scholarly journals In vivo adenovirus vector-mediated transfer of the human thrombopoietin cDNA maintains platelet levels during radiation-and chemotherapy- induced bone marrow suppression

Blood ◽  
1996 ◽  
Vol 88 (3) ◽  
pp. 778-784 ◽  
Author(s):  
A Ohwada ◽  
S Rafii ◽  
MA Moore ◽  
RG Crystal
Keyword(s):  
Bone Marrow ◽  
Platelet Count ◽  
Adenovirus Vector ◽  
Bone Marrow Suppression ◽  
Single Administration ◽  
Platelet Recovery ◽  
Platelet Production ◽  
Life Threatening ◽  
Bone Abnormalities

Abstract Thrombopoietin (TPO, c-mpl ligand) has emerged as a major hematopoietic cytokine stimulating megakaryocyte proliferation, endomitosis, and platelet production. This study shows that a single administration of an adenovirus (Ad) vector encoding TPO (AdCMV.TPO) abrogates thrombocytopenia induced in mice by carboplatin and irradiation. Normal Balb/c mice receiving the vector had increased platelet counts peaking at 7 days and returning to baseline by day 15. Mice rendered pancytopenic with 500 rads and 1.2 mg of carboplatin had a nadir platelet count of five percent of the baseline. Mice receiving AdCMV.TPO 3 days before receiving irradiation and chemotherapy achieved a platelet nadir fourfold higher, and had significant reduction in duration of thrombocytopenia, than mice receiving the control Ad vector. Introduction of AdCMV.TPO the same day of chemotherapy and irradiation was equally effective in acceleration of platelet recovery, but administration of AdCMV.TPO 3 days after chemotherapy-radiation had little effect on platelet recovery. At 30 days after therapy bone marrow and spleen of mice treated with AdCMV.TPO were populated with a large number of polyploid megakaryocytes, but there was no evidence of circulating megakaryocytes in the liver or lungs and no pathologic bone abnormalities such as osteosclerosis or myelofibrosis. These observations suggest that an Ad vector may be an excellent delivery system to provide adequate TPO production to maintain platelet levels in circumstances associated with life-threatening thrombocytopenia.

scholarly journals In vivo adenovirus vector-mediated transfer of the human thrombopoietin cDNA maintains platelet levels during radiation-and chemotherapy- induced bone marrow suppression

Blood ◽  
1996 ◽  
Vol 88 (3) ◽  
pp. 778-784 ◽  
Author(s):  
A Ohwada ◽  
S Rafii ◽  
MA Moore ◽  
RG Crystal
Keyword(s):  
Bone Marrow ◽  
Platelet Count ◽  
Adenovirus Vector ◽  
Bone Marrow Suppression ◽  
Single Administration ◽  
Platelet Recovery ◽  
Platelet Production ◽  
Life Threatening ◽  
Bone Abnormalities

Thrombopoietin (TPO, c-mpl ligand) has emerged as a major hematopoietic cytokine stimulating megakaryocyte proliferation, endomitosis, and platelet production. This study shows that a single administration of an adenovirus (Ad) vector encoding TPO (AdCMV.TPO) abrogates thrombocytopenia induced in mice by carboplatin and irradiation. Normal Balb/c mice receiving the vector had increased platelet counts peaking at 7 days and returning to baseline by day 15. Mice rendered pancytopenic with 500 rads and 1.2 mg of carboplatin had a nadir platelet count of five percent of the baseline. Mice receiving AdCMV.TPO 3 days before receiving irradiation and chemotherapy achieved a platelet nadir fourfold higher, and had significant reduction in duration of thrombocytopenia, than mice receiving the control Ad vector. Introduction of AdCMV.TPO the same day of chemotherapy and irradiation was equally effective in acceleration of platelet recovery, but administration of AdCMV.TPO 3 days after chemotherapy-radiation had little effect on platelet recovery. At 30 days after therapy bone marrow and spleen of mice treated with AdCMV.TPO were populated with a large number of polyploid megakaryocytes, but there was no evidence of circulating megakaryocytes in the liver or lungs and no pathologic bone abnormalities such as osteosclerosis or myelofibrosis. These observations suggest that an Ad vector may be an excellent delivery system to provide adequate TPO production to maintain platelet levels in circumstances associated with life-threatening thrombocytopenia.

scholarly journals RGS10 and RGS18 differentially limit platelet activation, promote platelet production, and prolong platelet survival

