Is land condition a useful indicator of soil organic carbon stock in Australia’s northern grazing land?

The grazing lands of northern Australia contain a substantial soil organic carbon (SOC) stock due to the large land area. Manipulating SOC stocks through grazing management has been presented as an option to offset national greenhouse gas emissions from agriculture and other industries. However, research into the response of SOC stocks to a range of management activities has variously shown positive, negative or negligible change. This uncertainty in predicting change in SOC stocks represents high project risk for government and industry in relation to SOC sequestration programs. In this paper, we seek to address the uncertainty in SOC stock prediction by assessing relationships between SOC stocks and grazing land condition indicators. We reviewed the literature to identify land condition indicators for analysis and tested relationships between identified land condition indicators and SOC stock using data from a paired-site sampling experiment (10 sites). We subsequently collated SOC stock datasets at two scales (quadrat and paddock) from across northern Australia (329 sites) to compare with the findings of the paired-site sampling experiment with the aim of identifying the land condition indicators that had the strongest relationship with SOC stock. The land condition indicators most closely correlated with SOC stocks across datasets and analysis scales were tree basal area, tree canopy cover, ground cover, pasture biomass and the density of perennial grass tussocks. In combination with soil type, these indicators accounted for up to 42% of the variation in the residuals after climate effects were removed. However, we found that responses often interacted with soil type, adding complexity and increasing the uncertainty associated with predicting SOC stock change at any particular location. We recommend that caution be exercised when considering SOC offset projects in northern Australian grazing lands due to the risk of incorrectly predicting changes in SOC stocks with change in land condition indicators and management activities for a particular paddock or property. Despite the uncertainty for generating SOC sequestration income, undertaking management activities to improve land condition is likely to have desirable complementary benefits such as improving productivity and profitability as well as reducing adverse environmental impact.

In vivo selection of human embryonic stem cell-derived cells expressing methotrexate-resistant dihydrofolate reductase

Human embryonic stem cells (hESCs) provide a novel source of hematopoietic and other cell populations suitable for gene therapy applications. Preclinical studies to evaluate engraftment of hESC-derived hematopoietic cells transplanted into immunodeficient mice demonstrate only limited repopulation. Expression of a drug resistance gene, such as Tyr22-dihydrofolate reductase (Tyr22-DHFR), coupled to methotrexate (MTX) chemotherapy has the potential to selectively increase engraftment of gene-modified hESC-derived cells in mouse xenografts. Here, we describe the generation of Tyr22-DHFR – GFP expressing hESCs that maintain pluripotency, produce teratomas and can differentiate into MTXr-hemato-endothelial cells. We demonstrate that MTX administered to nonobese diabetic/severe combined immunodeficient/IL-2Rγc^null (NSG) mice after injection of Tyr22-DHFR-derived cells significantly increases human CD34⁺ and CD45⁺ cell engraftment in the bone marrow (BM) and peripheral blood of transplanted MTX-treated mice. These results demonstrate that MTX treatment supports selective, long-term engraftment of Tyr22-DHFR-cells in vivo, and provides a novel approach for combined human cell and gene therapy.

Autonomic control of bronchial blood flow and airway dimensions during strenuous exercise in sheep

BACKGROUND

During exercise and recovery the transient and steady-state changes in autonomic activity regulating lower airway blood flow and dimensions are unknown. The aim of this study was to define changes in bronchial blood flow (Q(br)) and dimensions during moderate and strenuous exercise, and to analyse the role of vagal and sympathetic nerves.

METHODS

Nine ewes (34-44kg) underwent left thoracotomy during general anaesthesia (thiopentone/isoflurane) and either (5 sheep=Group 1) a pulsed Doppler transducer was placed on the bronchial artery, or (4 sheep=Group 2) a pulsed Doppler transducer was placed on the bronchial artery, and transit-time and single crystal sonomicrometers were mounted on the left main bronchus. These measured continuously Q(br), bronchial circumference (Circ(br)) and wall thickness (Th(br)). Aortic pressure (P(a)) and central venous pressure catheters were placed in the superficial cervical artery and vein. Trained sheep exercised on a horizontal treadmill, i.e. Group 1, moderate exercise 2.2mph over 1.6, 6min recovery, for analysis of changes in Q(br) before and after cholinoceptor blockade; Group 2, strenuous exercise 4.4mph over 2, 10min recovery for analysis of changes in Q(br) and airway dimensions, before and after cholinoceptor plus alpha(1)-, alpha(2)-adrenoceptor blockade. beta-adrenoceptor systems were intact.

RESULTS

In Group 1 during moderate exercise P(a) and heart rate (HR) rose. Q(br) and blood flow conductance (C(br)) fell immediately to 83% (P<0.001) before returning toward resting levels, but fell when exercise ceased to 89% (P<0.01) before recovering. Prior cholinoceptor blockade abolished the immediate fall in Q(br) and C(br), but not the recovery vasoconstriction. Later in recovery the bronchial bed dilated progressively over 6min (P<0.05). In Group 2 during strenuous exercise P(a) and HR rose substantially. Q(br) and C(br) fell to 68% and 54% (P<0.001), respectively, and there was early vasoconstriction in recovery. Circ(br) fell immediately and remained at 93% (P<0.01), and did not recover fully when exercise ceased. Th(br) did not change during or after exercise. Prior cholinoceptor plus alpha-adrenoceptor block caused P(a) and Q(br) to fall slightly during exercise, but the bronchovascular constriction during and after exercise was abolished, as was circumferential shortening in the airway.

CONCLUSIONS

At exercise onset and steady-state, resetting the arterial baroreflex upward in sheep increases parasympathetic cholinergic vasoconstrictor activity and causes bronchial wall and bronchovascular smooth muscle contraction in concert with sympathetic adrenergic constriction of systemic vascular beds. Whether the known sigmoid baroreflex control of tracheal smooth muscle tension at rest is extended to tracheobronchial smooth muscle and its circulation during exercise is yet to be determined.

Effects of graded exercise on bronchial blood flow and airway dimensions in sheep

Exercise stimulus-response relationships for airway blood supply and dimensions have not been described in mammalian species. These relationships are vital for postulates concerning integrated reflex factors normally controlling the airways and which may underlie the asthma syndromes of exercise. This study defines airways stimulus-response relationships in exercising sheep. Ewes between 35 and 40kg were instrumented at left thoracotomy under thiopentone/isoflurane general anaesthesia. Pulsed Doppler ultrasonic transducers were mounted on the bronchial artery, and transit-time plus single-crystal sonomicrometers on the left main bronchus. These recorded simultaneously and continuously bronchial blood flow (Q(br)) and conductance (C(br)), bronchial circumference (Circ(br)) and wall thickness (Th(br)). In Protocol 1 (P1), four sheep ran duplicate 5min protocols on a horizontal treadmill at continuous step-up-and-down speeds of 1min duration, namely, 0.8, 1.6, 2.2, 1.6 and 0.8mph (moderate exercise), followed by 10min recovery. In P2, four sheep ran duplicate 2min protocols at constant 4mph (strenuous exercise), and in P3, one sheep ran duplicate protocols each of 3min at 2.2, 4.4 and 6mph (severe exercise). Regression analysis and repeated measures ANOVA were used to assess differences between times, runs and exercise intensity. In P1, airway effects were directly related to graded exercise effort sustained over 5min. Peak effects occurred at 2.2mph, except for Th(br). Heart rate and P(a) rose (to 156% and 111% of resting, respectively), and Q(br) and C(br) fell (to 83% and 75%; both P<0.001). Circ(br) fell to 96% (P=0.02), and Th(br) rose at low speeds early and late, and thinned at the highest speed. In P2 and P3 for all variables the steady-state effects were systematically greater than for P1 (4.4mph: C(br) to 43%, Circ(br) to 93%; 6.6mph: C(br) to 25%, Circ(br) to 82%). There was no significant recovery hyperaemia, but there was residual post-exercise bronchoconstriction. The exercise stimulus-response relationships from rest to a maximal 6mph for sheep airway circumference and its bronchial circulation are inverse and functionally constrictor.

