Skin-Grafting and Dendritic Cell "Boosted" Humanized Mouse Models Allow the Pre-Clinical Evaluation of Therapeutic Cancer Vaccines

Vaccines have been hailed as one of the most remarkable medical advancements in human history, and their potential for treating cancer by generating or expanding anti-tumor T cells has garnered significant interest in recent years. However, the limited efficacy of therapeutic cancer vaccines in clinical trials can be partially attributed to the inadequacy of current preclinical mouse models in recapitulating the complexities of the human immune system. In this study, we developed two innovative humanized mouse models to assess the immunogenicity and therapeutic effectiveness of vaccines targeting human papillomavirus (HPV16) antigens and delivering tumor antigens to human CD141+ dendritic cells (DCs). Both models were based on the transference of human peripheral blood mononuclear cells (PBMCs) into immunocompromised HLA-A*02-NSG mice (NSG-A2), where the use of fresh PBMCs boosted the engraftment of human cells up to 80%. The dynamics of immune cells in the PBMC-hu-NSG-A2 mice demonstrated that T cells constituted the vast majority of engrafted cells, which progressively expanded over time and retained their responsiveness to ex vivo stimulation. Using the PBMC-hu-NSG-A2 system, we generated a hyperplastic skin graft model expressing the HPV16-E7 oncogene. Remarkably, human cells populated the skin grafts, and upon vaccination with a DNA vaccine encoding an HPV16-E6/E7 protein, rapid rejection targeted to the E7-expressing skin was detected, underscoring the capacity of the model to mount a vaccine-specific response. To overcome the decline in DC numbers observed over time in PBMC-hu-NSG-A2 animals, we augmented the abundance of CD141+ DCs, the specific targets of our tailored nanoemulsions (TNEs), by transferring additional autologous PBMCs pre-treated in vitro with the growth factor Flt3-L. The Flt3-L treatment bolstered CD141+ DC numbers, leading to potent antigen-specific CD4+ and CD8+ T cell responses in vivo, which caused the regression of pre-established triple-negative breast cancer and melanoma tumors following CD141+ DC-targeting TNE vaccination. Notably, using HLA-A*02-matching PBMCs for humanizing NSG-A2 mice resulted in a delayed onset of graft-versus-host disease and enhanced the efficacy of the TNE vaccination compared with the parental NSG strain. In conclusion, we successfully established two humanized mouse models that exhibited strong antigen-specific responses and demonstrated tumor regression following vaccination. These models serve as valuable platforms for assessing the efficacy of therapeutic cancer vaccines targeting HPV16-dysplastic skin and diverse tumor antigens specifically delivered to CD141+ DCs.

Targeting Staphylococcus aureus dominated skin dysbiosis in actinic keratosis to prevent the onset of cutaneous squamous cell carcinoma: Outlook for future therapies?

Cutaneous squamous cell carcinoma (cSCC) and its premalignant precursor, actinic keratosis (AK), present a global health burden that is continuously increasing despite extensive efforts to promote sun safety. Chronic UV exposure is a recognized risk factor for the development of AK and cSCC. However, increasing evidence suggests that AK and cSCC is also associated with skin microbiome dysbiosis and, in particular, an overabundance of the bacterium Staphylococcus aureus (S. aureus). Studies have shown that S. aureus-derived toxins can contribute to DNA damage and lead to chronic upregulation of proinflammatory cytokines that may affect carcinogenesis. Eradication of S. aureus from AK lesions and restoration of a healthy microbiome may therefore represent a therapeutic opportunity to alter disease progression. Whilst antibiotics can reduce the S. aureus load, antibiotic resistant S. aureus pose an increasing global public health threat. The use of specific topically delivered probiotics has been used experimentally in other skin conditions to restore eubiosis, and could therefore also present a non-invasive treatment approach to decrease S. aureus colonization and restore a healthy skin microbiome on AK lesions. This article reviews mechanisms by which S. aureus may contribute to cutaneous carcinogenesis, and discusses hypotheses and theories that explore the therapeutic potential of specific bacterial species which compete with S. aureus in an attempt to restore microbial eubiosis in skin.

Papillomavirus Immune Evasion Strategies Target the Infected Cell and the Local Immune System

Persistent infection with human papillomavirus (HPV) initiates ~5% of all human cancers, and particularly cervical and oropharyngeal cancers. HPV vaccines prevent HPV infection, but do not eliminate existing HPV infections. Papillomaviruses induce hyperproliferation of epithelial cells. In this review we discuss how hyperproliferation renders epithelial cells less sensitive to immune attack, and impacts upon the efficiency of the local immune system. These observations have significance for the design of therapeutic HPV cancer immunotherapies.

Murine HPV16 E7-expressing transgenic skin effectively emulates the cellular and molecular features of human high-grade squamous intraepithelial lesions

Currently available vaccines prevent HPV infection and development of HPV-associated malignancies, but do not cure existing HPV infections and dysplastic lesions. Persistence of infection(s) in immunocompetent patients may reflect induction of local immunosuppressive mechanisms by HPV, providing a target for therapeutic intervention. We have proposed that a mouse, expressing HPV16 E7 oncoprotein under a Keratin 14 promoter (K14E7 mice), and which develops epithelial hyperplasia, may assist with understanding local immune suppression mechanisms that support persistence of HPV oncogene-induced epithelial hyperplasia. K14E7 skin grafts recruit immune cells from immunocompetent hosts, but consistently fail to be rejected. Here, we review the literature on HPV-associated local immunoregulation, and compare the findings with published observations on the K14E7 transgenic murine model, including comparison of the transcriptome of human HPV-infected pre-malignancies with that of murine K14E7 transgenic skin. We argue from the similarity of i) the literature findings and ii) the transcriptome profiles that murine K14E7 transgenic skin recapitulates the cellular and secreted protein profiles of high-grade HPV-associated lesions in human subjects. We propose that the K14E7 mouse may be an appropriate model to further study the immunoregulatory effects of HPV E7 expression, and can facilitate development and testing of therapeutic vaccines.

Human papillomavirus E7 oncoprotein expression by keratinocytes alters the cytotoxic mechanisms used by CD8 T cells

Cervical cancer is a malignant transformation of keratinocytes initiated by the E7 oncoprotein of human papillomavirus (HPV). These tumors are characterized by keratinocyte hyperproliferation and are often infiltrated with activated CD8 T cells. HPV infection confers changes to gain immunological advantage to promote chronic infection, and these persist with malignant transformation. We investigated the relative importance of the many redundant mechanisms of cytotoxicity used by CD8 T cells to kill keratinocytes expressing HPV E7 oncoprotein using extended-duration time-lapse microscopy that allows examination of cell-to-cell interactions during killing. E7 expression by keratinocytes increased susceptibility to cell-mediated killing. However, while killing of non-transgenic keratinocytes was traditional, perforin-mediated, and caspase-dependent, E7-expression favored killing by perforin-independent, caspase-independent mechanisms. The roles of perforin, TNFα, IFNγ, Fas/FasL and PD1/PD-L1 were graded according to target cell survival to produce a hierarchy of killing mechanisms utilized in killing E7-expressing cells. TNFα was essential for perforin-mediated killing of E7-expressing cells, but not perforin-independent killing. IFNγ facilitated killing by Fas/FasL interaction, especially in the absence of perforin. Additionally, expression of E7 offered protection from killing by up regulation of PD-L1, Fas and FasL expression on keratinocytes promoting fight-back by target cells, resulting in effector cell death. This study shows that keratinocytes expressing E7 are highly susceptible to killing by CD8 T cells, but utilizing different armamentarium. Down-regulation of CD8 T cell cytotoxicity in HPV-related tumors may be due to suppression by E7-expressing keratinocytes. Immunotherapy for HPV-related cancers may be improved by suppression of PD-L1, or by suppression of FasL.

