FASLG and neoplasm: Pt38 CD3 + opT were primarily CD4 + T cells (figure 1D), and cytotoxic CD4 + cells are known to kill tumor cells by FasL-mediated mechanisms.24 25 Pt38 opT cells had higher expression levels of FasL than Pt3 (figure 2E), and anti-FasL antibody significantly inhibited killing mediated by Pt38 opT cells with no effect for Pt3 opT cells.