Recombinant Liver Stage Antigen-1 [LSA-1] formulated with AS01 or AS02 is safe, elicits high titer antibody and induces IFN-gamma/IL-2 CD4+ T cells but does not protect against experimental

Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA.
Vaccine (Impact Factor: 3.62). 10/2009; 28(31):5135-44. DOI: 10.1016/j.vaccine.2009.08.046
Source: PubMed


Plasmodium falciparum Liver Stage Antigen 1 (LSA-1) is a pre-erythrocytic stage antigen. Our LSA-1 vaccine candidate is a recombinant protein with full-length C- and N-terminal flanking domains and two of the 17 amino acid repeats from the central repeat region termed "LSA-NRC." We describe the first Phase I/II study of this recombinant LSA-NRC protein formulated with either the AS01 or AS02 adjuvant system. We conducted an open-label Phase I/II study. Thirty-six healthy malaria-naïve adults received one of four formulations by intra-deltoid injection on a 0 and 1 month schedule; low dose (LD) LSA-NRC/AS01:10microg LSA-NRC/0.5ml AS01 (n=5), high dose (HD) LSA-NRC/AS01: 50microg LSA-NRC/0.5ml AS01 (n=13); LD LSA-NRC/AS02: 10microg LSA-NRC/0.5ml AS02 (n=5) and HD LSA-NRC/AS02: 50microg LSA-NRC/0.5ml AS02 (n=13). Two weeks post-second immunization, the high dose vaccinees and 6 non-immunized infectivity controls underwent experimental malaria sporozoite challenge. The vaccines showed a reassuring safety profile but were moderately reactogenic. There were no serious adverse events. All subjects seroconverted after the first immunization. Following the second immunization, LSA-1-specific CD4+ T cells producing two cytokines (IL-2 and IFN-gamma) were found by intra-cellular staining in all subjects in the LD LSA-NRC/AS01B group and in 3 of 5 subjects in the LD LSA-NRC/AS02 group. In contrast, the HD LSA-NRC/AS01 and HD LSA-NRC/AS02 group subjects had fewer LSA-1-specific CD4+ T cells, and minimal to no IFN-gamma responses. There was no increase in LSA-1-specific CD8+ T cells found in any group. Per protocol, 22 high dose vaccinees, but no low dose vaccinees, underwent P. falciparum homologous malaria challenge (3D7 clone). All vaccinees became parasitemic and there was no delay in their pre-patent period versus controls (p=0.95). LSA-NRC/AS01 and LSA-NRC/AS02 elicited antigen-specific antibody and CD4+ T cell responses, but elicited no protective immunity. Although the optimal antigen dose of LSA-NRC may not have been selected for the challenge portion of the protocol, further vaccine development based upon LSA-1 should not be excluded and should include alternative vaccine platforms able to elicit additional effector mechanisms such as CD8+ T cells.

