Antigenic Properties of Experimental Leukemias. II. Immunological Studies In Vivo With C57BL/6 Radiation-Induced Leukemias

Summary

The serum of C57BL/6 mice immunized against an A strain TL+(thymus leukemia antigen) spontaneous leukemia was highly cytotoxic for the cells of several C57BL/6 leukemias. Paradoxically, this was not associated with resistance in vivo to the inoculation of 2 TL+ C57BL/6 radiation-induced leukemias highly sensitive to TL antisera in vitro. Leukemia cells recovered after their outgrowth in immunized C57BL/6 mice lost their sensitivity to TL antisera in vitro and their ability to absorb specific cytotoxic activity from TL antisera. A single further passage of these cells in normal untreated C57BL/6 hosts was accompanied by complete restoration of sensitivity, even after 3 consecutive passages in immunized hosts. Immunoselection, inadequate complementation, or interference by blocking antibody might account for the outgrowth of TL+ leukemia cells in immunized hosts, but the present evidence does not favor these interpretations. More probably the temporary changes in antigenicity reflect an adaptational alteration affecting the entire population of leukemia cells.