112 A novel primary human tumor explant platform provides a preclinical translational link from tissue culture to the clinic

Background: To explore a candidate immunotherapeutic (BiTE), a translational explant platform was developed consisting of cultures of thinly sectioned tissues from freshly resected solid tumors. The tumor explants are being used to study treatment responses in a model system that preserves the tumor architecture and microenvironment, including immune effector populations. Material and Methods: 18 freshly resected epithelial tumors were sectioned and treated in culture for 48 or 72 h with increasing concentrations (0, 5, 50 and 500 pM) of an EGFR-BiTE or a MEC14-BiTE (negative control). The culture supernatant was then collected to quantitate cytokines released as a measure of T-cell activation using Myriad’s CytokineMAP A v1.0 panel. CD25 and CD3 enumeration to demonstrate in situ T-cell activation was performed by IHC in FFPE tissues derived from the treated explants. In addition, the parental tumors were profiled by IHC to characterize the EGFR target levels together with the initial tumor T-cell infiltrate. Finally, gene expression profiles of the parental tumors were generated to explore potential resistance mechanisms. Results: Tumor resident T-cells are activated ex vivo by BiTE. A dose dependent increase of several cytokines including IFN-g, IL-2 and TNF-a was observed in conditioned media harvested from EGFR-BiTE treated but not in MEC14-BiTE treated explants. In addition, a dose dependent increase of granzyme B into media as measured by ELISA was observed. Importantly, a dose dependent increase of total CD25 counts and the %CD3CD25 is observed in the EGFR-BiTE explants vs. those treated with the control BiTE.