Virosomes as new carrier system for cancer vaccines.

HER-2/neu, a tumor-associated antigen (TAAg), plays a critical role in oncogenesis of various tumor types, and its selective overexpression by malignant tumor cells makes it an ideal target for immunotherapy. A prerequisite for clinical vaccines is the construction of safe and highly immunogenic reagents able to generate efficient immune responses against TAAg. Previous protein vaccines, consisting of the extracellular domain of HER-2/neu (pNeuECD), were shown to elicit an immune response that did not provide protection from transplantable tumors expressing HER-2/neu. Here we showed that virosomes, which consist of reconstituted viral envelopes without viral genetic material, can act as a carrier and an adjuvant for a truncated protein pNeuECD. Mice vaccinated with pNeuECD either encapsulated in virosomes or bound to the virosomal membrane (Vir-pNeuECD), generated rNeu-specific humoral and cytotoxic immune responses. In addition, Vir-p(NeuECD) induced significant tumor rejection and additionally did not lead to delayed tumor formation when compared with free pNeuECD in complete Freund's adjuvant. There was no difference between the virosomal constructs. Taken together these results suggest that virosomes, as clinically approved safe vaccines, can be used to elicit both humoral and cell-mediated responses against TAAg and induce tumor rejection. Our model is providing important preclinical data to design human vaccination trials for patients with tumors overexpressing HER-2/neu, either as a primary vaccination or as a boost in combination with other vaccines in a context of an adjuvant treatment plan.