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R K Shadduck

Publications and source records attributed to R K Shadduck.

At least 19 recordsLinked to original sources
PubMed2003

Localized lymphoid relapse in the pancreas following allogeneic hematopoietic stem cell transplant for chronic myelogenous leukemia.

The incidence of isolated extramedullary disease (EMD) following allogeneic hematopoietic stem cell transplant (allo-HSCT) for chronic myelogenous leukemia (CML) is not fully known. One review found the incidence of isolated myeloid EMD, or granulocytic sarcoma (GS), in an allo-HSCT treated CML/myelodysplastic subgroup to be just 0.22%. The incidence of lymphoid EMD in similar patients is extremely rare with only two cases reported in the literature. While the etiology of EMD in the post-transplant setting is not entirely clear, there may be inefficacy of immune surveillance function outside of the bone marrow cavity. Isolated CML GS following allo-HSCT carries a median interval to bone marrow relapse between 7 and 10 months and a median survival of 12 months. Less is known about lymphoid EMD. The treatment in these cases is ill defined with modalities ranging from involved field radiation to second allo-HSCT. We present a case of isolated pancreatic lymphoid EMD diagnosed 15 months after allo-HSCT for CML. Our patient was also treated with withdrawal of his immunosuppressive regimen. Unfortunately, at just over 4 months following pancreatic resection, he developed systemic relapse and died. While EMD can occur anywhere in the body, CML associated pancreatic EMD is not previously reported.

Adrenal Cortex Hormones↗
PubMed2001

Cryoprecipitate poor plasma does not improve early response in primary adult thrombotic thrombocytopenic purpura (TTP).

Thrombotic thrombocytopenic purpura (TTP) is a potentially fatal disease that is treated with plasma exchange and typically with replacement with fresh frozen plasma (FFP). This approach results in an approximate 50% response rate following 1 week of therapy and 80% survival. Cryoprecipitate poor plasma (CPP) is plasma from which the cryoprecipitate fraction is removed. CPP has been reported to be successful as salvage therapy in refractory TTP and has been suggested to be superior to FFP in retrospective studies. The present report compares initial therapy of TTP with exchange using replacement with either FFP or CPP in a multi-institutional prospective randomized study performed by the North American TTP Group (NATG Group) from 1993 to 1995. Initial therapy also included corticosteroids. Antiplatelet drugs or vinca alkaloids were not employed. A severity score index, response score, and individual clinical parameters (platelet count, LDH x upper limit of normal, hemoglobin level, and creatinine) were compared at their nadir or peak values, baseline, and days +6 and +13 of therapy. Thirteen patients were randomized to FFP exchange and 14 to CPP exchange. Results were equivalent for all parameters. Survival was equal with three deaths in each group. These data indicate that the efficacy of FFP and CPP are the same in the initial treatment of TTP in adults.

Adult↗
PubMed2000

Ex vivo expansion of human umbilical cord blood and peripheral blood CD34(+) hematopoietic stem cells.

The proliferation and expansion of human hematopoietic stem cells (HSC) in ex vivo culture was examined with the goal of generating a suitable clinical protocol for expanding HSC for patient transplantation.HSC were derived from umbilical cord blood (UCB) and adult patient peripheral blood stem cell collections. HSC were stimulated to proliferate ex vivo by a combination of two growth factors, flt-3 ligand (FL) and thrombopoietin/c-mpl ligand (TPO/ML), and assessed for expansion by flow cytometry.Ex vivo expansion cultures of UCB were maintained for prolonged periods (up to 16 weeks), and sufficient HSC were generated for adult transplantation. In contrast to UCB, FL + TPO/ML did not significantly increase CD34(+) peripheral blood stem cell (PBSC) numbers.UCB-HSC can be expanded in culture to numbers theoretically adequate for safe, rapid engraftment of adult patients. Additional studies are needed to establish the functional activity of expanded UCB-HSC.

Adult↗
PubMed1999

Altered development and cytokine responses of myeloid progenitors in the absence of transcription factor, interferon consensus sequence binding protein.