Commercial cotton nesting material as a predisposing factor for conjunctivitis in athymic nude mice

Environmental enrichment for rodents is beneficial, but compatibility between the enrichment device and the rodent strain must also be considered. The authors present a case in which the use of a specific form of environmental enrichment--cotton bedding material--proved detrimental to the health of athymic nude mice, increasing the likelihood of conjunctivitis.

Mild preconditioning and low-level engraftment confer methotrexate resistance in mice transplanted with marrow expressing drug-resistant dihydrofolate reductase activity

Effective engraftment of hematopoietic cells targeted for gene transfer is facilitated by cytoreductive preconditioning such as high-dose total body irradiation (TBI). To minimize the adverse side effects associated with TBI, experiments were conducted to determine whether sublethal doses of TBI would allow sufficient engraftment of MTX-resistant hematopoietic cells to confer survival on recipient mice administered MTX. FVB/N animals were administered 1, 2, or 4 Gy TBI (lethal dose, 8.5 Gy), transplanted with 10(7) FVB/N transgenic marrow cells expressing an MTX-resistant dihydrofolate reductase (DHFR) transgene, and then administered MTX daily for 60 days. Control mice administered 1 Gy with or without subsequent transplantation of normal marrow cells succumbed to MTX toxicity by day 45. In contrast, nearly all animals transplanted with transgenic marrow survived MTX administration, regardless of the TBI dose used for preconditioning. The donor DHFR transgenic marrow engraftment level was proportional to the preconditioning dose of TBI but was surprisingly reduced in animals given 2 or 4 Gy TBI and subsequently administered MTX when compared with control animals administered phosphate-buffered saline. Animals preconditioned with 1 Gy were also protected from MTX toxicity when transplanted with reduced amounts (5 x 10(6) and 1 x 10(6) cells) of DHFR transgenic donor marrow, resulting in low-level (approximately 1%) engraftment. In conclusion, very mild preconditioning allows sufficient low-level engraftment of genetically modified stem cells for in vivo manifestation of the modified phenotype, suggesting the usefulness of mild preconditioning regimens in human gene therapy trials targeting hematopoietic stem cells. (Blood. 2000;96:1334-1341)

Injury potential to venous valves from the Amplatz thrombectomy device

PURPOSE

To evaluate the acute effects of the Amplatz thrombectomy device (ATD) on peripheral venous valves in a canine model.

MATERIALS AND METHODS

ATD thrombectomy was performed in 17 veins, and control experiments with use of an 8-F sheath-dilator were performed in four veins. Prethrombectomy ascending venography was performed, followed by device passage across the vein segment. Post-thrombectomy ascending venography was then performed, followed by heparinization and euthanasia. The treated veins were carefully explanted and stored in formaldehyde for histopathologic examination. Severity of valve injury was graded on a scale of 0 to 4.

RESULTS

In ATD-treated veins: 10 veins sustained no injury [grade 0] (diameter, 6.7 mm +/- 1.7; antegrade/retrograde approach, 5/5), five veins sustained mild injury [grade 1-2] (diameter, 5.2 mm +/- 0.8; antegrade/retrograde, 3/2), while the remaining two veins sustained moderate-to-severe injury [grade 3-4] (diameter, 5 and 6 mm; antegrade/retrograde, 1/1). In sheath-dilator treated veins: no injury [grade 0] in any of the four treated veins (mean diameter, 5.5 mm +/- 0.6; all retrograde). In ATD-treated veins, valve injury (of any grade) was significantly more frequent in veins 6 mm or less in diameter than in veins at least 7 mm in diameter (seven of 12 vs zero of five; P < .03). There was no significant association between thrombectomy approach and injury grade.

CONCLUSION

Veins 7 mm or greater in diameter were associated with no significant valve injury during ATD thrombectomy. However, long-term and short-term effects on valvular function will need to be assessed.

In vivo toxicity and pharmacokinetic features of B43(Anti-CD19)-Genistein immunoconjugate

B43(anti-CD19)-Genistein immunoconjugate targets genistein, a naturally occurring protein tyrosine kinase inhibitory isoflavone to the membrane-associated anti-apoptotic CD19-LYN complexes and triggers apoptotic cell death. In this preclinical study, the toxicity profiles of B43-Genistein as well as unconjugated genistein were evaluated in mice. B43-Genistein and genistein were administered either as single bolus injections or daily injections for 10 consecutive days via the intraperitoneal route to mice. Genistein was not toxic to mice at the highest dose of 40 mg/kg and no test article-related histopathological lesions were found in any of the 64 genistein-treated mice. B43-Genistein had a significantly longer elimination half-life and slower plasma and tissue clearance than unconjugated genistein. B43-Genistein was not toxic to mice at the highest single dose of 40 mg/kg or highest cumulative dose of 100 mg/kg and no test article-related histopathological lesions were found in any of the 108 mice treated with B43-genistein. To our knowledge, this is the first preclinical toxicity and pharmacokinetic study of a tyrosine kinase inhibitor-containing immunoconjugate.

In vivo toxicity, pharmacokinetics, and anticancer activity of Genistein linked to recombinant human epidermal growth factor

Epidermal growth factor receptor (EGFR)-associated protein tyrosine kinase (PTK) complexes have vital anti-apoptotic functions in human breast cancer cells. We have shown previously that targeting the naturally occurring PTK inhibitor genistein to the EGFR-associated PTK complexes using the EGF-Genistein (Gen) conjugate triggers rapid apoptotic cell death in human breast cancer cells and abrogates their in vitro clonogenic growth. In the present study, we examined the in vivo toxicity profile, pharmacokinetics, and anticancer activity of EGF-Gen. No toxicities were observed in mice treated with EGF-Gen at dose levels as high as 40 mg/kg administered i.p. as a single dose or 140 mg/kg administered i.p. over 28 consecutive days. EGF-Gen significantly improved tumor-free survival in a severe combined immune deficiency (SCID) mouse xenograft model of human breast cancer, when it was administered 24 h after inoculation of tumor cells. At 100 microg/kg/day x 10 days (1 mg/kg total dose), which is >100-fold less than the highest tested and nontoxic cumulative dose (ie., 140 mg/kg) in mice, EGF-Gen was more effective than cyclophosphamide (50 mg/kg/day x 2 days), Adriamycin (2.5 mg/kg x 1 day), or methotrexate (0.5 mg/kg x 1 day), the most widely used standard chemotherapeutic drugs for breast cancer, and resulted in 60% long-term tumor-free survival. Furthermore, treating SCID mice with established s.c. human breast cancer xenografts of 0.5-cm diameter with EGF-Gen at this dose level resulted in disappearance of the tumors in two of five mice and >50% shrinkage in three of five mice within 10 days, whereas all of the control tumors in five PBS-treated mice as well as five mice treated with unconjugated Gen (1 mg/kg/day x 10 days) showed >200% increase in diameter during the same observation period. EGF-Gen treatment reduced the growth rate of breast cancer xenografts of 1.0-cm diameter, but unlike with tumors of 0.5-cm diameter, it failed to cause shrinkage or disappearance of these larger tumors. The level of EGF-Gen systemic exposure that was effective in SCID mice was achieved in cynomolgus monkeys without any significant side effects detectable by clinical observation, laboratory studies, or histopathological examination of multiple organs. EGF-Gen might be useful in the treatment of breast cancer as well as other EGFR-positive malignancies.

