Radiation sensitivity of human B-lineage lymphoid precursor cells

We studied the radiation sensitivity of eight immunophenotypically distinct B-lineage lymphoid precursor cell (LPC) lines of acute lymphoblastic leukemia (ALL) or fetal liver origin corresponding to discrete developmental stages of human B-cell ontogeny. The radiation sensitivity of B-lineage LPC showed a temporal association with the distinct stages of development. FL112 and FL114 fetal liver pro-B cells (Stage 0 B-lineage LPC) with germline immunoglobulin heavy chain (IgH) genes but rearranged T-cell receptor gamma (T gamma) genes (DO of FL112 = 80.3 cGy, DO of FL114 = 50.2 cGy), REH ALL pre-pre-B cells (Stage I B-lineage LPC) with rearranged IgH and T gamma genes (DO = 66.1 cGy), and NALM-6 ALL pre-pre-B/pre-B cells (Stage II B-lineage LPC) (DO = 50.5 cGy) corresponding to the earliest three stages of human B-lymphocyte development were the most radiation sensitive B-lineage LPC populations. By comparison, KM-3 ALL pre-B (Stage III B-lineage LPC) (DO = 194.7 cGy), HPB-NULL ALL pre-B (Stage IV B-lineage LPC) (DO = 134.6 cGy), and sIgM+ RAJI/NAMALWA early B (Stage Va/b B-lineage LPC) cell lines (DO of RAJI = 144.0 cGy, DO of NAMALWA = 165.5 cGy) corresponding to the later stages of human B-lymphocyte development were much more radiation resistant. These results indicate that the radiation sensitivity of B-lineage LPC decreases during maturation within the B-lineage lymphoid precursor pathway. By comparison, the S-phase index (% of S-phase cells as determined by DNA flow cytometry) or proliferation index (% S + G2M), cellular protein content, intracellular glutathione (GSH) level, glutathione-S-transferase (GST) activity, intracellular pH, or free cytoplasmic calcium concentration did not correlate with the radiation sensitivity of the B-lineage LPC.

Stimulation of protein tyrosine phosphorylation, phosphoinositide turnover, and multiple previously unidentified serine/threonine-specific protein kinases by the Pan-B-cell receptor CD40/Bp50 at discrete developmental stages of human B-cell ontogeny

CD40/Bp50 B-cell receptor has been implicated as having an important function for the regulation of human B-cell growth and maturation as well as antigen-driven selection of tonsillar B-cells in germinal centers. The purpose of the present study was to examine the biochemical events triggered by the engagement of the CD40 receptor in human B-lineage lymphoid cells corresponding to discrete developmental stages of human B-cell ontogeny. The engagement of the CD40 receptor on pro-B-, pre-pre-B-, pre-B-, or activated mature B-cells but not on resting mature B-cells with the agonistic anti-CD40 monoclonal antibody G28-5 resulted in enhanced tyrosine phosphorylation of four distinct phosphoproteins with molecular masses of 67, 72, 96, and 113 kDa and induced a rapid increase in the production of inositol 1,4,5-trisphosphate. Further, we have identified five electrophoretically distinct renaturable CD40-regulated serine/threonine-specific protein kinases (PK120, PK93, PK76, PK55, and PK48) that showed markedly increased in vitro activity after CD40 stimulation. Protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7) abrogated the stimulation of the in vitro activity of PK120, PK93, PK55, and PK48 and attenuated the stimulation of the in vitro activity of PK76 in response to the engagement of the CD40 receptor but did not influence the enhanced tyrosine phosphorylation of cellular substrates after CD40 stimulation. Notably, genistein and herbimycin A, two potent inhibitors of tyrosine-specific protein kinases, not only abrogated the CD40-induced enhanced tyrosine phosphorylation on the 67-, 72-, 96-, and 113-kDa substrates, but they also inhibited the CD40-induced stimulation of phosphoinositide turnover as well as the CD40-induced increase of the in vitro activity of renaturable serine/threonine-specific protein kinases.(ABSTRACT TRUNCATED AT 400 WORDS)

Engagement of interleukin-7 receptor stimulates tyrosine phosphorylation, phosphoinositide turnover, and clonal proliferation of human T-lineage acute lymphoblastic leukemia cells

The purposes of this study were to examine the biologic effects of the engagement of the interleukin-7 receptor (IL-7R) with recombinant human interleukin-7 (rhIL-7) in immunophenotypically distinct T-lineage acute lymphoblastic leukemia (ALL) blasts and to elucidate the biochemical nature of the IL-7R-linked transmembrane signal in rhIL-7-responsive T-lineage ALL blast populations. In the absence of costimulants, rhIL-7 stimulated the in vitro proliferation and colony formation of freshly isolated leukemic blasts from six to eight T-lineage ALL patients with a mean plating efficiency of 196 +/- 53 (background subtracted) colonies/10(5) blasts plated. Stimulation of T-lineage ALL blasts with rhIL-7 resulted in markedly enhanced tyrosine phosphorylation of six distinct phosphoproteins with molecular weights of 57, 72, 98, 123, 150, and 190 Kd, and induced a rapid increase in the production of inositol-1,4,5-trisphosphate (Ins-1,4,5-P3), which was inhibitable by the tyrosine-specific protein kinase inhibitor genistein, but not by the serine/threonine-specific protein kinase C inhibitor H7. Similarly, rhIL-7 stimulated Ins-1,4,5-P3 production in CEM-1.3 T-lineage ALL cells and this stimulation was inhibitable by the tyrosine-specific protein kinase inhibitors genistein and herbimycin A, but not by H-7. Thus, the transmembrane signal triggered by engagement of the IL-7R is intimately linked to a functional tyrosine-specific protein kinase pathway and stimulates the phosphoinositide (PI) turnover and proliferation of T-lineage ALL blasts. The presented data confirm and extend previous studies on the expression of functional IL-7R on T-lineage ALL blasts and support the hypothesis that IL-7 may play an important regulatory role in the biology of T-lineage ALL.

Interleukin 7 receptor engagement stimulates tyrosine phosphorylation, inositol phospholipid turnover, proliferation, and selective differentiation to the CD4 lineage by human fetal thymocytes

The purposes of this study were to elucidate the effects of recombinant human interleukin 7 (rhIL-7) on proliferation as well as differentiation of human fetal thymocytes and to analyze the biochemical nature of the IL-7 receptor-linked transmembrane signal. In the absence of costimulants, rhIL-7 stimulated the in vitro proliferation and colony formation of CD4+CD8+ double-positive immature fetal thymocytes. Furthermore, rhIL-7 promoted partial differentiation of immature thymocytes with a selective advantage for the development of CD4+CD8- single-positive thymocytes. Our observations suggest that IL-7 likely has an important regulatory role during the earliest stages of human T-cell ontogeny. Stimulation of fetal thymocytes with rhIL-7 resulted in enhanced tyrosine phosphorylation of three distinct phosphoproteins with molecular masses of 72, 98, 123, and 190 kDa and induced a rapid and biphasic increase in the production of inositol 1,4,5-trisphosphate, which was inhibitable by the tyrosine protein kinase inhibitor genistein. Thus, the transmembrane signal triggered by engagement of the IL-7 receptor is intimately linked to a functional tyrosine protein kinase pathway and stimulates the inositol phospholipid turnover and proliferation, as well as selective differentiation to the CD4 lineage, by human fetal thymocytes.

Comparative analysis of the in vivo radioprotective effects of recombinant granulocyte colony-stimulating factor (G-CSF), recombinant granulocyte-macrophage CSF, and their combination

The purpose of the present study was to evaluate and compare the in vivo radioprotective effects of pre-total body irradiation (TBI) conditioning with recombinant granulocyte colony-stimulating factor (rG-CSF) and recombinant granulocyte-macrophage CSF (rGM-CSF) in a large series of lethally and supralethally irradiated mice. Also analyzed were the radioprotective effects of simultaneous as well as sequential combinations of rG-CSF and rGM-CSF. Our findings in 1,180 mice provide direct evidence that in vivo administration of rG-CSF or rGM-CSF before TBI protects a significant fraction of mice from the lethal effects of LD100/30 TBI. At equivalent doses, rG-CSF displayed a more potent radioprotective activity than rGM-CSF. Not only was rG-CSF radioprotective at much smaller doses than rGM-CSF, the survival rate after lethal TBI was also significantly higher in mice receiving optimally radioprotective doses of rG-CSF as compared with mice receiving optimally radioprotective doses of rGM-CSF. Pretreatment of mice with rGM-CSF markedly attenuated the radioprotective affects of rG-CSF in lethally as well as supralethally irradiated mice. Pretreatment with rG-CSF followed by rGM-CSF was slightly more effective than rG-CSF alone in supralethally irradiated mice but not in lethally irradiated mice. Notably, marked differences among different strains of mice were noted regarding the optimally radioprotective doses of rG-CSF or rGM-CSF as well as probability of survival and median survival time after lethal or supralethal TBI. This report confirms and extends previous studies concerning the potential of cytokines in prevention or therapy of lethal radiation injury.

Interleukin 7 receptor ligation stimulates tyrosine phosphorylation, inositol phospholipid turnover, and clonal proliferation of human B-cell precursors

Functional interleukin 7 (IL-7) receptors are expressed on the surface of multiphenotypic, biphenotypic, and immature B-lineage human lymphoid precursor cells with germ-line immunoglobulin heavy-chain genes but not on more mature B-lineage lymphoid cells with rearranged and/or expressed immunoglobulin heavy-chain genes. Thus, IL-7 may have an important regulatory role during the earliest stages of human B-cell ontogeny. The engagement of the surface IL-7 receptors on immature B-cell precursor cells with recombinant human IL-7 (rhIL-7) results in enhanced tyrosine phosphorylation of multiple phosphoproteins, stimulates inositol phospholipid turnover and DNA synthesis, and promotes their clonal proliferation. These effects are (i) specific for rhIL-7, since rhIL-3, rhIL-4, rhIL-5, rhIL-6, and recombinant human granulocyte colony-stimulating factor do not elicit similar activities on IL-7 receptor-positive human pro-B cells; and (ii) mediated by IL-7 receptors, since they are not observed in IL-7 receptor-negative B-lineage lymphoid cell populations. rhIL-7-induced tyrosine phosphorylation on the 35-, 53-, 55-, 62-, 69-, 76-, 94-, 150-, 170-, and 190-kDa substrates as well as rhIL-7-induced stimulation of inositol phospholipid turnover are abrogated by the tyrosine kinase inhibitor genistein. These results demonstrate that the IL-7 receptor on immature human B-cell precursor populations is intimately linked to a functional tyrosine kinase pathway and tyrosine phosphorylation is an important and perhaps mandatory step in the generation of the IL-7 receptor-linked transmembrane signal.

