Table 1.

Engineering tumor immune microenvironments.

Design of Microfluidic Device	Key Cell Types	Findings	Ref.
Lymph-node-on-a-chip
Membrane-based perfusion bioreactor system containing multiple chambers for antigen-induced B-cell activation, DC–T-cell crosstalk, peripheral space to mimic lymphatic drainage and a DC-loaded hydrogel (Figure 3Ai).	B and T-lymphocytes from healthy donors Monocyte-derived human DCs	Migration of B- and T-cells from peripheral fluidic space towards DCs. LF structure formation upon immunization and activation. Controlled IgM release post-activation.	[44]
Membrane-based perfusion bioreactor system containing culture compartment with LN cells and MSCs -laden agarose gel discs.	Rat-derived MSCs LN cells derived from rat lymph nodes	Concanavalin A-stimulated LN cells showed reduced proliferation in MSC co-culture. MSC co-culture suppressed levels of proinflammatory molecules (TNFα and IFNγ) and induced IL-1a and IL-6 secretion.	[47]
Two chamber microfluidic system with recirculating flow to transport secreted signals between tumor and lymph-node tissue.	BALb/c-derived tumor and lymph node tissue slices	Real-time monitoring of tissue interactions, fluid flow and shear stress. Decreased IFNγ secretion within lymph nodes cultured with immunosuppressed T-cell containing tumor tissue	[50]
PDMS chip with one flow channel connected to two inlets and two outlets.	LPS-activated DCs CD8+ and CD4+ T-cells	Duration and strength of immune cell response depended upon shear stress. Stronger DC interaction with CD4+ T-cells.	[48]
Microdevice with chemotaxis compartment filled with DCs linked to a T-cell compartment. Separate media and chemokine channels.	MUTZ-3-derived DCs, T-lymphocytes	Design allowed chemotaxis of DCs under non-adherent conditions. CCR7-induced mature DC migration towards T-cells. Mature DCs showed stronger T-cell activation than immature DCs. Showed chemotaxis is critical in T-cell activation.	[49]
Two-channel device with media in upper channel and B- and T-cells laden Matrigel in bottom channel.	B-lymphocytes, T-lymphocytes	Perfusion stimulated the formation of LFs inside the chip. Formation of plasma B-cell clusters 7 days post-stimulation. Class-switching of B-cells was induced with specific cytokines and antibodies. Similar cytokine profiles were observed to human volunteers when exposed to Fluzone.	[51]
Bone-marrow-on-a-chip
Cylindrical PDMS device suitable for implantation.	HSCs Hematopoietic progenitor cells Osteoblasts Endothelial cells Perivascular cells Nestin+ MSCs	Formation and characterization of BM within device 8 weeks post-implantation. Presence of nestin+ cells indicate support of HSC and hematopoietic function. No expensive cytokines were needed to maintain cellular function.	[52]
Microfluidic chip device with central chamber containing BM tissue with underlying microfluidic channel, separated by a porous PDMS membrane.	In vivo-derived BM tissue	BM tissue produced and released blood cells into microfluidic circulation. Able to maintain viability and function of HSCs, which could differentiate into mature blood cells on-chip. Organ-level response to radiation toxicity. Showed that the hematopoietic microenvironment is crucial for modeling radiation toxicity.	[54]
Two-channel device with BM stem cell- and CD34+ progenitor cell-loaded hydrogel in top channel and endothelial cell lining in bottom vascular channel.	BM stem cells CD34+ progenitor cells Endothelial cells	Differentiation and maturation of different blood cell lineages, including neutrophils, erythroids and megakaryocytes. Maintain CD34+ viability up to 4 weeks Successful modeling of BM dysfunction using diseased CD34+ cells.	[55]
Microfluidic device consisting of a BM compartment and a compartment for other organs.	hMSCs HSPCs	Preculture of MSC on ceramic scaffold-induced ECM, which allowed maintenance of HSPC phenotype. Range of genes which are involved in multiple hematopoietic niche functions were observed.	[56]
Four-channel microfluidic platform filled with tumor cell, BMSC and HOB-laden collagen I.	Human Philadelphia chromosome positive B lineage ALL cell line BMSCs HOBs	Cell-matrix interactions influenced cell migration and invasion and led to cellular responses not observed in 2D. No BMSC spreading was observed in 3D dynamic condition. Decreased chemotherapeutic drug sensitivity was observed compared to 2D cultures.	[57]
Splenon-on-a-chip
