Influence of IL-3 functional fragment on cord blood stem cell ex vivo expansion and differentiation

Background: Recombinant human interleukin-3 (rhIL-3) is a multiple hematopoietic growth factor, which enhances stem cell expansion and hematopoiesis regeneration in vitro and in vivo, when administrated in combination with other cytokines. However, the structure-function study of rhIL-3 remains rarely studied, so far. The purpose of this study was to recognize the short peptide with similar function as rhIL-3, and assess the hematopoietic efficacy in umbilical cord blood (UCB) stem cell culture as well. Methods: Tw o novel monoclonal antibodies (mAb) (C1 and E1) were generated against rhIL-3 using hybridoma technique. Eleven short peptides were depicted and synthesized to overlap covering the full length sequence of rhIL-3. ELISA was employed to distinguish the antibody-binding peptide from the negative peptides. In addition, the multi-potential hematopoiesis capabilities of the positive peptides were evaluated by adding 25 ng/mL of each peptide to the culture medium of hematopoietic stem cells (HSCs) derived from UCB. Total nucleated cell number and the CD34⁺ cell number from each individual treatment group were calculated on day 7. Correlated antibodies at 0.5 or 2 molar fold to each peptide were also tested in the stem cell expansion experiment, to further confirm the bioactivity of the peptides. Results: Tw o peptides were recognized by the novel generated antibodies, using ELISA. Peptide 3 and 8 exhibited comparable hematopoiesis potentials, with 25.01±0.14 fold, and 19.89±0.12 fold increase of total nucleated cell number on day 7, respectively, compared with the basal medium control (4.93±0.55 fold). These biological effects were neutralized by adding the corresponding mAb at a dose dependent manner. Conclusions: Our results identified two specific regions of rhIL-3 responsible for HSC proliferation and differentiation, which were located from 28 to 49 amino acids (P3), and 107 to 127 amino acids (P8), respectively. The short peptide 3 and 8 might act synergistically, which could serve as an economic substitute to rhIL-3 in research laboratory.