Antibodies Of Different Affinities Research Articles

Hollow-microsphere-integrated optofluidic immunochip for myocardial infarction biomarker microanalysis

This work developed an optofluidic immunochip that uses whispering gallery mode with fiber laser enhancement, for the rapid detection of a key biomarker cardiac troponin I for acute myocardial infarction (AMI). The immunochip adopted an innovative design, using perforated hollow glass microspheres (HGMS) as carriers, with antibodies immobilized on the inner surface of the HGMS, thereby achieving ultra-low sample consumption. The performance of the immunochip was improved by fiber laser, including spectral width compression to 0.019 nm, optical signal-to-noise ratio amplification to 63.17 dB, and an enhancement in the limit of detection to 5 pg/mL. Moreover, this immunochip can provide results within 15 minutes, making it highly suitable for early AMI risk management. Compared to the standard electrochemiluminescence detection method, although some differences exist in the results of the immunochip due to the principle of detection and differences in antibody affinity, its positive reference value can be calculated as 0.0754 ng/mL, with a successful recognition rate of 88% for positive patients. The immunosensor is integrated on a polydimethylsiloxane substrate, with a compact size suitable for use in point-of-care devices and AMI self-screening, as well as rapid disease screening and microanalysis of various biomarkers, offering new possibilities for applications in these fields.

Antibody-free measurement of cerebrospinal fluid tau phosphorylation across the Alzheimer’s disease continuum

BackgroundAlzheimer’s disease is characterized by an abnormal increase of phosphorylated tau (pTau) species in the CSF. It has been suggested that emergence of different pTau forms may parallel disease progression. Therefore, targeting multiple specific pTau forms may allow for a deeper understanding of disease evolution and underlying pathophysiology. Current immunoassays measure pTau epitopes separately and may capture phosphorylated tau fragments of different length depending on the non-pTau antibody used in the assay sandwich pair, which bias the measurement.MethodsWe developed the first antibody-free mass spectrometric method to simultaneously measure multiple phosphorylated epitopes in CSF tau: pT181, pS199, pS202, pT205, pT217, pT231, and pS396. The method was first evaluated in biochemically defined Alzheimer’s disease and control CSF samples (n = 38). All seven pTau epitopes clearly separated Alzheimer’s disease from non-AD (p < 0.001, AUC = 0.84–0.98). We proceeded with clinical validation of the method in the TRIAD (n = 165) and BioFINDER-2 cohorts (n = 563), consisting of patients across the full Alzheimer’s disease continuum, including also young controls (< 40 years), as well as patients with frontotemporal dementia and other neurodegenerative disorders.ResultsIncreased levels of all phosphorylated epitopes were found in Alzheimer’s disease dementia and Aβ positron emission tomography-positive patients with mild cognitive impairment compared with Aβ-negative controls. For Alzheimer’s disease dementia compared with Aβ-negative controls, the best biomarker performance was observed for pT231 (TRIAD: AUC = 98.73%, fold change = 7.64; BioFINDER-2: AUC = 91.89%, fold change = 10.65), pT217 (TRIAD: AUC = 99.71%, fold change = 6.33; BioFINDER-2: AUC = 98.12%, fold change = 8.83) and pT205 (TRIAD: AUC = 99.07%, fold change = 5.34; BioFINDER-2: AUC = 93.51%, fold change = 3.92). These phospho-epitopes also discriminated between Aβ-positive and Aβ-negative cognitively unimpaired individuals: pT217 (TRIAD: AUC = 83.26, fold change = 2.39; BioFINDER-2: AUC = 91.05%, fold change = 3.29), pT231 (TRIAD: AUC = 86.25, fold change = 3.80; BioFINDER-2: AUC = 78.69%, fold change = 3.65) and pT205 (TRIAD: AUC = 71.58, fold change = 1.51; BioFINDER-2: AUC = 71.11%, fold change = 1.70).ConclusionsWhile an increase was found for all pTau species examined, the highest fold change in Alzheimer’s disease was found for pT231, pT217 and pT205. Simultaneous antibody-free measurement of pTau epitopes by mass spectrometry avoids possible bias caused by differences in antibody affinity for modified or processed forms of tau, provides insights into tau pathophysiology and may facilitate clinical trials on tau-based drug candidates.

Stabilization of Human Whole Blood Samples for Multicenter and Retrospective Immunophenotyping Studies.

