Glycoconjugates as vaccines for cancer immunotherapy: clinical trials and future directions

The immune system recognizes and potentially eliminates tumors that express antigenic molecules. The theory of "cancer immunosurveillance", describing lymphocytes as sentinels capable of recognizing nascent transformed cells and thus maintaining tissue homeostasis, has been proposed as far back as 50 years ago. The modern vision of immune responses against cancer is more complex because the immune system sculpts the immunogenic phenotype of developing tumors by not only facilitating their elimination, but also their progression in regards to the role of regulatory T cells and the subpopulation of natural killer T cells (NKT). Manipulation of adaptive immunity through therapeutic approaches is relevant to prevent metastasis and, in some cases, to treat primary tumors if the relevant antigens have been identified. Here we review the use of glycoconjugates containing tumor-associated carbohydrate antigens (TACA) in immunotherapy and their use as vaccines in clinical and pre-clinical trials. We also describe a new experimental vaccine model for the generation of CD8+ cytotoxic T cells (CTL) that involves designer TACA-containing glycopeptides with high affinity for class I molecules of the major histocompatibility complex (MHC).