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The murine lgG2a monoclonal antibody 6–19 binds to a wide variety of nonhematopoietic cells including human marrow-derived stromal cells but does not bind to marrow or peripheral blood cells. We studied the effects of this antibody and rabbit complement on marrow cells. Fibroblast colonies were eliminated from light density marrow cells by a single incubation with monoclonal antibody 6–19 and complement. The growth and composition of granulocytic and erythroid colonies were unaffected. Specific complement mediated cytotoxicity of the antibody was confirmed on passaged human fibroblasts derived from marrow (more than 99.6% of fibroblasts are killed by a single treatment). Similar results were obtained with human umbilical cord endothelial cells. In addition, such treatment abolished the initiation of Dexter culture stroma. Incubation of bone marrow cell suspensions with this antibody and complement will allow the study of stroma-free marrow cells in long-term liquid cultures.

Expression of differentiation markers in common acute lymphoblastic leukemia (cALL) cells from 25 patients was compared with subpopulations of normal common ALL antigen (CALLA) (CD10)-positive bone marrow lymphoid cells (cBMLs). In cBML, CD10 intensity is positively correlated with CD34 (MY10) and terminal transferase (TdT) expression and inversely correlated with common leukocyte antigen (CLA), CD20 (B1), and ctyoplasmic μchain (cμ) expression. In cALL, CD10 density was inversely correlated with CLA and cμ expression and strongly correlated with CD34 expression as in cBML. In contrast to cBML, TdT and CD20 expression were not related to CD10 density in cALL. Furthermore, cALL TdT intensity measured by enzyme immunoassay was not related to expression of CD10, CLA, or CD34, but was positively correlated with CD20 expression. cμ expression in cALL was inversely correlated with expression of CD34 and positively correlated with CLA as in cBML, but showed no association with TdT intensity or CD20 expression in contrast to the relationship found in cBMLs. Analysis of TdT intensity and Cμ expression in sorted subpopulations of cells from individual patients that were positive or negative for CD34, CD20, or CD10 was consistent with the data obtained by comparison of cells from different patients. These results indicate that from patient to patient and within individual patients, cALL cells express the markers CD34, CLA, CD10, and Cμ in a coordinated fashion similar to cBMLs, but demonstrate differences in expression of TdT and CD20 with respect to the marrow cells considered their normal counterparts. The cALL cells that are CD34 positive show increased expression of CD10 and are less likely to be CLA or Cμ positive, suggesting that they may represent a phenotypically less differentiated form of cALL than does CD34-neaative cALL.© 1987 by Grune & Stratton, Inc. 0006-4971/87/7003-0044%3.00/0

Adherent cell layers and their associated extracellular matrices form when human marrow is incubated in cultures containing hydrocortisone and horse serum. These stromal layers contain cells positive for alkaline phosphatase; secrete collagens types I and III and fibronectin, bind the anti-actin monoclonal antibodies (MoAbs) HHF and CGA-7; stain with oil red O, and express the acetylated LDL receptor. Highly purified CD34 (My10)-positive progenitor cells attach to these stromal layers, and a 16-fold enrichment of CFU-GM in both stromal attachment and semisolid agar assays was observed. Granulopoiesis persisted up to 40 days (mean duration 25 days) after passaged stroma were recharged with stromal cell-depleted target cells in a two-stage liquid marrow culture system. Although equal to marrow fibroblasts in their ability to bind CD34+ myeloid progenitors, stromal layers were better at supporting granulopoiesis. This system provides an in vitro model to characterize the components of stroma and stroma-cytomatrix that enhance marrow progenitor cell localization and maintenance.© 1989 by Grune & Stratton, Inc. 0006-4971/89/7307-0009$3.00/0

Proliferation of normal human lymphoid progenitors in culture is dependent on interaction with bone marrow–derived fibroblast-like cells (BM-FB). To investigate possible heterogeneity in this lymphoid-supportive microenvironment, we studied the interaction of a human B-precursor cell line (NALM-6) with BM-FB. NALM-6 cells associate with BM-FB by either adhesion or migration underneath the fibroblast. Individual fibroblasts in the BM-FB layer showed significant variation in the number of migrating NALM-6 cells. Migration of NALM-6 cells was primarily VLA-4–dependent, although residual migration observable after blocking with anti–VLA-α4 antibody was inhibited by anti–VLA-α5 antibody. Migration was not inhibited by blocking either of the known VLA-4 counterreceptors (VCAM-1 or fibronectin), although slight inhibition was observed using a combination of blocking antibodies to VCAM-1 and fibronectin. In contrast, NALM-6 adhesion without migration was significantly inhibitable by anti–VCAM-1 antibody. VCAM-1 or fibronectin expression on individual BM-FB did not correlate with NALM-6 migration. These results indicate that the adhesion and migration of human B-lymphoid precursors in the bone marrow microenvironment are mechanistically separable events and suggest the possibility of novel VLA-4 ligand(s), which may be important in human lymphopoiesis. Subpopulations of cells in the bone marrow microenvironment may preferentially support important aspects of lymphoid progenitor development.

