Diabody 31, a bispecific therapeutic antibody, is a heterodimer comprised of two types of chimeric single-chain variable fragments (scFv), that has been identified as a clone with high cytotoxicity against cancer cells. Diabody 31 is inactive as a homodimer and monomer, yet active as a heterodimer in solution. Herein, we examined the association between two kinds of diabodies, LH- and HL type, based on the behavior of four kinds of their constituent chimera scFvs, by size analysis. More than half of the LH diabody fraction, including two types of chimeric scFV that were equally expressed, and nearly all HL diabody fraction components, including one chimeric HL-L scFv, were in inactive form and changed components dynamically as time passed. The association of these diabodies corresponded to that of the scFv chimera, indicating that analysis of these chimeras could predict diabody quality. Furthermore, addition of the deficient HL-R chimera scFv, comprised of an unbalanced chimeric scFv ratio, to the HL diabody fraction increased cancer cell cytotoxicity, with maximal effects obtained upon repeating the process five times. These findings provide insights into the efficient construction of a functional diabody by noting the characteristics of associated diabodies and the molar ratio of expressed chimera scFvs.
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