In vivo toxicity and pharmacokinetic features of B43 (anti-CD19)-genistein immunoconjugate in nonhuman primates

B43 (anti-CD19)-genistein immunoconjugate targets genistein, a naturally occurring protein tyrosine kinase-inhibitory isoflavone to the membrane-associated antiapoptotic CD19-LYN complexes and triggers apoptotic cell death. In this preclinical study, the toxicity profiles of B43-genistein as well as unconjugated genistein were evaluated in cynomolgus monkeys. B43-genistein and genistein were administered either as single bolus injections or daily injections for 5-10 consecutive days via the i.v. route to monkeys. Neither genistein nor B43-genistein was toxic to cynomolgus monkeys, and no test article-related histopathological lesions were found in any of the two genistein-treated or five B43-genistein-treated cynomolgus monkeys. B43-genistein showed a favorable pharmacokinetics in monkeys, with a plasma half-life of 10-23 h. Plasma samples from B43-genistein-treated monkeys elicited potent and CD19 antigenspecific antileukemic activity against human CD19+ leukemia cells in vitro. To our knowledge, this is the first preclinical toxicity and pharmacokinetic study of a tyrosine kinase inhibitor-containing immunoconjugate in nonhuman primates.

In vivo biotherapy of HL-60 myeloid leukemia with a genetically engineered recombinant fusion toxin directed against the human granulocyte macrophage colony-stimulating factor receptor

Acute myeloid leukemia (AML) is the most common form of acute leukemia. Contemporary chemotherapy regimens fail to cure most patients with AML. We have genetically engineered a recombinant diphtheria toxin human granulocyte macrophage colony-stimulating factor (GMCSF) chimeric fusion protein (DTctGMCSF) that specifically targets the GMCSF receptor on fresh human AML cells and myeloid leukemia cell lines. At a nontoxic dose level, DTctGMCSF therapy was superior to the standard chemotherapeutic agents 1-beta-D-arabinofuranosylcytosine and Adriamycin, resulting in 60% long-term event-free survival of severe combined immunodeficient mice challenged with an otherwise invariably fatal cell dose of the human HL-60 myeloid leukemia. Notably, systemic exposure levels of DTctGMCSF, which were found to be therapeutic in the severe combined immunodeficient mouse xenograft model of human HL-60 myeloid leukemia, could be achieved in cynomolgus monkeys without any significant nonhematological toxicities. The recombinant DTctGMCSF fusion toxin might be useful in the treatment of AML patients whose leukemias have recurred and developed resistance to contemporary chemotherapy programs.

In vivo toxicity, pharmacokinetics, and antileukemic activity of TXU (anti-CD7)-pokeweed antiviral protein immunotoxin

We evaluated the TXU (anti-CD7)-pokeweed antiviral protein (PAP) immunotoxin in both murine and nonhuman primate models. TXU-PAP caused dose-limiting cardiac toxicity in BALB/c mice. In a SCID mouse model of invariably fatal human T-lineage acute lymphoblastic leukemia (ALL), TXU-PAP therapy resulted in a marked improvement of leukemia-free survival without any side effects. Whereas 100% of control mice treated with PBS, unconjugated TXU antibody, or B43-PAP (an immunotoxin that does not react with T-lineage ALL cells) died of disseminated human leukemia within 80 days (median survival, 37 days), 80 +/- 13% of SCID mice treated with 15 microgram of TXU-PAP (median survival, >120 days) and 100% of mice treated with 30 microgram of TXU-PAP (median survival, > 120 days) remained alive and free of leukemia for >120 days. In cynomolgus monkeys, TXU-PAP showed favorable pharmacokinetics with an elimination half-life of 8.1-8.7 h. The monkeys treated with TXU-PAP at dose levels of 0.05 mg/kg/day x 5 days and 0.10 mg/kg/day x 5 days tolerated the therapy very well, without any significant clinical compromise or side effects, and at necropsy, no gross or microscopic lesions were found. This study provides a basis for further evaluation of TXU-PAP as an investigational biotherapeutic agent in the treatment of T-lineage ALL.

Pharmacokinetic features, immunogenicity, and toxicity of B43(anti-CD19)-pokeweed antiviral protein immunotoxin in cynomolgus monkeys

We studied the pharmacokinetic features, immunogenicity, and toxicity of B43-pokeweed antiviral protein (PAP) immunotoxin in 13 cynomolgus monkeys. The disposition of B43-PAP in two monkeys, when administered as a single i.v. bolus dose, was characterized by a slow clearance (1-2 ml/h/kg) with a very discrete peripheral distribution. B43-PAP was retained and distributed largely in the blood as the sole compartment with no significant equilibration with the extravascular compartment. The circulating B43-PAP immunotoxin detected in monkey plasma samples by ELISA and protein immunoblotting was both immunoreactive with, and active against, human leukemic cells in vitro. In systemic immunogenicity and toxicity studies, which involved 11 cynomolgus monkeys, each monkey received a total of seven i.v. doses of B43-PAP at a specific dose level of the dose escalation schedule. B43-PAP-treated monkeys mounted a dose-dependent humoral immune response against both the mouse IgG and PAP moieties of the immunotoxin. When administered i.v. either on an every-day or every-other-day schedule, B43-PAP was very well tolerated, with no significant clinical or laboratory signs of toxicity at total dose levels ranging from 0.007 to 0.7 mg/kg. A transient episode of a mild capillary leak with a grade 2 hypoalbuminemia and 2+ proteinuria was observed at total dose levels equal to or higher than 0.35 mg/kg. At total dose levels of 3.5 and 7.0 mg/kg, B43-PAP caused dose-limiting renal toxicity due to severe renal tubular necrosis. The present study completes the preclinical evaluation of B43-PAP and provides the basis for its clinical evaluation in children with therapy-refractory B-lineage acute lymphoblastic leukemia.

Laboratory preparation of a deglycosylated ricin toxin A chain containing immunotoxin directed against a CD7 T lineage differentiation antigen for phase I human clinical studies involving T cell malignancies

An immunotoxin consisting of a monoclonal antibody specific for CD7, a cell surface determinant expressed on T acute lymphocytic leukemia (T-ALL) blast cells, was linked to the potent plant toxin deglycosylated ricin toxin A chain (dgRTA) and is currently under evaluation in phase I clinical trials. Scale-up production of this immunotoxin, called DA7, was simplified using a two-step purification protocol that resulted in a highly purified immunotoxin meeting FDA criteria for IND approval. The anti-CD7 antibody, 3Ale, an IgG2b, was coupled to toxin using two different heterobifunctional cross-linkers, (1) N-succinimidyl-3-(2-pyridyl-dithiolproprionate) (SPDP), considered a standard croslinker and (2) 4-succinimidyloxycarbonyl-alpha-methyl-alpha-(2-pyridyldithio)tolu ene (SMPT), designed to hinder the in vivo breakdown of the toxin/antibody disulfide bond. Since experiments revealed that SPDP-DA7 had similar pharmacokinetics and biodistribution in mice and higher yields than DA7 made with a hindered cross-linker, SPDP-DA7 was scaled up for clinical study. Yield of SPDP-DA7 was 25% relative to starting material. Fractions were collected containing a toxin: antibody ratio of 1:1 to 4:1 rather than only a 1:1 ratio since studies showed that this heterogenous fraction was just as toxic to proliferating CD7-expressing leukemia cells as a homogeneous 1:1 fraction. In vitro, the concentration of heterogenous SPDP-DA7 selectively inhibiting 50% activity (IC50) of the CD7+ CEM cell line was 0.01 microgram/ml to 0.05 microgram/ml for inhibiting activated T cells or T cell lines. In vivo, SPDP-DA7 showed a significant anti-tumor effect against CEM cells administered to scid/scid mice, but even more importantly was effective against primary T cell leukemias taken from patients and injected into scid/scid mice.

