Non-invasive myocardial work in aortic stenosis: validation and improvement in left ventricular pressure estimation

AIMS

The non-invasive myocardial work index (MWI) has been validated in patients without aortic stenosis (AS). A thorough assessment of methodological limitations is warranted before this index can be applied to patients with AS.

METHODS AND RESULTS

We simultaneously measured left ventricular pressure (LVP) by using a micromanometer-tipped catheter and obtained echocardiograms in 20 patients with severe AS. We estimated LVP curves and calculated pressure-strain loops using three different models: (i) the model validated in patients without AS; (ii) the same model, but with pressure at the aortic valve opening (AVO) adjusted to diastolic cuff pressure; and (iii) a new model based on the invasive measurements from patients with AS. Valvular events were determined by echocardiography. Peak LVP was estimated as the sum of the mean aortic transvalvular gradient and systolic cuff pressure. In same-beat comparisons between invasive and estimated LVP curves, Model 1 significantly overestimated early systolic pressure by 61 ± 5 mmHg at AVO compared with Models 2 and 3. However, the average correlation coefficients between estimated and invasive LVP traces were excellent for all models, and the overestimation had limited influence on MWI, with excellent correlation (r = 0.98, P < 0.001) and good agreement between the MWI calculated with estimated (all models) and invasive LVP.

CONCLUSION

This study confirms the validity of the non-invasive MWI in patients with AS. The accuracy of estimated LVP curves improved when matching AVO to the diastolic pressure in the original model, mirroring that of the AS-specific model. This may sequentially enhance the accuracy of regional MWI assessment.

The Alternative Complement Pathway Is Activated Without a Corresponding Terminal Pathway Activation in Patients With Heart Failure

Objective

Dysregulation of the complement system has been described in patients with heart failure (HF). However, data on the alternative pathway are scarce and it is unknown if levels of factor B (FB) and the C3 convertase C3bBbP are elevated in these patients. We hypothesized that plasma levels of FB and C3bBbP would be associated with disease severity and survival in patients with HF.

Methods

We analyzed plasma levels of FB, C3bBbP, and terminal C5b-9 complement complex (TCC) in 343 HF patients and 27 healthy controls.

Results

Compared with controls, patients with HF had elevated levels of circulating FB (1.6-fold, p < 0.001) and C3bBbP (1.3-fold, p < 0.001). In contrast, TCC, reflecting the terminal pathway, was not significantly increased (p = 0.15 vs controls). FB was associated with NT-proBNP, troponin, eGFR, and i.e., C-reactive protein. FB, C3bBbP and TCC were not associated with mortality in HF during a mean follow up of 4.3 years.

Conclusion

Our findings suggest that in patients with HF, the alternative pathway is activated. However, this is not accompanied by activation of the terminal pathway.

Left Ventricular Systolic Function in Long-Term Survivors of Allogeneic Hematopoietic Stem Cell Transplantation

Background

Allogeneic hematopoietic stem cell transplantation (allo-HSCT), a potentially curative therapy for malignant and nonmalignant diseases, is being increasingly used in younger patients. Although allo-HSCT survivors have an established increased risk of cardiovascular disease, there is limited knowledge of the long-term effects on cardiac function in survivors.

Objectives

The purpose of this study was to describe left ventricular (LV) systolic function in long-term allo-HSCT survivors treated in childhood, adolescence, or early adulthood.

Methods

Our cross-sectional cohort study included 104 patients (56% women), age 18 ± 10 years at time allo-HSCT with 17 ± 6 years of follow-up. Echocardiography included 2-dimensional (2D) and 3-dimensional (3D) analyses and speckle tracking imaging. In total, 55 healthy control subjects with a similar age, sex, and body mass index were used for comparison. Left ventricular systolic dysfunction (LVSD) was defined as reduced 2D left ventricular ejection fraction (LVEF) of <52% in men and <54% in women, and/or a reduced global longitudinal strain (GLS) of ≥−17%. Multivariable linear regression was used to determine independent predictors of 2D-LVEF and GLS.

