SARS-CoV-2 antigen-carrying extracellular vesicles activate T cell responses in a human immunogenicity model.

Extracellular vesicles (EVs) are entering the clinical arena as novel biologics for infectious diseases, potentially serving as the immunogenic components of next generation vaccines. However, relevant human assays to evaluate the immunogenicity of EVs carrying viral antigens are lacking, contributing to challenges in translating rodent studies to human clinical trials. Here, we engineered EVs to carry SARS-CoV-2 Spike to evaluate the immunogenicity of antigen-carrying EVs using human peripheral blood mononuclear cells (PBMCs). Delivery of Spike EVs to PBMCs resulted in specific immune cell activation as assessed through T cell activation marker expression. Further, Spike EVs were taken up largely by antigen-presenting cells (monocytes, dendritic cells and B cells). Taken together, this human PBMC-based system models physiologically relevant pathways of antigen delivery, uptake and presentation. In summary, the current study highlights the suitability of using human PBMCs for evaluating the immunogenicity of EVs engineered to carry antigens for infectious disease therapeutics.

A clinically relevant large-scale biomanufacturing workflow to produce natural killer cells and natural killer cell-derived extracellular vesicles for cancer immunotherapy.

Natural killer cell-derived extracellular vesicles (NK-EVs) have shown promising potential as biotherapeutics for cancer due to their unique attributes as cytotoxic nanovesicles against cancer cells and immune-modulatory activity towards immune cells. However, a biomanufacturing workflow is needed to produce clinical-grade NK-EVs for pre-clinical and clinical applications. This study established a novel biomanufacturing workflow using a closed-loop hollow-fibre bioreactor to continuously produce NK-EVs from the clinically relevant NK92-MI cell line under serum-free, Xeno-free and feeder-free conditions following GMP-compliant conditions. The NK92 cells grown in the bioreactor for three continuous production lots resulted in large quantities of both NK cell and NK-EV biotherapeutics at the end of each production lot (over 109 viable cells and 1013 EVs), while retaining their cytotoxic payload (granzyme B and perforin), pro-inflammatory cytokine (interferon-gamma) content and cytotoxicity against the human leukemic cell line K562 with limited off-target toxicity against healthy human fibroblast cells. This scalable biomanufacturing workflow has the potential to facilitate the clinical translation of adoptive NK cell-based and NK-EV-based immunotherapies for cancer with GMP considerations.

Hollow-fiber bioreactor production of extracellular vesicles from human bone marrow mesenchymal stromal cells yields nanovesicles that mirrors the immuno-modulatory antigenic signature of the producer cell.

BACKGROUND: Extracellular vesicles (EVs) produced by human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) are currently investigated for their clinical effectiveness towards immune-mediated diseases. The large amounts of stem cell-derived EVs required for clinical testing suggest that bioreactor production systems may be a more amenable alternative than conventional EV production methods for manufacturing products for therapeutic use in humans. METHODS: To characterize the potential utility of these systems, EVs from four hBM-MSC donors were produced independently using a hollow-fiber bioreactor system under a cGMP-compliant procedure. EVs were harvested and characterized for size, concentration, immunophenotype, and glycan profile at three separate intervals throughout a 25-day period. RESULTS: Bioreactor-inoculated hBM-MSCs maintained high viability and retained their trilineage mesoderm differentiation capability while still expressing MSC-associated markers upon retrieval. EVs collected from the four hBM-MSC donors showed consistency in size and concentration in addition to presenting a consistent surface glycan profile. EV surface immunophenotypic analyses revealed a consistent low immunogenicity profile in addition to the presence of immuno-regulatory CD40 antigen. EV cargo analysis for biomarkers of immune regulation showed a high abundance of immuno-regulatory and angiogenic factors VEGF-A and IL-8. CONCLUSIONS: Significantly, EVs from hBM-MSCs with immuno-regulatory constituents were generated in a large-scale system over a long production period and could be frequently harvested with the same quality and quantity, which will circumvent the challenge for clinical application.

A comprehensive proteomics profiling identifies NRP1 as a novel identity marker of human bone marrow mesenchymal stromal cell-derived small extracellular vesicles.

