Abstract 3972: Ex vivo profiling of PD-1 blockade using organotypic tumor spheroids

Abstract Despite the impressive activity of PD-1/PD-L1 immune checkpoint blockade in melanoma, lung, and other cancers, the majority of patients are intrinsically resistant to this therapy. Furthermore, despite years of effort few robust biomarkers of response exist, and tumor PD-L1 expression and mutational load are only partially predictive of activity. Nearly all attempts at biomarker development have relied on fixed tumor tissue or studies in plasma. Meanwhile, emerging functional approaches to study patient derived samples, such as organoid development and circulating tumor cell culture, lack features of the native tumor immune microenvironment and thus are limited in the ability to assess ex vivo anti-PD-1 response. We have developed a novel approach to study short-term ex vivo response to immune checkpoint blockade based upon short term culture of murine- and patient-derived organotypic tumor spheroids (MDOTS/PDOTS) in a 3-dimensional microfluidic system. Spheroids derived from fresh mouse and human tumor samples through partial collagenase digestion and filtration retain autologous tumor infiltrating immune cells, including PD-1 positive CD8 T lymphocytes. Using murine syngeneic mouse cancer models with known responsiveness or resistance to PD-1 blockade, we demonstrate the ability to recapitulate tumor killing ex vivo or lack thereof. Multiplexed cytokine profiling of conditioned media in this system further enables characterization of the cytokine and chemokine response to PD-1 and/or CTLA-4 blockade. We thus analyzed the secreted cytokine/chemokine response to PD-1 inhibition across a large panel of PDOTS, and observed pronounced induction of CCL19/CXCL13, which associated with % PD-1 positive CD8 T cells. This strategy further uncovered production of a class of myeloid attracting chemokines and cytokines in major proportion of samples, which clustered with the presence of plasmacytoid dendritic cells and myeloid derived suppressor cells. Importantly, the presence of this maladaptive cytokine/chemokine signature correlated with lack of response in the subset of patients that had been treated with PD-1 blockade. Together, these data demonstrate the ability to profile the functional response to tumor PD-1 blockade ex vivo and unveil a novel strategy to advance precision immuno-oncology. Citation Format: David A. Barbie, Russell Jenkins, Kwok-Kin Wong. Ex vivo profiling of PD-1 blockade using organotypic tumor spheroids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3972. doi:10.1158/1538-7445.AM2017-3972