Hemocyanins, the huge
oxygen-transporting
glycoproteins of some mollusks, are used as immunomodulatory
proteins with proven anti-
cancer properties. The biodiversity of
hemocyanins has promoted interest in identifying new anti-
cancer candidates with improved immunological properties.
Hemocyanins promote Th1 responses without known side effects, which make them ideal for long-term sustained treatment of
cancer. In this study, we evaluated a novel
hemocyanin from the limpet/gastropod Fissurella latimarginata (FLH). This
protein has the typical hollow, cylindrical structure of other known
hemocyanins, such as the
keyhole limpet hemocyanin (KLH) and the Concholepas
hemocyanin (CCH). FLH, like the KLH
isoforms, is composed of a single type of
polypeptide with exposed N- and O-linked
oligosaccharides. However, its immunogenicity was significantly greater than that of KLH and CCH, as FLH induced a stronger humoral immune response and had more potent anti-
tumor activity, delaying
tumor growth and increasing the survival of mice challenged with B16F10
melanoma cells, in prophylactic and therapeutic settings. Additionally, FLH-treated mice demonstrated increased IFN-γ production and higher numbers of
tumor-infiltrating CD4(+) lymphocytes. Furthermore, in vitro assays demonstrated that FLH, but not CCH or KLH, stimulated the rapid production of pro-inflammatory
cytokines (IL-6, IL-12, IL-23 and TNF-α) by dendritic cells, triggering a pro-inflammatory milieu that may explain its enhanced immunological activity. Moreover, this effect was abolished when deglycosylated FLH was used, suggesting that
carbohydrates play a crucial role in the innate immune recognition of this
protein. Altogether, our data demonstrate that FLH possesses increased anti-
tumor activity in part because it activates a more potent innate immune response in comparison to other known
hemocyanins. In conclusion, FLH is a potential new marine adjuvant for immunization and possible
cancer immunotherapy.