A heterologous prime-boost regime using DNA and recombinant vaccinia virus expressing the Leishmania infantum P36/LACK antigen protects BALB/c mice from cutaneous leishmaniasis

A heterologous prime-boost vaccination with DNA vectors and vaccinia virus recombinants (VVr) has been shown to enhance specific cellular immune responses and to elicit significant protection against pathogens in animal models. In this study, we have analyzed, in the leishmaniasis cutaneous murine model, the effectiveness of this prime-boost strategy by immunizing with a DNA vector followed by boost with a VVr expressing the same Leishmania infantum P36/LACK antigen. After DNA priming and VVr boost, we challenged susceptible BALB/c mice with live L. major promastigotes, and examined the increase in footpad lesion size and parasite load in draining lymph nodes. Compared to controls, we observed reduction of up to 70% in lesion size and 1000-fold in parasite load. DNA prime-VVr boost before challenge elicited a Th1 type immune response in spleen cells from immunized animals. This DNA/VVr vaccination approach could be of utility in the prophylaxis against leishmaniasis.

Protective immune response against cutaneous leishmaniasis by prime/booster immunization regimens with vaccinia virus recombinants expressing Leishmania infantum p36/LACK and IL-12 in combination with purified p36

In susceptible mice Leishmania infection triggers a CD4(+) Th2 response that has been correlated with evasion of the host immune system. To develop approaches that might trigger a Th1 response leading to protection against Leishmania we generated vaccinia virus recombinants (VVr) expressing the relevant p36/LACK protein of Leishmania infantum (VVp36) or co-expressing p36/LACK and interleukin-12 (VVp36IL12). Susceptible BALB/c mice were immunized with the VVr in various prime/booster protocols that included purified p36/LACK protein, followed 3 weeks later by a challenge with live L. major promastigotes. The course of the infection was monitored by measuring lesion development, parasite load and immunological parameters (IFN-gamma and IL-10 secretion by in vitro-stimulated lymphocytes, and specific IgG isotypes), before and after challenge. We found protocols of prime/booster immunization (VVp36/VVp36; VVp36IL12/p36; p36/VVp36IL12) that elicited different levels of protection in infected animals. The protocol of priming with purified p36 followed by a booster with VVp36IL12 induced 52% reduction in lesion size and a two-log unit reduction in parasite load. This partial protection correlated with activation of a specific Th1 type of immune response. These protocols could be of interest in the prophylaxis against Leishmania spp. and other parasitic diseases.

Chimeras between the human immunodeficiency virus (HIV-1) Env and vaccinia virus immunogenic proteins p14 and p39 generate in mice broadly reactive antibodies and specific activation of CD8+ T cell responses to Env

A vaccine based on the envelope protein (Env) of the human immunodeficiency virus type 1 (HIV-1) that triggers widely reactive antibodies might be a desirable approach to control virus infection. To expose epitopes which could induce broadly reactive antibodies against HIV-1 Env, we have generated vaccinia virus (VV) recombinants that express Env fused at its N- or C-terminus with two major antigenic proteins of VV, p14 (A27L gene) and p39 (A4L gene). Biochemical analysis of the chimeric proteins in cell cultures revealed that, in all cases, recombinant viruses expressed the correct fusion proteins. When p14 or p39 are fused at the N-terminus of Env the chimeric proteins are poorly glycosylated but when p14 or p39 are fused at the C-terminus of Env, the chimeric proteins are fully glycosylated. In Balb/c mice, immunisation with the referred VV recombinants induced similar levels of CD8+ T cell specific responses to Env as immunisation with the entire Env protein. The humoral immune response triggered by the fusion proteins was broader than in animals immunised with VV expressing the entire Env (VVEnv1), and was directed to epitopes outside of the V3 loop (V1/V2, C1, C2, C4). One of the chimeric constructs induced a better neutralising antibody response than VVEnv1. We conclude that fusing VV proteins p14 or p39 to Env provides an effective means to induce broadly reactive antibodies and CD8+ T cell responses to Env. This approach might have utility against HIV and other pathogens.

Enhanced CD8+ T cell response to HIV-1 env by combined immunization with influenza and vaccinia virus recombinants

With the aim to determine if immunization with two different live recombinant viral vectors could lead to an enhancement of the cellular immune response to HIV-1 antigens, we have characterized the CD8+ T cell response elicited against the V3 loop epitope from HIV-1 env protein in Balb/c mice immunized with either: a recombinant influenza virus (Flu-Env) expressing the V3 loop epitope from HIV-1 strain IIIB, a vaccinia virus recombinant (VV-Env) expressing the complete HIV-1-IIIB env protein, or a combination of both. The CD8+ T cell response, measured by the ELISPOT assay, in animals primed with Flu-Env and boosted with VV-Env was 5 to 6 times higher than in animals inoculated with either Flu-Env or VV-Env alone. Similar results were obtained with recombinant viruses expressing the V3 loop epitope or the complete env protein, respectively, from the MN strain of HIV-1. Our results indicate that the use of two different live vectors for priming and boosting has a synergistic effect on the immune response against HIV-1, and could represent a novel vaccination strategy against AIDS.

Leishmania infantum-specific T cell lines derived from asymptomatic dogs that lyse infected macrophages in a major histocompatibility complex-restricted manner

Protective immunity to leishmaniasis has been demonstrated in murine models to be mediated by T cells and the cytokines they produce. We have previously shown that resistance to experimental Leishmania infantum infection in the dog, a natural host and reservoir of the parasite, is associated with the proliferation of peripheral blood mononuclear cells (PBMC) to parasite antigen and to the production of interleukin-2 and tumour necrosis factor. In this study we show that PBMC from asymptomatic experimentally infected dogs produce interferon-gamma upon parasite antigen-specific stimulation, whereas lymphocytes from symptomatic dogs do not. In addition, we report for the first time the lysis of L. infantum-infected macrophages by PBMC from asymptomatic dogs and by parasite-specific T cell lines derived from these animals. These T cell lines were generated by restimulation in vitro with parasite soluble antigen and irradiated autologous PBMC as antigen-presenting cells. We show that lysis of infected macrophages by T cell lines is major histocompatibility complex restricted. Characterization of parasite-specific cytotoxic T cell lines revealed that the responding cells are CD8+. However, for some animals, CD4+ T cells that lyse infected macrophages were also found. In contrast to asymptomatic dogs, lymphocytes from symptomatic dogs failed to proliferate and produce interferon-gamma after Leishmania antigen stimulation in vitro and were not capable of lysing infected macrophages. These results suggest that both the production of interferon-gamma and the destruction of the parasitized host cells by Leishmania-specific T cells play an important role in resistance to visceral leishmaniasis.