4-1BB is an activation-induced costimulatory TNF receptor family member which is expressed on a variety of cell types such asactivated T cells, NK cells, dendritic cells, B cells, monocytes and Neutrophils. 4-1BB/4-1BBL interaction leads to a series of activationeffects including increased cytotoxic T lymphocytes (CTL) activity, cytokine induction, prevention of activation-induced cells death(AICD)