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Available from: Michele D Spring
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    • "Adjuvanted RTS,S (RTS,S/AS), a candidate malaria vaccine consisting of the recombinant protein RTS,S, which is comprised of sequences of the circumsporozoite protein (CSP) and hepatitis B surface antigen (HBsAg), is uniquely able to protect malaria-naïve adult subjects after experimental malaria challenge against infection [1] [2] [3] [4] [5], and African adults and children exposed to diverse strains against clinical and severe disease [6] [7] [8] [9] [10] [11]. Other strategies have been concurrently explored to improve the efficacy of adjuvanted RTS,S, including formulation with more potent adjuvants [12–14], prime-boost regimens with alternative vaccine platforms expressing the CSP [15] [16] [17] [18] and evaluation of other adjuvanted Plasmodium falciparum antigens [19] [20] [21] individually or in combination with RTS,S [22] [23]. We report two clinical evaluations which aimed at improving adjuvanted RTS,S by combining it with the recombinant thrombospondin related anonymous protein (TRAP) of P. falciparum, PfTRAP [24]. "
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    ABSTRACT: In an attempt to improve the efficacy of the candidate malaria vaccine RTS,S/AS02, two studies were conducted in 1999 in healthy volunteers of RTS,S/AS02 in combination with recombinant Plasmodium falciparum thrombospondin-related anonymous protein (TRAP). In a Phase 1 safety and immunogenicity study, volunteers were randomized to receive TRAP/AS02 (N = 10), RTS,S/AS02 (N = 10), or RTS,S + TRAP/AS02 (N = 20) at 0, 1 and 6-months. In a Phase 2 challenge study, subjects were randomized to receive either RTS,S + TRAP/AS02 (N = 25) or TRAP/AS02 (N = 10) at 0 and 1-month, or to a challenge control group (N = 8). In both studies, the combination vaccine had an acceptable safety profile and was acceptably tolerated. Antigen-specific antibodies, lymphoproliferative responses, and IFN-γ production by ELISPOT assay elicited with the combination vaccine were qualitatively similar to those generated by the single component vaccines. However, post-dose 2 anti-CS antibodies in the RTS,S + TRAP/AS02 vaccine recipients were lower than in the RTS,S/AS02 vaccine recipients. After challenge, 10 of 11 RTS,S + TRAP/AS02 vaccinees, 5 of 5 TRAP/AS02 vaccinees, and 8 of 8 infectivity controls developed parasitemia, with median pre-patent periods of 13.0, 11.0, and 12.0 days, respectively. The absence of any prevention or delay of parasitemia by TRAP/AS02 suggests no apparent added value of TRAP/AS02 as a candidate vaccine. The absence of significant protection or delay of parasitemia in the 11 RTS,S + TRAP/AS02 vaccine recipients contrasts with previous 2 dose studies of RTS,S/AS02. The small sample size did not permit identifying statistically significant differences between the study arms. However, we speculate, within the constraints of the challenge study, that the presence of the TRAP antigen may have interfered with the vaccine efficacy previously observed with this regimen of RTS,S/AS02, and that any future TRAP-based vaccines should consider employing alternative vaccine platforms.
    Full-text · Article · Nov 2014 · Vaccine
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    • "It has been shown that the gene products of liver-stage sporozoites are accessible to the host MHC class I-dependent antigen-processing machinery that is required for CD8 + T cell recognition and are thus considered potential vaccine targets against the disease (Birkett et al., 2013). Among these genes, the immunogenic properties of Plasmodium liver-stage antigen-1 have been investigated, and this antigen has been currently evaluated in vaccine protocols aimed at inducing protection from malaria liver-stage parasites (Hill et al., 1992; Pichyangkul et al., 2008; Rodríguez et al., 2009; Cummings et al., 2010). The choice of liver-stage development genes as vaccine targets seems to be of relevance because the antigens can be expressed early or late during parasite development in the liver, thus varying the efficacy of the immunity to the infected hepatocytes. "
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    ABSTRACT: Plasmodium sporozoites and liver stages express antigens that are targeted to the MHC-Class I antigen-processing pathway. After the introduction of Plasmodium sporozoites by Anopheles mosquitoes, bone marrow-derived dendritic cells in skin-draining lymph nodes are the first cells to cross-present parasite antigens and elicit specific CD8(+) T cells. One of these antigens is the immunodominant circumsporozoite protein (CSP). The CD8(+) T cell-mediated protective immune response against CSP is dependent on the interleukin loop involving IL-4 receptor expression on CD8(+) cells and IL-4 secretion by CD4(+) T cell helpers. In a few days, these CD8(+) T cells re-circulate to secondary lymphoid organs and the liver. In the liver, the hepatic sinusoids are enriched with cells, such as dendritic, sinusoidal endothelial and Kupffer cells, that are able to cross-present MHC class I antigens to intrahepatic CD8(+) T cells. Specific CD8(+) T cells actively find infected hepatocytes and target intra-cellular parasites through mechanisms that are both interferon-γ-dependent and -independent. Immunity is mediated by CD8(+) T effector or effector-memory cells and, when present in high numbers, these cells can provide sterilizing immunity. Human vaccination trials with recombinant formulations or attenuated sporozoites have yet to achieve the high numbers of specific effector T cells that are required for sterilizing immunity. In spite of the limited number of specific CD8(+) T cells, attenuated sporozoites provided multiple times by the endovenous route provided a high degree of protective immunity. These observations highlight that CD8(+) T cells may be useful for improving antibody-mediated protective immunity to pre-erythrocytic stages of malaria parasites.
    Full-text · Article · Aug 2014 · Frontiers in Microbiology
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    • "However, Phase I/IIa clinical trials in which humans were immunized with RTS, S/TRAP failed to provide protection in the majority of volunteers (unpublished data, as written by [30]). Moreover, immunization of humans with a recombinant liver-stage antigen-1 (LSA-1)-based vaccine elicited high antibody titers, but did also not protect against P. falciparum infection [31]. "
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    ABSTRACT: Long-lasting and sterile protective immunity against Plasmodium falciparum can be achieved by immunization of malaria-naive human volunteers under chloroquine prophylaxis with sporozoites delivered by mosquito bites (CPS-immunization). Protection is mediated by sporozoite/liver-stage immunity. In this study, the capacity of CPS-induced antibodies to interfere with sporozoite functionality and development was explored. IgG was purified from plasma samples obtained before and after CPS-immunization from two separate clinical trials. The functionality of these antibodies was assessed in vitro in gliding and human hepatocyte traversal assays, and in vivo in a human liver-chimeric mouse model. Whereas pre-treatment of sporozoites with 2 mg/ml IgG in the majority of the volunteers did not have an effect on in vitro sporozoite gliding motility, CPS-induced IgG showed a distinct inhibitory effect in the sporozoite in vitro traversal assay. Pre-treatment of P. falciparum sporozoites with post-immunization IgG significantly inhibited sporozoite traversal through hepatocytes in 9/9 samples when using 10 and 1 mg/ml IgG, and was dose-dependent, resulting in an average 16% and 37% reduction with 1 mg/ml IgG (p = 0.003) and 10 mg/ml IgG (p = 0.002), respectively. In vivo, CPS-induced IgG reduced liver-stage infection and/or development after a mosquito infection in the human liver-chimeric mouse model by 91.05% when comparing 11 mice receiving post-immunization IgG to 11 mice receiving pre-immunization IgG (p = 0.0008). It is demonstrated for the first time that CPS-immunization induces functional antibodies against P. falciparum sporozoites, which are able to reduce parasite-host cell interaction by inhibiting parasite traversal and liver-stage infection. These data highlight the functional contribution of antibody responses to pre-erythrocytic immunity after whole-parasite immunization against P. falciparum malaria.
    Full-text · Article · Apr 2014 · Malaria Journal
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