Anti-human Monoclonal Antibody Research Articles

Immunohistochemical assessment of PD-L1 expression using three different monoclonal antibodies in triple negative breast cancer patients

BackgroundPD-L1 receptor expression in breast cancer tissue can be assessed with different anti-human PD-L1 monoclonal antibodies. The performance of three specific monoclonal antibodies in a head-to-head comparison is unknown. In addition, a potential correlation of PD-L1 expression and clinico-pathological parameters has not been investigated.MethodsThis was a retrospective study on tissue samples of patients with histologically confirmed triple negative breast cancer (TNBC). PD-L1 receptors were immune histochemically stained with three anti-human PD-L1 monoclonal antibodies: 22C3 and 28-8 for staining of tumor cell membranes (TC) and cytoplasm (Cyt), SP142 for immune cell staining (IC). Three different tissue samples of each patient were evaluated separately by two observers in a blinded fashion. The percentage of PD-L1 positive tumor cells in relation to the total number of tumor cells was determined. For antibodies 22C3 and 28-8 PD-L1 staining of 0 to < 1% of tumor cells was rated "negative", 1–50% was rated "positive" and > 50% was rated "strong positive". Cyt staining was defined as “negative” when no signal was observed and as “positive”, when any positive signal was observed. For IC staining with SP142 all samples with PD-L1 expression ≥ 1% were rated as “positive”. Finally, the relationship between PD-L1 expression and clinico-pathological parameters was analyzed.ResultsTissue samples from 59 of 60 enrolled patients could be analyzed. Mean age was 55 years. Both the monoclonal antibodies 22C3 and 28-8 had similar properties, and were positive for both TC in 13 patients (22%) and for Cyt staining in 24 patients (40.7%). IC staining with antibody SP142 was positive in 24 patients (40.7%), who were also positive for Cyt staining. The differences between TC and Cyt staining and TC and IC staining were significant (p = 0.001). Cases with positive TC staining showed higher Ki67 expression compared to those with negative staining, 40 vs 30%, respectively (p = 0.05). None of the other clinico-pathological parameters showed any correlation with PDL1 expression.ConclusionsAntibodies 22C3 and 28-8 can be used interchangeably for PD-L1 determination in tumor cells of TNBC patients. Results for Cyt staining with 22C3 or 28-8 and IC staining with SP142 were identical. In our study PD-L1 expression correlates with Ki67 expression but not with OS or DFS.

A Defucosylated Mouse Anti-CD10 Monoclonal Antibody (31-mG2a-f) Exerts Antitumor Activity in a Mouse Xenograft Model of CD10-Overexpressed Tumors

CD10 is a glycosylated transmembrane protein and is known as a membrane endopeptidase. It is expressed on predifferentiated lymphocyte progenitor, epithelial, stromal, and tumor cells. Therefore, antibodies against CD10 are used for diagnosing follicular lymphoma and solid tumors, including renal carcinomas. In this study, we developed an anti-human CD10 monoclonal antibody, clone C10Mab-31 (IgG1, kappa), which detects CD10 by flow cytometry and shows high affinity for CD10-overexpressed CHO-K1 (CHO/CD10) cells. Furthermore, the defucosylated mouse IgG2a version of C10Mab-31 (31-mG2a-f) exhibits antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, and antitumor activities in mouse xenografts of CHO/CD10 cells. These results indicate that 31-mG2a-f exerts antitumor effects against CD10-expressing tumors and could be valuable as part of an antibody treatment regimen for them.

Strong ACE-2 expression in the choroidal vessels: do high choroid plexuses serve as a gateway for SARS-CoV-2 infection on the human brain?

Previous studies have confirmed the key mechanism by which SARS-CoV-2 enters human cells. It is well established that ACE2 is the receptor that can mark the beginning of the infection. In light of this, the organs that express higher levels of ACE2 are generally considered at higher risk, while those with lower levels should be somehow more protected. This - if related to the scarcity of ace2-expressing cells in the brain - seems to contrast with the presence of a variety of neurological symptoms that follow infection with ace2. The aim of this work was to analyze ACE2 expression in the human brain, focusing on the choroid plexuses. Twenty brain samples were obtained at autopsy from ten human fetuses and from ten adult subjects. All samples were selected to contain the choroid plexus. Specimens were fixed in 10% formalin, routinely processed and paraffin embedded. 5-micron sections were stained with Hematoxylin and Eosin (H&E) and immunostained with a commercial anti-human ACE2 rabbit monoclonal antibody at 1:100 dilution. We analyzed 20 samples by immunohistochemistry, and we noted that, as far as fetal samples are concerned, a strong reactivity for ACE2 was detected in the myxoid stroma of the choroid plexuses and in the endothelial cells in fetuses. The complete absence of the ACE2 marker was detected in epithelial cells, neurons and glial cells of the cerebral cortex, both in fetuses and in adults. Whereas a strong but selective reactivity for ACE2 was also detected in adult choroid plexuses, mainly localized in the endothelial cells of the choroid capillaries. Our study shows a strong expression of ACE in the fetal and adult brain choroid plexuses. This new histopathological finding may clarify the susceptibility of the human brain to SARS-COV-2 infection. Our data indicate the choroid plexus as the entry gate of virus for in the human brain; therefore, the entrance of SARS-CoV-2 into the cerebrospinal fluid through the choroid plexuses might represent the mechanism utilized by this coronavirus to cause direct injury to brain cells.