Mice deficient for the transcription factor, interferon consensus sequence binding protein (ICSBP), are immunodeficient and develop disease symptoms similar to human chronic myeloid leukemia (CML). To elucidate the hematopoietic disorder of ICSBP(-/-) mice, we investigated the growth, differentiation, and leukemogenic potential of ICSBP(-/-) myeloid progenitor cells in vitro, as well as by cell-transfers in vivo. We report that adult bone marrow, as well as fetal liver of ICSBP-deficient mice harbor increased numbers of progenitor cells, which are hyperresponsive to both granulocyte macrophage colony-stimulating factor (GM-CSF) and G-CSF in vitro. In contrast, their response to M-CSF is strongly reduced and, surprisingly, ICSBP(-/-) colonies formed in the presence of M-CSF are mostly of granulocytic morphology. This disproportional differentiation toward cells of the granulocytic lineage in vitro parallels the expansion of granulocytes in ICSBP(-/-) mice and correlates with a 4-fold reduction of M-CSF receptor expressing cells in bone marrow. Cell transfer studies showed an intrinsic leukemogenic potential and long-term reconstitution capability of ICSBP(-/-) progenitors. Further experiments demonstrated strongly reduced adhesion of colony-forming cells from ICSBP(-/-) bone marrow to fibronectin. In summary, ICSBP(-/-) myeloid progenitor cells share several abnormal features with CML progenitors, suggesting that the distal parts of signaling pathways of these two disorders are overlapping.

Adult↗
PubMed1999

Protective effects of BB-10010 treatment on chemotherapy-induced neutropenia in mice.

Chemotherapy-induced neutropenia is a major dose-limiting factor in the management of cancer patients. Most chemotherapeutic agents are active against proliferating cells, interfering with DNA replication and/or mitosis. A number of chemokines, notably macrophage inflammatory protein-1 alpha [MIP-1alpha], have been reported to induce cell-cycle arrest in immature hematopoietic progenitors, raising the possibility that chemokines, such as MIP-1alpha, could be used to reduce or even eliminate the hematologic toxicity of cycle-active chemotherapy. We tested the effectiveness of BB-10010 [a genetically engineered analog of human MIP-1alpha] in vivo against three different cytotoxic drugs [cyclophosphamide (Cy), 5-fluorouracil (5-FU) and cytosine arabinoside (Ara-C)] commonly used in cancer therapy. BB-10010 treatment reduced the toxicity of all three agents, though the precise mode of protection varied with the cytotoxic drug used. BB-10010 reduced the neutropenic interval in Cy-treated mice without affecting the neutropenic nadir, whereas the absolute neutrophil counts [ANC] of both 5-FU and Ara-C treated mice were significantly higher throughout the neutropenic interval for mice receiving BB-10010 prior to chemotherapy. These findings indicate that the ability to manipulate the cell cycle of hematopoietic progenitors with chemokines, such as BB-10010/MIP-1alpha and other negative regulators, may be exploited to reduce chemotherapy-induced neutropenia; furthermore, the fact that BB-10010 is effective against several different cytotoxic agents is cause for guarded optimism that this approach may be generally applicable, and, once optimized for patient use, may prove to be of significant clinical benefit.

Animals↗
PubMed1999

Allogeneic peripheral blood stem cell transplantation for hypereosinophilic syndrome with severe cardiac dysfunction.

A 42-year-old male underwent an HLA-matched sibling PBSC transplant for hypereosinophilic syndrome (HES) diagnosed in August 1995. Prior to transplant he experienced progressive cardiac and pulmonary dysfunction with red cell and platelet transfusion dependence despite therapy with hydroxyurea, steroids and interferon. He received busulfan (16 mg/kg) and cyclophosphamide (120 mg/kg) as conditioning and standard GVHD prophylaxis with cyclosporin A and methotrexate. At day +336 he was transfusion independent without GVHD. Prompt reduction of the eosinophil count (<500/microl) and rapid improvement of cardiac function were documented, demonstrating the reversibility of organ dysfunction. Allogeneic PBSCT is an effective therapeutic option for patients with HES who fail conventional therapy.

Adult↗
PubMed1999

Calpain activity in bone marrow transplant-associated thrombotic thrombocytopenic purpura.

