PREPS and L-particles: a new approach to virus-like particle vaccines

Conventional virus-like particles are usually composed of a single structural protein which spontaneously assembles into particles. L-particles, a little-known type of virus-like particle, are produced as part of the natural infectious process of many, if not all, alpha-herpesviruses. L-particles lack the nucleocapsid present in the infectious virion but contain all of the virus envelope and tegument proteins. L-particles contain no virus DNA and are noninfectious, though they are biologically competent, since they are capable of delivering viral envelope and tegument proteins to cells. When cells are infected with herpes simplex virus Type 1 under conditions where viral DNA synthesis is blocked, previral DNA replication enveloped particles are produced. These are similar to L-particles, but differ slightly in protein composition. This article reviews the available data regarding these vaccine candidates and explores the wide-ranging potential applications, including vaccine candidates against infectious diseases and cancer, as well as a protein delivery vector.     

Protection against filovirus infection: virus-like particle vaccines

Significant progress has been made in vaccine development against infection by Ebola and Marburg viruses, members of the Filoviridae, which cause severe hemorrhagic fevers in humans with no effective treatment and a mortality rate of up to 90%. Several vaccine strategies have been shown to effectively protect immunized animals against filovirus infection. Among these candidate vaccine strategies, virus-like particles represent a promising approach and have been shown to protect small laboratory animals as well as nonhuman primates against lethal challenge by Ebola and/or Marburg viruses. This review briefly summarizes filovirus epidemiology and pathogenesis, and focuses on the discussion of recent advances in filovirus vaccine development and the current understanding of protective immune responses against filovirus infection with an emphasis on the progress and challenge of filovirus virus-like particle vaccine development.     

HPV vaccines: the beginning of the end for cervical cancer

Vaccines prophylactic against infection with human papillomavirus (HPV) are based on alum adjuvanted virus-like particles. Two such vaccines have recently been shown to prevent persistent HPV infection and associated cervical cancer precursor lesions. The genotype-specific neutralising antibody directed at conformational epitopes of the L1 major capsid protein is likely to mediate protection. Vaccines therapeutic for persisting HPV infection can eliminate transplantable tumors in animal models, but are of limited efficacy in mice grafted with skin that expresses HPV antigens or in humans. This paradox has been partially resolved by data clarifying the immunoregulatory role of skin cytokines (e.g. transforming growth factor-beta and interleukin-10) and the consequences of antigen presentation by subsets of skin-associated antigen-presenting cells.     

Meningococcal vaccines: a progress report

Neisseria meningitidis causes a wide range of human disease and remains a common cause of septicaemia and meningitis. Meningococcal serogroups A, B, C and Y cause the majority of cases of invasive disease in the US and throughout the world, with epidemics usually caused by serogroups A and C. Most patients with meningococcaemia, with or without meningitis, respond to standard antimicrobial therapy with either penicillin or ampicillin, but the recent emergence of meningococcal strains that are intermediately resistant to penicillin may alter these recommendations in the future. Given the devastating nature of meningococcal disease and emergence of these resistant strains, prevention (specifically through vaccination) remains the best approach to control this serious infection. A polysaccharide meningococcal vaccine is efficacious against disease caused by serogroups A, C, Y and W135, but is not effective in infants and children aged <2 years, and the duration of efficacy decreases markedly during the first 3 years after a single dose of the vaccine. Conjugate meningococcal vaccines have been developed to address these concerns. Initial studies with the meningococcal C conjugate vaccine have shown that the vaccine is safe and immunogenic and provides a T cell-dependent antigen that can be boosted by further doses of vaccine, or following exposure to the homologous organism or cross-reacting antigens. The UK recently implemented routine vaccination with the meningococcal C conjugate vaccine to all infants, and to all persons aged >1 year in a catch-up programme to immunise all school-aged children and young adults up to 20 years of age. Early postlicensure data indicate that this vaccine has shown significant efficacy in reduction of invasive meningococcal disease in these age groups. The full impact of vaccination will be determined once all age groups are immunised.     

Prevalence of antibodies to human papillomavirus (HPV) type 16 virus-like particles in relation to cervical HPV infection among college women.

