160 Comprehensive TCR- and BCR- repertoire profiling and immunophenotyping in a lifestyle-induced susceptibility to immune-related adverse events (LISA) mouse model

<h3>Background</h3> Anti-PD-1 therapy significantly enhances the immune system’s ability to recognize and destroy cancer cells, offering new treatment options for patients with various types of cancer. Unfortunately, not all patients respond to therapy, and those responding can experience severe immune-related adverse events (irAEs). In this study, differences in the adaptive B- and T-cell repertoire were examined in a novel mouse model for irAEs generated via dietary and microbiome changes, which is termed the Lifestyle Induced Susceptibility to irAEs (LISA) model. The LISA mice were exposed to a high fat western diet versus the normal high fiber diet for the control mice, and anti-PD1 therapy administration led to systemic irAES in LISA mice. <h3>Methods</h3> BALB/c and C57BL/6 mice were subjected to either a conventional high fiber diet or the LISA model diet and treated with repeated doses of anti-PD-1 for three weeks (n=4-5 per group). RNA was extracted from blood and colon tissue samples and all seven chains of the adaptive immune system were co-amplified in the same reaction covering BCRs IgH (all isotypes), IgK and IgL and TCRs alpha, beta, delta, and gamma. In parallel, immunophenotyping was performed on all RNA samples using a panel of 106 immune expression markers. <h3>Results</h3> When utilizing blood to distinguish between control and LISA mice, the B-cell diversity and richness (total uCDR3) showed significant differences with greater richness and diversity in the IgH chain of LISA mice (FDR&lt;0.005). The isotype distribution profile was also skewed between the two groups for both blood and colon tissue with the Control group demonstrating more IgG (FDR&lt;0.005) and IgA (FDR&lt;0.05) expression and LISA having more IgM (FDR &lt;0.05). The gene expression data demonstrated significant differences between sample types of blood and colon tissue, but minimal differences between control and LISA mice. <h3>Conclusions</h3> This study demonstrates the utility of 7-chain immune repertoire profiling and immunophenotyping to comprehensively and efficiently characterize novel mouse models of disease. For the LISA model, we discovered several differences in the adaptive immune repertoire to serve as potential biomarkers for irAEs.