Antibodies against the human papillomavirus type 16 early proteins in human sera: correlation of anti-E7 reactivity with cervical cancer

High prevalence of human papillomavirus type 16 infection among children

Infection with high-risk human papillomaviruses (HPV), is the most significant risk factor for cervical cancer and it may be possible to prevent this malignancy by immunisation. Before immunisation programmes can be designed, however, it is necessary to know the age of acquisition and all routes of infection for these viruses. Sexual transmission is well documented and vertical transmission has also been demonstrated, although the frequency of transmission remains controversial. We previously showed that vertical transmission frequently results in persistent infection, and now present data on the prevalence of HPV-16 DNA (the most prevalent high-risk HPV type) in healthy children. Buccal samples from 267 healthy children aged 3-11 years were tested for HPV DNA by generic PCR (MY09/MY11), and a HPV-16 specific nested PCR. Reverse transcriptase (RT)-PCR was used to determine the prevalence of transcriptionally active HPV-16 infection in a subset of children. HPV-16 DNA was detected by nested PCR in 138 of 267 (51.7%) samples, whereas HPV DNA was detected in only 45 (16.8%) specimens by generic PCR, that has a lower analytical sensitivity. There were no significant differences in prevalence according to age or sex. Early region mRNA was detected by RT-PCR in six (11.3%) of 53 HPV-16 E5 DNA positive samples. HPV-16 E5 DNA sequences from 10 children confirmed the identity of the sequences detected and identified 13 HPV-16 variants.

Antibodies against oncoproteins E6 and E7 of human papillomavirus types 16 and 18 in patients with head-and-neck squamous-cell carcinoma

Human papillomaviruses (HPVs) have been recognized as an essential pathogenic factor in anogenital cancer. HPV DNA has also been found in a subgroup of head-and-neck squamous-cell carcinomas (HNSCCs), and a causative role of the virus in the development of these tumors has been suggested by the concomitant inactivation of the tumor-suppressor protein pRb. Using 4 second-generation ELISAs, we found antibodies against at least 1 of the oncoproteins E6 and E7 of the high-risk HPV types 16 and 18 in 11 of 92 sera (12%) taken from HNSCC patients at or near diagnosis, in 1 of 52 sera (2%) taken from HNSCC patients >6 months after diagnosis and in 10 of 288 sera (3. 5%) taken from sex- and age-matched healthy control individuals of the normal population. In 11 of the 12 seropositive HNSCC cases, antibodies were directed against HPV16 proteins. In patients, the HPV16 antibodies were mostly of high titer, and in 6 cases, antibodies against both HPV16 oncoproteins were present. Seven of the 8 HPV16 antibody-positive sera from the control group were of low titer, and none of the 10 antibody-positive sera reacted with both oncoproteins of the same HPV type. The HPV type of the antigens detected by the antibodies in HNSCC patients correlated well with that of the HPV DNA found in the tumor. Of 19 patients known to have HPV16 DNA-positive tumors, 7 (37%) also had HPV16 E6 and/or E7 antibodies. Our finding suggests that the antibodies were formed in an immune response against HPV E6 and E7 proteins expressed in the HNSCC and thus strongly supports the concept of a biologically active role of HPV in the development of a subgroup of HNSCC.

Antibodies against oncoproteins E6 and E7 of human papillomavirus types 16 and 18 in cervical-carcinoma patients from Russia

