A continuous flow cell culture system for precision cell stimulation and time-resolved profiling of cell secretion

Investigating dynamics of lentiviral vector secretion from HEK293T producer cells using a fractionated perfusion system

Mammalian cell culture is quickly becoming the go to engineering vehicle to mass produce viral vectors in a manner that is safe, convenient, reproducible, and cost and scale effective. Human embryonic kidney (HEK293) cells, in particular, have been utilized and customized (via differentiated transgene expression, modified culture parameters, addition of cytostatic culture agents) to increase vector yields. However, less attention has been made to understanding innate processes within the cells (such as, immune response, cell cycle, metabolism) themselves to better control or increase viral vector product yield. Accordingly, herein, the variation in viral production was studied from HEK cells over time using a one-way perfusion system and bioreactor to study the impact of external factors on secretion dynamics without retrotransduction. Specifically, the impact of cell density on viral titer, transduction efficiency, and LDH, was studied. Next, we look at the impact of using an inflammatory reporter cell line on viral output, and the secretion dynamics from HEK cells when we use sodium butyrate (cell cycle arrest agent). Lastly, we assess how downregulation of the PDK pathway increases viral titer. Altogether, we investigated the impact of various interventions to increase transient protein expression and viral output from HEK cells in a controlled and measurable environment to ultimately increase the efficiency of HEK cells for downstream clinical applications.

Therapeutic Extracellular Vesicles from Tonsil-Derived Mesenchymal Stem Cells for the Treatment of Retinal Degenerative Disease

BACKGROUND

Retinal degenerative disease (RDD), one of the most common causes of blindness, is predominantly caused by the gradual death of retinal pigment epithelial cells (RPEs) and photoreceptors due to various causes. Cell-based therapies, such as stem cell implantation, have been developed for the treatment of RDD, but potential risks, including teratogenicity and immune reactions, have hampered their clinical application. Stem cell-derived extracellular vesicles (EVs) have recently emerged as a cell-free alternative therapeutic strategy; however, additional invasiveness and low yield of the stem cell extraction process is problematic.

METHODS

To overcome these limitations, we developed therapeutic EVs for the treatment of RDD which were extracted from tonsil-derived mesenchymal stem cells obtained from human tonsil tissue discarded as medical waste following tonsillectomy (T-MSC EVs). To verify the biocompatibility and cytoprotective effect of T-MSC EVs, we measured cell viability by co-culture with human RPE without or with toxic all-trans-retinal. To elucidate the cytoprotective mechanism of T-MSC EVs, we performed transcriptome sequencing using RNA extracted from RPEs. The in vivo protective effect of T-MSC EVs was evaluated using Pde6b gene knockout rats as an animal model of retinitis pigmentosa.

RESULTS

T-MSC EVs showed high biocompatibility and the human pigment epithelial cells were significantly protected in the presence of T-MSC EVs from the toxic effect of all-trans-retinal. In addition, T-MSC EVs showed a dose-dependent cell death-delaying effect in real-time quantification of cell death. Transcriptome sequencing analysis revealed that the efficient ability of T-MSC EVs to regulate intracellular oxidative stress may be one of the reasons explaining their excellent cytoprotective effect. Additionally, intravitreally injected T-MSC EVs had an inhibitory effect on the destruction of the outer nuclear layer in the Pde6b gene knockout rat.

CONCLUSIONS

Together, the results of this study indicate the preventive and therapeutic effects of T-MSC EVs during the initiation and development of retinal degeneration, which may be a beneficial alternative for the treatment of RDD.

A cell culture system to model pharmacokinetics using adjustable-volume perfused mixing chambers

The pharmacokinetic (PK) profile of a drug is an essential factor in determining its efficacy, yet it is often neglected during in vitro cell culture experiments. Here, we present a system in which standard well plate cultures may be "plugged in" and perfused with PK drug profiles. Timed drug boluses or infusions are passed through a mixing chamber that simulates the PK volume of distribution specific to the desired drug. The user-specified PK drug profile generated by the mixing chamber passes through the incubated well plate culture, exposing cells to in vivo-like PK drug dynamics. The effluent stream from the culture may then optionally be fractionated and collected by a fraction collector. This low-cost system requires no custom parts and perfuses up to six cultures in parallel. This paper demonstrates a range of PK profiles the system can produce using a tracer dye, describes how to find the correct mixing chamber volumes to mimic PK profiles of drugs of interest, and presents a study exploring the effects of differing PK exposure on a model of lymphoma treatment with chemotherapy.