The pathophysiology of thrombotic thrombocytopenic purpura (TTP) is not well understood. Recent studies have described a platelet aggregating factor which has been characterized as a calcium-dependent cysteine protease (calpain) in patients with TTP. A type of TTP, sometimes called secondary TTP, has been associated with bone marrow transplantation (BMT). However, unlike primary adult TTP, BMT-TTP has important differences and often does not respond well to plasma exchange. We describe the measurement of calpain activity in a group of BMT patients (with and without the clinical syndrome of transplant-associated TTP). Calpain was measured using a functional assay (14C-serotonin platelet release with inhibition by the cysteine protease inhibitor, leupeptin) in the sera of patients following autologous (auto) or allogeneic (allo) BMT. We also independently diagnosed and graded the BMT-TTP on the day of blood sampling using a scale that related to the percentage schistocytes and lactic dehydrogenase level. Calpain activity was detected in 1/8 (13%) grade 0-1 (6 auto, 2 allo); 6/16 (38%) grade 2 (3 auto, 13 allo) 9/16 (56%) grade 3 (2 auto, 14 allo) and 8/8 (100%) grade 4 BMT-TTP. Pre-BMT samples were tested in 10 allo-BMT patients who had positive calpain results post-BMT. One patient gave positive results before the transplant. This patient developed grade 4 BMT-TTP (day 24 post-BMT) and died despite apheresis. Positive calpain results were highly associated with neurologic symptoms, P < 0.001. Nineteen of 24 (79%) patients with positive results had neurologic symptoms compared to three of 21 (14%) patients with negative results. In conclusion, calpain was detected in half of the BMT patients with mild to moderate BMT-TTP (grades 2-3) and was uniformly found in those with severe (grade 4) BMT-TTP. Typically the calpain activity develops as TTP complicates the transplant process. It is unknown whether calpain contributes to the pathogenesis of this disorder, or is a secondary event.

Adult↗
PubMed1998

Development of macrophage anticryptococcal activity in vitro is dependent on endogenous M-CSF.

We previously showed that nonactivated resident murine peritoneal macrophages (PM) from five strains (e.g., BALB/c) have C'-dependent fungistasis for Cryptococcus neoformans in 24-h coculture, but not CD-1 PM unless culture time was extended or M-CSF treatment was used. We studied effect of a rat IgG1 monoclonal (m) antibody (Ab) to murine M-CSF receptor on this anticryptococal activity. Culture of BALB/c PM with mAb, diluted 1:10, prechallenge reduced fungistasis from 58 to 21% (P < 0.01), whereas further 10-fold dilutions did not. Moreover, M-CSF pretreatment (5000 U/ml) significantly enhanced fungistasis (to 85%), whereas adding mAb 1:10 or 1:100 reduced that (to 58 and 77%, respectively, P < 0.01). In 48-h culture CD-1 PM had 39% fungistasis, reduced to 0% by mAb, M-CSF treatment of CD-1 PM increased fungistasis to 72%, which was reduced to 13 or 58% (P < 0. 001) by 1:10 or 1:100 mAb, respectively. Complete blocking by mAb of CD-1 PM activity was consistent with lack of measurable early endogenous CD-1 M-CSF production. Increasing exogenous M-CSF could overcome the inhibition by mAb (64% fungistasis BALB/c PM reduced to 11% with inhibition by mAb or increased to 94% with 5000 U/ml M-CSF; 37% with both mAb and M-CSF, 51% with mAb and 10,000 U/ml; P < 0.05, 5000 U/ml + mAb vs 10,000 U/ml + mAb). Moreover, rabbit Ab to M-CSF significantly reduced anticryptococcal activity of untreated BALB/c macrophages. In summary, development of PM fugistatic activity is dependent on endogenous M-CSF, since it is blocked by anti-receptor mAb (as is exogenous M-CSF stimulation) or anti-M-CSF Ab, and macrophages of the mouse strain with delayed activity had no measurable early M-CSF production.

Animals↗
PubMed1998

Plasminogen activator inhibitor (PAI-1) antigen levels in primary TTP and secondary TTP post-bone marrow transplantation.

