'Cryogel' bioreactor pumps out antibodies continuously

The new bioreactor is described in an early view article in the journal Biotechnology Progress and appears to be based upon the macroporous gel bioseparation technology developed by Protista which helped fund the research.

The new device uses a supermacroporous polyacrylamide gel, dubbed cryogel, as a matrix support for the cultivation of mouse hybridoma cells which has a continuous network of interconnected pores that allows the unhindered transport of solutes "The major advantage of the cryogel column is that it can be used as a disposable bioreactor for process development of monoclonal antibodies," write the researchers.

"In addition, it represents a completely new supporting material that is inexpensive and easy to handle."

mAbs are currently the largest class of proteins either in clinical trials or already having received FDA (US Food and Drug Administration) approval with US sales predicted to top $16bn (€12bn) by 2010 according to the paper's authors.

The growing demand for such therapeutics is already stretching the capacity of large-scale manufacturing techniques that currently involve either in vivo cultivation in mice or rabbits or in vitro cell culture flasks or bioreactors.

Recently, Integra Biosciences released the CELLine 1000 that supports a high cell density and can generate a much higher concentration of mAbs (up to 2.5mg/l) within a period of 2 months.

However, these devices can only produce up to 2l of culture per batch due to limited oxygen-transfer capabilities.

Larger scale bioreactors often suffer when used with the hybridoma cell culture suspensions needed as the cells are sensitive to shear and bubble damage, and this is where using cell cultures immobilised in a 'cryogel' may be advantagous.

The researchers evaluated the performance of the cryogel columns for long-term continuous mAb production using the M2139 cell line that produces IgG2b antibodies that induce arthritis in DBA/1 mice.

The hybridoma cells were immobilised into the cryogel by leaving them to stand in the column for 48 hours.

Culture medium was then circulated through the column at a rate of 02.ml/min for 36 days and the concentrations of lactate, mAb and glucose continuously monitored.

During the first 14 days the glucose uptake and lactic acid production remained constant, thereafter glucose consumption decreased while the lactic acid and mAb production increased.

After 36 days of circulation the glucose content dropped to 10mM and the mAb concentration reached 130ug/ml.

mAb production reached 6.5ug/ml during the exponential growth period which equates to a total concentration of 67.5mg/l after purification - three times greater than the amount of mAb obtained from T-flask batch cultivation.

The efficacy of the mAbs was tested using ELISA (enzyme-linked immunosorbent assay) as well as experiments in mice that showed the cryogel-produced mAbs did not differ from antibodies produced from cells grown in CELLine 1000 flasks.

The researchers write: "the cryogel reactor performance may be further improved, particularly by increasing oxygen transfer in the cryogel matrices, removing toxic metabolic products from the system and improving the capacity of the gel for long-term cultivation."