Two-layered microengineered device which mimicked the closed-fast and open-slow microcirculation.	Uninfected and infected red blood cells	Microfluidic device accurately mimicked the red pulp and thus the filtering function of the spleen with accurate recognition of different RBC types.	[68]
Inflammation-on-a-chip
Multichannel device incorporating a co-culture of neutrophils and endothelial cells, ECM and concentration gradients of various inflammatory proteins.	Neutrophils Endothelial cells	The system showed transendothelial migration of neutrophils. N-formyl-methionyl-leucyl-phenylalanine showed higher attraction than IL-8. Strong correlation between matrix stiffness and migration was found.	[71]
Microfluidic culture platform with lumen channel inside a protein matrix.	Neutrophils iPSC-derived endothelial cells	Precise control over lumen size, structure and configuration. Composition of the ECM influences the barrier function of endothelial cells. Secretion of angiogenic and inflammatory factors. Neutrophil chemotaxis towards IL-8 improved in presence of endothelial cells.	[72]
Microfluidic device containing a central cell loading chamber and a chemoattractant gradient along migration channel.	Primary human neutrophils Human monocytes	Maintains chemotactic gradients up to 48 h but does change over time. Allows single-cell resolution of chemotaxis of neutrophils. Indication of bidirectional communication between monocytes and neutrophils.	[73]
PDMS device with central loading inlet, leading to eight channels connected to the chemoattractant chambers.	Human whole blood	Assay allowed passaging of neutrophils only. Chemoattractant gradients were maintained up to 8 h. Showed that neutrophils could regulate their traffic in absence of monocytes.	[74]
Multichannel PDMS device which allowed migration of cells through migration channels towards cytokine-laden channels.	MF2.2D9 T0 cell hybridomas IC-21 macrophages Immortalized B6 macrophages LPS-activated DCs	Successful migration of cells by chemoattractant gradient. Phagocytosis stopped macrophages from migrating further. Little cell proliferation observed. CCL19-induced mature DC chemotaxis.	[75]
A three-organ device with a liver module, cardiac cantilevers and stimulation electrodes, skeletal muscle cantilevers and recirculating THP-1 monocytes in medium.	THP-1 monocytes Primary human hepatocytes Human cardiomyocytes Human skeletal muscle myoblasts	Non-selective damage to cells in three different organs. Increased proinflammatory molecule release. Amiodarone-induced M2 polarization indicated by increased IL-6 release.	[76]
Lung-on-a-chip
Two-channel device with a polyester membrane. Primary human airway epithelial cells cultured on membrane in upper channel, with medium flowing in bottom channel.	Primary human airway epithelial cells Epithelial cells derived from COPD patients.	Inflammatory response was induced by an IL-13 insult, resulting in a proinflammatory response with hyperplasia of mucus secreting goblet cells. Showed neutrophil recruitment to diseased epithelial cells.	[77]
Skin-on-a-chip
Multilayer device with layer of HaCaT cultured on top of a porous membrane and an immune cell layer positioned beneath the KC layer.	HaCaTs U937 cell line	U937 monoculture showed highest expression of inflammation after LPS treatment. Perfusion induced the formation of tighter junctions.	[80]
Multilayer chip consisting of a HaCaT layer, a fibroblast layer and an endothelial cell layer, separated by porous membranes.	HaCaTs HS27 fibroblasts HUVECs	Successful design of skin model to mimic epidermis, dermis and vessels of the skin. Dexamethasone prevented tight junction damage and lowered IL-1β, IL-6 and IL-8 expression, thereby showing recovery of skin with edema.	[81]
Multichambered microfluidic device with interchangeable lids and insets for developing a full-thickness skin-on-a-chip model.	Human primary foreskin-derived dermal fibroblasts Immortalized human N/TERT keratinocytes	Developed a flexible bioreactor for tissue culture, with the ability to perform TEER measurements, permeation assays and assessing the skin’s integrity. Potential to culture multiple organs in parallel or addition of immune system. Dynamic perfusion improved morphogenesis, differentiation and maturation.	[83]
Liver-on-a-chip