Human papillomavirus e7 oncoprotein transgenic skin develops an enhanced inflammatory response to 2,4-dinitrochlorobenzene by an arginase-1-dependent mechanism

We have shown that the expression of human papillomavirus type 16 E7 (HPV16.E7) protein within epithelial cells results in local immune suppression and a weak and ineffective immune response to E7 similar to that occuring in HPV-associated premalignancy and cancers. However, a robust acute inflammatory stimulus can overcome this to enable immune elimination of HPV16.E7-transformed epithelial cells. 2,4-Dinitrochlorobenzene (DNCB) can elicit acute inflammation and it has been shown to initiate the regression of HPV-associated genital warts. Although the clinical use of DNCB is discouraged owing to its mutagenic potential, understanding how DNCB-induced acute inflammation alters local HPV16.E7-mediated immune suppression might lead to better treatments. Here, we show that topical DNCB application to skin expressing HPV16.E7 as a transgene induces a hyperinflammatory response, which is not seen in nontransgenic control animals. The E7-associated inflammatory response is characterized by enhanced expression of Th2 cytokines and increased infiltration of CD11b(+)Gr1(int)F4/80(+)Ly6C(hi)Ly6G(low) myeloid cells, producing arginase-1. Inhibition of arginase with an arginase-specific inhibitor, N(omega)-hydroxy-nor-L-arginine, ameliorates the DNCB-induced inflammatory response. Our results demonstrate that HPV16.E7 protein enhances DNCB-associated production of arginase-1 by myeloid cells and consequent inflammatory cellular infiltration of skin.

Serologic response to human papillomavirus 16 among Australian women with high-grade cervical intraepithelial neoplasia

This study evaluated the detection of human papillomavirus (HPV) 16 antibody in HPV 16-associated cervical intraepithelial neoplasia (CIN) in Australian women. Seroreactivity to HPV 16 L1 virus-like particles was assessed in patients with CIN 2 (n= 169) and CIN 3 (n= 229) lesions previously tested for the presence of HPV DNA. Seropositivity was significantly commoner in women with HPV 16 DNA-positive lesions (98/184) than in women with no HPV DNA in the lesion (15/47) or with HPV of types other than 16 in the lesion (43/167) (P= 0.0004). In addition, seropositivity was observed in 33% (55/169) of women with CIN 2 and 46% (106/229) of women with CIN 3, in keeping with the lower fraction of CIN 2 (57/169) than CIN 3 (127/229) biopsies positive for HPV 16 DNA. HPV 16 seropositivity is most common in women with HPV 16-associated CIN, but many patients with HPV-associated CIN 3 are seronegative, and HPV 16 seropositivity is common in women with CIN associated with other HPV types. Overall, HPV 16 serology is a poor predictor of presence of HPV 16-associated CIN 3 in patient population studied.

Genomewide scans of red cell indices suggest linkage on chromosome 6q23

BACKGROUND

The red cell indices quantify the size, number and oxygen-carrying ability of erythrocytes. Although the genetic basis of many monogenic forms of anaemia is well understood, comparatively little is known about the genes responsible for variation in the red cell indices among healthy participants.

OBJECTIVE

To identify quantitative trait loci (QTLs) responsible for normal variation in the red cell indices of 391 pairs of dizygotic twins who were measured longitudinally at 12, 14 and 16 years of age.

RESULTS

Evidence suggesting linkage of red cell indices to haemoglobin concentration (LOD = 3.03) and haematocrit (LOD = 2.95) on chromosome 6q23, a region previously identified as possibly harbouring a QTL for haematocrit, was found. Evidence for linkage to several other regions of the genome, including chromosome 4q32 for red cell count and 7q for mean cell volume, was also found. In contrast, there was little evidence of linkage to the chromosomal regions containing the genes for erythropoietin (7q21) and its receptor (19p13.2), nor to the regions containing the genes for the haemoglobin alpha (16p13.3) and beta chains (11p15.5).

CONCLUSION

Findings provide additional evidence for a QTL affecting haemoglobin and haematocrit on chromosome 6q23. In contrast, polymorphisms in the genes coding for erythropoietin, its receptor and the haemoglobin alpha and beta chains do not appear to contribute substantially to variation in the red cell indices between healthy persons.

A major quantitative trait locus for CD4-CD8 ratio is located on chromosome 11

CD4-CD8 ratio is an important diagnostic measure of immune system functioning. In particular, CD4-CD8 ratio predicts the time taken for progression of HIV infection to acquired immune deficiency syndrome (AIDS) and the long-term survival of AIDS patients. To map genes that regulate differences between healthy individuals in CD4-CD8 ratio, we typed 757 highly polymorphic microsatellite markers at an average spacing of approximately 5 cM across the genome in 405 pairs of dizygotic twins at ages 12, 14 and 16. We used multipoint variance components linkage analysis to test for linkage between marker loci and CD4-CD8 ratio at each age. We found suggestive evidence of linkage on chromosome 11p in 12-year-old twins (LOD=2.55, P=0.00031) and even stronger evidence of linkage in the same region at age 14 (LOD=3.51, P=0.00003). Possible candidate genes include CD5 and CD6, which encode cell membrane proteins involved in the positive selection of thymocytes. We also found suggestive evidence of linkage at other areas of the genome including regions on chromosomes 1, 3, 4, 5, 6, 12, 13, 15, 17 and 22.

Expression of the HPV16E7 oncoprotein by thymic epithelium is accompanied by disrupted T cell maturation and a failure of the thymus to involute with age

Transgenic mice expressing the E7 protein of HPV16 from the keratin 14 promoter demonstrate increasing thymic hypertrophy with age. This hypertrophy is associated with increased absolute numbers of all thymocyte types, and with increased cortical and medullary cellularity. In the thymic medulla, increased compartmentalization of the major thymic stromal cell types and expansion of thymic epithelial cell population is observed. Neither an increased rate of immature thymocyte division nor a decreased rate of immature thymocyte death was able to account for the observed hypertrophy.

Thymocytes with reduced levels of expression of CD4 and/or CD8 were more abundant in transgenic (tg) mice and became increasingly more so with age. These thymic SP and DP populations with reduced levels of CD4 and/or CD8 markers had a lower rate of apoptosis in the tg than in the non-tg mice. The rate of export of mature thymocytes to peripheral lymphoid organs was less in tg animals relative to the pool of available mature cells, particularly for the increasingly abundant CD4^lo population. We therefore suggest that mature thymocytes that would normally die in the thymus gradually accumulated in E7 transgenic animals, perhaps as a consequence of exposure to a hypertrophied E7-expressing thymic epithelium or to factors secreted by this expanded thymic stromal cell population. The K14E7 transgenic mouse thus provides a unique model to study effects of the thymic epithelial cell compartment on thymus development and involution.

Construction and production of fluorescent papillomavirus-like particles

The green fluorescent protein (GFP) from the jellyfish Aequorea victoria has attracted widespread interest since it was demonstrated to be fluorescent in vivo when expressed in other organisms. In order to investigate papillomavirus life cycle which hampered by the unavailability of conventional cell culture system, we constructed a chimeric bovine papillomavirus (BPV) type 1 virus-like particles (VLPs) containing GFP. It was found that fluorescent VLPs could be assembled from L2 protein in which GFP is inserted into the N-terminal region of L2 (aa 88). The fluorescent VLPs could also be assembled from a GFP/L2 fusion protein in which part of the L2 sequence had been deleted. In vitro, fluorescent VLPs could bind to CV-1 cells, and this VLP/cell interaction could be analyzed by FACS assay. These results demonstrated that GFP could incorporate into BPV1 VLPs without disruption of the VLP structure. Fluorescent VLPs might be a useful tool for study of papillomavirus virus/cell interaction.

