CD28 and melanoma: To confirm that PDI-1 was not directly cytotoxic to human T cells or tumor cells, we examined the effects of incubation with up to 10 μM PDI-1 for 24 hours on the viability of activated human CD3+ T cells (incubated with anti-CD3/CD28-coupled beads for 2 days), two human NSCLC cell lines, NCI-H1975 and A549, and two human melanoma cell lines, A375 and SK-MEL-2.