BACKGROUND: Clinical applications have shown extracellular vesicles (EVs) to be a major paracrine effector in therapeutic responses produced by human mesenchymal stromal/stem cells (hMSCs). As the regenerative capacity of EVs is mainly ascribed to the transfer of proteins and RNA composing its cargo, and to the activity attributed by the protein surface markers, we sought to profile the protein composition of small EVs released from hMSCs to identify hMSC-EV biomarkers with potential clinical relevance. METHODS: Small EVs were produced and qualified from five human bone marrow MSC donors at low passage following a 48-h culture in exosome-depleted medium further processed by steps of centrifugation, filtration, and precipitation. Quantitative proteomic analysis comparing the protein profile of the EVs released from hMSCs and their parental cell was conducted using tandem mass tag labeling combined to mass spectrometry (LC-MS/MS) to identify enriched EV protein markers. RESULTS: Nanoparticle tracking analysis showed no differences in the EV concentration and size among the five hMSC donors (1.83 × 1010 ± 3.23 × 109/mL), with the mode particle size measuring at 109.3 ± 5.7 nm. Transmission electron microscopy confirmed the presence of nanovesicles with bilayer membranes. Flow cytometric analysis identified commonly found exosomal (CD63/CD81) and hMSC (CD105/CD44/CD146) markers from released EVs in addition to surface mediators of migration (CD29 and MCSP). Quantitative proteomic identified 270 proteins significantly enriched by at least twofold in EVs released from hMSCs as compared to parental hMSCs, where neuropilin 1 (NRP1) was identified among 21 membrane-bound proteins regulating the migration and invasion of cells, as well as chemotaxis and vasculogenesis. Validation by western blot of multiple batches of EVs confirmed consistent enrichment of NRP1 in the nanovesicles released from all five hMSC donors. CONCLUSION: The identification and verification of NRP1 as a novel enriched surface marker from multiple batches of EVs derived from multiple hMSC donors may serve as a biomarker for the assessment and measurement of EVs for therapeutic uses.

Efficient Nonviral Transfection of Human Bone Marrow Mesenchymal Stromal Cells Shown Using Placental Growth Factor Overexpression.

BACKGROUND: Human mesenchymal stromal/stem cells (hMSCs) hold great therapeutic potential due to their immunomodulatory and tissue regenerative properties. Enhancement of biological features of hMSCs by transfection has become a focus of investigation for cell- and gene-based therapies. However, many of the current transient transfection methods result in either low transfection efficiency or high cytotoxicity. METHODS: In order to find a transfection method that would address the current issues of low transfection efficiency and high cytotoxicity, 6 commercially available cationic lipid and polymer reagents were tested on human bone marrow-derived MSCs (hBM-MSCs) using GFP as a reporter gene. One transfection method using TransIT-2020 was selected and tested with an emphasis on cell quality (viability, identity, and yield), as well as efficacy with a human placental growth factor (PlGF) plasmid. RESULTS: TransIT-2020 yielded the highest fluorescence signal per cell out of the methods that did not decrease cell recovery. Transfecting GFP to 5 hBM-MSC donors using TransIT-2020 yielded 24-36% GFP-expressing cells with a viability of 85-96%. hBM-MSC identity was unaffected as CD90, CD105, and CD73 markers were retained (>95%+) after transfection. When this method was applied to PlGF expression, there was up to a 220-fold increase in secretion. Both growth and secretion of PlGF in overexpressing hBM-MSC were sustained over 7 days, confirming the sustainability and applicability of the TransIT-2020 transfection system. DISCUSSION: We report a simple and efficient method for transient transfection that has not been reported for hBM-MSCs, encompassing high levels of plasmid expression without significant changes to fundamental hBM-MSC characteristics.

Mesenchymal stromal cells from patients with acute myeloid leukemia have altered capacity to expand differentiated hematopoietic progenitors.

