no vaccine candidate has reached clinical trials to date. Advances in prime boost

immunization regimens, mucosal immunizations or the addition of novel adjuvants

in the formulation have resulted in positive outcomes in preclinical studies in mice,

rabbit, or rhesus macaque models, and great promises for the development of future

vaccine candidates (Table 10.1) [17,21,22].

Interest in Gag VLPs has not been limited to HIV-1 vaccines; the development

of chimeric VLPs against different diseases or for delivery strategies has been also

described in the literature. In Table 10.1, different applications entailing the use of

Gag VLPs are listed. Several authors have exploited the Gag polyprotein for antigen

presentation of influenza, Dengue, West Nile Virus, HPV, equine herpes virus and

pseudorabies immunogens (Table 10.1). Furthermore, genetic modifications into the

Gag sequence have been explored for the delivery of nucleic acids, enzymes, or

drugs. Vorácková and co-workers used M-PMV (Mason-Pfizer monkey virus) Gag

VLPs, as nanocages, producing the recombinant Gag subunits in E. coli and per-

forming their assembly ex vivo loading small interference RNA (siRNA) inside the

FIGURE 10.2 Structure of HIV-1 Gag VLP and mature HIV-1. (a) Schematic re-

presentation of HIV-1 genome with its 9 coding genes. The genome is composed of three

structural genes (gag, pol and env), four accessory genes in grey, and two regulatory genes

located throughout the 3 ORFs. Gag is further processed into six protein domains known as

matrix (MA or p17), capsid (CA or p24), spacer peptide 1 (SP1 or p2), nucleocapsid (NC or

p7), spacer peptide 2 (SP2 or p1), and p6 (Adapted from “Landmarks of the HIV genome”).

www.hiv.lanl.gov/content/sequence/HIV/MAP/landmark.html (b) Morphological structure

of Gag VLP and wildtype HIV-1. Wild-type HIV-1 is composed of the cleavage products of

three major viral polyproteins: Gag, Pol and Env. The sole expression of Gag polyprotein

gives rise to the generation of Gag virus-like particles, which are basically immature HIV-1

particles carrying uncleaved Gag capsids surrounded by a host cell lipid layer (adapted from

[ 17] with editorial permission).

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Bioprocessing of Viral Vaccines