Results

Allo-HSCT survivors had significantly reduced LV systolic function compared with control subjects: 2D-LVEF (55.2 ± 5.8% vs. 59.0 ± 2.9%; p < 0.001), 3D LVEF (54.0 ± 5.1% vs. 57.6 ± 2.7%; p < 0.001), and GLS (−17.5 ± 2.2% vs. −19.8 ± 1.4%; p < 0.001). LVSD was found in 44.2%, of whom 28.3% were symptomatic. Clinical factors independently associated with 2D-LVEF and/or GLS included age, anthracyclines, graft versus host disease (GVHD), heart rate, and hypertension. In the 45% of survivors pre-treated with anthracyclines, the effect of anthracyclines on 2D-LVEF and GLS was dose-dependent.

Conclusions

LVSD is common in long-term survivors of allo-HSCT treated in their youth. Pre-HSCT therapies with anthracyclines, age, heart rate, hypertension, and graft versus host disease are associated with measures of LV function.

Robust diffraction-limited near-infrared-to-near-ultraviolet wide-field imaging from stratospheric balloon-borne platforms-Super-pressure Balloon-borne Imaging Telescope performance

At a fraction of the total cost of an equivalent orbital mission, scientific balloon-borne platforms, operating above 99.7% of the Earth's atmosphere, offer attractive, competitive, and effective observational capabilities-namely, space-like seeing, transmission, and backgrounds-which are well suited for modern astronomy and cosmology. The Super-pressure Balloon-borne Imaging Telescope (SUPERBIT) is a diffraction-limited, wide-field, 0.5 m telescope capable of exploiting these observing conditions in order to provide exquisite imaging throughout the near-infrared to near-ultraviolet. It utilizes a robust active stabilization system that has consistently demonstrated a 48 mas 1σ sky-fixed pointing stability over multiple 1 h observations at float. This is achieved by actively tracking compound pendulations via a three-axis gimballed platform, which provides sky-fixed telescope stability at < 500 mas and corrects for field rotation, while employing high-bandwidth tip/tilt optics to remove residual disturbances across the science imaging focal plane. SUPERBIT's performance during the 2019 commissioning flight benefited from a customized high-fidelity science-capable telescope designed with an exceptional thermo- and opto-mechanical stability as well as a tightly constrained static and dynamic coupling between high-rate sensors and telescope optics. At the currently demonstrated level of flight performance, SUPERBIT capabilities now surpass the science requirements for a wide variety of experiments in cosmology, astrophysics, and stellar dynamics.

Specific amyloid β clearance by a catalytic antibody construct

Classical immunization methods do not generate catalytic antibodies (catabodies), but recent findings suggest that the innate antibody repertoire is a rich catabody source. We describe the specificity and amyloid β (Aβ)-clearing effect of a catabody construct engineered from innate immunity principles. The catabody recognized the Aβ C terminus noncovalently and hydrolyzed Aβ rapidly, with no reactivity to the Aβ precursor protein, transthyretin amyloid aggregates, or irrelevant proteins containing the catabody-sensitive Aβ dipeptide unit. The catabody dissolved preformed Aβ aggregates and inhibited Aβ aggregation more potently than an Aβ-binding IgG. Intravenous catabody treatment reduced brain Aβ deposits in a mouse Alzheimer disease model without inducing microgliosis or microhemorrhages. Specific Aβ hydrolysis appears to be an innate immune function that could be applied for therapeutic Aβ removal.

