Multiple Tolerization Reduces Antibody Binding Against Tolerogen Cells: Implications for the Production of Monoclonal Antibodies

Establishment of Membrane-Bound IgA1-Specific Antibody Possessing Antibody-Dependent Cellular Cytotoxicity Activity

Therapeutic agents targeting B cells, such as rituximab, have been proven to be effective in several diseases. However, since this therapy targets the whole B cell population, there are still concerns about critical adverse events. Therefore, a new type of antibody that can specifically deplete a particular type of B cell may have the potential to become an efficient and safer therapy. Membrane-bound IgA1 (mIgA1) is expressed on soluble IgA1 (sIgA1) producing B cells and/or their precursor, B cells. Although most of the amino acid sequence in the N-terminal regions of the extracellular domains of mIgA1 and sIgA1 is shared, there is a membrane type-specific region, named the membrane-bound immunoglobulin isotype-specific (migis-α) region, at the membrane-proximal region of mIgA1. We hypothesized that the migis-α region would be a suitable antigen for therapeutic antibodies to target mIgA1-expressing B cells without binding to sIgA1, which may cause undesired adverse effects and poor pharmacokinetics (PK). We established two anti-migis-α monoclonal antibodies (mAbs), KM4641 and KM4644, by immunization of the synthetic peptide corresponding to an migis-α region. These mAbs both showed robust binding to mIgA1-expressing transfectant cells. As we expected, neither mAbs bound to sIgA1 and we found that the mAbs recognized different seven to eight amino acid sequences within the migis-α region. Furthermore, the rat-human chimeric type of both mAbs showed antibody-dependent cellular cytotoxicity against mIgA1-expressing transfectant cells. Taken together, this study showed that established mAbs have therapeutic potential in IgA-related diseases, such as IgA nephropathy.

Multiple Tolerization Subtractive Immunization (MTSI) Protocol: Effects on Mice and Monoclonal Antibody Specificity

Monoclonal antibodies (mAbs) have been a valuable tool to elucidate several biological processes, such as stem cell differentiation and cancer, and contributed to virtually all areas of biomedical sciences. Yet, it remains a challenge to obtain mAbs specific to poorly expressed epitopes, or to epitopes that are actually involved in important biological phenomena, such as cell differentiation and metastasis. Drug-induced subtractive immunization, and recently the multiple tolerization subtractive immunization (MTSI) technique, reported by our group, have the potential to level up the field, as they direct the host´s immune response towards these epitopes. However, due to cyclophosphamide (CY) treatment, high mice mortality can be observed, and only a few data are available on how these techniques affect the immune system of mice. Tolerogen and immunogen cells, RWPE-1 and PC-3 cells, respectively, were individually seeded at 2 × 104 cells/cm2, and then adjusted to 2 × 106 cells per mouse before immunization, which was conducted in a subtractive approach (MTSI) with CY. Immunosuppression of mice was recorded via total white blood counting, as well the reactivity of circulating polyclonal antibodies (pAbs). General parameters, including weight, physical appearance, and behavior on mice subjected to three different concentrations of CY were recorded. mAbs were obtained using classical hybridoma techniques, using the spleen of immunized mice. After purification, antibodies were characterized by Western blotting, and Indirect immunofluorescence. In conclusion, all CY dosage were efficient in creating an immunosuppression state, but only the 100 mg/kg body weight was feasible, as the others resulted in extensive mice mortality. pAbs obtained in the peripheral blood of mice showed more reactivity towards tumor cells. MAbs 2-7A50 and 2-5C11 recognized antigens from tumor cells, but not from their non-tumor counterparts, as shown in western blotting and immunofluorescence assays. MTSI technique was successful in generating mAbs that recognize tumor-specific antigens.