Advanced Methods of Adenovirus Vector Production for Human Gene Therapy: Roller Bottles, Microcarriers, and Hollow Fibers
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2868B_Domstc 11/14/03 1:50 PM Page 75 CONFERENCE EXCLUSIVE Advanced Methods of Adenovirus Vector Production for Human Gene Therapy: Roller Bottles, Microcarriers, and Hollow Fibers BY TATYANA ISAYEVA, ovirus, poxvirus, adeno-associated respect to cell culture optimization and OLGA KOTOVA, virus, and herpesvirus vectors) aden- the virus propagation protocols oviruses exhibit the lowest pathogenici- employed in vector production. In this VICTOR KRASNYKH, ty yet still infect an extensive range of regard, the development of innovative and ALEXANDER KOTOV cell types with high efficiency. These cell culture techniques has become vital key characteristics make recombinant for optimizing vector production for adenoviruses efficient gene-delivery gene therapy. vehicles and excellent research tools. This article summarizes our testing arious types of viral vectors However, the time-consuming and of three different large-scale cell cultiva- are being employed exten- complex processes of generation, ampli- tion systems to produce two adenoviral sively as gene therapeutics fication, purification, and quality test- vectors, with the goal of developing the to treat cancer and genetic ing associated with production of most productive, reproducible, cost- diseases. Among the viruses recombinant adenoviruses make it diffi- effective, and scientifically sound man- Vthat have been produced for human cult for many researchers to utilize these ufacturing system. clinical trials (i.e. retrovirus, aden- vectors. This is particularly true with Table 1. Comparative yield of HEK 293 cells in different culture systems Total cell yield, x 106 Experiment Per T-flask Per Triple Nunc Per Roller Bottle Per 3-Liter ## 1-8 (175 sq cm) flask (500 sq cm) (850 sq cm) µ−carrier culture Average ± st dev 52 ± 3 120 ± 10 214 ± 18 4,605 ± 364 Microcarrier yield equivalent 90 39 21 1 (number of units) Working volume 50 mL 100 mL 200 mL 3000 mL Total volume 4500 mL 3900 mL 4200 mL 3000 mL Tatyana Isayeva, M.D., Ph.D. is a research associate in the department of pathology and Olga Kotova, M.D. is a research assis- tant in the division of human gene therapy, University of Alabama at Birmingham, Birmingham, AL. Victor Krasnykh, Ph.D. is an associate professor in the department of experimental diagnostic imaging, MD Anderson Cancer Center, University of Texas, Houston, TX. Corresponding author Alexander Kotov, M.D., Ph.D. ([email protected]) is the program director in the vector & vaccine production facility, University of Alabama at Birmingham, Birmingham, AL. www.bioprocessingjournal.com • September/October 2003 75 2868B_Domstc 11/14/03 1:50 PM Page 76 Materials and Methods and characterization of the ARM tion). Two adenoviral vectors, Ad5.Luc is available at The Williamsburg and Ad5.GFP, encoding either luciferase Cells and Viruses BioProcessing Foundation website, or green fluorescent protein, respective- The human embryonic kidney 293 www.wilbio.com. The cells were main- ly, were used in the virus production (HEK 293) cell line was used to propa- tained in DMEM: Ham’s F-12 (50:50 optimization experiments. gate adenovirus type 5 (Ad5)-based mix) medium supplemented with 10% recombinant vectors. Five vials of mas- fetal bovine serum (FBS) and 4 mM L- Cell Counting ter cell bank (MCB) HEK 293 cells Glutamine. Confluent cultures of HEK Infected cells were harvested from (Magenta Corporation, Rockville, MD) 293 cells were infected with the virus at the culture vessel (such as a flask or were used to generate the Working Cell a multiplicity of infection (MOI) of 100 roller bottle) and counted in a hemocy- Bank (WCB). Upon characterization, viral particles per cell, at which point tometer. Cell viability was determined the cells were accepted by the the growth medium was replaced with by trypan blue exclusion. In the micro- Adenovirus Reference Material Working the medium containing 2.5% FBS. carrier experiments, a simpler way of Group as a cell bank for the Adenovirus Infected cells were incubated until a monitoring cell growth was to count the Reference Material (ARM) project.1 All cytopathic effect (CPE) was observed released nuclei as originally described information regarding the development (typically 48 to 72 hours post-infec- by Sanford et al. with modifications by van Wezel.2,7 Specifically, cells grown on microcarriers were incubated in a hypotonic solution of citric acid and the nuclei released by lysis were stained with 0.1% w/v crystal violet, followed by enumeration in a hemocytometer. At least 100 cells (or nuclei) were counted for each time point, with these counts being performed in quadruplicate for each cell density data point. Cell Lysis, Virus Purification, and Analysis Once CPE developed, the cells were harvested and resuspended in the con- ditioned medium in a volume repre- senting 5% to 10% of the volume of cul- Microcarrier concentration, mg/mL tivation medium. The cells were then freeze/thawed three times in dry Figure 