Immunological enhancement of hybrid teratomas derived from yolk sac

Visceral yolk sac displaced outside the uterus after fetectomy differentiates into benign teratomas. This differentiation only occurs in a syngeneic pregnancy but never in hybrid pregnancy. Hybrid teratomas, however, were obtained after the induction of active or passive immunological enhancement. These hybrid teratomas, although smaller than the syngeneic, contained tissues derived from the three germ layers.