Our objectives were to measure and compare plasminogen activator inhibitor levels (PAI-1) in primary adult thrombotic thrombocytopenic purpura (TTP) and in secondary TTP associated with bone marrow transplantation (BMT)-TTP. PAI-1 antigen levels were measured by an enzyme linked immunosorbent assay on platelet poor plasma samples obtained from patients at the time of diagnosis of the TTP disorder and from a group of normal volunteers. The samples were frozen at -70 degrees C. Patients with TTP secondary to bone marrow transplantation had their grade determined by percentage fragmented cells and lactate dehydrogenase levels. The primary TTP samples were contributed by investigators in the multi-institutional North American TTP Group, and the bone marrow transplant samples were obtained from an adult bone marrow transplant program. Nineteen patients with adult TTP, and 47 patients with bone marrow transplant-TTP were evaluated. Of the latter, 14 had Grade 2, 13 had Grade 3, and 20 had Grade 4 BMT-TTP. PAI-1 levels were elevated compared to control volunteers in both primary adult TTP and BMT-TTP, P < 0.001. Levels did not differ from normal in Grade 2 BMT-TTP (median = 16 ng/ml; quartiles = 9-20). PAI-1 levels were similar in primary TTP (median = 32 ng/ml; quartiles = 25-51) and Grade 3 BMT-TTP (median = 35 ng/ml; quartiles = 19-48 ng/ml), P = 0.7. However, PAI-1 levels were significantly higher in Grade 4 BMT-TTP (median = 83 ng/ml; quartiles = 60-143) than Grade 3 BMT-TTP, and primary TTP, P < 0.001. PAI-1 levels are high in primary TTP and secondary bone marrow transplant-TTP (Grades 3-4). In contrast, normal levels are seen in Grade 2 BMT-TTP, which is a self-limited disorder. Therefore, high PAI-1 levels may contribute to hypofibrinolysis in the pathogenesis of primary TTP and of moderate to severe TTP (Grades 3-4) following bone marrow transplantation.

Adult↗
PubMed1998

Mobilization and transplantation of peripheral blood stem cells.

Two hundred nineteen patients underwent peripheral blood stem cell (PBSC) transplantation from 1990 to 1997. Stem cells were mobilized with cyclophosphamide (CY), or with CY plus Taxol or etoposide, followed by cytokines, and collected when leukocyte counts > or = 1,000/microl, or when CD34+ counts > or = 20/microl. On average, four to five collections were needed to obtain sufficient PBSC for engraftment. When CD34+ counts were used, the average number of collections decreased from 5.4 to 4.2. A discrepancy was noted in the extraction ratios and number of collections that depended on the optical density (I/O) setting of the leukapheresis machine. Patients collected at a setting of 100 had higher extraction ratios and required fewer collections (mean = 2.7) than those collected at 150 (mean = 4.4). This result was unexpected, because the entire mononuclear cell layer is collected at the higher I/O setting. Further analysis revealed that a larger volume of red cells was collected at 150 than at 100. These procedures used a small-volume collection chamber, so the chamber was apparently overloaded by RBC at the higher setting. More rapid recovery of neutrophil counts and platelet counts was seen in PBSC transplants than in autologous marrow transplants; moreover, PBSC transplant patients required fewer RBC and platelet transfusions. Sixteen out of 21 normal donors for allogeneic PBSC transplants gave adequate collections (> 2.5 x 10(6) CD34+ cells/kg), but three donors failed to yield > or = 1.5 x 10(6) CD34 cells/kg. This suggests an inherent difference among certain normal donors that may make PBSC mobilization difficult.

Antigens, CD34↗
PubMed1997

Phase II study of roquinimex in myelodysplastic syndrome.

A Phase II clinical trial was undertaken using roquinimex (Linomide) in patients with myelodysplastic syndromes (MDS). Roquinimex is an orally active drug with immunostimulating activities demonstrated in vitro and clinically. Seventeen patients with MDS were enrolled in the study. Eligibility was limited to cytopenic patients with <20% marrow blasts. The drug was given orally twice weekly for 12 weeks with frequent monitoring of clinical, hematologic, and immunologic parameters. An increase in CD8+ and CD56+/CD3- cells was detected by 3 weeks. There was, however, no augmentation of natural killer or lymphokine-activated killer cell activity; progenitor cells were unchanged. Four patients had improvement in neutrophil counts, and two patients had improvement in platelet counts. Despite this improvement, the responses were transient or not maintained after discontinuation of therapy. One patient with RAEB, who was red cell transfusion dependent, experienced a complete remission that has persisted 14 months after completion of therapy. Adverse events developed in >25% of patients and included arthralgia, fever, headache, and myalgia. These side effects led to early withdrawal of therapy in five patients. These findings suggest that roquinimex may be of occasional benefit to patients with myelodysplastic syndromes.

Adjuvants, Immunologic↗
PubMed1996

Plasma von Willebrand Factor Antigen (vWF:AG) and thrombomodulin (TM) levels in Adult Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndromes (TTP/HUS) and bone marrow transplant-associated thrombotic microangiopathy (BMT-TM).

