The invention provides a novel compounds derived from CD154, but without the intracellular domain. Notably, the invention provides TMZ-CD154 and a method to treat diseases in which the novel molecule TMZ-CD154 is used. In particular, TMZ-CD154 is used to modify the immune responses in patients with immune related diseases such as cancer and infectious disease. The invention also relates to a method to activate cells with the TMZ-CD154 in vitro either prior to using the activated cells for therapy or for diagnostic purposes.