Certain human papillomaviruses (HPV), mainly types 16 and 18, have been widely recognized as an essential etiologic factor for the development of carcinoma of the uterine cervix. The early HPV proteins E6 and E7 are consistently expressed in the tumor cells, and cervical-carcinoma patients can develop antibodies against these oncoproteins. For cervical-carcinoma patients from Eastern Europe and Russia, detailed information on HPV DNA prevalence and HPV-specific immune responses is limited. The presence of HPV DNA in 128 Russian cervical-carcinoma tissues was determined: HPV16 DNA was found in 78% of the cases, HPV18 DNA in 14%, and no HPV-DNA in 10%. Using 4 recently developed sensitive and highly specific second-generation enzyme-linked immunosorbent assays, we also analyzed the prevalence of antibodies against HPV16 and -18 E6 and E7 proteins in sera from 95 cervical-carcinoma patients, from 61 female patients with non-HPV-associated tumors and from 83 female healthy controls. The strong association of E6 and/or E7 antibodies with cervical carcinoma was confirmed, with 36% seropositives in this group against only 2% in the control groups. The detected antibodies are highly HPV-type-specific since all 26 HPV16-E6- or -E7-antibody-positive patients had HPV16 DNA in their tumor and 6 out of the 8 HPV18-antibody-positive patients had HPV18 DNA. Antibody responses to HPV16 E6 and E7 appear to be dependent on clinical stage of the disease, with 21% seropositives found in FIGO stage I, 42% in stage II and 53% in stage III. Antibody response to HPV16 E6 is more frequent than to E7, especially in early stages.

Detection of human papillomavirus DNA on the fingers of patients with genital warts

OBJECTIVE

To determine whether patients with genital warts carry human papillomavirus (HPV) DNA on their fingers.

METHODS

14 men and eight women with genital warts had cytobrush samples taken from genital lesions, finger tips, and tips of finger nails. Samples were examined for the presence of HPV DNA by the polymerase chain reaction.

RESULTS

HPV DNA was detected in all female genital samples and in 13/14 male genital samples. HPV DNA was detected in the finger brush samples of three women and nine men. The same HPV type was identified in genital and hand samples in one woman and five men.

CONCLUSION

This study has identified hand carriage of genital HPV types in patients with genital warts. Although sexual intercourse is considered the usual mode of transmitting genital HPV infection, our findings raise the possibility of transmission by finger-genital contact.

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.

High risk genital papillomavirus infections are spread vertically

It is well recognised that high-risk human papillomaviruses (HPVs) are spread by sexual activity, but the possibility of non-sexual transmission remains controversial. We present evidence for vertical transmission from at least 30% HPV positive mothers to their infants, resulting in persistent infection in children. That the mother is the source of infant infection has been confirmed by DNA sequencing. We also discuss the evidence for oral HPV-16 infection in children. In our own studies, HPV-16 DNA was detected in buccal cells from 48% children, aged 3-11 and transcriptionally active infection was confirmed in some children. Other studies have reported prevalences of 19%-27% among children less than 11 years of age. Studies that have failed to detect high-risk HPVs in children have used techniques which were insufficiently sensitive to detect the low levels of virus present. Serological studies also suggest that < or = 45% prepubertal children have acquired HPV-16. Thus, convincing evidence is now available for vertical transmission of high risk HPVs, which probably results in widespread infection among children. The consequences of such infections remain to be elucidated.

Clinical models of chemoprevention for cervical cancer

Cervical carcinoma creates a worldwide, significant population burden that potentially could be reduced by new preventive strategies for cervical cancer such as chemoprevention. Given the vast array of clinical and molecular information available relating to cervical cancer and the precursor lesions along with a growing number of new molecular techniques, a model is needed to guide further investigation. Such a model would facilitate research design, guide hypothesis development and testing, and focus the use of molecular data collection and analysis. This article reviews the clinical and molecular data of cervical cancer and the precursor lesions in order to develop a model for chemoprevention research in cervical cancer.

