Production of a High-affinity Monoclonal Antibody Reactive with Folate Receptors Alpha and Beta.

ABSTRACT

Folate receptors α (FRα) and ß (FRß) are two isoforms of the cell surface glycoprotein that binds folate. The expression of FRα is rare in normal cells and elevated in cancer cells. Thus, FRα-based tumor-targeted therapy has been a focus area of laboratory research and clinical trials. Recently, it was shown that a significant fraction of tumor-associated macrophages expresses FRß and that these cells can enhance tumor growth. Although FRα and FRß share 70% identity in their deduced amino acid sequence, a monoclonal antibody (MAb) reactive with both receptors has not been developed. A MAb that can target both FRα-expressing cancer cells and FRß-expressing tumor-associated macrophages may provide a more potent therapeutic tool for cancer than individual anti-FRα or anti-FRß MAbs. In this study, we developed a MAb that recognizes both FRα and FRß (anti-FRαß). The anti-FRαß specifically stained trophoblasts and macrophages from human placenta, synovial macrophages from rheumatoid arthritis patient, liver macrophages from cynomolgus monkey and common marmoset, and cancer cells and tumor-associated macrophages from ovary and lung carcinomas. Surface plasmon resonance showed that the anti-FRαß bound to soluble forms of the FRα and FRß proteins with high affinity (KD=6.26×10(-9) M and 4.33×10(-9) M, respectively). In vitro functional analysis of the anti-FRαß showed that this MAb mediates complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity, and antibody-dependent cellular phagocytosis of FRα-expressing and FRß-expressing cell lines. The anti-FRαß MAb is a promising therapeutic candidate for cancers in which macrophages promote tumor progression.