Mobilization of plasma cells in healthy individuals treated with granulocyte colony-stimulating factor for haematopoietic stem cell collection

Abstract

In mice, the plasma cell (PC) niche in the bone marrow is close to the haematopoietic stem cell (HSC) niche. We investigated whether PCs can be mobilized into the peripheral blood (PB) in healthy donors receiving granulocyte colony-stimulating factor (G-CSF) for the induction of HSC mobilization into the PB. G-CSF increased the count of circulating PCs 6-fold, that of circulating B lymphocytes 4-fold and that of circulating HSCs 44-fold. Mobilized circulating PCs comprised CD138(-) (62·2%) and CD138(+) (37·8%) PCs, the latter being more mature based on increased CD27, CD38 and cytoplasmic immunoglobulin expression. Mobilized PCs had a phenotype close to that of steady-state PB PCs or in vitro generated PCs, but they expressed L-selectin only weakly. Finally, a median value of 0·4 × 10(6) /kg donor PCs - one-thirtieth of the overall PC count in a healthy adult - was grafted into patients, which could contribute to immune memory recovery.

Figure 1

B lymphocytes and plasma cells present in leukapheresis products from healthy donors. Flow cytometric discrimination between B lymphocytes and plasma cells present in leukapheresis products from healthy donors stained for CD19, CD20, CD38, CD138, and membrane/cytoplasmic immunoglobulin kappa and lambda light chains (m/cyIgκ or m/cyIgλ) was performed. After gating out cell doublets, B lymphocytes were defined as m/cyIgκ⁺ or m/cyIgλ⁺ cells with a CD19⁺CD20⁺CD38^−/+CD138⁻ immunophenotypic profile (green dots). Plasma cells were gated as m/cyIgκ- or m/cyIgλ-expressing cells, which were CD20⁻ and showed high expression of CD38 (cIg⁺CD19^−/+CD20⁻CD38⁺⁺cells). Mobilized plasma cells comprised both CD138⁻ cells (pink dots) and CD138⁺cells (purple dots). Other cell populations in the sample are shown as grey dots. Data from one experiment representative of six experiments are shown. The table indicates mean percentages of B lymphocytes and CD38⁺⁺ plasma cells in leucocytes, and mean percentages of CD138⁻ plasmablasts and CD138⁺ plasma cells in CD38⁺⁺ plasma cells.

Figure 2

Expression of activation and homing molecules by peripheral blood (PB) mobilized B lymphocytes and mobilized CD138⁻ plasmablasts or CD138⁺ plasma cells. Detailed immunophenotypic profiles of B lymphocytes and both CD138⁻ plasmablasts and CD138⁺ plasma cells in leukapheresis samples from healthy donors analysed by multiparameter flow cytometry were obtained. The phenotypic profiles of B lymphocytes and both CD138⁻ plasmablasts and CD138⁺ plasma cells were defined after gating on CD19⁺CD20⁺CD38^−/+CD138⁻ B lymphocytes (green histograms), and both CD19^−/+CD20⁻CD38⁺⁺CD138⁻ (pink histograms) and CD19^−/+CD20⁻CD38⁺⁺CD138⁺ (purple histograms) cells, respectively. Grey histograms display the corresponding negative control for the same cell populations. Data from one experiment representative of between six and 30 experiments are shown. Values displayed in each panel indicate the mean percentage of positive cells from the gated cell population and the mean staining index obtained for each specific monoclonal antibody (mAb) used is shown in brackets. *, # or § indicates a significant difference in the staining index (P≤ 0.05; paired Student’s t-test) between B lymphocytes and CD138⁻ plasmablasts (*), between CD138⁻ plasmablasts and CD138⁺ plasma cells (#), and between B lymphocytes and CD138⁺ plasma cells (§).