Abstract LB-390: Intratumoral electroporation of plasmid-encoded IL-12 and membrane-bound anti-CD3 increases tumor immunogenicity and augments the function of T cell subsets

• Published in: Cancer research (Chicago, Ill.) Ill.), 2020-08, Vol.80 (16_Supplement), p.LB-390-LB-390
• Main Authors: Han, Mia, Mukhopadhyay, Anandaroop, Nguyen, Bianca, Lee, Jack Y., Browning, Erica, Salazar, Jon, Hermiz, Reneta, Svenson, Lauren, Baker, Chris, O'Connor, Daniel, Malloy, Kellie, Canton, David A., Twitty, Christopher G.
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2020-LB-390

Intratumoral (IT) delivery of plasmid IL-12 (tavokinogene telseplasmid; tavo) via electroporation (EP), collectively referred as IT-tavo-EP, generates immunologically-relevant levels of localized IL-12, triggering regression of both treated and distant tumors with minimal toxicity in preclinical and clinical studies. Our previous clinical trial data from melanoma patients treated with IT-tavo-EP identified a treatment-related increase of infiltrating T cells and transcripts related to immune activation, as well as a significant increase in the IFN-γ score of patients with a clinical benefit, suggesting that CD3+ tumor-infiltrating lymphocytes (TIL) may be critical in maximizing the anti-tumor effects of IT-tavo-EP. Furthermore, in-house biomarker data have identified an abundance of non-tumor reactive TIL that, if mobilized could additionally contribute to a clinical response. Accordingly, a plasmid-encoded membrane-bound polyclonal T cell-stimulating anti-CD3 (αCD3) hybrid antibody (scFv) was developed and used in combination with tavo (IT-tavo-αCD3-EP) to broaden the scope and depth of the T cell response. We previously demonstrated that membrane expression of αCD3 on neoplastic and stromal cells could activate CD3+ TIL, driving enhanced proliferation and cytotoxicity in a B16-OVA murine model. Here, using immune profiling of the tumor microenvironment (TME), we have demonstrated that this membrane-bound αCD3 therapeutic can significantly upregulate frequencies of CXCR3+CD8+ T cells and short-lived effector T cells, while reducing PD-1 expression on CD8+ T cells in vivo. Critically, naïve T cells, Treg cells, and exhausted T cells (subsets not typically associated with strong anti-tumor responses) displayed enhanced effector function (IFN-γ and granzyme B release) with engagement of membrane-bound αCD3 and IL-12. Furthermore, we found that this therapeutic approach could equally enhance proliferation of T cells regardless of the affinity for their cognate peptide:MHC, suggesting a TCR independent mechanism. Collectively, these observations demonstrate that IT-tavo-αCD3-EP can mobilize broad subsets of T cells beyond dominant anti-tumor effectors demonstrated. Thus, while enhanced cytolytic function is associated with this therapy, inclusion of additional atypical anti-tumor T cell subsets may also promote reshaping of the TME by production of effector cytokines upon engagement of surface-bound αCD3. Moreover, functional restoration of TIL isolated from a