Polynucleotide viral vaccines: codon optimisation and ubiquitin conjugation enhances prophylactic and therapeutic efficacy

Papillomavirus infection is a major antecedent of anogenital malignancy. We have previously established that the L1 and L2 capsid genes of papillomavirus have suboptimal codon usage for expression in mammalian cells. We now show that the lack of immunogenicity of polynucleotide vaccines based on the L1 gene can be overcome with codon modified L1, which induces strong immune responses, including conformational virus neutralising antibody and delayed type hypersensitivity. Conjugation of a ubiquitin gene to a hybrid gene incorporating L1 and the E7 non-structural papillomavirus protein improved E7 specific CTL responses, and induced protection against an E7 expressing tumour, but induced little neutralising antibody. However, a mixture of ubiquitin conjugated and non-ubiquitin conjugated polynucleotides induced virus neutralising antibody and E7 specific CD8 T cells. An optimal combined prophylactic/therapeutic viral vaccine might therefore comprise ubiquitin conjugated and non-ubiquitinated genes, to induce prophylactic neutralising antibody and therapeutic cell mediated immune responses.

Tolerance or immunity to a tumor antigen expressed in somatic cells can be determined by systemic proinflammatory signals at the time of first antigen exposure

Mice transgenic for the E7 tumor Ag of human papillomavirus type 16, driven from a keratin 14 promoter, express E7 in keratinocytes but not dendritic cells. Grafted E7-transgenic skin is not rejected by E7-immunized mice that reject E7-transduced transplantable tumors. Rejection of recently transplanted E7-transgenic skin grafts, but not of control nontransgenic grafts or of established E7-transgenic grafts, is induced by systemic administration of live or killed Listeria monocytogenes or of endotoxin. Graft recipients that reject an E7 graft reject a subsequent E7 graft more rapidly and without further L. monocytogenes exposure, whereas recipients of an E7 graft given without L. monocytogenes do not reject a second graft, even if given with L. monocytogenes. Thus, cross-presentation of E7 from keratinocytes to the adaptive immune system occurs with or without a proinflammatory stimulus, but proinflammatory stimuli at the time of first cross-presentation of Ag can determine the nature of the immune response to the Ag. Furthermore, immune effector mechanisms responsible for rejection of epithelium expressing a tumor Ag in keratinocytes are different from those that reject an E7-expressing transplantable tumor. These observations have implications for immunotherapy for epithelial cancers.

Association of clinical, radiological and synovial immunopathological responses to anti-rheumatic treatment in rheumatoid arthritis

OBJECTIVES

To compare immunohistochemical scoring with clinical scoring and radiology for the assessment of rheumatoid arthritis (RA) disease activity, synovial tissue (ST) biopsied arthroscopically was assessed from 18 patients before and after commencement of disease-modifying anti-rheumatic drug (DMARD) therapy.

METHODS

Lymphocytes, macrophages, differentiated dendritic cells (DC), vascularity, tumour necrosis factor (TNF) alpha and interleukin-1beta levels were scored. Clinical status was scored using the American College of Rheumatology (ACR) core set and serial radiographs were scored using the Larsen and Sharp methods. Histopathological evidence of activity included infiltration by lymphocytes, DC, macrophages, tissue vascularity, and expression of lining and sublining TNFalpha. These indices co-varied across the set of ST biopsies and were combined as a synovial activity score for each biopsy.

RESULTS

The change in synovial activity with treatment correlated with the ACR clinical response and with decreased radiological progression by the Larsen score. The ACR response to DMARD therapy, the change in synovial activity score and the slowing of radiological progression were each greatest in patients with high initial synovial vascularity.

CONCLUSIONS

The data demonstrate an association between clinical, radiological and synovial immunopathological responses to anti-rheumatic treatment in RA. High ST vascularity may predict favourable clinical and radiological responses to treatment.

Efficiency of delivery of DNA to cells by bovine papillomavirus type-1 L1/L2 pseudovirions

To investigate the efficiency of encapsidation of plasmid by papillomavirus virus-like particles (PV VLPs), and the infectivity of the resultant PV pseudovirions, Cos-1 cells were transfected with an 8-kb plasmid incorporating a green fluorescent protein (GFP) reporter gene (pGSV), and infected with bovine PV (BPV-1) L1/L2 recombinant vaccinia virus to produce BPV1 pseudovirions. Approximately 1 in 1.5 x 10(4) of dense (1.35 g/ml) PV pseudovirions and 0.3 in 10(4) of less-dense (1.29 g/ml) pseudovirions packaged an intact pGSV plasmid. The majority (>75%) of packaged plasmids contained deletions, and the deletions affected all tested genes. After exposure of Cos-1 cells to BPV-1 pseudovirions at an MOI of 40,000:1, 6% of cells expressed GFP, giving a calculated efficiency of delivery of the pGSV plasmid, by pseudovirions which had packaged an intact plasmid, of approximately 5%. Plasmid delivery was not effected by purified pGSV plasmid, was blocked by antiserum against BPV-1, and was not blocked by DNase treatment of pseudovirions, confirming that delivery was mediated by DNA within the pseudovirion. We conclude that a major limitation to the use of PV pseudovirions as a gene delivery system is that intact plasmid DNA is not efficiently selected for packaging by VLPs in cell-based pseudovirions production systems.

Nonspecific down-regulation of CD8+ T-cell responses in mice expressing human papillomavirus type 16 E7 oncoprotein from the keratin-14 promoter

The E7 oncoprotein of human papillomavirus 16 (HPV16) transforms basal and suprabasal cervical epithelial cells and is a tumor-specific antigen in cervical carcinoma, to which immunotherapeutic strategies aimed at cytotoxic T-lymphocyte (CTL) induction are currently directed. By quantifying major histocompatibility complex class I tetramer-binding T cells and CTL in mice expressing an HPV16 E7 transgene from the keratin-14 (K14) promoter in basal and suprabasal keratinocytes and in thymic cortical epithelium, we show that antigen responsiveness of both E7- and non-E7-specific CD8+ cells is down-regulated compared to non-E7 transgenic control mice. We show that the effect is specific for E7, and not another transgene, expressed from the K14 promoter. Down-regulation did not involve deletion of CD8+ T cells of high affinity or high avidity, and T-cell receptor (TCR) Vbeta-chain usage and TCR receptor density were similar in antigen-responsive cells from E7 transgenic and non-E7 transgenic mice. These data indicate that E7 expressed chronically from the K14 promoter nonspecifically down-regulates CD8+ T-cell responses. The in vitro data correlated with the failure of immunized E7 transgenic mice to control the growth of an E7-expressing tumor challenge. We have previously shown that E7-directed CTL down-regulation correlates with E7 expression in peripheral but not thymic epithelium (T. Doan et al., J. Virol. 73:6166-6170, 1999). The findings have implications for the immunological consequences of E7-expressing tumor development and E7-directed immunization strategies. Generically, the findings illustrate a T-cell immunomodulatory function for a virally encoded human oncoprotein.

Association of bovine papillomavirus type 1 with microtubules

Transport of BPV-1 virus from the cell membrane to the nucleus was studied in vitro in CV-1 cells. At reduced temperature (4 degrees C), BPV-1 binding to CV-1 cells was unaffected but there was no transport of virions across the cytosol. Electron microscopy showed BPV-1 virions in association with microtubules in the cytoplasm, a finding confirmed by co-immunoprecipitation of L1 protein and tubulin. Internalization of virus was unimpaired in cells treated with the microtubule-depolymerizing drug nocodazole but virions were retained in cytoplasmic vesicles and not transported to the nucleus. We conclude that a microtubule transport mechanism in CV-1 cells moves intact BPV-1 virions from the cell surface to the nuclear membrane.

