Optimization of Liposomes for Antigen Targeting to Splenic CD169+ Macrophages

Abstract

Despite promising progress in cancer vaccination, therapeutic effectiveness is often insufficient. Cancer vaccine effectiveness could be enhanced by targeting vaccine antigens to antigen-presenting cells, thereby increasing T-cell activation. CD169-expressing splenic macrophages efficiently capture particulate antigens from the blood and transfer these antigens to dendritic cells for the activation of CD8+ T cells. In this study, we incorporated a physiological ligand for CD169, the ganglioside GM3, into liposomes to enhance liposome uptake by CD169+ macrophages. We assessed how variation in the amount of GM3, surface-attached PEG and liposomal size affected the binding to, and uptake by, CD169+ macrophages in vitro and in vivo. As a proof of concept, we prepared GM3-targeted liposomes containing a long synthetic ovalbumin peptide and tested the capacity of these liposomes to induce CD8+ and CD4+ T-cell responses compared to control liposomes or soluble peptide. The data indicate that the delivery of liposomes to splenic CD169+ macrophages can be optimized by the selection of liposomal constituents and liposomal size. Moreover, optimized GM3-mediated liposomal targeting to CD169+ macrophages induces potent immune responses and therefore presents as an interesting delivery strategy for cancer vaccination.

Liposomal Nanovaccine Containing α-Galactosylceramide and Ganglioside GM3 Stimulates Robust CD8+ T Cell Responses via CD169+ Macrophages and cDC1

“…Moreover, liposomal strategies exploiting a synthetic CD169 ligand showed very specific binding to CD169 + bone marrow-derived macrophages and induced the proliferation of OVA-specific T cells [ 15 ]. Similarly, liposomes with a non-synthetic i.e., endogenous ligand for CD169, the sialic acid-containing glycosphingolipid GM3 ganglioside [ 16 ], have been reported to effectively bind to mouse CD169 + macrophages in the spleen and to human monocyte-derived and primary DCs and stimulate T cell responses [ 17 , 18 , 19 ]. Together, these data illustrate that ligand targeting in addition to antibody targeting is an effective strategy for antigen delivery to CD169 + macrophages.…”

Mimicking Pathogens to Augment the Potency of Liposomal Cancer Vaccines

“…PEG can also shield phospholipids in liposomal preparations, so that specific recognition of, for example, phosphatidylserine (PS), that is normally present on apoptotic cells and is a ligand for APCs, is hindered [ 47 , 53 ]. Similarly, PEG can shield specific targeting moieties on the liposome surface, and therefore liposomal stabilization with PEG may have an unfavorable effect on targeting capacity [ 54 ]. However, coupling of targeting ligands to the terminal ends of PEG can be utilized to overcome this [ 55 ].…”

“…We observed a lower magnitude of the immune response upon s.c. immunization versus i.v. immunization when we evaluated anionic liposomes [ 54 ].…”

“…When we assessed the peptide immunogenicity in vivo, we observed that incorporation of peptide in liposomes dramatically augmented the immunogenicity. While immunization with liposomal peptide resulted in potent CD8 + T cell responses, an equal dose of soluble antigen failed to elicit a noticeable immune response [ 54 ]. In agreement with these findings, encapsulation of peptide in liposomes was found to be an absolute requirement for anti-tumor activity [ 82 ].…”

“…While the main focus in cancer vaccination is on CD8 + T cells, the role of CD4 + T cells should not be overlooked [ 84 ]. We observed that the priming of CD4 + T cells was also markedly enhanced upon immunization with liposomal, rather than soluble, peptide [ 54 ]. In an elaborate study, Varypataki and co-workers corroborated the importance of CD4 + T cell epitope inclusion and peptide encapsulation.…”