Cell News 3/2013
18
RESEARCH NEWS
dually addressable tools for negative dielectrophoresis (nDEP)
and fusion, while the microfluidics deliver the different cell
types and transfer them into the fusion buffer immediately be-
fore fusion (Figure 3).
A hypoosmotic buffer is the prerequisite for electrofusion.
However, it strongly impacts cell viability in a manner depen-
dent on the duration of exposure (21-22). Therefore, we de-
signed a microfluidic system which is able to transport both
starting populations separately in their own culture medium
flowing laminarly in parallel to the fusion buffer. One cell of
each type is selected individually by deflection electrodes,
transferred into the fusion buffer and moved to the site of
fusion, i. e. the field cage (21). Inside the cage (DFC), nega-
tive dielectrophoresis (nDEP) serves to maximally press the
cells together with a radiofrequency signal. Then, fusion is in-
duced by applying a microsecond dc pulse or a 1 ms pulse train
of 12 kHz as has been suggested earlier (23). The cell models
used were human Jurkat lymphocytes and U-937 monocytes as
well as pairs of murine B cells and P3X myeloma cells, as they
are commonly employed for antibody production. The fusion
yield for the latter cell system reached 40% when up to four ac
bursts were applied. The possibility to closely define the expe-
rimental conditions allowed us to directly correlate the fate of
the single fusion products with the parameters of the handling
and fusion process. Due to the highly controlled cell trapping
and release from the field cage (DFC), the fusion products AB
could be collected individually in titer plates for continuous
analysis of their viability as well as proliferation. As mentioned
above, both properties are not equivalent. While most fused
cells survived over prolonged time frames, i. e. maintained their
membrane integrity for days and weeks, only 20% showed any
proliferation. In most of these cases, the clones died after one
ore two cell divisions, presumably because aneuploidies and
other biological aberrations accumulated to an unacceptable
level. In consequence, only very few fusion products prolife-
rated sufficiently to being expanded. In ongoing experiments,
the pulse parameters, e. g. frequency, electric field strength,
duration, will be further optimized to enhance the cell vitality
of the fusion products. The microfluidic nature of the approach
also allows for enhancing the throughput by parallelization.
Taken together, the well-controlled process of cell pairing and
the high fusion efficiency makes the described system a pro-
mising tool especially for the fusion of rare and valuable cells,
like purified primary cells or stem cells.
Acknowledgement
Richard A. Kroczek’s invaluable advice and help is gratefully acknowledged (Robert Koch
Institute, Berlin). Financial support was received from the DFG in the project Fu 345 / 12-1.
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Fraunhofer Institute for Biomedical Engineering (IBMT), Am Muehlenberg 13, 14476 Pots-
dam, Germany
Correspondence to: Magnus Jaeger,
