IMMU-21. MULTIDIMENSIONAL CHARACTERIZATION OF IMMUNE CELL POPULATIONS IN THE GLIOMA TUMOR MICROENVIRONMENT REVEALS A DOMINANT PROPORTION OF CELLS DERIVED FROM THE MYELO-MONOCYTIC LINEAGE

Immunotherapy represents an exciting new strategy to treat patients with malignant gliomas; however, we and others have previously shown that the presence of other immune cell populations in the tumor microenvironment can reduce the effectiveness of immunotherapy. To date, a comprehensive and quantitative examination of immune cell composition in the glioma microenvironment has not been performed. We purified CD45+ cells from freshly digested tumor samples of 35 malignant glioma patients undergoing surgical resection at UCLA and performed CyTOF mass cytometry. We then analyzed the lineage and functional marker expression of these populations. Next, to pursue an unbiased analysis of the multi-dimensional data, we used a computational algorithm that clusters cells into phenotypically distinct populations in an unsupervised manner. CD11b+ myelo-monocytic cells (1542.13 ± 306.82 cells/mg of tumor; 51.33 ± 6.43% of all cells) represented the dominant population and were more abundant than CD3+ T lymphocytes (233.65 ± 59.53 cell/mg of tumor; 8.41 ± 1.47% of all cells; p < 0.001). Meanwhile, our unsupervised clustering algorithm generated 12 distinct phenotypic clusters. Amongst the immune cells, 76.81% were grouped into 6 clusters that derived from populations of a monocytic lineage including a classical monocytic population, an inflammatory monocyte population, and a differentiated M2 macrophage population. 12.37% of the tumor-infiltrating immune cells grouped into 2 clusters of a NK lineage, 9.06% grouped into 2 clusters of a T cell lineage, 0.3% grouped into 1 cluster of a B cell lineage, and 1.46% cells in 1 cluster of an unable to be classified cell lineage. Cells of monocytic origin represented the dominant fraction of cells within the tumor-infiltrating immune cell population. Understanding the immune cell composition in the tumor microenvironment may help improve current and future immunotherapies against gliomas.