Primitive hematopoietic cell populations reside in the spleen: Studies in the pig, baboon, and human.
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).


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.


CONCLUSIONS
The adult spleen is a relatively rich source of very primitive HPCs, possibly hematopoietic stem cells (HSCs), and may be of therapeutic value.
Dor
Frank J M F
FJ
Transplantation Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Boston, Mass., USA.
Ramirez
Mario L
ML
Parmar
Kalindi
K
Altman
Erica L
EL
Huang
Christene A
CA
Down
Julian D
JD
Cooper
David K C
DK
D000328:Adult; D000818:Animals; D001854:Bone Marrow Cells / Q000276:immunology; D003114:Colony-Forming Units Assay; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells / Q000145:classification / Q000166:cytology* / Q000276:immunology; D006801:Humans; D016130:Immunophenotyping; D008297:Male; D008875:Middle Aged; D010215:Papio; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis; D013154:Spleen / Q000166:cytology* / Q000276:immunology; D013552:Swine
D019009:Proto-Oncogene Proteins c-kit