Human chorionic gonadotropin as a model for a fetal antigen

Human chorionic gonadotropin (hCG) has an important biological function and has clinical use as a hormone, yet its applications as an antigen are also numerous. Pregnancy tests have brought immunological reactions into the high street pharmacy and the home. As a secreted antigen hCG provides for choriocarcinoma of gestational or germ cell origin our closest approximation to the ideal tumour marker. It is unique in providing the basis of a biochemical screening test for a specific cancer in a high risk population. It has a valuable role in diagnosis and prognosis and in monitoring this disease and detecting tumours is unknown. It has been investigated as a target for radioimmunolocalization studies with 131I-labelled anti-hCG antibodies, and found useful in some patients. Attempts have been made to improve the technique using liposomes containing a second antibody. As a target for antibody therapy in fertility control and oncology, by active or passive immunization methods, much depends on whether hCG functions as a cell membrane antigen.