Introduction The tumor microenvironment(TME) is a complex system, where malignant cells co-exist and communicate with immune and non-immune cells(1). This interaction can induce an immune response by releasing cytokines that will regulate and recruit immune cells which may promote tumor shrinkage (2). High tumor-infiltrating lymphocytes (TILs) in the TME have been correlated with favorable prognosis in colorectal and pancreatic adenocarcinomas (CRC and PDAC) (3,4). Also, high number of NK cells has been associated with a better prognosis in different solid tumors (5). Therefore, a detailed analysis of immune cells' distribution in the TME could help understand which of these cells have higher tumor-infiltrating capacities and may be used as cell product of immunotherapy.

Experimental Procedure Fresh CRC (n=6) and PDAC (n=6) tumor specimens were obtained within 20 minutes after surgery. A specialized pathologist collected the central and peripheric regions (CR and PR, respectively) of the tumor. From each region, half of the specimen was used for immunophenotyping analysis and the other half was cultured with medium enriched in IL-2 (1000 IU/mL) for 12 days. Immunophenotyping was performed using CD45, CD19, CD3, CD4, CD8, CD56, CD16 and LiveDead marker through flow cytometry at days 0, 6 and 12 (% correspond to mean). Formalin-fixed paraffin-embedded blocks were generated with the ‘mirror' sample of the fresh collected specimens and immunohistochemistry (IHC) for CD8 and CD56 was performed.

Results In the PR of CRC we identified 12% of B-cells, 66% of T-cells (31% CD4+ and 23% CD8+ T-cells) and 5% of NK cells (17% CD56brightCD16 cells and 24% CD56+CD16+ cells). In the CR of CRC we observed 7% of B-cells, 70% of T-cells (40% CD4+ and 23% CD8+ T-cells), and 6% of NK cells (15% CD56brightCD16 cells and 44% CD56+CD16+ cells). In the PR of PDAC we observed 13% of B-cells, 76% of T-cells (38% CD4+ and 35% CD8+ T-cells) and 3% of NK cells (5% CD56brightCD16 cells and 40% CD56+CD16+ cells). In the CR of PDAC we identified 16% of B-cells, 66% of T-cells (31% CD4+ and 32% CD8+ T-cells) and 10% of NK cells (2% CD56brightCD16 cells and 55% CD56+CD16+ cells). During culture, the % of B-cells decreased while the % of T-cells and NK cells increased. IHC results show that CD8+ T-cells are more abundant in the TME and formed larger clusters than NK cells. Furthermore, although the majority of NK cells were found in the stroma, in some cases NK cells were located inside the malignant epithelium.

Conclusions Our data in this small set of specimens show that TME immune cells in PRs and CRs present different phenotypes for both CRC and PDAC. Indeed, the PRs show higher TIL and NK cells' infiltration than the central ones. Among different patients, the distribution and quantity of CD8+ T-cells and NK cells were different, which may have clinical significance. We also observed that immune cells may communicate with tumor cells both in CRC and PDAC since these cells were identified inside the malignant epithelium in some tumor specimens.

Citation Format: Andreia Maia, Joana R. Lérias, Luis Miguel Borrego, Mireia Castillo-Martin, Markus Maeurer. The immune profile of colorectal and pancreas adenocarcinomas: Differences between central and peripheric tumor regions [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P039.