INVESTIGATION OF EXTERNAL RADIATION DOSES DURING RESIDENTS' TEMPORAL STAY TO NAMIE TOWN, FUKUSHIMA PREFECTURE.

Namie Town in Fukushima Prefecture, the majority of which was an evacuation area as a result of the effects of the Fukushima Daiichi Nuclear Power Plant accident, carried out a 'temporal stay' in September 2016 so that residents could check their houses. Therefore, in cooperation with the town authorities, the authors distributed personal dosemeters and behaviour record forms to record the personal dose equivalent rate and investigate the relationship between residents' external radiation dose and their behaviour. When the personal dose equivalent rate was calculated from the measured personal dose equivalent per hour, the median was 0.12 µSv h-1, the maximum value and the minimum value were 0.58 and 0.06 µSv h-1, respectively. Meanwhile, since personal fluctuations were observed in personal dose equivalent, grasping the relationship between residents' behaviour and exposed dose can be applied to risk communication.

COMPARISON OF BACTERIAL FLORA IN RIVER SEDIMENTS FROM FUKUSHIMA AND AOMORI PREFECTURES BY 16S RDNA SEQUENCE ANALYSIS.

Monitoring of radioactive materials has been reported in rivers and soil in Fukushima post the Fukushima Daiichi Nuclear Power Plant accident in March 2011. However, there are few reports on the influence of this event on bacteria in forest soils and rivers. Therefore, through amplicon sequencing of 16S rDNA we compared the bacterial flora in river sediment soils from Fukushima prefecture and from an area not exposed to radioactive contamination, Aomori prefecture. The bacterial composition in the Aomori prefecture soil and Fukushima soil were found to be very similar at the phylum level. However, Fukushima soil had significantly fewer Bacteroidetes than the Aomori soil (p = 0.014), while the content of Firmicutes and Latescibacteria (WS3) was significantly higher (p = 0.001, 0.013 respectively). However, no increase in the content of radioactive-resistant bacteria was observed. In future studies, it is necessary to standardise the conditions for soil collection to assess its content of radioactive substances.

CHANGES OF ABSORBED DOSE RATE IN AIR BY CAR-BORNE SURVEY IN NAMIE TOWN, FUKUSHIMA PREFECTURE AFTER THE FUKUSHIMA DAIICHI NUCLEAR POWER PLANT ACCIDENT.

The latest car-borne survey was carried out by Hirosaki University in order to grasp the local distribution of the absorbed dose rate in air after the evacuation order was lifted on Namie Town in 2017. The car-borne survey of absorbed dose rate in air was carried out on most of the roads which were accessible by car in Namie Town using a 3-in × 3-in NaI(Tl) scintillation spectrometer. The range of the absorbed dose rate in air was calculated to be 0.041-11 µGy h-1. The distribution maps of the absorbed dose rate in air were drawn based on the data obtained during the surveys in 2011, 2015 and 2017. The comparison of these absorbed dose rates in air suggests that the elevated absorbed dose rate in air in Namie Town caused by the FDNPP accident may be decreasing faster than natural decline which includes weathering effect and physical decay due to the artificial decontamination.

COMPREHENSIVE EXPRESSION ANALYSIS OF MIRNAS IN MICE EXPOSED TO LETHAL RADIATION AND/OR RADIO-MITIGATIVE DRUG.

New minimally invasive indicators that are capable of predicting the biological effects and radiation damage to various organs and systems are urgently needed for the development of optimal treatment protocols for victims of radiation accidents. In the present study, we focused on microRNA (miRNA) that have recently emerged as biomarkers for predicting and diagnosing various pathological conditions and identified the serum miRNA signatures. All of the mice treated with lethal radiation alone strongly expressed certain serum miRNAs detectable for 24 h after radiation exposure, whereas the administration of radio-mitigative drug immediately after irradiation suppressed these miRNA expressions to the same levels as in control mice. These results suggest that serum miRNAs may reflect the degree of radiation damage and can be used to predict the radiation-mitigative information in victims of accidental radiation exposure.

Response of the Nrf2 protection system in human monocytic cells after ionising irradiation.