Physiological IgM class catalytic antibodies selective for transthyretin amyloid

Peptide bond-hydrolyzing catalytic antibodies (catabodies) could degrade toxic proteins, but acquired immunity principles have not provided evidence for beneficial catabodies. Transthyretin (TTR) forms misfolded β-sheet aggregates responsible for age-associated amyloidosis. We describe nucleophilic catabodies from healthy humans without amyloidosis that degraded misfolded TTR (misTTR) without reactivity to the physiological tetrameric TTR (phyTTR). IgM class B cell receptors specifically recognized the electrophilic analog of misTTR but not phyTTR. IgM but not IgG class antibodies hydrolyzed the particulate and soluble misTTR species. No misTTR-IgM binding was detected. The IgMs accounted for essentially all of the misTTR hydrolytic activity of unfractionated human serum. The IgMs did not degrade non-amyloidogenic, non-superantigenic proteins. Individual monoclonal IgMs (mIgMs) expressed variable misTTR hydrolytic rates and differing oligoreactivity directed to amyloid β peptide and microbial superantigen proteins. A subset of the mIgMs was monoreactive for misTTR. Excess misTTR was dissolved by a hydrolytic mIgM. The studies reveal a novel antibody property, the innate ability of IgMs to selectively degrade and dissolve toxic misTTR species as a first line immune function.

CD4 binding determinant mimicry for HIV vaccine design

The immunodominant epitopes expressed by the HIV-1 envelope protein gp120 are hypermutable, defeating attempts to develop an effective HIV vaccine. Targeting the structurally conserved gp120 determinant that binds host CD4 receptors (CD4BD) and initiates infection is a more promising route to vaccination, but this has proved difficult because of the conformational flexibility of gp120 and immune evasion mechanisms used by the virus. Mimicking the outer CD4BD conformational epitopes is difficult because of their discontinuous nature. The CD4BD region composed of residues 421–433 (CD4BD^core) is a linear epitope, but this region possesses B cell superantigenic character. While superantigen epitopes are vulnerable to a small subset of spontaneously produced neutralizing antibodies present in humans without infection (innate antibodies), their non-covalent binding to B cell receptors (BCRs) does not stimulate an effective adaptive response from B cells. Covalent binding at naturally occurring nucleophilic sites of the BCRs by an electrophilic gp120 (E-gp120) analog is a promising solution. E-gp120 induces the synthesis of neutralizing antibodies the CD4BD^core. The highly energetic covalent reaction is hypothesized to convert the abortive superantigens–BCR interaction into a stimulatory signal, and the binding of a spatially distinct epitope at the traditional combining site of the BCRs may furnish a second stimulatory signal. Flexible synthetic peptides can detect pre-existing CD4BD^core-specific neutralizing antibodies. However, induced-fit conformational transitions of the peptides dictated by the antibody combining site structure may induce the synthesis of non-neutralizing antibodies. Successful vaccine targeting of the CD4BD will require a sufficiently rigid immunogen that mimics the native epitope conformation and bypasses B cell checkpoints restricting synthesis of the neutralizing antibodies.

Antibodies to a superantigenic glycoprotein 120 epitope as the basis for developing an HIV vaccine

Failure to induce synthesis of neutralizing Abs to the CD4 binding determinant (CD4BD) of gp120, a central objective in HIV vaccine research, has been alternately ascribed to insufficient immunogen binding to Abs in their germline V region configuration expressed as BCRs, insufficient adaptive mutations in Ab V regions, and conformational instability of gp120. We employed peptide analogs of gp120 residues 421-433 within the CD4BD (CD4BD(core)) to identify Abs produced without prior exposure to HIV (constitutive Abs). The CD4BD(core) peptide was recognized by single-chain Fv fragments from noninfected humans with lupus that neutralized genetically diverse strains belonging to various HIV subtypes. Replacing the framework region (FR) of a V(H)4-family single-chain Fv with the corresponding V(H)3-family FRs from single-chain Fv JL427 improved the CD4BD(core) peptide-binding activity, suggesting a CD4BD(core) binding site outside the pocket formed by the CDRs. Replacement mutations in the FR site vicinity suggested the potential for adaptive improvement. A very small subset of serum CD4BD(core)-specific serum IgAs from noninfected humans without autoimmune disease isolated by epitope-specific chromatography neutralized the virus potently. A CD4BD(core)-specific, HIV neutralizing murine IgM with H and L chain V regions (V(H) and V(L) regions) free of immunogen-driven somatic mutations was induced by immunization with a CD4BD(core) peptide analog containing an electrophilic group that binds B cells covalently. The studies indicate broad and potent HIV neutralization by constitutive Abs as an innate, germline-encoded activity directed to the superantigenic CD4BD(core) epitope that is available for amplification for vaccination against HIV.