Multiple conformational epitopes are recognized by natural and induced immunity to the E7 protein of human papilloma virus type 16 in man

The reactivity of sera from patients with cervical cancer with the E7 protein of human papilloma virus type 16 (HPV16) was estimated using a novel non-radioactive immunoprecipitation assay and four established protein- and peptide-based immunoassays. Six of 14 sera from patients with cervical cancer and 1 of 10 sera from healthy laboratory staff showed repeated reactivity with E7 in at least one assay. Four of the 7 reactive sera were consistently reactive in more than one assay, but only one was reactive in all four assays. Following immunization with E7, 2 of 5 patients with cervical cancer had increased E7-specific reactivity, measurable in one or more assays. No single assay was particularly sensitive for E7 reactivity, or predictive of cervical cancer. Mapping of E7 reactivity to specific E7 peptides was unsuccessful, suggesting that natural or induced E7 reactivity in human serum is commonly directed to conformational epitopes of E7. These results suggest that each assay employed in this study measures a different aspect of E7 reactivity, and that various reactivities to E7 may manifest following HPV infection or immunization. This finding is of significance for monitoring of E7 immunotherapy and for serological screening for cervical cancer.

Low level expression of human papillomavirus type 16 (HPV16) E6 in squamous epithelium does not elicit E6 specific B- or T-helper immunological responses, or influence the outcome of immunisation with E6 protein

Mice transgenic for E6/E7 oncogenes of Human Papillomavirus type 16 display life-long expression of E6 in lens and skin epithelium, and develop inflammatory skin disease late in life, which progresses to papillomata and squamous carcinoma in some mice. We asked whether endogenous expression of E6 induced a specific immunological outcome, i.e. immunity or tolerance, or whether the mice remained immunologically naïve to E6. We show that prior to the onset of skin disease, E6 transgenic mice did not develop a spontaneous E6-directed antibody response, nor did they display T-cell proliferative responses to dominant T-helper epitope peptides within E6. In contrast, old mice in which skin disease had arisen, developed antibodies to E6. We also show that following immunisation with E6, specific antibody responses did not differ significantly among groups of E6-transgenic mice of different ages (and therefore of different durations and amounts of exposure to endogenous E6), and non-transgenic controls. Additionally, E6 immunisation-induced T-cell proliferative responses were similar in E6-transgenic and non-transgenic mice. These data are consistent with the interpretation that unimmunised E6-transgenic mice that have not developed inflammatory skin disease remain immunologically naïve to E6 at the B- and Th levels. There are implications for E6-mediated tumorigenesis in humans, and for the development of putative E6 therapeutic vaccines.

Papillomavirus virus-like particles for the delivery of multiple cytotoxic T cell epitopes

Chimeric papillomavirus (PV) virus-like particles (VLPs) based on the bovine papillomavirus type 1 (BPV-1) L1 protein were constructed by replacing the 23-carboxyl-terminal amino acids of the BPV1 major protein L1 with an artificial "polytope" minigene, containing known CTL epitopes of human PV16 E7 protein, HIV IIIB gp120 P18, Nef, and reverse transcriptase (RT) proteins, and an HPV16 E7 linear B epitope. The CTL epitopes were restricted by three different MHC class I alleles (H-2(b), H-2(d), HLA-A*0201). The chimeric L1 protein assembled into VLPs when expressed in SF-9 cells by recombinant baculovirus. After immunization of mice with polytope VLPs in the absence of adjuvant, serum antibodies were detected which reacted with both polytope VLPs and wild-type BPV1L1 VLPs, in addition to the HPV16E7 linear B cell epitope. CTL precursors specific for the HPV16 E7, HIV P18, and RT CTL epitopes were also detected in the spleen of immunized mice. Polytope VLPs can thus deliver multiple B and T epitopes as immunogens to the MHC class I and class II pathways, extending the utility of VLPs as self-adjuvanting immunogen delivery systems.

Differences in the post-translational modifications of human papillomavirus type 6b major capsid protein expressed from a baculovirus system compared with a vaccinia virus system

Virus-like particles (VLPs) are being currently investigated in vaccines against viral infections in humans. There are different recombinant-protein-expression systems available for obtaining the necessary VLP preparation for vaccination. However, the differences in post-translational modifications of the recombinant proteins obtained and their differences in efficacy in eliciting an anti-viral response in vaccines are not well established. In this study we have compared the post-translational modifications of human papillomavirus type-6b major capsid protein L1 (HPV 6bL1) expressed using recombinant baculovirus (rBV) in Sf9 (Spodoptera frugiperda) insect cells, with the protein expressed using recombinant vaccinia virus (rVV) in CV-1 kidney epithelial cells. Two-dimensional gel electrophoresis of biosynthetically labelled rBV-expressed HPV 6bL1 showed several post-translationally modified variants of the protein, whereas rVV-expressed HPV 6bL1 showed only a few variants. Phosphorylations were detected at threonine and serine residues for the L1 expressed from rBV compared with phosphorylation at serine residues only for the L1 expressed from rVV. HPV 6bL1 expressed using rBV incorporated [(3)H]mannose and [(3)H]galactose, whereas HPV 6bL1 expressed using rVV incorporated only [(3)H]galactose. We conclude that post-translational modification of recombinant HPV 6bL1 can differ according to the system used for its expression. Since recombinant L1 protein is a potential human-vaccine candidate, the implication of the observed differences in post-translational modifications on immunogenicity of L1 VLPs warrants investigation.

BPV1 E2 protein enhances packaging of full-length plasmid DNA in BPV1 pseudovirions

We studied determinants of efficient encapsidation of circular DNA, incorporating a PV early region DNA sequence (nt 584-1978) previously shown to enhance packaging of DNA within papillomavirus (PV)-like particles (VLPs). Insect coelomic cells (Sf-9) and cultured monkey kidney cells (Cos-1) were transfected with an 8-kb reporter plasmid incorporating the putative BPV packaging sequence and infected with BPV1 L1 and L2 recombinant baculovirus or vaccinia virus. Heavy (1.34 g/ml) and light (1.30 g/ml) VLPs were produced, and each packaged some of the input plasmid. In light VLPs, truncated plasmids, which nevertheless incorporated the PV-derived DNA packaging sequence, were more common than full-length plasmids. Packaging efficiency of the plasmid was estimated at 1 plasmid per 10(4) VLPs in both Cos-1 and Sf-9 cells. In each cell type, expression of the BPV1 early region protein E2 in trans doubled the quantity of heavy but not light VLPs and also increased the packaging efficiency of full-length circular plasmids by threefold in heavy VLPs. The resultant pseudovirions incorporated significant amounts of E2 protein. Pseudovirions, comprising plasmids packaged within heavy VLPs, mediated the delivery of packaged plasmid into Cos-1 cells, whereby "infectivity" was blocked by antisera to BPV1 L1, but not antisera to BPV1 E4. We conclude that (a) packaging of DNA within PV L1+L2 pseudovirions is enhanced by BPV1 E2 acting in trans, (b) E2 may be packaged with the pseudovirion, and (c) E2-mediated enhancement of packaging favors 8-kb plasmid incorporation over incorporation of shorter DNA sequences.

E2F-1 induces proliferation-specific genes and suppresses squamous differentiation-specific genes in human epidermal keratinocytes

Squamous differentiation of keratinocytes is associated with decreases in E2F-1 mRNA expression and E2F activity, and these processes are disrupted in squamous cell carcinoma cell lines. We now show that E2F-1 mRNA expression is increased in primary squamous cell carcinomas of the skin relative to normal epidermis. To explore the relationship between E2F-1 and squamous differentiation further, we examined the effect of altering E2F activity in primary human keratinocytes induced to differentiate. Promoter activity for the proliferation-associated genes, cdc2 and keratin 14, are inhibited during squamous differentiation. This inhibition can be inhibited by overexpression of E2F-1 in keratinocytes. Overexpression of E2F-1 also suppressed the expression of differentiation markers (transglutaminase type 1 and keratin 10) in differentiated keratinocytes. Blocking E2F activity by transfecting proliferating keratinocytes with dominant negative E2F-1 constructs inhibited the expression of cdc2 and E2F-1, but did not induce differentiation. Furthermore, expression of the dominant negative construct in epithelial carcinoma cell lines and normal keratinocytes decreased expression from the cdc2 promoter. These data indicate that E2F-1 promotes keratinocyte proliferation-specific marker genes and suppresses squamous differentiation-specific marker genes. Moreover, these data indicate that targeted disruption of E2F-1 activity may have therapeutic potential for the treatment of squamous carcinomas. Oncogene (2000).

