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BRIEF REPORT
Renal ossicles are ossified structures developed after the
implantation of a bone marrow (BM) plug beneath the kidney capsule. The
authors have investigated the origin of the hematopoietic cells in
murine renal ossicles by conducting sex-mismatched implants into
Ly-5 congenic mice. BM plugs from transgenic mice provided additional genotypic tracers. Flow cytometry analyses on nonadherent cells from long-term cultures established with ossicles excised at 17 to 40 weeks postimplantation evidenced the presence of 5% to 70% of
donor-derived myeloid cells. The genetic analysis of the day 12 colony-forming unit (CFU-S12) population in
ossicles excised at 10 to 40 weeks postimplantation revealed that 16%
to 93% of the colonies were of donor origin. Moreover, we describe for
the first time the presence of long-term repopulating cells of
donor origin in ossicles excised at 10 to 19 weeks postimplantation.
(Blood. 2000;96:2307-2309) The implantation of bone marrow (BM) plugs beneath
the murine renal capsule results in the generation of ossicles with
active hematopoiesis.1-3 The origin of the hematopoietic
and stromal cells in renal ossicles and in subcutaneously implanted BM
plugs and femurs has been investigated by means of chromosomal
markers2,4-8 and immunological techniques.8-10
These studies evidenced the donor origin of the stromal cells in these
transplantation models.8-10 On the other hand, the
pluripotent progenitors and differentiated cells lodged in these
ectopic hematopoietic foci have been shown to be predominantly of host
origin.2,7-9 In some instances, donor hematopoietic cells
have been detected longer than 6 months postimplantation,4,7,8 with an increasing ratio of donor versus host-derived contribution as the analysis period was
shortened.8
We have further investigated the nature of the hematopoietic
progenitors and repopulating cells (RCs) present in renal ossicles by
establishing long-term cultures (LTCs) and conducting spleen colony-forming unit (CFU-S) and repopulating assays. The origin of these precursors was unequivocally identified by the use of several
genetic (zfy-1 male and neomycin phosphotransferase [ neor] gene sequences) and phenotypic
(panleukocyte Ly-5 antigen) markers.
Mice
Long-term hematopoietic cultures
CFU-S and repopulating assays Cell suspensions from ground ossicles were intravenously injected into x-ray-conditioned recipients receiving a 24-hour split dose of 9.5 Gy for the CFU-S assay13 and 10 Gy for the repopulating assay. Irradiation was delivered at 1.03 Gy/min, 300 kV, and 12.8 mA (Philips MG324 equipment, Hamburg, Germany) (half-value layer: 3.2 mm Cu).Flow cytometry Samples were analyzed on an Epics ELITE ESP flow cytometer (Coulter, Hialeah, FL) after erythrocyte lysis with ammonium chloride and exclusion of nonviable cells by propidium iodide. The monoclonal antibodies (PharMingen, San Diego, CA) used included the phycoerythrin-coupled anti-CD45.1 (anti-Ly-5.1) and the fluorescein-conjugated anti-Ly-6G (anti-Gr-1).
Experimental model BM plugs from 2 femurs of transgenic Ly-5.2 female mice (F/Ly-5.2/neo) were implanted beneath the renal capsule of normal congenic male mice (M/Ly-5.1). The resulting ossicles were excised at periods longer than 10 weeks postimplantation. Each renal ossicle is coded with a number indicating the age (days postimplantation) followed by the transgenic strain (N1 or N2) used as BM donor. The origin of the hematopoietic progenitors lodged in renal ossicles was first investigated by anti-Ly-5.1 staining on supernatant cells from LTCs. These almost exclusively include myeloid cells (Gr-1+) in which the detection of Ly-5.1+ cells should result from ossicle-host-derived progenitors. On the other hand, the presence of Ly-5.1 cells in the supernatants
should result from donor-derived progenitors. The origin of the
CFU-S12 population and RCs was also investigated by
transplanting ossicle marrow cells into irradiated female recipients (F/Ly-5.2). The spleen colonies and lymphohematopoietic organs from the
reconstituted recipients were processed for DNA extraction and
hybridization analysis.14 Cells derived from BM donors
should give rise to DNA samples hybridizing with a probe for the
neor gene but not with a male probe
(zfy-1 gene probe). On the contrary, ossicle-host-derived
cells should hybridize with the zfy-1 gene probe but not
with the neor gene probe. Residual endogenous
hematopoietic cells in the transplanted recipient should not contribute
DNA hybridizing with either the neor or the
zfy-1 gene probes.
