Cationic Liposomes Containing Mycobacterial Lipids: a New Powerful Th1 Adjuvant System

Abstract

The immunostimulation provided by the mycobacterial cell wall has been exploited for many decades, e.g., in Freund's complete adjuvant. Recently, the underlying mechanism behind this adjuvant activity, including Toll receptor signaling, has begun to be unraveled, confirming the potential of mycobacterial constituents to act as adjuvants. In this study, the immunostimulatory properties of a Mycobacterium bovis BCG lipid extract were tested for their adjuvant activity. Administration of the lipids in dimethyl dioctadecyl ammonium bromide-based cationic liposomes induced a powerful Th1 response characterized by markedly elevated antigen-specific immunoglobulin G2a (IgG2a) isotype antibodies and substantial production of gamma interferon. The adjuvant formulation (designated mycosomes) elicited high levels of gamma interferon both in C57BL/6 as well as in Th2-prone BALB/c mice. Furthermore, the mycosomes induced immune responses to protein antigens from several sources including Mycobacterium tuberculosis, Chlamydia muridarum, and tetanus toxoid. In a tuberculosis challenge model, the mycosomes combined with the Ag85B-ESAT-6 fusion protein were demonstrated to have a unique ability to maintain sustained immunological memory at a level superior to live BCG.

Tuberculosis Subunit Vaccination Provides Long-Term Protective Immunity Characterized by Multifunctional CD4 Memory T Cells

“…In this regard, DDA-based liposomes are known to have depot-forming properties (13), and recent biodistribution data indicate that CAF01 can maintain 10 -20% of the original Ag content for slow and gradual long-term release at the site of injection (Y. Perrie, unpublished observations). Our demonstration of a pronounced memory response Ͼ1 year postvaccination dominated by TNF-␣ ϩ IL-2 ϩ and IFN-␥ ϩ TNF-␣ ϩ IL-2 ϩ T cells with a proliferative potential emphasizes the fact that the slow Ag release from this vaccine seems to strike a balance in which the response is both maintained at high numbers and is of high quality.…”

“…Stimulants were used at a concentration of 5 g/ml and cell culture supernatants were harvested after 72 h of incubation. The amounts of secreted IFN-␥ were determined by ELISA in duplicate readings from three or four individual mice as described elsewhere (13). ELISPOT assays for determining the frequency of IFN-␥ secreting cells were conducted in 200-l volumes containing either 2 ϫ 10 5 or 1 ϫ 10 6 cells.…”

“…This formulation, cationic adjuvant formulation (CAF) 01, comprises the quaternary ammonium dimethyldioctadecylammonium (DDA) and the immunomodulator trehalose 6,6Ј-dibehenate (TDB), a synthetic analog of mycobacterial cord factor trehalose 6,6Ј-dimycolate (11). DDA-based cationic liposomes have an extensive track record as adjuvants for TB subunit vaccines and have previously shown promising results in maintaining immunological memory (12)(13)(14). In this study we demonstrate that the Ag85B-ESAT-6/CAF01 vaccine maintained high levels of protective immune responses for Ͼ1 year and that the response was dominated by TNF-␣ ϩ IL-2 ϩ and IFN-␥ ϩ TNF-…”

Adjuvant modulation of the cytokine balance in Mycobacterium tuberculosis subunit vaccines; immunity, pathology and protection

“…Culture supernatants were harvested after 72 hr incubation and the amounts of IFN-c, tumour necrosis factor-a (TNF-a), IL-17 and IL-5 were determined by enzyme-linked immunosorbent assay (ELISA) as previously described. 19 To investigate the contribution of CD4 and CD8 T cells to IFN-c production, the T-cell receptors were blocked by adding monoclonal antibodies to the cultures as previously described. 20 …”

A case-study investigating the physicochemical characteristics that dictate the function of a liposomal adjuvant

“…7 DDA is known to induce cell-mediated immunity and delayed-type hypersensitivity 8 and, along with its cationic nature and surfactant properties, has been shown to be an effective adjuvant in numerous applications, including mucosal immunization, 9 gene delivery 10,11 and subunit vaccine delivery. [12][13][14][15] The mechanism of action behind the adjuvant effect of DDA has been attributed to its positive surface charge and its ability to associate antigens. 16 This was confirmed and further elaborated by using ovalbumin (OVA) as a model antigen.…”