1. Introduction
Mesenchymal stem cells (MSCs) possess excellent therapeutic properties,
including the ability to exert anti-inflammatory and immunosuppressive
effects and to differentiate into tissue-specific
cells.[1] In addition, MSCs are self-proliferating
and can be prepared on a large scale after isolation from a variety of
tissues.[2,3] Based on these superior features,
MSCs have been used in the treatment of graft-versus-host
disease,[4] autoimmune
diseases,[5] and inflammatory
diseases.[6] Although the therapeutic usefulness
of MSC transplantation in patients with these diseases has been
demonstrated in some cases, many studies have revealed that the survival
rate and duration of MSCs after transplantation are extremely low and
short, respectively.[7] Therefore, it is necessary
to increase the survival of administered MSCs for more efficient
MSC-based therapy.
Multicellular spheroids, which are three-dimensional cultured cell
aggregates, are highly functionalized cells, because spheroid formation
generally increases cellular function through extensive cell–cell
interactions.[8] It has been reported that
spheroid formation upregulates the expression of transporters in cancer
cells.[9] Therefore, cancer cell spheroids have
been used to screen for bioactive compounds, including anticancer
agents. In addition, Bartosh et al. reported that multicellular
spheroids derived from MSCs secrete large amounts of anti-inflammatory
cytokines.[10] Additionally, our previous studies
using poly(N-isopropylacrylamide)-coated polydimethylsiloxane-based
microwell plates showed that spheroid formation improved the survival of
mouse insulinoma NIT-1 cells after transplantation in
mice,[11] enhanced albumin secretion from human
hepatoblastoma HepG2 cells,[12] and forcibly
polarized mouse macrophage-like J774.1 cells to M1-type macrophages with
tumoricidal activity.[13] Furthermore, we
demonstrated that compared to suspended mouse adenocarcinoma colon26
cells, multicellular spheroids of colon26 cells efficiently accumulated
in the lung after intravenous injection in mice and established
pulmonary tumor colonies.[14] Therefore, we
hypothesized that spheroid formation could increase the survival of MSCs
after intravenous injection and improve their therapeutic effects in
lung diseases.
Here, we investigated the survival and function of MSC spheroids after
intravenous injection in mice. First, the murine adipose-derived MSC
line m17.ASC transfected with NanoLuc luciferase (NLuc) was cultured in
agarose-based microwell plates to obtain size-controlled m17.ASC
spheroids. Thereafter, tissue distribution was evaluated by measuring
NLuc activity after intravenous injection of m17.ASC spheroids or
suspended m17.ASC cells. Finally, the anti-inflammatory effect of
suspended m17.ASC cells or m17.ASC spheroids was evaluated in a
lipopolysaccharide (LPS)-induced inflammatory mouse model.