Immune responses induced by BCG recombinant for human papillomavirus L1 and E7 proteins

Recombinant bacille Calmette-Guerin (BCG) based vaccine delivery systems could potentially share the safety and effectiveness of BCG. We therefore prepared recombinant BCG vaccines which expressed the L1 late protein of the human papillomavirus (HPV) 6b or the E7 early protein of the HPV 16. The two recombinants were evaluated as immunogens in C57BL/6J and BALB/c mice, and compared with a conventional protein/adjuvant system using E7 or L1 mixed with Quil-A adjuvant. rBCG6bL1 and rBCG16E7 primed specific immune responses, represented by DTH, T-proliferation and antibody, and rBCG16E7 induced cytotoxic immune response to E7 protein. The magnitude of the observed responses were less than those elicited by protein/adjuvant vaccine. As recombinant BCG vaccines expressing HPV6bL1 or HPV16E7 persist at low levels in the immunised host, they may be beneficial to prime or retain memory responses to antigens, but are unlikely to be useful as a single component vaccine strategy.

T-helper epitopes identified within the E6 transforming protein of cervical cancer-associated human papillomavirus type 16

The E6 oncoprotein of human papillomavirus type 16 (HPV16 E6) produced by tumor cells of HPV16-associated cervical carcinoma is poorly immunogenic in patients, but nonetheless is a tumor-specific antigen to which therapeutic vaccine strategies may be directed. To investigate the subunit immunogenicity of E6 protein at the T-helper cell level, we immunized mice with overlapping peptides spanning the entire 158 amino acid sequence. Two peptides recalled a proliferative response in lymph node cells (LNC) from C57BL/6 (H-2b)-immunized mice. One of these peptides also recalled proliferative responses in the context of 5/5 other major histocompatibility complex (MHC) class II haplotypes, indicating a "promiscuous" T-epitope. Minimal consensus motif analysis identified the epitopes as 60VYRDGNPYA68 and 98GYNKPLCDLL107. LNC from mice immunized with T-epitope proliferated in response to challenge with whole E6 protein. Immunization with E6 T-epitopes linked to B-epitopes of HPV16 E7 protein elicited specific antibody indicating that T-cells recognizing the T-epitopes provided cognate "help" for B-cells. LNC from mice co-immunized with E6 T-epitope and the major T-helper epitope of HPV16 E7 (48DRAHYNI54) proliferated comparably when challenged with the peptides individually indicating co-dominance of the two T-epitopes. The findings have implications for incorporation of E6 into a therapeutic vaccine.

HPV6b virus like particles are potent immunogens without adjuvant in man

Subjects with genital warts were immunized three times or more with HPV6b VLPs without adjuvant. All immunized subjects had DTH to HPV6b L1 protein. Of 32 subjects, nine had HPV6b specific antibody prior to immunization and 22 acquired antibody with immunization. VLP specific antibody increased following a single immunization in 6 of 8 subjects with low level antibody at recruitment. Complete regression of genital warts was observed in 25 of 33 evaluable subjects over the 20-week observation period. We conclude that immunization with HPV6b L1 VLPs without adjuvant induces immunity to the L1 protein epitopes recognised during natural infection, and may accelerate regression of warts.

Genetic and environmental causes of variation in basal levels of blood cells

The genetic and environmental determinants of variation in blood cell size and number were investigated in 392 pairs of 12-year-old twins. The following blood cell indices were measured: haemoglobin, red blood cell count, haematocrit, mean corpuscular volume, platelet number, total white cell count, level of neutrophils, monocytes, eosinophils, total lymphocytes, CD3+ lymphocytes, CD4+ lymphocytes, CD8+ lymphocytes, CD19+ lymphocytes, CD56+ lymphocytes and CD4+/CD8+ ratio. Genetic factors contributed significantly to all blood cell measures accounting for between 61 and 96% of variance. Heritability estimates did not differ significantly between males and females, although the sample size of the present study was not large enough to exclude the possibility of sex-limited gene expression. Common environmental factors were important in determining red blood cell count and haematocrit, but were not important in determining basal levels of any white blood cell type.

Capture ElISA and in vitro cell binding assay for the detection of antibodies to human papillomavirus type 6b virus-like particles in patients with anogenital warts

To investigate human papillomavirus (HPV) virus-like particle (VLP)-specific antibody responses among anogenital warts patients, a VLP-based capture ELISA was established. Twenty-six percent (35/134) of control subjects and 50.0% (39/78) of patients with current anogenital warts showed IgG seropositivity to HPV 6b VLPs. HPV 6b VLP-specific antibody responses recognised native VLPs only, and had no cross-reaction with HPV type 16 VLPs. No differences in reactivity were observed between L1 and L1 + L2 VLPs, suggesting that L2 contributes little to the total immunogenicity of the papillomavirus virion. A VLP-cell binding assay was also established. Some sera from patients with anogenital warts specifically inhibited VLP binding to the surface of epithelial cells, suggesting that these antibodies might be functionally neutralising. These data show that serological responses to HPV 6b VLPs were induced among some but not all patients with anogenital warts, and give a proportional estimate of infection in the community.

Expression of the alpha6 integrin confers papillomavirus binding upon receptor-negative B-cells

Papillomaviruses (PV) bind to a wide range of cell lines in a specific and saturable manner. We have recently identified a candidate receptor for papillomavirus as the alpha6 integrin (Evander et al., J. Virol. 71, 2449-2456, 1997). We have further investigated the role the alpha6 integrin plays in PV binding. Here we show that the cells expressing the alpha6 integrin, partnered with either the beta4 integrin or the beta1 integrin, are equally able to bind PV HPV6b L1 virus-like particles, indicating that the beta partner does not play a major role in virus binding. In order to provide definitive evidence that the alpha6 integrin is required for PV binding we undertook to genetically complement the receptor-negative B-cell line DG75 by expressing the human alpha6A gene. The transduction of the alpha6 integrin gene into DG75 cells results in the cell surface expression of the alpha6 protein and this expression confers upon DG75 cells the ability to bind laminin, a normal ligand for alpha6 integrin. Furthermore, the alpha6 protein is partnered with the beta1 integrin in DG75 cells. Finally, we show that the DG75-alpha6 cells were able to bind papillomavirus VLPs and this binding was inhibited by a functionally blocking anti-alpha6 antibody. Together these data indicate that the alpha6 integrin is a primary cell receptor for papillomaviruses and is both necessary and sufficient for PV binding.

