Abstract A021: Peripheral T cell lymphoma not otherwise specified: Characterization of pet dogs as a model organism

Abstract

Human peripheral T cell lymphoma, not otherwise specified (PTCL-NOS) is a rare and aggressive subset of non-Hodgkin’s lymphoma with poor survival. Pet dogs develop a similar neoplasm, termed peripheral T cell lymphoma (PTCL), that shares histology, antigen expression and gene expression profiles with human PTCL-NOS. These dogs are an attractive model for the study of PTCL-NOS because they develop spontaneous disease in an immune competent host, live in the same environment as humans, have relatively short lifespans allowing for lifelong follow up and are treated with the same anthracycline based chemotherapeutics (CHOP) with outcomes similar to their human counterparts. In addition, human PTCL-NOS has been tentatively subdivided based on the expression of the transcription factors TBX21 and GATA3. According to previous RNA sequencing data from our lab, canine PTCL resembles the GATA3 subtype of PTCL-NOS. The disease in pet dogs is more frequent than seen in people; it is the second most common form of lymphoma in this species. The purpose of this study was to characterize the mutational profile of canine peripheral T cell lymphoma and establish a pre-clinical model of disease using patient canine derived xenograft models (PDX). We established the mutational profile of canine PTCL using whole exome sequencing (WES). DNA was isolated from 95 canine samples previously used for RNA sequencing. This DNA was then used for WES and analyzed for cancer-related mutations using GATK best practices. Top mutated genes included FAT3, KMT2D and mTOR. These mutations are involved in tumor suppression, epigenetic modification, and cell growth and proliferation respectively. The mTOR mutations occur within the catalytic domain of the protein and are consistent with previous RNAseq data from our lab showing upregulation of the PI3K-AKT-mTOR pathway. Several mutations (14/26) align with known human mutations in location and type. To establish an in vivo pre-clinical model of PTCL, primary canine tumor cells were injected into NSG mice intraperitoneally. Mice were monitored for tumor development through serial weights, abdominal palpation and observation. At the first sign of disease progression, mice were euthanized and a comprehensive necropsy was performed to identify gross and microscopic disease. Engraftment of primary cells was successful in 9/23 (39.1%) mice. After first passage, engraftment was successful in 4/6 (67%) mice. Across passages, the histologic and immunophenotypic characteristics of the tumors remained consistent. These results show that the PDX model was successfully established, and characteristics were maintained through multiple passages. Overall, these data show that pet dogs are an excellent model to study PTCL-NOS and that PDX models can be successfully established using canine samples. Future directions include testing novel therapies in PDX mice before moving them to pre-clinical trials in pet dogs.