Immunogenicity of synthetic peptide constructs based on PvMSP9E795-A808, a linear B-cell epitope of the P. vivax Merozoite Surface Protein-9

Abstract

Plasmodium vivax Merozoite Surface Protein-9 (PvMSP-9) is a malaria vaccine candidate naturally immunogenic in humans and able to induce high antibody titers in animals when delivered as a recombinant protein. Recently, we identified the sequence EAAPENAEPVHENA (PvMSP9 E795-A808) as the main linear B-cell epitope in naturally exposed individuals. However, the potential of PvMSP9 E795-A808 as an immunogen in experimental animal models remained unexplored. Here we assess the immunogenicity of PvMSP9 E795-A808 using synthetic peptides. The peptides tested in BALB/c mice include two repeats of the sequence EAAPENAEPVHENA tested alone (peptide RII), or linked to an autologous (PvMSP9 peptide pL; pLRII) or heterologous (p2 tetanus toxin universal T cell epitope; TTRII) T cell epitope. Immune responses were evaluated by ELISA, FLUOROSPOT, and indirect immunofluorescence. We show that all of the peptide constructs tested were immunogenic eliciting specific IgG antibodies at different levels, with a prevalence of IgG1 and IgG2. Animals immunized with synthetic peptides containing T cell epitopes (pLRII or TTRII) had more efficient antibody responses that resulted in higher antibody titers able to recognize the native protein by immunofluorescence. Relevantly, the frequency of IFN-c secreting SFC elicited by immunization with TTRII synthetic peptide was comparable to that reported to the PvMSP9-Nt recombinant protein. Taken together, our study indicates that PvMSP9 E795-A808 is highly immunogenic in mice and further studies to evaluate its value as promising vaccine target are warranted. Moreover, our study supports the critical role of CD4 T cell epitopes to enhance humoral responses induced by subunit based vaccines.

Identification of an Immunogenic Broadly Inhibitory Surface Epitope of the Plasmodium vivax Duffy Binding Protein Ligand Domain

“…Generally, both B-cell and T-cell responses play a role in naturally acquired immunity to malaria. Thus, the immunogenicity and functional activity of epitopes such as the 3C9 epitope can be enhanced (i) by incorporating a universal T-helper epitope (such as the P2 tetanus toxoid-derived T-cell epitope) (69), (ii) by using adjuvants such as TLR agonists (TLR4 and TLR5) (70) for immunization, which have been successfully used to enhance immunogenicity of a B-cell epitope of PvMSP9 and the prophylactic L2-based HPV vaccine, respectively, or (iii) by packaging the epitope on viruses and virus-like particles (VLPs) by presenting the peptide as an immunogen at high densities on the surface of the viral particle which elicit stronger, and longer-lasting immune responses. This platform has been used as the basis for developing the human papillomavirus (HPV) vaccine (71).…”

Identification and validation of specific B-cell epitopes of hantaviruses associated to hemorrhagic fever and renal syndrome

“…SHNP (G72-D110) and SHNP (P251-D264) epitopes were only recognized by sera from SHNP immunized mice, suggesting that these epitopes are non-conserved among HCPS-associated orthohantavirus and corroborating their potential as HFRS target. This strategy, based on experimental immunization assays using recombinant proteins, have been used to confirm in silico findings [41–44], however, considering the probable misdiagnose of Seoul orthohantavirus in Americas and the necessity of differential diagnosis of HFRS in New world, experiments using samples of naturally infected hosts (human and/or rodents) should be conducted in order to fully support the present data and to confirm the real potential of these epitopes as differential diagnostic tools.…”

Main B‐cell epitopes of PvAMA‐1 and PvMSP‐9 are targeted by naturally acquired antibodies and epitope‐specific memory cells in acute and convalescent phases of vivax malaria

“…43,44 Recently, PvMSP-9 (E795-A808) was confirmed as the main epitope in C terminal region of PvMSP-9, and specific antibodies from mice that were immunized with this epitope were also found capable of targeting P vivax merozoites in vitro. 45,46 Although the epitopes PvAMA-1 (S290-K307) and PvMSP-9 (E795-A808) are usually considered highly immunogenic and promising for future use in vaccine studies, here we provide the first evidence that they induce long-lasting antibodies and MBC during natural P vivax infections.…”

“…Likewise, naturally acquired antibodies to PvMSP‐9 have also been associated with reduction of the risk of clinical malaria among children under 3 years old . Recently, PvMSP‐9 (E795‐A808) was confirmed as the main epitope in C terminal region of PvMSP‐9, and specific antibodies from mice that were immunized with this epitope were also found capable of targeting P vivax merozoites in vitro …”