Nature and nurture of catalytic antibodies

Immunoglobulins (antibodies) frequently express constitutive functions. Two such functions are nucleophilic catalysis and the reversible binding to B-cell superantigens. Constitutive or "naturally-occurring" antibodies are produced spontaneously from germline genetic information. The antibody structural elements mediating the constitutive functions have originated over millions of years of phylogenic evolution, contrasting with antigen-driven, somatic sequence diversification of the complementarity determining regions (CDR) that underlies the better-known high affinity antigen binding function of antibodies. Often, the framework regions (FRs) play a dominant role in antibody constitutive functions. Catalytic antibody subsets with promiscuous, autoantigen-directed and microbe-directed specificities have been identified. Mucosal antibodies may be specialized to express high-level catalytic activity against microbes transmitted by the mucosal route, exemplified by constitutive production of IgA class antibodies in mucosal secretions that catalyze the cleavage of HIV gp120. Catalytic specificity can be gained by constitutive noncovalent superantigen binding at the FRs and by adaptive development of noncovalent classical antigen or superantigen binding, respectively, at the CDRs and FRs. Growing evidence suggests important functional roles for catalytic antibodies in homeostasis, autoimmune disease and protection against infection. Adaptive antibody responses to microbial superantigens are proscribed underphysiological circumstances. Covalent electrophilic immunogen binding to constitutively expressed nucleophilic sites in B-cell receptors bypasses the restriction on adaptive antibody production, and simultaneous occupancy of the CDR binding site by a stimulatory antigenic epitope can also overcome the downregulatory effect of superantigen binding at the FRs. These concepts may be useful for developing novel vaccines that capitalize and improve on constitutive antibody functions for protection against microbes.

Molecular cloning of a proteolytic antibody light chain

The cDNA for an antibody light chain raised by immunization against vasoactive intestinal peptide (VIP) was cloned in a bacterial expression vector, and the recombinant light chain was purified to electrophoretic homogeneity. The light chain catalyzed the hydrolysis of VIP efficiently owing to its comparatively high affinity for the substrate. In control experiments, the catalytic activity was preserved at a constant level after further chromatography of the light chain on anion-exchange and gel-filtration fast protein liquid chromatography columns, and it was removed by immunoadsorption with immobilized anti-mouse light chain antibody. The amide bond linking methylcoumarinamide (MCA) and arginine in a tripeptide unrelated in sequence to VIP was cleaved by the light chain with lower affinity and kinetic efficiency (kcat/Km). Hydrolysis of the peptidyl-MCA conjugate was inhibited competitively by the alternate substrate, VIP. The Ki and Km values for VIP were in the same range, indicating that peptide-MCA and VIP hydrolysis occurs at a common catalytic site in the light chain. Molecular modeling suggested the presence of a serine protease-like site in the light chain. This was supported by inhibition of the hydrolytic activity by serine protease inhibitors, but not by inhibitors of other classes of proteases. These observations suggest a poorly discriminatory catalytic site, with specificity for VIP arising chiefly by means of the antigen recognition function of the light chain combining site.

Rapid, non-separation electrochemiluminescent DNA hybridization assays for PCR products, using 3'-labelled oligonucleotide probes

Described are rapid assays for the analysis of PCR products in a one step, non-separation assay based on the use of electrochemiluminescence generated from a tris-bipyridine ruthenium (II) label. The assay uses PCR incorporation of a biotinylated oligonucleotide as a primer, with the inclusion of a labelled oligonucleotide. Oligonucleotides were labelled with an N-hydroxy succinimide ester of tris-bipyridine ruthenium (II) dihexafluorophosphate (Origen-label) by modifying the 3' and 3' 5' ends of the oligonucleotide probes. The assay makes use of the inherent thermal stability and absence of polymerase activity on such probes to allow the PCR and probe hybridization to be completed automatically on the thermocycler. The assay is concluded by the addition of PCR samples to streptavidin beads on an electrochemiluminescence analyser for binding and analysis. Target genes evaluated were the HIV-1 gag gene, and cystic fibrosis delta F-508 deletion mutation. The results obtained from these assays demonstrated the detection of 10 copies of the HIV-1 gag gene, and cystic fibrosis delta F-508 mutation in 1 ng of human DNA within 15 min. This assay format allows a rapid and simple determination of specific amplified DNA sequences, reducing the contamination risks due to washes and multiple pipetting.

