( ...)Principles and applications of electrical cell fusion

Kurt Lucas, Eppendorf AG

Significance of cell fusion

Electrical cell fusion is an essential step in some of the most innovative methods in modern biology, such as the production of monoclonal antibodies, the cloning of mammals, and vaccination against cancer. Compared to the chemically induced cell fusion via polyethylene glycol (PEG), electrical cell fusion is a highly efficient method.
The process was discovered in 1978 by Zimmermann [1-3], who has initiated ongoing development ever since.

The principle of electrical cell fusion

First, the cells are brought into very close contact via dielectrophoresis. Unlike electrophoresis, in which direct current is applied in order to move molecules, dielectrophoresis uses highfrequency alternating current. In particles such as living cells, dipoles are induced which cause cells to align in such a way that they resemble a string of pearls which are in very close contact with each other.

A very short high-voltage pulse is then applied, which causes permeation of the cell membrane and the subsequent combining of the membranes. The cells then fuse. In order to stabilize the process, alternating voltage is then applied for a brief period.

The resulting formation is described as a heterokaryon because, although the outer cell membrane has fused, two or more cell nuclei are still present. The cell nuclei also fuse at a later point within the cell. In most cases, this results in a drastic reduction in the number of chromosomes in the nucleus.

Producing monoclonal antibodies

Traceable to G. Khler and C. Milstein [4], this method revolutionized the production of antibodies. Primary B lymphocytes, which produce a specific antibody, are fused with tumor cells.

The numerous fusion products are isolated and selected. These single cells are replicated as clones, which is why the term monoclonal is used.

The fusion products, described as hybridoma, stand out for two reasons: they secrete a specific antibody and they can be replicated in culture almost infinitely. This has enabled mass production of specific antibodies.

For these achievements, G. Khler, C. Milstein, and N. K. Jerne were awarded the Nobel Prize for Medicine in 1984.

Cloning mammals

The famous case of Dolly, the cloned sheep [5], would not have been possible without cell fusion. The first step in mammalian cloning is the removal of the nucleus from an oocyte. This enucleated oocyte is then fused with a somatic cell (e.g. from connective tissue). This is carried out by using electrical cell fusion because it is the only method efficient enough to produce the desired result.

The fusion product is implanted into a surrogate mother and is then carried through the full gestation period.

Cloning mammals from embryonic cells was carried out as long ago as the late 1980s [6 -10] and aroused little public interest at the time.

Vaccination against cancer

The results of Vaccination against cancer [11], which have recently been the subject of extensive press coverage, were only possible as a result of cell fusion. In this process, tumor cells from a patient are fused with dendritic cells (DC). The dendritic cells belong to the antigen-presenting cells (APC) of the immune system. Their function is to activate T-cells, which then act specifically against the tumor cells.

The fusion product of the tumor cell and the dendritic cell is irradiated. The cell survives but cannot divide after irradiation. The patient is then injected with these dendritic cells. In this way, the patient's own T-cells are activated. These T-cells attack the metastases and, in many cases, cause their disintegration, reduction, or stagnation.

This method was recently tested on patients for the first time and the initial results are extremely promising.

Multiporator now with cell fusion

Eppendorf now offers electrical cell fusion as another option available on the Multiporator. Developed in cooperation with Professor U. Zimmermann, this device is ideal for the electrofusion of eukaryotes and plant cells.

Depending upon the chosen configuration, it is also possible to electroporate prokaryotes and yeasts, and/or eukaryotic cells. The new Fusion module consists of the following components: the micro fusion chamber and the helix fusion chamber.

Micro fusion chamber The micro fusion chamber (Figs. 4) is used to optimize the parameters for alignment and fusion pulse. This is monitored directly under the microscope. Small numbers of cells (20 50 l) can be fused directly in the micro fusion chamber. Helix fusion chamber

Large numbers of cells (in volumes up to 250 l) can be fused in the helix fusion chamber (Fig. 5).

The parameters obtained using the micro fusion chamber can be transferred directly.

This system thus represents a unique opportunity for simple scaling-up.

Fig. 5: The helix fusion chamber can be used to fuse large numbers of cells (in volumes up to 250 l) simultaneously. Support The Multiporator is the most compact, flexible electromanipulation device on the market. For help in the development of new applications, please contact our Hotline and our team of application specialists. Send your e-mails to: bioapps@brinkmann.com Bibliography

[1] Zimmermann, U., Pilwat, G. The relevance of electric field induced changes in the membrane structure to basic membrane research and clinical therapeutics and diagnosis. In , Kyoto, Japan, 140, 1978. Abstract IV-19-(H) of the 6th International Biophysics Congress

[2] Zimmermann, U., Vienken, J., Scheurich, P., Electric field induced fusion of biological cells. Biophys. Struct. Mech., 1980, 6 (Suppl.), 86.

[3] Zimmermann, U., Vienken, J., Pilwat, G., Development of drug carrier systems: electrical field induced effects in cell membranes. Bioelectrochem. Bioenerg., 1980, 7, 553.

[4] Khler. G., Milstein, C., Continuous cultures of fused cells secreting antibody of predefined specificity. Nature, 1975, Aug 7; 256 (5517): 495-497.

[5] Wilmut, I., Schnieke, A.E., McWhir, J., Kind, A.J., Campbell, K.H., Viable offspring derived from fetal and adult mammalian cells. Nature, 1997, Feb 27; 385 (6619): 810-813.

[6] Willadsen, S.M., Nuclear transplantation in sheep embryos. Nature , 1986, 320, 63.

[7] Prather, R.S., Barnes, F.L., Sims, M.M., Robl, J.M., Eyestone, W.H., First, N.L., Nuclear transplantation in the bovine embryo: assessment of donor nuclei and recipient oocyte, Biol. Reprod., 1987, 37, 859.

[8] Barnes, F.L., Prather, R.S., Robl, J.M., First, N.L., Multiplication of bovine embryos. Theriogenology, 1987, 27, 209.

[9] McLaughlin, K.J., Davies, L., Seamark, R.F., embryo culture in the production of identical merino lambs by nuclear transplantation, Reprod. Fertil. Dev., 1990, 2, 619. In vitro Reprod. Fertil. Dev

[10] Todorov, J., Todorova, T., Zimmermann, U., Arnold, W.M., Leiding, C., Hahn, R., Hahn, J., Geklontes Kalb in Neustadt geboren, Reprod. Dom. Anim., 1992, 27, 307.

[11] Kugler, A., Stuhler, G., Walden, P., Zller, G., Zobywalski, A., Brossart, P., Trefzer, U., Ullrich, S., Mller, C.A., Becker, V., Gross, A.J., Hemmerlein, B., Kanz, L., Mller, G.A., Ringert, R.-H., Regression of human metastatic renal cell carcinoma after vaccination with tumor cell-dendritic cell hybrids. Nature Medicine, 2000, Vol. 6, No. 3, 332-336.

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