, 1993, Abe et al., 1998, Nakano and Nagata, 2003, Davern

et al., 2008, te Velthuis et al., 2011 and Hoedemakers et al., 2012); many of the mAbs that we have produced against FLC do not bind FLC from up to a quarter of individual myeloma patients. The extent of FLC structural diversity is reflected in the LC gene structure. Thus, the κ immunoglobulin gene family contains 81 genes located on chromosome 2, of which, at least 40 functional genes are responsible for V region variability, giving rise to at least 4 major V region types (Vκ1, Vκ2, Vκ3, and Vκ4) (Sitnikova and Nei, 1998 and Davern et al., 2008). Further, there are 5 genes responsible for encoding the J region, and 1 constant region gene expressing 1 of 3 allotypic forms (κm1, κm2, κm3) ( Sitnikova and Nei, 1998, Davern et al., 2008 and Jefferis and Lefranc, 2009). The λ immunoglobulin gene family appears to Epacadostat mouse support more diversity, in that there are at least 40 functional genes responsible for V region variability that results in at least 5 major V region types (Vλ1, Vλ2, Vλ3, Vλ6, and Vλ8). Further, there are at least 5 genes responsible for encoding the J region, and up to 7 genes for the C PD-0332991 cell line region that gives rise to at least 3 C region isotypes (Cλ1, Cλ2/3, Cλ7) ( Solomon and Weiss, 1995 and Davern et al., 2008). FLC diversity is extended by somatic mutations in the encoding

genes and post-translational modifications of FLC. Given this multiplicity of human FLC structures, it is not surprising that it is difficult to produce mAbs that would detect the FLC from substantially all patients and neoplastic plasma cell clones. To be clinically reliable any new assay for FLC should be tested against a large number of serum and urine samples to show that the mAbs are at least close to the ideal of detecting FLC from all

patients and neoplastic plasma cell clones. In plasma samples containing SPTLC1 normal polyclonal FLC, obtained from healthy donors, each of the mAbs provided similar quantitation of absolute FLC levels. These samples were obtained from UK blood donors, which include persons up to the age of 65 years. It is likely that some of these donors had MGUS, and indeed, one donor found to have an abnormal FLC ratio detected by both the mAb assay and Freelite™, had a 30 g/L IgG λ paraprotein. Similarly, we cannot exclude the possibility that some donors had a degree of renal impairment. For both polyclonal and monoclonal λ FLC in a thousand consecutive serum samples, the two anti-λ FLC mAbs exhibited excellent correlations with each other, and displayed good clinical concordance with Freelite™. The diversity in FLC repertoire may explain the more divergent correlations demonstrated in this study between the mAb assay and Freelite™ for highly elevated monoclonal λ FLC paraproteins (see Fig. 4).