ALBERT

Description: Selective removal of malignant cells (purging) from bone marrow (BM) is a concern in autologous BM transplantation (ABMT). Use of vincristine, etoposide, or doxorubicin for purging could be rendered ineffective by the presence of multidrug-resistant (MDR) tumor cells. To circumvent this particular problem, we investigated whether 17F9, a monoclonal IgG2b antibody directed against the cell surface product of the MDR gene, P-glycoprotein, is effective in selective removal of MDR cells from BM when used with rabbit complement (C′). Using two different cell lines we have demonstrated that 17F9 + C′ selectively lyses MDR- positive cells. Three rounds of antibody + C′ resulted in 96.4% +/- 3.6% kill of K562/DOX and 100% +/- 0% of CEM/VLB cells. Mixtures of malignant cells and normal BM resulted in 99.85% removal of K562/DOX and 99.91% removal of CEM/VLB clonogenic cells. This treatment did not affect normal committed precursors compared with C′ alone. The addition of the cytotoxic agent etoposide (VP-16) following antibody purging results in a 4.6 log reduction of malignant cells. Furthermore, this antibody was effective when used against patients' leukemic blasts. These results suggest the use of 17F9 + C′ is effective and selective for removal of MDR cells from BM before ABMT and the addition of VP-16 enhances the purging efficacy.

Description: Selective removal of malignant cells (purging) from bone marrow (BM) is a concern in autologous BM transplantation (ABMT). Use of vincristine, etoposide, or doxorubicin for purging could be rendered ineffective by the presence of multidrug-resistant (MDR) tumor cells. To circumvent this particular problem, we investigated whether 17F9, a monoclonal IgG2b antibody directed against the cell surface product of the MDR gene, P-glycoprotein, is effective in selective removal of MDR cells from BM when used with rabbit complement (C′). Using two different cell lines we have demonstrated that 17F9 + C′ selectively lyses MDR- positive cells. Three rounds of antibody + C′ resulted in 96.4% +/- 3.6% kill of K562/DOX and 100% +/- 0% of CEM/VLB cells. Mixtures of malignant cells and normal BM resulted in 99.85% removal of K562/DOX and 99.91% removal of CEM/VLB clonogenic cells. This treatment did not affect normal committed precursors compared with C′ alone. The addition of the cytotoxic agent etoposide (VP-16) following antibody purging results in a 4.6 log reduction of malignant cells. Furthermore, this antibody was effective when used against patients' leukemic blasts. These results suggest the use of 17F9 + C′ is effective and selective for removal of MDR cells from BM before ABMT and the addition of VP-16 enhances the purging efficacy.

Description: Ninety-nine consecutive patients with acute leukemia in first complete remission under age 50 (median age 27 years; age range 1 to 47 years) with a histocompatible sibling donor were treated with fractionated total body irradiation (1,320 cGy) and high-dose etoposide (60 mg/kg) followed by allogeneic bone marrow transplantation. Sixty-one patients were diagnosed with acute myelogenous leukemia (AML), 34 patients with acute lymphoblastic leukemia (ALL), 3 patients with biphenotypic acute leukemia, and 1 patient with acute undifferentiated leukemia. Thirty of the 34 patients with ALL had at least one of the following high-risk factors: age greater than 30, white blood cell count at presentation 〉 25,000/microL, extramedullary disease, certain chromosomal translocations, or the need for greater than 4 weeks of induction chemotherapy to achieve first complete remission. Cumulative probabilities of disease-free survival and relapse at 3 years were 61% and 12%, respectively, for the 61 patients with AML and 64% and 12%, respectively, for the 34 patients with ALL. By stepwise Cox regression analysis, significant prognostic variables for patients with acute myelogenous leukemia were the presence of acute graft-versus-host disease and increasing age, whereas for patients with acute lymphoblastic leukemia, significant variables were age and the development of cytomegalovirus-associated interstitial pneumonia. Complications related to graft-versus-host disease and relapse of leukemia were the major causes of death.