The possibility of using anti-human monoclonal antibody CD3 as pan T-cell marker in guinea pigs

The present study was aimed to evaluate the possibility of using anti-human monoclonal antibody CD3 as pan T-cell marker in the guinea pigs’ trachea and lung in early and late manifestations of the allergic inflammatory process.&#x0D; Materials and methods.We have studied the distribution and quantitative changes of CD3-positive lymphocytes in trachea and lung of guinea pigs using histological, immunohistochemical, statistical methods in conditions of experimental inflammatory process.&#x0D; Results. Our results revealed the applicability of anti-Human monoclonal antibody CD3 (Clone SP7, «DAKO», Denmark) cross-reaction with T-cells of guinea pigs’ tracheas and lungs. The most statistically significant elevation of the number of CD3-positive lymphocytes, in comparison with the control group (p*/**&lt;0.05), observed in the experimental group III in the late stages of experimental inflammatory process. The elevation of the number of CD3-positive lymphocytes persists even after the termination of the allergen action, which indicates the continuation of the reaction of pulmonary local adaptive immunity to the allergen.&#x0D; Conclusions. The results of our study may be useful in conditions of the deficiency of guinea pig-specific tests. The immunohistochemical assessment of guinea pigs’ trachea and lungs proved the possibility to use anti-Human monoclonal antibody CD3 as a panT-cell marker in guinea pigs. We demonstrated the activation of adaptive immune response (T-cells), represented by their immunohistochemical changes, predominantly in the late stages of experimental inflammatory process.

Quantitative CK19 biomarker detection in breast cancer cell lines.

Cytokeratin19 (CK19) was detected as the most related marker for circulating tumor cells, which was assessed in specific cell lines. MCF7, SKBR3, T47D, and MDA-MB-231, and HeLa cell line as negative control were used. CK19 expression was confirmed by using mouse monoclonal anti-human CK19 antibody. CK19 detection in MDA-MB-231 was not observed. CK19 marker expression was compared in T47D, MCF7, and SKBR3 cell lines. T47D and MCF7 belonged to the luminal subtype of breast cancer (BC) that CK19 expression regulated with an ER marker. SKBR3 belonged to the HER2 positive subtype of BC. However, MDA-MB-231 belonged to the claudin-low subtype of BC that lack of CK19 expression strongly is related to negative ER, PR, and HER2. Therefore, there are not only quantitative differences in CK19 expression, but its expression could also link to the other markers of BC that should be considered in the molecular classification of breast carcinoma. Different expression levels related to cell classification could be useful in the prognosis and treatment of cancers with epithelial origins.

Epitope Mapping of an Anti-CD10 Monoclonal Antibody (MME/1870) Using Enzyme-Linked Immunosorbent Assay.

CD10 is a glycosylated transmembrane protein and is known as a membrane endopeptidase. CD10 is expressed on predifferentiated lymphocyte progenitor, epithelial, stromal, and tumor cells. Antibodies against CD10 are used for the diagnosis of follicular lymphoma. Anti-human CD10 monoclonal antibody (clone MME/1870) can be used for Western blotting and immunohistochemical analyses. This study examined the critical epitope of MME/1870 using enzyme-linked immunosorbent assay (ELISA) with synthesized peptides. First, we performed ELISA with deletion mutants, and MME/1870 reacted to the 501-520 amino acid sequence of CD10. Next, we analyzed the reaction to 20 point mutants, and MME/1870 did not recognize the alanine-substituted peptides of Y507A, I511A, I512A, and L515A. These results indicate that the binding epitope of MME/1870 includes Tyr507, Ile511, Ile512, and Leu515 of CD10.

