Selection of combination adjuvants for enhanced immunogenicity of a recombinant CelTOS vaccine against Plasmodium falciparum.

Recently, there has been significant interest in developing combination adjuvants to achieve efficient vaccines. However, it remains uncertain which combinations of adjuvants could best enhance the immune response to the recombinant antigen. In the current study, to improve the immunogenicity of Plasmodium falciparum cell traversal protein for ookinetes and sporozoites (PfCelTOS), we tested three different adjuvants: MPL, Poly I:C, and QS-21 alone or in a triple mixture (MPL/Poly I:C/QS-21; MPQ) and a dual mixture (Poly I:C/QS-21; PQ). BALB/c mice were immunized with recombinant PfCelTOS, either alone or combined with MPL, Poly I:C, QS-21, or with dual and triple adjuvant mixtures. Humoral and cellular immune responses were assessed in the various mouse groups, along with the functional activity of anti-PfCelTOS antibodies in oocyst inhibition. The results showed that administering the PfCelTOS antigen with triple or dual adjuvant mixtures significantly increased specific antibody levels, as well as IFN-ɣ and TNF cytokine production (P < 0.05), compared to PfCelTOS alone or combined with single adjuvants. These vaccine adjuvant mixtures also enhanced transmission-reducing activity (TRA), resulting in 76%-84% reductions in oocyst intensity in functional assays. Interestingly, comparable antibody levels and functional inhibitory activity were observed in the groups that received antigen with both dual and triple adjuvants (P > 0.05). The findings indicate that the dual mixture of Poly I:C and QS-21 is the most effective formulation for a vaccine against PfCelTOS. This discovery has important cost and safety implications by minimizing the adjuvants required to achieve an optimal immune response.

Pirahmadi S ，Zargar M ，Pourhashem Z ，Vand-Rajabpour H ，Sani JJ ，Yousefi H ，Afzali S ，Zakeri S ，Mehrizi AA ... -  《-》

Combining Monophosphoryl Lipid A (MPL), CpG Oligodeoxynucleotide (ODN), and QS-21 Adjuvants Induces Strong and Persistent Functional Antibodies and T Cell Responses against Cell-Traversal Protein for Ookinetes and Sporozoites (CelTOS) of Plasmodium falcip

Plasmodium falciparum cell-traversal protein for ookinetes and sporozoites (PfCelTOS) is an advanced vaccine candidate that has a crucial role in the traversal of the malaria parasite in both mosquito and mammalian hosts. As recombinant purified proteins are normally poor immunogens, they require to be admixed with an adjuvant(s); therefore, the objective of the present study was to evaluate the capacity of different vaccine adjuvants, monophosphoryl lipid A (MPL), CpG, and Quillaja saponaria Molina fraction 21 (QS-21), alone or in combination (MCQ [MPL/CpG/QS-21]), to enhance the immunogenicity of Escherichia coli-expressed PfCelTOS in BALB/c mice. This goal was achieved by the assessment of anti-PfCelTOS IgG antibodies (level, titer, IgG isotype profile, avidity, and persistence) and extracellular Th1 cytokines using an enzyme-linked immunosorbent assay (ELISA) on postimmunized BALB/c mouse sera and PfCelTOS-stimulated splenocytes, respectively. Also, an assessment of the transmission-reducing activity (TRA) of anti-PfCelTOS obtained from different vaccine groups was carried out in female Anopheles stephensi mosquitoes by using a standard membrane feeding assay (SMFA). In comparison to PfCelTOS alone, administration of PfCelTOS with three distinct potent Th1 adjuvants in vaccine mouse groups showed enhancement and improvement of PfCelTOS immunogenicity that generated more bias toward a Th1 response with significantly enhanced titers and avidity of the anti-PfCelTOS responses that could impair ookinete development in A. stephensi However, immunization of mice with PfCelTOS with MCQ mixture adjuvants resulted in the highest levels of induction of antibody titers, avidity, and inhibitory antibodies in oocyst development (88%/26.7% reductions in intensity/prevalence) in A. stephensi It could be suggested that adjuvant combinations with different mechanisms stimulate better functional antibody responses than adjuvants individually against challenging diseases such as malaria.

Pirahmadi S ，Zakeri S ，Mehrizi AA ，Djadid ND ，Raz AA ，Sani JJ ... -  《-》

Cell-traversal protein for ookinetes and sporozoites (CelTOS) formulated with potent TLR adjuvants induces high-affinity antibodies that inhibit Plasmodium falciparum infection in Anopheles stephensi.