Description: To characterize immune suppressive and hematopoietic features of enriched subsets of human marrow cells, we separated these cells on Percoll density gradients. CD4+ and CD8+ T cells (CD3+) were enriched in the high-density marrow cell fractions and reduced in low-density fractions. CD4-CD8- (CD3+) T cells expressing the alpha beta T-cell antigen receptor were at least 10 times less numerous than the CD4+ and CD8+ T cells in all fractions. Purified populations of the CD4-CD8- alpha beta + T cells obtained by flow cytometry suppressed the mixed leukocyte reaction (MLR). Another population of suppressor cells that expressed neither T-cell (CD3) nor natural killer cell (CD16) surface markers was also identified. The latter cells had the phenotypic and functional characteristics of “natural suppressor” cells. Suppressor cell activity was enriched in the low-density fractions along with hematopoietic progenitors (colony-forming unit-granulocyte-macrophage and burst-forming unit-erythroid). The progenitor and suppressor cell activities were depleted in high-density fractions. The latter fractions made vigorous responses in the MLR. The low-density fractions, which accounted for less than 10% of the input marrow cells, suppressed the MLR and did not respond. Further evaluation of the low-density fractions may be of value in allogeneic bone marrow transplantation due to the reduction of CD4+ and CD8+ T cells and the enrichment of hematopoietic progenitors as well as immune suppressor cells that may inhibit graft-versus-host disease.

Description: Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is a polypeptide mediator, elaborated by certain tumors and other cell types, that exerts multiple effects on endothelium via interaction with a class of high-affinity binding sites. In this report, the interaction of VPF/VEGF with human mononuclear phagocytes (MPs) is characterized. Radioligand binding studies at 4 degrees C showed the presence of a single class of binding sites, kd approximately 300 to 500 pmol/L (approximately 20 times lower affinity than the high-affinity binding site on endothelial cells [ECs]), the occupancy of which correlated with VPF/VEGF-induced MP migration and expression of tissue factor. These binding results were paralleled by functional experiments which indicated that the same VPF/VEGF preparations were about an order of magnitude less effective in stimulating MP chemotaxis than in inducing EC proliferation. When MPs with surface-bound 125I-VPF/VEGF were warmed to 37 degrees C, endocytosis and degradation occurred. Occupancy of VPF/VEGF binding site resulted in subsequent activation of intracellular signal transduction mechanisms, as shown by an increase in MP intracellular calcium concentration. Cross-linking studies with 125I-VPF/VEGF showed a new high-molecular weight band (corresponding to putative 125I- VPF/VEGF-receptor complex), the appearance of which was blocked by excess unlabeled VPF/VEGF. Consistent with these results, immunoprecipitation of 32PO4-labeled MPs exposed to VPF/VEGF showed a single band of similar mobility, not seen in untreated controls. These results demonstrate that the interaction of VPF/VEGF with MPs, though of lower affinity than that observed with ECs, also results from interaction of the polypeptide with a specific cell-surface protein and leads to activation of intracellular transduction mechanisms.

Description: Interleukin-12 (IL-12) is a potent proinflammatory and immunoregulatory cytokine skewing T lymphocytes to express a type 1 cytokine pattern. Optimal expression of IL-12 mRNA and bioactivity in vitro requires specific priming of monocytes by interferon-γ (IFN-γ) or granulocyte-macrophage colony-stimulating factor (GM-CSF) before lipopolysaccharide (LPS) stimulation. We show here for the first time that the production of IL-12 by IFN-γ– or GM-CSF–primed human monocytes can be completely suppressed by preincubation with LPS (fromEscherichia coli Serotype 055:B5) for 6 to 24 hours before the priming procedure. A dose-dependent suppression of IL-12p70 was measured on the levels of intracellular cytokine production and cytokine secretion. mRNA studies on the expression of p40 and p35 showed an LPS-induced downregulation of both subunits. The results of several different experimental approaches suggest that IL-12 downregulation was not due to endogenous IL-10, IL-4, prostaglandin E2 (PGE2), tumor necrosis factor- (TNF-), or nitric oxide (NO) production induced by LPS. Moreover, preincubation of monocytes with LPS did not lead to a downregulation of the CD14 antigen, which is an LPS receptor. LPS preincubation in this experimental setting did not result in a general hyporesponsiveness of the monocytes, as IL-6 production as well as IFN-γ–induced upregulation of CD54 did not decline. Downregulation of IL-12 was not due to changes in mRNA stability. These findings show that the immunoregulatory important cytokine, IL-12, underlies itself a complex regulation.