Whole blood is often collected for large-scale immune monitoring studies to track changes in cell frequencies and responses using flow (FC) or mass cytometry (MC). In order to preserve sample composition and phenotype, blood samples should be analyzed within 24 h after bleeding, restricting the recruitment, analysis protocols, as well as biobanking. Herein, we have evaluated two whole blood preservation protocols that allow rapid sample processing and long-term stability. Two fixation buffers were used, Phosphoflow Fix and Lyse (BD) and Proteomic Stabilizer (PROT) to fix and freeze whole blood samples for up to 6months. After analysis by an 8-plex panel by FC and a 26-plex panel by MC, manual gating of circulating leukocyte populations and cytokines was performed. Additionally, we tested the stability of a single sample over a 13-months period using 45 consecutive aliquots and a 34-plex panel by MC. We observed high correlation and low bias toward any cell population when comparing fresh and 6months frozen blood with FC and MC. This correlation was confirmed by hierarchical clustering. Low coefficients of variation (CV) across studied time points indicate good sample preservation for up to 6months. Cytokine detection stability was confirmed by low CVs, with some differences between fresh and fixed conditions. Thirteen months regular follow-up of PROT samples showed remarkable sample stability. Whole blood can be preserved for phenotyping and cytokine-response studies provided the careful selection of a compatible antibody panel. However, possible changes in cell morphology, differences in antibody affinity, and changes in cytokine-positive cell frequencies when compared to fresh blood should be considered. Our setting constitutes a valuable tool for multicentric and retrospective studies. © 2020 International Society for Advancement of Cytometry.

Cross-validation of commercial enzyme-linked immunosorbent assay and radioimmunoassay for porcine C-peptide concentration measurements in non-human primate serum.

C-peptide concentration is widely used as a marker of insulin secretion and is especially relevant in evaluating islet graft function following transplantation, because its measurement is not confounded by the presence of exogenous insulin. To address the shortage of human islet donors, the use of porcine islets has been proposed as a possible solution and the stringent pig-to-non-human primate (NHP) model is often the most relevant for pre-clinical evaluation of the potential for diabetes reversal resulting from an islet xenograft. The Millipore radioimmunoassay (RIA) was exclusively used to measure porcine C-peptide (PCP) until 2013 when the assay was discontinued and subsequently a commercially available enzyme-linked immunosorbent assay (ELISA) from Mercodia has been widely adopted. Both assays have been used in pre-clinical trials evaluating the therapeutic potential of xenograft products in reversing diabetes in the pig-to-NHP model, to interpret data in a comparable way it may be useful to perform a harmonization of C-peptide measurements. We performed a method comparison by determining the PCP concentration in 620 serum samples collected from 20 diabetic cynomolgus macaques transplanted with adult porcine islets. All analyses were performed according to manufacturer instructions. With both assays, we demonstrated an acceptable detection limit, precision, and recovery. Linearity of the ELISA met acceptance criteria at all concentrations tested while linearity of the RIA only met acceptance criteria at five of the eight concentrations tested. The RIA had a detection limit of 0.16ng/mL, and recovery ranged from 82% to 96% and met linearity acceptance criteria at 0.35ng/mL and from 0.78 to 2.33ng/mL. The ELISA had a detection limit of 0.03ng/mL, and recovery ranged from 81% to 115% and met linearity acceptance criteria from 0.08 to 0.85ng/mL. Both assays had intra-assay precision <11% and inter-assay precision <14%. PCP concentration measured by ELISA demonstrated a significant correlation with RIA (R2 =.9721, P<.0001). This strong correlation supports use of the regression equation y=2.029x+0.0897 to transform ELISA data to RIA or inversely y=0.4930x-0.0456 to convert RIA data to ELISA for direct comparison between assays in the concentration range of 0-3.0ng/mL. Measured C-peptide concentration was lower with the ELISA than with the RIA; individual measurements plotted against the averages of the pair demonstrated that the variability from the mean strongly depended on increasing concentration. Porcine C-peptide can be reliably measured in NHP serum using the Mercodia ELISA, making this assay interchangeable with the Millipore RIA. Inherent differences in antibody affinity and calibration factors may explain the lower ELISA values as compared to the RIA; however without access to a traceable reference standard, it is not possible to determine which assay is most accurate. Regression modeling resulted in a correction factor appropriate for conversion of ELISA data to RIA-equivalent data facilitating comparison of assay results longitudinally and between groups.