To define the relationship between human immunodeficiency virus type 1 (HIV-1) infection in hematopoietic stem cells and virus production by their progeny, we performed kinetic studies infecting bone marrow (BM) stem cells and culturing them in the presence of hematopoietic growth factors. CD34-positive (CD34+), CD4-negative (CD4–) BM cells were isolated and infected in vitro with the monocyto-tropic HIV-1JR-FLstrain or the laboratory-maintained HTLV-IIIBstrain at a high multiplicity of infection. The cells were susceptible to productive infection only with HIV-1JR-FL, and virus production as measured by p24 protein release was markedly increased (more than fivefold) in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). Macrophage CSF (M-CSF) was less stimulatory and granulocyte CSF (G-CSF) had no effect on virus production. Virus production coincided with proliferation of mononuclear phagocytes but was not related to granulocytic proliferation in G-CSF-treated BM cultures. Although peak virus production from GM-CSF–treated macrophages occurred 2 to 3 weeks after infection, peak virus production in infected stem cells was observed 5 to 6 weeks after. Enhancement in virus production had a more rapid onset when CD34+/CD4– cells were cultured in the presence of both GM-CSF and IL-3 for 7 or 14 days. Under these conditions there was a 10-fold enhancement in virus production after 7 days of preincubation and a 50-fold enhancement after 14 days. These data indicate that while the stem cell compartment may be susceptible to infection with a monocy-totropic HIV-1 strain, productive and sustained infection is realized only after macrophage differentiation. The lack of effect of G-CSF on virus production is likely because of the limited effect of this hematopoietin on mononuclear phagocyte generation and function.

Adhesion of hematopoietic progenitor cells to marrow-derived adherent cells has been noted for erythroid, myeloid, and lymphoid precursors. In this report, we have characterized very late antigen (VLA) integrin expression on normal CD34+ marrow progenitors, on leukemic cell lines, and on blasts from patients with acute myelogenous or monocytic leukemias. CD34+progenitor cells expressed the integrin β1chain (CD29), VLA-4α(CD49d), and VLA-5α(CD49e). The myeloid lines KG1 and KG1a also expressed CD49d and CD49e as did the Mo7e megakaryoblastic line. CD29, CD18, and CD11 a were also present on each of these cell lines. Only the Mo7e line expressed the cytoadhesins GPIIbllla or GPIb. Binding of KG1a to marrow stroma was partially inhibited by antibodies to CD49d and its ligand, vascular cell adhesion molecule (VCAM-1). The majority of leukemic blasts studied expressed CD49d and CD49e as well. Blasts from patients with acute myelomonocytic leukemia consistently bound to stroma at levels greater than 20%, and adhesion to stroma could in some cases be partly inhibited by anti-CD49d. No role for glycosylphosphatidylinositol (GPI)-linked structures was demonstrated in these binding assays because the adhesion of leukemic blasts to stroma was not diminished after treatment with phosphatidylinositol-specific phospholipase C (PI-PLC). These studies indicate that CD34+myeloid progenitors, myeloid leukemic cell lines, and leukemic blasts possess a similar array of VLA integrins. Their functional importance individually or in combination with other mediators of attachment in adhesion, transendothelial migration, and differentiation has yet to be fully elucidated.

Bone marrow samples from normal adults and children with nonhematologic malignancies not involving the marrow, acute lymphoblastic leukemia (ALL) in continued remission, and immune cytopenias were studied by two-color immunofluorescence (IF) and flow cytometry to characterize common acute lymphoblastic leukemia antigen (CALLA)-positive marrow lymphoid cells. Marrow was separated by Ficoll/Hypaque centrifugation followed by passage over a monoclonal antibody affinity column to remove myeloid cells prior to IF staining. A higher proportion of CALLA-positive cells was found in the pediatric marrows (mean, 33.7% ± 6.3% SEM) than in the adult marrows (mean, 4.5% ± 1.6% SEM). Two subpopulations of CALLA-positive cells identified by cell sorting to be of lymphoid morphology were found in both adult and pediatric marrows. A small subpopulation comprising 12.3% of the total CALLA-positive cells was characterized by a high intensity of CALLA, terminal deoxynucleotidyl transferase (TdT), and MY10 expression, but low B1, common leukocyte antigen, and peanut agglutinin receptor expression. The remainder of the CALLA-positive cells displayed low intensity of CALLA expression, positivity for the common leukocyte antigen, B1 and peanut agglutinin, and negative reaction with TdT and MY10. Both CALLA-positive subpopulations were positive for HLA-DR and the pan-B cell marker B4, but negative for cytoplasmic immunoglobulin, B2 and Leu 1. BrdU labelling studies showed that a similar proportion of cells in each subpopulation was in S phase. A slightly higher proportion of the strongly CALLA-positive cells possessed the morphologic features of high nuclear/ cytoplasmic (N/C) ratio and prominent nucleoli. These studies suggest that a discrete maturation step occurs among CALLA-positive marrow lymphoid cells, resulting in the loss of TdT and MY10 expression, but gradual acquisition of the B cell marker B1 and the common leukocyte antigen. The presence of B4 antigen in nearly all CALLA-positive cells suggests that both subpopulations of normal CALLA-positive marrow cells are committed to the B cell lineage.