Description: Tumor cells have been found in autologous hematopoietic cell transplants used after high-dose chemotherapy. To specifically eliminate contaminating mammary tumor cells during ex vivo expansion of CD34+ hematopoietic progenitor cells, we used recombinant immunotoxins (ITs) directed against cell-surface antigens expressed on mammary carcinoma cells. ITs were expressed from fusion cDNAs combining a single-chain antibody fragment (scFv) directed against the Erb-B2 or epidermal growth factor (EGF) receptors with a truncatedPseudomonas exotoxin A fragment devoid of its cell-binding domain. CD34+ hematopoietic progenitor cells did not express Erb-B2 and EGF receptors as detected by Western blotting. Ex vivo expansion of total hematopoietic cells or of colony-forming cells from CD34+ progenitors in the presence of stem-cell factor (SCF), interleukin-1 (IL-1), IL-3, IL-6, and erythropoietin (Epo) was not affected when ITs were added to the cultures. In contrast, MDA-MB 453 and MCF-7 mammary carcinoma cells were depleted in a dose- and time-dependent manner by more than 3 log in coculture with CD34+ cells over a period of 7 days in the presence of 100 to 1,000 ng/mL of anti–Erb-B2 IT. This included elimination of the subpopulations with regrowth potential. Similarly, addition of either anti–Erb-B2 or anti-EGF receptor ITs to primary breast cancer cells isolated from patients with metastatic disease resulted in elimination of cytokeratin-positive cells in seven of seven samples. ITs are highly efficient and convenient to use for the depletion of mammary tumor cells during ex vivo expansion of hematopoietic progenitor-cell autografts.

Description: Fifty-three patients with high-risk acute lymphoblastic leukemia (ALL) under age 50 with a histocompatible sibling donor received high-dose radiochemotherapy followed by allogeneic bone marrow transplantation (BMT). The high-risk factors used to identify the patients were: white blood cell count at initial presentation, cytogenetic abnormalities, age, extramedullary leukemic infiltration, and time from initial therapy to complete remission. Patients with one or more of the above risk factors who received BMT have a disease-free survival of 61% with a median follow-up of 66 months (range 11 months to 10.6 years), and an actuarial relapse rate of 10%. This study demonstrates that patients with high-risk ALL achieve a significant disease-free survival and cure rate with the use of allogeneic fully matched sibling BMT. However, a properly designed prospective study comparing the outcome of BMT with the best currently available chemotherapy data is required to define the ultimate role of BMT in this group of patients.

Description: The spleen plays a central role in the pathogenesis of chronic idiopathic thrombocytopenic purpura (ITP); it produces massive quantities of antiplatelet antibodies, leading to accelerated phagocytosis of platelets. Lymphoid hyperplasia typically occurs in the spleen, characterized by large numbers of lymphatic nodules with active germinal centers. Whether changes in splenic microcirculatory pathways also occur is not known. We have studied this question by scanning electron microscopy of corrosion casts, comparing spleens removed from patients with ITP with normal spleens obtained from organ transplant donors. The casts demonstrate two major changes in microcirculatory pathways in ITP. Firstly, a striking proliferation of arterioles and capillaries is found in the white pulp and marginal zone (MZ), seen as extensive vascularization in 92.3% of lymphatic nodules (n = 191) versus 0.6% (n = 224) in normal spleens. Secondly, the marginal sinus, a series of flattened, anastomosing vascular spaces between the white pulp and MZ, is absent in 89.4% of lymphatic nodules versus 4.9% in normal spleens. The cause of these microcirculatory changes, which may not be exclusive to ITP, is presently unknown. Absence of the marginal sinus may affect distribution of blood flow through the MZ such that platelets spend increased amounts of time in the proximity of macrophages. In the presence of antiplatelet antibodies found in ITP spleens, this delayed transit would lead to greatly increased platelet destruction.

Description: In autoimmune hemolytic anemia (AIHA), there is accumulating evidence for an involvement of FcγR expressed by phagocytic effector cells, but demonstration of a causal relationship between individual FcγRs and IgG isotypes for disease development is lacking. Although the relevance of IgG isotypes to human AIHA is limited, we could show a clear IgG isotype dependency in murine AIHA using pathogenic IgG1 (105-2H) and IgG2a (34-3C) autoreactive anti–red blood cell antibodies in mice defective for FcγRIII, and comparing the clinical outcome to those in wild-type mice. FcγRIII-deficient mice were completely resistent to the pathogenic effects of 105-2H monoclonal antibody, as shown by a lack of IgG1-mediated erythrophagocytosis in vitro and in vivo. In addition, the IgG2a response by 34-3C induced a less severe but persistent AIHA in FcγRIII knock-out mice, as documented by a decrease in hematocrit. Blocking studies indicated that the residual anemic phenotype induced by 34-3C in the absence of FcγRIII reflects an activation of FcγRI that is normally coexpressed with FcγRIII on macrophages. Together these results show that the pathogenesis of AIHA through IgG1-dependent erythrophagocytosis is exclusively mediated by FcγRIII and further suggest that FcγRI, in addition to FcγRIII, contributes to this autoimmune disease when other IgG isotypes such as IgG2a are involved.