Peptidolytic monoclonal antibody elicited by a neuropeptide

We report evidence that a monoclonal antibody raised by immunization with a vasoactive intestinal peptide (VIP)-carrier protein conjugate selectively hydrolyzes VIP and a fluorescence quenched decapeptide (FQ14-22D), representing the region of VIP most susceptible to autoantibody-mediated cleavage (residues 14-22). A high affinity of the antibody for VIP and a lower affinity for FQ14-22D were revealed by kinetic studies and further substantiated by potent inhibition of FQ14-22D cleaving activity by full-length VIP. Sequencing of FQ14-22D hydrolysis products indicated selective cleavage at one peptide bond. These observations suggest that antibodies induced against naturally occurring polypeptide antigens can express peptidolytic activity targeted for specific sequences in the recognition epitope.

Improved Electrochemiluminescent Label for DNA Probe Assays: Rapid Quantitative Assays of HIV-1 Polymerase Chain Reaction Products

We describe the characterization and utility of a new electrochemiluminescent (ECL) label for oligonucleotides, utilizing phosphoramidite chemistry. This phosphoramidite of the tris(2,2-bipyridine)ruthenium(II) complex, bis(2,2-bipyridine)(4-[4-(2-cyanoethoxy-N,N-diisopropyl-amino) phosphinoxybutyl]4'-methyl)2,2-bipyridine ruthenium(II) dihexafluorophosphate or Origen phosphoramidite, enables the direct incorporation of the label during automated DNA synthesis. Efficiency of this automated synthesis allows the direct utilization of probes without further purification. Introduction of this labeling group is reproducible, and the ECL signal recovered is not influenced by hybridization. Furthermore, neither hybridization kinetics nor hybrid stability was affected by our label. We also demonstrate the utility of these labels for the development of rapid assays with oligonucleotides direct from automated synthesis. The clinical utility of these labeled oligonucleotides is shown with assays of total nucleic acid, extracted from peripheral blood lymphocytes of patients with acquired immunodeficiency syndrome (AIDS), to detect the human immunodeficiency virus (HIV-1). The results demonstrate the ability of the assay to quantify 30-2000 copies of HIV1 gag genes and to rapidly detect (less than 45 min) HIV-1 gag genes in a nonseparation assay. The application of this assay to clinical samples demonstrates the utility of these assays for rapid and quantitative analysis.

Improved electrochemiluminescent label for DNA probe assays: rapid quantitative assays of HIV-1 polymerase chain reaction products

We describe the characterization and utility of a new electrochemiluminescent (ECL) label for oligonucleotides, utilizing phosphoramidite chemistry. This phosphoramidite of the tris(2,2-bipyridine)ruthenium(II) complex, bis(2,2-bipyridine)(4-[4-(2-cyanoethoxy-N,N-diisopropyl-amino) phosphinoxybutyl]4'-methyl)2,2-bipyridine ruthenium(II) dihexafluorophosphate or Origen phosphoramidite, enables the direct incorporation of the label during automated DNA synthesis. Efficiency of this automated synthesis allows the direct utilization of probes without further purification. Introduction of this labeling group is reproducible, and the ECL signal recovered is not influenced by hybridization. Furthermore, neither hybridization kinetics nor hybrid stability was affected by our label. We also demonstrate the utility of these labels for the development of rapid assays with oligonucleotides direct from automated synthesis. The clinical utility of these labeled oligonucleotides is shown with assays of total nucleic acid, extracted from peripheral blood lymphocytes of patients with acquired immunodeficiency syndrome (AIDS), to detect the human immunodeficiency virus (HIV-1). The results demonstrate the ability of the assay to quantify 30-2000 copies of HIV1 gag genes and to rapidly detect (less than 45 min) HIV-1 gag genes in a nonseparation assay. The application of this assay to clinical samples demonstrates the utility of these assays for rapid and quantitative analysis.

