Dietary supplementation with L-arginine: Modulation of tumour-infiltrating lymphocytes in patients with colorectal cancer

Background: Dietary supplementation with L-arginine enhances natural cytotoxicity in peripheral blood lymphocytes but its effect on infiltrating lymphoreticular cells within a tumour microenvironment is unknown. The effects of dietary supplementation with L-arginine on tumour-infiltrating lymphocytes (TILs) in patients with colorectal cancer were evaluated. Methods: Eighteen patients received either a standard hospital diet (controls) or a standard diet supplemented with 30 g per day of L-arginine for 3 days before surgery. Tumour biopsies were taken at surgery and lymphocyte subsets (CD antigens) and macrophages examined immunohistochemically. Results: Tumours from patients receiving L-arginine contained increased numbers of specific cell subsets within the tumour which expressed CD16 (P = 0.004) and CD56 (P = 0.001) surface markers, when compared with tumours from control patients. There were no differences in the total number of T and B cells, T helper and T suppressor cells. Conclusion: Dietary supplementation with L-arginine significantly alters the spectrum of TILs in human colorectal cancers in vivo. These findings have important implications for new strategies in anticancer treatment.