Abstract
Several tumour-forming cell lines are known to secrete the precursor of a lysosomal cysteine proteinase, procathepsin L. The function in tumour growth and proliferation of this neutral-pH-labile proteinase or its precursor outside lysosomes is as yet unknown. Murine myeloma cells (P3X63Ag8.653) secrete procathepsin L and exhibit a high potential for malignant tumour growth and metastasis. Such cells were fused with spleen cells of mice immunized with cathepsin L. Clones of the resulting hybridoma cells continued to secrete procathepsin L, but also secreted the antibody to cathepsin L. Here we show that the hybridoma cells producing an antibody to cathepsin L have, to a great extent, lost the potential that they otherwise exhibit for inducing solid tumours after implantation into mice.