Selection of an Immunoresistant Moloney Lymphoma Subline With Decreased Concentration of Tumor-Specific Surface Antigens2

Abstract

The ascites form of the Moloney lymphoma YAC is highly sensitive to the cytotoxic action of Moloney-specific antiserum in vitro.and carries a high concentration of Moloney-specific surface antigens, as judged by quantitative absorption and membrane immunofluorescence tests. We attempted to establish an immunoresistant subline by prolonged immunoselection in vitro.and in vivo. Serial exposure to cytotoxic antiserum, in the presence of complement, before each inoculation during 20 passages did not lead to a stable immunoresistant subline, although occasionally cytotoxic sensitivity decreased temporarily. Subsequently, the same subline was subjected to in vivo selection, by inoculation into preimmunized syngeneic mice. A stable immunoresistant subline YAC-IR could be isolated from a preimmunized recipient inoculated with 10³ cells. YAC-IR cells were completely resistant to Moloney-specific cytotoxicity but maintained full sensitivity to isoantisera directed against H-2 antigens. Their Moloney-specific surface antigen concentration showed an approximately tenfold decrease in quantitative absorption tests. In the membrane immunofluorescence tests, surface staining with diluted Moloney antisera decreased uniformly, but the proportion of reactive cells, comprising 80–90% of the cell population, remained unchanged. The difference in the antigenicity of YAC and YAC-IR did not appear to be due to a change in cellular localization, with diminished surface expression, since there was an analogous difference when cell homogenates were compared. The decreased antigen concentration and the immunoresistance of the YAC-IR subline were stable and showed no reversion after 13 passages in untreated syngeneic hosts. Two or three passages through hosts neonatally infected with, and immunologically tolerant to, the Moloney virus resulted in partial or full reversion to sensitivity, however. Preliminary absorption experiments indicated that the YAC-IR line has a slightly higher surface expression of H-2^a isoantigens than the YAC line. The two lines did not differ in immunogenicity, as judged by their ability to induce the formation of anti-Moloney antibodies.