CD4 and CD8 are positive regulators of T cell receptor signal transduction in early T cell differentiation

Although cortical (CD4+CD8+) thymocytes mobilize intracellular calcium poorly when CD3/TCR is ligated, we have found that murine cortical thymocytes can transduce strong biochemical signals in response to ligation of the CD3/Ti TCR complex (CD3/TCR) and that the signals are regulated by CD4 and CD8 interactions with CD3/TCR. Striking increases in intracellular calcium were observed in cortical thymocytes from transgenic mice containing productively rearranged alpha and beta TCR genes, when CD3 or TCR was cross-linked with CD4 or CD8 using heteroconjugated mAb. However, in mature T cells derived from lymph nodes of these mice, identical stimuli elicited calcium responses that were significantly smaller in magnitude. A thymocyte cell line that expresses a low level of the transgenic TCR and has a phenotype characteristic of cortical thymocytes (CD4+CD8+J11d+Thy-1+) was established from a female alpha beta TCR transgenic mouse. Cross-linking of CD4 or CD8 molecules to CD3/TCR induced strong calcium responses in these cells. Responses were weak or absent when CD3 or TCR were aggregated alone. Heteroconjugates of Thy-1xCD3 did not increase the intracellular calcium concentration in transgenic thymocytes or in the thymocyte cell line, although Thy-1 is highly expressed on immature cells. Enhanced tyrosine phosphorylation was observed when CD3 or TCR was cross-linked with CD4 or CD8 on transgenic thymocytes or on the thymocyte cell line, in comparison with aggregation of CD3/TCR alone. Taken together, these data show that CD4 and CD8 molecules allow the weakly expressed CD3/TCR of cortical thymocytes to transduce strong intracellular signals upon receptor ligation. These signals may be involved in selection processes at the CD4+CD8+ stage of differentiation.

CD4 and CD8 are positive regulators of T cell receptor signal transduction in early T cell differentiation

Although cortical (CD4+CD8+) thymocytes mobilize intracellular calcium poorly when CD3/TCR is ligated, we have found that murine cortical thymocytes can transduce strong biochemical signals in response to ligation of the CD3/Ti TCR complex (CD3/TCR) and that the signals are regulated by CD4 and CD8 interactions with CD3/TCR. Striking increases in intracellular calcium were observed in cortical thymocytes from transgenic mice containing productively rearranged alpha and beta TCR genes, when CD3 or TCR was cross-linked with CD4 or CD8 using heteroconjugated mAb. However, in mature T cells derived from lymph nodes of these mice, identical stimuli elicited calcium responses that were significantly smaller in magnitude. A thymocyte cell line that expresses a low level of the transgenic TCR and has a phenotype characteristic of cortical thymocytes (CD4+CD8+J11d+Thy-1+) was established from a female alpha beta TCR transgenic mouse. Cross-linking of CD4 or CD8 molecules to CD3/TCR induced strong calcium responses in these cells. Responses were weak or absent when CD3 or TCR were aggregated alone. Heteroconjugates of Thy-1xCD3 did not increase the intracellular calcium concentration in transgenic thymocytes or in the thymocyte cell line, although Thy-1 is highly expressed on immature cells. Enhanced tyrosine phosphorylation was observed when CD3 or TCR was cross-linked with CD4 or CD8 on transgenic thymocytes or on the thymocyte cell line, in comparison with aggregation of CD3/TCR alone. Taken together, these data show that CD4 and CD8 molecules allow the weakly expressed CD3/TCR of cortical thymocytes to transduce strong intracellular signals upon receptor ligation. These signals may be involved in selection processes at the CD4+CD8+ stage of differentiation.

Accessory receptors regulate coupling of the T-cell receptor complex to tyrosine kinase activation and mobilization of cytoplasmic calcium in T-lineage acute lymphoblastic leukemia

T-lineage acute lymphoblastic leukemia (T-ALL) cells have abundant cytoplasmic CD3/Ti but express low amounts on the cell surface and are deficient in CD3/Ti-mediated signal transduction. Nevertheless, plating T-ALL cells on dishes containing immobilized anti-CD3 monoclonal antibodies with a source of growth factors induced the expression of CD25 (interleukin-2 receptor alpha chain) and stimulated the formation of blast colonies in 12 of 14 cases studied. The proliferative response to CD3 ligation was modulated by the presence of antibodies to the CD2, CD4, or CD8 accessory T-cell receptors. The effect of these accessory receptors on signal transduction mediated by CD3/Ti was next investigated by monitoring cytoplasmic calcium concentration [( Ca2+]i) and by measuring tyrosine phosphorylation after stimulation. Crosslinking CD3, CD2, CD4, or CD8 alone did not induce cytoplasmic calcium mobilization in T-ALLs, but crosslinking the accessory receptors with CD3/Ti induced calcium responses in three of the T-ALLs and enhanced calcium responses in three of the T-ALL cell lines, including HPB-ALL, MOLT-4, and CEM. Crosslinking CD4 but not CD2 with CD3/Ti greatly enhanced tyrosine phosphorylation of multiple substrates in comparison with crosslinking either CD4 or CD3/Ti separately on both normal mature T cells and the CEM T-ALL cell line. Thus, CD4 regulates CD3/Ti signal transduction in T-ALL cells through the tyrosine phosphorylation of substrates whereas CD2 may regulate [Ca2+]i signal transduction through a separate mechanism.

CD45 cross-linking regulates phospholipase C activation and tyrosine phosphorylation of specific substrates in CD3/Ti-stimulated T cells

In lymphocytes, CD45 regulates the increase in cytoplasmic calcium concentration that occurs after receptor cross-linking. Here we show that T cell receptor complex (CD3/Ti)-mediated inositol phosphate production was inhibited by CD45 ligation in Jurkat cells. CD3/Ti signaling in normal T cells was also inhibited by CD45 ligation, but coupling of CD4 with CD3/Ti gave augmented calcium signals that were entirely resistant to the inhibitory effect of CD45. In contrast, CD3-induced T cell proliferation was suppressed by immobilized CD45 mAb even in the presence of CD4 mAb. The effect of CD45 and CD4 ligation on tyrosine phosphorylation during T cell activation was directly examined by immunoblotting with anti-phosphotyrosine. Using immobilized mAb, CD45 ligation suppressed the tyrosine phosphorylation of specific substrates induced by CD3/Ti stimulation, including almost complete suppression of 150-, 36-, and 35-kDa proteins and partial suppression of 76- and 80-kDa proteins. Other tyrosine-phosphorylated proteins induced by CD3/Ti stimulation, including 135- and 21-kDa proteins, were not suppressed by simultaneous ligation of CD3/Ti and CD45. Simultaneous ligation of CD3 and CD4 enhanced tyrosine phosphorylation of all substrates, but did not overcome the CD45-mediated suppression of tyrosine phosphorylation of the 35- and 36-kDa proteins. The CD45-mediated suppression of phospholipase C activation is therefore modulated by association with CD4 without altering the specific inhibition of tyrosine phosphorylation and T cell proliferation after co-ligation of CD45 and CD3/Ti.

CD45 cross-linking regulates phospholipase C activation and tyrosine phosphorylation of specific substrates in CD3/Ti-stimulated T cells

In lymphocytes, CD45 regulates the increase in cytoplasmic calcium concentration that occurs after receptor cross-linking. Here we show that T cell receptor complex (CD3/Ti)-mediated inositol phosphate production was inhibited by CD45 ligation in Jurkat cells. CD3/Ti signaling in normal T cells was also inhibited by CD45 ligation, but coupling of CD4 with CD3/Ti gave augmented calcium signals that were entirely resistant to the inhibitory effect of CD45. In contrast, CD3-induced T cell proliferation was suppressed by immobilized CD45 mAb even in the presence of CD4 mAb. The effect of CD45 and CD4 ligation on tyrosine phosphorylation during T cell activation was directly examined by immunoblotting with anti-phosphotyrosine. Using immobilized mAb, CD45 ligation suppressed the tyrosine phosphorylation of specific substrates induced by CD3/Ti stimulation, including almost complete suppression of 150-, 36-, and 35-kDa proteins and partial suppression of 76- and 80-kDa proteins. Other tyrosine-phosphorylated proteins induced by CD3/Ti stimulation, including 135- and 21-kDa proteins, were not suppressed by simultaneous ligation of CD3/Ti and CD45. Simultaneous ligation of CD3 and CD4 enhanced tyrosine phosphorylation of all substrates, but did not overcome the CD45-mediated suppression of tyrosine phosphorylation of the 35- and 36-kDa proteins. The CD45-mediated suppression of phospholipase C activation is therefore modulated by association with CD4 without altering the specific inhibition of tyrosine phosphorylation and T cell proliferation after co-ligation of CD45 and CD3/Ti.

Production of a pokeweed antiviral protein (PAP)-containing immunotoxin, B43-PAP, directed against the CD19 human B lineage lymphoid differentiation antigen in highly purified form for human clinical trials

We describe a standardized method for the preparation and purification of a potent immunotoxin against B-lineage leukemia/lymphoma cells, constructed with the ribosome inhibitory single chain plant toxin pokeweed antiviral protein (PAP) and a murine IgG1 monoclonal antibody (MoAb) specific for the human B lineage differentiation antigen CD19 for human clinical trials. PAP was prepared from spring leaves of Phytolacca americana plants by ammonium sulfate precipitation and purified to homogeneity by successive steps of ion exchange chromatography. B43 MoAb was produced in vitro by hollow fiber technology and purified to homogeneity by affinity chromatography. PAP toxin and B43 MoAb were modified via their free amino groups prior to their intermolecular conjugation. 2-iminothiolane was used to introduce reactive sulfhydryl groups into PAP and N-succinimidyl 3-(2-pyridyldithio) propionate was used to introduce 2-pyridyl disulfide bonds into B43 MoAb. Modified PAP was reacted with modified B43 MoAb resulting in a sulfhydryl-disulfide exchange reaction and yielding disulfide linked PAP-B43 MoAb conjugates, which we refer to as B43-PAP immunotoxin. B43-PAP immunotoxin was subjected to preparative gel filtration chromatography and cation exchange chromatography to obtain a highly purified, sterile, and pyrogen-free immunotoxin preparation with less than 5% free antibody contamination and less than 0.5% free PAP contamination. The final product displayed a high affinity for and a very potent anti-leukemic activity against B lineage leukemia cells. With slight modifications, the procedures detailed in this report should be generally applicable to preparation of other PAP-MoAb conjugates for treatment of cancer or AIDS.

