Figure 2.

Proposed mechanism of action of prophylactic vaccine. (a) Prophylactic vaccination is used to manipulate antitumor immune responses. Individuals who are at high risk of developing tumors or have been diagnosed with premalignant changes in target tissues would receive prophylactic vaccines prior to the occurrence of tumors. A vaccine based on antigens expected to be expressed by the anticipated tumor is administered in an immunostimulatory preparation (with adjuvant) that can activate Langerhans cells—epidermal dendritic cells (DCs). Activated Langerhans cells transport tumor antigens to the draining lymph node, where they present antigens to T-cells. B-cells are also activated, with the expected result of clonal expansion of tumor-specific T-cells and antibody production. This clonal expansion of effector cells is followed by the generation of a pool of memory cells specific for the tumor antigen/s over time. (b) If a tumor grows in the future, tumor antigens that reach the draining lymph node will reactivate tumor-specific memory cells and trigger a rapid secondary immune response. This response will be distinguished by a large number of effector T-cells, a high titer of antibodies, and continuous activation of DCs at the tumor site, allowing for continuous processing and presentation of tumor antigens and further immune amplification. (c) Since the incipient tumor has not grown large and heterogeneous, it is easily eliminated by the prepared immune response. Furthermore, the memory compartment is expanded by this tumor-mediated boost.