Blood ◽  
2020 ◽  
Vol 136 (15) ◽  
pp. 1773-1782 ◽  
Author(s):  
Daniel DeHelian ◽  
Shuchi Gupta ◽  
Jie Wu ◽  
Chelsea Thorsheim ◽  
Brian Estevez ◽  
...  
Keyword(s):  
Platelet Count ◽  
G Protein ◽  
Platelet Activation ◽  
Platelet Reactivity ◽  
Rgs Proteins ◽  
Platelet Recovery ◽  
Platelet Production ◽  
Platelet Survival

Abstract G protein–coupled receptors are critical mediators of platelet activation whose signaling can be modulated by members of the regulator of G protein signaling (RGS) family. The 2 most abundant RGS proteins in human and mouse platelets are RGS10 and RGS18. While each has been studied individually, critical questions remain about the overall impact of this mode of regulation in platelets. Here, we report that mice missing both proteins show reduced platelet survival and a 40% decrease in platelet count that can be partially reversed with aspirin and a P2Y12 antagonist. Their platelets have increased basal (TREM)-like transcript-1 expression, a leftward shift in the dose/response for a thrombin receptor–activating peptide, an increased maximum response to adenosine 5′-diphosphate and TxA2, and a greatly exaggerated response to penetrating injuries in vivo. Neither of the individual knockouts displays this constellation of findings. RGS10−/− platelets have an enhanced response to agonists in vitro, but platelet count and survival are normal. RGS18−/− mice have a 15% reduction in platelet count that is not affected by antiplatelet agents, nearly normal responses to platelet agonists, and normal platelet survival. Megakaryocyte number and ploidy are normal in all 3 mouse lines, but platelet recovery from severe acute thrombocytopenia is slower in RGS18−/− and RGS10−/−18−/− mice. Collectively, these results show that RGS10 and RGS18 have complementary roles in platelets. Removing both at the same time discloses the extent to which this regulatory mechanism normally controls platelet reactivity in vivo, modulates the hemostatic response to injury, promotes platelet production, and prolongs platelet survival.

Platelet Factor 4 Regulates Platelet Count In Vivo: Implications for Platelet Recovery after Cytotoxic Therapy.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3144-3144
Author(s):  
Michele P. Lambert ◽  
M. Anna Kowalska ◽  
Mortimer Poncz
Keyword(s):  
Bone Marrow ◽  
Platelet Count ◽  
Mononuclear Cells ◽  
Physiological Role ◽  
Platelet Factor 4 ◽  
Cytotoxic Therapy ◽  
Platelet Factor ◽  
Platelet Recovery ◽  
Platelet Counts