Cytokine expression in squamous intraepithelial lesions of the uterine cervix: implications for the generation of local immunosuppression

We have addressed the notion that the progression of cancer of the uterine cervix is associated with a preferential constraint on the development of a type 1 cellular mediated response, which is necessary to efficiently eliminate (pre)neoplastic cells. Based on the importance of cytokines in the regulation of an appropriate immune response, we have evaluated the expression of IL-12p40, IL-10 and transforming growth factor-beta 1 (TGF-beta1). Using reverse transcriptase-polymerase chain reaction (RT-PCR), the expression of these three cytokines was evaluated in both low-grade (LG) and high-grade (HG) cervical squamous intraepithelial lesions (SIL) and in normal exocervix and transformation zone biopsies. Our results show that the average level of IL-12 increases within both the LG and HG SIL, compared with both control groups. Interestingly, the percentage of HG SIL expressing IL-12p40 was lower compared with LG SIL. In contrast, the expression of IL-10 increased in parallel with the severity of the lesion to a maximal level in HG SIL. Using immunohistochemistry, we ascertained the presence of IL-12 protein in SIL and IL-10 protein in the transformation zone and SIL biopsies. Both IL-12- and IL-10-producing cells were localized in the stroma, not within the SIL. Furthermore, in this study we also observed that the region of the cervix the most sensitive to lesion development, the transformation zone, was associated with higher average levels of the immunosuppressive cytokines IL-10 and TGF-beta1.

HPV-16-related proteins as the serologic markers in cervical neoplasia

OBJECTIVE

Recently, a variety of HPV-related proteins have been synthesized and their utility as diagnostic and prognostic markers in cervical cancers needs to be assessed. The ability to generate preparative amounts of HPV-16 L1/L2 VLPs and E6, E7 proteins may have implications for the development of a serologic assay to detect anti-HPV-16 virion immune responses. The purpose of the study is to improve the way of proper management of the cervical cancer by investigating the utility of the recently developed HPV-16 L1/L2 VLPs, HPV-16 E6, E7 proteins as the clinical serologic markers through antibody reactions by comparison with those of SCCA and CEA which have been used as tumor markers for cervical cancer.

METHODS

The serologic responses in Korean women with cervical neoplasia by ELISA using HPV-16 L1/L2 VLPs and radioimmunoprecipitation assay (RIPA) using in vitro translated HPV-16 E6, E7 proteins were investigated. PCR using E6 type-specific primers for HPV-16/18 was used to determine the presence and type of HPV infection (normal controls, 15 cases; preinvasive lesions, 28 cases; invasive cervical cancers, 124 cases).

RESULTS

The sera of 34% (42/124) of cervical cancers were positive for SCCA and the sera of 18% (22/124) of cervical cancers were positive for CEA. The positivity of SCCA was increased with advancing clinical stages, but the antibody levels were not correlated with clinical stage of disease. The sera of 7% (1/15) of normal controls, 39% (11/28) of preinvasive lesions, and 56% (70/124) of patients with cervical cancer were ELISA positive for HPV-16 L1/L2 VLPs (P < 0.05). The sera of 7% (2/28) of preinvasive lesions and 51% (63/124) of cervical cancers were positive for in vitro translated HPV-16 E6 protein (P < 0.05) and the sera of 11% (3/28) of preinvasive lesions and 33% (41/124) of cervical cancers were positive for in vitro translated HPV-16 E7 protein (P < 0.05). The antibody levels to HPV-16 E7 protein were correlated to clinical stage and tumor burden in a significant number of cervical cancers.

CONCLUSIONS

These data suggest that a considerable number of patients with cervical neoplasia generated positive antibody response to L1/L2 VLPs and in vitro translated E6, E7 proteins of HPV-16. These HPV-16-associated proteins might be disease-specific markers which could be useful in an adjunctive diagnostic assay and a seroepidemiologic study of HPV-related cervical neoplasia. In particular, the monitoring of antibody to HPV-16 E7 protein seems to be valuable in the proper management of cervical cancers for specific tumor markers.

