- Email: [email protected]
'Flu vaccine decided
News & Comment
‘Flu vaccine decided
TRENDS in Microbiology Vol.9 No.4 April 2001
Letters
Listeriolysin – a useful cytolysin
The composition of the influenza vaccine for the year 2001–2002 northern hemisphere influenza season has been decided and communicated to vaccine manufacturers by the WHO, following agreement on its content by international experts at a WHO meeting held in Geneva, Switzerland in February 2001. It has been recommended that the vaccine contain the following three components: an A/New Caledonia/20/99(H1N1)-like virus, an A/Moscow/10/99(H3N2)-like virus and a B/Sichuan/379/99-like virus. Between November 2000 and February 2001, influenza activity was mainly attributed to influenza A(H1N1) virus, which cocirculated with influenza B viruses in some countries. Influenza A(H3N2) viruses were isolated sporadically. CK http://www.who.int
Cornucopia of Archaea We might never be safe from surprises, thanks to the immense biodiversity on the planet. Archaea have long been characterized as organisms of extreme environments, but new studies sponsored by the US National Science Foundation have revealed that vast amounts of Archaea populate the open sea. Researchers David Karl, Markus Karner and Edward DeLong are part of the Hawaii Ocean Time-series (HOT) project to study the north Pacific Ocean. Their findings describe high numbers of pelagic euryarchaeota and pelagic crenarchaeota in the ocean waters. Genomics, suggests DeLong, is the key to overcoming our ignorance of life on Earth. AV http://www.nsf.gov/od/lpa/news/press/01/ pr0105.htm
In Brief compiled by Cathel Kerr ([email protected]) and Alexandra Venter ([email protected])
161
The erudite review of the use of listeriolysin O (LLO), a cytolysin secreted by Listeria monocytogenes, to target compounds into the cytosol of mammalian cells for pharmacological and/or immunological purposes that appeared in the January 2001 issue of Trends in Microbiology1 covered an important facet of this versatile molecule. However, we have recently discovered another useful property of LLO that lies outside its hemolytic ability. We have shown that fusing an antigen to a truncated form of LLO improves the immunogenicity of the antigen. Thus, a L. monocytogenes strain that expresses and secretes a fusion protein of the E7 protein from human papilloma virus (HPV) strain 16 and listeriolysin is a more potent immunotherapeutic agent for HPVimmortalized tumors than is a strain of L. monocytogenes that secretes the E7 protein alone (G.R. Gunn III et al., unpublished). This effect is not caused by the ability of listeriolysin to dissolve endosomal membranes because the LLO used in the fusion protein has lost the domain responsible for the lytic activity. It is also not peculiar to the HPV-16 E7 antigen, as in a model system using a recombinant L. monocytogenes strain that secretes truncated LLO fused to influenza nucleoprotein (NP), an immunotherapeutic effect is observed in mice bearing established tumors of a renal cell carcinoma transformed with NP (Refs 2,3); L. monocytogenes expressing only NP is largely ineffective against this tumor (Pan et al., unpublished). Additionally, to verify that the efficacy of the fusion protein is independent of the vector, we constructed a recombinant vaccinia virus that carried the gene encoding the LLO–E7 fusion protein and demonstrated that it was more immunotherapeutic for HPVimmortalized tumors than was an isogenic strain that expressed either E7 alone or E7 fused to a lysosomalassociated membrane protein signal sequence, which targets antigens to the major histocompatibility complex (MHC) class II pathway for antigen processing (A. Lamikanra et al., unpublished).
If it is not the ability of LLO to dissolve phagosomal membranes that confers improved anti-tumor immunogenicity on the carrier antigen then what is it? A recent publication4 provides a possible explanation for our findings. Decatur and Portnoy have shown that a PEST-like sequence present at the amino terminus of LLO is required for L. monocytogenes virulence4. LLO is toxic to host cells and can lyse the plasma membrane, resulting in the release of the invading bacteria before they replicate. The presence of the PEST-like sequence in LLO marks the protein for rapid destruction by the host proteolytic machinery so that when it has served its function – to facilitate the escape of L. monocytogenes from the phagolysosomal vacuole – it is destroyed before it can damage the cell4. In eukaryotic proteins, PEST sequences are rich in proline (P), glutamic acid, (E), serine (S) and threonine (T) residues, and are generally flanked by clusters containing several positively charged residues, which target the protein to the ubiquitin-proteosome pathway for degradation5. This pathway is also used by eukaryotic cells to generate immunogenic peptides that bind MHC class I (Ref. 6). Prokaryotic proteins do not commonly contain these sequences because they do not have this enzymatic pathway. We believe that the enhanced antitumor immunogenicity of LLO–E7 compared with E7 – whether introduced to the immune system by vaccinia or by L. monocytogenes – is the result of the presence of the PEST-like sequence in the fusion protein enhancing MHC class I-restricted T-cell immunity. It is noteworthy that the construct that is an ineffective anti-tumor immunotherapeutic contains the promoter, signal sequence and first seven amino acid residues of LLO (these residues were included to promote appropriate processing of the signal sequence), but does not contain the PESTlike sequence. We are currently exploring the use of PEST sequences, which are not unique to Listeria but are found in other bacterial virulence factors, as possible carriers for tumor-associated antigens for cancer immunotherapy.
http://tim.trends.com 0966-842X/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.