Is tocilizumab effective in cytokine release syndrome in patients diagnosed with COVID-19?: a retrospective preliminary study

Objectives: Although the prognosis is good in the vast majority of patients who are diagnosed with COVID-19, there are cases in which Acute Respiratory Distress Syndrome (ARDS) and multiple organ failure occur rapidly and result in death in a short time. It has been reported that severe clinical presentation is caused by cytokine release syndrome, and studies are currently conducted on treatments to reduce mortality in these patients. There are studies reporting the positive effects of anti-Human IL-6 Receptor Monoclonal Antibody, tocilizumab (TCZ), which specifically inhibits the functions of IL-6, in cases with cytokine storm. Data on TCZ use in intensive care are very limited. Methods: The medical records of 20 patients diagnosed with COVID-19 who were treated with standard treatment and TCZ in the ICU were retrospectively reviewed. Results: Twenty patients were included in the review. Nine (45%) received TCZ. The median length of stay in the ICU was 20 days in the TCZ group, and 14 days in the standard treatment group (p = 0.21). Mortality rate was 22.2% in TCZ group and 45.5% in the standard treatment group (p = 0.27). Conclusions: At day 28, mortality rate and clinical improvement was not statistically different in patients receiving standard treatment with TCZ and patients in standard treatment group. Additional data are needed to understand the eficacy and safety of TCZ.

Preparation of the Murine Anti-Human P2X7 Receptor Monoclonal Antibody (Clone L4).

The murine anti-human P2X7 receptor monoclonal antibody (mAb) (clone L4) has been used to study the expression and function of the P2X7 receptor on primary leukocytes, keratinocytes, osteoblasts and neuronal cells, as well as various cell lines. This antibody has also been used to characterize polymorphic variants and isoforms of the P2RX7 gene and P2X7 site-directed mutations, and to identify molecules coassociated with P2X7 in the plasma membrane. This chapter describes the maintenance and cryopreservation of the L4 hybridoma cell line, as well as the generation of tissue culture supernatant containing the anti-human P2X7 mAb, and its subsequent purification by Protein A chromatography and conjugation to DyLight™ 488. Moreover, this chapter describes flow cytometric assays to assess the blocking activity and binding of the anti-human P2X7 mAb against P2X7 on human RPMI 8226 multiple myeloma cells.

Flow Cytometry Assay of Plasmodium Falciparum-Specific B-Cell Proportions.

Detection of P. falciparum-specific subpopulations of B-cells is important for studies of immunity in malaria. This protocol relies on the photostability and protein loading capacity of carboxylated quantum dots to detect a broad range of different P. falciparum-specific B-cells. Infected red blood cell ghosts, obtained by permeabilization of infected cells with Streptolysin O, are coupled with carboxyl quantum dots using N-ethyl-N-dimethylaminopropyl-carbodiimide condensation. Immunophenotyping of P. falciparum-specific B-cells is performed by flow cytometry using Fc-receptor block, quantum dot-infected red blood cell ghost conjugates, and fluorochrome-conjugated anti-human CD19 mouse monoclonal antibodies.

Macrophages and Natural Killer Cells Characteristics in Variously Colored Endometriotic Lesions: A Cross-Sectional Analytic Study.

Background:Dysregulation of the immune response contribute to a significant role in endometriosis. This research examined macrophages and natural killer (NK) cells numbers in endometriotic lesions and their association with the different lesion colors: red, black, and white. To investigate the amount of the CD68 and CD56 in eutopic endometrium and different type of the endometriotic lesions.Materials and Methods:A cross-sectional analytic study was conducted. Women suspected endometriosis requiring laparoscopic surgery between July 2016 and January 2017 were recruited. Their lesions were classified as red, black, or white and these lesions were excised by standard laparoscopic surgery. Twenty-four endometriotic lesions from each color group were obtained from 45 women who met the inclusion criteria. One type of lesion was collected from 25 women. Two different lesion types and three-color lesion types were collected from the same women in 13 and 7 subjects, respectively. Immunohistochemistry staining with anti-human mouse cluster of differentiation (CD) 68 monoclonal antibody for macrophages and mouse anti-human CD56 monoclonal antibody for NK cells were performed.Results:The number of CD68 macrophages in red lesions was higher than in black and white lesions [median (25th-75th percentile); 10 (5-19.4), 0 (0-6.9), 0 (0-2.5) cells per mm2, respectively, adjusted P=0.001 for red vs. black lesions and red vs. white lesions, and adjusted P=1.000 for black and white lesions]. The number of CD56 NK cells was not significantly different among red, black, and white lesions [median (25th-75th percentile; 5 (2-16.5), 3.8 (0-14.4), 1.3 (0-6.9) respectively, adjusted P=1.000 for red vs. black lesions and black vs. white lesions, and adjusted P=0.617 for red vs. white lesions].Conclusion:The dynamic changes in the immune cells in ectopic endometrium were specific to the macrophages but not to the NK cells, as demonstrated by the highest number of CD68 macrophages in the red lesion, the earliest established ectopic endometrium. NK cells in endometriosis may have a role in the uterus.

Tracing Human IgE B Cell Antigen Receptor-Bearing Cells With a Monoclonal Anti-Human IgE Antibody That Specifically Recognizes Non-Receptor-Bound IgE.

