Single administration of stem cell factor, FLT-3 ligand, megakaryocyte growth and development factor, and interleukin-3 in combination soon after irradiation prevents nonhuman primates from myelosuppression: long-term follow-up of hematopoiesis

Angiotensin II AT1 receptor blockade normalizes CD11b+ monocyte production in bone marrow of hypercholesterolemic monkeys

The enhanced production of monocytes expressing pro-inflammatory markers such as the integrin CD11b in patients with hypercholesterolemia may promote vascular inflammation and exacerbate atherogenesis. The objective of the present study was to determine whether hypercholesterolemia stimulates the production of CD11b(+) monocytes in bone marrow, and whether the renin-angiotensin system participates in this process and thus provides a target for therapeutic intervention. The dietary induction of hypercholesterolemia in adult male cynomolgus monkeys was accompanied by increased bone marrow cellularity and elevated peripheral blood and bone marrow monocyte CD11b expression. Isolated bone marrow CD34(+) hematopoietic stem cells (HSCs) evaluated by in vitro functional assays exhibited enhanced myeloproliferative capacity and differentiation into CD11b(+) monocytes. Treatment of hypercholesterolemic monkeys with the angiotensin II AT(1) receptor blocker losartan for 15 weeks reduced bone marrow cellularity, suppressed peripheral blood and bone marrow monocyte CD11b expression, and normalized CD34(+) cell function assays. All variables returned to pretreatment levels 6 weeks after discontinuation of losartan treatment. Hypercholesterolemia was associated with increased CD34(+) cell AT(1) receptor expression and an exaggerated in vitro myeloproliferative response to angiotensin II stimulation that positively correlated to plasma LDL concentrations. In vitro exposure to native low-density lipoproteins (LDL) also increased CD34(+) cell AT(1) receptor expression and the myeloproliferative response to angiotensin II stimulation in a dose-dependent and receptor-mediated manner. Our data provide support for a positive regulatory role of plasma LDL on AT(1) receptor-mediated HSC differentiation and the production of pro-atherogenic monocytes. LDL-regulated HSC function may explain in part hypercholesterolemia-induced inflammation as well as the anti-inflammatory and anti-atherosclerotic effects of AT(1) receptor blockers.

Antiapoptotic cytokines in combination with pegfilgrastim soon after irradiation mitigates myelosuppression in nonhuman primates exposed to high irradiation dose

OBJECTIVE

Preservation of hematopoietic stem and progenitor cells from early radiation-induced apoptosis is the rationale for emergency antiapoptotic cytokine therapy (EACK) after radiation accidents. This strategy is based on the combination of stem cell factor + Flt3-ligand + thrombopoietin + interleukin 3 (SFT3). The long-term safety and efficacy of EACK in managing severe radiation exposure were evaluated.

MATERIAL AND METHODS

Early administration of SFT3 + pegfilgrastim was assessed in 7-Gy gamma total body-irradiated (TBI) monkeys. Efficiency of delayed administration was also addressed after 5-Gy TBI.

RESULTS

Here we showed that a single, intravenous injection of SFT3 2 hours after 7-Gy TBI reduced the period of thrombocytopenia (platelet count <20 x 10(9)/L: 0.8 +/- 1.5 day vs 23.8 +/- 15.9 days in controls; p < 0.05) and blood transfusion needs. Moreover, addition of pegfilgrastim to SFT3 treatment shortened the period of neutropenia compared with SFT3 and control groups (neutrophil count <0.5 x 10(9)/L: 7 +/- 1.4 days vs 13 +/- 3.2 days and 15.2 +/- 1.5 days; p < 0.05). In both SFT3 groups, bone marrow activity recovered earlier and, in contrast with controls, platelet count returned to baseline values from 250 days after irradiation. Furthermore, delayed (48 hours) single SFT3 administration in 5-Gy irradiated monkeys significantly reduced thrombocytopenia compared to controls. Finally, SFT3 did not increase frequency of total chromosome translocations observed in the blood lymphocytes of controls 1 year after 5 Gy TBI.

CONCLUSION

These results suggest the safety and efficacy of EACK in managing severe radiation exposure.

Revisiting therapeutic strategies in radiation casualties

OBJECTIVE

Nuclear/radiological threats have evolved and scenarios for terrorist attacks involving radioactive material have been identified as complex situations. Mass casualty scenarios may happen, and individuals may be exposed to intentionally hidden sources of high activity, resulting in delayed diagnosis and treatment of acute radiation syndrome (ARS). Moreover, ARS must be considered as an emergency in order to better anticipate delayed radiation toxicity. In this context, therapeutic strategies in radiation casualties have to be revisited and new pharmacological approaches developed.