P2.01-027 A Comparison of Five Different Immunohistochemistry Assays for Programmed Death Ligand-1 Expression in Non-Small Cell Lung Cancer Samples

Randomized trials have shown treatment with programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) inhibitors can provide a survival benefit to patients with advanced stage non-small cell lung cancer (NSCLC). PD-L1 expression, determined by immunohistochemistry (IHC) using different protocols, antibodies and thresholds for positivity for different inhibitors, has been reported to be potentially predictive of clinical outcome. The objective of this study was to compare the staining patterns of prominent PD-L1 IHC assays in clinically relevant NSCLC samples. Consecutive full sections of 20 NSCLC samples, comprising five each of resection, core biopsy, cytology, and pleural fluid samples, underwent IHC with the following anti-PD-L1 antibodies/autostainers: 22C3/Link 48, 28-8/Bondmax, SP142/Bondmax, SP263/Benchmark XT, E1L3N/Benchmark XT according to publicly-available protocols. PD-L1 expression were scored manually by pathologists according to the percentage of tumor cells (%TC) stained on a continuous scale. Using published tumor cell percentage thresholds for 22C3, 28-8, SP142 and SP263 of ≥50%, ≥1%, ≥5%, and ≥25%, the frequency of PD-L1 positive cases were 10%, 15%, 70%, and 15% of cases respectively. When a ≥1% threshold was applied, the corresponding frequencies were 70%, 15%, 95%, 65% respectively, and 55% for E1L3N. Using published thresholds, cases were positive according to 1, 2, 3, 4 and 5 antibodies in 15%, 25%, 25%, 0% and 5% of cases respectively. Sorting of cases according to increasing %TC staining revealed a similar order of cases between antibodies, albeit with differences in %TC quanta and occasional exceptions to the order. Spearman rho analysis indicated %TC staining significantly (p<0.05) correlated between most antibody pairs, except 28-8 and 22C3, 28-8 and SP142, and 28-8 and E1L3N. Unsupervised hierarchical clustering revealed two subgroups, comprising of SP142/SP263 and 22C3/28-8/E1L3N. The classification of cases as PD-L1 positive can vary significantly according to the antibody and protocol used. Differences were more likely due to protocol dependent staining intensities and nominated thresholds for positivity, rather than differences in antibody affinity for different epitopes.

Validation of endothelin B receptor antibodies reveals two distinct receptor-related bands on Western blot

Antibodies are important tools for the study of protein expression but are often used without full validation. In this study, we used Western blots to characterize antibodies targeted to the N or C terminal (NT or CT, respectively) and the second or third intracellular loop (IL2 or IL3, respectively) of the endothelin B receptor (ETB). The IL2-targeted antibody accurately detected endogenous ETB expression in rat brain and cultured rat astrocytes by labeling a 50-kDa band, the expected weight of full-length ETB. However, this antibody failed to detect transfected ETB in HEK293 cultures. In contrast, the NT-targeted antibody accurately detected endogenous ETB in rat astrocyte cultures and transfected ETB in HEK293 cultures by labeling a 37-kDa band but failed to detect endogenous ETB in rat brain. Bands detected by the CT- or IL3-targeted antibody were found to be unrelated to ETB. Our findings show that functional ETB can be detected at 50 or 37kDa on Western blot, with drastic differences in antibody affinity for these bands. The 37-kDa band likely reflects ETB processing, which appears to be dependent on cell type and/or culture condition.

A fully automated capillary western system for absolute quantitation of endogenous PKC proteins: An approach to correlate protein quantity with function.

31 Background: The human prostate cell line LNCaP and the human myelocytic leukemia cell line U937 differ dramatically in their responses to the two protein kinase C (PKC) targeted ligands phorbol 12-myristate 13-acetate (PMA) and bryostatin 1 and show complex differences in the patterns of transcriptional responses that they induce. Quantitation of relative abundance of individual PKC isoforms in the two cell lines may help to link the downstream effects of the two compounds to these isoforms. Methods: Simple Western is a capillary-based automated Western system recently developed by ProteinSimple. All steps following sample preparation are fully automated in the Simple Western system, including sample loading, size-based protein separation, immunoprobing, washing, detection and data analysis. Simple Western is gel-free and blot-free, uses less amount of samples, and produces highly quantitative, reproducible information that cannot be generated using regular Western assays. Using the Simple Western system, we developed a method for absolute quantitation of endogenous proteins in cell lysates and quantified PKC isoforms in LNCaP and U937 cells. Results: PKC isoforms were measured at levels of picogram or sub-picogram per nanogram cell lysate. PKC delta was identified as the dominant PKC isoforms in both cell lines. In LNCaP cells, PKC delta expression is ~20-fold higher than PKC alpha, ~40-fold higher than PKC epsilon, and at least 20-fold higher than PKC beta. In U937 cells, PKC delta expression is similar to PKC beta, at least 200 fold higher than PKC alpha, and ~50-fold higher than PKC epsilon. Conclusions: The Simple Western system, with its high-quality data quantitation and excellent assay reproducibility, allowed us to detect both the relative abundance of the PKC isoforms and their absolute quantitation in the tested cells. It circumvents the problem that antibodies of different affinities for different proteins yield a misleading impression of relative abundance and it provides an approach to accurately correlate protein quantities with their function.

