Bioengineering of Artificial Antigen Presenting Cells and Lymphoid Organs

Purpose: Immune cell/organ therapies based on manipulation, infusion, and implantation of autologous or allogeneic cells/organs are costly, time-consuming, and sometimes limited in clinical effectiveness. Biomimetic materials and strategies offer an alternative by enabling artificial immune cells and lymphoid organs that are ready-to-use and scalable for immunotherapy. ---

Hypothesis: The central thesis is: if biomimetic materials can mimic the three signals of natural antigen-presenting cells and the architecture of lymphoid organs, then engineered artificial APCs (aAPCs) and artificial lymphoid organs can provide safe, effective, and scalable alternatives for T cell activation/expansion and immunotherapy. ---

Aims: - Survey the latest studies on engineering biomimetic materials for immunotherapy. - Focus on bioengineering artificial antigen-presenting cells (aAPCs) and artificial lymphoid organs. - Discuss opportunities and challenges in the field. - Highlight design considerations for ex vivo and in vivo applications. ---

Delivery system: Artificial antigen-presenting cells (aAPCs): - Lipid-based: - Liposomes containing MHC - Microdomain liposomes / RAFTsomes (enriched epitope/MHC complexes) - Supported lipid bilayers (SLBs) on solid particles - Nanoporous silica core–SLB protocells - Cell membrane-coated particles (e.g., cancer cell membrane-coated PLGA nanoparticles) - Polymeric: - PLGA biodegradable microparticles (surface anti-CD3, anti-CD28, pMHC; encapsulated IL-2) - Sepharose or polystyrene beads (non-biodegradable) - Non-spherical/ellipsoidal PLGA microparticles - Filamentous polymers: poly(isocyanide dipeptide)-co-oligo(ethylene oxide) with anti-CD3 - pHEMA-g-pDMAEMA comb/sunflower polymers - Inorganic: - Magnetic beads and magnetic nano-aAPCs (anti-CD3/anti-CD28) - Magnetic Janus microparticles (anti-CD3 on one face) - Carbon nanotubes (anti-CD3 coated) - Carbon nanotube–polymer composite (CNP; carbon nanotubes + magnetite + PLG nanoparticles loaded with IL-2) - Signals used: - Signal 1: peptide–MHC or anti-CD3 - Signal 2: anti-CD28, CD80/CD86 - Signal 3: IL-2, IL-7, IL-15, IL-21 - Checkpoint blockade: anti-PD-1 Artificial lymphoid organs: - Scaffold materials: fibroin, spidroin, alginate, collagen, PLG, PLA, PGA, mesoporous silica rods (MSRs) - Lymph node models: macroporous matrix bioreactor; fibroblast reticular cell–lymphatic flow model; RGD-loaded hydrogel with silicate nanoparticles; injectable DC-carrying alginate gels; collagen matrix with TEL-2-LTα cells + DCs; PLG matrix with GM-CSF/danger signals/tumor antigens/CpG ODN; alginate cryogels with GM-CSF/CpG/RGD - Thymus: Foxn1-reprogrammed MEFs into thymic epithelial cells (TECs); artificial thymic organoids - Spleen/mucosal tissue: neonatal rat spleen units on PGA-collagen scaffold; neointestine on PGA-collagen tubes ---

Approach: Review of preclinical and clinical literature. Model systems include: - In vitro: T cell proliferation/expansion assays, DC–T cell interaction models, artificial lymph node bioreactors. - In vivo: Mouse models of melanoma, lymphoma, and other tumors; GvHD models; SCID mice; BALB/c mice; adoptive transfer models. - Clinical: ACT trials using anti-CD3/anti-CD28-coated magnetic beads for ex vivo T cell expansion. - Disease context: Cancer immunotherapy, autoimmune disease, allograft rejection, infectious disease. ---

Key methods: Techniques highlighted across cited studies: - SEM and TEM for particle morphology - Fluorescence/confocal microscopy for aAPC–T cell binding - Flow cytometry for T cell expansion, subset analysis, and PD-1 expression - ELISA for IFN-γ, IL-2, antigen-specific IgG - T cell proliferation and expansion assays - In vivo tumor growth delay and survival analysis - Immunohistochemistry (e.g., PNAd, B220, PECAM-1) - H&E staining for tissue architecture - Magnetic separation for aAPC–cell isolation ---

Key results: - PLGA aAPCs with anti-CD3, anti-CD28, pMHC, and encapsulated IL-2 showed stable ligand presentation for ~20 days, significant IFN-γ secretion, and 45-fold T cell expansion; 6–10 μm particles were most effective. - Ellipsoidal PLGA aAPCs were more efficient than spherical particles; nanoellipsoidal aAPCs stimulated stronger in vivo immune responses at reduced protein dose and showed enhanced pharmacokinetics. - Filamentous anti-CD3 polymers induced more robust T cell responses than PLGA microparticles due to structural flexibility and multivalency. - Magnetic nano-aAPCs with an applied magnetic field enhanced TCR clustering and achieved >1000-fold expansion of tumor-specific T cells in one week. - Carbon nanotube aAPCs: anti-CD3-coated tubes induced higher specific T cell activation and IL-2 production than other high-surface-area materials. CNP expanded T cells ex vivo, delayed tumor growth in a murine melanoma model, and increased T cell infiltration. - Artificial lymph node organoids: collagen matrix with TEL-2-LTα and DCs formed organized T/B cell clusters, HEV markers, and antigen-specific IgG in transplants. PLG scaffolds with GM-CSF, tumor lysate, and CpG induced CTL responses and regression of local/metastatic tumors. MSR scaffolds recruited more cells than polymer scaffolds and increased CD8+ T cells in spleen. - Artificial thymus: Foxn1 expression in MEFs generated TECs; co-culture produced CD4+CD8+ thymocytes and mature CD4+/CD8+ T cells. Grafts were recovered in 4/6 iTEC vs 0/6 control MEF recipients. - Tissue-engineered spleen protected against overwhelming pneumococcal sepsis in a rodent model; tissue-engineered small intestine developed mucosal immune cells after 20 weeks. ---

Interpretation: The authors claim that bioengineering artificial immune cells and lymphoid organs holds great promise for enhancing immunotherapy, overcoming limitations of natural cells/organs, and creating desired therapy options. They emphasize that aAPCs can specifically encapsulate/release soluble molecules and present biological proteins to trigger T cell signaling, and that further optimization of surface ligands, cytokines, material size/shape, ligand mobility/orientation, and anisotropy is needed. They also highlight neoantigen-specific personalized therapies, GMP challenges, and the potential of patient-derived iPSCs for artificial lymphoid organs. ---

Limitations: - Clinical translation faces GMP standardization and cost challenges. - Many approaches rely on gene-modified mouse cell lines, which are not directly patient-applicable. - Tumor heterogeneity limits single-antigen-specific T cell therapies. - In vivo interaction of aAPCs with T cells requires further study. - Non-biodegradable materials (e.g., sepharose, polystyrene, magnetic beads, carbon nanotubes) may pose safety concerns. - Liposome stability is limited; SLB systems are not extensively applied. - Lymphoid organogenesis and molecular signaling are incompletely understood. - Long-term function and safety of implanted artificial lymphoid organs remain to be established.