Inhibition of HIV-1 replication in seropositive patients' CD4+ T-cells by pokeweed antiviral protein-monoclonal antibody conjugates

Pokeweed antiviral protein (PAP) inhibits HIV-1 replication in HIV-1 infected CD4+ cells and PAP targeted to CD4+T-cells by conjugation with monoclonal antibodies (mAb) against CD4 is approximately 1000 times more potent than non-conjugated PAP. Furthermore, PAP-antiCD4 inhibits HIV-1 production in seropositive patients' CD4+ T-cells activated with mAb to CD3 which was found to be the most potent means to activate HIV-1 production. These findings, together with previous observations that PAP-mAb conjugates have an in vivo plasma half-life of about 30 times that of non-conjugated PAP, suggest that PAP-antiCD4 may be a useful therapy in HIV-infected humans. Additionally, because PAP is known to have antiviral activity against several other human viruses, PAP-mAb conjugates may also have clinical potential for treating other viral diseases.

Temporal association of CD40 antigen expression with discrete stages of human B-cell ontogeny and the efficacy of anti-CD40 immunotoxins against clonogenic B-lineage acute lymphoblastic leukemia as well as B-lineage non-Hodgkin's lymphoma cells

Detailed immunophenotypic analyses of immunologically classified leukemias and lymphomas showed that CD40 displays an exquisite B-lineage specificity within the human lymphopoietic system. Notably, 82% of B-lineage chronic lymphocytic leukemias (CLLs), 82% of B-lineage hairy cell leukemias (HCLs), 86% of B-lineage non-Hodgkin's lymphomas (NHLs), and 29% of B-lineage acute lymphoblastic leukemias (ALLs) were CD40+. Quantitative analyses of the correlated expression of CD40 and other B-lineage differentiation antigens on fetal lymphoid precursor cells by multiparameter two-color/three-color flow cytometry, combined with analyses of sequential antigen expression on fluorescence-activated cell fluorescence activated cell sorter (FACS) isolated immunologically distinct fetal B-cell precursor subpopulations during in vitro proliferation and differentiation, provided evidence that the acquisition of CD40 antigen in human B-cell ontogeny occurs subsequent to the expression of CD10 and CD19 antigens but before the surface expression of CD20, CD21, CD22, CD24, and surface immunoglobulin M (sIgM). Some leukemic pro-B cells from ALL patients as well as normal pro-B cell clones from fetal livers displaying germline Ig heavy chain genes were CD40+, indicating that the acquisition of CD40 antigen likely precedes the rearrangement of Ig heavy chain genes. CD40+ FACS-sorted malignant cells from B-lineage ALL as well as B-lineage NHL patients were capable of in vitro clonogenic growth, indicating the CD40 antigen is expressed on clonogenic leukemia and lymphoma cells. This hypothesis was confirmed by the ability of an anti-CD40 immunotoxin that we used as an antigen-specific cytotoxic probe to effectively kill clonogenic B-lineage ALL and NHL cells.

Autologous bone marrow transplantation in high-risk remission T-lineage acute lymphoblastic leukemia using immunotoxins plus 4-hydroperoxycyclophosphamide for marrow purging

Fourteen patients with high-risk T-lineage acute lymphoblastic leukemia (ALL) in complete remission underwent autologous bone marrow transplantation (BMT) in an attempt to eradicate their residual disease burden. A combined immunochemotherapy protocol using a cocktail of two immunotoxins directed against CD5/Tp67 and CD7/Tp41 T-lineage differentiation antigens in combination with the in vitro active cyclophosphamide congener 4-hydroperoxy-cyclophosphamide (4-HC) was used to purge autografts. Despite high dose pretransplant radiochemotherapy and effective purging of autografts, 9 of 14 patients relapsed at a median of 2.5 months (range, 1.2 to 16.8 months) post BMT. Two patients remain alive and disease free at 26 and 28 months post BMT. We used a novel quantitative minimal residual disease (MRD) detection assay, which combines fluorescence activated multiparameter flow cytometry and cell sorting with leukemic progenitor cell (LPC) assays, to analyze remission bone marrow (BM) samples from T-lineage ALL patients for the presence of residual LPCs. Notably, high numbers of residual LPC detected in remission BM before BMT constituted a poor prognostic indicator, providing the first evidence for the biologic significance and clinical value of in vitro T-lineage ALL LPC assays. The median value for the residual leukemia burden before BMT, was approximately 8.6 x 10(3) LPC/10(8) mononuclear cells (MNC) (approximately 0.0086% LPC). Patients with a residual leukemia burden less than this median value appeared to have a better outlook for remaining free of relapse after autologous BMT than patients with a greater leukemia burden (53 +/- 25% v 14 +/- 13%, P = .006, Mantel-Cox). By comparison, the log kill efficacy of purging, the remaining numbers of LPC in purged autografts, or the estimated numbers of reinfused LPC, did not correlate with the probability of disease-free survival (DFS). These results indicate that the primary reason for the recurrence of leukemia was inefficient pretransplant radiochemotherapy rather than inefficient purging of autografts.

In vivo radioprotective effects of recombinant human granulocyte colony-stimulating factor in lethally irradiated mice

The purpose of this study was to investigate the in vivo radioprotective effects of recombinant human granulocyte colony stimulating factor (rhG-CSF) in lethally irradiated BALB/c mice. We initially analyzed the effects of increasing doses of rhG-CSF on survival of mice receiving 700 cGy (LD100/30) single dose total body irradiation (TBI). While 1 microgram/kg to 100 micrograms/kg doses of rhG-CSF were not radioprotective, a dose-dependent radioprotection was observed at 200 micrograms/kg to 4,000 micrograms/kg rhG-CSF. We next compared four different rhG-CSF treatment regimens side by side for their radioprotective effects in LD100/30 irradiated mice. One hundred percent of control mice receiving phosphate buffered saline died within 21 days after TBI with a median survival of 14 days. The median survival was prolonged to 20 days and the actuarial 60-day survival rate was increased to 27% when mice received 2,000 micrograms/kg rhG-CSF 24 hours before TBI (P = .0002; Mantel-Peto-Cox). Similarly, the median survival time was prolonged to 24 days and the actuarial 60-day survival rate was increased to 33%, when mice were given 2,000 micrograms/kg rhG-CSF 30 minutes before TBI. Optimal radioprotection was achieved when 2,000 micrograms/kg rhG-CSF was administered in two divided doses of 1,000 micrograms/kg given 24 hours before and 1,000 micrograms/kg given 30 minutes before TBI. This regimen prolonged the median survival time of LD100/30 irradiated mice to more than 60 days and increased the actuarial 60-day survival rate to 62% (P = .0001; Mantel-Peto-Cox). By comparison, no survival advantage was observed when mice received rhG-CSF 24 hours post-TBI. Similar radioprotective effects were observed when mice were irradiated with 650 cGy (LD80/30). The presented findings provide conclusive evidence that rhG-CSF has significant in vivo radioprotective effects for mice receiving LD100/30 or LD80/30 TBI.

Thermal sensitivity and thermal tolerance of human B-lineage acute lymphoblastic leukemia (ALL) cells

The thermal sensitivities of four B-cell precursor acute lymphoblastic (ALL) cell lines (REH and KM-3 = pre pre B-ALL; NALM-6 and HPB-NULL = pre B-ALL), and 1 B-cell ALL (NAMALWA) cell line were studied and compared to the thermal sensitivity of the T-lineage ALL cell line MOLT-3 using an in vitro clonogenic assay system by limiting dilution. B-lineage ALL cells were as sensitive to hyperthermia as were T-lineage ALL cells. D0 values at 42 degrees C ranged from 44.9 min (NALM-6) to 85.6 min (NAMALWA), D0 values at 43 degrees C ranged from 15.3 min (NALM-6) to 35.7 min (KM-3), and D0 values at 44 degrees C ranged from 11.1 min (NALM-6) to 23.8 min (HPB-NULL). By comparison, the D0 values of MOLT-3 cells were 95.1 min at 42 degrees C, 23.8 min at 43 degrees C, and 14.7 min at 44 degrees C. The maximum log kill values which were observed ranged from 0.8 log (KM-3 and HPB-NULL) to 1.3 logs (NALM-6) at 42 degrees C, from 1.4 logs (KM-3) to 4.2 logs (NALM-6) at 43 degrees C, and from 3.8 logs (HPB-NULL) to 4.8 logs (NALM-6) at 44 degrees C. A thermal tolerant plateau was observed in the hyperthermia survival curves of REH, NALM-6, and HPB-NULL cells, providing circumstantial evidence that thermal tolerance may develop in some B-cell precursor ALL cells after 90-120 min of continuous heating. In contrast, no thermal tolerant plateau was observed in the hyperthermia survival curves of pre-pre-B-ALL/KM-3 B-cell ALL/NAMALWA or T-lineage ALL/MOLT-3 cells. The kinetics of development and decay of thermotolerance was studied for NALM-6 cells. Thermotolerance after a priming heat exposure to 42 degrees C for 30 min was maximum at 8 hr with a maximum thermotolerance ratio of 2.0, and it decayed by 24 hr. These findings extend previous studies on the thermal sensitivity of human leukemia cells and provide new information on the thermal sensitivity and thermotolerance of B-lineage ALL cells.

