Priming with recombinant human hematopoietic cytokines before bone marrow harvest expands in vivo and enhances ex vivo recovery of myeloid progenitors in short-term liquid cultures.

BACKGROUND AND AIM

Short-term liquid marrow cultures (STLMC) are a potential source for autografting. We have previously shown that the quality of such grafts from transplantation candidates may be improved by hematopoietic cytokine support, especially if purified CD34-positive progenitors are cultured. The aim of this preclinical work was to quantitate ex vivo recovery of myeloid progenitors (colony-forming units-granulocyte/macrophage [CFU-GM]) in STLMC before and after short-term, in vivo treatment with recombinant human granulocyte colony-stimulating factor (rhG-CSF), granulocyte-macrophage colony-stimulating factor (rhGM-CSF), or interleukin-3 (rhIL-3).

EXPERIMENTAL SETUP

Twenty-two sequential patients in marrow remission for hematological malignancies and eligible for autologous marrow transplantation received rhG-CSF or rhGM-CSF for 5 days or rhIL-3 for 10 days before marrow harvest. Marrow samples before and after in vivo priming were studied for CFU-GM in pre- and post-STLMC.

RESULTS

After priming with rhG-CSF, rhGM-CSF, or rhIL-3, the number of isolated light-density cells increased nine-, six-, and two-fold, respectively. The total number of sampled (18 mL marrow) myeloid progenitors preculture (day 7/14 CFU-GM x 10(4) increased significantly from median 0.7/1.1 before to 37.3/26.7 after priming with rhG-CSF (n = 8) and from 5.6/3.4 before to 46.6/44.9 after priming with rhGM-CSF (n = 8) but remained unchanged (3.7/1.5 to 3.6/5.7) after priming with rhIL-3 (n = 6). The number of myeloid progenitors postculture (day 7/14 CFU-GM x 10(4) per 18 mL marrow) in cytokine-supported STLMC significantly increased from median 0.3/0.6 before to 7.0/5.3 after priming with rhG-CSF and from 1.9/1.6 before to 24.4/14.4 after priming with rhGM-CSF but remained unchanged (0.4/0.6 to 0.4/0.2) after priming with rhIL-3. Cytokine-primed and purified CD34+ marrow cells may be expanded in STLMC by a cytokine-driven differentiation into late myeloid progenitors and endstage cells.

CONCLUSION

In vivo priming of bone marrow cells by hematopoietic cytokines significantly increases the recovery of harvested pre- and postculture myeloid progenitors. During cytokine-supported STLMC, early myeloid progenitors may differentiate into a "very late" progenitor pool with a potential for fast marrow regeneration. The number of such progenitors in cytokine-supported short-term liquid cultures may be sufficient for fast myeloid engraftment and complete peripheral blood or marrow stem-cell support after high-dose chemotherapy.