Adjuvant properties of listeriolysin O protein in a DNA vaccination strategy

Abstract

The use of infectious agents as vaccine adjuvants has shown utility in both prophylactic and therapeutic vaccinations. Listeria monocytogenes has been used extensively as a vaccine vehicle due to its ability to initiate both CD4(+) and CD8(+) immune responses. Previous work from this laboratory has used transgenic Listeria to deliver vaccine constructs. A chimeric protein composed of tumor antigen and a non-hemolytic variant of the Listeria protein, listeriolysin O (LLO), has demonstrated effective tumor protection beyond that of antigen alone expressed in the same system. To address the question of how fusion with LLO improves vaccine efficacy, we constructed a number of DNA plasmid vaccines to isolate this effect in the absence of other endogenous Listeria effects. Here we have analyzed the ability of these vaccines to induce the regression of previously established tumors. A vaccine strategy using DNA vaccines bearing the tumor antigen either alone or in combination with LLO in addition to plasmids encoding MIP-1alpha and GM-CSF was examined. Further, LLO was used either as a chimera or in a bicistronic construct to address the importance of fusion between these elements. Notably, the strategies employing both chimeric and bicistronic vaccines were effective in reducing tumor burden suggesting that LLO can act as an adjuvant that does not require fusion with the tumor antigen to mediate its effect.

Listeria monocytogenes-Derived Listeriolysin O Has Pathogen-Associated Molecular Pattern-Like Properties Independent of Its Hemolytic Ability

“…In accordance with the PAMP hypothesis, LLO has been reported to improve antigen presentation in the context of major histocompatibility complex (MHC) class I molecules and to enhance T cell-mediated immune responses when genetically fused to (12)(13)(14), mixed with (15), or conjugated to (16) antigens. The adjuvant properties of LLO have been demonstrated not only in the context of L. monocytogenes (17) but also in various vaccine platforms, such as modified vaccinia virus Ankara (MVA) or plasmid DNA (pDNA), and as a protein carrier for anti-idiotypic immune therapy of non-Hodgkin's lymphoma (12,13,(17)(18)(19)(20), suggesting broad applicability in immunotherapeutic strategies.…”

“…The adjuvant properties of LLO have been demonstrated not only in the context of L. monocytogenes (17) but also in various vaccine platforms, such as modified vaccinia virus Ankara (MVA) or plasmid DNA (pDNA), and as a protein carrier for anti-idiotypic immune therapy of non-Hodgkin's lymphoma (12,13,(17)(18)(19)(20), suggesting broad applicability in immunotherapeutic strategies. Although there are sufficient data supporting LLO as a potent immune activator, how it exerts these effects is unknown.…”

Cancer immunotherapy using Listeria monocytogenes and listerial virulence factors

“…In addition to enhanced proteasomal degradation and presentation on MHC I, we hypothesized that differences in the efficacy of the two vaccines were linked, in part, to the ability of each of the vaccine strains to render otherwise immature professional antigen presenting cells such as dendritic cells (DCs) into effective, mature APCs [31]. In vitro comparisons of Lm-E7, Lm-LLO-E7, and wild-type Listeria monocytogenes revealed enhanced upregulation by Lm-LLO-E7 of MHC II as well as CD40, CD80, CD86, B7-HI, and B7-DC on bone marrow derived DCs.…”

“…In order to separate the non-specific effects of Lm infection from the adjuvant effect of LLO for these studies, we employed the use of a eukaryotic expression vector to produce a series of DNA vaccines [31]. The DNA vaccines expressed either E7 alone (pcDNA3.1-E7), LLO alone (pcDNA3.1-LLO), LLO fused to E7 (pcDNA3.1-LLOE7), or LLO and E7 expressed as a bicistronic message (pcDNA3.1-LLO-IRES-E7).…”

Listeriolysin O as a strong immunogenic molecule for the development of new anti-tumor vaccines

“…In fact, Paterson's group showed that LLO can act as an adjuvant for anti-tumor vaccines without being fused to the tumor antigen and can be expressed alone without reducing the vaccine potency. 124 A heterologous prime-boost immunization strategy is currently predominantly utilized to conquer the problem of vectorpointing immune responses in cancer immunotherapy. To date, the heterologous prime-boost regimen is among the most potent strategy used to induce cellular immune responses.…”