Lethal factor (LF) is a component of anthrax lethal toxin (LeTx).was approximately one-third that of 3C16C3 (0.63 g/ml) in the in vitro LeTx-neutralization assay. The 5B13B1 antibody, which had the highest neutralizing activity, provided perfect protection against LeTx challenge in an in vivo LeTx neutralization assay using Fisher 344 rats. In addition, the antibody showed pre-and postexposure prophylactic effects in the animal experiments. This is the first report that an MAb binding to domain III of LF has neutralizing activity against LeTx. The 5B13B1 antibody may be useful in prophylaxis against anthrax poisoning.

Thrombopoietin (TPO) is a megakaryocyte growth and differentiation factor that is currently being investigated as a therapeutic for cancer patients undergoing myelosuppressive chemotherapy. We generated monoclonal antibodies (MAbs) specific for human thrombopoietin (hTPO) by genetic immunization using an hTPO expression plasmid and an adjuvant plasmid that encodes mouse granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). All genetically immunized mice exhibited a high humoral immune response. Splenocytes from these mice were used to generate hybridomas. Two MAbs, designated 2B9A10 and 4C16B15 (of IgG1 and IgG3 isotypes, respectively), were subsequently selected and produced. They specifically recognized and precipitated recombinant hTPO produced by mammalian cells and were effective in sandwich enzyme-linked immunosorbent assays (ELISAs) for hTPO quantitation. Our results demonstrate that these MAbs should be useful for purification and quantitation of hTPO in clinical and laboratory settings.