METHODS

B6D2F1 mice were total-body irradiated (TBI) with a 9 Gy gamma dose and then received intraperitoneal doses of either early (stem cell factor + FLT-3 ligand + thrombopoietin + interleukin-3 [SFT3] +/- keratinocyte growth factor (KGF); stem cell factor + erythropoietin + Peg-filgrastim [SEG]) or delayed treatments (SFT3 +/- KGF, erythropoietin, or hyaluronic acid). Survival was monitored and bone marrow hematopoiesis evaluated at 300 days following early treatments.

RESULTS

SFT3 anti-apoptotic cytokine combination administered early (2 hours and 24 hours) after lethal TBI induced 60% survival versus 5% in controls. Early SEG treatment may be an alternative to SFT3 in terms of survival (55%), but SEG benefit might be obtained at the expense of long-term hematopoiesis. SFT3 + KGF induced 75% survival. No effectiveness was observed, over antimicrobial supportive care, when administration of SFT3 or its tested combinations was delayed at 48 hours.

CONCLUSION

As a potentially multi-organ failure, ARS requires global therapy, beyond the hematopoietic syndrome, which may include pleiotropic cytokines such as KGF.

Hematopoietic stem cells promote the expansion and function of adoptively transferred antitumor CD8 T cells

Depleting host immune elements with nonmyeloablative regimens prior to the adoptive transfer of tumor-specific CD8(+) T cells significantly enhances tumor treatment. In the current study, superior antitumor efficacy was achieved by further increasing the intensity of lymphodepletion to a level that required HSC transplantation. Surprisingly, the HSC transplant and not the increased lymphodepletion caused a robust expansion of adoptively transferred tumor-specific CD8(+) T cells. The HSC-driven cell expansion of effector, but not of naive, CD8(+) T cells was independent of in vivo restimulation by MHC class I-expressing APCs. Simultaneously, HSCs also facilitated the reconstitution of the host lymphoid compartment, including inhibitory elements, not merely via the production of progeny cells but by enhancing the expansion of cells that had survived lymphodepletion. Profound lymphodepletion, by myeloablation or by genetic means, focused the nonspecific HSC boost preferentially toward the transferred tumor-specific T cells, leading to successful tumor treatment. These findings indicate that CD8(+) T cell-mediated tumor responses can be efficiently driven by HSCs in the myeloablative setting and have substantial implications for the design of new antitumor immunotherapies.

CD41+/CD45+Cells Without Acetylcholinesterase Activity Are Immature and a Major Megakaryocytic Population in Murine Bone Marrow

Murine megakaryocytes (MKs) are defined by CD41/CD61 expression and acetylcholinesterase (AChE) activity; however, their stages of differentiation in bone marrow (BM) have not been fully elucidated. In murine lineage-negative (Lin(-))/CD45(+) BM cells, we found CD41(+) MKs without AChE activity (AChE(-)) except for CD41(++) MKs with AChE activity (AChE(+)), in which CD61 expression was similar to their CD41 level. Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs could differentiate into AChE(+), with an accompanying increase in CD41/CD61 during in vitro culture. Both proplatelet formation (PPF) and platelet (PLT) production for Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs were observed later than for Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs, whereas MK progenitors were scarcely detected in both subpopulations. GeneChip and semiquantitative polymerase chain reaction analyses revealed that the Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are assigned at the stage between the progenitor and PPF preparation phases in respect to the many MK/PLT-specific gene expressions, including beta1-tubulin. In normal mice, the number of Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs was 100 times higher than that of AChE(+) MKs in BM. When MK destruction and consequent thrombocytopenia were caused by an antitumor agent, mitomycin-C, Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs led to an increase in AChE(+) MKs and subsequent PLT recovery with interleukin-11 administration. It was concluded that MKs in murine BM at least in part consist of immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs and more differentiated Lin(-)/CD41(++)/CD45(+)/AChE(+) MKs. Immature Lin(-)/CD41(+)/CD45(+)/AChE(-) MKs are a major MK population compared with AChE(+) MKs in BM and play an important role in rapid PLT recovery in vivo.