Correlation of T-helper secretory differentiation and types of antigen-presenting cells in squamous intraepithelial lesions of the uterine cervix

This study addressed the notion that the progression of cervical cancer is associated with a T-helper 2 (TH2) immunodeviation by analysing cytokine expression in 60 cervical biopsy specimens, spanning the spectrum from normal cervical tissue to high-grade squamous intraepithelial lesions (SILs). The biopsies were analysed by immunohistochemistry for the expression of TH1 [interleukin-2 (IL2), interferon gamma (IFN gamma)] and of TH2-type cytokines (IL4, IL6). Positive cells were usually observed in the subepithelial connective tissue, where most CD4+ cells were also detected. The density of IL2+ cells was significantly lower in high-grade SILs than in normal tissues taken either from the ectocervix or from the transformation zone. In contrast, significantly higher densities of IL4+ cells and, to a lesser degree, IL6+ cells were found in SIL biopsies compared with histologically normal tissues taken from the adjacent ectocervical region. A significantly higher IL4+/CD4+ cell ratio was also found in high-grade SILs (82 per cent) than in normal cervical biopsies taken from the transformation zone of healthy women showing squamous metaplasia (27 per cent). The elevated density of TH2+ cells in SIL biopsies was associated with both the expression of HLA-DR by keratinocytes and a diminished number of intraepithelial Langerhans' cells (CD1a+). In conclusion, the increased TH2+/CD4+ cell ratio in SIL biopsies suggest the presence, during cervical carcinogenesis, of a TH2 immunodeviation that could participate in the immunoescape of preneoplastic cervical keratinocytes.

Serologic response to the E4, E6, and E7 proteins of human papillomavirus type 16 in pregnant women

OBJECTIVE

In a seroepidemiologic study the effects of pregnancy and other factors on humoral response to human papillomavirus type 16 infection were examined.

STUDY DESIGN

Multiple serum samples were taken at 3-month intervals for 15 months from 77 pregnant and 85 nonpregnant women. Serologic response to human papillomavirus type 16 proteins was analyzed with a peptide-based enzyme-linked immunosorbent assay.

RESULTS

Seroreactivity was higher in nonpregnant women than in pregnant women, suggesting a reduced humoral immune response against human papillomavirus infections during pregnancy. Among the pregnant women a twofold to threefold decrease in mean reactivity in the E4 protein-based assay was detected between early gestation and delivery. The presence of human papillomavirus type 16 or 18 deoxyribonucleic acid was significantly associated with reactivity to the E6 protein (p = 0.0005) and the E4 protein (p = 0.06). Reactivity to the E4 protein also correlated with an abnormal Papanicolaou smear.

CONCLUSIONS

The observation of changes in humoral response to genital human papillomavirus infections during pregnancy warrants further investigation with highly seroreactive assays.

Identification of antigenic differences between the phosphorylated and nonphosphorylated forms of the E7 protein of human papillomavirus type 16

To analyze the antigenic properties of the human papillomavirus type 16 E7 oncoprotein, two monoclonal antibodies, VD6 and IB10, that have different reactivities to the E7 protein were generated. While the VD6 antibody reacted strongly with E7 protein in CaSki cell extracts, the other antibody, IB10, showed much weaker reactivity with E7. This reactivity increased in a dose-dependent manner in the presence of the casein kinase II-specific inhibitor DRB (5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole). Antigenic site estimation and an in vitro phosphorylation assay, using bacterially expressed E7 protein, demonstrated that the weak reactivity of IB10 was related to the phosphorylation status of the E7 protein. Phosphorylation of E7 reduced considerably the reactivity of IB10 but did not affect the reactivity of VD6, which reacts with the N-terminal portion of E7. In immunoprecipitation (IP) assays, IB10 precipitated weakly the E7 protein from CaSki cell extracts. Together, these data suggest that unphosphorylated E7 protein shows distinct antigenic character compared to its phosphorylated form under denaturing conditions; however, under native conditions, the phosphorylated and nonphosphorylated E7 proteins have some antigenic cross-reactivity.

