  Background These last decades have seen the emergence and development of
cell-based therapies, notably those based on mesenchymal stromal cells (MSCs).
The advancement of these promising treatments requires increasing the
throughput of processed cell for industrialization in order to reduce
production costs. Among the various bioproduction challenges, downstream
processing (DSP), including medium exchange, cell washing, cell harvesting and
volume reduction, remains a critical step on which improvements are needed.
Typically, these processes are performed by centrifugation. However, this
approach limits the automation, especially in small batch productions where it
is performed manually in open system. Methods An acoustophoresis-based system
was developed for cell washing. The cells were transferred from one stream to
another via the acoustic forces and were collected in a different medium. The
optimal flow rates of the different streams were assessed using Red Blood Cells
(RBCs) suspended in an albumin solution. Finally, the impact of acoustic
washing on adipose tissue-derived MSCs (AD-MSCs) transcriptome was investigated
by RNA-sequencing. Results With a single passage through the acoustic device at
input flow rate of 45 mL/h, the albumin removal was up to 90% while recovering
99% of RBCs. To further increase the protein removal, a loop washing in two
steps was performed and has allowed an albumin removal $\ge$99% and a
RBCs/AD-MSCs recovery of 99%. After loop washing of AD-MSCs, only 2 genes, HES4
and MIR-3648-1, were differently expressed compared to the input. Conclusion In
this study, we developed a continuous cell washing system based on
acoustophoresis. The process allows a high cell throughput while inducing
little gene expression changes. These results highly suggest that cell washing
based on acoustophoresis is a relevant and promising solution for numerous
applications in cell manufacturing.
