Initial Characterization of Canine T-cell Receptor Repertoires Using RNA-seq Data from Different Diseases and Tissues

The dog serves as a key translational model in cancer immunotherapy. Understanding the T cell receptor (TCR) repertoire is needed for various cancer immunotherapies. Compared to humans where >300 million TCRs have been identified, <100 canine TCRs are reported. To address this deficiency, we assembled >200,000 complete TCR complementarity-determining region 3 (CDR3) sequences from RNA-seq data published for [~]2,000 canine samples of blood, lymph node, and other tissues, of which 613 are tumors. We collected 1,324 human RNA-seq samples to compare the similarities and differences in T-cell repertoires between humans and dogs. Notably, our analysis revealed distinct variable gene usage patterns between blood samples and solid tissues in both canine and human samples for TRA and TRB loci. Moreover, our investigation led to the discovery of novel V gene and allele candidates in the canine genome. Our findings also revealed that the canine CDR3 resembled human CDR3 in terms of length and motifs. Additionally, our study unveiled shared traits in cancer TCRs between dogs and humans, including longer lengths and higher hydrophobicity of private CDR3s. Our results indicated the diversity of canine to be more comparable to that of humans than mice. Our study provides an initial landscape of the canine TCR repertoire, highlighting both its similarities and differences with the human counterpart, thus laying the groundwork for future research in comparative immunology and vaccine development.