Endothelial damage is thought to be a contributing factor in the pathogenesis of Thrombotic Thrombocytopenic Purpura/Hemolytic Uremic Syndromes (TTP/HUS). The present studies measured two markers of endothelial cell stimulation and/or activation [von Willebrand Factor (vWF:Ag) and thrombomodulin (TM)] in patients with TTP/HUS disorders and compared them to controls. The patient groups consisted of adults with TTP/HUS, with (n = 13) and without (n = 14) peak Cr levels >2.0 mg/dl. Additionally, 52 patients with Bone Marrow Transplant-associated Thrombotic Microangiopathy (BMT-TM) following allogeneic BMT were evaluated. Both vWF:Ag and TM were elevated in all patient groups compared to controls. TTP/HUS patients with peak Cr >2.0 mg/dl had higher TM levels (P < 0.001) than did those with peak Cr levels below 2 mg/dl. However, thrombomodulin/ creatinine (TM/Cr) ratios did not differ in these two groups nor did they differ from controls. BMT-TM pts had higher vWF:Ag levels and higher TM/Cr ratios than controls and TTP/ HUS, P < 0.001. The median TM/Cr ratio in BMT-TM was 91 (range = 34-229) compared to 38 (range = 29-50) in controls, P < 0.001 and 38 (range = 6 to 156) in TTP/HUS, P < 0.001. Additionally both TM (P < 0.001) and TM/Cr (P < 0.02) were higher in patients with Grades 3 and 4 BMT-TM compared to those with Grade 2 BMT-TM. These results suggest that endothelial cell activation occurs in TTP/HUS and BMT-TM. Since TM/Cr ratios were higher in BMT-TM compared to TTP/HUS, these findings suggest that the mechanism of elevated TM in BMT-TM cannot be explained solely by altered renal excretion. Taken together, these findings strongly indicate a role of endothelial cell damage in BMT-TM.

Adult↗
PubMed1996

Apheresis in grade 4 bone marrow transplant associated thrombotic microangiopathy: a case series.

Bone marrow transplant-associated thrombotic microangiopathy (BMT-TM) ranges in severity from a self-limited to a fatal disorder. There has been no specific therapy for this condition. We have previously described a clinical grading system for BMT-TM, based upon lactate dehydrogenase level (LDH) and percentage fragmented cells (FC) as follows: grade 0, normal or increases LDH and % FC < or = to 1.2%; grade 1, normal LDH and FC > or = to 1.3%; grade 2, increases LDH and FC = 1.3-4.8%; grade 3, increases LDH and FC = 4.9-9.6%; and grade 4, increases LDH and FC > or = to 9.7%. Patients with grade 4 BMT-TM usually have fulminant disease and generally succumb. This study summarizes results using a variety of apheresis procedures in a series of 16 patients with grade 4 BMT-TM. The apheresis procedures consisted of plasma exchange (with replacement with fresh frozen plasma or cryo-poor plasma), and protein A immunoadsorption (PAI). The PAI exchanges were not done concurrently with plasma exchange procedures. Fifteen patients had undergone an allogeneic BMT and the 16th patient had undergone an autologous peripheral blood stem cell transplant. Half showed hematologic improvement with a downstaging of their TM to grades 1-3. All non-responders died a median of 11 days following the onset of grade 4 BMT-TM. The median survival in the responders was significantly (P = 0.001) increased to 218 days with three responders surviving more than 400 days following the onset of this severe complication. These results suggest a role for apheresis in the treatment of this lethal complication. Nevertheless grade 4 BMT-TM represents a major complication of BMT; the median survival in this group of 16 patients with grade 4 BMT-TM was only 31 days.

Adult↗
PubMed1996

UVB radiation interrupts cytokine-mediated support of an epidermal-derived dendritic cell line (XS52) by a dual mechanism.

We have established long-term dendritic cell lines from the epidermis of newborn mice. These cell lines (XS series) proliferate maximally in response to granulocyte/macrophage-colony stimulating factor, as well as to CSF-1, which is produced by skin-derived NS fibroblast lines and by keratinocytes (albeit in smaller amounts). The purpose of this study was to examine the impact of UVB radiation on CSF-1-mediated interaction of dendritic cells with fibroblasts and keratinocytes. Exposure of NS cells to UVB radiation (unfiltered FS20 sunlamp) decreased CSF-1 production at mRNA and protein levels. Both changes occurred in a dose-dependent fashion, with 50 J/m2 causing a significant reduction. UVB radiation also downregulated CSF-1 mRNA expression by Pam 212 keratinocytes. UVB exposure of XS cells diminished the surface expression of CSF-1 receptors, with 50 J/m2 causing a significant reduction. Thus, UVB radiation interrupts CSF-1-mediated cell-cell interaction by a dual mechanism: downregulating CSF-1 production and abrogating CSF-1 receptor expression. Importantly, granulocyte/macrophage-colony stimulating factor receptor expression by XS cells was also inhibited by UVB radiation, once again, with 50 J/m2 producing significant inhibition. We propose that the resulting CSF-1 deficiency in epidermal microenvironment and unresponsiveness by dendritic cells to relevant growth factors may contribute to UVB-mediated loss of resident epidermal dendritic cells (i.e., Langerhans cells) in skin.

