In an in vivo experiment using HER2+, NCI-N87 cells in immunodeficient mice, several mice in the SolidT + trastuzumab group experienced complete tumor clearance. These mice were monitored until day 84, then rechallenged with NCI-N87 cells along with a new control group. After tumor establishment, mice were treated only with trastuzumab weekly for two weeks. While tumors in the control group progressed, the tumors in the rechallenged mice were completely cleared with a trastuzumab boost only, suggesting a SolidT cell memory response. Bone marrow from these rechallenged mice was analyzed and revealed the presence of effector memory SolidT cells. The SolidT model was then studied in a human, CD20+ lymphoma model in vitro and in vivo in immunodeficient mice. SolidT + rituximab was more potent in-vivo against CD20+ lymphoma cells than rituximab. In vivo, mice treated with SolidT + rituximab had significantly greater survival, lower tumor burden, and fewer sites of metastases than mice treated with rituximab alone. Bone marrow from these mice was analyzed and revealed the presence of effector memory SolidT cells in mice treated with SolidT + rituximab. We demonstrated that marrow resident SolidT cells developed an effector memory phenotype that positively correlated with outcome in HER2+ and CD20+ xenograft models, consistent with earlier data from a syngeneic B16 melanoma model. We further demonstrated that SolidT cells can be reactivated in a rechallenge model with only the addition of tumor targeting mAb, resulting in the eradication of the recurring tumors. This data further confirms that the SolidT platform can be targeted against different tumor antigens by using different tumor targeting mAbs. The SolidT platform could represent a paradigm shift in the approach to engineered cellular therapy for hematological malignancies and solid tumors.
Citation Format: Shahar Dotan, Noam Pilpel, Peleg Rider, Hana Shpilt, Diana Rasoulouniriana, Yaron Carmi, James E. Wooldridge. A modified FcγRI expressing T cell (SolidT) exhibits profound anti-tumor activity followed by maturation into effector memory t cells that can be reactivated to kill a secondary tumor [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 5230.