Cell-type-specific cytotoxicity of anti-CD4 and anti-CD8 ricin immunotoxins against human alloreactive T-cell clones

Potent T-cell subset-directed immunotoxins (ITs) were generated by conjugating the anti-CD4 monoclonal antibody (MoAb) G17-2 and the anti-CD8 MoAb G10.1 to the ribosome-inhibitory protein, ricin. The cell-type-specific cytotoxicities of the generated ITs were evaluated at the clonal level using human alloreactive T-cell clones. The kinetics of anti-CD4 ricin-induced inactivation of protein synthesis in target CD4+ cloned T-cells was first order with no detectable lag period and a maximum rate of 0.07 logs per hour (t10 = 13.6 hours; first-order rate constant/K = 0.17 hr-1). The alloantigen specific lytic function of the CD4+ cytolytic T-cell clone JMAC28 was acutely sensitive to anti-CD4 ricin, and no residual lytic activity against allogeneic targets was detectable 24 hours after treatment with as little as 0.5 mmol/L anti-CD4 ricin. Notably, both anti-CD4 ricin and anti-CD8 ricin elicited a selective and dose-dependent inhibition of clonal proliferation of target T-cell clones with a maximum kill of greater than 3 logs at 5 nmol/L. No significant "bystander effects" were observed for non-target cells. Bone marrow progenitor cells CFU-GM, BFU-E, and CFU-GEMM were only minimally affected by either IT. We conclude that these ITs show considerable potential for effective depletion of T-cell subpopulations from allogeneic donor marrow grafts for clinical graft-versus-host disease (GVHD) prophylaxis.

Radiobiological features of human pluripotent bone marrow progenitor cells (CFU-GEMM)

The purpose of this study was to evaluate the radiobiologic features of human pluripotent bone marrow progenitor cells (CFU-GEMM; colony forming unit-granulocyte-erythroid-macrophage/monocyte-megakaryocyte). Experiments were performed using fresh bone marrow cells as well as bone marrow cells stimulated with recombinant granulocyte-macrophage-colony stimulating factor (rGM-CSF) to increase the CFU-GEMM pool. The D0 values for CFU-GEMM in normal bone marrow samples (n = 9) ranged from 30.9 cGy to 85.7 cGy (mean +/- SE = 54.4 cGy +/- 6.2 cGy) and the D0 value of the composite radiation survival curve was 56.9 cGy, indicating that CFU-GEMM were acutely sensitive to the lethal effects of ionizing radiation. There was no distinct shoulder on the single dose radiation survival curves with Dq values ranging from -29.6 cGy to 4.4 cGy, and no increase in CFU-GEMM survival was observed when the radiation was fractionated. Hence, CFU-GEMM were unable to repair sublethal radiation damage. These findings confirm and extend previous studies on the radiobiologic features of human hematopoietic progenitor cell populations.

Detection and characterization of human high molecular weight B cell growth factor receptors on leukemic B cells in chronic lymphocytic leukemia

Human high molecular weight-B cell growth factor (HMW-BCGF) (60 kD) stimulates activated normal B cells, B cell precursor acute lymphoblastic leukemia (BCP-ALL) cells, hairy cell leukemia (HCL) cells, prolymphocytic leukemia (PLL) cells, and chronic lymphocytic leukemia (CLL) cells. The expression of human high molecular weight B cell growth factor (HMW-BCGF) receptors (R) on clonal populations of leukemic B cells in CLL was studied by ligand binding assays using 125I-labeled HMW-BCGF as well as by immunofluorescence/flow cytometry and Scatchard analyses using an anti-HMW-BCGF R monoclonal antibody (MAb), designated BA-5. There was a high correlation between HMW-BCGF R expression and responsiveness to HMW-BCGF. 60% of CLL cases constitutively expressed HMW-BCGF R and showed a marked proliferative response to HMW-BCGF in [3H]TdR incorporation assays as well as colony assays. Similarly, HCL cells, PLL cells, and activated normal B cells expressed functional HMW-BCGF R, as determined by ligand binding assays using 125I-HMW-BCGF, [3H]TdR incorporation assays, and reactivity with BA-5 MAb. Scatchard analyses indicated the existence of approximately 3,000 HMW-BCGF R/cell on HMW-BCGF responsive CLL cells with an apparent Ka value of 4.6 X 10(7) M-1. The concentrations of HMW-BCGF required for maximum stimulation of CLL cells were two to three orders of magnitude lower than those needed for half maximal receptor occupancy, indicating that only a small fraction of HMW-BCGF R need to be occupied to stimulate leukemic CLL B cells. Crosslinking of surface bound 125I-HMW-BCGF (60 kD) with the bivalent crosslinker DTSSP to its binding site on fresh CLL cells identified a 150-kD HMW-BCGF/HMW-BCGF R complex, suggesting an apparent molecular weight of 90 kD for the receptor protein. The growth stimulatory effects of HMW-BCGF on clonogenic CLL cells did not depend on accessory cells or costimulant factors. The anti-HMW-BCGF R monoclonal antibody BA-5 disrupted HMW-BCGF/HMW-BCGF R interactions at the level of clonogenic CLL cells and inhibited HMW-BCGF-stimulated CLL colony formation in vitro. To our knowledge, this study represents the first detailed analysis of expression, function, and structure of HMW-BCGF R on B lineage CLL cells.

Leukemic B-cell precursors constitutively express functional receptors for human interleukin-1

This study analyzes the expression of functional interleukin-1 (IL-1) receptors on leukemic B-cell precursors (BCPs) from B-cell precursor acute lymphoblastic leukemia (BCP ALL) patients. We first investigated the specific binding of 125I-labeled recombinant IL-1 (125I-rIL-1) (4 x 10(17) cpm/mol) to fresh marrow blasts from 11 BCP ALL patients. In five of 11 cases, the binding of 125I-rIL-1 was significantly blocked by excess cold rIL-1. In these five cases, the cell-bound radioactivity ranged from 146 cpm/10(6) cells to 2,412 cpm/10(6) cells (mean +/- SE = 782 +/- 414 cpm/10(6) cells), indicating that 4 to 60 femtomols (mean +/- SE = 20 +/- 10 femtomols) of 125I-rIL-1 specifically bound per 10(7) cells. The estimated number of 125I-rIL-1 molecules bound per cell ranged from 219 to 3,618 (mean +/- SE = 1173 +/- 621). In all five cases, BCP colony formation was stimulated by 10 ng/mL (570 femtomolar) rIL-1, and the background-subtracted colony numbers ranged from 130 to 298 (mean +/- SE = 226 +/- 31). In contrast, no stimulation was observed in six cases that showed no significant 125I-rIL-1 binding. Hence, there was a high correlation between 125I-rIL-1 binding and IL-1 responsiveness, indicating that functional IL-1 receptors were detected in ligand binding assays. Scatchard plot analysis of the specific equilibrium binding data for leukemic BCPs from two IL-1-responsive BCP ALL cases yielded straight linear regression lines, indicating the existence of a single class of 132 to 154 high affinity IL-1 receptors/cell. The apparent affinity constants (Ka) values ranged from 5.2 x 10(9) mol/L-1 to 1.2 x 10(10) mol/L-1. Notably, the concentrations of IL-1 required for half-maximal receptor occupancy (kd = 83 pmol/L to 190 pmol/L) were approximately three orders of magnitude higher than those needed to elicit a half-maximal proliferative response of leukemic BCPs in colony assays (0.1 to 1.0 ng/mL = 5.7 to 57 femtomolar), indicating that only a small fraction of IL-1 receptors need to be occupied to stimulate leukemic BCPs. Notably, IL-1 unresponsive leukemic BCPs from one BCP ALL patient and two BCP ALL cell lines (REH, KM-3) did not exhibit any significant IL-1 binding (less than 10 IL-1 binding sites/cell), and two additional IL-1 unresponsive BCP ALL cell lines (NALM-6, HPB-NULL) expressed only 24 to 54 IL-1 binding sites/cell with a Ka of 7.8 to 9.8 x 10(9) mol/L-1.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of aromatic and aliphatic maleimide crosslinkers on anti-CD5 ricin immunotoxins

The aromatic maleimide crosslinkers m-maleimidobenzoyl-N-hydroxysuccinimide ester (MBS), sulfosuccinimidyl 4-(p-maleimidophenyl) butyrate (S-SMPB) and m-maleimidobenzoylsulfosuccinimide ester (S-MBS) and the aliphatic crosslinker N-gamma-maleimidobutyryloxysuccinimide ester (GMBS) were used to make anti-CD5 intact ricin immunotoxins (IT). IT made with the various crosslinkers were compared under standard conjugation conditions for differences in yield, toxicity of the toxin moiety, binding of the antibody moiety, IT activity, and IT specificity. Our findings showed that IT yield was dramatically improved using crosslinkers with an aromatic, rather than an aliphatic configuration. Gel analysis showed that all IT were of similar, but not identical composition. Conjugation resulted in several IT species including antibody linked to one or two molecules of ricin. For MBS IT and S-SMPB IT, differences in amounts of IT in final fractions and IT in fractions after removal of IT species containing galactose binding sites showed that differences in yield may be attributable to the formation of IT species with obstructed galactose binding sites. All IT bound selectively by FACS analysis and blocking studies. The aliphatic GMBS crosslinker yielded the most toxic IT in cell-free translation assays as well as in shorter-term protein synthesis inhibition and mitogen assays. However, evaluation in the longer-term, more sensitive clonogenic assay showed that at 1000 ng/ml there were no differences in potency between any of the IT. We conclude that the yield of intact ricin IT can be improved using aromatic maleimide crosslinkers without sacrificing IT potency.

