Hybrid Mouse Strains with the Growth of a P a R E N T a L T U M O R in Vivo

Suppressor cells have been shown to be involved in the regulation of immune responses m genetic nonresponder animals (1, 2), as well as in those animals which have been tolerized to certain ant igens (3, 4). Cells exhibiting suppressor activity have been recently identified in the spleens of tumor-bearing hosts (5, 6). These cells were able to nonspecifically suppress a variety of immune responses by normal syngeneic cells. It is not known whether this type of suppression observed in tumor-bearing animals involves immunological mechanisms such as those responsible in the ant igen systems described above, or whether the suppression is due to overloading the immune system of the host with tumor cells.