Induction of IgM, IgA and IgE antibodies in colorectal cancer patients vaccinated with a recombinant CEA protein.
Previous clinical studies have indicated that natural IgM antibodies have the ability to induce apoptosis of tumor cells but IgE and IgA may also mediate tumor cell killing (in addition to IgG). The aim of the study was to analyse induction of IgM, IgA and IgE antibodies in patients vaccinated with the tumor associated antigen CEA. Twenty-four resected CRC patients without macroscopic disease were immunized seven times with CEA ± GM-CSF. Four different dose schedules were used over a 12-month period. IgM, IgA and IgE antibody responses against recombinant CEA were determined by ELISA. Patients were monitored immunologically for 36 months and clinically for 147 months. GM-CSF significantly augmented the anti-CEA response for all three antibody classes. Low dose of CEA tended to induce a higher IgM, IgA or IgE anti-CEA antibody response than higher. Anti-CEA IgA antibodies could lyse CEA positive tumor cells in antibody dependent cellular cytotoxicity (ADCC) as well as in complement dependent cytotoxicity (CDC). A significant correlation between survival and high IgA anti-CEA titers was noted (p = 0.02) irrespective of GM-CSF treatment. The observation that IgA anti-CEA antibodies were cytotoxic and associated with improved survival might indicate that also these antibodies may exert a clinical anti-tumor effect.