Animals↗
PubMed1996

Tumor necrosis factor administration is associated with increased endogenous production of M-CSF and G-CSF but not GM-CSF in human cancer patients.

In humans, tumor necrosis factor (TNF) treatment has been associated with characteristic changes in circulating white blood cell populations (leukopenia followed by leukocytosis) and increased cell-surface expression of integrins. A similar pattern of effects on leukocytes occurs with granulocyte-macrophage colony-stimulating factor (GM-CSF) and G-CSF treatment. To determine whether these effects were caused directly by TNF or as a result of secondary CSF release, G-GM-, and M-CSF levels were measured after TNF infusion (9.6 x 10(6) U/mg protein; < 5.0 endotoxin U/mg protein) in cancer patients during two phase I trials of TNF. One patient with aggressive fibromatosis was treated with TNF alone (200 micrograms/m2, days 1-5 every third week) and 10 patients (four colon cancer, four head and neck cancer; one melanoma; one sarcoma) received mitomycin C (15 mg/m2, day 1) followed by TNF (60-180 micrograms/m2, days 1-3) every sixth week. All treatments were given IV, mitomycin C over 5 minutes and TNF over 2 hours. Serum samples were collected at times 0 (before mitomycin C and TNF) and 1, 2, 4, 6, 12, and 24 hours after TNF initiation on day 1 and at similar times on subsequent treatment days. M-CSF samples were analyzed by radioimmunoassay (RIA) and G-CSF and GM-CSF by ELISA. The mean baseline M-CSF levels in normal control subjects (n = 12) was 158.4 +/- 36.2 (SD) U/mL, and in pretreatment cancer patients (n = 10) 235.7 +/- 60.9 U/mL (p = 0.004, Wilcoxon test). M-CSF levels increased 4 hours after TNF initiation (mean 354.7 +/- 96.3 U/mL; p = 0.020), remained elevated at 6 hours (305.6 +/- 45.4 U/mL; p = 0.004, Wilcoxon signed-rank test), and subsequently declined. This pattern was seen in all patients treated with TNF, whether treatment was TNF alone or TNF with mitomycin C. In patients treated with mitomycin C and TNF, G-CSF levels increased at 4 hours after TNF initiation (mean 3886 +/- 2009 pg/mL; p = 0.004), remained elevated at 6 hours (mean 2140 +/- 1131 pg/mL; p = 0.004), and subsequently declined. GM-CSF levels were not measurable before or after treatment with TNF. The changes in all three endogenous cytokines were not temporally related to the previously described leukopenia and integrin upregulation on circulating leukocytes and, therefore, appear to be unrelated to this event. However, release of endogenous G-CSF and M-CSF under the influence of TNF does temporally coincide with the previously described leukocytosis, suggesting a possible role for these endogenous cytokines in the release of bone marrow cellular stores.

Colonic Neoplasms↗
PubMed1996

Paradoxical stimulation of normal and leukemic rat hematopoiesis by monoclonal antibody to CSF-1 receptor.

We have recently developed a rat monoclonal antibody directed against the murine M-CSF receptor (c-fms). This reagent also inhibits in vitro colony formation by leukemic and normal rat splenocytes in response to M-CSF. At high antibody concentrations, the antibody augments, rather than inhibits, colony formation by rat cells in the presence of M-CSF, an effect that is not seen when murine cells are used as responders. The costimulatory and inhibitory activities of the monoclonal antibody preparations copurify in a number of purification methods, indicating that the costimulatory activity is intrinsic to the antireceptor antibody. Conversion of the antibody into monovalent Fab fragments by papain digestion destroys costimulatory activity. This finding raises a cautionary note for the in vivo use of intact monoclonal antibodies directed against growth factor receptors for the treatment of hematologic malignancies.

Animals↗