Table 4 Strategies for increasing MSCs immunomodulatory potential and their impact on ICPs and ICPLs expression

Preconditioning

Small molecule and pharmacological priming

Advantage

1. Inexpensive and simple methodology

2. Wide availability of GMP compounds

Disadvantage

1. Possible off-target effects on MSC

2. Risk of mutagenesis

Not investigated

Desferrioxamine

1. ↓ Mitochondrial activity

2. Apoptosis of MSCs

[276]

Dimethyloxalylglycine

1. ↑ HIF-1α, VEGF production

2. ↑ MSC survival

[277]

Anesthetic isofurane

1. ↑ SDF-1, HIF-1α, and CXCR4 production

2. MSC survival

[278]

All-trans retinoic acid

1. ↑ COX-2, VEGF, HIF-1α, CCR2, CXCR4, and Ang-2 production

2. ↑ Rat wound healing

3. ↑ IL-6 secretion

4. ↓ Th17 differentiation

5. ↓ TNF-α and IFN-γ production

[279, 280]

Rapamycin

1. ↑ COX-2 and PGE2

2. ↓ IFN-γ induced MHC-II on MSCs

[281]

Inhibit Gal-9 secretion from MSCs

α-lactose

↑ T cells proliferation and differentiation to Th1 and Th17 compared to intact MSCs

[228]

Cytokine priming

Advantage

↑ Immunomodulatory potential

Disadvantage

1. Heterogeneity within batches due to culturing and isolation methods

2. Large-scale production safety

↑ PD-L1 expression synergistically in combination with IFN-γ

Pretreat with TNF-α

1. ↓ IL-1β, IL-18 and IL-6 from Kupffer cells in coculture system

2. ↓ AST and ALT in transplantation for liver disease

3. Inhibits the activation of NLRP3 in macrophage

[180, 282]

↑ ICOSL expression

Pretreat with IL-1β

1. ↑ COX-2, IL-6 and IL-8 expression

2. ↑ CXCR4 expression and migration ability

3. ↑ Secretion of G-CSF

[283, 284]

Not investigated

Stimulate with IL-6

1. ↑ miR-455-3p in MSC-exosomes

2. ↑ PI3K signaling pathway mediated inhibition macrophage activation

[285]

1. ↑ PD-L1 experssion

2.↑ Secretion of sEV-PD-L1 from MSCs

3. ↑ Production of soluble Gal-9

Pretreat with IFN-γ

1. ↑ Anti-inflammatory macrophage (M2) differentiation

2. ↑ Treg differentiation

3. ↑ MSC-EVs immunomodulatory effects

[286]

TLR ligands priming

 N/A

1. ↑ PD-L1 experssion

2. ↑ Gal9 expression

Pretreat with Poly I:C (TLR3)

Suppresses T cell proliferation and functions

[227]

↑ Gal9 expression

1. Pretreat with zymosan (TLR2)

2. Pretreat with LPS (TLR4)

Suppresses T cell proliferation and functions

[227]

Hypoxia priming

1. Using a dedicated hypoxia station

2. Hypoxia chambers

3. Using cobalt chloride (CoCl2)

Advantage

↑ Immunomodulatory and survival

Disadvantage

1. Enhances cell proliferation and efficacy during manufacture

2. Requires specific manufacturing equipment

↑ Expression of sCTLA-4

CoCl2

1. ↑ MSCs undifferentiated states duration

2. ↑ MSCs Proliferation and survival

3. ↑ MSC mobilization and homing

4. ↑ HGF, HIF1α, VEGF, IL-6, IL-10, and IDO production from MSCs

5. ↓ Senescence associated β-galactosidase in MSCs

[287]

Genetic engineering

Knockout or knockin

1. Lentivirus

2. Adenovirus

3. Retrovirus

4. Plasmid transfection

5. Zinc finger nuclease (ZFN)

6. TALEN

7. CRISPR/Cas9

Advantage

1. Relative high efficiency

2. Precise gene edition

3. Precise gene edition for CRISPR/Cas9

Disadvantage

1. Off-target effects risk

2. Complicated design

3. Risk of insertional mutagenesis

Variable based on manipulated gene

SOX2, PAX6, OTX2, AGO2

Multiple genes can be targeted for inducible knockout

[35, 288]

IDO

Affects immune cell proliferation

[289]

SLCO1A2, SLCO1B3

↓ Cell death in iPSC-derived cardiomyocytes

[290]

PD-L1

1. ↓ MSCs-sEVs potential to suppress T-cell responses

[191]

Knockdown

1. siRNA

2. miRNA

 N/A

↓ PD-L1 experssion by MSCs

Anti-PD-L1 siRNA

↓ Inducing Treg differentiation

[184]

3D cultures

1. Hanging Drops

2. Non-cross-linked hyaluronic acid gel

3. Multiwell hydrogel system

4. Chitosan films

5. Spheroid dishes

6. Rocker system

7. 3D rotational culture system

8. Ultra-low attachment plates

Advantage

1. ↑ MSC immunophenotypic and molecular profile stability

2. ↑ Angiogenic properties

3. ↑ Exosome production

4. ↑ Cell-to-cell communication

5. ↑ Anti-apoptotic and anti-fibrotic

Disadvantage

1. High-cost requirement

2. Heterogonous distribution of cells

3. Size variability depends on the technique

Not investigated

Spheroids

1. ↑ Regenerative and therapeutic effect by suppressing inflammatory responses

2. ↑ IFN-γ, IL-6, FGF2 and HGF experssion

3. ↓ CXCL2/MIP2, TNF-α, IL-1β, and PGE2 expression

4. ↑ Proliferation of MSCs

5. ↑ Trafficking efficacy

6. ↓ Neutrophil activity

[32, 291]