Reduced immunogenicity of Plasmodium falciparum gamete surface antigen (Pfs48/45) in mice after disruption of disulphide bonds – evaluating effect of interferon‐γ‐inducible lysosomal thiol reductase

Abstract

SummarySexual stages of Plasmodium are critical for malaria transmission and stage-specific antigens are important targets for development of malaria transmission-blocking vaccines. Plasmodium falciparum gamete surface antigen (Pfs48/45) is important for male gamete fertility and is being pursued as a candidate vaccine antigen. Vaccine-induced transmission-blocking antibodies recognize reduction-sensitive conformational epitopes in Pfs48/45. Processing and presentation of such disulphide-bondconstrained epitopes is critical for eliciting the desired immune responses. Mice lacking interferon-c-inducible lysosomal thiol reductase (GILT), an enzyme that mediates reduction of S-S bonds during antigen processing, were employed to investigate immunogenicity of Pfs48/45. It has been well established that the ability to reduce S-S bonds in antigens guides effective T-cell immune responses; however, involvement of GILT in the induction of subsequent B-cell responses has not been explored. We hypothesized that the ability to reduce S-S bonds in Pfs48/45 will impact the generation of T-cell epitopes, and so influence helper T-cell responses required for specific B-cell responses. Non-reduced and reduced and alkylated forms of Pfs48/45 were employed to evaluate immune responses in wild-type and GILT knockout mice and studies revealed important differences in several immune response parameters, including differences in putative T-cell epitope recognition, faster kinetics of waning of Pfs48/45-specific IgG1 antibodies in knockout mice, differential patterns of interferon-c and interleukin-4 secretions by splenocytes, and possible effects of GILT on induction of long-lived plasma cells and memory B cells responsible for antigen-recall responses. These studies emphasize the importance of antigen structural features that significantly influence the development of effective immune responses.

Immunological Cross-Reactivity between Malaria Vaccine Target Antigen P48/45 in Plasmodium vivax and P. falciparum and Cross–Boosting of Immune Responses

“…Fragment F1, F4 and F5 were also recognized differentially by some of the sera tested. A similar pattern of recognition has been observed in previous observation in which anti-Pfs48/45 immune sera were tested against the same panel of Pfs48/45 fragments [ 29 ]. Previous studies have shown that the two cysteine-rich subdomains of Pfs48/45 at the amino- and carboxyl- termini can induce transmission blocking antibody responses in experimental animals [ 12 , 27 ].…”

Immunogenicity and malaria transmission reducing potency of Pfs48/45 and Pfs25 encoded by DNA vaccines administered by intramuscular electroporation

“…Various technical limitations have restricted progress towards the development of TBV vaccine based on Pfs48/45. It has been difficult to express Pfs48/45 in appropriate conformation in recombinant expression systems and reduced and alkylated form of Pfs48/45 has been shown to be poorly immunogenic [45]. While epitope analysis of Pfs48/45 has revealed surface targets of transmission blocking monoclonal antibodies [46], lack of any structural information and knowledge of conformational target epitopes has resulted in limited success in the development of recombinant TBV based on Pfs48/45.…”

The s48/45 six-cysteine proteins: mediators of interaction throughout the Plasmodium life cycle

“…Similar to Pfs230, Pfs48/45 is a transmission-blocking vaccine candidate and correct epitope conformation is also very important for eliciting effective blocking antibodies, however, protection is not complement-dependent (Vermeulen et al, 1985b; Carter et al, 1990; Targett, 1990; Roeffen et al, 1996; Healer et al, 1997; Milek et al, 1998b; Merino et al, 2016). The best epitope for blocking transmission was originally mapped to the third s48/45 domain at the C-terminus, however more recent constructs include different regions or even the full-length protein (Carter et al, 1990; Outchkourov et al, 2007, 2008; Chowdhury et al, 2009; Kapulu et al, 2015; Singh et al, 2015).…”