Production of Heterologous Antibodies Specific for Murine B-Cell Leukemia (BCL₁) Immunoglobulin by Immunization with Synthetic Peptides Homologous to Heavy Chain Hypervariable Regions

Three peptides homologous to each heavy chain hypervariable region expressed by murine B-cell leukemia, BCLi, were synthesized in vitro by solid phase peptide synthesis. All three synthetic peptides elicited responses in rabbits which were immunized with synthetic peptide or synthetic peptide conjugated to the carrier keyhole limpet hemocyanin. Six individual rabbits were immunized, five of which responded by producing antisera which react specifically in radioimmunoassay with the synthetic peptide used as immunogen. One antiserum has specificity for the peptide homologous to the first hypervariable region, three antisera have specificity for the peptide homologous to the second hypervariable region, and one has specificity for the peptide homologous to the third hypervariable region. The five antisera with high titers of antibody recognizing synthetic peptide also specifically recognize native immunoglobulin M secreted by BCLi tumor cells as demonstrated by immunoprecipitation followed by sodium dodecyl sulfaterpolyacrylamide gel electrophoresis and autoradiography. These five antisera do not show reactivity with immunoglobulin secreted by spleen cells from normal BALB/cAn mice or by B-cells from unrelated tumors and cell lines. However, as determined by absorption experiments, the majority of antibodies in each antiserum are directed against the respective synthetic peptide, and only a small portion are reactive with native immunoglobulin M. Nonetheless, these results indicate use of synthetic peptides as a potential alternative source of immunogen for production of antitumor antibody.