Abstract Platelet factor 4 (PF4), a platelet-specific CXC chemokine, was the first reported negative autocrine regulator of megakaryopoiesis in vitro. To define the physiological role(s) of PF4, we established mice that either were deficient in murine (m) PF4 (mPF4−/−) or that over-expressed human (h) PF4 (hPF4+/+). These mice had a level of PF4 ~6-fold greater than that present in human platelet controls. All lines studied had been backcrossed onto a C57Bl/6J background for >10 generations. Platelet counts in these animals correlated inversely with PF4 determined expression, beginning with a low platelet count of 702 ± 57 x 103/μL in the hPF4+/+ mice < hPF4+ < wildtype (WT) < mPF4+/− < mPF4−/− mice in which the platelet count was 1,404 ± 117 x 103/μL. The half-life of the platelets from the hPF4+/+ was identical to that of WT mice. Cultured bone marrow mononuclear cells (BMMNC) in serum-free media showed that each line had identical efficiency in growing megakaryocyte colonies, suggesting that megakaryocyte progenitor cells in these different genetic lines were intrinsically normal. Megakaryocyte colony numbers derived from WT BMMNC were reduced by the addition of recombinant PF4 or supernatant from irradiated bone marrow of hPF4+ mice, but not from mPF4−/− mice, suggesting that megakaryocyte lysis in vivo during cytoreductive therapy may contribute to the subsequent thrombocytopenia by releasing PF4. Additionally, a rabbit polyclonal anti-mPF4 antibody (Ab) was able in culture to significantly reverse this inhibitory effect of PF4 on megakaryopoiesis. Preliminary cytoreductive studies using either 600 cGy or 150 mg/kg of 5-fluorouracil (5-FU) intraperitoneally (IP) were performed. In irradiation studies, mPF4−/− mice began to recover on the same day as WT littermates, but they clearly had higher platelet counts at their nadir, with a drop to only 42 ± 7% of baseline vs. 32 ± 6% in the WT mice (n =12 in each arm, p = 0.06). By Day 13, 9 of 12 mPF4−/− mice had recovered to >75% of baseline, while only 3 of 12 WT mice had recovered (p <0.001). hPF4+ mice (n = 7) were studied after 5-FU treatment. Compared to WT littermates (n = 9), the hPF4+ recovered later (15.6 ± 2.2 vs. 11.2 ± 1.5 days, p < 0.0003), and clearly had significantly greater drop to 30 ± 6% vs. 56 ± 9% of baseline (p < 0.00001). By day 15, all of the WT mice had recovered, but only 43% of hPF4+ mice had returned to >75% of baseline platelet count (p = 0.009). To examine if anti-mPF4 Ab was protective of cytotoxic therapy-induced thrombocytopenia, WT mice were treated with 180 mg/kg of 5-FU and were given either anti-mPF4 Ab (25 mg/kg, IV, x 2) or an equal volume of vehicle. By day 5, the Ab-treated group had a platelet count of 45 ± 6% vs. 32 ± 4% in the untreated (n > 13 per arm, p = 0.015). Platelet counts remained higher in the Ab-treated arm throughout the study. By day 10 after intervention, 9 of 16 mice of the Ab-treated arm had platelet counts over 75% of the baseline, while only 3 of 13 control mice did (p < 0.001). Thus, it appears that PF4 is an important negative autocrine regulator of platelet count in vivo. Excessive release of PF4 following cytotoxic therapy may be a mediator of treatment-related thrombocytopenia. Strategies directed to alleviate the consequence of released PF4 may have clinical benefit in ameliorating this thrombocytopenia.

Thrombocytopoiesis in normal and sublethally irradiated dogs: response to human interleukin-6

Blood ◽  
1992 ◽  
Vol 80 (2) ◽  
pp. 420-428 ◽  
Author(s):  
SA Burstein ◽  
T Downs ◽  
P Friese ◽  
S Lynam ◽  
S Anderson ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Alkaline Phosphatase ◽  
Platelet Count ◽  
Interleukin 6 ◽  
Clinical Symptoms ◽  
Bone Marrow Suppression ◽  
Platelet Recovery ◽  
Consistent Change ◽  
Total Body ◽  
Significant Increment

The response of megakaryocytes and platelets to the administration of recombinant human interleukin-6 (IL-6) was investigated in normal and sublethally irradiated dogs. IL-6 was administered for 2 weeks at doses of 10 to 160 micrograms/kg/d to normal animals to assess dose-response and toxicity. Subsequently, 40, 80, or 160 micrograms/kg/d for 2 weeks was administered to animals treated with 200 cG total body irradiation. Analysis of normal dogs showed a significant increment in the platelet count detectable approximately 11 days after initiation of IL-6 at all administered doses. Large platelets greater than 6.3 microns in diameter were observed 1 day after beginning IL-6, progressively increasing to as many as 19.1% of the total circulating platelets by day 10. The ploidy distribution of the marrow megakaryocytes did not differ from the normal at doses of less than or equal to 80 micrograms/kg/d, but at 160 micrograms/kg/d, a shift toward higher ploidy cells was noted. No change in total white count was noted; however, a decrease in hematocrit was seen at all doses. In the irradiated animals, the platelet count recovered earlier in the IL-6- treated dogs than in the controls, but no consistent change in the ploidy distribution was observed irrespective of dose. Large platelets were also noted in the treated animals, comprising up to 6.9% of the total platelet count. Fibrinogen levels were elevated to greater than 4 times normal. A significant decrease in hematocrit was seen in all animals, while no consistent change was noted in the white count. Elevations in serum cholesterol, triglycerides, and alkaline phosphatase, together with a decline in serum albumin were observed in all the treated animals (both normal and irradiated), but clinical symptoms were observed only in the dogs receiving greater than or equal to 80 micrograms/kg/d. The data show that IL-6 alone is capable of enhancing platelet recovery in dogs with bone marrow suppression.