A human papillomavirus type 16 (HPV-16) virus-like particle (VLP)-based enzyme-linked immunosorbent assay (ELISA) was used to measure serum antibody to capsid proteins in 376 sexually active college women who were also screened for the presence of genital HPVs by PCR and interviewed for demographic and behavioral risk factors for HPV infection. The seroprevalence was 46% in women with HPV-16 DNA in the genital tract. The corresponding values for women who harbored other HPV types or no HPV in the genital tract were 30 and 19%, respectively (HPV-16 group versus no-HPV group; odds ratio [OR], 3.7; 95% confidence interval [CI], 1.5 to 8.9). The antibody response was significantly higher among women with a high viral load than among those with a low viral load (median optical density value, 0.838 versus 0.137, P = 0.009). Comparable levels of seroreactivity were observed among women infected with HPV types distantly or closely related genetically to HPV-16. Seroreactivity was significantly associated with an age of 25 to 30 years (OR, 2.3; 95% CI, 1.2 to 4.4), three or more lifetime sexual partners (OR, 2.9; 95% CI, 1.1 to 10), and history of a sexually transmitted disease other than HPV (OR, 3.1; 95% CI, 1.5 to 6.3). The percent seropositivity increased linearly with number of lifetime sexual partners until reaching a plateau at 35% for women with more than six partners (chi for linear trend, P < 0.001). The low sensitivity of HPV-16 VLP-based ELISA may limit the usefulness of the assay as a diagnostic test for HPV-16 infection. However, the assay appears to have adequate specificity and should be useful as an epidemiological marker of HPV-16 infection and sexual behavior.     

Vaccination to prevent and treat cervical cancer

Human papillomaviruses (HPVs) are the primary etiologic agents of cervical cancer. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by HPV vaccines. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. However, because the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are coexpressed in the majority of HPV-containing carcinomas. Thus, therapeutic vaccines targeting E6 and E7 may provide the best option for controlling HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or protein, in nucleic acid form, as components of chimeric virus-like particles, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. If these preventive and therapeutic HPV vaccines prove successful in patients, as they have in animal models, then oncogenic HPV infection and its associated malignancies may be controllable by vaccination.     

Cervical cancer vaccines: recent advances in HPV research

Carcinomas of the anogenital tract, particularly cancer of the cervix, account for almost 12% of all cancers in women, and so represent the second most frequent gynecological malignancy in the world (48). It is well established that chronic infection of cervical epithelium by human papillomaviruses (HPV) is necessary for the development of cervical cancer. In fact, HPV DNA has been demonstrated in more than 99.7% of cervical cancer biopsy specimens, with high-risk HPV16 and HPV18 sequences being most prevalent (45,73). Therefore, an effective vaccine that would mount an immune response against HPV-related proteins might contribute to the prevention or elimination of HPV expressing lesions. This review will concentrate on the most recent advances in vaccine-mediated prevention and immunotherapy of HPV-induced cervical cancer, including presentations from the 20(th) International HPV Conference held in October 2002 in Paris.     

Plant-derived vaccines: An approach for affordable vaccines against cervical cancer

Several types of human papillomavirus (HPV) are causatively associated with cervical cancer, which is the second most common cancer in women worldwide. HPV-16 and 18 are among the high risk types and responsible for HPV infection in more than 70% of the cases. The majority of cervical cancer cases occur in developing countries. Currently available HPV vaccines are expensive and probably unaffordable for most women in low and middle income countries. Therefore, there is a need to develop cost-effective vaccines for these countries. Due to many advantages, plants offer an attractive platform for the development of affordable vaccines. These include low cost of production, scalability, low health risks and the potential ability to be used as unprocessed or partially processed material. Among several techniques, chloroplast transformation is of eminent interest for the production of vaccines because of high yield of foreign protein and lack of transgene transmission through pollen. In this commentary, we focus on the most relevant aspects of plant-derived vaccines that are decisive for the future development of cost-effective HPV vaccines.     