Generation and Signaling Function of CD19 Chimeric Antigen Receptor Modified CD8+ T Cells Derived From Virus-Specific Central Memory Cells for Adoptive Therapy After Allogeneic Hematopoietic Stem Cell Transplant

Abstract 2978Allogeneic hematopoietic stem cell transplantation (allo-HCT) is the most effective post-consolidation therapy for high-risk B cell acute lymphocytic leukemia (ALL) in pediatric and adult patients. However, relapse after allo-HCT remains a common cause of failure, and treatment of ALL that has recurred after transplant, either with additional chemotherapy or with donor lymphocyte infusions to enhance a graft-versus-leukemia effect is mostly unsuccessful and can cause graft-versus-host disease (GVHD). The adoptive transfer of donor T cells that have been genetically modified to recognize leukemia could prevent or treat leukemia relapse after allo-HCT. However, adoptive therapy after allo-HCT should be performed with T cells that have a defined endogenous T cell receptor (TCR) specificity to avoid GVHD, and with T cells that have the capacity to persist in vivo to ensure leukemia eradication. Our lab has previously shown that donor virus-specific T cells can be adoptively transferred without causing GVHD, and identified a role for cell intrinsic properties of central memory T (TCM) cells in determining cell persistence after adoptive transfer. Thus, we developed a strategy for deriving virus-specific T cells from CD45RA−CD62L+CD8+ TCM cells purified from donor blood with clinical grade reagents, and redirecting their specificity to the B-cell lineage marker CD19 through lentiviral transfer of a gene encoding an anti-CD19 ectodomain, a CD3 ζ and CD28 endodomain, and a truncated epidermal growth factor receptor as a transduction marker downstream of a T2A sequence. CD8+ TCM were enriched by first depleting CD4+, CD14+, and CD45RA+ cells from PBMC using clinical grade monoclonal antibodies (mAbs) conjugated to paramagnetic beads, and then positively selecting CD62L+ cells from the depleted subset with a biotinylated anti-CD62L mAb and clinical grade anti-biotin beads. After this two-step selection, the enriched virus-specific TCM were selectively transduced by exposure to the CD19-CAR lentivirus after stimulation with viral peptides. This procedure resulted in a selective expansion of bi-specific (CD19-CAR+/virus-specific) T cells that could be readily expanded by stimulation with CD19+ EBV-transformed lymphoblastoid cells (LCL). The bi-specific subset was further enriched to high purity using reversible class I MHC Streptamers (Stage Cell Therapeutics) folded with viral peptides. The frequency of tetramer positive and CD19-CAR+ cells in the final cell product was ∼90% (range, 80.7–96.3%) and ∼85% (range, 77.9–95.3%) respectively, and this high frequency of bi-specific T cells was maintained through additional in vitro expansion. With this procedure, large numbers of highly pure bi-specific TE cells that are derived from CD8+ TCM precursors and engineered to express a CD19-CAR could be readily generated for adoptive immunotherapy of allo-HCT recipients in ∼30–35 days from 400 ml of donor blood.CAR binding to its ligand is structurally distinct from that of a TCR, and a direct comparison of effector functions and signaling through an introduced CAR and the endogenous TCR on the same cell could reveal differences that might affect cellular functions and therapeutic efficacy. To compare functions after CAR- and TCR-stimulation, we transduced K562 tumor cells with the costimulatory molecules CD80 and CD86, and with CD19 or HLA molecules to serve as antigen presenting cells. Activation of bi-specific T cells through the CAR or the virus-specific TCR elicited comparable lytic function and induced equivalent phosphorylation of downstream signaling molecules (CD3 ζ, Zap70, p38, ERK, JNK) with similar kinetics. Signaling through either CAR or TCR induced comparable production of IL-2, IFN- γ, and TNF- α as assessed by intracellular cytokine staining and Luminex assay, and T cell proliferation as assessed by CFSE dye dilution and absolute cell count. These studies identify a strategy for tumor-specific immunotherapy with CAR-modified T cells after allo-HCT, and for comparative studies of signaling through the TCR and CARs derived from antibodies of different affinities and containing distinct signaling domains. Disclosures:No relevant conflicts of interest to declare.

