Abstract 3195: Intratumoral electroporation of plasmid IL-12 and CXCL9 with membrane-bound anti-CD3 elicits robust anti-tumor immunity

Preclinical and clinical studies have demonstrated that plasmid IL-12 (tavokinogene telseplasmid) delivered intratumorally via electroporation (TAVO) induces local expression of IL-12p70, converting immunologically excluded tumors into inflamed immunogenic lesions, which is fundamental to generating objective responses in both treated and untreated distant tumors. Recent optimization of electroporation parameters and plasmid design has yielded a significant increase in intratumoral expression and anti-tumor efficacy in preclinical models. To further develop this platform, longitudinal biomarker data from TAVO clinical trials was interrogated to identify key immunological components associated with an effective therapy. This analysis revealed that the composition of TAVO-inflamed lesions, specifically the frequency of CD8+ TIL and the chemokines necessary for their maintenance relative to suppressive intratumoral immune subsets, coincided with clinical responses. We therefore developed a plasmid that encodes both IL-12 and the effector T cell chemokine, CXCL9, which, when transfected into a tumor, are functionally active both in vitro as well as in vivo, yielding abscopal responses and increased survival. To further amplify this technology, a strategy was developed to engage the highly relevant and recently described bystander non-tumor reactive T cells in the tumor microenvironment (TME). To accomplish this pan-T cell amplification, a separate therapeutic plasmid encoding membrane-bound anti-CD3 scFv (145-2C11) was used to decorate transfected tumors with the potent polyclonal T cell stimulator. Membrane expression of anti-CD3 in vivo was confirmed by immunoblot and flow cytometry. Combination of IL-12/CXCL9 with anti-CD3 delivered by electroporation (collectively, “SPARK”) increased both antigen-specific and polyclonal T cells responses, demonstrated by in vivo CTL and proliferation assays. Finally, SPARK upregulated the transcription of key immunological genes, leading to regression of both treated and untreated tumors, which heightens its ability to reshape the TME and drive systemic anti-tumor immunity. In conclusion, this data supports a model whereby IL-12 in concert with CXCL9 inflames the lesion, leading to a brisk T cell infiltrate, which in sequence with anti-CD3 stimulation, drives a broad yet robust systemic T cell response. SPARK represents a significant advancement in cytokine-based immunotherapy. Note: This abstract was not presented at the meeting. Citation Format: Mia Han, Anandaroop Mukhopadhyay, Bianca Nguyen, Kurt Sakurada, Jack Lee, David A. Canton, Christopher G. Twitty. Intratumoral electroporation of plasmid IL-12 and CXCL9 with membrane-bound anti-CD3 elicits robust anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3195.