Chantal Woodson, Loryn Holokai, Dr. Jayati Chakrabarti, Dr. Jiang Wang, Dr. Syed Ahmad, Dr. Yana Zavros
University of Cincinnati College of Medicine
Introduction: Pancreatic Ductal Adenocarcinoma (PDAC) has a survival rate of only 8.5%. Resistant tumors show increased PD-L1 expression inducing cessation of anti-tumor activity in cytotoxic T Cells (CTLs). The mechanism by which PD-L1+ PDAC tumors evade the immune response is not well understood. Myeloid cells (MDSCs) block anti-tumor CTL response partially by activating the PD-L1 checkpoint on CTLs. Depleting the MDSC population enables an endogenous anti-tumor CTL response in PDAC patients.
Hypothesis: 1) Organoids derived from resected PDAC tumors provide an in vitro model for predicting personalized therapy. 2) Chemoresistant PD-L1+ organoids are sensitive to combinatorial therapy involving both checkpoint inhibition and MDSC depletion.
Methods: Organoids were generated from resected PDAC patient tumors. Autologous CTLs were isolated from whole blood of patients. Monocytes and dendritic cells were differentiated from Peripheral Blood Mononuclear Cells. HLA-DR+ dendritic cells isolated by FACS were co-cultured with CTLs to activate them against autologous PDAC tumor. Activated CTLs and/or MDSCs were co-cultured with organoids derived from the same PDAC tumor. Flow cytometry measured organoid PD-L1 expression and CTL proliferation in response to standard-of-care chemotherapy alone or in combination with checkpoint inhibition and/or MDSC depletion.
Results: 1) Patients that exhibited chemoresistance showed increased G-MDSC infiltration within their tumor tissue. 2) In an autologous organoid/CTL co-culture derived from a chemoresistant patient with elevated G-MDSC infiltration, approximately 50% PD-L1+ organoid cell death was observed when cultures were treated with either PD-1 inhibitor (PD-1I, Nivolumab) alone or in combination with chemotherapy. Importantly, the inclusion of G-MDSCs in the organoid/CTL co-culture hindered the efficacy of checkpoint inhibition by PD-1I. Depleting the co-culture of MDSCs using Cabozantinib maximized the efficacy of checkpoint inhibition in combination with chemotherapy to induce cancer organoid death. 3) Organoid/CTL co-cultures generated from chemo-naive patients were used to predict the efficacy of combinatorial therapy for these individuals.
Conclusions: Depletion of MDSCs within the PDAC tumor microenvironment may enable the CTL anti-tumor response. Thus, patient-derived organoid/immune cell co-cultures provide an approach to predict efficacy of combinatorial therapy and improve PDAC patient outcome.