Biphenotypic leukemic lymphocyte precursors in CD2+CD19+ acute lymphoblastic leukemia and their putative normal counterparts in human fetal hematopoietic tissues

During detailed immunophenotypic analyses of marrow blasts from 336 acute lymphoblastic leukemia (ALL) patients, a very small percentage of cases reactive with B-cell-directed as well as T-cell-directed monoclonal antibodies (MoAbs) were identified. Five ALL cases were biphenotypic since they coexpressed CD2 (Tp50) and CD19 (Bp95) antigens at the single-cell level. The composite immunophenotype of these biphenotypic ALL cases was [TdT+HLA-ABC+CD2+CD3-CD10+CD13-CD14-CD16-CD19+CD20+ ++-CD21-CD33-CD34+Bgp95-C mu- slg-]. Low-molecular-weight B-cell growth factor (LMW-BCGF), recombinant interleukin-2 (rIL-2), and rIL-3 stimulated the proliferative activity of biphenotypic leukemic lymphocyte precursors without inducing differentiation. In the presence of the phorbol ester TPA, leukemic blasts from two cases differentiated along the B precursor pathway to the [CD2-CD10+CD19+CD20+C mu+slg-] pre-B cell stage. Biphenotypic ALL cases did not share a common configuration and gene rearrangement pattern of the immunoglobulin heavy chain genes or T-cell receptor (TCR) genes. Three cases had rearranged C mu genes but germline TCR genes, one case showed rearrangement of both C mu and TCR genes, and the remaining case had rearranged TCR genes but germline C mu genes. All five patients attained prompt remission after standard induction chemotherapy. Three to four years after initial diagnosis, four patients are now off chemotherapy and remain alive in their first remission. One patient relapsed at 3 years, 7 months, but promptly achieved complete remission after reinduction chemotherapy and remains in second remission off chemotherapy greater than 3 years after her reinduction therapy. With two-color immunofluorescence staining techniques and multiparameter flow cytometric analyses, we identified a small population of CD2+CD19+ lymphoid cells in fetal livers (FLs) and fetal bone marrows (FBMs), which may represent the putative normal counterparts of biphenotypic ALL blasts. A CD2+CD19+ normal biphenotypic lymphoid precursor cell line, designated FL 8.2 CD2+, was established from an FL of 8-weeks of gestational age by Epstein-Barr virus (EBV)-induced blastoid transformation. The composite immunophenotype of FL 8.2 CD2+ cell line was [TdT+HLA-ABC+HLA-DR+ CD2+CD5-CD7-CD10+/-CD13-CD19+CD20-CD21+ CD22+CD33-CD34+/-Bgp95-CDw40+C mu-slgD-slgM-]. FL 8.2 CD2+ cells showed germline patterns of immunoglobulin heavy-chain joining region, heavy-chain constant region, kappa light-chain constant region genes, and TCR beta-chain genes. Cross-linking of CD2 as well as CD19 antigens on FL 8.2 CD2+ cells caused an increase of intracellular ionized calcium.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhanced transmembrane signalling activity of monoclonal antibody heteroconjugates suggests molecular interactions between receptors on the T cell surface

Signal transduction occurs through multiple receptors expressed on mature, resting T cells. In addition to the CD3-T cell receptor complex, the CD2, CD4, CD5, CD7, CD8 and CD28 receptors mobilize cytoplasmic calcium within minutes of binding with monoclonal antibodies and additional crosslinking occurs on the cell surface. As an approach to study the interactions between these receptors and their transduced signals, monoclonal antibodies to each of these receptors were covalently coupled as heteroconjugates and investigated for activity in cytoplasmic calcium mobilization using indo-1 and flow cytometry. Of a total of 35 conjugates studied, there were seven heteroconjugates that showed an increase in activity and these consisted of either certain conjugates of anti-CD3 or certain conjugates of anti-CD5. The CD3-CD2, CD3-CD4, CD3-CD6 and CD3-CD8 heteroconjugates each gained two to three orders of magnitude in titer in calcium mobilization compared to unconjugated CD3 or the CD3-CD3 conjugate. The increase in activity was not accompanied by an increase in binding titer, indicating that signal transduction occurred at lower levels of receptor occupancy. The increased activity was dependent in each case on the relevant second receptor, since unconjugated CD2, CD4, CD6 or CD8 MAb could block the activity of the corresponding heteroconjugate. Neither CD3-CD5, CD3-CD28 or CD3-CD3 conjugates gained activity, whereas CD3-CD7 heteroconjugates gained slightly in activity. The heteroconjugates with CD5 that acquired ability to mobilize calcium at low concns (less than 5 micrograms/ml) were CD5-CD4, CD5-CD8 and CD5-CD6. Their activity could be inhibited by either CD5 MAb or the second MAb of the heteroconjugate. The increased activity of CD3 or CD5 heteroconjugates was observed in the absence of extracellular calcium. Size exclusion chromatography of heteroconjugates demonstrated that 1:1 ratios were optimal, but larger conjugates were also active. These results suggest that certain receptors are capable for molecular interactions on the cell surface to form complexes with enhanced activity in signal transduction leading to calcium mobilization.

Leukemic B-cell precursors express functional receptors for human interleukin-3

The purpose of this study was to analyze the expression of functional interleukin-3 (IL-3) receptors on leukemic B-cell precursors (BCPs) from 12 BCP acute lymphoblastic leukemia (ALL) patients and five BCP ALL cell lines. The specific binding of biosynthetically labeled 35S-recombinant (r) IL-3 to freshly obtained leukemic marrow blasts was initially investigated. In five of 12 BCP ALL cases, the binding of 35S-rIL-3 was markedly blocked by excess cold rIL-3, and the percentage of inhibitable binding ranged from 53% to 78% (mean +/- SE = 65% +/- 4%). In these cases, the cell-bound radioactivity ranged from 146 cpm/10(7) cells to 1,433 cpm/10(7) cells (mean +/- SE = 627 +/- 250 cpm/10(7) cells), indicating that 1 to 14 femtomole (mean +/- SE = 6 +/- 2 fms) of [35S]rIL-3/10(7) cells were specifically bound (= 60 to 840 molecules per cell). rIL-3 stimulated the proliferative activity of leukemic BCPs in a dose-dependent fashion without inducing differentiation, and the half-maximal stimulatory activity was observed at a concentration of 17 to 34 pmol/L. Fluorescence-activated cell sorter (FACS)-isolated virtually pure populations of CD10+CD19+ leukemic BCPs from two BCP ALL patients, as well as from two of five BCP ALL cell lines, showed a marked proliferative response to highly purified rIL-3, providing formal evidence that the observed IL-3 responses were not mediated by accessory cells. There was a high correlation between [35S]rIL-3 binding and proliferative response in colony assays, indicating that functional IL-3 receptors were detected in ligand binding assays. Scatchard plot analysis of the specific equilibrium binding data for IL-3-responsive leukemic BCPs from one BCP ALL patient and two BCP ALL cell lines yielded a straight linear regression line, indicating the existence of a single class of 60 to 210 high-affinity IL-3 binding sites/cell. The calculated apparent affinity constant (Ka) values ranged from 3.6 x 10(9) to 5.9 x 10(9) mol/L-1. Hence, the concentration of IL-3 required to produce 50% maximal receptor occupancy (Kd) was in the range of 168 to 280 pmol/L. These concentrations are approximately tenfold higher than those required to induce 50% maximal proliferative response from leukemic BCPs in colony assays, indicating that low receptor occupancy is sufficient for growth stimulation of leukemic BCPs by rIL-3. In comparison, less than 10 to 20 IL-3 molecules/cell were bound to IL-3 unresponsive leukemic BCPs even when the concentration of free-[35S]rIL-3 was as high as 2 nmol/L.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of recombinant growth factors on radiation survival of human bone marrow progenitor cells

The purpose of this study was to evaluate the individual radioprotective effects of 4 distinct purified recombinant human hematopoietic growth factors, namely recombinant human granulocyte-macrophage colony stimulating factor (rGM-CSF), recombinant human granulocyte colony stimulating factor (rG-CSF), recombinant human interleukin 1 (rIL-1), and recombinant human interleukin 2 (rIL-2) on human myeloid (CFU-GM) and erythroid (BFU-E) bone marrow progenitor cells. We demonstrate that (a) preconditioning with rGM-CSF, rG-CSF, or rIL-1 enables CFU-GM to repair sublethal radiation damage and renders CFU-GM less radiosensitive, (b) preconditioning with rGM-CSF or rIL-1 enables BFU-E to repair sublethal radiation damage, and (c) preconditioning with rIL-2 does not increase the radiation survival of CFU-GM or BFU-E. The effects of recombinant growth factors, in particular rGM-CSF, on the radiation damage repair, radiosensitivity, and proliferative activity of bone marrow progenitor cells resulted in a substantial increase in the mean numbers of progenitor cell-derived hematopoietic colonies in irradiated marrow samples. The effects of rGM-CSF on the radiation response of CFU-GM and BFU-E, and the effects of rG-CSF as well as rIL-1 on the radiation response of CFU-GM did not appear to require the presence of T-cells/T-cell precursors, NK-cells, B-cells/B-cell precursors, monocytes, macrophages, MY8 antigen positive non-CFU-GM myeloblasts, promyelocytes, myelocytes, metamyelocytes, granulocytes, or glycophorin A positive erythroid cells since virtually identical results were obtained with unsorted marrow samples or highly purified fluorescence activated cell sorter (FACS) isolated progenitor cell suspensions. To our knowledge, this report represents the first study on recombinant human growth factor-induced modulation of the radiation responses of normal human bone marrow progenitor cells.

Immunophenotype-karyotype associations in human acute lymphoblastic leukemia

The present study is a detailed analysis of the cytogenetic features of leukemic cells from 104 immunologically classified acute lymphoblastic leukemia (ALL) (78 B lineage and 26 T lineage) cases. Clonal chromosomal abnormalities were found in marrow blasts from 77 of 104 (74%) cases. Hyperdiploidy was much more frequent in B-lineage ALL cases, whereas normal diploidy was more common in T-lineage ALL cases. Fifty-nine of 104 cases (46 of 78 B-lineage ALL and 13 of 26 T-lineage ALL cases) had structural chromosomal abnormalities. Structural abnormalities involving 2p11, 7p13, 7p22, proximal q arm of 7 (7q11 or 7q22), 11q23-24, and translocations involving 12p11-13 appeared to be B-lineage specific. By comparison, structural abnormalities involving 7p15, 7q32, and 14q11 displayed T-lineage specificity. Structural abnormalities involving 9p22-p23 or 14q32, del (6)(q21-q23), del (12)(p11-p13), and the Philadelphia chromosome were found in B-lineage as well as T-lineage ALL cases. This study expands the current knowledge about immunophenotype-karyotype associations in ALL.