Methotrexate dose-escalation studies in transgenic mice and marrow transplant recipients expressing drug-resistant dihydrofolate reductase activity

Methotrexate (MTX) dose-escalation studies were conducted in two inbred lines of FVB/N transgenic mice expressing distinct drug-resistant dihydrofolate reductases (DHFRs) and in animals transplanted with transgenic marrow. Survival of animals expressing a tryptophan-31 variant DHFR transgene was only slightly improved over that of normal animals, and survival of tryptophan-31 variant DHFR marrow transplant recipients was indistinguishable from that of normal animals (at a MTX dose of 4 mg/kg i.p. daily). In contrast, extended survival was observed for animals expressing an arginine-22 variant (Arg22) DHFR transgene, with the last three of eight animals in this group succumbing at a final MTX dose of 14 mg/kg i.p. daily. Survival was slightly reduced for normal animals transplanted with Arg22 marrow. Interestingly, demise of animals in both Arg22 groups was not associated with the profound drop in hematocrit levels usually observed in MTX-treated animals. These animals were instead characterized by severe atrophy of the gastrointestinal tract, whereas hematocrit levels and marrow histology were relatively normal. Kidney pathology (mesangiocapillary glomerulopathy) was also observed in Arg22 marrow recipients but not in Arg22 transgenics, consistent with expression of the drug-resistance gene in kidney tissues of the transgenics, as demonstrated by ribonuclease protection analysis. Immediate dose-response studies in Arg22 marrow transplant recipients defined a maximum tolerated dose of 4 mg/kg/day MTX, 2 to 3 times that of animals transplanted with normal marrow or of normal untransplanted animals. These results define the extent of chemoprotection afforded by drug-resistant DHFR expression and serve to identify alternate sites of toxicity in animals administered the higher levels of MTX afforded by drug-resistant DHFR expression in the marrow.

Treatment of human B-cell precursor leukemia in SCID mice using a combination of the investigational biotherapeutic agent B43-PAP with cytosine arabinoside

Combined immunochemotherapy regimens using the investigational biotherapeutic agent B43(anti-CD19)-poke-weed antiviral protein (PAP) immunotoxin may offer an effective treatment for refractory B-cell precursor leukemias. The purpose of the present study was to explore and identify effective combinations of B43-PAP with standard chemotherapeutic drugs, including the anthracyclin doxorubicin, the epipodophyllotoxin etoposide, the nitrosurea carmustine, and the antimetabolite cytosine arabinoside. Here, we report that the B43-PAP plus cytosine arabinoside combination has potent antileukemic activity against human B-cell precursor leukemia in SCID mice and leads to 100% long-term event-free survival from an otherwise invariably fatal leukemia. Surprisingly, none of the other treatment protocols tested, including combinations of B43-PAP with carmustine, doxorubicin, or etoposide, proved more effective than B43-PAP alone.

Selective homing of human leukemic B-cell precursors to specific lymphohematopoietic microenvironments in SCID mice: a role for the beta 1 integrin family surface adhesion molecules VLA-4 and VLA-5

We used a SCID mouse xenograft model to study the in vivo growth patterns of primary leukemic cells from six patients with newly diagnosed B-cell precursor (BCP) acute lymphoblastic leukemia (ALL), including two patients with t(1;19) ALL, two patients with t(4;11) ALL, and two patients with t(9;22) ALL. Leukemic cells from these six patients caused overt leukemia in SCID mice with extensive multiple organ involvement. Leukemic BCP from SCID mice xenografted with leukemic cells from two t(9;22) ALL patients expressed very high levels of both VLA-4 and VLA-5 regardless of the tissue of origin. By comparison, in SCID mice xenografted with leukemic cells from the two patients with t(1;19) ALL and two patients with t(4;11) ALL, leukemic BCP from the bone marrow samples expressed high levels of VLA-4 as well as VLA-5, whereas the vast majority of leukemic BCP in the liver or spleen samples expressed neither of these adhesion molecules at significant levels. These results suggest that the expression of VLA-4 and VLA-5 on t(1;19) or t(4;11) leukemia cells likely determines their binding capacity to bone marrow stroma and may affect their migration to extramedullary tissues. Our findings are in accord with and extend previous studies which demonstrated that extracellular matrix and integrins influence development, compartmentalization, and migration of BCP during B-cell ontogeny. The described SCID mouse model system provides a unique opportunity to study the adhesion receptors which regulate the selective homing of human leukemic BCP to specific SCID mouse organs.

Toxicity profile of the investigational new biotherapeutic agent, B43 (anti-CD19)-pokeweed antiviral protein immunotoxin

The investigational biotherapeutic agent, B43(anti-CD19)-pokeweed antiviral protein (PAP) immunotoxin, has shown substantial anti-leukemic activity in SCID mouse models of human B-lineage leukemia and lymphoma. In this report, we describe the results of a comprehensive preclinical toxicity study which determined the toxicity profile of B43-PAP in BALB/c mice. Administration of unconjugated B43 monoclonal antibody was not associated with any toxicity, whereas B43-PAP caused dose-limiting and cardiac and renal toxicities which were fatal. In addition, B43-PAP also caused multifocal skeletal myofiber necrosis, which was associated with abnormal gait and lethargy. Notably, parenteral administrations of methylprednisolone, pentoxyphylline, or dopamine were able to markedly reduce B43-PAP related toxicity. This study provides a basis for further evaluation of the toxicity of B43-PAP in monkeys and humans.

In vitro and in vivo antileukemic activity of B43-pokeweed antiviral protein against radiation-resistant human B-cell precursor leukemia cells

B-cell precursor (BCP) leukemia is the most common form of childhood cancer and represents one of the most radiation-resistant forms of human malignancy. In this study, we examined the antileukemic efficacy of the B43 (anti-CD19)-pokeweed antiviral protein (B43-PAP) immunotoxin against radiation-resistant BCP leukemia cells. B43-PAP caused apoptosis of radiation-resistant primary BCP leukemia cells, killed greater than 99% of radiation-resistant primary leukemic progenitor cells from BCP leukemia patients, and conferred extended survival to severe combined immunodeficiency (SCID) mice xenografted with radiation-resistant human BCP leukemia. Furthermore, the combination of B43-PAP and total body irradiation (TBI) was more effective than TBI alone in two SCID mouse bone marrow transplantation models of radiation-resistant human BCP leukemia. Thus, B43-PAP may prove useful in the treatment of radiation-resistant BCP leukemia.