The bone marrow microenvironment may be permissive to the emergence and progression of acute myeloid leukemia (AML). Studying interactions between the microenvironment and leukemia cells should provide new insight for therapeutic advances. Mesenchymal stromal cells (MSCs) are central to the maintenance of the hematopoietic niche. Here we compared the functions and gene expression patterns of MSCs derived from bone marrow aspirates of healthy donors and patients with AML. MSCs expanded from AML patients had heterogeneous morphology and displayed a wide range of proliferation capacity compared to MSCs from healthy controls. The ability of AML-MSCs to support the expansion of committed hematopoietic progenitors from umbilical cord blood-derived CD34+ cells may be impaired while the expression of genes associated with maintaining hematopoietic quiescence appeared to be increased in AML-MSCs compared to healthy donors. These results highlight important potential differences in the biologic profile of MSCs from AML patients compared to healthy donors that may contribute to the emergence or progression of leukemia.

The globoseries glycosphingolipid SSEA-4 is a marker of bone marrow-derived clonal multipotent stromal cells in vitro and in vivo.

The therapeutic potential of multipotent stromal cells (MSC) may be enhanced by the identification of markers that allow their discrimination and enumeration both in vivo and in vitro. Here, we investigated the ability of embryonic stem cell-associated glycosphingolipids to isolate human MSC from both whole-bone-marrow (BM) and stromal cell cultures. Only SSEA-4 was consistently expressed on cells within the CD45loCD105hi marrow fraction and could be used to isolate cells with the capacity to give rise to stromal cultures containing MSC. Human stromal cultures, generated in either the presence or absence of serum, contained heterogeneous cell populations discriminated by the quantity of SSEA-4 epitopes detected on their surface. A low level of surface SSEA-4 (SSEA-4lo) correlated with undetectable levels of the α2,3-sialyltransferase-II enzyme required to synthesize SSEA-4; a reduced proliferative potential; and the loss of fat-, bone-, and cartilage-forming cells during long-term culture. In vitro, single cells with the capacity to generate multipotent stromal cultures were detected exclusively in the SSEA-4hi fraction. Our data demonstrate that a high level of surface epitopes for SSEA-4 provides a definitive marker of MSC from human BM.

Identification of a candidate proteomic signature to discriminate multipotent and non-multipotent stromal cells.

Bone marrow stromal cell cultures contain multipotent cells that may have therapeutic utility for tissue restoration; however, the identity of the cell that maintains this function remains poorly characterized. We have utilized a unique model of murine bone marrow stroma in combination with liquid chromatography mass spectrometry to compare the nuclear, cytoplasmic and membrane associated proteomes of multipotent (MSC) (CD105+) and non-multipotent (CD105-) stromal cells. Among the 25 most reliably identified proteins, 10 were verified by both real-time PCR and Western Blot to be highly enriched, in CD105+ cells and were members of distinct biological pathways and functional networks. Five of these proteins were also identified as potentially expressed in human MSC derived from both standard and serum free human stromal cultures. The quantitative amount of each protein identified in human stromal cells was only minimally affected by media conditions but varied highly between bone marrow donors. This study provides further evidence of heterogeneity among cultured bone marrow stromal cells and identifies potential candidate proteins that may prove useful for identifying and quantifying both murine and human MSC in vitro.

Non-multipotent stroma inhibit the proliferation and differentiation of mesenchymal stromal cells in vitro.

BACKGROUND AIMS: The ability to expand and maintain bone marrow (BM)-derived mesenchymal stem cells (MSC) in vitro is an important aspect of their therapeutic potential. Despite this, the exact composition of stromal cell types within these cultures and the potential effects of non-stem cells on the maintenance of MSC are poorly understood. METHODS: C57BL/6J BM stroma was investigated as a model to determine the relationship between MSC and non-multipotent cells in vitro. Whole BM and single-cell derived cultures were characterized using flow cytometry and cell sorting combined with multipotent differentiation. Proliferation of individual stromal populations was evaluated using BrdU. RESULTS: At a single-cell level, MSC were distinguished from committed progenitors, and cells lacking differentiation ability, by the expression of CD105 (CD105+). A 3-fold reduction in the percentage of CD105+ cells was detected after prolonged culture and correlated with loss of MSC. Depletion of CD105+ cells coincided with a 10-20% increase in the frequency of proliferating CD105(-) cells. Removal of CD105(-) stroma caused increased proliferation in CD105+ cells, which could be diminished by conditioned media from parent cultures. Comparison of the multipotent differentiation potential in purified and non-purified CD105+ cells determined that MSC were detectable for at least 3 weeks longer when cultured in the absence of CD105(-) cells. CONCLUSIONS: This work identifies a simple model for characterizing the different cellular components present in BM stromal cultures and demonstrates that stromal cells lacking multipotent differentiating capacity greatly reduce the longevity of MSC.