Immunobiologic differences between normal and leukemic human B-cell precursors

The early stages of normal human B-cell differentiation were studied by flow cytometry and cell sorting based on expression of CD10 (CALLA) and CD19 antigens in fetal liver. Both CD10+ CD19+ and CD10+ CD19- precursor populations proliferated in vitro to form B-cell precursor colonies under stimulation from low molecular weight B-cell growth factor (L-BCGF) or recombinant interleukin 3 but did not respond to high molecular weight B-cell growth factor (H-BCGF). The colonies derived from the CD10+ CD19- fraction showed induction of CD19 expression in 10-50% of growing cells, suggesting that CD10 expression precedes CD19 expression in B-cell ontogeny. This hypothesis was corroborated by less-differentiated marker profiles of the progeny of CD10+ CD19- B-cell precursors as compared to CD10+ CD19+ B-cell precursors in BCGF-stimulated cultures and by higher percentages of CD10+CD19- versus CD10-CD19+ B-cell precursors. CD19 crosslinking on normal fetal liver or bone marrow B-cell precursors was associated with an increase in cytoplasmic calcium concentration, but was inhibitory for colony formation. Leukemic B-cell precursors from acute lymphoblastic leukemias (ALLs) differed from normal B-cell precursors in their in vitro proliferative responses, since (i) they responded not only to L-BCGF and rIL-3 but also to H-BCGF and (ii) their proliferation was stimulated rather than inhibited by CD19 crosslinking. A clonogenic leukemic counterpart for the CD10+CD19- normal B-cell precursor population does not exist among malignant cells from B-cell precursor ALL patients, suggesting that the CD19 receptor may be involved in leukemogenesis of human B-cell precursor ALL.

Radiobiological features of fresh leukemic bone marrow progenitor cells in acute lymphoblastic leukemia

The radiobiological features of leukemic progenitor cells (LPC) freshly obtained from 14 T-lineage acute lymphoblastic leukemia (ALL) and 11 B-lineage ALL patients were evaluated using LPC colony assays. No significant radiobiological differences were observed between T-lineage versus B-lineage ALL LPC. Notably, the D0 values displayed a significant interpatient variation in both groups, indicating a pronounced heterogeneity in the radiation sensitivity of LPC. LPC from some patients were very radioresistant, and in additional experiments using cryopreserved bone marrow blasts, up to 32% of LPC could survive 1600 cGy delivered at 100 cGy/min. In six of 11 T-lineage ALL cases and five of ten B-lineage ALL cases, a distinct initial shoulder was present on the single dose radiation survival curves, providing circumstantial evidence that LPC are able to repair sublethal radiation damage. A greater proportion of LPC survived 400 cGy when the dose was delivered in two fractions instead of a single dose, providing direct evidence that LPC in ALL possess a substantial capacity to repair sublethal radiation damage. The interpatient differences in Dq and recovery factor values indicated a marked heterogeneity in the ability of LPC to repair sublethal radiation damage. Analysis of the dose rate effects on the radiation survival of LPC in four ALL cases suggested that the radiation sensitivity of LPC is dose rate dependent. Normal bone marrow progenitor cells (colony-forming unit, granulocyte-macrophage, and burst-forming unit, erythroid) were more radiosensitive and unable to repair sublethal radiation damage. To our knowledge, this report represents (a) the first detailed comparative analysis of the radiobiological features of freshly obtained LPC in T-lineage and B-lineage ALL patients, and (b) the first elucidation of radiobiological differences between leukemic ALL versus normal bone marrow progenitor cells.

Immunotoxins for ex vivo marrow purging in autologous bone marrow transplantation for acute nonlymphocytic leukemia

Two potent antimyeloid immunotoxins (IT) were generated by conjugating AML-2-23 (anti-CD14) and MCS-2 (anti-CD13) monoclonal antibodies (mAb) to the ribosome-inactivating phytotoxin, ricin. Both IT selectively bound to target cells, inhibited protein synthesis, and prevented the clonogenic growth of fresh marrow blasts from acute nonlymphocytic leukemia patients as well as KG-1 (ANLL) cells. Cryopreservation did not inhibit IT activity. We conclude that AML-2-23-ricin and MCS-2-ricin show potential for effective ex vivo marrow purging in autologous bone marrow transplantation (ABMT) for ANLL. To our knowledge, this study represents the first evidence of the clinical potential of IT in high-risk ANLL.

Use of colony assays and anti-T cell immunotoxins to elucidate the immunobiologic features of leukemic progenitor cells in T-lineage acute lymphoblastic leukemia

The specific binding of radioiodinated rIL-2 to fresh marrow blasts from T-lineage acute lymphoblastic leukemia (ALL) patients was initially investigated. The estimated number of radioiodinated rIL-2 molecules bound per blast ranged from undetectable to 1948. In colony assays, 72% of 32 cases analyzed showed a significant proliferative response to rIL-2, which depended on PHA-stimulated lymphocyte conditioned medium activation. Colony stimulation indices correlated with the number of radioiodinated rIL-2 molecules bound per blast but not with expression of CD25/Tac Ag on fresh marrow blasts or primary colony blasts. These findings provide evidence that in T-lineage ALL functional IL-2R proteins are expressed on leukemic progenitor blasts which may be distinct from Tac Ag. We used the mAb 35.1, T101, and G3.7 to test for expression of CD2, CD5, and CD7 on fresh marrow blasts from 126 T-lineage ALL patients. CD2, CD5, and CD7 were expressed in 84%, 93%, and 99% of cases, respectively. Furthermore, colony blasts that represent the early progeny of leukemic progenitor blasts were also CD2+CD5+CD7+. Ricin conjugates of 35.1, T101, and G3.7 mAb were used as Ag-specific cytotoxic probes to test for expression of CD2, CD5, and CD7 at the level of T-lineage leukemic progenitor blasts. Each immunotoxin was able to selectively eliminate greater than 99% of leukemic progenitor blasts, providing unique and direct evidence that these cells co-express CD2, CD5, and CD7. Neither mixtures of anti-CD5 and anti-CD7 nor anti-CD2, anti-CD5, and anti-CD7 immunotoxins were more effective against blast progenitor cells than the individual immunotoxins alone, confirming that CD2, CD5, and CD7 are not expressed on non-overlapping progenitor cell subpopulations.

Use of colony assays and anti-T cell immunotoxins to elucidate the immunobiologic features of leukemic progenitor cells in T-lineage acute lymphoblastic leukemia

The specific binding of radioiodinated rIL-2 to fresh marrow blasts from T-lineage acute lymphoblastic leukemia (ALL) patients was initially investigated. The estimated number of radioiodinated rIL-2 molecules bound per blast ranged from undetectable to 1948. In colony assays, 72% of 32 cases analyzed showed a significant proliferative response to rIL-2, which depended on PHA-stimulated lymphocyte conditioned medium activation. Colony stimulation indices correlated with the number of radioiodinated rIL-2 molecules bound per blast but not with expression of CD25/Tac Ag on fresh marrow blasts or primary colony blasts. These findings provide evidence that in T-lineage ALL functional IL-2R proteins are expressed on leukemic progenitor blasts which may be distinct from Tac Ag. We used the mAb 35.1, T101, and G3.7 to test for expression of CD2, CD5, and CD7 on fresh marrow blasts from 126 T-lineage ALL patients. CD2, CD5, and CD7 were expressed in 84%, 93%, and 99% of cases, respectively. Furthermore, colony blasts that represent the early progeny of leukemic progenitor blasts were also CD2+CD5+CD7+. Ricin conjugates of 35.1, T101, and G3.7 mAb were used as Ag-specific cytotoxic probes to test for expression of CD2, CD5, and CD7 at the level of T-lineage leukemic progenitor blasts. Each immunotoxin was able to selectively eliminate greater than 99% of leukemic progenitor blasts, providing unique and direct evidence that these cells co-express CD2, CD5, and CD7. Neither mixtures of anti-CD5 and anti-CD7 nor anti-CD2, anti-CD5, and anti-CD7 immunotoxins were more effective against blast progenitor cells than the individual immunotoxins alone, confirming that CD2, CD5, and CD7 are not expressed on non-overlapping progenitor cell subpopulations.

Antigen-independent regulation of cytoplasmic calcium in B cells with a 12-kDa B-cell growth factor and anti-CD19

Increases in cytoplasmic free calcium ([Ca2+]i) can be induced in resting B cells either by a low molecular weight (12-kDa) B-cell growth factor (LMW-BCGF) or by crosslinking the B-cell antigen CD19 with monoclonal antibody (mAb). LMW-BCGF causes a slow [Ca2+]i increase in peripheral blood and tonsillar B cells but has no effect on [Ca2+]i in resting T cells. B-cell [Ca2+]i responses mediated by anti-surface immunoglobulin (sIg) or anti-CD19 are potentiated by LMW-BCGF, but anti-sIg and anti-CD19 do not show additive [Ca2+]i responses. LMW-BCGF- and anti-CD19-induced [Ca2+]i signals are similar to the sIgM or sIgD-mediated signals in that they are inhibited by prior treatment with phorbol 12-myristate 13-acetate. However, LMW-BCGF- and CD19-mediated signals do not depend on the expression of sIg, since they were also observed on sIg-B-cell precursor acute lymphoblastic leukemia (ALL) cells. Both anti-CD19 and LMW-BCGF stimulated in vitro colony formation by ALL cells and showed additive effects when used together. [Ca2+]i responses to LMW-BCGF or CD19 cross-linking were also evident on certain pre-B-cell and lymphoma B-cell lines.

Detailed studies on expression and function of CD19 surface determinant by using B43 monoclonal antibody and the clinical potential of anti-CD19 immunotoxins

Extensive immunologic surface marker analyses and binding competition assays demonstrated that B43 monoclonal antibody (MoAb) is a new member of the CD19 cluster that recognizes the same surface epitope as several other anti-CD19 MoAbs. We used B43 MoAb to test for CD19 expression on neoplastic cells from 340 leukemia and 151 malignant lymphoma patients and on nonneoplastic cells in normal lymphohematopoietic and nonlymphohematopoietic tissues. Our study more than doubles the total number of cases with classified hematologic malignancies that have been examined for CD19 antigen expression. The data presented confirm that CD19 is the most reliable B lineage surface marker and support our view that this B lineage-restricted surface determinant may be an important functional receptor. Our findings provide unique and direct evidence that (a) CD19 is expressed on leukemic B lineage lymphoid progenitor cells freshly obtained from B lineage acute lymphoblastic leukemia patients but not on normal myeloid, erythroid, megakaryocytic, or multilineage bone marrow progenitor cells; (b) ligation of CD19 with B43 MoAb induces sustained increases in [Ca2+]i when crosslinked and inhibits high-molecular weight B cell growth factor (HMW-BCGF)-induced proliferation of activated B cells without affecting their low-molecular weight B cell growth factor (LMW-BCGF) response; therefore CD19 may be a unique signal receptor; (c) HMW-BCGF and LMW-BCGF augment expression of CD19, which suggests that CD19 and BCGF receptors may be under coordinate regulatory control; (d) approximately two million B43 MoAb molecules per cell can be bound to target B lineage lymphoma cells with a Ka of 1.9 x 10(8)/mol/L; (e) CD19 can undergo B43 MoAb-induced internalization; and (f) the opportunity is thus provided for using anti-CD19 MoAb to deliver toxins to B lineage neoplastic cells for more effective treatment of high-risk leukemia/lymphoma patients.

B-cell growth factor receptor expression and B-cell growth factor response of leukemic B cell precursors and B lineage lymphoid progenitor cells

The purpose of this study was to analyze the expression of B cell growth factor (BCGF) receptors and to elucidate the biologic effects of biochemically purified natural BCGF at the B cell precursor stage of human B lineage lymphoid differentiation. The specific binding of radioiodinated high-mol-wt BCGF (125I-HMW-BCGF) and low-molecular-wt BCGF (125I-LMW-BCGF) to fresh marrow blasts from B cell precursor acute lymphoblastic leukemia (ALL) patients was initially investigated. The estimated number of radioiodinated BCGF molecules bound per blast ranged from undetectable to 24.3 X 10(3) for HMW-BCGF, and from 11.5 X 10(3) to 457.8 X 10(3) for LMW-BCGF. In 3H-TdR incorporation assays, 75% of cases showed a significant response to LMW-BCGF with a median stimulation index of 9.3. By comparison, only 33% of cases showed a significant response to HMW-BCGF with a median stimulation index of 2.4. Subsequently, B cell precursor colony assays were performed to assess and compare the biologic effects of BCGF on leukemic B lineage lymphoid progenitor cells. Among 28 cases studied, 57% responded to both HMW-BCGF and LMW-BCGF, 21% responded only to LMW-BCGF, and the remaining cases showed no proliferative response to either growth factor. The response patterns of virtually pure populations of FACS-sorted leukemic B cell precursors were essentially identical to the proliferative responses of unsorted leukemic B-cell precursors. Synergistic effects between HMW-BCGF and LMW-BCGF were observed in 80% of the cases that responded to both. The numbers of cell-bound radioiodinated BCGF molecules, the stimulation indices, as well as the number of B cell precursor colonies in BCGF-stimulated cultures showed a marked interpatient variation. Patients with structural chromosomal abnormalities (SCAs) involving 12p11-13 or patients with a Philadelphia chromosome showed a greater HMW-BCGF response at the level of leukemic progenitor cells than did other patients (P = .02). The LMW-BCGF response was significantly greater for patients with SCA than for patients without SCA (P = .04). The response of leukemic progenitor cells to HMW-BCGF or LMW-BCGF did not correlate with sex, age, disease status, FAB morphology, WBC at diagnosis, or immunophenotype. To our knowledge, this study represents the first detailed analyses of BCGF receptor expression and BCGF effects in B cell precursor ALL. The data presented provide direct evidence for the expression of functional receptors for both HMW-BCGF and LMW-BCGF in B cell precursor ALL.

Heterogeneity of cultured leukemic lymphoid progenitor cells from B cell precursor acute lymphoblastic leukemia (ALL) patients

Colony assays were performed for 50 patients with B cell precursor acute lymphoblastic leukemia (ALL). Blast colony formation was observed for 33 patients, and the plating efficiency (PE) showed a marked interpatient variation, which indicates a pronounced biological heterogeneity at the level of leukemic progenitor cells. Notably, the mean PE of leukemic B cell precursors from patients with a pseudodiploid or near-diploid karyotype with structural chromosomal abnormalities (SCA) was significantly higher than the mean PE of normal diploid or hyperdiploid cases. All patients who had SCA involving 7p13, 11q23-24, or 12p11-13, and patients with a Philadelphia chromosome had high PE values. The S phase percentage, expression of CD19 antigen, and relapse status were also correlated with PE. Significantly, colony blasts had slightly different surface marker profiles in each case and were common ALL antigen negative in 33% of cases, which indicates the existence of a marked immunological heterogeneity at the level of leukemic progenitor cells.

Combined immunochemotherapy of human solid tumors in nude mice

In vivo immunochemotherapy of human solid tumors was studied in a nude mouse model. Large tumors (3 to 6 cm3) were induced by s.c. injection of the acute lymphoblastic leukemia T-cell line CEM. Transient tumor inhibition could be achieved by intratumoral injection of an intact-ricin immunotoxin that specifically recognizes a determinant CD5 (T,p67) expressed on the cell surface. Injection of the in vitro active cyclophosphamide congener mafosfamid had little effect on the progression of tumor growth. A combination regimen of immunotoxin and mafosfamid induced the most dramatic antitumor effect; a 72 to 100% reduction in tumor volume was observed within 3 to 4 days posttreatment. However, tumors relapsed within 5 to 13 days. Persistent, tumor regression was observed only when protocols using successive injections of combined immunotoxin/mafosfamid were used. All seven mice undergoing this treatment had a precipitous decrease in tumor size, and 86% survived greater than 30 days posttreatment. No residual tumor was detectable on Day 30 in five of seven mice. Regression was partly attributed to the selective activity of immunotoxin, since successive injections of an irrelevant control immunotoxin coupled to ricin in combination with mafosfamid did not reduce tumor size. Thus, we have demonstrated that a combination of anticancer chemotherapy and immunotoxin therapy yielded a greater antitumor effect than either therapy alone.

Marrow purging in autologous bone marrow transplantation for T-lineage acute lymphoblastic leukemia: efficacy of ex vivo treatment with immunotoxins and 4-hydroperoxycyclophosphamide against fresh leukemic marrow progenitor cells

A lymphoblast progenitor cell assay was used to evaluate the antileukemic efficacy of marrow-purging protocols that employed intact ricin immunotoxins (IT) and 4-hydroperoxycyclophosphamide (4-HC) against clonogenic primary T-lineage marrow blasts freshly obtained from 12 T-lineage acute lymphoblastic leukemia (ALL) patients. Residual T-lineage blast colonies were observed after treatment with 1 micrograms/mL T101 (anti-CD5)-Ricin (R) + G3.7 (anti-CD7)-R in eight of 12 cases and after 100 micrograms/mL 4-HC in six of nine cases. By comparison, a combination of IT and 4-HC proved very effective against T-lineage leukemic progenitor cells, and no residual blast colonies were observed in any of the eight cases studied. We conclude that future trials should consider combined treatment protocols such as IT + 4-HC for more effective purging of autologous marrow grafts.

Use of a novel colony assay to evaluate the cytotoxicity of an immunotoxin containing pokeweed antiviral protein against blast progenitor cells freshly obtained from patients with common B-lineage acute lymphoblastic leukemia

We report a novel colony assay for B-lineage progenitor cells in acute lymphoblastic leukemia (ALL). The primary plating efficiency of blast progenitors freshly obtained from common B-lineage ALL patients varied between 0.09 and 2.63%. Morphological, cytochemical, and immunological analyses of cells from day 7 colonies provided the evidence that they are B-lineage lymphoblasts. Immunological marker analyses of cultured blasts using BA-2 (anti-CD9), BA-3 (anti-CD10), BA-1 (anti-CD24), and B43 mAb have allowed us to define two distinct immunological groups. The first group had BA-2+, BA-3+, BA-1+, B43+ marker profiles, consistent with the phenotype of uncultured bone marrow blasts. The second group differed in that the cells in the blast colonies were BA-3 (anti-CD10)-negative, although many of the cells in the bulk population were BA-3+ before culture. Blasts from both groups were able to proliferate and form secondary colonies when recultured. A pan-B immunotoxin was synthesized by linking B43, a human B cell-specific mAb, to pokeweed antiviral protein (PAP). This study showed that B43-PAP can effectively eradicate leukemic progenitor cells freshly obtained from patients with common B-lineage ALL. B43-PAP eliminated greater than 99.96% of blast progenitors under conditions in which only minimal inhibition of normal bone marrow progenitor cells (CFU-GM, CFU-E, CFU-MK, CFU-GEMM) was observed. Our results establish that the surface determinant recognized by B43 is expressed on B-lineage progenitor cells in ALL, and that these cells are sensitive to PAP at the ribosomal level. To our knowledge, B43-PAP is the first IT to prove effective against common B-lineage ALL cells.

Immunotoxins show rapid entry of diphtheria toxin but not ricin via the T3 antigen

We compared immunotoxins made with ricin and diphtheria toxin (DT) and with two monoclonal antibodies against different T cell-specific antigens, CD5 (T101) and CD3 (UCHT1). Only one reagent, UCHT1 linked to DT (UCHT1-DT), had exceptional properties. UCHT1-DT killed human peripheral T cells and T leukemia cells (Jurkat) at 2 to 10 pM, a concentration 10- to 100-fold lower than UCHT1-ricin and 10 to 500 times lower than native DT. The toxicity was blocked 50- to 100-fold by excess UCHT1 antibody. Human multipotent stem cells were not killed at up to 2000 pM UCHT1-DT. UCHT1-DT shows greater selectivity between T cells and stem cells than UCHT1-ricin, and may better prevent graft-vs-host disease in allogeneic bone marrow transplantation. The kinetics of UCHT1-DT were extremely rapid. UCHT1-DT inhibited Jurkat cell protein synthesis faster than DT and had a different ratio of lag time to inactivation rate. UCHT1-DT killed 90% of Jurkat cells within 2 hr at concentrations nontoxic to human stem cells. In contrast, UCHT1-ricin required more than 18 hr to kill one log of Jurkat cells. Another monoclonal antibody, T101, against the 65 kD CD5 antigen on Jurkat cells was linked to DT and ricin, and was compared with the UCHT1 immunotoxins. UCHT1-DT was 100 times more potent and five to 10 times faster than T101-DT and T101-ricin. Standardization to other antibodies with regard to the number of molecules bound per cell shows that UCHT1-DT is 10 to 100 times faster than previously reported immunotoxins. The role of the T3 antigen in transporting DT to the cytosol is discussed.

Immunotoxins show rapid entry of diphtheria toxin but not ricin via the T3 antigen

We compared immunotoxins made with ricin and diphtheria toxin (DT) and with two monoclonal antibodies against different T cell-specific antigens, CD5 (T101) and CD3 (UCHT1). Only one reagent, UCHT1 linked to DT (UCHT1-DT), had exceptional properties. UCHT1-DT killed human peripheral T cells and T leukemia cells (Jurkat) at 2 to 10 pM, a concentration 10- to 100-fold lower than UCHT1-ricin and 10 to 500 times lower than native DT. The toxicity was blocked 50- to 100-fold by excess UCHT1 antibody. Human multipotent stem cells were not killed at up to 2000 pM UCHT1-DT. UCHT1-DT shows greater selectivity between T cells and stem cells than UCHT1-ricin, and may better prevent graft-vs-host disease in allogeneic bone marrow transplantation. The kinetics of UCHT1-DT were extremely rapid. UCHT1-DT inhibited Jurkat cell protein synthesis faster than DT and had a different ratio of lag time to inactivation rate. UCHT1-DT killed 90% of Jurkat cells within 2 hr at concentrations nontoxic to human stem cells. In contrast, UCHT1-ricin required more than 18 hr to kill one log of Jurkat cells. Another monoclonal antibody, T101, against the 65 kD CD5 antigen on Jurkat cells was linked to DT and ricin, and was compared with the UCHT1 immunotoxins. UCHT1-DT was 100 times more potent and five to 10 times faster than T101-DT and T101-ricin. Standardization to other antibodies with regard to the number of molecules bound per cell shows that UCHT1-DT is 10 to 100 times faster than previously reported immunotoxins. The role of the T3 antigen in transporting DT to the cytosol is discussed.

Anti-CD2 (T, p50) intact ricin immunotoxins for GVHD-prophylaxis in allogeneic bone marrow transplantation

We evaluated the inhibitory effects of two immunotoxins (IT) synthesized by linking two different anti-CD2 (T, p50) murine monoclonal antibodies (MoAb) to intact ricin (R). Pretreatment with 1000 ng ml-1 35.1-R or OKT 11a-R inhibited PHA-induced T-cell proliferation by 93% and 86%, respectively. At this IT concentration generation of alloreactive cytotoxic T-cells (CTL) was inhibited by more than 99% by either IT. 35.1-R and OKT 11a were minimally toxic to natural killer (NK) effectors or pluripotent bone marrow progenitor cells (CFU-GEMM). Blocking experiments suggested that 35.1-R and OKT 11a-R might recognize different epitopes of the CD2 (T, p50) surface determinant. Our findings show that anti-CD2 IT may be useful for T-cell depletion in allogeneic bone marrow transplantation. We compared TU3, an equimolar mixture of T101 [anti-CD5]-R, UCHT-1 [anti-CD3]-R and 35.1 [anti-CD2]-R with the TUT-cocktail (a mixture of T101-R, UCHT-1-R and TA-1 [anti-CDw18]-R. TUT is currently under evaluation in Phase 1 clinical trials as a T-cell depletion regimen for GVHD prophylaxis. TU3 was as effective as TUT-cocktail in inhibition of PHA response and CTL generation but unlike TUT spared NK effectors. Cocktails of immunotoxins directed against subpopulations of lymphocytes may be useful for more effective anti-GVHD strategies, and to circumvent problems of graft failure/rejection associated with current purgation regimens.

Increased efficacy in selective elimination of leukemic cell line clonogenic cells by a combination of monoclonal antibodies BA-1, BA-2, BA-3 + complement and mafosfamid (ASTA Z 7557)

Studies were undertaken to examine the efficacy of combining monoclonal antibodies BA-1, BA-2, BA-3 + complement with a stabilized derivative of cyclophosphamide (mafosfamid) for elimination of leukemic cell line clonogenic cells. In a series of experiments conducted with leukemic cell lines a combination of two cycles of treatment with BA-1, 2, 3 + complement combined with 25 micrograms/ml-1 mafosfamid was superior to either modality alone in killing clonogenic leukemic cells. Identical treatment of normal bone marrow had no effect on the monopotent stem cells CFU-E and CFU-GM, or the pluripotent stem cell CFU-MIX, but some inhibition of the monopotent stem cell CFU-MK did occur. These results suggest that consideration be given to incorporation of BA-1, 2, 3 + complement and mafosfamid combination treatment in autologous bone marrow transplantation for acute lymphoblastic leukemia.

B lymphocyte regulation of human hematopoiesis

Epstein Barr virus (EBV)-transformed B lymphoblastoid cell lines (BLCL) were derived from seven different individuals. The ability of BLCL supernatants to stimulate hematopoietic colony formation in vitro was tested in a conventional stem cell assay system. Supernatants promoted the growth of single (GM, E, MK) as well as multi-lineage (GEMM) colonies in bone marrow cultures. Our results indicate that EBV-transformed B lymphocytes produce cytokines that affect in vitro stem cell proliferation and differentiation. These studies demonstrate the regulatory potential of activated B lymphocytes in human hematopoiesis.

B lymphocyte regulation of human hematopoiesis

Epstein Barr virus (EBV)-transformed B lymphoblastoid cell lines (BLCL) were derived from seven different individuals. The ability of BLCL supernatants to stimulate hematopoietic colony formation in vitro was tested in a conventional stem cell assay system. Supernatants promoted the growth of single (GM, E, MK) as well as multi-lineage (GEMM) colonies in bone marrow cultures. Our results indicate that EBV-transformed B lymphocytes produce cytokines that affect in vitro stem cell proliferation and differentiation. These studies demonstrate the regulatory potential of activated B lymphocytes in human hematopoiesis.

Anti-T cell immunotoxins containing pokeweed anti-viral protein: potential purging agents for human autologous bone marrow transplantation

The ex vivo anti-leukemic efficacy and stem cell toxicity of two different T cell directed immunotoxins containing pokeweed antiviral protein (PAP) were studied by clonal assays. 5E9-11-PAP, an immunotoxin directed against human transferrin receptors, elicited a maximum leukemic cell kill of 3.9 logs. However, it was also toxic against normal pluripotent stem cells, and therefore is not a clinically useful purgative reagent. PAP conjugated to 3-A1, a monoclonal antibody directed against CD7 (T, p41), was more effective against leukemic T cells than 5E9-11-PAP and eliminated a maximum of 4.8 log of cells. 3A1-PAP was only slightly toxic to pluripotent stem cells: 13% of CFU-GEMM were lost after treatment with 3000 ng of 3A1-PAP/ml, a concentration that eliminated 99.96% of contaminating leukemic T cells from a 200-fold excess of normal bone marrow. Cryopreservation of treated cells by conventional methods did not affect the extreme selectivity and potency of 3A1-PAP. Incubation of 3A1-PAP with peripheral blood mononuclear cells resulted in the complete inhibition of phytohemagglutinin-induced mitogenic response, illustrating the possibility of using this immunotoxin as a potent anti-T cell reagent for prophylaxis against graft vs host disease in allogeneic BMT as well.

Anti-T cell immunotoxins containing pokeweed anti-viral protein: potential purging agents for human autologous bone marrow transplantation

The ex vivo anti-leukemic efficacy and stem cell toxicity of two different T cell directed immunotoxins containing pokeweed antiviral protein (PAP) were studied by clonal assays. 5E9-11-PAP, an immunotoxin directed against human transferrin receptors, elicited a maximum leukemic cell kill of 3.9 logs. However, it was also toxic against normal pluripotent stem cells, and therefore is not a clinically useful purgative reagent. PAP conjugated to 3-A1, a monoclonal antibody directed against CD7 (T, p41), was more effective against leukemic T cells than 5E9-11-PAP and eliminated a maximum of 4.8 log of cells. 3A1-PAP was only slightly toxic to pluripotent stem cells: 13% of CFU-GEMM were lost after treatment with 3000 ng of 3A1-PAP/ml, a concentration that eliminated 99.96% of contaminating leukemic T cells from a 200-fold excess of normal bone marrow. Cryopreservation of treated cells by conventional methods did not affect the extreme selectivity and potency of 3A1-PAP. Incubation of 3A1-PAP with peripheral blood mononuclear cells resulted in the complete inhibition of phytohemagglutinin-induced mitogenic response, illustrating the possibility of using this immunotoxin as a potent anti-T cell reagent for prophylaxis against graft vs host disease in allogeneic BMT as well.

Combined ex vivo treatment with immunotoxins and mafosfamid: a novel immunochemotherapeutic approach for elimination of neoplastic T cells from autologous marrow grafts

We evaluated a novel ex vivo "purging" protocol for selective elimination of neoplastic T cells from human marrow by using a sensitive clonogenic assay. Immunotoxins (IT) were synthesized by conjugating ricin (R) to four different monoclonal antibodies (MoAb) directed against distinct markers of T cell lineage. Treatment with anti-p67-R produced effective elimination of leukemic T cells from human marrow. The cyclophosphamide congener mafosfamid (ASTA Z 7577) markedly enhanced the target cell cytotoxicity of IT and extended the final level of clonogenic kill 2 to 3 logs. Our data show that anti-p67-R in combination with mafosfamid resulted in a maximum elimination of 6.2 logs of neoplastic T cells with minimal toxicity to normal bone marrow progenitors. The efficiency of this protocol was not reduced in the presence of excess normal bone marrow cells. Similar findings were obtained by using a cocktail of four different anti-T cell IT. This approach is unique in combining both immunologic (IT) and chemical (mafosfamid) strategies for more effective ex vivo bone marrow purging in autologous bone marrow transplantation for T cell acute lymphoblastic leukemia/lymphoblastic lymphoma.