Abstract
ObjectivesWith a rapidly growing list of candidate immune‐based cancer therapeutics, there is a critical need to generate highly reliable animal models to preclinically evaluate the efficacy of emerging immune‐based therapies, facilitating successful clinical translation. Our aim was to design and validate a novel in vivo model (called Xenomimetic or ‘X’ mouse) that allows monitoring of the ability of human tumor‐specific T cells to suppress tumor growth following their entry into the tumor.MethodsTumor xenografts are established rapidly in the greater omentum of globally immunodeficient NOD‐scid IL2Rγnull (NSG) mice following an intraperitoneal injection of melanoma target cells expressing tumor neoantigen peptides, as well as green fluorescent protein and/or luciferase. Changes in tumor burden, as well as in the number and phenotype of adoptively transferred patient‐derived tumor neoantigen‐specific T cells in response to immunotherapy, are measured by imaging to detect fluorescence/luminescence and flow cytometry, respectively.ResultsThe tumors progress rapidly and disseminate in the mice unless patient‐derived tumor‐specific T cells are introduced. An initial T cell‐mediated tumor arrest is later followed by a tumor escape, which correlates with the upregulation of the checkpoint molecules programmed cell death‐1 (PD‐1) and lymphocyte‐activation gene 3 (LAG3) on T cells. Treatment with immune‐based therapies that target these checkpoints, such as anti‐PD‐1 antibody (nivolumab) or interleukin‐12 (IL‐12), prevented or delayed the tumor escape. Furthermore, IL‐12 treatment suppressed PD‐1 and LAG3 upregulation on T cells.ConclusionTogether, these results validate the X‐mouse model and establish its potential to preclinically evaluate the therapeutic efficacy of immune‐based therapies.
Highlights
The emergence of cancer immunotherapy in the last decade, illustrated by advances in adoptive cellular therapy and immune cell-targeted monoclonal antibody therapy, has resulted in a vast improvement in the overall survival of patients with advanced-stage cancer.[1]
Tumorspecific cells used in our study are TKT R438W and TMEM48 F169L, derived from patient MEL21, and a detailed characterisation of these T cells has been previously reported[19] (Supplementary figure 1)
No PD-L1+ cells were detected in xenografts established using only DM6Mut cells (Supplementary figure 7d), indicating that T cells were required for PD-L1 expression in the xenografts. While these results show the presence of PD-L1 in DM6 cells expressing mutated neoantigens (DM6-Mut) tumor xenografts, a careful examination of these micrographs reveals that all tumor cells are not PD-L1+, and does not rule out the possibility that PD-L1 may be expressed on nontumor cells such as T cells in the tumor microenvironment
Summary
The emergence of cancer immunotherapy in the last decade, illustrated by advances in adoptive cellular therapy and immune cell-targeted monoclonal antibody (mAb) therapy, has resulted in a vast improvement in the overall survival of patients with advanced-stage cancer.[1]. Starting from the first successful engraftment of human tumors into immunodeficient mice over 30 years ago,[4] a number of xenograft models have been reported[5,6,7,8] with attempts made to assess the efficacy of immunotherapies.[7,9,10,11,12] More recently, humanised NOD-scid IL2Rcnull (NSG) mice (HuNSG) mice were developed by implanting hematopoietic stem and progenitor cells into conditioned NSG mice, resulting in the generation of multiple human immune cells including T cells, B cells, plasma cells, dendritic cells and myeloid cells.[13,14,15] These HuNSG mice, which develop a partially functional immune system,[7,13,16] overcome some limitations of the earlier PDX models While this approach has great potential for evaluating immune-based strategies,[17,18] it is logistically challenging, requiring up to 12 weeks to generate these functional immune cells, a further 60 days to establish tumor xenografts and several additional weeks to assess the response of the T cells to tumors. PDX models, including the humanised mouse model, have been logistically challenging and difficult to standardise as it has not been possible in most cases to control the number of tumor-specific T cells in the xenografts or to confirm and to identify the tumor specificity of the T cells in the model.[17,18]
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