Sustained expression of human cytomegalovirus glycoprotein B (UL55) in the seeds of homozygous rice plants.

Production of recombinant subunit vaccines in transgenic plants may be a means of reducing vaccine costs while increasing availability and safety. A plant-derived product found safe and effective for oral administration would provide additional advantages when used as a vaccine. Outstanding issues with the technology include transgene stability through successive generations and consistent bioproduction. We previously reported expression of glycoprotein B (gB) of human cytomegalovirus in seeds of transgenic tobacco. Here the goal was to determine if gB could be similarly expressed in rice, and if so, to examine expression over several plant generations. Results show that immunoreactive gB was successfully expressed in transgenic rice seeds, with sustained expression over three generations. The gB contained several neutralizing epitopes and was stable over 27 months.

Plasminogen and angiostatin interact with heat shock proteins.

Previous studies from this laboratory have demonstrated that plasminogen and angiostatin bind to endothelial cell (EC) surface-associated actin via their kringles in a specific manner. Heat shock proteins (hsps) like hsp 27 are constitutively expressed by vascular ECs and regulate actin polymerization, cell growth, and migration. Since many hsps have also been found to be highly abundant on cell surfaces and there is evidence that bacterial surface hsps may interact with human plasminogen, the purpose of this study was to determine whether human plasminogen and angiostatin would interact with human hsps. ELISAs were developed in our laboratory to assess these interactions. It was observed that plasminogen bound to hsps 27, 60, and 70. In all cases, binding was inhibited (85-90%) by excess (50 mM) lysine indicating kringle involvement. Angiostatin predominantly bound to hsp 27 and to hsp 70 in a concentration- and kringle-dependent manner. As observed previously for actin, there was concentration-dependent inhibition of angiostatin's interaction with hsp 27 by plasminogen. In addition, 30-fold molar excess actin inhibited (up to 50%), the interaction of plasminogen with all hsps. However, 30-fold molar excess actin could only inhibit the interaction of angiostatin with hsp 27 by 15-20%. Collectively, these data indicate that (i) while plasminogen interacts specifically with hsp 27, 60, and 70, angiostatin interacts predominantly with hsp 27 and to some extent with hsp 70; (ii) plasminogen only partially displaces angiostatin's binding to hsp 27 and (iii) actin only partially displaces plasminogen/angiostatin binding to hsps. It is conceivable therefore that surface-associated hsps could mediate the binding of these ligands to cells like ECs.

Increased yield of heterologous viral glycoprotein in the seeds of homozygous transgenic tobacco plants cultivated underground.

The use of transgenic plants in the production of recombinant proteins for human therapy, including subunit vaccines, is being investigated to evaluate the efficacy and safety of these emerging biopharmaceutical products. We have previously shown that synthesis of recombinant glycoprotein B (gB) of human cytomegalovirus can be targeted to seeds of transgenic tobacco when directed by the rice glutelin 3 promoter, with gB retaining critical features of immunological reactivity (E.S. Tackaberry et al. 1999. Vaccine, 17: 3020-3029). Here, we report development of second generation transgenic plant lines (T1) homozygous for the transgene. Twenty progeny plants from two lines (A23T(1)-2 and A24T(1)-3) were grown underground in an environmentally contained mine shaft. Based on yields of gB in their seeds, the A23T(1)-2 line was then selected for scale-up in the same facility. Analyses of mature seeds by ELISA showedthat gB specific activity in A23T(1)-2 seeds was over 30-fold greater than the best T0 plants from the same transformation series, representing 1.07% total seed protein. These data demonstrate stable inheritance, an absence of transgene inactivation, and enhanced levels of gB expression in a homozygous second generation plant line. They also provide evidence for the suitability of using this environmentally secure facility to grow transgenic plants producing therapeutic biopharmaceuticals.