Expansion and differentiation of ex vivo cultured erythroblasts in scalable stirred bioreactors

Transfusion of donor-derived red blood cells (RBCs) is the most common form of cell therapy. Production of transfusion-ready cultured RBCs (cRBCs) is a promising replacement for the current, fully donor-dependent therapy. A single transfusion unit, however, contains 2 × 10¹² RBC, which requires large scale production. Here, we report on the scale-up of cRBC production from static cultures of erythroblasts to 3 L stirred tank bioreactors, and identify the effect of operating conditions on the efficiency of the process. Oxygen requirement of proliferating erythroblasts (0.55-2.01 pg/cell/h) required sparging of air to maintain the dissolved oxygen concentration at the tested setpoint (2.88 mg O₂ /L). Erythroblasts could be cultured at dissolved oxygen concentrations as low as 0.7 O₂ mg/ml without negative impact on proliferation, viability or differentiation dynamics. Stirring speeds of up to 600 rpm supported erythroblast proliferation, while 1800 rpm led to a transient halt in growth and accelerated differentiation followed by a recovery after 5 days of culture. Erythroblasts differentiated in bioreactors, with final enucleation levels and hemoglobin content similar to parallel cultures under static conditions.

The Effect of Catabolite Concentration on the Viability and Functions of Isolated Rat Hepatocytes

The treatment of patients with hepatic failure by means of hybrid liver support devices using primary xenogeneic hepatocytes is currently hindered by the rapid loss of cell metabolic functions. Similarly to what happens with other mammalian cells, accumulation of catabolites in the neighborhood of cultured hepatocytes might significantly affect their viability and functions. In this paper, we investigated the effects of high concentrations of catabolites, such as ammonia and lactic acid, on the viability and functions of rat hepatocytes cultured on collagen coated Petri dishes. The effects on hepatocyte functions were established with respect to their ability to synthesize urea and to eliminate ammonia. Indeed, high catabolite concentrations effected both hepatocyte viability and functions. The number of viable hepatocytes decreased with increasing ammonia concentrations in the culture medium. High ammonia concentrations had also both an inhibitory and a toxic effect on hepatocyte functions. In fact, the hepatocytes synthesized urea and eliminated ammonia at rates that decreased with increasing ammonia concentrations. Similarly, high lactic acid concentrations were toxic to the cells and also inhibited their synthetic functions.

Mass Transfer Limitations to the Performance of Membrane Bioartificial Liver Support Devices

A number of membrane bioartificial devices have been proposed for liver support. However, their design does not yet ensure the successful treatment of acute liver insufficiency. In this paper, the Author reviews the limitations of the mass transport phenomena to the performance of a membrane bioartificial liver support device. First of all the requirements that an optimal membrane bioartificial liver support device has to meet for the therapy to be effective are presented. On these grounds, the issues that are still to be addressed to optimize the performance of such devices are discussed: particular attention is devoted to the mass transport phenomena in each region of the membrane bioartificial device. Finally, the main transport features of the membrane bioartificial liver support devices proposed so far are illustrated and examined.

The Effect of Oxygen Transport Resistances on the Viability and Functions of Isolated Rat Hepatocytes

The treatment of fulminant hepatic failure with a bioartificial liver support device relies on the possibility of replacing the detoxification and synthetic functions of the injured liver for as long as needed for patient recovery. In spite of progress in cell culture techniques, the effective use of isolated hepatocytes in liver support devices is currently hampered by a lack of information on the metabolic factors limiting long term hepatocyte culture. In this paper, we report our investigation on the effects of oxygen transport resistances on the viability and functions of isolated rat hepatocytes cultured on collagen coated Petri dishes. Detoxification and synthetic functions of the hepatocytes were studied with respect to ammonia and phenolsulphonphthalein elimination and urea synthesis. Lower resistances to oxygen transport favored hepatocyte survival. The isolated hepatocytes synthesized urea at rates that decreased as the resistance to oxygen transport increased. The rate at which urea was synthesized also decreased during the culture. Neither PSP, nor ammonia elimination rate was greatly affected by increasing oxygen transport resistances and remained rather constant up to a week of culture.

Heat and Mass Transfer during the Cryopreservation of a Bioartificial Liver Device: A Computational Model

Bioartificial liver devices (BALs) have proven to be an effective bridge to transplantation for cases of acute liver failure. Enabling the long-term storage of these devices using a method such as cryopreservation will ensure their easy off the shelf availability. To date, cryopreservation of liver cells has been attempted for both single cells and sandwich cultures. This study presents the potential of using computational modeling to help develop a cryopreservation protocol for storing the three dimensional BAL: Hepatassist. The focus is upon determining the thermal and concentration profiles as the BAL is cooled from 37 degrees C-100 degrees C, and is completed in two steps: a cryoprotectant loading step and a phase change step. The results indicate that, for the loading step, mass transfer controls the duration of the protocol, whereas for the phase change step, when mass transfer is assumed negligible, the latent heat released during freezing is the control factor. The cryoprotocol that is ultimately proposed considers time, cooling rate, and the temperature gradients that the cellular space is exposed to during cooling. To our knowledge, this study is the first reported effort toward designing an effective protocol for the cryopreservation of a three-dimensional BAL device.