Multilayer biochip containing a HUVEC/macrophage layer with monocytes freely flowing in the media and a hepatocyte/hepatic stellate cell layer at the bottom.	HepaRG hepatocytes HUVECs LX-2 stellate cells Peripheral blood mononuclear cell-derived macrophages Primary monocytes THP-1 monocytes	Migration and M1 polarization of monocytes upon LPS treatment. IL-10 production upon monocyte invasion, inducing M2 polarization. Monocyte invasion inhibited inflammation-related cell death and induced the recovery of metabolic functions.	[89]
Gut-on-a-chip
Two-channel device with porous membrane coated with ECM, with one side of the membrane coated with intestinal epithelial cells and the other with endothelial cells. Incorporation of vacuum chambers allowed recapitulation of peristaltic movements.	Caco-2 intestinal epithelial cells Human capillary endothelial cells. Human lymphatic microvascular endothelial cells E. coli strain	Formation of intestinal villi in 5 days. Inflammation was induced by co-culture with the E. coli strain, leading to secretion of TNF-α, IL-1β, IL-6 and IL-8 Growth of bacteria also resulted in epithelial deformation and disturbance of peristaltic movements.	[82,90,94]
Multichambered chip with separately controlled microbial and epithelial cell microchambers.	Caco-2 intestinal epithelial cells Noncancerous colonic cell line Primary CD4+ T-cells Lactobacillus rhamnosus GG	Successful incorporation of co-culture of human and microbial cells. Independently controlled chambers allowed for anaerobic culture conditions for the microbial cells. Slight inflammatory response after addition of microbial cells. Showed crosstalk between microbial and human cells, depicted by alteration of several genes and miRNAs.	[95]
Microfluidic device with apical and basolateral compartments separated by a porous membrane.	U937 cells Caco-2 intestinal epithelial cells	Full, confluent layers formed 5 days after Caco-2 cell seeding. Dynamic cell culture conditions improved viability. LPS and cytokine addition increased permeability of the epithelial cell layer.	[96]
Tumor-microenvironment-on-a-chip
Central immune chamber with floating IFN-DCs connected to two side tumor chambers with treated and untreated cancer cells in type I collagen.	IFN-DCs RI+ and RI- SW620 CRCs	IFN-DCs migrated towards RI-treated cancer cells. Increased antigen take up resulting in increased phagocytosis and antitumor function.	[99]
CAR-T cells delivered through microfluidic channels. Tumor cells in GelMA between two oxygen diffusion barriers.	HER2+ SKOV3 human OCCs Anti HER2 CAR-T cells	Hypoxia alters PD-L1 expression. Limited CAR-T infiltration due to matrix stiffness and oxygen concentration. Hypoxia promotes immunosuppression.	[100]
Channel containing tumor spheroids embedded with NK cells in collagen. Two endothelial vascular lamina on lateral sides.	MCF7 breast tumor spheroids NK-92CD16V NK cells HUVECs	Delayed anti-EpCAM-IL-2 antibody penetration by endothelial barrier and cell–cell interactions. NK cell cytotoxicity and ADCC was enhanced by anti-EpCAM-IL-2.	[101]
Tubular lymphatic vessel adjacent to lumen filled with breast cancer cells, co-cultured in collagen hydrogel.	Estrogen-positive MCF-7 cells MDA-MB-231 breast cancer cells Human lymphatic endothelial cells (HLECs)	Co-culture with MCF-7 led to alteration of multiple HLEC genes, which correlated to functional changes in endothelial barrier capacity.	[105]
One channel filled with liver tumor cells in type I collagen. Second channel containing tumor specific T-cells. Control over oxygen levels and inflammatory cytokines.	TCR engineered T-cells HBV+ HepG2 cells	T-cells are dependent on tumor cells for migration and induction of apoptosis. Level of oxygen and cytokines important factor in their optimal activity.	[106]
Multiplexed microfluidic device laden with tumor tissue. Infusion of tumor infiltrating lymphocytes.	MC38 tumors and cells PD38+ T-cells Human tumor tissue CD45+ tumor infiltrating lymphocytes	Presence of anti-PD-1 inhibitor led to higher cell death and infiltration into the tumor tissue.	[107]
Breast cancer cells seeded into type I collagen. Separate microchannels mimicking the lymphatic and blood vessels.	MCF-7 breast cancer cells Microvascular endothelial cells	Research on cutoff pore size, ECM structure and lymphatic drainage showed that extravasation and interstitial diffusion was significantly decreased with particles of 100 to 200 nm (smaller than EPR window).	[108]
Two culture chambers (melanoma and splenocytes compartment) connected via narrow capillary migration channels.	B16.F10 murine melanoma cells Murine splenocytes	Absence of IFN regulatory factor 8 (IRF-8) led to poor splenocyte migration towards and interaction with cancer cells.	[109,110]