Synthetic Liposomal Mimics of Biological Viruses for the Study of Immune Responses to Infection and Vaccination

Abstract

Human viruses possess very complex supramolecular structures. Both icosahedral and enveloped viruses typically display an array of viral-encoded protein antigens at varied spatial densities on the viral particle surface. The viral nucleic acid genome, on the other hand, is encapsulated inside the viral particle. Although both the surface antigen and the interior nucleic acids could independently produce immunological responses, how B cells integrate these two types of signals and respond to a typical virus particle to initiate activation is not well understood at a molecular level. The study of these fundamental biological processes would benefit from the development of viral structural mimics that are well constructed to incorporate both quantitative and qualitative viral features for presentation to B cells. These novel tools would enable researchers to systematically dissect the underlying processes. Here we report the development of such particulate antigens based on liposomes engineered to display a model protein antigen, hen egg lysozyme (HEL). We developed methods to overexpress and purify various affinity mutants of HEL from E. coli. We conjugated the purified recombinant HEL proteins onto the surface of a virion-sized liposome in an orientation-specific manner at defined spatial densities and also encapsulated nucleic acid molecules into the interior of the liposome. Both the chemical conjugation of the HEL antigen on liposome surfaces and the encapsulation of nucleic acids were stable under physiologically relevant conditions. These liposomes elicited antigen-specific B-cell responses in vitro, which validate these supramolecular structures as a novel and effective approach to mimic and systematically isolate the role of essential viral features in directing the B-cell response to particulate antigens.

NR4A nuclear receptors restrain B cell responses to antigen when second signals are absent or limiting

“…Recombinant HEL, HEL-2X (R73E, D101R), HEL-3X (R73E, D101R, R21Q) proteins were a gift from W. Cheng, University of Michigan 56 . Complete culture media was prepared with RPMI-1640 + L-glutamine (Corning-Gibco), Penicillin Streptomycin L-glutamine (Life Technologies), 10 mM HEPES buffer pH7.2-7.5 (Life Technologies), 55 mM β-mercaptoethanol (Gibco), I mM sodium pyruvate [ (Life Technologies), Non-essential Amino acids (Life Technologies), 10% heat inactivated FBS (Omega Scientific).…”

Nanomedicine strategies to target coronavirus

“…Liposomes can be designed to mimic the viral composition, eventually rendering their characteristics and behavior ( Fig. 8 ) [ 19 , 241 , 242 ]. The use of liposomes as model virus in CoV is an interesting approach in particular due to higher safety in handling compared to live viruses allowing laboratories that do not own facilities to handle SARS-CoV, MERS-CoV or SARS- CoV-2 to investigate potential treatment in a realistic fashion as well as due to the high tunability of the model properties and characteristics.…”

“…Such virus mimics have been generated in the past to investigate the process of binding and fusion of the viral envelopes with the endosomal membranes as well as potential pH triggered release mechanisms [ 241 ]. Furthermore, the conjugation of viral antigens (hen egg lysozyme) onto the liposome and encapsulation of nucleic acids, mimicking the viral genome, was used to study the specific response of B cells towards these antigens, demonstrating the use of such systems to investigate underlying mechanisms in a controlled fashion [ 242 ]. Such systems can be similarly used to investigate the behavior of CoVs in a realistic and well-controlled environment.…”

Potential of Flavonoid-Inspired Phytomedicines against COVID-19

“…The docking study results above suggest that smart nanoparticles with flavonoids might be more effective in binding the ACE2 receptor and could represent a significant improvement or advance in targeting such indications. Smart nanoparticles can also be constructed along the lines of the multi-compartment liposome [29], which have hydrophobic and hydrophilic compartments to carry flavonoids or other drugs for more effective targeting to enhance their effectiveness. In general, advantages of using such smart technology includes better disease targeting, ability to cross membranes and enter cells, longer duration drug action, lower doses, and reduced side effects, which is of vital importance.…”