Pirahmadi S ，Zakeri S ，A Mehrizi A ，D Djadid N ，Raz AA ，J Sani J ，Abbasi R ，Ghorbanzadeh Z ... -  《MALARIA JOURNAL》

The Plasmodium falciparum Cell-Traversal Protein for Ookinetes and Sporozoites as a Candidate for Preerythrocytic and Transmission-Blocking Vaccines.

Recent studies have shown that immune responses against the cell-traversal protein for Plasmodium ookinetes and sporozoites (CelTOS) can inhibit parasite infection. While these studies provide important evidence toward the development of vaccines targeting this protein, it remains unknown whether these responses could engage the Plasmodium falciparum CelTOS in vivo Using a newly developed rodent malaria chimeric parasite expressing the P. falciparum CelTOS (PfCelTOS), we evaluated the protective effect of in vivo immune responses elicited by vaccination and assessed the neutralizing capacity of monoclonal antibodies specific against PfCelTOS. Mice immunized with recombinant P. falciparum CelTOS in combination with the glucopyranosyl lipid adjuvant-stable emulsion (GLA-SE) or glucopyranosyl lipid adjuvant-liposome-QS21 (GLA-LSQ) adjuvant system significantly inhibited sporozoite hepatocyte infection. Notably, monoclonal antibodies against PfCelTOS strongly inhibited oocyst development of P. falciparum and Plasmodium berghei expressing PfCelTOS in Anopheles gambiae mosquitoes. Taken together, our results demonstrate that anti-CelTOS responses elicited by vaccination or passive immunization can inhibit sporozoite and ookinete infection and impair vector transmission.

Espinosa DA ，Vega-Rodriguez J ，Flores-Garcia Y ，Noe AR ，Muñoz C ，Coleman R ，Bruck T ，Haney K ，Stevens A ，Retallack D ，Allen J ，Vedvick TS ，Fox CB ，Reed SG ，Howard RF ，Salman AM ，Janse CJ ，Khan SM ，Zavala F ，Gutierrez GM ... -  《-》

Liposomes containing monophosphoryl lipid A and QS-21 serve as an effective adjuvant for soluble circumsporozoite protein malaria vaccine FMP013.

Malaria caused by Plasmodium falciparum continues to threaten millions of people living in the tropical parts of the world. A vaccine that confers sterile and life-long protection remains elusive despite more than 30years of effort and resources invested in solving this problem. Antibodies to a malaria vaccine candidate circumsporozoite protein (CSP) can block invasion and can protect humans against malaria. We have manufactured the Falciparum Malaria Protein-013 (FMP013) vaccine based on the nearly full-length P. falciparum CSP 3D7 strain sequence. We report here immunogenicity and challenge data on FMP013 antigen in C57BL/6 mice formulated with two novel adjuvants of the Army Liposome Formulation (ALF) series and a commercially available adjuvant Montanide ISA 720 (Montanide) as a control. ALF is a liposomal adjuvant containing a synthetic monophosphoryl lipid A (3D-PHAD®). In our study, FMP013 was adjuvanted with ALF alone, ALF containing aluminum hydroxide (ALFA) or ALF containing QS-21 (ALFQ). Adjuvants ALF and ALFA induced similar antibody titers and protection against transgenic parasite challenge that were comparable to Montanide. ALFQ was superior to the other three adjuvants as it induced higher antibody titers with improved boosting after the third immunization, higher serum IgG2c titers, and enhanced protection. FMP013+ALFQ also augmented the numbers of splenic germinal center-derived activated B-cells and antibody secreting cells compared to Montanide. Further, FMP013+ALFQ induced antigen-specific IFN-γ ELISPOT activity, CD4+ T-cells and a TH1-biased cytokine profile. These results demonstrate that soluble CSP can induce a potent and sterile protective immune response when formulated with the QS-21 containing adjuvant ALFQ. Comparative mouse immunogenicity data presented here were used as the progression criteria for an ongoing non-human primate study and a regulatory toxicology study in preparation for a controlled human malaria infection (CHMI) trial.

Genito CJ ，Beck Z ，Phares TW ，Kalle F ，Limbach KJ ，Stefaniak ME ，Patterson NB ，Bergmann-Leitner ES ，Waters NC ，Matyas GR ，Alving CR ，Dutta S ... -  《-》