In response to reactive oxygen species (ROS) or electrophiles, the transcription factor nuclear factor-erythroid 2 (NF-E2)-related factor 2 (Nrf2) rapidly translocates into the nucleus and induces the expression of various antioxidant genes, such as heme oxygenase-1 (HO-1). Low linear energy transfer (LET) ionising radiations such as X-rays generate ROS, which cause biological damage. However, little is known about whether the Nrf2 system in human monocytic cells is activated by low LET ionising irradiation. Therefore, in this study, the response of the Nrf2 system to X-irradiation in human monocytic THP1 cells was investigated. Following exposure of THP1 cells to X-rays (1-5 Gy), intracellular ROS levels were measured using 2',7'-dichlorodihydrofluorescein diacetate, Nrf2 localisation was determined using immunofluorescence staining and HO-1 mRNA and protein expression were examined. Although ROS were generated by irradiation in a dose-dependent manner, they disappeared immediately after irradiation. Nrf2 translocation into the nucleus was observed 6 h after 5 Gy X-irradiation but was not detected following 1-2 Gy irradiation or in non-irradiated controls. HO-1 expression was significantly higher in 5 Gy-irradiated cells after 24 h than in non-irradiated controls. These results indicate that high-dose irradiation (5 Gy) activates Nrf2 and that the Nrf2 protection system may function from 24 h after irradiation in human monocytic cells.

Radioprotective effects of (-)-epigallocatechin-3-gallate on human erythrocyte/granulocyte lineages.

Epigallocatechin-3-gallate (EGCg) is widely recognised as a powerful antioxidant and free radical scavenger. This study examined the radioprotective effects of EGCg on human granulopoiesis and erythropoiesis. Highly purified human CD34(+) haematopoietic stem/progenitor cells were prepared from human placental/umbilical cord blood. The cells were exposed to X rays at a dose rate of ∼1 Gy min(-1) and then cultured in a medium supplemented with either granulocyte colony-stimulating factor (G-CSF) or erythropoietin (EPO). EGCg (100 nM) was added to the culture immediately before or after X-irradiation. The concentration of 100-nM EGCg was determined in the authors' previous study. The number of granulocyte and erythrocyte colonies generated by X-irradiated CD34(+) cells decreased in a dose-dependent manner. Although EGCg addition yielded an ∼2-fold increase in the proliferation of each haematopoietic progenitor, no significant protective effect was observed in the surviving fraction of granulocyte progenitors (G-CSF alone: D(0)=1.06 Gy, n=1.14). However, EGCg addition before or after irradiation conferred a significantly higher protective effect on erythrocyte colony formation compared with the control (EPO alone: D(0)=0.66 Gy, n=1.56; EGCg (before): D(0)=0.43 Gy, n=5.48). EGCg addition before irradiation significantly improved the survival of erythroid progenitors subjected to radiation of <1 Gy. These results suggest that EGCg is more protective of erythropoiesis than granulopoiesis from radiation damage.

Inhibition of HIF-1alpha by the anticancer drug TAS106 enhances X-ray-induced apoptosis in vitro and in vivo.

In a previous study, we showed that a novel anticancer drug, 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (TAS106, ECyd) increased the antitumour efficacy of X-irradiation. However, its effects on hypoxic cells in tumours remain unclarified. Here, we show that TAS106 enhances the induction of apoptosis in X-irradiated human gastric adenocarcinoma MKN45 and MKN28 cells under hypoxia in vitro. At the same time, the accumulation of HIF-1alpha observed under hypoxia was shown to be decreased to the level of normoxia in the presence of 0.1 microM TAS106. To study the function of HIF-1alpha protein in apoptosis of hypoxic cells, we employed an HIF-1alpha reductive approach using its specific antisense oligodeoxynucleotide. The reduction of HIF-1alpha gene expression dramatically enhanced X-ray-induced apoptosis in hypoxic cells. In in vivo experiments in which MKN45 cells were transplanted into severe combined immunodeficient (SCID) mice, TAS106 (0.5 mg kg(-1)) suppressed HIF-1alpha expression and subsequently reduced the area of the hypoxic region in the tumour and enhanced the induction of apoptosis in the hypoxic region when combined with 2 Gy of X-irradiation. These results suggest the possibility that TAS106 acts as a potent radiosensitiser through the inhibition of HIF-1alpha expression and can be a useful agent against radiotherapy-resistant hypoxic cells in solid tumours.

Post-irradiation hypoxic incubation of X-irradiated MOLT-4 cells reduces apoptotic cell death by changing the intracellular redox state and modulating SAPK/JNK pathways.

