Table 1 |.
Engineering primary immune organs and cells
| Characteristics | Engineering approach | Reported findings | Limitations | Refs |
|---|---|---|---|---|
| 2D bone marrow HSC niche | ||||
| Regions with varying ECM composition and biophysical properties | Fibronectin-coated, collagen-coated and laminin-coated PA substrates; seeded with HSCs from C57Bl/6 mice | Altered HSC fate in response to varying substrate stiffness and ECM protein composition | Combinations of ECM proteins not tested; only thin gels explored | 41 |
| 2D thymus | ||||
| T cell differentiation | Murine DLL1-expressing OP9 stromal cells co-cultured with human cord blood-derived HSCs | DLL1-dependent expansion of HSCs and differentiation along T cell lineages | Requires genetic manipulation of cells; suboptimal yield of CD4 or CD8 single-positive cells | 170 |
| Magnetic polystyrene microbeads functionalized with DLL4; co-cultured with human cord blood-derived HSCs and OP9 stromal cells | Controlled density, orientation and timing of DLL4 and induction of T cell progenitors | Level of T cell development and functionality not determined | 71 | |
| Human cord blood-derived HSCs cultured on DLL1-coated plates in the presence of VCAM1 | Induction of T cell progenitors in feeder cell-free and serum-free conditions | Differentiation limited to progenitor T cells; positive and negative selection mechanisms not present | 72 | |
| 3D bone marrow HSC niche | ||||
| ECM matrix proteins that promote HSPC adhesion | Fibronectin-immobilized and collagen-immobilized PET scaffolds; seeded with human cord blood-derived HSCs | Significant increase in CD34+ cell expansion; expanded cells differentiate into multiple haematopoietic lineages in bone marrow of NOD-SCID mice | Mechanisms driving HSPC differentiation unclear | 39 |
| Structural topology of bone marrow matrix with large surface area, high porosity and mimetic stromal tissue function | Silicate or PA scaffolds with ICC geometry coated layer-by-layer with PDDA and clay; seeded with a cocktail of human stromal cells and human HSCs | Significant (P < 0.05) increase in CD34+ cell proliferation, B cell differentiation and antibody production in ICC cultures compared with 2D controls after 28 days | Contributions from specific stromal cells are unclear | 37 |
| Cell-cell interactions within the 3D vascular niche | Human femur-derived bone scaffolds; seeded with hBMSC-HUVEC feeder co-cultures and human cord blood-derived HSCs | Significant (P < 0.05) expansion of short-term and long-term repopulating CD34+ cells and increased HSC quiescence by co-cultures compared with hBMSCs or HUVECs alone after 14 days | Unclear whether HUVECs directly affect HSCs or whether effects were due to HUVEC-induced osteogenic differentiation of hBMSCs | 43 |
| Overlapping patterns of niche-specific cells and matrix constituents | Microfluidic mixing platform fabricated with gradients of cells and type I collagen hydrogel with defined densities; seeded with HSPCs from C57Bl/6 mice and MC3T3 osteoblasts | Demonstrated overlapping gradients of fluorescently tagged cells and ability to isolate subregions of the gradient for cell analysis | Modest reduction in viability of HSPCs observed after 3 days | 45 |
| Platelet production by MKs within vascular niche | Porous films of varying stiffness; topography fabricated using silk solution, PEO porogens and ECM proteins patterned onto PDMS moulds; gel-spun vascular microtubes with incorporated HMECs; seeded with HSC-derived MKs | Modulation of MK adhesion and proplatelet formation by film topography and stiffness, respectively; ECM protein-functionalization and presence of HMECs enhance these outputs | Platelet generation low relative to in vivo production | 50 |
| Platelet production by MKs within perfusable vascular niche | Perfusion bioreactor system containing porous, multichannel silk sponge; seeded with HSC-derived MKs | Proportional increase in production of functional platelets with increasing silk channels; perfusion-facilitated platelet collection | Incorporation of multiple niche-specific cells not explored with this system | 52 |
