Survey of the Immunogenomic Landscape of Solid Tumors Through Clinical DNA and RNA Sequencing

2019 ASCO-SITC Clinical Immuno-Oncology Symposium Presentation
Authors Denise Lau, Alan Chang, Jason Perera, Ariane Lozac'hmeur, Alexandria Bobe, and Aly Khan

Background: In the past decade, immunotherapy has emerged as an important new modality in cancer treatment. However, studies have shown that only a fraction of patients will experience any clinical benefit when treated with immune checkpoint blockade drugs. Given the cost and potent adverse events associated with immunotherapy, the need for effective biomarkers is clear. We sought to understand the role of key immunotherapy biomarkers, like tumor mutational burden (TMB), microsatellite instability (MSI), and PD-L1 immunohistochemistry (IHC), in the context of the greater immunogenomic landscape of solid tumors in patients.

Methods: We analyzed data from a cohort of 500 patients across 10 cancer types who received the Tempus xT 595 gene targeted DNA sequencing assay and whole transcriptome sequencing assay as part of their clinical care. We determined the TMB, MSI status, and neoantigen load for each sample using the DNA sequencing data. We used the RNA expression data to evaluate immune activation and tumor infiltration by determining the expression of inflammatory gene signatures and estimating the relative proportion of key immune cell types.

Results: Integrative analysis of the DNA and RNA sequencing data showed that the immunogenicity of the tumor, as measured by TMB or neoantigen load, correlates with levels of immune activation and tumor infiltration. Inflammatory immune cells, like CD8 T cells and M1 polarized macrophages, were significantly higher in TMB-high samples; while non-inflammatory immune cells, like monocytes, were significantly lower in TMB-high samples. Additionally, samples could be clustered into immunologically active “hot” tumors or immunologically silent “cold” tumors based on gene expression. The immunologically “hot” population was enriched for samples that were TMB-high, MSI-high or PD-L1 IHC positive.

Conclusions: Paired next generation DNA and RNA sequencing assays allows for the identification of patients that have immunologically active tumors that lack traditional immunotherapy biomarkers. These patients represent an interesting new population who may potentially benefit from immunotherapy.