SELL and neoplasm: Thus, while MDSC expansion early during tumor progression (i.e., 7 days post-4T1 implantation) coincided with significant L-selectin downregulation on naïve CD4+ and CD8+ T cell subsets, even greater L-selectin loss occurred at later time-points with higher 4T1 tumor burdens at subcutaneous sites or the mammary fat pad (Figure 1—figure supplement 2B–D).