Cleavage of vasoactive intestinal peptide at multiple sites by autoantibodies

Vasoactive intestinal peptide (VIP) fragments generated by autoantibodies purified from the blood of two human beings were separated and sequenced. Based on the identity of these fragments, seven peptide bonds cleaved by the antibodies were identified. Six of the seven scissile bonds are clustered in the region of VIP spanning residues 14-22 and were cleaved by antibodies from both human subjects. The seventh scissile bond is located at residues 7-8 and was cleaved by antibodies from one of the subjects. The scissile bonds link amino acid residues with different size, charge, and hydrophobicity. The hydrolytic activity of the antibodies was selective in that they failed to hydrolyze polypeptides unrelated in sequence to VIP (insulin and atrial natriuretic peptide). These observations demonstrate substrate specific hydrolysis by naturally occurring antibodies and expand the range of peptide bonds hydrolyzed by these antibodies.

Site specificity of a catalytic vasoactive intestinal peptide antibody. An inhibitory vasoactive intestinal peptide subsequence distant from the scissile peptide bond

Ten fragments of vasoactive intestinal peptide (VIP) were tested for reactivity with a human catalytic autoantibody that cleaves full-length VIP(1-28) at the Gln16-Met17 peptide bond. A large COOH-terminal subsequence, VIP(15-28), was bound by the autoantibody with high affinity (Ki 1.25 nM), suggesting that it is the antibody binding epitope. VIP(22-28), a short subsequence distant from the scissile bond, inhibited the binding (Ki 242 microM) and hydrolysis (Ki 260 microM) of full-length VIP by the catalytic autoantibody in a competitive fashion. The autoantibody did not show detectable binding of short VIP subsequences that encompass the scissile bond (VIP(15-21), VIP(11-17), and VIP(13-20]. These data show that residues 22-28, located four amino acids distant from the scissile bond, contribute in recognition of VIP by the catalytic autoantibody.

Catalytic hydrolysis of vasoactive intestinal peptide by human autoantibody

Vasoactive intestinal peptide (VIP) labeled with 125I, [Tyr10-125I]VIP, can be hydrolyzed by immunoglobulin G (IgG) purified from a human subject, as judged by trichloroacetic acid precipitation and reversed-phase high-performance liquid chromatography (HPLC). The hydrolytic activity was precipitated by antibody to human IgG, it was bound by immobilized protein G and showed a molecular mass close to 150 kilodaltons by gel filtration chromatography, properties similar to those of authentic IgG. The Fab fragment, prepared from IgG by papain treatment, retained the VIP hydrolytic activity of the IgG. Peptide fragments produced by treatment of VIP with the antibody fraction were purified by reversed-phase HPLC and identified by fast atom bombardment-mass spectrometry and peptide sequencing. The scissile bond in VIP deduced from these experiments was Gln16-Met17. The antibody concentration (73.4 fmol per milligram of IgG) and the Kd (0.4 nM) were computed from analysis of VIP binding under conditions that did not result in peptide hydrolysis. Analysis of the antibody-mediated VIP hydrolysis at varying concentrations of substrate suggested conformity with Michaelis-Menton kinetics (Km). The values for Km (37.9 X 10(-9) M) and the turnover number kcat (15.6 min-1) suggested relatively tight VIP binding and a moderate catalytic efficiency of the antibody.