Up to 30% of the population suffers from immunoglobulin E (IgE)-mediated allergies. Despite current stepwise gating approaches, the unambiguous identification of human IgE-producing cells by flow cytometry and immunohistology remains challenging. This is mainly due to the scarcity of these cells and the fact that IgE is not only expressed in a membrane-bound form on the surface of IgE-producing cells in form of the B cell antigen receptor (BCR), but is more frequently found on various cell types bound to the low and high affinity receptors, CD23 and FcϵRI, respectively. Here we sought to develop a sequential gating strategy for unambiguous detection of cells bearing the IgE BCR on their surface. To that aim we first tested the monoclonal anti-IgE antibody omalizumab for its ability to discriminate between IgE BCR and receptor-bound IgE using cells producing IgE or bearing IgE bound to CD23 as well as basophils exhibiting FcϵRI receptor-bound IgE. Using flow cytometry, we demonstrated that omalizumab recognized IgE producing cells with a high sensitivity of up to 1 IgE+ cell in 1000 human peripheral blood mononuclear cells (PBMCs). These results were confirmed by confocal microscopy both in cell suspensions as well as in nasal polyp tissue sections. Finally, we established a consecutive gating strategy allowing the clear identification of class-switched, allergen-specific IgE+ memory B cells and plasmablasts/plasma cells in human PBMCs. Birch pollen specific IgE+ memory B cells represented on average 0.734% of total CD19+ B cells in allergic patients after allergen exposure. Thus, we developed a new protocol for exclusive staining of non-receptor bound allergen-specific IgE+ B cell subsets in human samples.

40. Lenzilumab Efficacy and Safety in Newly Hospitalized COVID-19 Subjects: Results From a Phase 3 Randomized Double-Blind Placebo-Controlled Trial

BackgroundSevere coronavirus disease 2019 (COVID-19) often results from the immune-mediated cytokine storm, triggered by granulocyte macrophage-colony stimulating factor (GM-CSF), potentially leading to respiratory failure and death. Lenzilumab, a novel anti-human GM-CSF monoclonal antibody, neutralizes GM-CSF and demonstrated potential to improve clinical outcomes in a matched case-cohort study of patients with severe COVID-19 pneumonia. This Phase 3 randomized, double-blind, placebo-controlled trial investigated the efficacy and safety of lenzilumab to improve the likelihood of survival without invasive mechanical ventilation (SWOV), beyond available treatments. MethodsHypoxic patients, hospitalized with COVID-19 (n=520), requiring supplemental oxygen, but not invasive mechanical ventilation, were randomized on Day 0 to receive lenzilumab (1800mg, n=261) or placebo (n=259), and available treatments, including remdesivir and/or corticosteroids; and were followed through Day 28. ResultsBaseline demographics were comparable between groups: male, 64.7%; mean age, 60.5 years; median CRP, 79.0 mg/L. Patients across both groups received steroids (93.7%), remdesivir (72.4%), or both (69.1%). Lenzilumab improved the primary endpoint, likelihood of SWOV in the mITT population, by 1.54-fold (HR: 1.54; 95%CI: 1.02-2.32, p=0.0403). Lenzilumab improved SWOV by 1.91-fold (nominal p=0.0073) and 1.92-fold (nominal p=0.0067) in patients receiving remdesivir or remdesivir and corticosteroids, respectively. A key secondary endpoint of incidence of IMV, ECMO or death was also improved in patients receiving remdesivir (p=0.020) or remdesivir and corticosteroids (p=0.0180). Treatment-emergent serious adverse events were similar across both groups.ConclusionLenzilumab significantly improved SWOV in hypoxic COVID-19 patients upon hospitalization, with the greatest benefit observed in patients receiving treatment with remdesivir and corticosteroids. NCT04351152Disclosures Zelalem Temesgem, MD, Humanigen, Inc (Grant/Research Support) Jason Baker, MD, Humanigen, Inc (Grant/Research Support) Christopher Polk, MD, Atea (Research Grant or Support)Gilead (Advisor or Review Panel member, Research Grant or Support)Humanigen (Research Grant or Support)Regeneron (Research Grant or Support) Claudia R. Libertin, MD, Gilead (Grant/Research Support) Colleen F. Kelley, MD, MPH, Gilead Sciences (Individual(s) Involved: Self): Grant/Research Support; Moderna (Individual(s) Involved: Self): Grant/Research Support; Novavax (Individual(s) Involved: Self): Grant/Research Support; Viiv (Individual(s) Involved: Self): Grant/Research Support Vincent Marconi, MD, Bayer (Consultant, Scientific Research Study Investigator)Eli Lilly (Consultant, Scientific Research Study Investigator)Gilead Sciences (Consultant, Scientific Research Study Investigator)ViiV (Consultant, Scientific Research Study Investigator) Victoria Catterson, PhD, Humanigen, Inc (Consultant) William Aronstein, MD, PhD, Humanigen, Inc (Consultant) Cameron Durrant, MD, Humanigen, Inc (Employee) Dale Chappell, MD, Humanigen, Inc (Employee) Omar Ahmed, PharmD, Humanigen, Inc (Employee) Gabrielle Chappell, MSc, Humanigen, Inc (Consultant) Andrew Badley, M.D., AbbVie (Consultant) for the LIVE-AIR Study Group, n/a, Humanigen, Inc (Grant/Research Support)