| Cell diversity and toxicological responses of HSC niche | In vivo marrow formation via subcutaneous implantation of type I collagen with bone-inducing factors in mice; engineered bone marrow explanted and maintained in microfluidic device | Morphology and architecture of engineered bone marrow mimetic of native tissue, with comparable heterogeneous niche-specific cell populations; ex vivo culture supported HSC and HSPC maintenance and function | Long-term ex vivo culture not yet evaluated | 46 |
| 3D bone marrow HSC niche (cont.) | ||||
| Long bone tissue compartments with spatially different cues | Non-mineralized and mineralized macroporous PEGDA-co-A6ACA hydrogels, mimicking skeletal and haematopoietic compartments of bone; seeded with donor murine-derived intact whole bone marrow flush or cells isolated from bone marrow flush and implanted subcutaneously in recipient mice | Abundant CD34+ cell population within inner, non-mineralized compartment and hardened bone tissue restricted to mineralized compartment after 4 weeks in vivo; migration of donor cells into circulation | Species-specific responses may not translate to human application | 56 |
| 3D thymus | ||||
| Differentiation of mature T cells from HSPCs | Murine DLL1-expressing stromal cells aggregated with HSPCs and seeded on cell culture insert | Long-term maintenance of lymphoid progenitors; T cell differentiation resembling thymopoiesis; enhanced positive selection | Bias towards CD8+ T cell maturation owing to absence of MHC class II-dependent positive selection | 74 |
| ECM composition and architecture | Thymus from B6 athymic mice decellularized and seeded with TECs and non-epithelial cells from thymic digests; engrafted in nude mice | Maintenance of ECM composition and conformation; recruitment of haematopoietic progenitors; increased epithelial cell retention and survival supporting thymopoiesis | Thymopoiesis not displayed ex vivo. When engrafted, thymocyte number does not differ from controls prepared by isolation and reaggregation of thymic cells (reaggregate thymic organ culture) | 77 |
| Maintenance of donor epithelial cells to support tolerance to allografts | Decellularized murine thymus seeded with thymic fibroblasts and epithelial cells and bone marrow progenitors transplanted in B6 nude mice | Survival of functional TECs; lymphocyte homing after implantation and induction of immune tolerance | Lack of TEC organization and compartmentalization, resulting in less diverse T cell repertoire; thymopoiesis not displayed ex vivo; decellularized matrix shows batch-to-batch variability | 58 |
| Lymphocyte-stromal cell interaction for thymopoiesis | Self-assembling amphiphilic EAK16-II and EAKIIH6 peptides modified with histidine tags; tethered with TECs using complexes of antibodies and recombinant proteins | Clusters of TECs formed, resulting in development of mature functional T cells after implantation in athymic nude mice | Lacks segregation of niche-specific thymic epithelial cells | 80 |
DLL, delta-like ligand; EAK16-II, peptide (AEAEKAKAEAEAKAK); EAKIIH6, peptide (AEAEKAKAEAEAKAKHHHHHH); ECM, extracellular matrix; hBMSC, human bone marrow-derived mesenchymal stem cell; HMEC, human microvascular endothelial cell; HSC, haematopoietic stem cell; HSPC, haematopoietic stem or progenitor cell; HUVEC, human umbilical vein endothelial cell; ICC, inverted colloidal crystal; MHC, major histocompatibility complex; MK, megakaryocyte; NOD-SCID, nonobese diabetic-severe combined immunodeficient; PA, polyacrylamide; PEGDA-co-A6ACA, polyethylene glycol-diacrylate-co-N-acryloyl 6-aminocaproic acid; PDDA, poly(diallyldimethylammonium chloride); PDMS, polydimethylsiloxane; PEO, polyethylene oxide; PET, polyethylene terephthalate; TEC, thymic epithelial cell; VCAM1, vascular cell adhesion protein 1.