1. Effect of microcarrier concentration on final cell density ice/ethanol bath, cell debris was removed by centrifugation, and the clarified lysate was treated with sterile Benzonase enzyme at 50 U/ml for 30 minutes at room temperature to digest cellular DNA. The supernatant was lay- ered onto a preformed step gradient of CsCl with a density range of 1.4 to 1.25 g/ml and centrifuged at 23,000 rpm for 90 minutes at 4° C in a Beckman SW28 rotor (Beckman Coulter, Inc., Fullerton, CA). Banded virus was collected, dilut- ed twice with 10mM Tris-HCl, pH 8.0, 2mM MgCl2 and purified by equilibri- um centrifugation in the same CsCl gra- dient once more. The virus was dialyzed against 10mM Tris-HCl, pH8.0, 2mM MgCl2 , 10% glycerol and stored at –80º C. The virus’ physical and infectious titers were determined according to Figure 2. Effect of starting cell/bead ratio on final cell density of HEK 293 cells in microcarrier standard operating procedures (SOPs), culture established at the University of Alabama 76 BioProcessing Journal • September/October 2003 2868B_Domstc 11/14/03 1:50 PM Page 77 at Birmingham (UAB) vector and vaccine production facility. The concentration of adenoviral particles in purified preparation of virus was measured by UV spectrophotometry at 260 nm. The infectious titer method used CPE that adenoviruses have on cells as the read- out to detect infection in HEK 293 cells 10 days post-infection with an adenovirus sample (tissue culture infectious dose, TCID-50 assay). Both optical density at 260 nm and the TCID-50 protocols were adapted from ARM SOPs. Virus Propagation The cells were propagated and aden- ovirus vectors were produced in 500- cm2 triple flasks (Nalge Nunc International, Rochester, NY) that were placed in a regular CO2 incubator, 850- cm2 roller bottles (Corning Incorporated, Figure 3. 3-liter Cell Optimizer System (Wheaton) with microcarriers Acton, MA) at 0.25 rpm, and in two condition-controlled systems. One of filtration rate, thereby improving cell the most economical in terms of media these was the 3-L Cell Optimizer System viability. This design allows the cells to costs. (Wheaton Science Products, Millville, grow on and around the fibers to At this point in the study, we NJ) that was employed with Cytodex 3 extremely high densities or more than employed roller bottles as a standard microcarriers (Amersham Biosciences, 108 cells/ml. A typical system consists technique for vector production with Piscataway, NJ). Cell growth and virus of a microprocessor-controlled pump, a good results. While scaling up the pro- propagation in the Cell Optimizer medium reservoir, and a cartridge. duction process, our concerns were: System took place in a spinner flask The microprocessor-controlled pump improved control of culture parameters with four side arms. The system’s assembly allows control of pressure (pH and gas tensions, for example), Control Tower and Support Unit auto- wave shape and provides flexible control reduced requirements for labor, and matically controlled pH via addition of options. The system’s positive-pressure lower risk of contamination, all benefits sodium bicarbonate and CO2, whereas displacement pumping system ensures of microcarrier culture. Although the dissolved oxygen was adjusted with long cartridge life and facilitates nutri- microcarrier culture is an advanced airflow. The volumetric airflow rate was ent and waste exchange across the fiber. technique, it is based on prior knowl- from 4 to 10 liters per liquid liter per edge of a cell type’s growth characteris- hour throughout the production cycle. Results tics. Information about cell morpholo- Temperature was maintained with a gy, plating efficiency, and other growth heating pad, which eliminated the need Before proceeding to virus produc- properties in traditional monolayer cul- for an incubator. The system’s BIOPRO tion, preliminary experiments to deter- ture is invaluable when optimizing cell software provided the data acquisition mine the yield of the HEK 293 cells in propagation on microcarriers. In this capability for the controller and records each propagation system were per- regard, the most efficient technique storage. formed. The cells were maintained as ensures maximum attachment of the The other system used was the described in the Materials and Methods cell inoculum to the microcarriers and FiberCell Hollow Fiber Cell Culture section. Table 1 shows the average total results in a rapid, homogeneous growth System (Bellco Glass, Inc., Vineland, yield in each system type (in million of cells to the highest possible density. NJ). Hollow fibers are relatively new cells) after 72 hours of cultivation. The To determine such a technique, sev- tools in cell cultivation that allow data was calculated based on eight inde- eral optimization experiments were designing compact systems.3 Potted pendent measurements after harvesting performed. Figure 1 shows the effect of at both ends with medical-grade cells from each cell propagation system. microcarrier concentration on the final polyurethane, these hollow fiber filters These results indicate that the same cell density.