Abstract
609 Background: KRAS-mutant (KRASmut) colorectal cancers (CRCs) are associated with worse prognosis and resistance to therapy. We have previously shown that KRASmut CRCs have different transcriptomic signature of stromal and immune-related genes compared to KRAS-wild type (KRASwt) tumors. Here, we validated the immune-related changes in the tumor microenvironment associated with the KRAS mutation in CRC to guide the design of novel immunotherapy strategies. Methods: The expression of different immune markers (T cells, B cells, macrophages, natural killer cells, and immune check ligands) were assessed using multiplex immunofluorescence (M-IF) technique in both tumor core (TC) and invasive margin (IM). Sequential slides were cut from paraffin blocks of CRC resected at our institute. Each slide was stained with 4 immune markers using M-IF technique. The stained slides were scanned, and quantification of immune cells was done using ImageJ software. Student’s t test was used for statistical analyses. DNA was extracted from each tumor and profiled for 420 cancer genes using targeted exome-capture sequencing (MSK-IMPACT assay). DNA mismatch-repair (MMR) proteins deficiency were analyzed by immunohistochemistry. Only MMR-proficient (pMMR) tumors were included. Results: A total of 39 patients with pMMR CRC were included. AJCC stages (I-III) were not different between KRASmut (n = 15) and KRASwt (n = 25) tumors. M2-macrophages (CD68+CD163+ cells) and IL-17-producing cells (IL17+ cells) were significantly higher (p = 0.002, and 2.9e-6 respectively), while T-helper cells (CD3+CD4+cells) were significantly lower (p = 3.9e-4) in TC of KRASmut tumors compared to KRASwt. Treg (CD3+CD4+FOXP3+cells) were significantly higher in IM of KRASmut tumors (p = 0.01). KRASmut tumors had significantly higher ratios of Treg:T-helper cells, and Treg:T cytotoxic cell (p = 0.008, and p = 0.04; respectively). Conclusions: KRAS oncogene is associated with more pro-tumorigenic (M2 macrophages, IL17 and Treg) and less anti-tumorigenic (CD4 T-helper) immune cells in CRC. These results can be used to guide further research to design novel immunotherapy strategies against KRASmut CRC.
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