Table 2 |.

Engineering secondary immune organs and cells

Characteristics	Engineering approach	Reported findings	Limitations	Refs
2D activated T cells
Immune synapse: T cell-APC interface	Glass-supported planar bilayer with pMHC and an adhesion ligand; ICAM1 for imaging	Immune synapse formation between a T cell and the synthetic surface	Quantitative, qualitative and pattern shape studies cannot be achieved	171
	Alternative patterns of GPI-linked pMHC and ICAM1 into a supported lipid bilayer membrane using electron-beam lithography on silica substrates	Chromium barriers enable investigation of basic mechanisms of immunological synapse formation; membrane lipid mobility allows molecular motion in lipid-linked T cell ligands to generate alternatively patterned synapse	Quantitative and qualitative studies cannot be achieved	86
	Aqueous solvent-based photoresist and polyelectrolyte bilayers for printing multi-biotinylated protein arrays	Altered secretion of IL-2 and IFNγ from CD4+ T cells by spatial patterns; PKCθ exhibits aberrant clustering, which resulted in reduced production of IFNγ if patterns of activation sites preclude centralized clustering of TCR ligands	Complex procedure for fabricating multicomponent patterns	92,172
	Selective patterns of the immune synapse generated by incorporating multiple rounds of microcontact printing using a topological PDMS mould	Increased IL-2 and IFNγ production by CD4+ T cells if CD28 receptor clusters are segregated from the cSMAC-localized CD3 receptor and located in the periphery of an artificial immune synapse	Low degree of control over quantity of transferred protein; protein drying process required prior to stamping	93
Intercellular mechanical forces: T cell-APC interface	Elastomeric PDMS micropillar arrays for regulation of the T cell mechanical force under CD3 and CD28 co-stimulation	CD28 binding increases traction forces associated with CD3 by stimulating a signalling pathway involving PI3K, causing pillar array deformation	Manufacturing process may lead to pillar defects, resulting in low accuracy of intercellular force measurements	173
	Polyacrylamide hydrogels (Matrigen) and PDMS micropillars to measure force exertion across the synapse and the kinetics of perforin pore formation in the target cell	CD8+ cell-mediated cytotoxic activity; increased tunnelling of T cells through APC membranes on stiffer substrate; exerted forces across the synapse affect kinetics of perforin pore formation, enhancing cytotoxic capabilities	2D environment cannot fully capture 3D aspects; therefore, it is unclear whether force exertion is solely responsible for cytotoxic activity	96
2D germinal centre B cells
Memory B cell and plasma cell formation	Murine spleen-derived B cells cultured with BALB/c 3T3 fibroblasts expressing CD40 ligand and BAFF in the presence of IL-4	Induction and expansion of germinal centre B cells; B cell receptor class switching and differentiation into memory B cells; additional culture with IL-21 leads to plasma cell formation	Unaltered immunoglobulin genes in germinal centre B cells after stimulation with IL-21 and CD40L	123
Antigen-specific B cell expansion	Polyvalent presentation of CD40 ligand, complexed with HA peptide, on iron oxide microbeads coated with anti-HA antibody	Expansion of antigen-specific B cells; class switching; germinal centre B cell differentiation in the absence of feeder cells	Influence of microbead properties unknown	125
Antigen-specific B cell responses	Multi-layered lipid vesicles covalently crosslinked and maleimide-functionalized for presentation of malaria antigen	Germinal centre formation; improved strength and breadth of antibody response relative to conventional adjuvants; induction of antigen-specific follicular helper T cells	Unknown whether a wide range of clinically relevant adjuvants, except monophosphoryl lipid A, is effective with lipid vesicle vaccine platform	174
3D artificial APCs
T cell activation and expansion	Chemically treated bundles of SWNTs embedded with anti-CD3	Chemical treatment induced surface defects lead to increased anti-CD3 absorption; increased IL-2 release following culture with T cells	Incorporation of stimuli for T cell activation was not explored	100
	Carbon nanotube-PLGA composite containing magnetite and IL-2, as a platform for T cell stimuli delivery	Magnetite and IL-2 incorporation increases cytotoxic T cell population through maximizing cell isolation and enrichment; adoptive therapy for murine melanoma by transferring CD8+ T cells delays tumour growth	Difficult to remove carbon nanotube residues from isolated T cells; nanocomposite is cytotoxic	101
	Paramagnetic iron-dextran nanoparticles system for activation and expansion of the naive T cell repertoire	Iron-dextran nanoparticles conjugated with an MHC-immunoglobulin dimer and anti-CD28 increases target T cell population by positive selection from the naive T cell pool, inducing expansion of target cell	Incorporation of multiple signals for T cell expansion not explored; suboptimal T cell expansion	106
	Composite of mesoporous silica microrods and supportive lipid bilayers with soluble IL-2 and anti-T cell receptors	Higher efficiency in polyclonal and antigen-specific T cell expansion than commercial T cell expansion beads; antitumour efficacy in a model of Burkitt’s lymphoma	Density, quantity or spatial distribution of factors for T cell activation cannot be controlled	102
3D B cell follicle
Germinal centre B cell differentiation	RGD peptide-functionalized gelatin hydrogel with silicate nanoparticles, splenic B cells from C57BL6 mice and stromal cells presenting CD40 and BAFF; stimulated with IL-4	Enhanced, rapid B cell proliferation and differentiation, with antibody class switching	B cell responses not antigen-specific	127
	Degradable and tuneable maleimide-crosslinked polyethylene glycol hydrogels presenting integrin ligands; seeded with murine splenic B cells and stromal cells presenting CD40 and BAFF; stimulated with IL-4	Modulation of B cell differentiation; antibody class switching; enrichment of antigen-specific B cells	Additional niche-specific signals required to mimic complexity of germinal centre reactions	131

APC, antigen-presenting cell; BAFF, B cell activating factor; CD40L, CD40 ligand; cSMAC, central supramolecular activation cluster; GPI, glycosylphosphatidylinositol; HA peptide, human influenza haemagglutinin tag (YPYDVPDYA); ICAM1, intercellular adhesion molecule 1; IFNγ, interferon-γ; IL, interleukin; MHC, major histocompatibility complex; PDMS, polydimethylsiloxane; PI3K, phosphoinositide 3-kinase; PKCθ, protein kinase Cθ; PLGA, poly(lactide-co-glycolide); pMHC, peptide-MHC; RGD, Arg-Gly-Asp; SWNT, single-walled carbon nanotube; TCR, T cell receptor.