Epitope Mapping of an Anti-CD20 Monoclonal Antibody (C20Mab-60) Using Enzyme-Linked Immunosorbent Assay.

CD20 is a glycosylated transmembrane protein and is expressed on normal B cells and B cell malignancies. Therapeutic antibodies against CD20 are developed and used in clinic. The understanding of antibody-antigen binding by revealing the epitope is essential for future application to antibody technology. Previously, we developed an anti-human CD20 monoclonal antibody, C20Mab-60 (IgG2a, kappa), using the Cell-Based Immunization and Screening (CBIS). C20Mab-60 can be used for flow cytometry, Western blot, and immunohistochemical analyses. In this study, we examined the critical epitope of C20Mab-60 using enzyme-linked immunosorbent assay (ELISA) with synthesized peptides. We performed ELISA with deletion mutants, and C20Mab-60 reacted to the 160-179 amino acids sequence of CD20. Next, we analyzed the reaction to 20 point mutants, and C20Mab-60 did not recognize the alanine-substituted peptides of N171A, P172A, S173A, and E174A. The results indicate that the binding epitope of C20Mab-60, developed by CBIS, includes Asn171, Pro172, Ser173, and Glu174 of CD20.

Reassessment of SST4 Somatostatin Receptor Expression Using SST4-eGFP Knockin Mice and the Novel Rabbit Monoclonal Anti-Human SST4 Antibody 7H49L61.

Among the five somatostatin receptors (SST1–SST5), SST4 is the least characterized, which is in part due to the lack of specific monoclonal antibodies. We generated a knockin mouse model that expresses a carboxyl-terminal SST4-eGFP fusion protein. In addition, we extensively characterized the novel rabbit monoclonal anti-human SST4 antibody 7H49L61 using transfected cells and receptor-expressing tissues. 7H49L61 was then subjected to immunohistochemical staining of a series of formalin-fixed, paraffin-embedded normal and neoplastic human tissues. Characterization of SST4-eGFP mice revealed prominent SST4 expression in cortical pyramidal cells and trigeminal ganglion cells. In the human cortex, 7H49L61 disclosed a virtually identical staining pattern. Specificity of 7H49L61 was demonstrated by detection of a broad band migrating at 50–60 kDa in immunoblots. Tissue immunostaining was abolished by preadsorption of 7H49L61 with its immunizing peptide. In the subsequent immunohistochemical study, 7H49L61 yielded a predominant plasma membrane staining in adrenal cortex, exocrine pancreas, and placenta. SST4 was also found in glioblastomas, parathyroid adenomas, gastric and pancreatic adenocarcinomas, pheochromocytomas, and lymphomas. Altogether, we provide the first unequivocal localization of SST4 in normal and neoplastic human tissues. The monoclonal antibody 7H49L61 may also prove of great value for identifying SST4-expressing tumors during routine histopathological examinations.

PD-L1 expression on circulating tumor cells and platelets in patients with metastatic breast cancer.

BackgroundImmune checkpoint inhibition is effective in several cancers. Expression of programmed death-ligand 1 (PD-L1) on circulating tumor or immune effector cells could provide insights into selection of patients for immune checkpoint inhibition.MethodsWhole blood was collected at serial timepoints from metastatic breast cancer patients and healthy donors for circulating tumor cell (CTC) and platelet PD-L1 analysis with a phycoerythrin-labeled anti-human PD-L1 monoclonal antibody (Biolegend clone 29E.2A3) using the CellSearch® assay. CTC PD-L1 was considered positive if detected on at least 1% of the cells; platelet PD-L1 was considered positive if ≥100 platelets per CellSearch frame expressed PD-L1.ResultsA total of 207 specimens from 124 metastatic breast cancer patients were collected. 52/124 (42%) samples at timepoint-1 (at or close to time of progressive disease) had ≥5 CTC/7.5ml whole blood. Of those, 21 (40%) had positive CTC PD-L1. In addition, platelet PD-L1 expression was observed in 35/124 (28%) at timepoint-1. Platelet PD-L1 was not detected in more than 70 specimens from 12 healthy donors. Platelet PD-L1 was associated with ≥5 CTC/7.5ml whole blood (p = 0.0002), less likely in patients with higher red blood cell counts (OR = 0.72, p<0.001) and a history of smoking tobacco (OR = 0.76, p<0.001). Platelet PD-L1 staining was not associated with tumor marker status, recent procedures or treatments, platelet-affecting drugs, or CTC PD-L1 expression.ConclusionPD-L1 expression was found in metastatic breast cancer patients on both CTC and platelets in an independent fashion. Inter-patient platelet PD-L1 expression was highly heterogeneous suggesting that it is a biological event associated with cancer in some but not all patients. Taken together, our data suggest that CTC and platelet PD-L1 expression could play a role in predicting which patients should receive immune checkpoint inhibition and as a pharmacodynamics biomarker during treatment.

