Antigens and cytokine genes in antitumor vaccines: the importance of the temporal delivery sequence in antitumor signals.

Studies against cancer, including clinical trials, have shown that a correct activation of the immune system can lead to tumor rejection whereas incorrect signaling results in no positive effects or even anergy. We have worked assuming that two signals, GM-CSF (granulocyte and macrophage colony-stimulating factor) and tumor antigens are necessary to mediate an antitumor effective response. To study which is the ideal temporal sequence for their administration, we have used a murine model of antimelanoma vaccine employing whole B16 tumor cells or their membrane protein antigens (TMPs) in combination with gm-csf transfer before or after the antigen delivery. Our results show that: (i) When gm-csf tisular transfection is performed before TMP delivery, a tumor growth inhibition is observed, but with a limit effect when administering high antigen doses; in contrast, when signals are inverted, the limited effect is lost and greater antitumor efficacy is obtained. (ii) A similar behavior, but with stronger positive results, is observed employing gm-csf transfection and whole tumor cells as antigens. While negative results are obtained with gm-csf before cells, the best results (total survival of treated mice) are obtained when GM-CSF is administered in transfected cells. We conclude that optimal antitumoral response can be obtained when the antigen signal is given before (or simultaneous with) GM-CSF production, while the inversion of the signals could result in the undesired inhibition or anergy of the immune response.