Biologic activity of native CD30L expressed on the surface of malignant cells from myeloid (A) and lymphoid (B) tumors as assessed by proliferation assays for HDLM-2 (□) or Karpas 299 (▪) in the presence of a titration of paraformaldehyde-fixed leukemia/lymphoma cells. Primary leukemia/lymphoma cells (0.5 × 105/mL to 2.0 × 105/mL) were fixed in 0.5% paraformaldehyde and cocultured in 96-well U-bottomed microplates with 1 × 105 cells/mL HDLM-2 or Karpas 299 cells for 72 hours. Cultures were pulsed with 0.5 μCi/well 3H-thymidine for the final 12 hours of culture, harvested onto glass fiber membranes, and counted in a liquid scintillator β-counter. As further controls, 2.0 × 105/mL paraformaldehyde-fixed leukemia/lymphoma cells were cocultured as described above with HDLM-2 (□ at the far right) or Karpas 299 (▪ at the far right) cells in the presence of an excess (10 mg/mL) of soluble CD30-Fc fusion protein. Results are expressed as cpm ± SEM of quadruplicate cultures and are representative of three independent experiments.
