Abstract 4984: Development of an improved humanized patient-derived xenograft, Hu-PDX, mouse model for evaluation of antitumor immune response in lung cancer

Current preclinical models of non-small cell lung cancer (NSCLC) do not recapitulate the human tumor microenvironment. Mice reconstituted with a human immune system and bearing human patient derived xenografts may be advantageous in evaluating human anti-tumor immune response. We developed an improved NOD scid gamma (NSG) mouse model derived from non-expanded CD34 + stem cells, without CD3 + T cell contamination, to evaluate antitumor responses to immunotherapy in NSCLC. Using fresh CD34 + from umbilical cord blood reduced humanization time significantly. Human CD45 + cell reconstitution with increased functional human lymphoid (B, T, monocytes and NK cells) and myeloid (macrophages and MDSCs) lineage repopulation, without the onset of GvHD, was achieved as early as 4 weeks post-stem cell engraftment. Published studies using expanded CD34 + derived humanization reveal compromised purity of CD34 + stem cells with an increasing number of mononuclear cells. Reconstitution of CD8 + and CD4 + T cells is not achieved until 12 to 15 weeks post-engraftment at much lower levels than fresh CD34 + humanization. Single cell suspension analysis shows levels of human reconstituted T, B, NK, DC and MDSC cells at 4 weeks, which increased significantly at 6 and 9 weeks in peripheral blood, spleen and bone marrow. Human repopulated T cells were functionally active in secretion of IFN-γ by mitogenic stimuli such as PMA and IL-2 and by allogenic human cancer cells. Antigen specific CTL responses were observed when reconstituted human T cells from PDX bearing humanized mice were challenged with PDX tumor. No non-antigen specific responses were observed when T cells were co-cultured with HLA-matched human bronchial epithelial cells (HBEC). To evaluate the applicability of the humanized mouse in lung cancer translational research, we combined it with Hu-PDX or Hu-xenograft tumors and analyzed tumor growth and treatment response to the anti-PD1 checkpoint inhibitor pembrolizumab. We found that efficient engraftment of PDXs and xenograft tumors were not dependent on donor HLA-status. Similar to the clinical outcome, treatment with pembrolizumab, inhibited tumor growth significantly in both Hu-PDX, and Hu-xenograft mice regardless of donor HLA-types, increasing cytotoxic T cells and decreasing MDSC levels. Pembrolizumab had no effect on the non-humanized NSG controls. In concordance with our previous study with a syngeneic mouse tumor, the antitumor effect of check point blockade was significantly enhanced when combined with nanoparticle systemically delivered TUSC2 , a tumor suppressor and immunomodulatory gene, in a KRAS mutant lung metastasis humanized mouse model. In conclusion, fresh CD34 + are more effective than their expanded counterparts in humanizing mice, do so in much reduced time, and recapitulate the immune response to cancer. Citation Format: Ismail M. Meraz, Mourad Majidi, Feng Meng, RuPing Shao, Min Jin Ha, Shinya Neri, Bingliang Fang, Steven H. Lin, Peggy T. Tinkey, Elizabeth J. Shpall, Jeffrey Morris, Jack A. Roth. Development of an improved humanized patient-derived xenograft, Hu-PDX, mouse model for evaluation of antitumor immune response in lung cancer [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 4984.