A Novel Allogeneic Cell Therapy That Targets Pathogenic Autoantibodies for the Treatment of Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by low platelet counts (<100x10 9/L) and increased risk of bleeding. ITP is predominantly driven by immunoglobulin G (IgG)-autoantibodies directed against platelet surface antigens resulting in platelet destruction by the spleen and/or impaired platelet production by bone marrow megakaryocytes. Approximately 60% of ITP patients have measurable levels of anti-platelet autoantibodies in plasma and about 70% of them have autoantibodies directed against the fibrinogen receptor glycoprotein (GP) IIbIIIa.Current treatment strategies for ITP include non-specific immunosuppression (steroids, rituximab), inhibition of platelet clearance (immunoglobulins, splenectomy, anti-D immunoglobulin, and the Syk inhibitor fostamatinib) and stimulation of platelet production (thrombopoietin receptor agonists). In addition, therapeutics targeting the neonatal Fc receptor, responsible for IgG recycling, are under clinical investigation for ITP. Despite these treatment options, some patients with ITP are refractory or have inadequate responses to existing therapy.Here we describe a novel allogeneic cellular therapy, entitled platelet-like cells (PLC), that specifically targets pathogenic IgG for the treatment of thrombocytopenia in ITP. PLC are produced by differentiating a human induced pluripotent stem cell (hiPSC) line into megakaryocyte-like cells (MLC) which are further processed in a proprietary bioreactor that mimics the bone marrow environment and induces the release of anucleate PLC which are then cryopreserved. Analyses of PLC demonstrate sizes ranging between 65 nm and 10 μm. Expression of GPIIbIIIa protein as measured by enzyme-linked immunosorbent assay (ELISA) is evident in all particle sizes. PLC were administered intravenously (IV) into NOD-scid IL2Rgamma null (NSG) mice to evaluate their pharmacokinetics and biodistribution. PLC were rapidly cleared from the mouse circulation and predominantly distributed to the mouse liver where they colocalized primarily with Kupffer cells. PLC clearance through the liver was significantly inhibited by pre-treating mice with liposomes expressing phosphatidylserine (PS), indicating that one mechanism of PLC clearance is dependent on PS exposure on the PLC outer plasma membrane.The ability of PLC to bind anti-GPIIbIIIa autoantibodies was evaluated in an in vitro assay where PLC were incubated with ITP patient plasmas and subsequently removed by centrifugation and filtration. The concentration of anti-GPIIbIIIa autoantibodies remaining in the plasmas decreased following PLC treatment (96.6% ± 2.4%).The ability of PLC to clear anti-human GPIIbIIIa antibodies in circulation was evaluated by using a passive mouse model of ITP. Here, a fluorescently labeled mouse anti-human GPIIbIIIa monoclonal antibody (PAB-1) was dosed intravenously (IV) into NSG mice to achieve a circulating level of antibody comparable to those observed in ITP patients. The GPIIbIIIa antibody persisted in circulation for over 24 hours following a single dose in untreated mice and did not induce clearance of mouse platelets. Following administration of PLC in the passive ITP model, a decrease in antibody fluorescence in blood was observed within 2 minutes and full antibody clearance was observed at 3 hours post dosing. Furthermore, clearance of the antibody was observed to be both dose responsive and specific since PLC treatment did not affect the antibody concentration of an isotype matched control antibody. PLC activity in clearing the anti-GPIIbIIIa antibody was observed in all particle sizes. Fluorescence quantification of liver and spleen tissue demonstrated that PLC driven anti-GPIIbIIIa antibody clearance occurred preferentially in the liver. Taken together, these data indicate that by specifically binding and rapidly removing anti-platelet antibodies from circulation, PLC may disrupt the platelet degradation mechanisms underlying ITP pathogenesis and restore platelet counts. DisclosuresPatel-Hett: PlateletBio: Current Employment. Giannini: Platelet Biogenesis: Current Employment. Peters: Platelet Biogenesis: Current Employment. Dykstra: Platelet Biogenesis: Current Employment. Lehmann: Platelet Biogenesis: Current Employment. Russo: Platelet Biogenesis: Current Employment. Kohnke: Platelet Biogenesis: Current Employment. Carpenter: Platelet Biogenesis: Current Employment. Tomczak: Platelet Biogenesis: Current Employment. Lazarus: Platelet Biogenesis: Consultancy. Masuko: Platelet Biogenesis: Current Employment. Leung: Platelet Biogenesis: Current Employment. Meredith: Platelet Biogenesis: Current Employment. Pete: Platelet Biogenesis: Current Employment. Lee: Platelet Biogenesis: Current Employment. Falb: Platelet Biogenesis: Current Employment.

