CD123

Summary

CD123 is the alpha-chain of the receptor for IL-3 IL-3ra . CD123 is expressed on many though not all leukaemic blast cells, but is largely absent from normal precursors including immature haematogones (although it is detected on more mature haematogones). Diagnostically the principle useful property of CD123 relates to its high level of expression on typical hairy cells although it can have value in other disorders (see below).

Diagnostic Use

• In acute leukaemia its diagnostic value is limited since its expression may be variable, although high expression is seen in KMT2A rearrangements and FLT3-ITD mutations
• CD123 is also expressed by early lymphoid precursors
• In blastic plasmocytoid dendritic cell neoplasms (BPDCN) CD123 is frequently expressed and forms part of the diagnostic criteria
• In B-LPD a high level of CD123 has value in the identification of hairy cell leukaemia where high expression is expected, though overall expression of CD123 is probably a less reliable indicator of HCL than CD103 and CD25

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