Immune Thrombocytopenia Plasma-Derived Exosomes Impaired Megakaryocyte and Platelet Production through an Apoptosis Pathway

2020 ◽  
Author(s):  
Wenjing Miao ◽  
Baoquan Song ◽  
Bingyu Shi ◽  
Qi Wan ◽  
Quansheng Lv ◽  
...  
Keyword(s):  
Platelet Count ◽  
Healthy Volunteers ◽  
Immune Thrombocytopenia ◽  
In Vivo Study ◽  
Platelet Recovery ◽  
Apoptosis Pathway ◽  
Platelet Production

AbstractReduced megakaryocyte (MK) apoptosis and insufficient platelet production play important roles in the pathogenesis of immune thrombocytopenia (ITP). The contribution of plasma-derived exosomes to the decreased platelet count in ITP has not been entirely understood. Here, we found the percentage of apoptotic MKs in patients with ITP was significantly lower than those in healthy volunteers. In the presence of ITP plasma-derived exosomes (ITP-Exo), the apoptosis of MKs was reduced during the process of MK differentiation in vitro, which contributed to the reduced platelet production by Bcl-xL/caspase signaling. Furthermore, in vivo study demonstrated that ITP-Exo administration led to significantly delayed platelet recovery in mice after 3.5 Gy of irradiation. All these findings indicated that ITP-Exo, as a regulator of platelet production, impaired MK apoptosis and platelet production through Bcl-xL/caspase signaling, unveiling new mechanisms for reduced platelet count in ITP.

scholarly journals Thrombocytopoiesis in normal and sublethally irradiated dogs: response to human interleukin-6

Blood ◽  
1992 ◽  
Vol 80 (2) ◽  
pp. 420-428 ◽  
Author(s):  
SA Burstein ◽  
T Downs ◽  
P Friese ◽  
S Lynam ◽  
S Anderson ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Alkaline Phosphatase ◽  
Platelet Count ◽  
Interleukin 6 ◽  
Clinical Symptoms ◽  
Bone Marrow Suppression ◽  
Platelet Recovery ◽  
Consistent Change ◽  
Total Body ◽  
Significant Increment

Abstract The response of megakaryocytes and platelets to the administration of recombinant human interleukin-6 (IL-6) was investigated in normal and sublethally irradiated dogs. IL-6 was administered for 2 weeks at doses of 10 to 160 micrograms/kg/d to normal animals to assess dose-response and toxicity. Subsequently, 40, 80, or 160 micrograms/kg/d for 2 weeks was administered to animals treated with 200 cG total body irradiation. Analysis of normal dogs showed a significant increment in the platelet count detectable approximately 11 days after initiation of IL-6 at all administered doses. Large platelets greater than 6.3 microns in diameter were observed 1 day after beginning IL-6, progressively increasing to as many as 19.1% of the total circulating platelets by day 10. The ploidy distribution of the marrow megakaryocytes did not differ from the normal at doses of less than or equal to 80 micrograms/kg/d, but at 160 micrograms/kg/d, a shift toward higher ploidy cells was noted. No change in total white count was noted; however, a decrease in hematocrit was seen at all doses. In the irradiated animals, the platelet count recovered earlier in the IL-6- treated dogs than in the controls, but no consistent change in the ploidy distribution was observed irrespective of dose. Large platelets were also noted in the treated animals, comprising up to 6.9% of the total platelet count. Fibrinogen levels were elevated to greater than 4 times normal. A significant decrease in hematocrit was seen in all animals, while no consistent change was noted in the white count. Elevations in serum cholesterol, triglycerides, and alkaline phosphatase, together with a decline in serum albumin were observed in all the treated animals (both normal and irradiated), but clinical symptoms were observed only in the dogs receiving greater than or equal to 80 micrograms/kg/d. The data show that IL-6 alone is capable of enhancing platelet recovery in dogs with bone marrow suppression.

