Chemical and biological characterization of vaccine adjuvant QS-21 produced via plant cell culture.

Many vaccines, including those using recombinant antigen subunits, rely on adjuvant(s) to enhance the efficacy of the host immune responses. Among the few adjuvants clinically approved, QS-21, a saponin-based immunomodulatory molecule isolated from the tree bark of Quillaja saponaria (QS) is used in complex formulations in approved effective vaccines. High demand of the QS raw material as well as manufacturing scalability limitation has been barriers here. We report for the first-time successful plant cell culture production of QS-21 having structural, chemical, and biologic, properties similar to the bark extracted product. These data ensure QS-21 and related saponins are broadly available and accessible to drug developers.

A strong CD8+ T cell response is elicited using the synthetic polypeptide from the C-terminus of the circumsporozoite protein of Plasmodium berghei together with the adjuvant QS-21: quantitative and phenotypic comparison with the vaccine model of irradiated sporozoites.

Stable protective immunity can be achieved against malaria by the injection of radiation-attenuated sporozoites (gamma-spz) and is mediated by IFN-gamma producing CD8+ T cells targeting the pre-erythrocytic stages. An efficient malaria vaccine should mimic this immunity. We compared the immune response specific for the circumsporozoite protein (CSP) of Plasmodium berghei (P. berghei), an important target of this protective response, elicited in mice immunized with the long synthetic polypeptide (LSP) PbCS 242-310, representing the C-terminus of the CSP of P. berghei, with the adjuvant QS-21 or injected with gamma-spz. The ex vivo evaluation of the CD8+ T cell response by IFN-gamma ELISPOT assay revealed that the injection of LSP with QS-21 induced, compared to gamma-spz, a similar frequency of peptide-specific lymphocytes in the spleen but a eight-fold increase in the draining lymph-nodes. A very high frequency of CD8+ T cells, specific for the sequence PbCS 245-253, a H-2Kd-restricted CTL epitope, was obtained in the liver and spleen of mice immunized with the two regimens. Even though the frequency of H-2Kd PbCS 245-253 multimer+, CD8+ T cells was higher in gamma-spz immunized mice, the frequency of IFN-gamma producing CD8+ T cells was comparable. The phenotype of the CD8+ T cell responses was characterized with the help H-2Kd PbCS 245-253 multimer and most of the CSP-specific CD8+ T cells represented an intermediate subset between effector and central memory with CD44(high), CD45RB(high), CD62L(low) and CD122(high). The number of memory CD8+ T cells decreased after the last LSP immunization but could be boosted to higher level with live spz. The unique combination of LSP PbCS 242-310 and the adjuvant QS-21 induced an immune response that was comparable in terms of quality to the one generated with gamma-spz. This confirmed the potential of LSP as malaria vaccine candidates as well as for the study of the repertoire of targets of protective immunity in the gamma-spz vaccine model.

Current vaccine adjuvants: an overview of a diverse class.

Numerous compounds are under evaluation as immunological adjuvants for improvement of vaccine performance. This review will briefly summarize some of the many diverse substances that are currently being utilized as vaccine adjuvants in preclinical and clinical studies.

Epidermal powder immunization of mice and monkeys with an influenza vaccine.

Epidermal powder immunization (EPI) with an influenza vaccine and an adjuvant such as QS-21, LTR72, or cholera toxin elicited augmented serum and mucosal antibody responses in mice. Rhesus macaques, which have an immune system and skin structure similar to humans, were used to further evaluate the immunogenicity of the influenza vaccine following EPI. EPI of rhesus macaques with an influenza vaccine and QS-21 adjuvant elicited significantly higher serum hemagglutination inhibition (HI) titers than antigen alone administered by EPI or by intramuscular (IM) injection using a needle and syringe. In the absence of QS-21, EPI and IM injection elicited comparable HI titers in the monkeys. This study suggests that EPI is a promising technique for administering human vaccine and that QS-21 augments the immunogenicity of co-administered influenza vaccine.

Influence of adjuvants in inducing immune responses to different epitopes included in a multiepitope, multivalent, multistage Plasmodium falciparum candidate vaccine (FALVAC-1) in outbred mice.

FALVAC-1, a vaccine against Plasmodium falciparum was developed by joining 21 epitopes from P. falciparum vaccine antigens and an universal T helper epitope from tetanus toxoid. Since adjuvants influence different aspects of immune responses, in this study we investigated the effect of four adjuvants aluminum hydroxide (alum), nonionic copolymer adjuvant P1005 (water-in-oil emulsion), CpG oligodeoxynucleotides (ODN), and QS-21 in eliciting immune responses in outbred mice. QS-21 and copolymer adjuvants were the best formulations in inducing higher and long-lasting antibody titers to the whole vaccine compared to alum and CpG. QS-21 was the only adjuvant to elicit predominantly IgG2a response and antibodies reactive with all epitopes incorporated in the vaccine construct. Vaccine elicited antibodies recognized sporozoites and asexual blood-stage parasites. FALVAC-1 immunized mice induced lymphoproliferative and IFN-gamma response to the vaccine. QS-21 and CpG adjuvants were able to elicit T proliferative responses to 20 of the 22 epitopes in the vaccine. In conclusion, this study demonstrated that with suitable adjuvant such as QS-21, it is possible to elicit immune responses to most of the epitopes included in the FALVAC-1 vaccine.

QS-21 structure/function studies: effect of acylation on adjuvant activity.

QS-21 is a natural saponin adjuvant derived from the tree Quillaja saponaria Molina. Previous studies over a limited dose range suggested the acylation is critical to adjuvant activity. In this study, we prepared DS-1 (deacylated QS-21) and RDS-1 (reacylated DS-1 with dodecylamine at a different site than QS-21) to determine the effect on a dose-response curve over a wider range in mice. DS-1 and RDS-1 induced IgG1 responses at higher doses compared to that induced by QS-21. DS-1 was inactive for inducing IgG2a or CTL responses at any doses. RDS-1 showed moderate IgG2a response at 240 microg, but did not show CTL response at any dose evaluated.