To elucidate radiobiological effects of hypoxia on X-ray-induced apoptosis, MOLT-4 cells were treated under four set of conditions: (1) both X irradiation and incubation under normoxia, (2) X irradiation under hypoxia and subsequent incubation under normoxia, (3) X irradiation under normoxia and subsequent incubation under hypoxia, and (4) both X irradiation and incubation under hypoxia, and the induction of apoptosis was examined by fluorescence microscopy. About 28-33% apoptosis was observed in cells treated under conditions 1 and 2, but this value was significantly reduced to around 18-20% in cells treated under conditions 3 and 4, suggesting that post-irradiation hypoxic incubation rather than hypoxic irradiation mainly caused the reduction of apoptosis. The activation and expression of apoptosis signal-related molecules SAPK/JNK, Fas and caspase-3 were also suppressed by hypoxic incubation. Effects of hypoxic incubation were canceled when cells were treated under conditions 3 and 4 with an oxygen-mimicking hypoxic cell radiosensitizer, whereas the addition of N-acetyl-L-cysteine again reduced the induction of apoptosis. From these results it was concluded that hypoxia reduced the induction of apoptosis by changing the intracellular redox state, followed by the regulation of apoptotic signals in X-irradiated MOLT-4 cells.

High sensitivity of megakaryocytic progenitor cells contained in placental/umbilical cord blood to the stresses during cryopreservation.

In placental/umbilical cord blood (PCB) banking and PCB transplantation (PCBT), long-term cryopreservation of hematopoietic stem and progenitor cells is a unique requirement as compared to that for bone marrow transplantation and cytokine-mobilized peripheral blood transplantation. A long period of severe thrombocytopenia is a problem in many patients after PCBT. The object of this study was to define whether megakaryocytic progenitor cells (CFU-Meg), which produce platelets, are more sensitive to cryopreservation than the other myeloid progenitor cells in PCB. The leukocyte concentrates (LCs) obtained from clinical PCB banks were cryopreserved, and progenitor cell recoveries were determined by differential count of colony-forming cells (CFCs). The LCs were exposed to stresses which cells face during freezing, thawing, and washing out cryoprotectants. Most of the myeloid progenitor cells contained in the LCs showed good survival when cryopreserved at slow cooling rates, although cellular injury was observed at higher cooling rates and higher osmolalities. In contrast, the recovery rate of CFU-Meg was significantly lower than other progenitor cells, indicating a higher sensitivity to the various stresses they were exposed to during cryopreservation. Thrombocytopenia observed in patients receiving PCBT may be explained, at least in part, by the disappearance of CFU-Meg during cryopreservation.

[Effects of glycosaminoglycans on the in vitro colony formation of CD34+ megakaryocytic progenitor cells in human placental/umbilical cord blood].

The in vitro effect of various glycosaminoglycans (GAGs) on the clonal growth of CD34+ megakaryocytic progenitor cells (CFU-Megs) isolated from human placental/umbilical cord blood (CB) was evaluated in human plasma containing semisolid culture stimulated by recombinant human thrombopoietin (TPO). The GAGs, including hyaluronic acid from human umbilical cords (HA-h), pig skins (HA-p) and rooster combs (HA-r), or keratan sulfate (KS), various chondroitin sulfates (CS-A, B, C, D, E), and heparan sulfate (HS), were tested. Each GAG alone did not affect the clonal growth of CFU-Meg. In the presence of TPO, adding of HA-p or HS (100 micrograms/ml) resulted in an approximately 1.3-fold increase, in the total number of colonies, due to an increase in large megakaryocyte colonies. In contrast, CS-E led to a marked decrease in CFU-Meg growth. At the end of the culture, the total number of cells increased 3.0-fold of the initial value of the control, but adding HA-p or HS showed an approximately 9.1-fold or 18.3-fold increase. Similarly, the total number of CFU-Meg detected in the harvested cells increased to 4.8-fold of the initial value, while, an approximately 18.3-fold or 38.8-fold increase was observed in the culture containing HA-p or HS, respectively. Flow cytometric analysis of the harvested cells showed no significant difference in the expression of surface antigens and DNA ploidy distribution of megakaryocytes between the control and GAG treatments. These results suggest that HA-p and HS promote the proliferation of immature CB CD34+ CFU-Meg in the presence of TPO.