HPV detection in children prior to sexual debut

Knowledge of the epidemiology of infection with human papillomavirus (HPV) in childhood is important, since HPV infection early in life could represent a risk factor for later development of anogenital cancer. A random sample of Danish children aged 0 to 17 years was tested for the presence of HPV in the anal region and the oral cavity by the polymerase chain reaction using a consensus HPV L1 primer. Only 4 of 249 anal beta-globin-positive samples and one of 392 oral beta-globin-positive samples were HPV-positive. All HPV-positive samples were of unknown types. We conclude that the prevalence of anogenital HPV infection in childhood is very low indeed and that the oral cavity does not seem to act as a reservoir for HPV infection in childhood. This indicates that anogenital types of HPV are not transmitted to any measureable degree by non-sexual routes and further supports the notion that HPV infection takes place mainly later in life.

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.

Chimeric papillomavirus-like particles

We have constructed chimeric papillomavirus-like particles (CVLPs) by replacing the 34-carboxy-terminal amino acids of the HPV 16 L1 protein with various parts of the HPV 16 E7 protein. Chimeric proteins were expressed by recombinant baculoviruses and analyzed by electron microscopy for their ability to assemble into virus capsids. We were able to produce CVLPs in high efficiencies with inserts of up to 60 amino acids. CVLPs are able to induce a neutralizing antibody response, assayed by inhibition of hemagglutination of mouse erythrocytes. CVLPs are interacting with the putative receptor for papillomaviruses as they were shown to hemagglutinate mouse red blood cells and bind to and penetrate cells in vitro. As CVLPs follow a similar intracellular pathway as observed earlier for BPV VLPs, we speculate that CVLPs can be used to deliver peptides into mammalian cells in vitro and in vivo, possibly reaching the pathway for MHC class I presentation.

Human papillomavirus-associated tumors of the skin and mucosa

This review discusses diseases of the lower genital tract in which the presence of human papillomavirus (HPV) DNA is well documented. We discuss epidemiologic, clinical, and experimental data supporting a causative role for HPV in mucosal malignancies, with emphasis on the role of viral and host factors in their pathogenesis. Of special interest is the recently discovered association of cutaneous tumors with HPVs, previously known only for tumors in epidermodysplasia verruciformis (EV). The frequent detection of EV-specific or EV-related HPVs in immunosuppressed persons and in cutaneous tumors in the general population supports the importance of EV as a model of cutaneous oncogenesis. We also discuss recent serologic findings based on enzyme-linked immunosorbent assay results with the use of viruslike particles. This is important both for detection of present or past HPV infection and for epidemiologic and immunologic studies. Novel therapeutic modalities for HPV tumors and prospects for prophylactic and therapeutic vaccination are presented.

Seropositivity against HPV 16 capsids: a better marker of past sexual behaviour than presence of HPV DNA

OBJECTIVES

To assess if seropositivity to human papillomavirus type 16 capsids is a better marker of sexual history than the presence of HPV DNA.

STUDY DESIGN

A population based age stratified random sample of 234 Norwegian women (mean age 32.8 years, range 20-44) was examined for HPV serum antibodies, cervical HPV DNA, cytology and age in relation to sexual behaviour.

RESULTS

Neither age nor age at first sexual intercourse was associated with HPV 16 antibodies. Adjusted ORs for 4-5; 6-10 and > 10 versus 0-1 lifetime sexual partners, were 13.1 (95% CI 1.5-110.8), 8.2 (1.0-69.6) and 10.5 (1.2-94.0) for HPV 16 seropositivity, respectively; and 2.6 (0.2-27.8), 3.4 (0.4-31.7) and 4.1 (0.4-42.8) for HPV 16 DNA positivity, respectively.

CONCLUSION

Seropositivity to HPV 16 capsids is positively associated with the number of sexual partners, suggesting that HPV 16 is predominantly sexually transmitted. The fact that serology had a stronger association with number of sexual partners than viral DNA suggests that seroreactivity is a better measure of lifetime history of HPV infection.