Effects of whole-body gamma irradiation and 5-androstenediol administration on serum G-CSF

5-Androstenediol (5-AED) is a natural circulating adrenocortical steroid hormone that interconverts in vivo with other members of the 5-androstene family of steroids: dehydroepiandrosterone and 5-androstenetriol. These steroids stimulate immune responses and resistance to infection. 5-AED has been identified as a systemic radiation countermeasure that enhances survival in mice exposed to gamma irradiation and ameliorates radiation-induced neutropenia in mice and nonhuman primates. 5-AED mitigates radiation-induced decreases in platelets, natural killer (NK) cells, red blood cells, and monocytes. Administration of 5-AED causes functional activation of circulating granulocytes (phagocytic ability), monocytes (oxidative burst), and NK cells (surface CD11b expression). The effects of 5-AED on survival and hematological parameters are consistent with induction of hematopoietic cytokines. To test this hypothesis, we measured serum cytokines by ELISA, Luminex, and a cytokine array. A cytokine array was used for 62 different cytokines, chemokines, growth factors, and soluble receptors. 5-AED caused significant increases in circulating granulocyte colony-stimulating factor (G-CSF) in irradiated and unirradiated animals as observed with ELISA and Luminex. The cytokine array results suggest induction of G-CSF and additional cytokines, and related molecules. Since G-CSF is an important hematopoietic cytokine, the results support our hypothesis that the previously observed increases in numbers of hematopoietic progenitors, circulating innate immune cells and platelets, and functional activation of granulocytes, monocytes, and NK cells result from a cytokine cascade induced by 5-AED.

Regeneration of Megakaryocytopoiesis and ThrombopoiesisIn Vitrofrom X-Irradiated Human Hematopoietic Stem Cells

In the present study, we investigated whether X-irradiated hematopoietic stem cells can be induced to undergo megakaryocytopoiesis and thrombopoiesis in vitro using cytokine combinations that have been demonstrated to be effective for conferring increased survival on irradiated human CD34(+) megakaryocytic progenitor cells (colony-forming unit megakaryocytes; CFU-Meg), such as thrombopoietin (TPO), interleukin 3 (IL3), stem cell factor and FLT3 ligand. Culture of nonirradiated CD34(+) cells in serum-free medium supplemented with multiple cytokine combinations led to an approximately 200- to 600-fold increase in the total cell numbers by day 14 of culture. In contrast, the growth of X-irradiated cells was observed to be one-sixth to one-tenth that of the nonirradiated cultures. Similarly, total megakaryocytes were increased by 50- to 130-fold, while culture of X-irradiated cells yielded one-fourth to one-eighth of the control numbers. At this time, CD41(+) particles, which appeared to be platelets, were produced in the medium harvested from nonirradiated and irradiated cultures. Although radiation suppressed cell growth and megakaryocytopoiesis, there were no significant differences in thrombopoiesis between the two types of culture. These results suggest that X-irradiated CD34(+) cells can be induced to undergo nearly normal terminal maturation through megakaryocytopoiesis and thrombopoiesis by stimulation with appropriate cytokine combinations.

Vascular Endothelial Cells Produce Soluble Factors That Mediate the Recovery of Human Hematopoietic Stem Cells after Radiation Injury

The risk of terrorism with nuclear or radiologic weapons is considered to be high over the coming decade. Ionizing radiation can cause a spectrum of hematologic toxicities, from mild myelosuppression to myeloablation and death. However, the potential regenerative capacity of human hematopoietic stem cells (HSCs) after radiation injury has not been well characterized. In this study, we sought to characterize the effects of ionizing radiation on human HSCs and to determine whether signals from vascular endothelial cells could promote the repair of irradiated HSCs. Exposure of human bone marrow CD34+ cells to 400 cGy caused a precipitous decline in hematopoietic progenitor cell content and primitive cells capable of repopulating nonobese diabetic/severe combined immunodeficient mice (SCID-repopulating cells), which was not retrievable via treatment with cytokines. Conversely, culture of 400 cGy-irradiated bone marrow CD34+ cells with endothelial cells under noncontact conditions supported the differential recovery of both viable progenitor cells and primitive SCID-repopulating cells. These data illustrate that vascular endothelial cells produce soluble factors that promote the repair and functional recovery of HSCs after radiation injury and suggest that novel factors with radiotherapeutic potential can be identified within this milieu.

