Immunobiology of complete molar pregnancy and gestational trophoblastic tumor.

The unique curability of gestational trophoblastic tumors may in part be attributable to a host immunologic response. The occurrence of rapidly progressive and fatal choriocarcinoma may be favored by histocompatibility between patients and their partners. However, histocompatibility is not a prerequisite for the development and persistence of gestational choriocarcinoma. The expression of HLA by choriocarcinoma cells in culture is enhanced following incubation with gamma-interferon and this may be of both biologic and clinical significance. Complete molar pregnancy is a complete allograft because all molar chromosomes are of paternal origin. Patients with complete mole are sensitized to paternal HLA antigen which is expressed in molar tissue. Other polymorphic antigen systems including trophoblast-leukocyte common antigens and placental-type alkaline phosphatase are also expressed in molar tissue. We have studied the immunopathology of the molar implantation site to investigate possible humoral and cellular immune responses. The relationships among normal placenta, complete mole and choriocarcinoma are not clearly understood. The pattern of expression of oncofetal antigens in these three gestational tissues may be used to assess trophoblastic differentiation. In studies to date, molar trophoblast has the same pattern of expression of oncofetal antigens as normal placental trophoblast. We will review recent advances in our understanding of the immunobiology of gestational trophoblastic disease and suggest new directions for further research.