Protection of mice from lethal doses of methotrexate by transplantation with transgenic marrow expressing drug-resistant dihydrofolate reductase activity

Marrow cells from previously established lines of transgenic mice expressing either of two different methotrexate (MTX)-resistant dihydrofolate reductases (DHFRs) were transplanted into recipient animals to determine the resultant in vivo protective effect against toxicity associated with MTX administration. Sublethally irradiated, untransplanted animals were first used to establish conditions of low-dose MTX administration resulting in substantial hematopoietic toxicity with undetectable gastrointestinal toxicity. Under these conditions, low survival rates were observed for normal or transgenic animals not expressing drug-resistant DHFR activity, whereas transgenic animals expressing either the arg22 (line 04) or trp31 (line 03) DHFR variants survived. Transplantation of 10(6) marrow cells from either transgenic lines 03 or 04 rescued normal FVB/N recipient animals from low-dose MTX administration, which was lethal for animals transplanted with 10(6) normal FVB/N marrow cells. Reduced survival of transgenic line 04 marrow recipients was observed when twofold or fourfold doses of MTX were administered. However, when 10(7) transgenic line 04 marrow cells were infused, the recipients were found to be resistant to a MTX dose that was not only lethal for animals transplanted with 10(7) normal FVB/N marrow cells, but also lethal for normal, untransplanted FVB/N mice. Histologic analysis showed protection of both marrow and gastrointestinal tissues from MTX toxicity in transgenic line 04 marrow transplant recipients. Thus, exclusive expression of MTX-resistant DHFR activity in the marrow had a substantial, systemic chemoprotective effect in animals, which could be applied for improved utilization of MTX for antitumor chemotherapy.

Biotherapy for xenografted human central nervous system leukemia in mice with severe combined immunodeficiency using B43 (anti-CD19)-pokeweed antiviral protein immunotoxin

The study of central nervous system (CNS) leukemia has been hampered by the lack of a suitable animal model. We report that severe combined immunodeficiency (SCID) mice invariably develop rapidly progressive fatal CNS leukemia within 3 weeks after intravenous injection of NALM-6 pre-B acute lymphoblastic leukemia (ALL) cells. Colonization of the dura mater and subarachnoid space, usually of the distal spinal cord with occasional extension into the Virchow-Robin spaces of blood vessels subjacent to the meninges, followed involvement of bone marrow in the skull, vertebrae, and, occasionally, the appendicular skeleton. Occult CNS leukemia was detectable by polymerase chain reaction amplification of human DNA as early as 8 days postinoculation of leukemia cells. We used this in vivo model of human CNS leukemia to examine the therapeutic efficacy and toxicity of intrathecally administered B43 (anti-CD19)-pokeweed antiviral protein (PAP), an anti-B-lineage ALL immunotoxin directed against the pan-B-cell antigen CD19/Bp95. Intrathecal therapy with B43 (anti-CD19)-PAP immunotoxin at nontoxic dose levels significantly improved survival of SCID mice and was superior to intrathecal methotrexate therapy.

Leukemic cell growth in SCID mice as a predictor of relapse in high-risk B-lineage acute lymphoblastic leukemia

Mice with severe combined immunodeficiency (SCID) provide a model system to examine the in vivo homing, engraftment, and growth patterns of normal and malignant human hematopoietic cells. The relation between leukemic cell growth in this model and the treatment outcome in patients from whom cells were derived has not been established. Leukemic cells from 42 children with newly diagnosed high-risk B-lineage acute lymphoblastic leukemia were inoculated intravenously into CB.17 SCID mice. Mice were killed at 12 weeks or when they became moribund as a result of disseminated leukemia. All mice were necropsied and subjected to a series of laboratory studies to assess their burden of human leukemic cells. Twenty-three patients whose leukemic cells caused histopathologically detectable leukemia in SCID mice had a significantly higher relapse rate than the 19 patients whose leukemic cells did not (estimated 5-year event-free survival: 29.5% v 94.7%; 95% confidence intervals, 11.2% to 50.7% v 68.1% to 99.2%; P < .0001 by log-rank test). The occurrence of overt leukemia in SCID mice was was a highly significant predictor of patient relapse. The estimated instantaneous risk of relapse for patients whose leukemic cells caused overt leukemia in SCID mice was 21.5-fold greater than that for the remaining patients. Thus, growth of human leukemic cells in SCID mice is a strong and independent predictor of relapse in patients with newly diagnosed high-risk B-lineage acute lymphoblastic leukemia.

Human t(4;11)(q21;q23) acute lymphoblastic leukemia in mice with severe combined immunodeficiency

Mice with severe combined immunodeficiency (SCID) were injected intravenously with primary bone marrow blasts from 12 children with newly diagnosed t(4;11)(q21;q23) acute lymphoblastic leukemia (ALL). Blasts from eight patients caused overt disseminated leukemia, whereas blasts from the other four patients produced occult leukemia that was detectable only by the polymerase chain reaction (PCR) technique. Only one patient among eight whose blasts caused disseminated leukemia in SCID mice remains alive and disease-free at 48.4 months postdiagnosis. In contrast, three of the other four patients whose blasts did not cause overt leukemia in SCID mice remain alive and disease-free at 6.1, 23.6, and 35.9 months, respectively. Thus, the occurrence of overt leukemia in SCID mice may be a predictor of patients' disease-free survival. The described SCID mouse model system may prove useful for designing more effective treatment strategies against therapy-refractory t(4;11) ALL.

Childhood acute myeloid leukemia in mice with severe combined immunodeficiency

Primary bone marrow blasts from 4 children with t(8;21) acute myeloid leukemia (AML), 6 children with inv(16) AML, and 2 children with t(9;11) AML were injected intravenously or transplanted under the kidney capsule of sublethally irradiated mice with severe combined immunodeficiency (SCID). Leukemic cells from all AML patients infiltrated the SCID mouse thymus, suggesting that the thymic microenvironment supports the survival and growth of human AML blasts. Blasts from 1 of 4 t(8;21) AML patients and 4 of 6 inv(16) AML patients caused histopathologically detectable disseminated leukemia. Blasts from the remaining patients produced disseminated occult leukemia that was only detected by polymerase chain reaction. Occurrence of histopathologically detectable disseminated leukemia was dependent on intravenous injection of leukemic cells; none of the mice challenged with an inoculum transplanted under the kidney capsule developed overt leukemia. No obvious association was noted between occurrence of leukemia in SCID mice and clinical or laboratory features presented by patients, including age, sex, or leukocyte count at diagnosis. To our knowledge, this study is the first to show that leukemic blasts from children with newly diagnosed AML, especially inv(16) AML, can cause disseminated human leukemia in SCID mice without exogenous cytokine support. The SCID mouse model system may prove particularly useful for designing more effective treatment strategies against childhood AML.

Retroperitoneal inoculation of murine neuroblastoma results in a reliable model for evaluation of the antitumor immune response

To more closely mimic the natural site of human neuroblastoma and the original spontaneous arising paraspinal murine tumor, the authors developed a new model system in which murine neuroblastoma cells (neuro-2a) are implanted directly into the retroperitoneal space. This method of administration resulted in an aggressive and reproducible neuroblastoma model, with death occurring at a median of 20.3 days after tumor implantation using 1 x 10(6) neuro-2a cells, compared with the intraperitoneal (median, 31 days) and subcutaneous routes (median, 35.1 days) (P < .001). Adoptive transfer of single cell suspensions from livers, spleens, and bone marrows of mice with retroperitoneal tumors into healthy hosts resulted in tumor growth, confirming the presence of metastatic foci in these organs. The retroperitoneal murine neuroblastoma model was used to assess the importance of natural killer (NK) and T cells in regulating the growth of neuro-2a in vivo. T cells played an equally protective role as NK cells; depletion of either T or NK populations significantly decreased survival as compared with undepleted mice. Elimination of both NK and T cells further accelerated mortality of neuro-2a-bearing mice as compared to those depleted of either T or NK populations. The retroperitoneal murine model is a highly relevant in vivo system for preclinical studies of new therapeutic approaches for neuroblastoma.