Oral oxymetholone reduces mortality induced by gamma irradiation in mice through stimulation of hematopoietic cells

Oxymetholone is a 17alpha -alkylated anabolic-androgenic steroid. This drug can stimulate bone marrow cells and increase the blood cells in the peripheral blood vessels. It has been used for the treatment of anemia caused by low red cell production. Since oxymetholone has hematopoietic effect, we studied radioprotective effects of this drug in mice. In this study, we determined percentage of survival, dose-reduction factor (DRF) and hematological parameters in irradiated mice which treated with or without oxymetholone. Oxymetholone administrated at different doses 80, 160, 320, 640 mg/kg by gavages at 24 h before 8 Gy gamma irradiation. At 30 days after treatment, the following percentage of animals survival in each group was as: 80 mg/kg, 50%; 160 mg/kg, 50%; 320 mg/kg, 55%; 640 mg/kg, 75% and vehicle, 15%. Percentage of survival increased in all of treated groups statistically compared with irradiated-vehicle group. In the groups treated by oxymetholone, maximum protection was realized at 640 mg/kg. In order to calculate the DRF for oxymetholone, mice were exposed to whole-body gamma irradiation with dose ranges between 5.83 and 11.23 Gy. The probit line for oxymetholone-treated mice was shifted to the right with a DRF of 1.14. In mice exposed to whole-body gamma-irradiation (4 Gy), an oral administration of 640 mg/kg oxymetholone ameliorated radiation-induced decreases in circulating platelets and erythrocytes, but had a less effect on total number of WBC. These results demonstrate that oxymetholone stimulates myelopoiesis and thrombocytopenia and enhances survival in mice after ionizing radiation.

Cytokine-based treatment of accidentally irradiated victims and new approaches

A major goal of medical management of acute radiation syndrome following accidental exposures to ionizing radiation (IR) is to mitigate the risks of infection and hemorrhage related to the period of bone marrow aplasia. This can be achieved by stimulating the proliferation and differentiation of residual hematopoietic stem and progenitor cells (HSPC) related to either their intrinsic radioresistance or the heterogeneity of dose distribution. This is the rationale for treatment with hematopoietic growth factors. In fact, apoptosis has recently been shown to play a major role in the death of the continuum of more or less radiosensitive HSPC, soon after irradiation. Therefore, administration of antiapoptotic cytokine combinations such as stem cell factor, Flt-3 ligand, thrombopoietin, and interleukin-3 (4F), may be important for multilineage recovery, particularly when these factors are administered early. Moreover, acute exposure to high doses of IR induces sequential, deleterious effects responsible for a delayed multiple organ dysfunction syndrome. These considerations strongly suggest that therapeutics could include tissue-specific cytokines, such as keratinocyte growth factor, and pleiotropic agents, such as erythropoietin, in addition to hematopoietic growth factors to ensure tissue damage repair and mitigate the inflammatory processes. Noncytokine drugs have also been proposed as an alternative to treat hematopoietic or nonhematopoietic radiation effects. To develop more effective treatments for radiation injuries, basic research is required, particularly to improve understanding of stem cell needs within their environment. In the context of radiological terrorism and radiation accidents, new growth promoting molecules need to be approved and available cytokines stockpiled.

Nonhuman primate embryonic stem cells as a preclinical model for hematopoietic and vascular repair

Stem cell-based regenerative medicine therapies have been touted recently as a novel therapeutic approach to treat and cure a wide range of diseases. Both adult and embryonic stem (ES) cells can serve as important sources of precursor cells to derive more mature cells potentially utilized for clinical applications. Nonhuman primates have proven useful as a preclinical model, as demonstrated in studies of hematopoietic cell transplantation, gene therapy, and other areas. The derivation of nonhuman primate ES cells now provides an optimal resource to characterize and test ES cell-based therapies prior to trials with human ES cells. This review describes work to define strategies and mechanisms to derive blood and endothelial cells from nonhuman primate ES cells isolated from various species. Preclinical testing that solely relies on studies of putative therapeutic cells derived from mouse ES cells transplanted into other mice, or analyses of human ES cell-derived cells transplanted into immunodeficient or immunosuppressed rodents may not be predictive of efficacy in subsequent human trials. However, future testing using nonhuman primate ES cell-derived therapeutic cells done as an allogeneic transplant may best predict success for subsequent studies using human ES cells. Therefore, additional research on nonhuman primate ES cells, in addition to work on mouse and human ES cells, is greatly needed to facilitate clinical translation of new stem cell treatments.

Mesenchymal stem cells rescue CD34+ cells from radiation-induced apoptosis and sustain hematopoietic reconstitution after coculture and cografting in lethally irradiated baboons: is autologous stem cell therapy in nuclear accident settings hype or reality?

