Abstract 4990: Flow cytometric characterization of the tumor-infiltrating immune compartment: Significant differences in the tumor immune repertoire versus peripheral blood

Abstract

Abstract Characterization of the tumor microenvironment (TME) is expected to be critical in informing prognosis and guiding response prediction1,2. Recent studies have classified the TME based on tumor infiltrating leukocytes (TILs), programmed death-ligand 1 (PDL1) expression, and the nature of inflammatory responses1,3. Tumor studies involving transcript profiling and IHC have begun to inform the diversity and complexity of the tumor-infiltrated immune compartment (TIIC) by defining aspects of cellular composition, spatial distribution, and function. The use of flow cytometry allows the elucidation of an array of immune cell subtypes across entire samples. This study characterizes immune cell population subsets and tumor cells in four cancer types (breast, head and neck, colorectal, and gall bladder) from patients using multi-color flow cytometry. A good correlation was observed (r= 0.89, p=0.003) between tumor content, as evaluated by a pathologist (Hematoxylin and Eosin staining), and tumor content (EpCAM/panCK[7/8]+ cells) as estimated by flow cytometry (for all cancers excepting head and neck). Using pathology scoring we divided the samples into high-content (>10% tumor) and low-content (<10% tumor) samples. Samples with high tumor content were further examined by comparing the immune population in the tissue with their matched peripheral blood mononuclear cells (PBMC). We observed significantly higher proportions of T-cells, T-regulatory cells (Tregs) and exhausted T-cells (PD-1+ T-cells) in TIIC in comparison to its matched PBMC, while a lower proportion of B-cells and NK cells was noted. Also, samples with high tumor content had a significantly increased proportion of CD8 T-cells, Tregs and NK cells and a lower proportion of effector CD4 (CD4+Foxp3-) T-cells in comparison to the samples with low tumor content. The results from this study demonstrate the differences in the peripheral immune repertoire from the TIIC, reaffirming the need to robustly characterize the local TME. Additionally, the similarity in Treg and exhausted T-cell profiles across the indications examined may support a broad utility for therapeutics that can successfully target immune exhaustion or suppression.