Figure 2. Durable surface coupling (a–c) versus rapid internalization (d–f) of therapeutic material following different cell surface engineering strategies. (a) Attachment of micrometer scale polymer layers to cell membranes.

Schematic of a multilayer hyaluronic acid-functionalized polymer patch attached to the surface of a T lymphocyte through intrinsic CD44 membrane receptors (left panel). Confocal microscopy image of a patch- (green fluorescence) functionalized T-cell. Scale bar, 10 μm (right panel). Adapted with permission from Swiston et al. (2008). (b) Tethering nanostructures to biotinylated cell membrane proteins. Schematic illustration of NeutrAvidin-coated nanoparticulate patches anchored onto a biotinylated plasma membrane (left panel). Scanning electron microscopy images of nanoparticle cluster on a human mesenchymal stem cell membrane (right panel). Adapted with permission from Cheng et al. (2010). (c) Covalent coupling maleimide-functionlized nanocarriers to free thiol groups on membrane proteins. Schematic of maleimide-based conjugation of synthetic lipid-coated nanoparticles (NP) to cell surface thiols and subsequent quenching of residual maleimide headgroups on nanoparticles by in situ conjugation to thiol-terminated polyethylene glycol (PEGylation) (left panel). Confocal microscopy images of CD8⁺ effector T cells immediately after conjugation with fluorescent multilamellar lipid nanoparticles and after 4-d in vitro T cell expansion (right panel). Scale bar, 2 μm. Adapted with permission from Stephan et al. (2010). (d) Incorporation of bioactive synthetic glycopolymers into cellular membranes. Schematic of synthetic mucin-mimic glycopolymers exogenously inserted into the cellular membrane through hydrophobic anchors (left panel). Fluorescent microscopy image of ldlD CHO cells incubated for 1 h with synthetic glycopolymer (green). Nuclei are stained with Hoechst 33342 in blue (right panel). Scale bar, 10 μm. Colocalization of glycopolymers and early endosomes was confirmed. Adapted with permission from Rabuka et al. (2008). (e) Selective targeting of antibody-conjugated nanoparticles to T lymphocyte T cell receptors. Schematic illustration of an anti-CD3 antibody-functionalized nanoparticle (NP) coupled to the T cell receptor CD3 complex. To immobilize biotinylated anti-CD3 antibodies nanoparticles were modified with NeutrAvidin (left panel). Confocal microscopy image of CD3⁺ Jurkat cells cultured in the presence of FITC-conjugated anti-CD3-NP for 4 h. To visualize cellular membranes cells were counterstained with Alexa fluor 594-conjugated concanavalin A (right panel). Scale bar, 8 μm. Adapted with permission from Balthasar et al. (2005). (f) Tethering particulate carriers to CD8 antigen on human effector T lymphocytes. Illustration of an antibody-nanoparticle (NP) conjugate targeted to the CD8 antigen on the surface of a human CD8⁺ T cell (left panel). Confocal microscopy of a human CD8⁺ effector T lymphocyte incubated with anti-CD8-decorated fluorescent nanoparticles for 45 minutes (right panel). Scale bar, 3 μm (M.T. Stephan, unpublished data).