Dynamics of Ex Vivo Mesenchymal Stromal Cell Potency under Continuous Perfusion

Mesenchymal stromal cells (MSCs) are a candidate for cell immunotherapy due to potent immunomodulatory activity found in their secretome. Though studies on their secreted substances have been reported, the time dynamics of MSC potency remain unclear. Herein, we report on the dynamics of MSC secretome potency in an ex vivo hollow fiber bioreactor using a continuous perfusion cell culture system that fractionated MSC-secreted factors over time. Time-resolved fractions of MSC-conditioned media were evaluated for potency by incubation with activated immune cells. Three studies were designed to characterize MSC potency under: (1) basal conditions, (2) in situ activation, and (3) pre-licensing. Results indicate that the MSC secretome is most potent in suppressing lymphocyte proliferation during the first 24 h and is further stabilized when MSCs are prelicensed with a cocktail of pro-inflammatory cytokines, IFNγ, TNFα, and IL-1β. The evaluation of temporal cell potency using this integrated bioreactor system can be useful in informing strategies to maximize MSC potency, minimize side effects, and allow greater control for the duration of ex vivo administration approaches.

Bioactive, full-length parathyroid hormone delivered using an adeno-associated viral vector

Delivering the parathyroid hormone (PTH) gene has been attempted preclinically in a handful of studies, but delivering full-length PTH (1-84) using adeno-associated viral (AAV) vectors has not. Given the difficulty in achieving therapeutic levels of secreted proteins using gene therapy, this study seeks to determine the feasibility of doing so with PTH. An AAV vector was used to deliver human PTH driven by a strong promoter. We demonstrate the ability to secrete full-length PTH from various cell types in vitro. PTH secretion from hepatocytes was measured over time and a fluorescent marker was used to compare the secretion rate of PTH in various cell types. Potency was measured by the ability of PTH to act on the PTH receptors of osteosarcoma cells and induced proliferation. PTH showed potency in vitro by inducing proliferation in two osteosarcoma cell lines. In vivo, AAV was administered systemically in immunocompromised mice which received xenografts of osteosarcoma cells. Animals that received the highest dose of AAV-PTH had higher liver and plasma concentrations of PTH. All dosing groups achieved measurable plasma concentrations of human PTH that were above the normal range. The high-dose group also had significantly larger tumors compared to control groups on the final day of the study. The tumors also showed dose-dependent differences in morphology. When looking at endocrine signaling and endogenous bone turnover, we observed a significant difference in tibial growth plate width in animals that received the high-dose AAV as well as dose-dependent changes in blood biomarkers related to PTH. This proof-of-concept study shows promise for further exploration of an AAV gene therapy to deliver full-length PTH for hypoparathyroidism. Additional investigation will determine efficacy in a disease model, but data shown establish bioactivity in well-established models of osteosarcoma.

Multi-Stream Perfusion Bioreactor Integrated with Outlet Fractionation for Dynamic Cell Culture

Certain cell and tissue functions operate within the dynamic time scale of minutes to hours that are poorly resolved by conventional culture systems. This work has developed a low-cost perfusion bioreactor system that allows culture medium to be continuously perfused into a cell culture module and fractionated in a downstream module to measure dynamics on this scale. The system is constructed almost entirely from commercially available parts and can be parallelized to conduct independent experiments in conventional multi-well cell culture plates simultaneously. This video article demonstrates how to assemble the base setup, which requires only a single multichannel syringe pump and a modified fraction collector to perfuse up to six cultures in parallel. Useful variants on the modular design are also presented that allow for controlled stimulation dynamics, such as solute pulses or pharmacokinetic-like profiles. Importantly, as solute signals travel through the system, they are distorted due to solute dispersion. Furthermore, a method for measuring the residence time distributions (RTDs) of the components of the perfusion setup with a tracer using MATLAB is described. RTDs are useful to calculate how solute signals are distorted by the flow in the multi-compartment system. This system is highly robust and reproducible, so basic researchers can easily adopt it without the need for specialized fabrication facilities.