B-1 cells secrete antibodies with anti-tumor properties

Abstract It is well known that B-1 cells are the main B cell subset responsible for the production of natural antibodies. Several studies suggest that natural IgM antibodies play an important role in immunosurveillance against transformed cells in humans, preferentially binding glycolipids and carbohydrate structures. NeuGcGM3 ganglioside is a sialic acid containing glycosphingolipid that has been considered an attractive target for cancer immunotherapy since is not naturally expressed in healthy human tissues but is overexpressed in several tumors. We previously described the existence of cytotoxic anti-tumor antibodies against NeuGcGM3 ganglioside in healthy young subjects. However, whether this anti-tumor antibody response has a “natural origin” is unknown. With the present work we aimed to elucidate whether B-1 cells have the potential to secrete anti-NeuGcGM3 antibodies. First we generated four mouse monoclonal antibodies from Balb/c mouse peritoneal B cells. All hibridomas secreted IgM which bound NeuGcGM3 but no other gangliosides and recognized and killed NeuGcGM3 positive tumor cells. All the anti-NeuGcGM3 IgM-producing hybridomas were CD5+ B-1 cells. Then naïve, memory, plasma and B-1 cells were purified from healthy human donors PBMC and stimulated in vitro to produce immunoglobulins. All the B-1 cell supernatants reacted with NeuGcGM3 and most of them also recognized tumor cells expressing this ganglioside. Only 40% of memory samples, and none from naïve or plasma cells, recognized this antigen. These data suggest a protective role for B-1 cells against malignant cells through the production of natural antibodies reactive to tumor associated antigens such as NeuGcGM3 ganglioside.