T cell-mediated and non-specific inflammatory mechanisms contribute to the skin pathology of HPV 16 E6E7 transgenic mice

One of three lines of mice transgenic for the E6 and E7 genes of human papillomavirus type 16 (HPV16) expressed from an alphaA-crystallin promoter also expresses the transgene ectopically in the skin. This line, designated alphaACE6E7#19, develops skin disease from 3 months of age, characterised by epidermal hyperplasia and eventual skin loss. Administration of complete Freund's adjuvant (CFA) to alphaACE6E7#19 mice, but not to non-transgenic littermate controls, induced local epidermal hyperplasia which was histologically similar to the spontaneously arising skin pathology. Local application of 2,4-dinitrochlorobenzene (DNCB) to DNCB-sensitised alphaACE6E7#19 mice, but not DNCB-sensitised controls, also induced hyperplasia. Treatment with cyclosporin A (CsA) or systemic depletion of CD4+ cells significantly reduced the incidence of skin disease. These data suggest that local inflammation, and cytokines produced by T helper cells, contribute to the induction of hyperplastic skin disease in alphaACE6E7#19 mice. Spontaneous skin disease with similar histological appearance, frequency, age of onset and severity in alphaACE6E7#19 mice was observed in scid-/- alphaACE6E7#19 mice, despite immune paresis. Antigen-specific immune responses and T-cell cytokines are therefore not necessary for the induction of skin disease. We propose that epidermal hyperplasia associated with HPV16 E6 and E7 expression in skin is accelerated by local secretion of pro-inflammatory cytokines, whose production can be enhanced by activated CD4+ T cells.

Nucleotides 1506-1625 of bovine papillomavirus type 1 genome can enhance DNA packaging by L1/L2 capsids

We have previously described a DNA-packaging assay using bovine papillomavirus type 1 (BPV-1) virus-like particles (VLPs) and have identified a region of the BPV genome that assists in packaging. In this study, we identify a specific BPV sequence involved in DNA packaging by BPV-1 VLPs. In the initial screening of BPV-1 genomic sequences essential for DNA packaging, we observed that a plasmid with deletions between nucleotides (nt) 948 and 2113 failed to be packaged into BPV-1 VLPs. However, plasmids containing nt 948 to 2113 were efficiently packaged, suggesting that this 1.2-kb fragment contains a packaging enhancement sequence (PES). Further mapping of the BPV-1 genome showed that this packaging sequence lies between nt 1506 and 1625. Furthermore, this packaging sequence is also recognized by HPV6b VLPs, suggesting that a common packaging mechanism may be used by the two papillomavirus types. Given the phylogenetic difference between these two viral types, it is likely that other papillomavirus types may also use the same packaging mechanism. Identification of the PES has allowed a minimal viral genome sequence to be used in the packaging assay, improving the usefulness of the assay in studying the process of papillomavirus DNA encapsidation.

Potential strategies utilised by papillomavirus to evade host immunity

The co-evolution of papillomaviruses (PV) and their mammalian hosts has produced mechanisms by which PV might avoid specific and non-specific host immune responses. Low level expression of PV proteins in infected basal epithelial cells, together with an absence of inflammation and of virus-induced cell lysis, restricts the opportunity for effective PV protein presentation to immunocytes by dendritic cells. Additionally, PV early proteins, by a range of mechanisms, may restrict the efficacy of antigen presentation by these cells. Should an immune response be induced to PV antigens, resting keratinocytes (KC) appear resistant to interferon-gamma-enhanced mechanisms of cytotoxic T-lymphocyte (CTL)-mediated lysis, and expression of PV antigens by resting KC can tolerise PV-specific CTL. Thus, KC, in the absence of inflammation, may represent an immunologically privileged site for PV infection. Together, these mechanisms play a part in allowing persistence of PV-induced proliferative skin lesions for months to years, even in immunocompetent hosts.

Post translational modifications of recombinant human papillomavirus type 6b major capsid protein

We have determined the post-translational modifications of the major capsid protein, L1 of human papillomavirus (HPV) type 6b. Since this virus cannot be cultured in the laboratory to obtain sufficient material for a study, a recombinant L1 protein produced in a vaccinia virus expression system was used in this investigation. Our results show that this protein is phosphorylated at serine residues and is also glycosylated. No myristoylation or palmitoylation was detected. The fraction of L1 protein incorporated into virus-like particles was not glycosylated. Since recombinant L1 protein is a potential human vaccine candidate, knowledge of the post-translation modifications of this protein may prove useful for the design of anti-HPV vaccines.

Expression, purification and immunological characterization of the transforming protein E7, from cervical cancer-associated human papillomavirus type 16

E7 is the major oncogenic protein produced in cervical cancer-associated human papillomavirus type 16 (HPV16). This protein was expressed in Escherichia coli as a glutathione-S-transferase (GST) fusion protein. E7-enriched inclusion bodies were collected from bacterial lysates, were solubilized in 10 M urea, and the protein was purified using anion exchange column chromatography. After removal of endotoxin with serial Triton X-114 extractions, material of high purity (about 90%) was obtained, which is suitable for use in a human clinical trial. This material was immunogenic, and when used as a vaccine, protected mice against challenge with an HPV16 E7 DNA transfected tumour cell line. Based on this observation, the E7GST fusion protein is currently being used in a human clinical trial of a vaccine against HPV16-induced cervical cancer. This fusion protein could be cleaved with thrombin to remove the GST fusion part and further purified by preparative SDS gel electrophoresis to obtain free E7 with > 98% purity.

Mucosal immunisation with papillomavirus virus-like particles elicits systemic and mucosal immunity in mice

It has been shown previously that recombinant virus-like particles (VLPs) of papillomavirus can induce VLP-specific humoral and cellular immune responses following parenteral administration. To test whether mucosal administration of bovine papillomavirus type 1 (BPV1) VLPs could produce mucosal as well as systemic immune responses to VLPs, 50 micrograms chimeric BPV1 VLPs containing an HPV16 E7 CTL epitope (BPVL1/E7 VLP) was administered intranasally to mice. After two immunisations, L1-specific serum IgG and IgA were observed. L1-specific IgG and IgA were also found in respiratory and vaginal secretions. Both serum and mucosal antibody inhibited papillomavirus VLP-induced agglutination of RBC, indicating that the antibody induced by mucosal immunisation may recognize conformational determinants associated with virus neutralisation. For comparison, VLPs were given intramuscularly, and systemic and mucosal immune responses were generally comparable following systemic or mucosal delivery. However, intranasal administration of VLP induced significantly higher local IgA response in lung, suggesting that mucosally delivered HPV VLP may be more effective for mediating local mucosal immune responses. Intranasal immunisation with HPV6b L1 VLP produced VLP-specific T proliferative responses in splenocytes, and immunisation with BPVL1 VLP containing an HPV16 E7 CTL epitope induced E7-specific CTL responses. We conclude that immunisation with papillomavirus VLPs via mucosal and intramuscular routes, without adjuvant, can elicit specific antibody at mucosal surfaces and also systemic VLP epitope specific T cell responses. These findings suggest that mucosally delivered VLPs may offer an alternative HPV VLP vaccine strategy for inducing protective humoral immunity to anogenital HPV infection, together with cell-mediated immune responses to eliminate any cells which become infected.

Histologic and immunohistochemical responses after aortic valve allografts in the rat

BACKGROUND

Human aortic valve allografts elicit a cellular and humoral immune response. It is not clear whether this is important in promoting valve damage. We investigated the changes in morphology, cell populations, and major histocompatibility complex antigen distribution in the rat aortic valve allograft.

METHODS

Fresh heart valves from Lewis rats were transplanted into the abdominal aorta of DA rats. Valves from allografted, isografted, and presensitized recipient rats were examined serially with standard morphologic and immunohistochemical techniques.

RESULTS

In comparison with isografts, the allografts were infiltrated and thickened by increased numbers of CD4+ and CD8+ lymphocytes, macrophages, and fibroblasts. Thickening of the valve wall and leaflet and the density of the cellular infiltrate was particularly evident after presensitization. Endothelial cells were frequently absent in presensitized allografts whereas isografts had intact endothelium. Cellular major histocompatibility complex class I and II antigens in the allograft were substantially increased. A long-term allograft showed dense fibrosis and disruption of the media with scattered persisting donor cells.

CONCLUSIONS

The changes in these aortic valve allograft experiments are consistent with an allograft immune response and confirm that the response can damage aortic valve allograft tissue.