Heparan sulfate proteoglycans interact exclusively with conformationally intact HPV L1 assemblies: basis for a virus-like particle ELISA

In this article, we demonstrate that interaction of human papillomavirus-like particles (HPV-VLPs) with the putative glucosaminoglycan binding receptor is strictly dependent on conformational integrity. Such conformations are present on VLPs and capsomeres but not on monomers of the major capsid protein, L1, confirming reports that capsomeres can induce virus-neutralizing antibodies. Furthermore, we show the suitability of this specific interaction for development of VLP-based enzyme-linked immunosorbent assays (ELISAs), using heparin for indirect coupling of VLPs to microtiter plates, which may add an intrinsic quality control. This avoids presentation of linear, often highly cross-reactive epitopes of L1. In addition, heparin specifically interacts with a wide variety of HPV types, making it a prime candidate for a universal capture molecule.     

Development of vaccines to prevent malaria in pregnant women: WHO MALVAC meeting report

The major public health consequences of malaria in pregnancy have long been acknowledged. However, further information is still required for development and implementation of a malaria vaccine specifically directed to prevent malaria in pregnant women and improve maternal, fetal and infant outcomes. The WHO Malaria Vaccine Advisory Committee (MALVAC) provides guidance to the WHO on strategic priorities and research needs for development of vaccines to prevent malaria. Here we summarize the discussions and conclusions of a MALVAC scientific forum meeting on considerations in the development of vaccines to prevent malaria in pregnant women. This report includes brief summaries of what is known, and major knowledge gaps in disease burden estimation, pathogenesis and immunity, and the challenges with current preventive strategies for malaria in pregnancy. We conclude with the formulation of a conceptual framework for research and development for vaccines to prevent malaria in pregnant women.     

Enhanced influenza virus-like particle vaccines containing the extracellular domain of matrix protein 2 and a Toll-like receptor ligand

The extracellular domain of matrix protein 2 (M2e) is conserved among influenza A viruses. The goal of this project is to develop enhanced influenza vaccines with broad protective efficacy using the M2e antigen. We designed a membrane-anchored fusion protein by replacing the hyperimmunogenic region of Salmonella enterica serovar Typhimurium flagellin (FliC) with four repeats of M2e (4.M2e-tFliC) and fusing it to a membrane anchor from influenza virus hemagglutinin (HA). The fusion protein was incorporated into influenza virus M1-based virus-like particles (VLPs). These VLPs retained Toll-like receptor 5 (TLR5) agonist activity comparable to that of soluble FliC. Mice immunized with the VLPs by either intramuscular or intranasal immunization showed high levels of systemic M2-specific antibody responses compared to the responses to soluble 4.M2e protein. High mucosal antibody titers were also induced in intranasally immunized mice. All intranasally immunized mice survived lethal challenges with live virus, while intramuscularly immunized mice showed only partial protection, revealing better protection by the intranasal route. These results indicate that a combination of M2e antigens and TLR ligand adjuvants in VLPs has potential for development of a broadly protective influenza A virus vaccine.     

Celiac disease: a progress report.

Celiac disease (CD) has a wide range of clinical presentations and is being diagnosed with increasing frequency in patients in the 4th and 5th decades of life. The diagnosis of CD is confirmed by a combination of clinical, serological, and morphological findings associated with a response to a gluten-free diet. In small-bowel mucosal biopsy specimens, abnormalities range from minimal (increased villous intraepithelial lymphocytes only) to severe (complete villous blunting with crypt hyperplasia). Recognition of CD is important because appropriate therapy of this condition will obviate the risk of its severe complications.     

Metastasis of cancer to cancer: report of a case.

A case of primary, widely disseminated prostatic carcinoma causing bilateral urinary tract obstruction, hydronephrosis, and papillary necrosis and metastasizing in the substance of an unusual histologic variant of renal cell carcinoma and tubular adenoma of the same kidney is presented. Unusual incidental findings include isolated cardiac amyloidosis and myocardial abscesses. A brief review of the literature is presented. The peculiar tendency for renal cell carcinoma to be the host tumor for other primary carcinomas and various theories to account for this phenomenon are commented upon briefly.