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Infection and Immunity, August 2008, p. 3742-3753, Vol. 76, No. 8
0019-9567/08/$08.00+0     doi:10.1128/IAI.00390-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Constitutive Activation of the PrfA Regulon Enhances the Potency of Vaccines Based on Live-Attenuated and Killed but Metabolically Active Listeria monocytogenes Strains{triangledown}

Peter Lauer,1* Bill Hanson,1 Edward E. Lemmens,1 Weiqun Liu,1 William S. Luckett,1 Meredith L. Leong,1 Heather E. Allen,1 Justin Skoble,1 Keith S. Bahjat,1,{dagger} Nancy E. Freitag,2 Dirk G. Brockstedt,1 and Thomas W. Dubensky Jr.1

Anza Therapeutics, Inc. (formerly a division of Cerus Corporation), Concord, California,1 Department of Microbiology and Immunology, University of Illinois, Chicago, Illinois2

Received 27 March 2008/ Returned for modification 10 May 2008/ Accepted 31 May 2008

Recombinant vaccines derived from the facultative intracellular bacterium Listeria monocytogenes are presently undergoing early-stage clinical evaluation in oncology treatment settings. This effort has been stimulated in part due to preclinical results that illustrate potent activation of innate and adaptive immune effectors by L. monocytogenes vaccines, combined with efficacy in rigorous animal models of malignant and infectious disease. Here, we evaluated the immunologic potency of a panel of isogenic vaccine strains that varied only in prfA. PrfA is an intracellularly activated transcription factor that induces expression of virulence genes and encoded heterologous antigens (Ags) in appropriately engineered vaccine strains. Mutant strains with PrfA locked into a constitutively active state are known as PrfA* mutants. We assessed the impacts of three PrfA* mutants, G145S, G155S, and Y63C, on the immunologic potencies of live-attenuated and photochemically inactivated nucleotide excision repair mutant (killed but metabolically active [KBMA]) vaccines. While PrfA* substantially increased Ag expression in strains grown in broth culture, Ag expression levels were equivalent in infected macrophage and dendritic cell lines, conditions that more closely parallel those in the immunized host. However, only the prfA(G155S) allele conferred significantly enhanced vaccine potency to KBMA vaccines. In the KBMA vaccine background, we show that PrfA*(G155S) enhanced functional cellular immunity following an intravenous or intramuscular prime-boost immunization regimen. These results form the basis of a rationale for including the prfA(G155S) allele in future live-attenuated or KBMA L. monocytogenes vaccines advanced to the clinical setting.

* Corresponding author. Mailing address: 2550 Stanwell Drive, Concord, CA 94520. Phone: (925) 771-2910. Fax: (925) 671-9267. E-mail: plauer{at}anzatherapeutics.com

{triangledown} Published ahead of print on 9 June 2008.

Editor: A. Camilli

{dagger} Present address: Discovery Research, Medarex, Milpitas, CA 95035.

Infection and Immunity, August 2008, p. 3742-3753, Vol. 76, No. 8
0019-9567/08/$08.00+0     doi:10.1128/IAI.00390-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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