Origin of nonadherent cells in LTCs established with renal ossicles We used 125d-N1 and 132d-N1 ossicles to establish LTCs. LTCs were also initiated with BM from the 125d-N1 ossicle host and from Ly-5.1 and Ly-5.2 control mice (Figure 1A). As expected, most nonadherent myeloid cells from the Ly-5.1 and Ly-5.2 control cultures were Ly-5.1+ and Ly-5.1 ,
respectively. No significant numbers of Ly-5.1 cells
(phenotype of the implanted BM) were detected in the LTC supernatants
from the 125d-N1 ossicle host BM. However, ossicle-derived LTC
supernatants always contained a significant proportion of myeloid cells
from BM donor (7.3% to 64.9% of Ly-5.1 cells).
We analyzed 3 further ossicle-derived LTCs (198d-N1, 281d-N2, and
282d-N2 ossicles). In all instances, chimeric supernatants bearing 5%
to 33% of Ly-5.1 Orgin of the CFU-S12 population in renal ossicles Hybridization analyses on CFU-S12 from 77d-N2, 133d-N1, 136d-N1, and 281d-N2 ossicles are summarized in Table 1. This table also shows the proportion of hematopoietic cells from BM-donor and ossicle-host origin in the ossicle marrow as deduced by Ly-5.1 staining. Only 3 of 144 spleen colonies analyzed were of endogenous origin. Between 16% and 93% of the exogenous CFU-S12 in the ossicle marrow were of donor origin. Interestingly, even when the ossicle marrow cells were predominantly of host origin, a large proportion of donor-derived CFU-S12 was detected. We presume that the intense vascularization of the ossicles may account for this observation.1 Taken together, these data are consistent with studies detecting donor-derived CFU-S9 in subcutaneous femurs at 2 to 40 weeks postimplantation.5,8
Origin of the RCs in renal ossicles Marrow cells from the 77d-N2 ossicle were transplanted into myeloablated F/Ly-5.2 mice. The origin of the RCs in the lymphohematopoietic organs from these recipients was investigated by means of hybridization analyses performed at the third (R1), fourth (R2-R3), and sixth month (R4-R10) posttransplantation (Figure 1B). Although the exogenous RCs in some recipients were predominantly from ossicle hosts (zfy-1+, ie, R1, R5, and R9), the remaining recipients were predominantly repopulated by BM-donor-derived cells (neo+). Similar results were obtained when marrow grafts from 78d-N1 and 133d-N1 ossicles were transplanted and recipients analyzed at 3 to 7 months posttransplantation (not shown).Long-term RCs (LTRCs) had been previously reported in ossicles generated following the subcutaneous implantation of gelatin capsules containing recombinant human bone morphogenetic protein-2.18 Our study, however, reports for the first time the presence of LTRCs in mouse renal ossicles. Moreover, we demonstrate a significant repopulating contribution from donor origin. Given that we could not detect donor-derived progenitors in any ossicle host BM, we propose that donor RCs have been preserved at the implantation site. Nevertheless, we cannot rule out the possibility that donor RCs reached these organoids as a secondary process after the engraftment and subsequent mobilization from the host BM. Our observations suggest the relevance of testing the origin of the hematopoietic populations in experimental models of heterotopic BM transplantation aiming to dissect the contribution of donor precursors to particular hematopoietic deficiencies.3,19 In addition, our data open new possibilities regarding the stable transplantation of donor hematopoietic stem cells in nonconditioned recipients.
The authors thank Thomas Graf for discussion on the manuscript, Antonio Bernad for collaboration to establish the N1 transgenic mouse line, Sergio García for technical assistance, and J. Martínez for careful maintenance of the animals.
Departamento de Biología Molecular y Celular y Terapia Génica, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain.
Submitted December 1, 1999; accepted May 25, 2000.
Supported by grant SAF 98-0008-C04-01 from the Comisión Interministerial de Ciencia y Tecnología.
The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 U.S.C. section 1734.
Reprints: Florencio Varas, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Departamento de Biología Molecular y Celular y Terapia Génica, Edificio 7, Avenida Complutense 22, 28040-Madrid, Spain; e-mail: florencio.varas{at}ciemat.es.
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© 2000 by The American Society of Hematology.
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