Immobilized mammalian cell cultivation in hollow fiber bioreactors

Cultivation of animal cells for the production of recombinant proteins is an important method for manufacturing complex proteins requiring posttranslational processing. One of the often considered methods for cultivation is by immobilization of the cells in hollow fiber bioreactors (HFBRs). These systems allow the cells to grow to high densities in a shear protected environment; furthermore the product can be accumulated in high concentration in the case of ultrafiltration HFBRs. Operation and scale-up are constrained by nutrient and product transport with oxygen transfer to growing cells being the most critical parameter. Mathematical models describing HFBRs have proved to be useful in quantitating and understanding the constraints and guiding the scale-up of this approach to animal cell cultivation.

Extracellular pH affects the proliferation of cultured human T cells and their expression of the interleukin-2 receptor

Ex vivo expansion of T cells is an important aspect of many cellular immunotherapy protocols, and the effects of the culture environment on the cells must be understood to produce large numbers of functional cells. Extracellular pH is a fundamental parameter that has many different effects on cultured cells. In this study, peripheral blood mononuclear cells were stimulated with phytohemagglutinin and cultured at pH values of 7.0, 7.2, or 7.4. The effects of pH on the cells were studied during the 2 to 3 weeks of proliferation resulting from phytohemagglutinin stimulation, in order to examine the culture kinetics over realistic time scales for ex vivo expansion. The proliferation capacity of the T cells increased more than three-fold for the pH 7.0 and 7.2 cultures compared with the pH 7.4 cultures. The culture pH also affected the kinetics of the interleukin-2 receptor down-regulation process. The faster receptor down-regulation in both the pH 7.2 and 7.4 cultures resulted in a more than twofold greater fraction of interleukin-2 receptor(+) cells in the pH 7.0 cultures. Although the fraction of apoptotic cells (using the Annexin V flow-cytometric method) remained less than 10%, we observed 27% more apoptosis in the pH 7.4 cultures than in the 7.2 cultures and 49% more apoptosis in the pH 7.4 cultures than in the 7.0 cultures. These effects on interleukin-2 receptor expression and cellular apoptosis may partially explain the observed effects of pH on T-cell proliferation.

Use of micropathways to improve oxygen transport in a hepatic system

Establishing suitable oxygen transport pathways within bioartificial liver replacement devices continues to be an important engineering challenge. Oxygen delivery is critical since this is one of the nutrients necessary to maintain hepatocyte viability and function. In the current study, the microporosity of a collagen extracellular matrix has been modified to permit both diffusion and convection mass transport. Using fluorescent visualization, the enhancement technique was found to extend the oxygen transport distance from 170 microns to 360 microns. Furthermore, in hepatocyte culture studies, the enhancement technique was observed to yield a sixfold increase in the amount of viable hepatocytes able to be sustained by a single O2 source. Normalized function studies confirm that hepatocyte function was also improved in the enhanced collagen configurations.

Calcium alginate immobilized hybridomas grown using a fluidized-bed perfusion system with a protein-free medium

Hybridoma SPO1 cells were immobilized in calcium alginate beads and were further grown in a fluidized-bed perfusion system with a protein-free medium. The presence of serum in the steps of entrapment was shown to be helpful for the preservation of cell viability. Each step during immobilization was investigated with respect to the extent of cell damage caused. The immobilization process using small beads caused a lower cell viability initially but allowed a higher rate of cell growth subsequently, compared to those in large beads. In a perfusion system for the continuous production of monoclonal antibodies (MAb), the viable cell density reached 2 x 10(7) cells per ml of beads with a viability of 40%. Compared with the cells in suspension culture, the immobilized SPO1 cells showed higher viable cell based specific rates of substrate uptake (glucose and glutamine) and of MAb production. A significant drop in the formation of lactate after the cell growth entered a steady state suggested a higher activity of the Tricarboxylic Acid Cycle in the cells when the cell density became high.

Mammalian cell culture processes

Over the past year, mammalian cell culture research has been aimed at investigating the influence of culture conditions on viability, productivity and the consistency of post-translational modifications. Studies of the effect of medium conditions and the development of kinetic models are being made in relation to current efforts to develop fed-batch strategies that will optimize recombinant protein production processes. Recent advances have included novel biosensor and bioreactor developments. New technologies have also been applied to investigate high cell density bioreactor and culture conditions.