230 Preclinical efficacy of CLEC-1 antagonist as novel myeloid immune checkpoint therapy for oncology

BackgroundC-type lectin receptors (CLRs) are powerful pattern recognition receptors shaping immune cell-mediated tissue damage by positively or negatively regulating myeloid cell functions and hence tumor elimination or evasion. We previously reported that the orphan CLR CLEC-1 expressed by dendritic cells (DCs) tempers T cell’s responses in vivo by limiting antigen cross-presentation by cDC1. Furthermore, we observed that CLEC-1 is highly expressed by myeloid cells purified from human tumor microenvironment, in particular tumor-associated macrophages.MethodsMacrophages were generated from monocytes of healthy volunteers for phagocytosis assays. MC38 and Hepa 1.6 murine tumor cells were implanted in Clec1a KO or KI mice for immunotherapeutic treatment evaluation.ResultsUsing newly developed anti-human CLEC-1 monoclonal antibodies (mAbs), we found that antagonist anti-CLEC-1 mAbs with the capacity to block CLEC-1/CLEC-1Ligand interaction, as opposed to non-antagonist CLEC-1 mAbs, increase the phagocytosis of CLEC-1Ligand-positive human tumor cells by human macrophages, in particular when opsonized by tumor-associated antigen mAbs (Rituximab, Cetuximab, Trastuzumab) or with anti-CD47 mAb (Magrolimab). In-vivo, CLEC-1 knock-out (KO) mice (n=19) display significant prolonged survival in monotherapy as compared to wild-type littermates (n=12) in an orthotopic hepatocellular carcinoma (HCC) model and anti-tumor memory responses was demonstrated by tumor rechallenge in cured mice. CLEC1 KO mice also illustrate significant eradication of MC38 colorectal tumors in combination with chemotherapy promoting CLEC-1Ligand expression by tumor cells (n=16 with Gemcitabine or n=11 with Cyclophosphamide). HCC tumor microenvironment analysis after 2 weeks of tumor implantation shows significantly higher number of CD8+ and memory CD8+ T cells with reduced PD1 expression in CLEC1 KO animals (n=16 versus n=12 for KO vs WT mice respectively). Finally, we recently generated human CLEC-1 knock-in mice expressing the extracellular human CLEC1 domain fused to the intracellular mouse CLEC1 tail and confirmed preclinical efficacy in vivo with anti-human CLEC1 antagonist mAb in monotherapy in the orthotopic HCC model.ConclusionsThese data illustrate that CLEC-1 inhibition represents a novel therapeutic target for immuno-oncology modifying T cell immune responses and tumor cell phagocytosis by macrophages.

Bio-conjugation of anti-human CD3 monoclonal antibodies to magnetic nanoparticles by using cyanogen bromide: A potential for cell sorting and noninvasive diagnosis

The conjugation of monoclonal antibodies with superparamagnetic iron oxide nanoparticles (SPIONs) has appeared as a potential multifunctional clinical tool, which can effectively diagnose cancers and monitor their treatment, specifically. Despite the presence of different methods for conjugating antibodies to iron oxide nanoparticles, novel cost-effective and simpler conjugation techniques should be performed in this regard. In current study, an anti-CD3 monoclonal antibody was conjugated to the Fe3O4 coated by carboxymethyl dextran (CMD) using cyanogen bromide (CNBr). Moreover, EDC/NHS techniques were applied as a positive control. The experimental results showed that the Conjugation was performed and the presence of the antibody conjugated to the MNPs in human xenograft tumors was confirmed using Prussian blue (PB) staining, following magnetic resonance imaging (MRI), 30 min after injection. This conjugation method was shown to be able to separate CD3+ T lymphocytes efficiently from whole blood with high purity. Accordingly, this type of bio-conjugation method can be utilized in the future for cell sorting, and can be applied for adopted cell therapies such as CAR-T cell (Chimeric antigen receptor T cell) therapy, as well as targeted MRI imaging.