Mapping protein interactions by combining antibody affinity maturation and mass spectrometry

Mapping protein interactions by immunoprecipitation is limited by the availability of antibodies recognizing available native epitopes within protein complexes with sufficient affinity. Here we demonstrate a scalable approach for generation of such antibodies using phage display and affinity maturation. We combined antibody variable heavy (VH) genes from target-specific clones (recognizing Src homology 2 (SH2) domains of LYN, VAV1, NCK1, ZAP70, PTPN11, CRK, LCK, and SHC1) with a repertoire of 108 to 109 new variable light (VL) genes. Improved binders were isolated by stringent selections from these new “chain-shuffled” libraries. We also developed a predictive 96-well immunocapture screen and found that only 12% of antibodies had sufficient affinity/epitope availability to capture endogenous target from lysates. Using antibodies of different affinities to the same epitope, we show that affinity improvement was a key determinant for success and identified a clear affinity threshold value (60nM for SHC1) that must be breached for success in immunoprecipitation. By combining affinity capture using matured antibodies to SHC1 with mass spectrometry, we identified seven known binding partners and two known SHC1 phosphorylation sites in epidermal growth factor (EGF)-stimulated human breast cancer epithelial cells. These results demonstrate that antibodies capable of immunoprecipitation can be generated by chain shuffling, providing a scalable approach to mapping protein–protein interaction networks.

Structural requirements of anti-GD1a antibodies determine their target specificity

The acute motor axonal neuropathy (AMAN) variant of Guillain-Barré syndrome (GBS) is associated with anti-GD1a and anti-GM1 IgG antibodies. The basis of preferential motor nerve injury in this disease is not clear, however, because biochemical studies demonstrate that sensory and motor nerves express similar quantities of GD1a and GM1 gangliosides. To elucidate the pathophysiology of AMAN, we have developed several monoclonal antibodies (mAbs) with GD1a reactivity and reported that one mAb, GD1a-1, preferentially stained motor axons in human and rodent nerves. To understand the basis of this preferential motor axon staining, several derivatives of GD1a were generated by various chemical modifications of N-acetylneuraminic (sialic) acid residues (GD1a NeuAc 1-amide, GD1a NeuAc ethyl ester, GD1a NeuAc 1-alcohol, GD1a NeuAc 1-methyl ester, GD1a NeuAc 7-alcohol, GD1a NeuAc 7-aldehyde) on this ganglioside. Binding of anti-GD1a mAbs and AMAN sera with anti-GD1a Abs to these derivatives was examined. Our results indicate that mAbs with selective motor axon staining had a distinct pattern of reactivity with GD1a-derivatives compared to mAbs that stain both motor and sensory axons. The fine specificity of the anti-GD1a antibodies determines their motor selectivity, which was validated by cloning a new mAb (GD1a-E6) with a chemical and immunocytochemical binding pattern similar to that of GD1a-1 but with two orders of magnitude higher affinity. Control studies indicate that selective binding of mAbs to motor nerves is not due to differences in antibody affinity or ceramide structural specificity. Since GD1a-reactive mAb with preferential motor axon staining showed similar binding to sensory- and motor nerve-derived GD1a in a solid phase assay, we generated computer models of GD1a based on binding patterns of different GD1a-reactive mAbs to different GD1a-derivatives. These modelling studies suggest that critical GD1a epitopes recognized by mAbs are differentially expressed in motor and sensory nerves. The GD1a-derivative binding patterns of AMAN sera resembled those with motor-specific mAbs. On the basis of these findings we postulate that both the fine specificity and ganglioside orientation/exposure in the tissues contribute to target recognition by anti-ganglioside antibodies and this observation provides one explanation for preferential motor axon injury in AMAN.

Fate Discrimination of Normal B Cells When Cross-Linked with Anti-IgM Antibodies of Different Affinities and Valence.

The B-cell receptor (BCR) is a key signaling molecule that engages antigens and triggers pathways that induce survival, proliferation, differentiation, anergy, or apoptosis. The “choice” of which functional fate the B cell makes is decided upon by a series of receptor and cellular interactions. The potential for ligand-initiated signal transduction through the BCR is assessed in terms of ligand binding affinity for membrane Ig. We have used a series of anti-IgM H chain mAb that differ in their affinities (HB57 − Ka = 5x108 “high”, Mu53 − Ka = 2x107 “intermediate”, and P24 − Ka = ~2x106 M−1 “low”) in both soluble and immobilized forms as models for antigenic stimulation of the BCR, and assessed the response of normal B cells isolated by negative selection from peripheral blood. Proliferative responses were observed upon cross-linking the BCR with antibodies of all affinities at 10 ug/ml of immobilized antibodies for 72 hours, with a modest stimulation at 1ug/ml and no stimulation at either 0.01 or 0.1 ug/ml. Interestingly, the low affinity antibody P24 showed the highest proliferative response (3.3 fold), while stimulation with the moderate affinity antibody was intermediate (2.2 fold) and the response of the high affinity antibody, was negligible. Soluble antibodies did not stimulate proliferation at any concentration tested. When B cells were co-incubated with soluble anti-IgM antibodies plus IL 4,10ug/ml of either high or intermediate affinity induced proliferation with stimulation indices of 2.5 and 1.9, respectively, while the low affinity antibody still had no effect. Co-incubation with IL 4 and immobilized anti-IgM antibodies induced the same pattern of responses as seen with antibody alone, slightly increasing proliferation induced with 1 ug/ml low and intermediate and markedly increasing stimulation by all three antibodies at 10ug/ml. Our results suggest that even in the absence of T cell help, normal B cells can be activated via the BCR upon cross-linking and the efficiency at which this is accomplished is largely dependent on affinity for the BCR.