Transplantable primate tumors induced by Rous sarcoma virus. I. Induction of tumors transplantable into young marmosets

The tumors induced in white-lipped marmosets (Saguinus fuscicollis, S. nigricollis) by Rous sarcoma virus (RSV) of chicken origin (RSV-SR) were not transplantable to allogeneic hosts. In contrast, RSV rescued from these tumors (RSV-M) induced sarcomas that were transplantable to young but not to adult marmosets. The tumors induced by RSV-M and the transplants rapidly enlarged, metastasized to various organs, and killed the recipients 29-59 days post inoculation. Cell lines were readily established from all transplantable sarcomas. No virus expression was detected in transplantable tumor cell lines by electron microscopy or by biochemical and biological assays. However, RSV of the same subgroup as RSV-SR was rescued from both short-term and long-term tumor cell cultures by cocultivation with chicken embryo fibroblasts (CEF). The rescued viruses transformed marmoset cells 100-fold more efficiently than CEF cells, although CEF cells remained permissive for virus replication. Cytogenetic studies revealed extensive chromosome abnormalities in tumor transplants but not in RSV-M-induced sarcomas. All cell lines were hyperploid and contained structurally abnormal, large metacentric and telocentric chromosomes. Immunologic studies failed to detect group-specific (gs) antigen of the avian sarcoma-leukemia complex in either RSV-M-induced, transformed cells or tumor transplants. By complement-dependent cytotoxicity assays, with the use of marmoset anti-gs serum, RSV-associated antigen could be detected on the surfaces of tumor cells. No differences in the expression of this antigen existed between transplantable and nontransplantable marmoset sarcomas. All transplantable cell lines contained abnormal amounts of lipids and glycogen in comparison to RSV-SR-induced tumors and normal marmoset cell lines. The glycogen was associated with unique cytoplasmic membrane complexes and was surrounded by either single- or double-membraned vesicles.

A 3-dimensional tumor growth inhibition assay for testing monoclonal antibody cytotoxicity

A 3-dimensional tumor growth inhibition assay [18] has been adapted to test the cytotoxic activity of a panel of monoclonal antibodies directed to various antigenic determinants on the surface of mouse mammary tumor cells. Target cells can be prepared from either cultured cells or from pieces of fresh tumor. Antibody and complement are added when cells are growing actively and cell growth can be measured, non destructively, over a 7-10-day period. Effective diffusion of antibody through collagen gel and binding to target cells embedded in the gel is demonstrated by indirect immunofluorescent staining. The specificity of monoclonal antibody AMT 101 cytotoxicity for mouse mammary tumor cells is the same in trypan blue exclusion assays of single-cell suspensions as in collagen gel assays, with complete killing seen in the collagen gel assay only. The collagen gel assay allows the testing of repeated treatments in vitro, as well as combined treatment with multiple antibodies. It also allows cell-cell interaction and preserves all cell components in the tumor. The collagen gel assay has potential as a method of predicting the outcome of monoclonal antibody treatment of solid tumors.

Viral epitopes and monoclonal antibodies: isolation of blocking antibodies that inhibit virus neutralization

The inability of pathogenic animal viruses to be completely neutralized by antibodies can lead to chronic viral infections in which infectious virus persists even in the presence of excess neutralizing antibody. A mechanism that results in this nonneutralized fraction of virus was defined by the topographical relationships of viral epitopes identified with monoclonal antibodies wherein monoclonal antibodies bind to virus and sterically block the binding of neutralizing antibodies.

Monoclonal antibodies identify individual determinants on mouse mammary tumor virus glycoprotein gp52 with group, class, or type specificity

Hybrid cell lines producing monoclonal antibodies against the C3H strain of mouse mammary tumor virus (C3H MMTV) were prepared by the fusion of mouse myeloma cells with the lymphocytes of BALB/c mice that were immunized with C3H MMTV. Approximately 10% of the hybrid cells initially plated after cell fusion produced immunoglobulins that reacted in antibody-binding assays with C3H MMTV; 40 of these cells were cloned, and 6 eventually yielded stable cell lines. High concentrations of monoclonal antibodies (5 to 20 mg/ml) were obtained from serum and ascites fluid of syngeneic mice inoculated with the hybrid cells. All of the monoclonal antibodies were directed against the envelope glycoprotein gp52. Three of the hybrid cell lines produced immunoglobulins of the immunoglobulin M subclass and three produced immunoglobulin G2a. The monoclonal antibodies showed limited charge heterogeneity in light and heavy chains when analyzed by high-resolution, two-dimensional gel electrophoresis. Three serologically distinct specificities were observed when these ascites fluids were tested against different strains of MMTV. The antigenic determinants detected were the following: (i) a type-specific determinant unique to the C3H strain of MMTV; (ii) class-specific determinants shared between C3H and GR MMTVs; and (iii) a group-specific determinant found on C3H, GR, RIII, and the endogenous C3H (C3Hf) MMTVs. Because monoclonal antibodies recognize single antigenic determinants, these results demonstrate for the first time that the three patterns of antigenic reactivity for MMTV are related to individual determinants on the gp52 molecule and also clearly show that one strain of MMTV can be distinguished from other strains.

