Dendritic cells phagocytose pathogens leading to maturation and cross-presentation on MHC class I. We found that the efficiency of cross-priming in mice after vaccination with biodegradable poly(D,L-lactide-co-glycolide) microspheres (MSs) was enhanced when ovalbumin was coencapsulated together with either a CpG oligonucleotide or polyI:C as compared to co-inoculation of ovalbumin-bearing MS with soluble or separately encapsulated adjuvants. A single immunization with MS containing coencaspsulated CpG and ovalbumin yielded 9% SIINFEKL/H-2K(b) tetramer positive CTLs, production of IFN-gamma, efficient cytolysis, and protection from vaccinia virus infection. Taken together, coencapsulation of adjuvant and antigen is an important paradigm for the generation of potent CTL responses.

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Poly(lactide-co-glycolide) (PLGA) microparticles (MP) possess immunological adjuvant properties. Yet, exploitation of their full potential has just begun. The purpose of this study was to explore opportunities arising from surface modifications, and attachment and entrapment of combinations of antigen and a Toll-like receptor (TLR) ligand. The cytotoxic T lymphocyte (CTL)-restricted OVA ovalbumin peptide SIINFEKL was microencapsulated into bare, chitosan-coated, and protamine-coated PLGA MP using a microextrusion-assisted solvent extraction process. A TLR-ligand (CpG ODN) was either covalently coupled or physically adsorbed onto the MP surface. The peptide encapsulation efficiency decreased from 71% for uncoated particles to 62% and 45% upon coating with chitosan and protamine, respectively. CpG adsorption efficiency decreased from 93% for protamine-coated particles to 19% and 8% for chitosan and bare particles. Release of the adsorbed CpG was slow and incomplete (23% within 7 days) with the protamine coating, intermediate (>90% within 3 days) with the chitosan coating, and immediate (100% within 3 h) without coating. Interestingly, only the uncoated PLGA MP with adsorbed CpG mediated a prominent CTL response in mice at 6 days after immunization, as determined from IFN-gamma release from antigen-specific CD8+ cells; failure of the other MP formulations was ascribed to the low release of antigen and CpG within the first week after immunization. The study illustrates novel opportunities for PLGA MP vaccines by combining antigens and immunostimulatory ligands.

Building tissue from cells as the basic building block based on principles of self-assembly is a challenging and promising approach. Understanding how far principles of self-assembly and self-sorting known for colloidal particles apply to cells remains unanswered. In this study, we demonstrate that not just controlling the cell–cell interactions but also their dynamics is a crucial factor that determines the formed multicellular structure, using photoswitchable interactions between cells that are activated with blue light and reverse in the dark. Tuning dynamics of the cell–cell interactions by pulsed light activation results in multicellular architectures with different sizes and shapes. When the interactions between cells are dynamic, compact and round multicellular clusters under thermodynamic control form, while otherwise branched and loose aggregates under kinetic control assemble. These structures parallel what is known for colloidal assemblies under reaction- and diffusion-limited cluster aggregation, respectively. Similarly, dynamic interactions between cells are essential for cells to self-sort into distinct groups. Using four different cell types, which expressed two orthogonal cell–cell interaction pairs, the cells sorted into two separate assemblies. Bringing concepts of colloidal self-assembly to bottom-up tissue engineering provides a new theoretical framework and will help in the design of more predictable tissue-like structures.