An update of circulating rare cell types in healthy adult peripheral blood: findings of immature erythroid precursors.

Background: Circulating rare cells (CRCs) are benign or malignant minuscule events in the peripheral blood or other bodily fluids. The detection and quantification of certain CRC types is an invaluable or proposed candidate biomarker for diagnosis, prognosis and prediction of various pathological conditions. The list of CRC types and biomarker applicability thereof continues to expand along with improvements in cell selection technology. Past findings may suggest commonness of healthy donor peripheral blood circulating mature erythroblasts. This work suggests the occurrence of morphologically distinct bone marrow native circulating early erythroid precursors that we intend to add to the list of CRCs.

Methods: We tested 15 healthy individuals that varied in age and gender employing a negative cell selection assay based on magnetic bead technology to characterize healthy adult circulating CD45 negative cell events using cell surface markers CD71 and glycophorin-A.

Results: Positive events were detected and varied in cell and nuclear size ranging between 7.5 µm till 15 µm and 4.5 till 9.2 µm, respectively with distinct appearance under bright field microscope. Cell rarity increased with cell and nuclear size. Largest cells exceeded 13.5 µm in cell diameter and were found in 7 out of 15 donors.

Conclusions: Circulating erythroid precursors occur at different stages of maturation and may be part of the benign CRC spectrum.