PEGylation and Multimerization of the Anti-p185HER-2 Single Chain Fv Fragment 4D5

A major goal in antibody design for cancer therapy is to tailor the pharmacokinetic properties of the molecule according to specific treatment requirements. Key parameters determining the pharmacokinetics of therapeutic antibodies are target specificity, affinity, stability, and size. Using the p185HER-2 (HER-2)-specific scFv 4D5 as model system, we analyzed how changes in molecular weight and valency independently affect antigen binding and tumor localization. By employing multimerization and PEGylation, four different antibody formats were generated and compared with the scFv 4D5. First, dimeric and tetrameric miniantibodies were constructed by fusion of self-associating, disulfide-linked peptides to the scFv 4D5. Second, we attached a 20-kDa PEG moiety to the monovalent scFv and to the divalent miniantibody at the respective C terminus. In all formats, serum stability and full binding reactivity of the scFv 4D5 were retained. Functional affinity, however, did change. An avidity increase was achieved by multimerization, whereas PEGylation resulted in a 5-fold decreased affinity. Nevertheless, the PEGylated monomer showed an 8.5-fold, and the PEGylated dimer even a 14.5-fold higher tumor accumulation than the corresponding scFv, 48 h post-injection, because of a significantly longer serum half-life. In comparison, the non-PEGylated bivalent and tetravalent miniantibodies showed only a moderate increase in tumor localization compared with the scFv, which correlated with the degree of multimerization. However, these non-PEGylated formats resulted in higher tumor-to-blood ratios. Both multimerization and PEGylation represent thus useful strategies to tailor the pharmacokinetic properties of therapeutic antibodies and their combined use can additively improve tumor targeting.

Antitumor Activity of a Dual Cytokine/Single-chain Antibody Fusion Protein for Simultaneous Delivery of GM-CSF and IL-2 to Ep-CAM Expressing Tumor Cells

Cytokine targeting to tumor-associated antigens via antibody cytokine fusion proteins has demonstrated potent antitumor activity in numerous animal models and has led to the clinical development of 2 antibody-interleukin-2 (IL-2) fusion proteins. We previously reported on the construction and in vitro properties of a "dual" cytokine fusion protein for simultaneous targeted delivery of human granulocyte macrophage-colony stimulating factor (GM-CSF) and IL-2 to human tumors. The fusion protein is based on a heterodimerized core structure formed by human CH1 and Ckappa domains (heterominibody) with C-terminally fused human cytokines and N-terminally fused single-chain antibody fragments specific for the tumor-associated surface antigen epithelial cell adhesion molecule (Ep-CAM). For testing the antitumor activity in syngeneic mouse xenograft models, we developed "dual cytokine heterominibodies" with murine cytokines (mDCH). mDCH fusion proteins and, as controls, "single cytokine heterominibodies" (SCH) carrying either murine GM-CSF (mGM-CSF) or murine IL-2 (mIL-2) were constructed, of which all retained the specific activities of cytokines and binding to the Ep-CAM antigen on human Ep-CAM transfected mouse colon carcinoma CT26-KSA cells. Over a 5-day treatment course, DCH fusion proteins induced significant inhibition of established pulmonary CT26-KSA metastases in immune-competent Balb/c mice at low daily doses of 1 mug of fusion protein per mouse. However, with the tested dosing schemes, antitumor activity of mDCH was largely independent of cytokine targeting to tumors as demonstrated by a control protein with mutated Ep-CAM binding sites. Single cytokine fusion proteins mSCH-GM-CSF and mSCH-IL-2 showed similar antitumor activity as the dual cytokine fusion protein mDCH, indicating that GM-CSF and IL-2 in one molecule did not significantly synergize in tumor rejection under our experimental conditions. Our results seem to contradict the notion that IL-2 and GM-CSF can synergize in antitumor activity and that with conventional dose regimens, their specific targeting to tumors, as tested here with 2 antibodies of different affinities, enhances their antitumor activity.