Translational approaches to functional platelet production ex vivo

2016 ◽  
Vol 115 (02) ◽  
pp. 250-256 ◽  
Author(s):  
Christian A. Di Buduo ◽  
Alessandra Balduini ◽  
David L. Kaplan
Keyword(s):  
Bone Marrow ◽  
Developmental Process ◽  
Ex Vivo ◽  
Platelet Production ◽  
Life Threatening ◽  
Human Use ◽  
And Function ◽  
Tissue Models ◽  
Insight Into

SummaryPlatelets, which are released by megakaryocytes, play key roles in haemostasis, angiogenesis, immunity, tissue regeneration and wound healing. The scarcity of clinical cures for life threatening platelet diseases is in a large part due to limited insight into the mechanisms that control the developmental process of megakaryocytes and the mechanisms that govern the production of platelets within the bone marrow. To overcome these limitations, functional human tissue models have been developed and studied to extrapolate ex vivo outcomes for new insight on bone marrow functions in vivo. There are many challenges that these models must overcome, from faithfully mimicking the physiological composition and functions of bone marrow, to the collection of the platelets generated and validation of their viability and function for human use. The overall goal is to identify innovative instruments to study mechanisms of platelet release, diseases related to platelet production and new therapeutic targets starting from human progenitor cells.

scholarly journals Posttranslational Modification in Megakaryocytes Regulates β1 Integrin Expression, Migration and Platelet Production in Vivo

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 1435-1435
Author(s):  
Silvia Giannini ◽  
Max Adelman ◽  
Antonija Jurak Begonja ◽  
Karin M Hoffmeister
Keyword(s):  
Bone Marrow ◽  
Posttranslational Modification ◽  
Fetal Liver ◽  
Marrow Transplant ◽  
Β1 Integrin ◽  
Integrin Expression ◽  
Platelet Recovery ◽  
Platelet Production

Abstract Platelet recovery following bone marrow transplant and radiochemotherapy is crucial to prevent bleeding complications. Defects in glycosylation have been associated with decrease in blood platelet counts. However, the role of posttranslational modification in platelet production remains elusive. We here investigated the role of β1,4 galactosyltransferase 1 (β4GalT1), the key glycosyltransferase regulating lactosaminoglycan (LacNAc or βGal1,4 GlcNAc) expression by adding galactose (Gal) to terminal N-acetylglucosamine (GlcNAc), in platelet production. Stromal cell-derived factor 1 (SDF-1), but not thrombopoietin promotes megakaryocyte (MK) migration towards the bone marrow sinusoids, thereby increasing platelet production. SDF-1 (CXCL12) upregulated LacNAc expression in fetal liver wild type (WT), but not β4galt1-null megakaryocytes (MKs) lacking β4GalT1, suggesting that SDF-1 promotes LacNAc expression in vivo to regulate MK migration and platelet production. In support of this hypothesis, β4galt1-null mice had severe macrothrombocytopenia with increased bone marrow MK numbers, but normal platelet clearance. Ploidy, expression of the major glycoproteins (GPIbα/V/IX and αIIbβ3) and the surface expression of the SDF-1 receptor CXCR4 were normal in β4galt1-null bone marrow MKs. However, β4galt1-null bone marrow MKs had increased surface and total β1 integrin expression, as determined by flow cytometry, immunoblot and immunofluorescence. Mature CD42b/CD41 positive β4galt1-null MKs co-localized poorly with endoglin positive bone marrow sinusoids (49.9 ± 2.1 %), compared to WT MKs (72.4 ± 0.6 %). Expression of laminin, the major β1 integrin ligand, was upregulated in β4galt1-null MKs, suggesting that loss of LacNAc expression on β1 integrin increased its function. To exclude an extrinsic contribution to the failure of β4galt1-null MKs to migrate, β4galt1-null fetal liver (E14.5) hematopoietic cells (FLHCs) were transplanted in lethally irradiated WT mice. Transplanted β4galt1-null FLHCs restored bone marrow MKs, but failed to migrate to sinusoids and produce circulating platelets. In marked contrast, production of β4galt1-null white blood cells was normal. Together, our results suggest that SDF-1 upregulates β4GalT1-dependent LacNAc expression to promote MK migration and interaction with BM sinusoids, likely regulating MK β1 integrin expression and interaction with components of the extracellular matrix, specifically laminin. Understanding of the mechanisms regulating posttranslational modifications induced by various hematopoietic stimulating chemokines and cytokines will contribute to better platelet recovery following bone marrow transplant and radiochemotherapy. Disclosures No relevant conflicts of interest to declare.

scholarly journals The Y14-p53 Regulatory Circuit in Megakaryocyte Differentiation and Thrombocytopenia

2020 ◽  
Author(s):  
Chun-Hao Su ◽  
Wei-Ju Liao ◽  
Wei-Chi Ke ◽  
Ruey-Bing Yang ◽  
Woan-Yuh Tarn
Keyword(s):  
Bone Marrow ◽  
Platelet Count ◽  
Ex Vivo ◽  
Critical Role ◽  
Platelet Production ◽  
Noncoding Regions ◽  
Regulatory Circuit ◽  
Hel Cells ◽  
Absent Radius ◽  
Megakaryocyte Differentiation