Autologous stem cell therapy (ACT) has been proposed to prevent irradiated victims from bone marrow (BM) aplasia by grafting hematopoietic stem and progenitor cells (HSPCs) collected early after damage, provided that a functional graft of sufficient size could be produced ex vivo. To address this issue, we set up a baboon model of cell therapy in which autologous peripheral blood HSPCs collected before lethal total body irradiation were irradiated in vitro (2.5 Gy, D0 1 Gy) to mimic the cell damage, cultured in small numbers for a week in a serum-free medium in the presence of antiapoptotic cytokines and mesenchymal stem cells (MSCs) and then cografted. Our study shows that baboons cografted with expanded cells issued from 0.75 and 1 x 10(6)/kg irradiated CD34+ cells and MSCs (n=2) exhibited a stable long-term multilineage engraftment. Hematopoietic recovery became uncertain when reducing the CD34+ cell input (0.4 x 10(6)/kg CD34+ cells; n=3). However, platelet recovery was accelerated in all surviving cografted animals, when compared with baboons transplanted with unirradiated, unmanipulated CD34+ cells (0.5-1 x 10(6)/kg, n=4). Baboons grafted with MSCs alone (n=3) did not recover. In all cases, the nonhematopoietic toxicity remained huge. This baboon study suggests that ACT feasibility is limited.

Mesenchymal stem cells support expansion of in vitro irradiated CD34(+) cells in the presence of SCF, FLT3 ligand, TPO and IL3: potential application to autologous cell therapy in accidentally irradiated victims

Ex vivo expansion of residual autologous hematopoietic stem and progenitor cells collected from victims soon after accidental irradiation (autologous cell therapy) may represent an additional or alternative approach to cytokine therapy or allogeneic transplantation. Peripheral blood CD34+ cells could be a useful source of cells for this process provided that collection and ex vivo expansion of hematopoietic stem and progenitor cells could be optimized. Here we investigated whether mesenchymal stem cells could sustain culture of irradiated peripheral blood CD34+ cells. In vitro irradiated (4 Gy 60Co gamma rays) or nonirradiated mobilized peripheral blood CD34+ cells from baboons were cultured for 7 days in a serum-free medium supplemented with stem cell factor+thrombopoietin+interleukin 3+FLT3 ligand (50 ng/ml each) in the presence or absence of mesenchymal stem cells. In contrast to cultures without mesenchymal stem cells, irradiated CD34+ cells cultured with mesenchymal stem cells displayed cell amplification, i.e. CD34+ (4.9-fold), CD34++ (3.8-fold), CD34++/Thy-1+ (8.1-fold), CD41+ (12.4-fold) and MPO+ (50.6-fold), although at lower levels than in nonirradiated CD34+ cells. Fourteen times more clonogenic cells, especially BFU-E, were preserved when irradiated cells were cultured on mesenchymal stem cells. Moreover, we showed that the effect of mesenchymal stem cells is related mainly to the reduction of apoptosis and involves cell-cell contact rather than production of soluble factor(s). This experimental model suggests that mesenchymal stem cells could provide a crucial tool for autologous cell therapy applied to accidentally irradiated victims.

Soluble factor(s) from bone marrow cells can rescue lethally irradiated mice by protecting endogenous hematopoietic stem cells

OBJECTIVE

Ionizing radiation-induced myeloablation can be rescued via bone marrow transplantation (BMT) or administration of cytokines if given within 2 hours after radiation exposure. There is no evidence for the existence of soluble factors that can rescue an animal after a lethal dose of radiation when administered several hours postradiation. We established a system that could test the possibility for the existence of soluble factors that could be used more than 2 hours postirradiation to rescue animals.

MATERIALS AND METHODS

Animals with an implanted TheraCyte immunoisolation device (TID) received lethal-dose radiation and then normal bone marrow Lin- cells were loaded into the device (thereby preventing direct interaction between donor and recipient cells). Animal survival was evaluated and stem cell activity was tested with secondary bone marrow transplantation and flow cytometry analysis. Donor cell gene expression of five antiapoptotic cytokines was examined.

RESULTS

Bone marrow Lin- cells rescued lethally irradiated animals via soluble factor(s). Bone marrow cells from the rescued animals can rescue and repopulate secondary lethally irradiated animals. Within the first 6 hours post-lethal-dose radiation, there is no significant change of gene expression of the known radioprotective factors TPO, SCF, IL-3, Flt-3 ligand, and SDF-1.

CONCLUSION

Hematopoietic stem cells can be protected in lethally irradiated animals by soluble factors produced by bone marrow Lin- cells.