Abstract PR04: Inflammatory responses within the lung tumor microenvironment correlate with oncogenic mutation and histologic subtype
Authors: Busch Stephanie E. , Kargl Julia , Hanke Mark L. , Metz Heather E. , Kim Kyoung-Hee , Houghton A McGarry 
Published: October 2016

Abstract
Lung cancer is a heterogeneous disease comprised of multiple histologic subtypes that harbor disparate mutational landscapes. Small cell lung carcinoma (SCLC), in which RB1 and TP53 mutations are common, accounts for 10-20% of lung cancer diagnoses. Approximately half of non-small cell lung carcinoma cases are classified as lung adenocarcinomas (ADCA), in which KRAS, EGFR, and TP53 mutations are the predominant genetic drivers. Novel immunotherapeutic strategies have offered new hope for the management of ADCA and SCLC, but the clinical success of immunomodulatory agents will depend on a strong foundational knowledge of the cells that comprise the lung tumor microenvironment (TME) in these molecularly and histologically distinct diseases. We therefore sought to determine whether the host immune response to lung cancer is predicated, at least in part, by histologic and genetic differences, as such correlations would have important clinical ramifications.
Using three mouse models of lung ADCA KrasLSL-G12D, KrasLSL-G12D;Trp53Fl/Fl, and EgfrL858R as well as the Rb1Fl/Fl;Trp53Fl/Fl model of SCLC, we show that SCLC and ADCA tumors exhibit unique immune cell composition. Lung specimens from tumor-bearing and control animals (n ≥ 5 per cohort) were harvested at multiple time points and subjected to histological assessment and comprehensive flow cytometric immunophenotyping. Tumor-associated inflammation was discernibly lower in SCLC compared to all ADCA models. Moreover, the leukocyte composition of SCLC was dominated by cells of the adaptive rather than innate arm of the host immune system, a finding subsequently validated in 2 human SCLC surgical specimens. We further identified key differences in leukocyte content of mouse ADCA that correlated with oncogenic mutation. Although Egfr-mutant cancers displayed robust myeloid cell recruitment, they failed to mount a CD8+ cellular immune response. In contrast, Kras-mutant tumors displayed significant expansion of multiple immune cell types, including CD8+ cells, regulatory T cells, IL17-producing lymphocytes, and myeloid cells. Although loss of Trp53 promoted malignancy, it had minimal effect on immune cell composition within the Kras TME. Pre-clinical in vivo investigations with immune checkpoint inhibitor compounds are currently being conducted to assess the importance of these distinct immune responses to tumor progression and survival.
To determine whether the differential inflammatory responses observed in mice are clinically relevant, we conducted an immune profiling study of a large lung cancer patient cohort that included 55 ADCA specimens. Notably, patients with EGFR mutations (n = 5) exhibited fewer total CD8+ T cells, as well as decreased exhausted CD8+PD1+ and CD8+TIM3+ content, compared to all other ADCA cases, thereby substantiating the murine phenotype. Taken together, these findings establish a strong foundational knowledge of the immune cell contexture of lung ADCA and SCLC and suggest that molecular and histological traits shape the host immune response to cancer.
This abstract is also presented as Poster A01.
Citation Format: Stephanie E. Busch, Julia Kargl, Mark L. Hanke, Heather E. Metz, Kyoung-Hee Kim, A McGarry Houghton. Inflammatory responses within the lung tumor microenvironment correlate with oncogenic mutation and histologic subtype. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr PR04.