SUMMARYThrombocytopenia-absent radius syndrome is caused by a deletion in chromosome 1q21.1 in trans with RBM8A mutations in the noncoding regions. We generated megakaryocyte-specific Rbm8a knockout (Rbm8aKOMK) mice that exhibited marked thrombocytopenia, internal hemorrhage, and splenomegaly, indicating a disorder of platelet production. Rbm8aKOMK mice accumulated immature megakaryocytes in the bone marrow and spleen. Depletion of Y14/RBM8A in human erythroleukemia (HEL) cells inhibited phorbol ester-induced polyploidy and downregulated the signaling pathways associated with megakaryocyte maturation. Accordingly, Rbm8aKOMK mice had reduced expression of surface glycoproteins on platelets and impaired coagulation. Moreover, p53 level was increased in Y14-depleted HEL cells and Rbm8aKOMK megakaryocytes. Treatment with a p53 inhibitor restored ex vivo differentiation of Rbm8aKOMK megakaryocytes and unexpectedly activated Y14 expression in HEL cells. Knockout of Trp53 in part restored the platelet count of Rbm8aKOMK mice. These results indicate that the Y14-p53 circuit plays a critical role in megakaryocyte differentiation and platelet production.

scholarly journals Acceleration of hematopoietic reconstitution with a synthetic cytokine (SC-55494) after radiation-induced bone marrow aplasia

Blood ◽  
1996 ◽  
Vol 87 (2) ◽  
pp. 581-591 ◽  
Author(s):  
AM Farese ◽  
F Herodin ◽  
JP McKearn ◽  
C Baum ◽  
E Burton ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Pharmacokinetic Analysis ◽  
Pharmacokinetic Parameters ◽  
Platelet Recovery ◽  
Hematopoietic Reconstitution ◽  
Radiation Induced ◽  
Complete Blood Counts ◽  
60Co Gamma Radiation

The synthetic cytokine (Synthokine) SC-55494 is a high-affinity interleukin-3 (IL-3) receptor ligand that stimulates greater in vitro multilineage hematopoietic activity than native IL-3, while inducing no significant increase in inflammatory activity relative to native IL-3. The aim of this study was to investigate the in vivo hematopoietic response of rhesus monkeys receiving Synthokine after radiation-induced marrow aplasia. Administration schedule and dose of Synthokine were evaluated. All animals were total-body irradiated (TBI) with 700 cGy 60Co gamma radiation on day 0. Beginning on day 1, cohorts of animals (n = 5) received Synthokine subcutaneously (SC) twice daily with 25 micrograms/kg/d or 100 micrograms/kg/d for 23 days or 100 micrograms/kg/d for 14 days. Control animals (n = 9) received human serum albumin SC once daily at 15 micrograms/kg/d for 23 days. Complete blood counts were monitored for 60 days postirradiation and the durations of neutropenia (NEUT; absolute neutrophil count [ANC] 500/microL) and thrombocytopenia (THROM; platelet count 20,000/microL) were assessed. Synthokine significantly (P .05) reduced the duration of THROM versus the HSA-treated animals regardless of dose or protocol length. The most striking reduction was obtained in the animals receiving 100 micrograms/kg/d for 23 days (THROM = 3.5 v 12.5 days in HSA control animals). Although the duration of NEUT was not significantly altered, the depth of the nadir was significantly lessened in all animal cohorts treated with Synthokine regardless of dose versus schedule length. Bone marrow progenitor cell cultures indicated a beneficial effect of Synthokine on the recovery of granulocyte-macrophage colony-forming units that was significantly higher at day 24 post-TBI in both cohorts treated at 25 and 100 micrograms/kg/d for 23 days relative to the control animals. Plasma pharmacokinetic parameters were evaluated in both normal and irradiated animals. Pharmacokinetic analysis performed in irradiated animals after 1 week of treatment suggests an effect of repetitive Synthokine schedule and/or TBI on distribution and/or elimination of Synthokine. These data show that the Synthokine, SC55 94, administered therapeutically post-TBI, significantly enhanced platelet recovery and modulated neutrophil nadir and may be clinically useful in the treatment of the myeloablated host.

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