CD40 and central nervous system cancer: Among the possibilities, agonistic aCD40 is particularly interesting because it can work at many levels, for example, by activating DCs to more efficiently stimulate T cells, by triggering macrophages to exhibit antitumor functions, or even by directly interacting with certain CD40-expressing tumor cells, as proposed for certain human gliomas (41, 42), although this would not be the case for the CD40-negative mouse models used here (15).