Mechanism of Nanoparticle-Enhanced Turbidimetric Assays Applying Nanoparticles of Different Size and Immunoreactivity

The mechanism of a novel assay technique for nanoparticle-enhanced immunoturbidimetric assays is investigated. In a mixture of latex particles of two different sizes, coated with antibodies of different affinities, the aggregation behavior is monitored, which correlates with the antigen concentration. At low antigen concentrations, only the bigger latex particles coated with the high-reactivity antibody aggregate, whereas at higher antigen concentrations, the smaller latices coated with a lower reactivity antibody follow up in the aggregation process. This is shown for an immunoassay (C-reactive protein) by theoretical considerations based on a diffusion-controlled reaction and by transmission electron microscopy, analytical ultracentrifugation, and static light scattering as complementary qualitative and quantitative analytical techniques.

Maternal antibodies to HIV-1 envelope domains: No correlation with HIV-1 vertical transmission in patients from Argentina.

The role of the maternal antibody response in relation to vertical human immunodeficiency virus type 1 (HIV-1) transmission was investigated in HIV-1-infected mothers from Argentina. Sera from 23 transmitting and 18 nontransmitting HIV-1-infected mothers were tested for the presence of antibodies to V3 loop gp120 peptides representing both Argentinian sequences and several well-characterized viral isolates from different geographic areas. Argentinian sera from transmitting mothers had significantly higher capacity to react with four of 14 V3 loop peptides tested than sera from nontransmitting mothers. Frequency of reactivity against the other peptides did not differ between the two maternal groups. Furthermore, no differences in antibody affinity were found between transmitting and nontransmitting mothers. Sera were also tested against overlapping peptides covering a neutralizing epitope of the HIV-1 MN gp41 (amino acids 648-677). Statistical analysis indicated that no correlation between anti-gp41 antibodies and vertical transmission exists. Although we used V3 loop peptides based on local HIV-1 sequences, our data showed that maternal antibodies to these peptides, as well as to gp41 peptides, are not correlated with protection against HIV-1 vertical transmission.

Characterization of anti-DNA B cells that escape negative selection.

One of the challenges in the study of autoimmunity is to understand which autoreactive cells are subject to regulation and what mechanisms of regulation are operative. In mice transgenic for the R4A-gamma2b heavy chain of an anti-double stranded (ds) DNA antibody, the gamma2b heavy chain can pair with the full spectrum of endogenous light chains to produce a multitude of antibodies, including anti-dsDNA antibodies of different affinities and fine specificities. We have previously demonstrated the existence of two populations of anti-DNA B cells in non-autoimmune hosts: a high-affinity population which is rendered anergic in vivo, and a second high-affinity population which is deleted. We have now identified a third population of dsDNA-binding B cells. These cells produce germ-line-encoded antibodies with an apparent affinity for dsDNA that is 1 to 4 logs lower than the apparent affinities of antibodies made by anergic or deleted B cells, and represent a non-tolerized population which escapes regulation. Based on its characterization, we can define a molecular threshold for tolerance induction, and can speculate on the fate of these B cells when they are recruited to an immune response and undergo somatic mutation to become high-affinity anti-DNA B cells.

The Influence of Antibody Functional Affinity on the Effector Functions Involved in the Clearance of Circulating Immune Complexes Anti-BSA IgG/BSA

A systematic study was carried out to investigate the role of antibody functional affinity in the capacity of immune complexes (IC) to activate the complement system and to trigger subsequently the molecular events involved in the handling of IC by providing a clearance mechanism. For this purpose, two populations of polyclonal anti-BSA IgG antibodies of different affinities were prepared, with values of 1.89 × 108 M−1 and 4.94 × 108 M−1. First we studied the capacity of IC formed at equivalence with both antibodies to activate the classical and the alternative pathways of human complement and the ability of the complexes to bind to erythrocyte C3b-C4b receptors (CR1; CD35). The data showed that the highest affinity antibodies were more efficient in activating complement by both pathways. However, their binding to erythrocyte CR1 was significantly lower compared to the binding of the lowest affinity IgG. Second we compared these IC in terms of their ability to stimulate the respiratory burst of neutrophils (PMN) and to induce the release of PMN lysosomal enzymes. In general, both of these PMN functions were better stimulated by the IC prepared with the IgG antibodies having a highest affinity, although the effects were variable for different IC concentrations. The suggestion to be drawn from the data is that the antibody affinity has an influence on the formation of the immune complex lattice, modulating its three-dimensional structure and the arrangement of the antibody Fc fragments, interfering with complement activation and access to the neutrophil IgG receptors. The significance of these observations for the understanding of how affinity influences the precise biological mechanism that participates in the fate of IC is discussed.