Mice with spontaneous mammary tumors develop type-specific neutralizing and cytotoxic antibodies against the mouse mammary tumor virus envelope protein gp52

Sera from C3H mammary tumor-bearing mice contain cytotoxic antibodies for mouse mammary tumor virus (MMTV)-producing cells, based on (51)Cr release in a complement-dependent serum cytotoxicity assay. The cytotoxic antibodies could be absorbed by purified C3H MMTV gp52 and C3H MMTV-infected cat cells (C3H [MMTV] CrFK) containing cell surface MMTV gp52. However, purified MMTV p27 and uninfected CrFK cat cells were negative. Absorption of the sera with GR (MMTV) CrFK cells also removed all of the cytotoxicity, whereas absorption with RIII (MMTV) CrFK cells was negative, even though all three infected cat cells contained equivalent amounts of gp52. The same C3H cytotoxic sera also neutralized the focus-forming capacity of a C3H MMTV pseudotype of Kirsten sarcoma virus containing MMTV gp52. In contrast, sera from mammary tumor-bearing GR and RIII mice did not neutralize the pseudotype. Furthermore, neutralization could be achieved only by anti-gp52 but not by anti-gp36, -p27, -p14, or -p10 C3H MMTV sera. The gp52's of C3H, GR, and RIII MMTV could also be distinguished by using a type-specific competition radioimmunoassay employing (125)I-gp52 of C3H MMTV and a hyperimmune rabbit anti-C3H MMTV serum. To demonstrate these differences directly, we studied the primary structure of gp52 on the surface of the C3H, GR, and RIII (MMTV) CrFK cells. Two-dimensional tryptic peptide maps of the cell surface lactoper-oxidase-catalyzed iodinated gp52's revealed a greater number of peptides common to the gp52's of C3H and GR MMTVs than to RIII MMTV gp52. These results demonstrate that gp52 is a major target antigen for both cytotoxic and neutralizing antibodies, that the cell surface and virion-associated gp52's of C3H, GR, and RIII MMTV contain both group- and type-specific determinants, and that C3H and GR MMTV gp52's are antigenically more related to each other than to RIII MMTV gp52. Furthermore, C3H mammary tumor-bearing mice develop type-specific antibodies capable of recognizing unique gp52 determinants and, therefore, are able to distinguish the gp52 of C3H MMTV from the gp52's of GR and RIII MMTV.

Spontaneous human mononuclear cell cytotoxicity to cultured tumor cells: reproducibility of serial measurements with the use of a chromium-51-release microcytotoxicity assay

Twenty-three healthy human adults with naturally occurring (spontaneous) mononuclear cell cytotoxicity (MCC) to cultured human tumor cells were evaluated in a serial study over 23 months to determine whether their initial MCC levels remained stable. A 3-hour 51Cr-release microcytotoxicity assay, in which the HBT-3 cancer-derived cell line with HeLa markers and the ALAB breast cancer-derived cell line were used, was standardized and its suitability for such serial studies was evaluated. The data showed that the 51Cr-release assay is reproducible and suitable for use in serial studies of MCC. The intrinsic technical error for a single assay averaged 12.5% (2-26%) coefficient of variation. The greatest sources of technical variation with time were the passage level of the target cells and the temperature at which the effector cells were stored and handled. When these technical factors were controlled, naturally occurring MCC was fairly reproducible with time. Of the healthy individuals with initial high or low MCC levels, 61% tended to retain these levels in a stable fashion, but the remaining 39% studied showed fluctuations of MCC greater than 33% coefficient of variation.