Multiplicity of uses of monoclonal antibodies that define papillomavirus linear immunodominant epitopes

During the last 10 yr, we have derived monoclonal antibodies from animals immunized with denatured bovine papillomaviruses type 1 major capsid (L1) protein, mapped their corresponding immunodominant epitopes to within a single amino acid (aa), and compared the reactivity of authentic L1 proteins to the predicted response by collinear analysis of the aa sequences of the same and other papillomaviruses (PVs). The data obtained from this approach has provided us with new insights into the sensitivity and specificity of the antibody response to viral proteins. We have included here some observations and conclusions that appear to be generic for the immune response, some of which might have applications for working with linear epitopes in other experimental systems.

Immunomanipulative strategies for the control of human papillomavirus associated cervical disease

Three vaccine strategies that target human papillomavirus (HPV) are likely to be effective in the control of HPV-associated preneoplastic and neoplastic lesions of the uterine cervix. 1. Immunotherapy for HPV-associated cervical cancer targeted at two nonstructural PV proteins expressed in cancer cells (E6 and E7). 2. Vaccines against existing HPV infection and early premalignant lesions targeted at early viral proteins expressed in suprabasal stem cells of infected anogenital epithelium. 3. Prophylactic vaccines to prevent HPV infection involving immunization with genetically engineered virus-like particles to elicit neutralizing antibody. Strategies 1 and 2 will need to evoke cytotoxic T-cell (CTL) mediated responses.

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.

The E7 protein of human papillomavirus (HPV) type 16 expressed by recombinant vaccinia virus can be used for detection of antibodies in sera from cervical cancer patients

Sera from 128 Mexican cervical cancer patients (age 30-80; mean 53.6) and from 47 healthy women (age 25-69; mean 49.2) were investigated using a newly developed assay for the detection of serum antibodies to the human papillomavirus (HPV) type 16 early protein E7. This test (CIPA), based upon immunoprecipitation followed by Western blot analysis, uses the complete E7 protein expressed in HeLa cells infected with recombinant vaccinia virus. To determine the sensitivity and specificity of this assay, these results were compared with previous results of the same sera tested by enzyme-linked immunosorbent assay (ELISA; using synthetic peptides derived from HPV 16 E7) and radio-immunoprecipitation (RIPA) using in vitro translated HPV 16 E7 protein. CIPA (45% positives) demonstrated a significant increase in detection rate compared to the peptide-ELISA (30% positives; P = 0.014, chi2-test) and only a slight increase compared to RIPA (38% positives; P = 0.204, chi2-test). Based on the testing of sera from patients with HPV 16 DNA positive tumors the specificity and sensitivity of the CIPA were 0.98 and 0.59, respectively.

Serological responses to human papillomavirus type 6 and 16 virus-like particles in patients with cervical neoplastic lesions

Serum samples from 36 cervical carcinoma patients, 33 patients with high-grade squamous intraepithelial lesions, and 31 cytologically normal women were tested by enzyme-linked immunosorbent assay (ELISA) using human papilloma virus type 6 (HPV 6) and HPV 16 virus-like particles as antigens. Forty serum specimens from 1-year-old children were used to assign cutoff points. When serum samples from the subjects infected with HPV 16 were tested in an HPV 16 ELISA detecting immunoglobulin A (IgA), IgG, and IgM binding, 61% showed IgA, 44% showed IgG, and 39% showed IgM reactivity. Of HPV 6- or 11- or HPV 18-infected subjects. fewer than 17% showed IgA or IgG responses and 33% showed IgM reactivity. In contrast, 13% showed IgA, 10% showed IgG, and 16% showed IgM reactivity in the HPV DNA-negative controls. The results suggest that the IgA and IgG responses are HPV 16 specific and the IgM response is cross-reactive to different HPV types. On the other hand, the serological responses to HPV 6 did not differ in the patient and control groups. The percentages of patients positive for both IgA and IgG antibodies were significantly higher in the groups with high-grade squamous intraepithelial lesions (12% [4 of 33]; P = 0.04) and cancer (17% [6 of 36]; P = 0.02) than in the healty women (0% [0 of 31]), and the percentages for either IgA or IgG were higher for the cancer group (47% [17 of 36]; P = 0.01) than in the normal group (19% [6 of 31]). Most sera positive for IgA and IgG in the patient groups showed higher titers than those in the normal group. All these results suggest that high IgA and IgG responses are good indicators for estimating HPV 16 infection.

