Characterizing intra-tumor and inter-tumor variability of immune cell infiltrates in murine syngeneic tumors

By using serial-sectioning methodology combined with immunohistochemistry (IHC) and whole-slide digital image analysis (DIA), we present a systematic analysis of intra-tumor and inter-tumor variability in the abundance of nine immune cell biomarkers in multiple murine tumor models. Our analysis shows that inter-tumor variability is typically the dominant source of variation in measurements of immune cell densities. Statistical power analysis reveals how group size and variance in immune cell density estimates affect the predictive power for detecting a statistically meaningful fold-change in immune cell density. Inter-tumor variability in the ratio of immune cell densities show distinct patterns in select tumor models and reveal the existence of strong correlations between select biomarker pairs. Further, we show that the relative proportion of immune cells at different depths across tumor samples is preserved in some but not all tumor models thereby revealing the existence of compositional heterogeneity. The results and analyses presented here reveal the complex nature of immunologic heterogeneity that exists in murine tumor models and provide guidelines for designing preclinical studies for immuno-oncology research and drug development.