CD4 and neoplasm: To further test whether Zn supplementation directly impacts the expression of PD-1, as it does so in vivo in tumor-bearing mice, the sorted CD4+ T cells and CD8+ T cells from the spleen of healthy C57BL/6 mice were activated with α-CD3 and α-CD28 antibodies for 48–72 h with or without Zn (50 μM) supplementation.