ELEVATED CIRCULATING ENDOTHELIAL CELLS AND SUCCESS IN ENDOTHELIAL COLONY-FORMING CELLS ISOLATION

Circulating endothelial cells (CEC) have been associated with vascular injury and are described as potential biomarkers for cardiovascular disease (1). Besides, current optimized methodologies enable the isolation of a well-characterized subtype of endothelial progenitor known as Endothelial colony-forming cells (ECFCs) (2,3). Although ECFC isolation methodologies are well described; some discrepancies remain in relation to their isolation efficiency. To evaluate the isolation efficacy ECFCs and CEC frequency in human peripheral blood. The Ethics Research Committee of the University of Campinas approved the experimental procedures and all donors signed the informed consent form. CEC enumeration was assessed by flow cytometry in the peripheral blood of 18 donors. 100 μL of blood (with a leukocyte concentration between 5 and 10 ×10³/μL) was incubated with monoclonal anti-human antibodies (CD45 PerCp, CD133 APC, CD31 FITC, and CD146 PE). FACS lysing solution was used for red blood cell removal. 300,000 events or the total volume of the tube were acquired using a FACSCalibur® flow cytometer (4). To determine the number of cells/μL, the percentage of events was multiplied per number of leucocytes and divided per 100. Cell culture from venous blood was used to isolate ECFCs which were confirmed by their cobblestone morphology and immunophenotyping for endothelial markers (CD31, CD146, CD309, and CD144). ECFC isolation was successful in 9 out of 18 donors (1 male, 8 females; mean age: 35.8 ±11.1 years), and not successful in the other half of donors (2 male, 7 females; mean age: 37.7 ±9.7 years). CEC frequency was significantly higher (p=0.004) in the group with successful ECFC isolation when compared to the group that did not yield ECFCs (2.9 ±1.2 CECs/μL against 1.2 ±0,8 CECs/μL). This suggests that the success in ECFC isolation might be related to the number of CECs, and therefore ECFC mobilization into circulation may also be linked to vascular injury. Increased number of CECs might be associated with the success of ECFCs isolation.

Salvianolic acid B and ferulic acid synergistically promote angiogenesis in HUVECs and zebrafish via regulating VEGF signaling

Induced vascular growth in the myocardium has been widely acknowledged as a promising intervention strategy for patients with ischemic coronary artery disease. Yet despite long-term efforts on gene, protein or cell-based pro-angiogenic therapies, the clinical translation remains challenging. Noticeably, multiple medicinal herbs have long-term documented effects in promoting blood circulation. Salvia miltiorrhiza and Ligusticum stratum are two representative traditional Chinese medicine herbs with suggested roles in enhancing organ blood supply, and Guanxinning Tablet (GXNT), a botanical drug which is formulated with these two herbs, exhibited significant efficacy against angina pectoris in clinical practices. This study aimed to examine the pro-angiogenic activity of GXNT and its major components, as well as to explore their pharmacological mechanism in promoting angiogenesis. In vitro, the pro-angiogenic effects of GXNT and its major components were examined on human umbilical vein endothelial cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT), scratch assay, and endothelial cell tube formation assay. In vivo, the pro-angiogenic effects were examined on the ponatinib-induced angiogenesis defective zebrafish model. The active compounds were identified through phenotype-based screening in zebrafish, and their pharmacological mechanism was explored in both in vitro and in vivo models by immunofluorescent staining, cell cycle analysis, quantitative PCR and whole embryo in-situ hybridization. We demonstrated strong pro-angiogenic effects of GXNT in both human umbilical vein endothelial cells and zebrafish model. Moreover, through phenotype-based screening in zebrafish for active compounds, pro-angiogenic effects was discovered for salvianolic acid B (Sal B), a major component of Salvia miltiorrhiza, and its activity was further enhanced when co-administered with ferulic acid (FA), which is contained in Ligusticum stratum. On the cellular level, Sal B and FA cotreatment increased endothelial cell proliferation of sprouting arterial intersomitic vessels in zebrafish, as well as largely restored G1-S cell cycle progression and cyclin D1 expression in angiogenic defective HUVECs. Through quantitative transcriptional analysis, increased expression of vegfr2 (kdr, kdrl) and vegfr1 was detected after GXNT or SalB/FA treatment, together with upregulated transcription of their ligands including vegf-a, vegf-b, and pgfb. Bevacizumab, an anti-human VEGF-A monoclonal antibody, was able to significantly, but not completely, block the pro-angiogenic effects of GXNT or SalB/FA, suggesting their multi-targeting properties. In conclusion, from a traditional Chinese medicine with effects in enhancing blood circulation, we demonstrated the synergistic pro-angiogenic effects of Sal B and FA via both in vitro and in vivo models, which function at least partially through regulating the expression of VEGF receptors and ligands. Future studies are warranted to further elaborate the molecular interaction between these two compounds and the key regulators in the process of neovascularization.