Experimental atrial septal defect closure with a new, transcatheter, self-centering device

BACKGROUND

Despite two decades of research, a transcatheter atrial septal defect closure device is not available for clinical use. We have designed a new superelastic Nitinol-Dacron, double-disk, self-centering, atrial septal defect closure device and studied its efficacy in a canine model of atrial septal defects.

METHODS AND RESULTS

Atrial septal defects were created surgically in 20 adult dogs using either a 7.5-mm or 10-mm punch. Percutaneous transcatheter closures were attempted using a new device. The device sizes used were 20 mm in 6 dogs, 22 mm in 9, and 25 mm in 5 (22.1 +/- 1.9 mm, mean +/- SD). The stretched atrial septal defect diameter was 10.5 +/- 1.3 mm, and the device to stretched atrial septal defect diameter ratio was 2.1 +/- 0.3. Closures were successful in 19 studies and unsuccessful in 1. Angiography showed a left-to-right shunt in all 20 dogs before closure. Immediately after closure (n = 19), there were no shunts in 17 and trivial shunts in 2. Six dogs were followed for a period of 4.7 +/- 3.0 months (range, 2 to 8 months). The trivial shunt present in 1 animal immediately after closure had closed by the time of the repeat study. Spontaneous embolization of the device was not seen during follow-up. A solitary wire fracture was found 8 months after closure in 1 device. Light microscopy at 8 weeks in 3 dogs showed the devices to be covered by smooth endocardium, enmeshed in mature collagen tissue, with a minimal mononuclear cell infiltration. Retrievability was assessed by deliberately embolizing 4 devices in 2 dogs into the right atrium (n = 1) and pulmonary artery (n = 3). All devices were successfully retrieved with a snare.

CONCLUSIONS

This feasibility study demonstrates that this new self-centering atrial septal defect closure device has a number of design features that permit effective and safe closures in a canine model. These results support the investigation of this device in human clinical trials.

Human t(1;19)(q23;p13) pre-B acute lymphoblastic leukemia in mice with severe combined immunodeficiency

Severe combined immunodeficient (SCID) mice were injected intravenously with 5 x 10(6) primary bone marrow (BM) blasts from newly diagnosed patients with E2A-PBX1 fusion transcript positive t(1;19)(q23;p13) pre-B acute lymphoblastic leukemia (ALL). A marked variation existed in the pattern and extent of leukemic cell engraftment in SCID mice challenged with t(1;19) pre-B ALL blasts. Blasts from some patients caused disseminated leukemia that was detected by histopathology and/or flow cytometry, whereas blasts from other patients produced occult leukemia that was only detected by flow cytometry and/or polymerase-chain reaction. Notably, the ability of primary t(1;19) pre-B ALL blasts to cause disseminated leukemia in SCID mice was associated with poor prognosis. Six of six patients whose blasts caused disseminated leukemia in SCID mice relapsed at a median of 7.8 months (range: 5.7 to 25.2 months). In contrast, the remaining four patients whose blasts did not engraft or only partially engrafted remain in complete remission at 28 to 47 months. A new E2A-PBX-1 fusion transcript positive t(1;19) pre-B ALL cell line (designated LC1;19) with the composite immunophenotype CD7-CD10+CD19+CD45-HLA-DR+C mu+ was established by expanding BM blasts from a SCID mouse, which died of human t(1;19) ALL at 7 weeks after inoculation of primary leukemic blasts from a t(1;19) ALL patient. This cell line caused disseminated and invariably fatal leukemia when greater than 10(4) cells were injected intravenously into SCID mice. Total body irradiation followed by syngeneic BM transplantation (BMT) showed limited efficacy against LC1;19 leukemia in SCID mice. To our knowledge, this study is the first to (1) examine the in vivo growth of primary t(1;19) pre-B ALL blasts in SCID mice and (2) show that leukemic blasts from a majority of newly diagnosed t(1;19) pre-B ALL patients cause disseminated human leukemia in SCID mice. Our results indicate that t(1;19) pre-B ALL is biologically heterogeneous with regard to its in vivo growth pattern in SCID mice, a feature that may be predictive of prognosis. The described LC1;19 SCID mouse model may prove particularly useful for designing more effective treatment strategies against poor-prognosis t(1;19) ALL.

In vivo anti-leukemic efficacy of anti-CD7-pokeweed antiviral protein immunotoxin against human T-lineage acute lymphoblastic leukemia/lymphoma in mice with severe combined immunodeficiency

Mice with severe combined immunodeficiency (SCID) were injected with 1 x 10(7) MOLT-3 human T-lineage acute lymphoblastic leukemia cells to provide a model for the evaluation of anti-CD7-pokeweed antiviral protein (PAP) immunotoxin directed against the human CD7 antigen. Of control SCID mice (treated with phosphate-buffered saline, PBS) challenged intravenously with 1 x 10(7) MOLT-3 cells, 5/5 died at 29 to 35 days after inoculation, with a median event-free survival of 33 days. Similarly, 6/6 anti-CD19-PAP treated control SCID mice died of MOLT-3 leukemia at a median of 36 days. In contrast, treatment with anti-CD7-PAP (15 micrograms total dose in 5 micrograms intraperitoneal injections on days 1-3) significantly improved event-free survival of SCID mice challenged with 1 x 10(7) MOLT-3 cells. Of nine SCID mice treated with anti-CD7-PAP, four died at 54-149 days and five remained alive for > 172 days without clinical evidence of leukemia (median event-free survival > 172 days). When long-term survivors among the anti-CD7-PAP treated SCID mice were electively killed at 173 days to assess their leukemia burden, histopathologic examination and polymerase chain reaction provided evidence of disseminated leukemia in some of these mice. Intriguingly, marked differences in morphology, tissue distribution, and histologic pattern of organ invasion existed between leukemic blasts killing 100% of PBS-treated control mice at a median of 33 days and 'therapy-refractory' leukemic blasts detected in anti-CD7-PAP-treated long-term survivors. This novel SCID mouse model of disseminated human T-lineage ALL provides a unique in vivo system to investigate the therapeutic potential of new treatment strategies and to study possible mechanisms of in vivo immunotoxin resistance.