‘Flu vaccine decided
TRENDS in Microbiology Vol.9 No.4 April 2001
Letters
Listeriolysin – a useful cytolysin
The composition of the influenza vaccine for the year 2001–2002 northern hemisphere influenza season has been decided and communicated to vaccine manufacturers by the WHO, following agreement on its content by international experts at a WHO meeting held in Geneva, Switzerland in February 2001. It has been recommended that the vaccine contain the following three components: an A/New Caledonia/20/99(H1N1)-like virus, an A/Moscow/10/99(H3N2)-like virus and a B/Sichuan/379/99-like virus. Between November 2000 and February 2001, influenza activity was mainly attributed to influenza A(H1N1) virus, which cocirculated with influenza B viruses in some countries. Influenza A(H3N2) viruses were isolated sporadically. CK http://www.who.int
Cornucopia of Archaea We might never be safe from surprises, thanks to the immense biodiversity on the planet. Archaea have long been characterized as organisms of extreme environments, but new studies sponsored by the US National Science Foundation have revealed that vast amounts of Archaea populate the open sea. Researchers David Karl, Markus Karner and Edward DeLong are part of the Hawaii Ocean Time-series (HOT) project to study the north Pacific Ocean. Their findings describe high numbers of pelagic euryarchaeota and pelagic crenarchaeota in the ocean waters. Genomics, suggests DeLong, is the key to overcoming our ignorance of life on Earth. AV http://www.nsf.gov/od/lpa/news/press/01/ pr0105.htm
In Brief compiled by Cathel Kerr ([email protected]) and Alexandra Venter ([email protected])
161
The erudite review of the use of listeriolysin O (LLO), a cytolysin secreted by Listeria monocytogenes, to target compounds into the cytosol of mammalian cells for pharmacological and/or immunological purposes that appeared in the January 2001 issue of Trends in Microbiology1 covered an important facet of this versatile molecule. However, we have recently discovered another useful property of LLO that lies outside its hemolytic ability. We have shown that fusing an antigen to a truncated form of LLO improves the immunogenicity of the antigen. Thus, a L. monocytogenes strain that expresses and secretes a fusion protein of the E7 protein from human papilloma virus (HPV) strain 16 and listeriolysin is a more potent immunotherapeutic agent for HPVimmortalized tumors than is a strain of L. monocytogenes that secretes the E7 protein alone (G.R. Gunn III et al., unpublished). This effect is not caused by the ability of listeriolysin to dissolve endosomal membranes because the LLO used in the fusion protein has lost the domain responsible for the lytic activity. It is also not peculiar to the HPV-16 E7 antigen, as in a model system using a recombinant L. monocytogenes strain that secretes truncated LLO fused to influenza nucleoprotein (NP), an immunotherapeutic effect is observed in mice bearing established tumors of a renal cell carcinoma transformed with NP (Refs 2,3); L. monocytogenes expressing only NP is largely ineffective against this tumor (Pan et al., unpublished). Additionally, to verify that the efficacy of the fusion protein is independent of the vector, we constructed a recombinant vaccinia virus that carried the gene encoding the LLO–E7 fusion protein and demonstrated that it was more immunotherapeutic for HPVimmortalized tumors than was an isogenic strain that expressed either E7 alone or E7 fused to a lysosomalassociated membrane protein signal sequence, which targets antigens to the major histocompatibility complex (MHC) class II pathway for antigen processing (A. Lamikanra et al., unpublished).
If it is not the ability of LLO to dissolve phagosomal membranes that confers improved anti-tumor immunogenicity on the carrier antigen then what is it? A recent publication4 provides a possible explanation for our findings. Decatur and Portnoy have shown that a PEST-like sequence present at the amino terminus of LLO is required for L. monocytogenes virulence4. LLO is toxic to host cells and can lyse the plasma membrane, resulting in the release of the invading bacteria before they replicate. The presence of the PEST-like sequence in LLO marks the protein for rapid destruction by the host proteolytic machinery so that when it has served its function – to facilitate the escape of L. monocytogenes from the phagolysosomal vacuole – it is destroyed before it can damage the cell4. In eukaryotic proteins, PEST sequences are rich in proline (P), glutamic acid, (E), serine (S) and threonine (T) residues, and are generally flanked by clusters containing several positively charged residues, which target the protein to the ubiquitin-proteosome pathway for degradation5. This pathway is also used by eukaryotic cells to generate immunogenic peptides that bind MHC class I (Ref. 6). Prokaryotic proteins do not commonly contain these sequences because they do not have this enzymatic pathway. We believe that the enhanced antitumor immunogenicity of LLO–E7 compared with E7 – whether introduced to the immune system by vaccinia or by L. monocytogenes – is the result of the presence of the PEST-like sequence in the fusion protein enhancing MHC class I-restricted T-cell immunity. It is noteworthy that the construct that is an ineffective anti-tumor immunotherapeutic contains the promoter, signal sequence and first seven amino acid residues of LLO (these residues were included to promote appropriate processing of the signal sequence), but does not contain the PESTlike sequence. We are currently exploring the use of PEST sequences, which are not unique to Listeria but are found in other bacterial virulence factors, as possible carriers for tumor-associated antigens for cancer immunotherapy.
http://tim.trends.com 0966-842X/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved.