Interleukin Cells through a Pathway Independent of CD40L and Genetically Modified Dendritic Cells Prime Autoreactive T

Genetic immunization through ex vivo transduction of dendritic cells has been suggested as an effective approach to enhance antitumor immunity by activating both CD4 and CD8 T cells. Immunizing mice with dendritic cells transduced with an adenovirus expressing the human melanoma antigen glycoprotein 100 (DCAdhgp100) as a cancer vaccine, we demonstrated complete protective immunity and a potent CTL response against melanomas expressing murine glycoprotein 100 in a CD4 cell-dependent manner. Surprisingly, however, effective tumor rejection was not the result of cooperation between CD4 and CD8 T cells. Protective immunity was completely lost when CD4 cells were depleted immediately before tumor challenge, whereas it was unaffected by removal of CD8 cells, establishing a principal role for CD4 cells in the effector phase of tumor rejection. Neither protective immunity nor CTL generation in this model required interleukin 12, in spite of high levels of IFN-g secretion by tumor-reactive T cells. Most notably, the DCAdhgp100 vaccine could elicit protective antitumor CD4 cells in the absence of CD40 ligand, although it does not bypass the need for CD40mediated signals to generate melanoma-reactive CTLs. Thus, in contrast to the current thinking that the optimal cancer vaccine should include determinants for both CD4 and CD8 cells, the potency of the DCAdhgp100 vaccine appears to be a result of its ability to directly prime autoreactive CD4 cells through a process that does not require interleukin 12 and CD40 signals.