Effective immunochemotherapy of human t(4;11) leukemia in mice with severe combined immunodeficiency (SCID) using B43 (anti-CD19)-pokeweed antiviral protein immunotoxin plus cyclophosphamide

Human mixed lineage leukemia cell line RS4;11 with the t(4;11)(q21;q23) translocation causes disseminated and invariably fatal leukemia in mice with severe combined immunodeficiency. Whereas an immunotoxin constructed from the murine anti-CD19(B43) monoclonal antibody and the plant toxin pokeweed antiviral protein (B43-PAP) has a potent in vitro anti-leukemic effect against clonogenic RS4;11 cells, its activity is further potentiated by the active cyclophosphamide congener mafosfamid. These intriguing observations prompted us to evaluate the in vivo antileukemic efficacy of combined immunochemotherapy employing B43-PAP immunotoxin plus cyclophosphamide against human t(4;11) leukemia cells in an RS4;11 severe combined immunodeficiency (SCID) mouse model system. Intravenous injections of B43-PAP or cyclophosphamide improved survival of SCID mice challenged with RS4;11 leukemia, as reflected by markedly prolonged median survival times. After intravenous inoculation of 5 x 10(7) RS4;11 leukemia cells, the median survival times were 41 days for saline-treated control mice (n = 12), 44 days for control mice treated with unconjugated B43 monoclonal antibody and PAP (n = 12), 56 days for mice treated with the control immunotoxin G17.2 (anti-CD4)-PAP (n = 6), 79 days for B43-PAP-treated test mice (n = 12), and 80 days for cyclophosphamide-treated test mice (n = 16). Notably, combined immunochemotherapy using B43-PAP plus cyclophosphamide was significantly more effective than either B43-PAP or cyclophosphamide alone. The median survival time for a total of 22 SCID mice undergoing combined immunochemotherapy with B43-PAP followed by cyclophosphamide (n = 12) or cyclophosphamide followed B43-PAP (n = 10) was > 150 days. The Kaplan-Meier estimates and standard errors of the probability of event-free survival at 5 months after inoculation of 5 x 10(7) RS4;11 cells were 21 +/- 13% for B43-PAP-treated mice, 7 +/- 6% for cyclophosphamide-treated mice, 90 +/- 10% for mice treated with B43-PAP followed by cyclophosphamide (n = 12), and 90 +/- 10% for mice treated with cyclophosphamide followed by B43-PAP (n = 10). Our results lead us to recommend that initial consideration be given to combined immunochemotherapy protocols using B43-PAP immunotoxin plus cyclophosphamide for treatment of refractory or relapsed t(4;11) leukemias.

Natural history of atherosclerosis and hyperlipidemia in heterozygous WHHL (WHHL-Hh) rabbits. II. Morphologic evaluation of spontaneously occurring aortic and coronary lesions

This study evaluated the morphologic appearance of spontaneous aortic and coronary atherosclerotic lesions in 21 of the 28, 3-year old, heterozygous Watanabe heritable hyperlipidemic (WHHL-Hh) rabbits whose lipid profiles were presented in part I of this report. In situ perfusion fixation of the arteries showed 100% of the aortas involved with one or another type of intimal lesion. In male rabbits (n = 13), the abdominal aortas had more severe fibrosis and more diffuse intima thickening than the thoracic aortas, (p < 0.001). In female rabbits (n = 8), fatty streaks and fibrous lesions were more predominant in the thoracic than in the abdominal aorta (p < 0.05). Fatty aortic plaques in the female were more commonly found in the abdominal than in the thoracic aorta, but this finding was not statistically significant. In contrast, fatty aortic plaques were not found in the male aortas; however, larger areas of diffuse intimal thickening with fatty deposits were more common in the abdominal aortas of the males (p < 0.01). Annular arteriosclerotic lesions, exclusive to the thoracic aorta, occurred in three of 21 rabbits. Histologically, the aortas demonstrated subintimal fibrosis, fragmentation of the lamina elastica interna, focal medial degeneration, and cholesterol clefts. The coronary arteries were involved in 85% of the males and in 86% of the females. Lesions were more common in the left than in the right coronary artery and primarily consisted of mild nonobstructing intimal hyperplasia with fibrosis. Based on these observations, we consider older WHHL-Hh rabbits excellent models for studying atherosclerosis. Because of their genetic and age-related lesions, WHHL-Hh rabbits may be superior to the cholesterol-fed rabbit model with respect to comparability with human atherosclerotic lesions.

Effective immunochemotherapy of CALLA+C mu+ human pre-B acute lymphoblastic leukemia in mice with severe combined immunodeficiency using B43 (anti-CD19) pokeweed antiviral protein immunotoxin plus cyclophosphamide

A highly aggressive human CALLA+C mu+ pre-B acute lymphoblastic leukemia (ALL) cell line (NALM-6-UM1) causes disseminated and invariably fatal leukemia in CB.17 mice with severe combined immunodeficiency (SCID). We used this SCID mouse model of human pre-B ALL to evaluate and compare, in a total of 434 SCID mice, the antileukemic efficacy of B43 (anti-CD19)-pokeweed antiviral protein (PAP) immunotoxin and cyclophosphamide (CPA) as individual reagents and as combined immunochemotherapeutic regimens. B43-PAP plus CPA was superior to either the immunotoxin or drug alone, and combined immunochemotherapy markedly improved the event-free survival (EFS) of SCID mice challenged with NALM-6-UM1 pre-B ALL cells. Notably, 90% to 100% of SCID mice challenged with 1 x 10(6) leukemia cells and then treated with B43-PAP plus CPA combined immunochemotherapy regimens became long-term survivors, a result not achieved with B43-PAP alone or CPA alone. The advantage was particularly evident in mice inoculated with 5 x 10(6) leukemia cells. While neither 15 micrograms B43-PAP (median survival, 58 days) nor 1 mg CPA (median survival, 49 days) resulted in long-term EFS of SCID mice challenged with 5 x 10(6) NALM-6-UM1 pre-B ALL cells, the probability of EFS at 6 months was 50% +/- 16% for SCID mice treated with 15 micrograms B43-PAP plus 1 mg CPA (median survival, greater than 180 days) (P less than .0001). The probability of long-term EFS was only 14% +/- 7% for mice treated with 30 micrograms B43-PAP and 0% +/- 0% for mice treated with 1 mg CPA, but 40% +/- 16% for mice treated with 30 micrograms B43-PAP plus 1 mg CPA (P less than .0001). Similarly, the probability of EFS at 6 months was 40% +/- 16% for mice treated with 2 mg CPA alone, 70% +/- 15% for mice treated with 2 mg CPA plus 15 micrograms B43-PAP, and 70% +/- 15% for mice treated with 2 mg CPA plus 30 micrograms B43-PAP. Ten SCID mice in the B43-PAP plus CPA combined immunochemotherapy arms surviving long term after the inoculation of 5 x 10(6) NALM-6-UM1 pre-B ALL cells were electively killed at 174 to 181 days to assess their leukemia burden. We found no evidence of leukemia in any of the bone marrow specimens by two-color immunofluorescence and multiparameter flow cytometry.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo efficacy of B43 (anti-CD19)-pokeweed antiviral protein immunotoxin against BCL-1 murine B-cell leukemia

We show that a highly aggressive subclone of murine BCL-1 B-lineage leukemia expresses a single 2.4-kb transcript hybridizing to the human CD19 cDNA probe and reacts strongly with the anti-human CD19 monoclonal antibodies (MoAb) B43, B4, Leu-12, and J3-119. In contrast to their strong reactivity with anti-human CD19 MoAb, BCL-1 cells show no reactivity with MoAb directed against human CD22, CD72, HLA-DR, IgD, or IgM. Western blot analysis of BCL-1 whole cell lysates with the anti-human CD19 MoAb J3-119 showed a single 69-Kd protein band, which was not detected by the negative control MoAb G19.4 (anti-CD3). In contrast to BCL-1 cells, normal BALB/c splenocytes or mouse splenocyte/myeloma hybridoma cell lines did not (1) express any transcripts that hybridized to the human CD19 cDNA probe, (2) react with B43/anti-CD19 MoAb, or (3) express the 69-Kd protein that reacts with the anti-human CD19 MoAb J3-119. Murine BCL-1 B-cell leukemia thus provides a unique model of disseminated B-lineage leukemia to evaluate the antileukemic efficacy of anti-CD19 immunotoxins. This model was subsequently used to evaluate the in vivo homing ability, pharmacokinetics, and antileukemic efficacy of B43 MoAb conjugated to the plant hemitoxin pokeweed antiviral protein (PAP). B43-PAP immunotoxin (1) showed strong and antigen-specific reactivity with BCL-1 cells, (2) promptly penetrated the spleens of leukemic mice, (3) rapidly reduced the BCL-1 leukemia burden of leukemic mice and, most importantly, (4) improved survival. Finally, B43-PAP immunotoxin was more effective against BCL-1 leukemia than 700 cGy (LD100/30) total body irradiation (TBI) followed by syngeneic bone marrow transplantation (BMT).