Effect of immunoglobulin variable region structure on C3b and C4b deposition

Many of the biological activities of immunoglobulins, including interaction with the complement system, are attributed to the structure of the heavy chain constant domains. However, previous studies indicated that immune complexes formed with independently derived isotype-matched pairs of monoclonal antibodies vary with respect to their capacity to activate complement and to serve as targets for C3b and C4b deposition. The goal of the present study was to provide a structural basis for explaining how variable domains influence C3b and C4b deposition on immunoglobulins. Heavy and light chain variable domains from a pair of IgG2a antibodies previously shown to differ in terms of complement activation and C3b and C4b deposition were cloned and sequenced. The two clones utilize distinct heavy and light variable region genes and the translated amino acid sequence reveals several residues that could serve as potential targets for complement deposition which differs between the two antibodies. Molecular modeling suggests that many of the relevant differences between the two antibodies are located in solvent exposed portions of the heavy and light chain variable domains and that some of the relevant sites are located within the complementarity determining regions. Differences in antibody affinity do not provide an explanation for the previously observed role of variable domains on interactions with the complement system. These data suggest that sequence variations within solvent-exposed variable domain residues may play a key role in C3b and C4b deposition on immunoglobulins.

NA-phenotype-dependent differences in neutrophil Fc gamma RIIIb expression cause differences in plasma levels of soluble Fc gamma RIII.

Soluble Fc gamma RIII in plasma is primarily derived from neutrophils and is a measure of the total body neutrophil mass. We have developed a new, sensitive 'sandwich' ELISA to measure soluble Fc gamma RIII in plasma and released Fc gamma RIII in cell supernatants. Both sFc gamma RIIIa, derived from NK cells and sFc gamma RIIIb, derived from neutrophils are detected in the assay. However, plasma analysis of Fc gamma RIIIB gene-deficient donors suggested that sFc gamma RIIIa contributes only marginally to the total amount measured in healthy individuals. Furthermore, we observed that plasma of homozygous NA1-positive donors contained lower amounts of sFc gamma RIII than plasma of homozygous NA2-positive donors. Heterozygous donors were found to have intermediate levels of sFc gamma RIII in their plasma. Hemizygous Fc gamma RIIIB gene-deficient donors were found to have half the amount of sFc gamma RIII in their plasma compared to donors with two Fc gamma RIIIB alleles. These NA phenotype-dependent differences in plasma sFc gamma RIII could not be contributed to either an assay artefact or NA-dependent differences in shedding of Fc gamma RIIIb upon neutrophil activation. Calibration curves constructed with plasma of homozygous donors did nor reveal NA-dependent differences in antibody affinity. Measurement of released Fc gamma RIIIb in supernatants of neutrophils stimulated with PMA, and inhibition of this signal with human IgG revealed no NA-dependent differences. However, NA-dependent differences in neutrophil Fc gamma RIIIb expression were present, comparable to the differences found in plasma levels of sFc gamma RIII. Differences in the amounts of released Fc gamma RIII in supernatants of NA-typed apoptotic neutrophils were similar to initial differences in Fc gamma RIIIb expression, again being lower in NA1-positive than in heterozygous and NA2-positive donors. In conclusion, NA-dependent differences in plasma levels of soluble Fc gamma RIII seem to be caused by differences in expression of the receptor on the neutrophil membrane.

The upright position of brush border-type microvilli depends on myosin filaments.

We have studied the correlation between the actomyosin organization and microvillar position in an epithelial cell line derived from the proximal pig kidney tubule (LLC-PK1). When grown on glass, these cells are approximately 5-6 microns in height and develop numerous microvilli that project from the dorsal membrane. A fairly homogeneous distribution of microvilli was achieved by synchronization of the cell cycle. These microvilli are of the brush border type, as defined by their content of villin and their anchorage in a myosin-rich terminal web-like structure. When LLC-PK1 cells were injected with two monoclonal antibodies against pig brain nonmuscle myosin, in concentrations yielding a 1:1 ratio of antibody to myosin, neither microvillar number nor length was affected. However, when we examined the cells by scanning electron microscopy 1-3 h after microinjection, we found that one of the antibodies (a-PBM 4) had a profound effect on microvillar position: more than 50% were seen tilted or lying prone on the plasma membrane. The microvilli of cells injected with the other antibody (a-PBM 9) were not significantly different from those of cells injected with control antibodies. This difference correlates with in vitro properties of the antibodies: a-PBM 4 decreases the actin-activated Mg(2+)-ATPase of pig brain nonmuscle myosin quite substantially, while a-PBM 9 affects it only moderately. These differential effects are probably a consequence of the different epitope location as determined for both antibodies, not of differences in antibody affinity. Our data are compatible with the hypothesis that a-PBM 4 also interferes with the actomyosin interaction in situ, thus decreasing the effective cross-linking of microvillar rootlets by myosin filaments in the terminal web. On the basis of this model, we suggest that myosin filaments are essential for the upright position of brush-border type microvilli.