Expansion of megakaryocyte progenitors from cryopreserved leukocyte concentrates of human placental and umbilical cord blood in short-term liquid culture.

Long-term severe thrombocytopenia following human placental and umbilical cord blood (CB) transplantation is a significant clinical problem. We studied the ex vivo expansion of megakaryocytic progenitor cells (CFU-Meg) from cryopreserved/thawed leukocyte concentrates (LC) of CB prepared by the Tokyo Cord Blood Bank protocol. The LC cells were cultured in serum-free culture medium supplemented with a combination of early-acting cytokines including thrombopoietin (TPO), flt3-ligand (FL), and stem cell factor (SCF). Combination of TPO plus FL, TPO plus SCF, and all of these cytokines together resulted in 8.9-, 7.7-, and 8.4-fold increases in CFU-Meg, respectively, by Day 5 of culture. Our results showed that this simple expansion strategy has the potential for expanding CFU-Meg from cryopreserved/thawed LC cells from CB.

Effect of murine kidney extracts on the proliferation of hematopoietic progenitor cells in human umbilical cord blood.

We examined the effect of murine kidney extract (MKE) on the clonal growth of highly purified CD34+ hematopoietic progenitor cells from human umbilical cord blood. MKE did not affect the total number of colonies of erythroid burst-forming units (BFU-E), granulocyte-macrophage colony-forming units (CFU-GM) or granulocyte-erythroid-macrophage-megakaryocyte colony-forming units (CFU-Mix/CFU-GEMM) in a methylcellulose culture with exogenous recombinant human granulocyte colony-stimulating factor, granulocytemacrophage colony-stimulating factor, interleukin-3, stem cell factor and erythropoietin. MKE significantly increased the proportion of BFU-E- or CFU-Mix-derived colonies, and suppressed the formation CFU-GM-derived colonies depending on the MKE dose. However, because of an increase in small megakaryocyte colonies derived from mature CFU-Meg MKE increased by approximately 40% the growth of megakaryocyte colony-forming units (CFU-Meg) in plasma clot culture stimulated by recombinant human thrombopoietin. Also MKE promoted an increase in hyperploid megakaryocytes, suggesting that the active factor(s) in MKE acts on the mature CFU-Meg and promotes the maturation of megakaryocytes. Gel-filtration high performance liquid chromatography of MKE showed that the promoting factor(s) in MKE was approximately 45 kDa. These results indicate that the factor(s) detected in MKE influence human hematopoiesis in vitro, especially thrombopoiesis.

The frequency and proliferative potential of megakaryocytic colony-forming cells (Meg-CFC) in cord blood, cytokine-mobilized peripheral blood and bone marrow, and their correlation with total CFC numbers: implications for the quantitation of Meg-CFC to predict platelet engraftment following cord blood transplantation.

CFC numbers have shown to correlate with success of engraftment and speed of neutrophil recovery following cord blood (CB) transplantation. To investigate whether the number of Meg-CFC in a CB stem cell preparation might correlate with time to platelet engraftment, we evaluated the frequency of Meg-CFC among all CFC types in 134 CB, 21 adult bone marrow (BM) and 52 cytokine-mobilized peripheral blood (PB) stem cell preparations. The correlation of Meg-CFC with the total number of CFC and mixed cell-CFC was also assessed. The frequency of Meg-CFC was highest in CB and correlated significantly with total CFC numbers (mean 20.8%, correlation coefficient (r) 0.84, P = 0.0001) compared with Meg-CFC from mobilized PB (mean 13.1%, r = 0.29, P = 0.07) and BM (mean 4%, r = 0. 39, P = 0.13). In addition, mixed-cell CFC numbers in CB were highly correlated with the total number of Meg-CFC (r = 0.7, P = 0.0001). No such correlations were found with mobilized PB or BM. We conclude that, based on the high degree of correlation between Meg-CFC and non-Meg-CFC numbers in CB, no additional information concerning time to platelet engraftment would be gained by routinely performing Meg-CFC assays in addition to non-Meg-CFC assays. The fact that CB Meg-CFC and mixed-cell CFC are strongly correlated suggests that CB Meg-CFC are more primitive than their counterparts in BM and PB and may reflect the number of stem cells in CB. Bone Marrow Transplantation (2000).

