Abstract 3623: Fluctuating antibody response and CD4-positive T-cells in a small-cell lung cancer mouse model

Patients with small-cell lung cancer (SCLC), a highly metastatic type of lung cancer, show a dismal 5-year survival of only 5%. Effective therapies are urgently needed. Notably, about fifteen-percent of SCLC-patients harbor anti-Hu autoantibodies, which are associated with improved survival. This suggests that the anti-Hu response might be harnessed for immunotherapy. A conditional SCLC mouse model with floxed Rb1 and p53 alleles, in which the cancer is induced by instilling Cre-recombinase into the lungs via intratracheal intubation, offers a unique opportunity to study the immune response in detail. We have previously shown that, just like human SCLC patients, a fraction of these SCLC-carrying mice show an anti-Hu autoantibody response. Here we examine the presence of anti-Hu reactive T-cells using a prospective cohort (n=45) of SCLC-induced mice. All mice develop SCLC, showing systemic disease in 4-7 months following inactivation of floxed Rb1 and p53 alleles. Monthly autoantibody analysis by western blotting revealed an antibody response in a subset of mice, sometimes as early as 1 month after induction. Reactivity usually peaked approximately 3-4 months after induction and declined as disease progressed. This suggests an immune escape mechanism and/or antibody adsorption by the rapidly proliferating tumors. T-cells were isolated at euthanasia from the spleens of moribund mice. Proliferating anti-HuD CD4-positive T-cells were detected in fifty-one-percent of mice (eighteen out of thirty-five) by flow cytometry. Anti-HuD T-cell proliferation from spleen cells was validated in a subsequent prospective cohort (n=45) of SCLC-induced mice using thymidine incorporation. Stratifying for antibody positive and negative mice using an stringent cutoff, there was no significant difference in T cell response between the two groups (p=0.11), however four mice in the antibody positive group showed the most elevated anti-HuD T-cell response. Our observations warrant a much larger study, in which in-depth characterization of the humoral and cellular the anti-HuD immune response is carried out at multiple time points and correlated with a detailed analysis of the stage of tumor development and mestastasis. Preliminary data hints at a negative correlation between the anti-HuD antibody and T-cell response on one hand and tumor size and metastasis on the other. The observation that the Hu antigen in mice with SCLC is a target for both humoral and cellular immune responses underscores the utility of this mouse model in the preclinical evaluation the anti-Hu immune response for therapy and clinical translation. Citation Format: Mario A. Pulido, Vincent Lombardi, Diane Lee, Yiwei Wang, Eric Chung, Lina Wang, W. Martin Kast, Omid Akbari, Ite A. Laird-Offringa. Fluctuating antibody response and CD4-positive T-cells in a small-cell lung cancer mouse model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3623. doi:10.1158/1538-7445.AM2014-3623