Heterologous Immunization With Defined RNA and Subunit Vaccines Enhances T Cell Responses That Protect Against Leishmania donovani

Abstract

The rapid generation of strong T cell responses is highly desirable and viral vectors can have potent CD8+ T cell-inducing activity. Immunity to leishmaniasis requires selective T cell responses, with immunization schemes that raise either CD4 or CD8 T cell responses being protective in small animal models. We have defined the leishmaniasis vaccine candidate recombinant fusion antigens, LEISH-F2 and LEISH-F3+, that when formulated in a stable emulsion with a Toll-like receptor (TLR) 4 agonist, induce protective CD4+ T cell responses in animal models as well as providing therapeutic efficacy in canine leishmaniasis and in clinical trials in leishmaniasis patients. We used the genetic sequences of these validated vaccine antigens to design RNA vaccine constructs. Immunization of mice with the RNA replicons induced potent, local innate responses that were surprisingly independent of TLR7 and activated antigen-presenting cells (APC) to prime for extremely potent antigen-specific T helper 1 type responses upon heterologous boosting with either of the subunit vaccines (recombinant antigen with second generation glucopyranosyl lipid A in stable oil-in-water emulsion; SLA-SE). Inclusion of RNA in the immunization schedule also generated MHCI-restricted T cell responses. Immunization with LEISH-F2-expressing RNA vaccine followed later by subunit vaccine afforded protection against challenge with Leishmania donovani. Together, these data indicate the utility of heterologous prime-boost immunization schemes for the induction of potent antigen-specific CD4 and CD8 T cell responses for protection against intracellular pathogens.

An Alphavirus -derived replicon RNA vaccine induces SARS-CoV-2 neutralizing antibody and T cell responses in mice and nonhuman primates

“…Building on experience with the attenuated Venezuelan equine encephalitis virus TC-83 strain (22,(30)(31)(32)(33)(34), we generated repRNAs incorporating sequences from the SARS-CoV-2 S protein, including full-length S (repRNA-CoV2S) ( Fig. 1A).…”

Enlisting the mRNA Vaccine Platform to Combat Parasitic Infections

“…Multiple groups have developed self-replicating or replicon mRNA vaccine products in order to make mRNA transfection more efficient [38,39]. The construction of a self-amplifying mRNA includes non-structural parts of the genome of positive-strand viruses, e.g., sindbis virus, Semliki Forest virus, or Venezuelan equine encephalitis virus [40], which encode for their own RNA replication system [41,42] (Figure 3). The viral structural protein sequences are replaced with the sequence of the antigen of interest.…”

“…Recently, it was shown that protection against Leishmania donovani infection was accomplished by vaccinating mice with a heterologous mRNA-a subunit vaccine strategy. Duthie et al developed a naked mRNA replicon encoding for the LEISH-F2 gene [40]. When this F2-RNA was given as a prime vaccination and mice were boosted with the recombinant LEISH-F2 protein in glucopyranosyl lipid A in a stable oil-in-water emulsion (SLA-SE), a significant reduction in the parasite burden in the liver was observed.…”

Protective or Detrimental? Understanding the Role of Host Immunity in Leishmaniasis

“…An alternative and attractive vaccine approach is the delivery of recombinant nucleic acids (DNA and RNA) encoding Leishmania antigenic proteins that can be expressed in vivo and loaded into MHC molecules on transfected cells [162,163]. Some of the advantages of nucleic acid-based vaccines are their stability, the number of antigens and adjuvants that can be encoded by a single vector, the expression of structurally unaltered immunogenic proteins in recipient cells and the antigen-specific stimulation of CD4+ and CD8+ T cell responses [153,164].…”