SELL and neoplasm: To analyze effects of these tumor-released signals on biological aging of circulating neutrophils, we subsequently evaluated the surface expression of the chemokine receptors L-selectin/CD62L, CXCR2, and CXCR4 (which gradually increase (CXCR4) or decrease (L-selectin/CD62L, CXCR2) with biological aging of these leukocytes in the systemic circulation under homeostatic conditions)12 13 17 18 on blood neutrophils in SCC VII or 4T1 tumor-bearing mice.