Primitive hematopoietic cell populations reside in the spleen: Studies in the pig, baboon, and human
Received 30 March 2006; received in revised form 9 June 2006; accepted 23 June 2006.
Objective
We previously observed high levels (>40%) of multilineage hematopoietic cell chimerism following spleen transplantation across full MHC barriers in immunosuppressed miniature swine. We therefore investigated the spleen as a source of hematopoietic progenitor cells (HPCs).
Materials and methods
Specific cell-surface markers were used to identify HPCs in the spleen and bone marrow (BM) of young adult (n = 15) and fetal (n = 9) miniature swine by flow cytometry. Hoechst dye-effluxing side population (SP) cells were analyzed in adult spleen, BM, and blood for their expression of c-kit. Functional HPC activity of varying repopulation potential in vitro was investigated by the ability of spleens and BM to give rise to colony-forming units (CFUs) and cobblestone area–forming cells (CAFCs) in long-term stromal cultures. Studies were also carried out on baboon and human spleens and BM.
Results
Spleen c-kit+ cells co-expressed more lymphoid markers, but equal myeloid markers, when compared with BM c-kit+ cells. BM and spleen both contained significant percentages of c-kit+ SP cells. Although the frequency of early-forming CFUs in the spleen was only 0.1 to 1.3% of that in the BM, the frequency of CAFCs developing after 8 weeks in culture was comparable to that of BM. Secondary CFUs in long-term culture-initiating cell assays confirmed the presence of long-term repopulating cells at comparable frequencies in spleen and BM. Similar findings were found with regard to baboon and human spleen cells.
Conclusion
The adult spleen is a relatively rich source of very primitive HPCs, possibly hematopoietic stem cells (HSCs), and may be of therapeutic value.
aTransplantation Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, Mass., USA
bDepartment of Surgery, Erasmus MC, Rotterdam, The Netherlands
cDepartment of Radiation Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Mass., USA
dGenetix Pharmaceuticals, Inc., Cambridge, Mass., USA
Offprint requests to: David K.C. Cooper, M.D., Ph.D., F.R.C.S., Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Center, Biomedical Sciences Tower East, Room E1550A, 200 Lothrop Street, Pittsburgh, PA 15261, USA
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