The 4A5 monoclonal antibody binds to the glycosylated type I membrane protein ROR1 (Receptor-tyrosine-kinase-like Orphan Receptor 1). The ROR1 and ROR2 related proteins are highly conserved evolutionarily and are primarily expressed during embryogenesis. ROR1 is not expressed on normal peripheral blood lymphocytes. ROR1 is similar to tropomyosin receptor kinase (Trk family) neurotropic receptors and shares a cysteine-rich domain with Frizzled receptors for Wnt-family signaling proteins, which are involved in the regulation of embryogenesis and carcinogenesis. Furthermore, there is mounting evidence that aberrant ROR1 expression contributes to human malignancy.
The antibody was conjugated to BD Horizon™ BUV661 which is part of the BD Horizon Brilliant™ Ultraviolet family of dyes. This dye is a tandem fluorochrome of BD Horizon BUV395 with an Ex Max of 348-nm and an acceptor dye with an Em Max at 661-nm. BD Horizon Brilliant BUV661 can be excited by the ultraviolet laser (355 nm) and detected with a 670/25 filter and a 630 nm LP. Due to cross laser excitation of this dye, there may be significant spillover into channels detecting APC-like emissions (eg, 670/25-nm filter).
Due to spectral differences between labeled cells and beads, using BD™ CompBeads can result in incorrect spillover values when used with BD Horizon BUV661 reagents. Therefore, the use of BD CompBeads or BD CompBeads Plus to determine spillover values for these reagents is not recommended. Different BUV661 reagents (eg, CD4 vs. CD45) can have slightly different fluorescence spillover therefore, it may also be necessary to use clone-specific compensation controls when using these reagents.