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

Abstract

Murine tumors are indispensable model systems in preclinical immuno-oncology research. While immunologic heterogeneity is well known to be an important factor that can influence treatment outcome, there is a severe paucity of data concerning the nature of this heterogeneity in murine tumor models. Using serial sectioning methodology combined with immunohistochemistry and whole-slide image analysis, the depth dependent variation in immune cell abundance in tumor specimens was investigated at single cell resolution. Specifically, intra-tumor and inter-tumor variability in cell density was quantified for nine immune cell biomarkers in multiple murine tumor models. The 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 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, it is observed 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. Taken together, these results reveal novel insights into the nature of immunologic heterogeneity, which is not accessible through bind and grind omics approaches.