Immunotherapy has had a limited clinical benefit in pancreatic ductal adenocarcinoma (PDAC). In a pre-clinical mouse model of PDAC treated with glucocorticoid-induced TNFR-related protein (GITR) agonist, the tumours showed nondurable and heterogeneous responses to the GITR agonist. We hypothesised that resistance to GITR agonist is associated with a unique symbiotic interaction between persistent and emergent tumour clones resistant to therapy response.
Cutting-edge DNA-barcoding technology was applied to study heterogeneity in vivo using 3275 KPC (LSL-KrasG12D/+; LSL-Trp53R172H/+; Pdx-1-Cre) cell line. Two distinct oligo-clones representing different morphologies and molecular characteristics (assessed using Western blot and gene expression profiling) were selected. Response to GITR agonist and vehicle was assessed after orthotopic injection of cells into immunocompetent mice in vivo.
DNA-barcoding experiment showed reduced clone size and heterogeneity in 3275 orthotopic tumours treated with GITR agonist compared with the control. This clonal heterogeneity was partly associated with two oligo-clones: A) an epithelial-like and B) a mesenchymal-like oligo-clones from parent 3275 cell line. The epithelial-like in vivo mouse tumours had increased viral-mimicry pathways and immune infiltrations, whereas the mesenchymal-like tumours showed immunodesert and epithelial-mesenchymal transition gene profiles. When these oligo-clones were mixed and co-cultured in vitro or injected in vivo in mice, we observed a unique symbiotic relationship between them. Moreover, treatment of the mixed tumours showed that while mesenchymal-like cells persisted with intrinsic resistance, epithelial-like cells emerged as adaptive resistance after treatment.
This study showed symbiotic interaction between persisted and emerging oligo-clones supporting each other leading to heterogenous and non-durable responses after treatment with GITR agonist. Further studies are required to understand the interaction between these oligo-clones to identify additional potential targets to perturb the symbiotic interaction for durable immunotherapy responses.
The authors.
Ian Harty Charitable Trust.
A. Sadanandam: Financial Interests, Institutional, Research Grant: BMS. All other authors have declared no conflicts of interest.