The role of the immune system in anogenital human papillomavirus

There is substantial evidence from experiments of nature that immune competence plays a major part in determining the outcome of anogenital human papillomavirus (HPV) infection. Cellular rather than humoral immunity would appear to be the key to the control and eradication of HPV-induced warts. It seems likely that the HPV early proteins, which are responsible for viral replication (E1 and E2) and for promoting tissue proliferation (E6 and E7) will be the target antigens recognized by antigen-specific T cells. Natural infection is slow to produce an appropriate therapeutic immune response to these proteins, probably because HPV has adopted a strategy to prevent the effective presentation of viral antigens to the host immune system. Human papillomavirus infection is non-lytic so there is little release of viral antigen to professional antigen-presenting cells. Additionally no local proinflammatory cytokine production and no local inflammation is induced by HPV infection. An optimal therapeutic strategy for anogenital HPV infection would be, therefore, to accelerate the induction of a strong virus-specific immune response by inducing local inflammation and the cytokines necessary to invoke HPV-specific immunity.

Simplifying the molecular mechanisms of human papillomavirus

Human papillomaviruses are a common human pathogen responsible for diseases varying in severity from warts to cervical cancer. This article examines the functions of the viral gene products and how they interact with cellular factors to replicate themselves and cause disease.

Th2-type CD4+ cells neither enhance nor suppress antitumor CTL activity in a mouse tumor model

Many cervical cancers express the E7 protein of human papillomavirus 16 as a tumor-specific Ag (TSA). To establish the role of E7-specific T cell help in CD8+ CTL-mediated tumor regression, C57BL/6J mice were immunized with E7 protein or with a peptide (GF001) comprising a minimal CTL epitope of E7, together with different adjuvants. Immunized mice were challenged with an E7-expressing tumor cell line, EL4.E7. Growth of EL4.E7 was reduced following immunization with E7 and Quil-A (an adjuvant that induced a Th1-type response to E7) or with GF001 and Quil-A. Depletion of CD8+ cells, but not CD4+ cells, from an immunized animal abrogated protection, confirming that E7-specific CTL are necessary and sufficient for TSA-specific protection in this model. Immunization with E7 and Algammulin (an alum-based adjuvant) induced a Th2-like response and provided no tumor protection. To investigate whether a Th2 T helper response to E7 could prevent the development of an E7-specific CTL-mediated protection, mice were simultaneously immunized with E7/Algammulin and GF001/Quil-A or, alternatively, were immunized with GF001/Quil-A 8 wk after immunization with E7/Algammulin. Tumor protection was observed in each case. We conclude that an established Th2 response to a TSA does not prevent the development of TSA-specific tumor protective CTL.

Split tolerance to a viral antigen expressed in thymic epithelium and keratinocytes

When expressed as a transgene from the keratin 14 (K14) promoter in an MHC class II-deficient mouse, I-Ab expressed in thymic cortical epithelium promotes positive but not negative selection of I-Ab-restricted CD4+ T cells (Laufer, T. M. et al., Nature 1996. 383:81-85). Transgenic mice expressing the E7 protein of human papilloma virus 16 from the K14 promoter were studied to determine the consequence of expression of a cytoplasmic/ nuclear protein from the K14 promoter. K14E7-transgenic mice express E7 in the thymus and skin without evidence for autoimmunity to E7. Repeated immunization of FVB(H-2q) or F1(C57BL/6JxFVB) mice with E7 elicited similar antibody responses to the defined B cell epitopes of E7 in K14E7-transgenic and non-transgenic animals. In contrast, for each genetic background, a single immunization with E7 elicited demonstrable T cell proliferative responses to the major promiscuous T helper epitope of E7 in the transgenic but not the non-transgenic animals. Further, E7-immunized non-transgenic F1 (FVBxC57BL/6J) animals developed strong E7-specific cytotoxic T lymphocyte (CTL) responses and were protected against challenge with E7+ tumors, whereas similarly immunized K14E7-transgenic animals had a markedly reduced CTL response to E7 and no E7-specific tumor protection was observed, although the antibody and CTL response to ovalbumin was normal. Expression of E7 protein as a transgene from the K14 promoter in the skin and thymus thus induces E7-specific tolerance in the cytotoxic T effector repertoire, together with expansion of the E7-specific T helper repertoire. These findings demonstrate that limited tissue distribution of an autoantigen may result in "split" tolerance to that autoantigen.

Vaccine-induced Th1-type responses are dominant over Th2-type responses in the short term whereas pre-existing Th2 responses are dominant in the longer term

The effect of adjuvant on induction of human papillomavirus type 16 E7 protein-specific cytotoxic T lymphocytes (CTL) and immunoglobulin G (IgG)2a antibody was studied in C57BL/6 J mice immunized with various adjuvants and E7 protein. Quil-A adjuvant, but not complete Freund's adjuvant (CFA) or Algammulin, induced a T-helper 1 (Th1)-type response to E7, which was characterized by CTL activity against a tumour cell line transfected with E7 protein and by E7-specific IgG2a. All tested adjuvants elicited comparable levels of E7-specific IgG1. The longest duration and greatest magnitude of CTL response was seen following two immunizations with the highest dose of E7 and Quil-A. Simultaneous immunization with a Th1 and a T helper 2 (Th2)-promoting adjuvant gave a Th1-type response. However, E7 and Quil-A were unable to induce a Th1-type response (as measured by the inability to generate anti-E7 IgG2a antibody) in animals with a pre-existing Th2-type response to E7. These results suggest that saponin adjuvants may be suitable for immunotherapy in humans where a Th1-type response is sought, provided that there is no pre-existing Th2-type response to the antigen.

DNA packaging by L1 and L2 capsid proteins of bovine papillomavirus type 1

Encapsidation of circular DNA by papillomavirus capsid protein was investigated in Cos-1 cells. Plasmids carrying both an SV40 origin of replication (ori) and an E. coli ori were introduced into Cos-1 cells by DNA transfection PV capsid proteins were supplied in trans by recombinant vaccinia viruses. Pseudovirions were purified from infected cells and their packaged DNA was extracted and used to transform E. coli as an indication of packaging efficacy. VLPs assembled from BPV-1 L1 alone packaged little plasmid DNA, whereas VLPs assembled from BPV-1 L1 + L2 packaged plasmid DNA at least 50 times more effectively. BPV-1 L1 + L2 VLPs packaged a plasmid containing BPV-1 sequence 8.2 +/- 3.1 times more effectively than a plasmid without BPV sequences. Using a series of plasmid constructs comprising a core BPV-1 sequence and spacer DNA it was demonstrated that BPV VLPs could accommodate a maximum of about 10.2 kb of plasmid DNA, and that longer closed circular DNA was truncated to produce less dense virions with shorter plasmid sequences. The present study suggests that packaging of genome within PV virions involves interaction of L2 protein with specific DNA sequences, and demonstrates that PV pseudovirions have the potential to be used as DNA delivery vectors for plasmids of up to 10.2 kb.

Type specific and genotype cross reactive B epitopes of the L1 protein of HPV16 defined by a panel of monoclonal antibodies

Mouse monoclonal antibodies (mAbs) were raised against the major capsid protein, L1, of human papillomavirus type 16 (HPV16), produced in Escherichia coli with the expression plasmid pTrcL1. Epitope specificity could be assigned to 11 of these 12 antibodies using a series of linear peptides and fusion proteins from HPV16. One mAb (MC53) recognized a novel linear epitope that appears to be unique to the HPV16 genotype. A further 11 mAbs were characterized as recognizing novel and previously defined linear and conformational epitopes shared among more than one HPV genotype. The apparently genotype specific mAb could be useful for the development of diagnostic tests for vegetative virus infection in clinical specimens.

