The Signal Peptide Sequence Impacts the Immune Response Elicited by a DNA Epitope Vaccine

Abstract

We examined the effect of two leader sequences, one from a transmembrane molecule (H2-L d ) and another from a secreted molecule (rat KC chemokine), on the immunogenicity of DNA epitope vaccines. The chemokine leader enhanced vaccine immunogenicity, thus underscoring the importance of the leader sequence in DNA epitope vaccine design.DNA vaccines have been shown to elicit strong humoral and cell-mediated immune responses in many animal models (2,12,13,23). Studies suggest that the inoculated DNA is internalized by the local antigen-presenting cells (APCs), which then express and present the plasmid-encoded antigen to cytotoxic lymphocytes (CTLs) or T helper (T H ) cells. Also, in vivo-transfected cells at the site of inoculation, such as keratinocytes and myocytes, can secrete the encoded antigen, which can be processed and presented by APCs (4,6,11,23,25).The immune responses elicited by DNA vaccines have had varied results in different animal models, underscoring the need for optimization (1,22,23). An advantage of DNA vaccines is the ease with which one can introduce changes to qualitatively and quantitatively affect their immunogenicity (13,23,35). A number of approaches have been employed to enhance the efficacy of DNA vaccines, which include optimizing antigen processing (24) and presentation (5, 9, 17, 27, 29-31, 33, 37), using epitope-carrier protein fusion molecules (41), employing different delivery methods (18,21,22,28,34), and introducing immunomodulatory sequences in the plasmid vaccines (3,8,10,13,19,22,23,40). In both full-length and minigene DNA vaccines, leader sequences have been used to directly target the encoded antigen/epitope to the endoplasmic reticulum (ER) for major histocompatibility complex class I (MHC I) presentation with mixed success (5,7,9,17,33). Studies have shown that signal sequences exhibit wide diversity, impacting their function and role in protein targeting, release, and maturation (15,20,32,38,39,42). Therefore, the alteration of the leader sequence can influence the immunogenicity of DNA epitope vaccines.In this study, we compared the immune responses elicited by two minigene DNA vaccines encoding different leaders, one derived from the murine H-2L d molecule and the other derived from the rat KC chemokine, a member of the platelet factor 4 neutrophil chemoattractant family (16). We rationalized that a leader from a secreted molecule (the rat KC) would target the class I epitope to the ER more efficiently than would the other leader. We have analyzed and compared the immune responses elicited by the two vectors and demonstrate that the KC chemokine leader improved the immunogenicity of the DNA epitope vaccines.To assess the role of the leader sequence in the DNA epitope vaccine immunogenicity, we constructed two vectors to be used in mouse immunizations (Fig. 1A). The first one, SAOLL, encodes a CTL epitope, HIV gp120 IIIB (318-327) (A), which is targeted to the ER by the murine H-2L d leader (S). The plasmid also contains a T H epitope, ovalbumin (OVA) (323-339) (O), ...

Naturally acquired antibody kinetics against Plasmodium vivax antigens in people from a low malaria transmission region in western Thailand

“…Factors potentially influencing the persistence of antibody responses were also investigated. These included the presence of signal peptides (SP) [ 33 , 34 ], Plasmodium exported element (PEXEL) motifs [ 35 , 36 ], transmembrane domains (TMDs) [ 37 ], glycosylphosphatidylinositol (GPI) anchors [ 38 , 39 ], predicted domains [ 40 – 42 ] and low complexity regions (LCRs) [ 43 – 45 ]. These insights will be critical for applying recently developed sero-surveillance markers [ 46 ], and testing the inference that they can identify individuals with recent P. vivax infections, as well as improving our understanding of what drives a long-lived antibody response and how this could be exploited for selection of candidate antigens or improving vaccine design.…”

Protective Immunity to Dengue Virus Induced by DNA Vaccines Encoding Nonstructural Proteins in a Lethal Challenge Immunocompetent Mouse Model

“…As expected, immunization with each plasmid, or their combination, induced immune responses against these antigens, as measured by the number of spleen and brain-infiltrating monocytes cells producing IFN- γ after ex vivo stimulation with peptides derived from the respective NS proteins. On the other hand, immunized mice did not produced detectable levels of antigen-specific IgG, probably due the lack of a signal peptide in the DNA construction, resulting in production of the target recombinant protein only intracellular which may hamper the gathering of B cells with the vaccine targets, resulting in no antibody production ( 71 ). These results are in agreement with several previous observations showing that DNA vaccines encoding NS proteins induce Th1-biased immune responses that correlate with different degrees of protection in different mouse models ( 19 , 20 , 52 , 72 ).…”

A multi-epitope DNA vaccine co-administered with monophosphoryl lipid A adjuvant provides protection against tick transmitted Ehrlichia ruminantium in sheep

“…When administered intramuscularly and intradermaly in the presence of MPL applied topically, none of the constructs could protect sheep against tick challenge. The pSignal plus construct contained an additional CXCL1 signal sequence for antigen export [18,27] and subsequent uptake by antigen presenting cells (APC) or recognition by B-cells [28], while the LAMP-antigen chimeras are directly targeted to the lysosome for association with MHC class II in situ [19,29]. However, animals immunised with the pSignal construct had slightly higher RI values and were less effective at Th1 immune response induction than those immunised with pLamp, indicating that this signal sequence lowered the efficacy of this vaccine construct and should perhaps only be included with epitopes specific for B cells.…”

“…Two DNA vaccine constructs derived from twelve sheep codon optimised nucleotide sequences of E. ruminantium CD4 (p2540-21, p7140-6, p7140-7, p7140-20, p7320-21, p7350-9, p7620-12 and p8010-8), and CD8 CTL (p2540-6, p2540-16, p2540-19 and p2540-20) peptides were engineered as follows. The first construct, pSignal plus contained sheep CXCL1 signal sequence [18], a MHC II targeting sequence (LAMP sequence, RRKSYAGYQTL) [19] followed by eight CD4 epitopes with GPGPG spacers in between [20] and a CpG motif (CpG2135) [21]. This was followed by an IRES and an UB signal [10] before the four CD8 epitopes with AYY spacers in between [9] and a CpG2135 motif (Supplementary Figure 1A).…”