Abstract 3214: In situ vaccination with CCL21-modified dendritic cells (CCL21-DC) combined with checkpoint blockade in murine models of NSCLC
Authors: Lim Raymond J. , Salehirad Ramin , Liu Bin , Li Rui , Tran Linh M. , Krysan Kostyantyn , Ong Stephanie , Huang Zi L. , Shackelford David B. , Sharma Sherven , Dubinett Steven M. 
Published: August 2019

Abstract
Studies that target the PD-1/PD-L1 axis of immune checkpoints have demonstrated clinical responsesin approximately 20% of non-small cell lung cancer (NSCLC) patients.However, majority of the patients do not benefit from the initial treatment.Mechanistic studies reveal that responses to PD-1/PD-L1 blockade are associated with high tumor mutational burden (TMB) andincreased CD8+T cell tumor infiltration and high baseline tumor PD-L1 expression. Furthermore, recent studies have identified Stk11/Lkb1 loss as a major driver of primary resistance to PD-1 blockade in inKRAS-mutant lung adenocarcinoma (LUAC), a major subtype of NSCLC. One potential approach to enhance the effectiveness of checkpoint inhibitors is to enhance tumor antigen presentation and tumor-specific T cell immune responses by in situvaccination, taking advantage of the full repertoire of available tumor antigens. In preclinical and clinical studies, we have demonstrated that CCL21-secreting dendritic cells (CCL21-DC) have the capacity to induce the infiltration of DC and T cells into the TME and to promote tumor-specific T cell activation both locally and systemically. This response, however, was accompanied by the upregulation of PD-L1 expression in the tumor. We hypothesize that in situvaccination with CCL21-DC could restore tumor antigen presentation and T lymphocyte infiltration into the tumor, thereby sensitizing non-responsive NSCLC tumors to checkpoint blockade. To test this hypothesis, we first established novel genetically-engineered murine models (GEMMs) of lung cancer that bear the common driver mutations (KPL; KrasG12D;Tp53-/-;Lkb1-/-) and varying mutational loads to accurately reflect the clinical disease. This was achieved by exposing KPL cells in vitroto the tobacco carcinogen N-methyl-N-nitrosourea (MNU) with various duration. Using these models, we demonstrated that (1) KPL with higher TMB is more sensitive to anti-PD-1 monotherapy as compare to low TMB, consistent with previous studies; (2) Intratumoral (IT) administration of CCL21-DC in combination with anti-PD-1 resulted in significantly enhanced anti-tumor response compared to either monotherapy alone. Further work is underway to evaluate the efficacy of the combination therapy with IT CCL21-DC and PD-1 inhibition in multiple murine models of NSCLC. In addition, mechanistic studies will be performed to understand the anti-tumor effect mediated by the CCL21-DC and anti-PD-1 combination therapy, including immune phenotyping of TME and functional studies of DC and T cells. As we prepare to initiate our clinical trial that combines IT CCL21-DC with PD-1 inhibition in advanced NSCLC patients with low baseline PD-L1 expression, we anticipate these preclinical models will serve as a platform to enhance our understanding of the molecular mechanisms of response and resistance to immunotherapy.
Citation Format: Raymond J. Lim, Ramin Salehirad, Bin Liu, Rui Li, Linh M. Tran, Kostyantyn Krysan, Stephanie Ong, Zi L. Huang, David B. Shackelford, Sherven Sharma, Steven M. Dubinett. In situ vaccination with CCL21-modified dendritic cells (CCL21-DC) combined with checkpoint blockade in murine models of NSCLC [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 3214.