Should cultivated exoerythrocytic parasites be considered as a source of antigen for a malaria vaccine?

Routine procedures for growing exoerythrocytic stages of avian malaria parasites in continuous culture have been available for many years. This system, adapted for the cultivation of mammalian forms, would have certain advantages in vaccine production, the great advantage being the potential for self-replication by both the host cell and the parasite. Many obstacles must be overcome, however, before efforts in this direction can be successful. The recent demonstration that merozoites of the exoerythrocytic cycle are immunogenic supports the view that efforts should be made to develop a mammalian culture system based on the exoerythrocytic stage.