Immunogenicity of Leukemia L1210 Cells After Neuraminidase Treatment<xref ref-type="fn" rid="FN1">2</xref>

Abstract

The kinetics of sialic acid release by Vibrio cholerae (VC) neuraminidase from L1210 tumor cells and the subsequent change of immunogenicity of such cells in OBA/2Ha mice were studied. Various concentrations of neuraminidase resulted in 3 possible conditions of immunogenicity of L1210 cells. 1) At low enzyme concentrations, cleavage of neuraminidase-susceptible sialic acid was incomplete and all recipients died from tumor after inoculation with enzymatically treated cells. 2) Enzyme concentrations of 20–50 IU/2.5 × 107 cells/ml incubation medium represented the optimal condition for L1210 cell treatment: Oncogenicity was lost and mice could be immunized. All immunized mice were refractory to 105 untreated L1210 cells, which represents about 100,000 times the LD50 of this tumor in DBA/2Ha mice. 3) Incubation of L1210 tumor cells with neuraminidase >75 IU caused loss of oncogenic properties, but at the same time, immunogenicity of such treated cells was eliminated. This reduced immunogenicity was evidenced by a decreasing fraction of mice resistant to the challenge by 105 untreated L1210 cells. Treatment of L1210 cells with VC neuraminidase caused a significant release of protein-bound sialic acid, e.g., N-acetylneuraminic acid and N-glycolylneuraminic acid. In addition to low molecular-weight substances, radioactive glycoprotein appeared in the incubation medium, irrespective of the incubation condition. Thus the increased immunogenicity in VC neuraminidase- treated L1210 cells is most likely attributable to the enzymatic removal of sialic acid rather than to release of a protein from tumor cell surfaces. Other neuraminidases and enzymes did not eliminate the oncogenicity of leukemia L1210; this precluded a study of their effect on immunogenicity.