Allogeneic and autologous melanoma vaccines: where have we been and where are we going?

The past three decades have seen substantial research on vaccines for the treatment of metastatic melanoma and the prevention of recurrence following resection. Despite their enormous promise, the actual results have been disappointing, with several high-profile vaccine clinical trials failing to show a benefit. Nonetheless, enthusiasm for melanoma vaccines remains and has increased with our expanding understanding of the immune response to tumor. Cellular vaccines can be divided into autologous, derived from the patient's own tumor and allogeneic vaccines. Autologous vaccines have the advantage of containing all potentially relevant tumor-associated antigens for that particular patient. However, autologous vaccines are difficult to obtain from most patients with advanced disease and impossible to obtain from patients who present after resection of all clinically evident disease. No consensus exists for how tumors should be processed, preserved, modified, and delivered to serve as an effective vaccine. The amount of autologous tumor available is rarely enough to produce more than two or three vaccination doses, and the time between initial tumor harvest and ultimate availability of the vaccine may result in interval tumor progression that diminishes the likelihood of vaccine efficacy. All these drawbacks of autologous tumor vaccination limit its applicability and also limit the ability to test autologous vaccines in prospective trials. Allogeneic vaccines avoid many of these problems, but may not contain all of the tumor-associated antigens present on the patient's own tumor. In particular, neoantigens created by mutations in the patient's tumor would be unlikely to be represented in an allogeneic vaccine. Although allogeneic vaccines can be manufactured in sufficient quantities to allow large-scale trials, there remain significant limiting issues in the manufacture and standardization of the vaccine product.