Comparison of development of serum antibodies to HPV16 and HPV33 and acquisition of cervical HPV DNA among sexually experienced and virginal young girls. A longitudinal cohort study

OBJECTIVES

To study the importance of sexual activity and early coitus debut on the risk for acquiring infection with human papillomavirus (HPV) type 16 or 33.

STUDY DESIGN

Ninety-eight healthy adolescent girls were followed up with consecutive interviews and donations of serum and cervical brush samples during 2 years.

RESULTS

Fourteen percent of sexually experienced girls had serum immunoglobulin G to HPV16 and/or HPV33 capsids, and 14% also had cervical HPV16 or HPV33 DNA. Seropositivity for HPV correlated with detection of cervical HPV DNA. None of the 36 girls without coital experience was seropositive or harbored cervical HPV DNA. Seropositivity for HPV was correlated strongly with the number of sexual partners: Odds ratio for > 1 sexual partner was 16.3 (P < 0.001), and for early coitus debut (younger than 17 years of age), it was 14.3 (P < 0.002).

CONCLUSIONS

Both HPV serology and HPV DNA testing indicated that the number of sexual partners and earliness of coitus debut determined the risk for acquiring HPV infection and that nonsexually transmitted infections are rare or nonexistent among adolescent girls.

Immunisation of mice using Salmonella typhimurium expressing human papillomavirus type 16 E7 epitopes inserted into hepatitis B virus core antigen

Live vaccines based on BRD509, an attenuated S. typhimurium (aroA, aroD) strain, were constructed that directed the expression of hepatitis B core antigen particles (HBcAg) (BRD969) or HBcAg harbouring human papillomavirus type 16 E7 protein sequences (BRD974), under the control of the in vivo inducible nirB promoter. These strains were used to orally or intravenously immunise different inbred mouse strains and humoral, secretory and cellular anti-E7 and anti-HBcAg responses were monitored. Both BRD969 and BRD974 induced anti-HBcAg humoral IgG responses following oral or intravenous immunisation of B10 mice, although responses were higher in BRD969 immunised animals. IgG subclass analysis revealed a predominantly IgG2a response in these animals. BRD974, but not BRD969, induced anti-E7 humoral IgG responses. Anti-HBcAg (BRD969 and BRD974) and anti-E7 (BRD974) IgA responses were detected in the intestines of orally immunised mice. Anti-Salmonella but not anti-HBcAg or anti-E7 T helper cell responses were detected in mice immunised with BRD509, BRD969 and BRD974. Thus Salmonella vaccine strains can be used to efficiently deliver HBcAg and E7 epitopes to the mucosal and systemic immune systems.

T-cell proliferative response to human papillomavirus type 16 peptides: relationship to cervical intraepithelial neoplasia

The incidence of human papillomavirus (HPV)-related cervical intraepithelial neoplasia (CIN) and cervical cancer is increased with immunodeficiency, but the role of immune response, including cell-mediated immunity, in disease prevention is not well understood. In this study, T-cell proliferative responses to six synthetic peptides with predicted immunogenic determinants from the HPV-16 E4, E6, E7, and L1 open reading frames were analyzed in 22 sexually active women with new-onset CIN and 65 sexually active women without cervical disease, characterized by cytology, colposcopy, and HPV testing. T-cell proliferative responses were demonstrated to all six HPV-16 peptides. Although not statistically significant, rates of reactivity to E6 (24-45) were higher among sexually active women without disease (26%) than among women with current CIN (7%), as was the overall number of peptides stimulating a response. Women with CIN may not respond to selected HPV antigens as well as women without disease do.