In vivo efficacy of B43 (anti-CD19)-pokeweed antiviral protein immunotoxin against human pre-B cell acute lymphoblastic leukemia in mice with severe combined immunodeficiency

A highly aggressive subclone of the human CALLA+C mu+ pre-B acute lymphoblastic leukemia (ALL) cell line NALM-6 (designated NALM-6-UM1) caused disseminated and fatal leukemia in CB.17 mice with severe combined immunodeficiency (SCID). An intravenous challenge with 1 x 10(6) (NALM-6-UM1 cells caused 15 of 27 (56%) SCID mice to become paraplegic at 31 +/- 2 days (median = 33 days) and 27 of 27 (100%) mice to die of disseminated leukemia at 38 +/- 1 days (median = 39 days). We used this SCID mouse model of aggressive human pre-B ALL to evaluate the in vivo antileukemic efficacy of B43 (anti-CD19)-pokeweed antiviral protein (PAP) immunotoxin. A 3-day treatment with nontoxic doses of B43-PAP markedly reduced the incidence of paraplegia and improved event-free survival (EFS) in SCID mice challenged with 1 x 10(6) NALM-6-UM1 pre-B ALL cells, as reflected by significantly higher cumulative proportions of mice free of paraplegia or alive at 1 to 7 months, as compared with phosphate-buffered saline (PBS) treated control mice. The Kaplan-Meier estimates and standard errors of the probability of developing paraplegia after inoculation of 1 x 10(6) NALM-6-UM1 cells was 64% +/- 10% for PBS-treated mice (median time to paraplegia = 37 days) (N = 27), 18% +/- 8% for mice treated with 15 micrograms B43-PAP (5 micrograms/mouse/d x 3 days) (N = 23) and 5% +/- 5% for mice treated with 30 micrograms B43-PAP (10 micrograms/mouse/d x 3 days) (N = 21). While 27 of 27 PBS-treated control SCID mice died of leukemia at 38 +/- 1 days (range = 24 to 54 days), only 16 of 44 B43-PAP-treated mice developed leukemia at 74 +/- 12 days (range = 30 to 182 days), consistent with greater than or equal to 6 logs kill of clonogenic NALM-6-UM1 cells in 64% of SCID mice. The Kaplan-Meier estimates and standard errors of the probability of long-term EFS after inoculation of 1 x 10(6) NALM-6-UM1 cells were 65% +/- 10% for mice treated with 15 micrograms B43-PAP and 60% +/- 11% for mice treated with 30 micrograms B43-PAP with a median survival time of greater than 7 months for both groups. In contrast, neither unconjugated B43 monoclonal antibody nor the anti-T-cell immunotoxin G17.2 (anti-CD4)-PAP decreased the incidence of paraplegia or improved EFS.(ABSTRACT TRUNCATED AT 400 WORDS)

Colonization of rabbits by Pasteurella multocida: serum IgG responses following intranasal challenge with serologically distinct isolates

Enzyme-linked immunosorbent assays (ELISAs) and immunoblots were used to measure serum IgG responses in rabbits which were intranasally challenged with Pasteurella multocida. The responses to two serologically distinct isolates (isolate 1, serotype 3:A and isolate 10, serotype 1:D) were compared and then correlated with the ability of the isolates to colonize the nasal passages. Five rabbits were challenged with each isolate (10(5) CFU); nasal washings and sera were collected weekly for 8 weeks. Serum IgG levels were measured by ELISA and immunoblots, using bacterial whole cells and lipopolysaccharides (LPSs) as antigens. The serum IgG response to isolate 1 was evident earlier and was significantly stronger than the response to isolate 10 (P less than 0.025). Immunoblots supported this observation and confirmed that both isolates elicited antibodies which reacted with bacterial protein and LPS antigens, with antibody to protein detectable before antibody to LPS. Results of weekly nasal cultures suggested that the antibody response data could be explained by a difference in the ability of the isolates to colonize the nasal passages: isolate 1 was recovered from four of five rabbits for 8 weeks, whereas isolate 10 was recovered for a maximum of 2 weeks, even when the challenge dose was increased tenfold. The strong response elicited by isolate 1 was therefore probably a result of persistent colonization, whereas the weak response to isolate 10 may have resulted from an inability to persistently colonize the nasal passages. The results of this study demonstrate that isolates of P. multocida elicit antibody responses of differing intensities and vary in their ability to colonize the nasal passages.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial characterization of plasmids from rabbit isolates of Pasteurella multocida

Plasmids have not been reported for isolates of Pasteurella multocida from rabbits. We assayed 28 isolates of rabbit P. multocida for plasmids and sought to determine whether or not plasmid presence correlated with clinical or pathologic findings, serotype, toxin production, possession of pili, or biochemical characteristics. Fourteen isolates bore a single 1.6 Md (covalently closed circular form in 0.7% agarose gels) plasmid. An additional isolate had two plasmids which migrated as a closely-spaced doublet, centered around 1.6 Md. Eleven isolates appeared to have identical plasmids, according to Hae III and Hinf I digests. The apparent linear size of this common plasmid in 2% agarose gels was 2.1 Md, as calculated from the sums of the sizes of Hae III or Hinf I digestion fragments. Linearization of the common plasmid with Msp I produced an apparent size of 2.5 Md in 0.7% agarose gels. No correlations between presence of the common plasmid and somatic serotype, toxigenicity, presence of pili, antimicrobial resistance, selected biochemical characteristics, anatomic site from which the bacteria were cultured, or disease status of the host were found.

An enzyme-linked immunosorbent assay for detection of chronic subclinical Pasteurella pneumotropica infection in mice

Serum samples from seventy-five, 3- to 12-week-old and 16 retired breeder male Swiss mice from a conventional colony with enzootic chronic subclinical Pasteurella pneumotropica infection were tested by enzyme-linked immunosorbent assay (ELISA) and Western blots for IgG antibodies to whole cell (WC) and lipooligosaccharide (LOS) antigens of P. pneumotropica. In 3- to 12-week-old mice, serum antibody levels to LOS exceeded those to the WC preparation. Western blots of sera from mice in this age group substantiated that a major component of the early IgG antibody response was directed against LOS antigens. Higher antibody levels to both antigen preparations in 3-week-old mice compared to mice 4 and 6 weeks old were interpreted as reflecting a decline in antibodies acquired from the dam. Active immunity indicative of infection was first detected at 8 weeks of age. Serum samples from retired breeder mice (28 weeks of age) also had substantial antibody titers to LOS but, in contrast to sera from mice in the younger age groups, retired breeders had significantly greater IgG reactivity to WC preparations than to LOS antigens. The superior specificity of the LOS antigen compared to the WC preparation in the ELISA was demonstrated by testing serum samples from retired breeder mice against WC and LOS antigens from P. ureae, P. multocida, and P. hemolytica. The reactivity of IgG against LOS antigens from these organisms was negligible, whereas substantial titers were evident to WC antigens. This ELISA, using LOS preparations as antigen, is a useful serologic assay for the detection of subclinical P. pneumotropica infection in mice.