Radiation sensitivity of megakaryocyte colony-forming cells in human placental and umbilical cord blood.

The in vitro radiation sensitivity of CFU-Meg isolated from human placental and umbilical cord blood was evaluated in plasma clot cultures stimulated by recombinant human cytokines, including thrombopoietin, the FLT3 ligand (FLT3LG), interleukin-3, interleukin-11 and stem cell factor. The CD34(+) cells were irradiated with X rays at a dose rate of 73 cGy/ min. The megakaryocyte colonies were identified by using an FITC-conjugated antibody to glycoprotein IIbIIIa and were classified into two groups based on colony size: large colonies (immature CFU-Meg) and small colonies (mature CFU-Meg). Treatment with thrombopoietin alone or in combination with FLT3LG and/or interleukin-11 gave exponential radiation survival curves (D(0) for immature CFU-Meg = 56-77 cGy, D(0) for mature CFU-Meg = 86 cGy-1.12 Gy), while marked shoulders were observed on the survival curves for colonies supported by the combination of thrombopoietin, interleukin-3 and stem cell factor (D(0) for immature CFU-Meg = 89- 98 cGy; D(0) for mature CFU-Meg = 1. 25-1.31 Gy). Our results showed that the immature CFU-Meg were more radiosensitive than the mature CFU-Meg and that the combination of cytokines, including thrombopoietin, interleukin-3 and stem cell factor, affected the radiation sensitivity of CFU-Meg to the same extent as with thrombopoietin alone or in combination with FLT3LG and/or interleukin-11.

Inhibitory effect of murine kidney extracts on the proliferation of murine mast cells.

We examined the effect of murine kidney extract (MKE) on the clonal growth of mast cells from murine peritoneal cells. Adding MKE resulted in a 40% inhibition of colony formation of mast cells in a methylcellulose culture, and a 90% decrease in mast cell numbers and histamine content in mast cells in a liquid culture containing stem cell factor and interleukin-3. The mast cell inhibitory factors in MKE were heat sensitive proteins of approximately 560 and 24 kDa. These results suggest that MKE contains regulators that suppress the growth of murine mast cells and histamine synthesis.

Colony-promoting activity in mice kidneys with phenylhydrazine hemolytic anemia.

Aqueous anemic mice kidney extracts (MKE) were assessed colony-promoting activity (CPA) of hematopoietic progenitor cells in serum-free cultures stimulated by interleukin-3 and erythropoietin (Epo). Mice with hemolytic anemia followed by phenylhydorazine (PHZ) injection for 3 days showed a decrease in the hematocrit (25.4%) and an increase in serum Epo by 14-fold of the control on day 3 after the treatment. At 3 days, the total number of hematopoietic progenitor cells in the bone marrow of PHZ mice decreased by 67% of the control, while these cells in the spleen increased to 22-fold of the control on day 3 and 55-fold on day 6. A significant increase in CPA was observed in MKE prepared from PHZ mice kidneys. Additionally, bone marrow suppressive anemia induced by 5-fluorouracil resulted in enhanced CPA the same as for PHZ mice, but in contrast, anemia with suppression of Epo-production due to nephrotoxicity induced by cisplatin caused a decrease in CPA. These results suggest that CPA in MKE correlates with hematopoietic conditions, and may have a definite role in hematopoiesis through the function of the kidney.

Effect of carboxy-PTIO, a nitric oxide scavenger, on the proliferation of murine hematopoietic progenitor cells in vitro.

We investigated the effect of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (c-PTIO), a specific nitric oxide scavenger and a stable radical compound, on the proliferation of murine hematopoietic progenitor cells in vitro. The c-PTIO promoted colony formation by erythropoietin and either interleukin-6 (IL-6) or the c-kit ligand/stem cell factor (SCF) in a methylcellulose culture, where the number of colonies increased 2.2-fold and 1.7-fold, respectively. During the addition of c-PTIO to the liquid cultures of murine bone marrow cells containing a combination of IL-6 and SCF, colony-forming cells in vitro (CFC) and the colony-forming unit in the spleen (CFU-S) increased about 1.8-fold and 1.7-fold, respectively, higher than the control culture after 7 day of culture. When c-PTIO was added twice at days 0 and 2 during the culture, 3.6-fold and 1.7-fold increases over the control were observed in the number of CFC and CFU-S. These results suggest the possibility that c-PTIO regulates the proliferation and differentiation of hematopoietic stem/progenitor cells in vitro.

