Description

Myeloid Derived Suppressor Cells Arising from Tumor Resections Severely Suppresses Natural Killer Cells ex vivo

Leonard Angka^1,2, Michael Kennedy¹, Christiano T. De Souza¹, Katherine Baxter^1,2, Manahil Sadiq¹, Rebecca C. Auer^1,3
1Ottawa Hospital Research Institute, ²University of Ottawa, ³Division of General Surgery

Background: Surgical resection is the best chance for cure in the treatment of solid malignancies but results in profound immune suppression, in particular Natural Killer (NK) cell dysfunction, which contributes to relapse and metastases. In this study we evaluate the hypothesis that NK cell impairment is mediated by myeloid derived suppressor cells (MDSCs), expanded in the postoperative period in response to surgical stress and characterize these MDSCs with respect to their phenotypic and functional characteristics.

Methods: MDSC were collected and analyzed 1 day following surgery (laparotomy) from murine splenocytes or fresh peripheral blood mononuclear cells by flow cytometry. MDSC suppression was measured by co-culturing sorted MDSCs (murine CD11b+Ly6G+ or human CD33+IL-4Rα+) with NK cells from naïve mice (DX5+) or the human NK92 cell line, followed by a 4hr incubation with labelled NK target cells (murine Yac1 or human K562). Arginase-1 (Arg1) activity was measured by quantifying urea production from MDSC lysates.

Results: In mice, there is a 4.3 fold increase in granulocytic MDSCs (CD11b⁺Ly6G⁺Ly6C^lo) expressing IL-4Rα and Arg1, 1 day after surgery. These MDSCs had greater suppressive capacity vs MDSCs from no surgery controls and also had higher Arg1 activity (8.25ng vs 20.9ng of urea produced). Notably, adding L-arginine (2mM) to the co-culture prevented NK suppression. In humans, CD33⁺CD14⁺CD15⁺HLA-DR^lo MDSCs with increased IL-4Rα expression accumulated on postoperative day 1, irrespective of the cancer or surgical procedure. Co-culturing these MDSC with NK92s caused a significant reduction in NK92 cytotoxicity.

Conclusion: Surgery-induced MDSCs have increased IL-4Rα expression and Arg1 activity and are highly suppressive of NK cells. These cells are likely responsible for the observed NK cell dysfunction seen in the postoperative period.