Papillomavirus virus-like particles can deliver defined CTL epitopes to the MHC class I pathway

To evaluate an antigen delivery system in which exogenous antigen can target the major histocompatibility complex (MHC) class I pathway, a single human papillomavirus (HPV) 16 E7 cytotoxic T lymphocyte (CTL) epitope and a single HIV gp160 CTL epitope were separately fused to the C-terminus of bovine papillomavirus 1 (BPV1) L1 sequence to form hybrid BPV1L1 VLPs. Mice immunized with these hybrid VLPs mounted strong CTL responses against the relevant target cells in the absence of any adjuvants. In addition, the CTL responses induced by immunization with BPV1L1/HPV16E7CTL VLPs protected mice against challenge with E7-transformed tumor cells. Furthermore, a high titer-specific antibody response against BPV1L1 VLPs was also induced, and this antiserum could inhibit papillomavirus-induced agglutination of mouse erythrocytes, suggesting that the antibody may recognize conformational determinates relevant to virus neutralization. These data demonstrate that hybrid BPV1L1 VLPs can be used as carriers to target antigenic epitopes to both the MHC class I and class II pathways, providing a promising strategy for the design of vaccines to prevent virus infection, with the potential to elicit therapeutic virus-specific CTL responses.

Presentation of the HPV16E7 protein by skin grafts is insufficient to allow graft rejection in an E7-primed animal

The E7 transforming protein of Human Papillomavirus type 16 (HPV16) is expressed in the skin of a line of FVB mice transgenic for the E6 and E7 open reading frames of HPV16 driven from the alpha A crystallin promoter (FVB alpha AcryHPV16E6E7). We have transferred skin from FVB alpha AcryHPV16E6E7 mice to naive or E7-primed syngeneic FVB recipients to assess whether the E7 protein of HPV16 can function as a minor transplantation antigen (MTA) and promote skin graft rejection. FVB mice did not reject E7 expressing tail or flank skin grafts. E7 immunized FVB x C57BL/6J mice recipients of FVB alpha-AcryHPV16E6E7 x C57BL/6J skin generated humoral and DTH responses to E7 in vivo and E7-specific CTL precursors in the spleen, but failed to reject E7 expressing tail skin grafts by 100 days posttransfer. Thus although HPV16 E7 + ve mesenchymal and endodermal tumors can be eliminated by an E7-specific immune response, the same protein is unable to act as a MTA and promote graft rejection when expressed in skin cells. Lack of rejection of grafts expressing MTAs such as E7 may be relevant to the immunology of epithelial tumors expressing tumor-specific antigens and to our understanding of the immunology of diseases of the skin.

E7 oncoprotein of human papillomavirus type 16 expressed constitutively in the epidermis has no effect on E7-specific B- or Th-repertoires or on the immune response induced or sustained after immunization with E7 protein

A line of FVB (H-2q) mice transgenic for the E6/E7 open reading frames of Human Papillomavirus type 16 driven from the alpha-A crystallin promoter expresses E7 mRNA in lens and skin epithelium. E7 protein is detectable in adult skin, coinciding with the development of inflammatory skin disease, which progresses to papillomata and squamous carcinomata in some mice. By examining the outcome of parenteral immunization with E7 protein, we sought to determine whether endogenous expression of E7 in skin had induced a preexisting immune outcome, i.e., specific immunity or tolerance, or whether the mice remain naive ("ignorant") to E7. Our data show that the antibody response to defined E7 B-epitopes, the proliferative response to Th epitopes, and the delayed-type hypersensitivity (DTH) response to whole E7 did not differ between groups of young and old E6/E7 transgenic mice (likely having different degrees of lifetime exposure to E7 protein) or between E6/E7-transgenic and nontransgenic parental strain control mice. Although an E7-specific CTL response could not be induced in the H-2q background of these mice, incorporation of a Db allele into the genome allowed comparison of Db-restricted CTL responses in E6/E7 transgenic and nontransgenic mice. Experiments indicated that the E7-immunization-induced CTL response did not differ significantly between E6/E7 transgenic and nontransgenic mice. We interpret these results to indicate that in spite of expression of E7 protein in adult skin, E6/E7 transgenic mice remain immunologically naive (ignorant) of E7 epitopes presented by immunization.

Identification of the alpha6 integrin as a candidate receptor for papillomaviruses

Papillomaviruses (PVs) bind in a specific and saturable fashion to a range of epithelial and other cell lines. Treatment of cells with trypsin markedly reduces their ability to bind virus particles, suggesting that binding is mediated via a cell membrane protein. We have investigated the interaction of human PV type 6b L1 virus-like particles (VLPs) with two epithelial cell lines, CV-1 and HaCaT, which bind VLPs, and a B-cell line (DG75) previously shown not to bind VLPs. Immunoprecipitation of a mixture of PV VLPs with [35S]methionine-labeled cell extracts and with biotin-labeled cell surface proteins identified four proteins from CV-1 and HaCaT cells of 220, 120, 87, and 35 kDa that reacted with VLPs and were not present in DG75 cells. The alpha6beta4 integrin complex has subunits corresponding to the VLP precipitated proteins, and the tissue distribution of this complex suggested that it was a candidate human PV receptor. Monoclonal antibodies (MAbs) to the alpha6 or beta4 integrin subunits precipitated VLPs from a mixture of CV-1 cell proteins and VLPs, whereas MAbs to other integrin subunits did not. An alpha6 integrin-specific MAb (GoH3) inhibited VLP binding to CV-1 and HaCaT cells, whereas an anti-beta4 integrin MAb and a range of integrin-specific and other MAbs did not. Furthermore, human laminin, the natural ligand for the alpha6beta4 integrin, was able to block VLP binding. By use of sections of monkey esophagus, the distribution of alpha6 integrin expression in the basal epithelium was shown to coincide with the distribution of bound VLPs. Taken together, these data suggest that VLPs bind specifically to the alpha6 integrin subunit and that integrin complexes containing alpha6 integrin complexed with either beta1 or beta4 integrins may act as a receptor for PV binding and entry into epithelial cells.

The role of vaccines in the control of STDs: HPV vaccines

Prophylactic vaccines for genital human papillomavirus (HPV) infection have been shown to be feasible in animal models, and suitable vaccine material based on virus-like particles can be produced in bulk at reasonable cost. Initiation of phase III clinical trials will follow definition of trial outcome measures through further epidemiological studies, and development of assays of host protective immunity. Vaccines could in principle eliminate HPV-related disease, as the human race is the only natural host for the relevant papillomaviruses (PVs). Therapeutic vaccines for genital HPV infection are also possible, but have not yet been demonstrated as feasible in practice because the choice of vaccine antigens is difficult, the method of their optimal delivery is uncertain, and the nature of the relevant antiviral immunity is unknown. PV species specificity will require trials to be conducted in man, which will slow definition of an ideal vaccine.

Human aortic valve allografts elicit a donor-specific immune response

OBJECTIVE

The nature and magnitude of the immunologic response to implantation of human cryopreserved aortic valve allografts was investigated.

METHODS

Twenty aortic valve allograft recipients were investigated for donor-specific antibody and T-cell-mediated responses with serial flow cytometric and microlymphocytotoxic crossmatch assays and one-way mixed lymphocyte cultures.

RESULTS

Donor-specific immunoglobulin G antibodies to class I and II human leukocyte antigens were first detected in the serum of all aortic valve allograft recipients at 30 days after implantation and persisted in substantial amounts in all but one of the recipients at day 365. Recipient T-cell alloreactivity toward donor lymphocytes was significantly increased at day 30 compared with levels before and 10 days after operation.

CONCLUSIONS

Cryopreserved aortic valve allografts elicit a substantial allogeneic response in recipients. This alloreactivity may contribute to the observed morphologic changes in aortic valve allografts and eventual long-term deterioration of allograft function.