Effects of alpha-phenyl N-tert-butylnitrone, a spin trap reagent, on the proliferation of murine hematopoietic progenitor cells in vitro.

We investigated the effect of alpha-phenyl N-tert-butylnitrone (PBN), a spin trap reagent, on the proliferation of murine hematopoietic progenitor cells in vitro. During the addition of PBN to the liquid cultures of murine bone marrow cells containing a combination of interleukin-3, interleukin-6 and the c-kit ligand/stem cell factor, colony-forming cells in vitro (CFC) and the colony-forming unit in the spleen (CFU-S) increased about 1.6-fold and 2.0-fold, respectively, higher than the control culture. These effects were not observed when using dimethyl sulfoxide, which has the ability to scavenge radicals, and 5,5-dimethyl-1-pyrroline N-oxide, another spin trap reagent. Analysis of cultured cells from a 7-day liquid culture with PBN revealed that the ratio of the intracellular glutathione (GSH) and GSH/GSSG (oxidized GSH) content was higher than the control. Adding thiol N-acetylcysteine, a thiol reagent and a precursor of intracellular GSH, also showed similar effects on the liquid culture of murine hematopoietic progenitor cells and the level of intracellular GSH. In contrast, adding DL-buthionine-[S,R]-sulfoximine, a gamma-glutamylcysteine synthetase inhibitor, decreased the intracellular GSH level and did not increase the number of CFC and CFU-S. These results suggest that PBN regulates the content of intracellular thiol molecules, and the possibility of a relationship between the intracellular redox state and the proliferation and differentiation of hematopoietic stem cells.

[Biological properties of the colony-promoting activity in extracts prepared from murine kidney].

Aqueous extracts prepared from the murine kidney (MKE) promoted colony formation derived from murine hematopoietic progenitor cells in serum-free cultures stimulated by interleukin-3 (IL-3) and erythropoietin (Epo). MKE itself did not stimulate any colony formation. MKE preferentially enhanced granulocyte-macrophage colony forming units (CFU-GM), but did not promote any erythroid colony formation. The CFU-GM colony promotion by MKE was observed at day 6 after the culture started, and the colony-promoting activity (CPA) was maintained at the same level until day 16. MKE showed no CPA in the cultures using cells obtained from 5-FU-injected mice and from c-kit(+)-enriched treatment. Furthermore, MKE acted synergistically with granulocyte-colony-stimulating factor (CSF), macrophage-CSF, IL-6 and IL-11 on colony formation, but did not act with GM-CSF, stem cell factor and Epo. From the results of various experiments and gel-filtration chromatography, it is estimated that the colony-promoting factor detected in MKE is a heat stable protein with about 20 KDa molecular weight. These results suggest that MKE promotes colony formation by murine myeloid progenitor cells, and that the target cell populations of MKE are relatively mature in the hematopoietic differentiation pathway.

The effect of a hematopoietic-promoting factor (HPF) extracted from porcine kidney on the proliferation of human hematopoietic progenitor cells.

Hematopoietic-promoting factor (HPF), which was found in porcine kidney, has been demonstrated to act synergistically with colony-stimulating factor and erythropoietin on murine myeloid colony formation. We investigated the effect of HPF on the proliferation of human hematopoietic progenitor cells prepared from cord blood cells (CB) and peripheral blood cells (PB). HPF enhanced granulocyte colony-stimulating factor plus interleukin-3 and erythropoietin-induced colony formation, where the number of colonies were increased by 7.9-fold in CB and by 1.8-fold in PB, respectively. When we compared the effect of HPF with stem cell factor (SCF) on the colony formation derived from PB in serum-free cultures, HPF enhanced the number of erythroid burst-forming units (BFU-E) to the same extent as SCF. But the effect of HPF on promoting the growth of granulocyte-macrophage colony-forming units (CFU-GM) was less than SCF. When the enriched CD34+ cells from CB and PB were incubated in liquid culture with HPF and IL-3 for 7 days, CFU-GM was increased by 48-fold in CB, and by 25-fold in PB, respectively. The data demonstrate that HPF can potentiate expansion of hematopoietic stem cells to the same extent as SCF, and that the effects of HPF on hematopoitic stem cells differ from that of SCF.