Perinatal infection and persistence of human papillomavirus types 16 and 18 in infants

Perinatal transmission of genital human papillomaviruses (HPVs), including HPV-16 and -18 which are associated with anogenital carcinomas have been described previously [Pakarian et al. (1994): British Journal of Obstetrics and Gynaecology 101:514-517; Kaye et al. (1994) Journal of Medical Virology 44:415-421]. A study was undertaken to investigate whether HPV-16 and -18 DNA in infants contaminated at delivery persists until they are 6 months of age. Of 61 pregnant women recruited, 42 (68.8%) were HPV-16 and 13 (21.3%) were HPV-18 DNA positive. At 24 hr there were transmission rates from HPV DNA positive mothers to their infants of about 73% (HPV-16: 69%; HPV-18: 76.9%). Ten mothers who were both HPV-16 and -18 DNA positive produced six (60%) infants who were also doubly positive at 24 hr. HPV DNA persisted to 6 weeks in 79.5% (HPV-16: 84%; HPV-18: 75%) of those infants who were positive at birth. At 6 months of age, persistent HPV-16 DNA was detected in 83.3% of cases, but HPV-18 DNA persistence at this time was 20%. To extend these observations over a greater age range of children HPV-16 L1 and L2 proteins were expressed in insect cells via recombinant baculoviruses and sera from 229 children were examined to determine at what age IgM antibodies to HPV were acquired. There was a bimodal distribution of IgM seropositivity which peaked between 2 and 5 and 13 and 16 years of age, suggesting that two distinct modes of transmission may occur. The observation that infection with high cancer risk genital HPVs may occur in early life and persist is of considerable importance for HPV vaccine strategies.

Human papillomaviruses, cervical cancer and the developing world

Carcinoma of the uterine cervix is the commonest cancer of women in the majority of developing countries; in developed countries it is much less common, as well as being less frequent than some other cancers, such as those of breast, lung and colon. The discovery of human papillomavirus (HPV) as an aetiological agent of cervical cancer (and of other anogenital malignancies) has prompted a great deal of interest in the biology and oncogenicity of this virus, including large-scale epidemiological surveys comparing the prevalence of HPV and other possible causative agents between areas of high and low incidence of cervical carcinoma. These studies have thrown up tantalizing clues concerning the virus' pathogenesis and disease associations. Sexual practices, parity, diet, smoking, other diseases (including sexually transmissible diseases) and immunogenetic characteristics may all play a contributory role in the development of cervical carcinoma. These factors may be independent of each other and of association with HPV infection. Immunization to prevent papillomavirus infection and thus cervical cancer is an attractive prospect. Although the potential in using such an approach has been demonstrated in several animal models, there are several major theoretical problems to solve before HPV vaccination becomes a practicality. Intervention to prevent exposure to other aetiological factors and to improve screening may be a more practicable strategy for reducing the burden of cervical cancer.

A vaccine conjugate of 'ISCAR' immunocarrier and peptide epitopes of the E7 cervical cancer-associated protein of human papillomavirus type 16 elicits specific Th1- and Th2-type responses in immunized mice in the absence of oil-based adjuvants

TraT protein, known as ISCAR (= Immunostimulatory Carrier), is one of a family of integral membrane proteins (Imps) of Escherichia coli representing powerful carrier molecules which when injected into experimental animals generate substantial antibody and T proliferative responses to molecules conjugated to it. We extend these findings to show that ISCAR functions to stimulate Th1- and Th2-type responses, including specific cytotoxic T cells and tumour protection. We report here that by conjugating to ISCAR a 19mer peptide containing linear B epitopes, a T helper (Th) epitope, and a H-2b-restricted T cytotoxic (CTL) epitope of E7 protein of human papillomavirus type 16 (HPV16), and immunizing C57B1/6 (H-2b) mice, we elicited (i) specific IgG2a and IgG1 antibodies; (ii) IL-2 and IL-4 production by specifically recalled lymph node cells in vitro; (iii) cytotoxic T lymphocytes which specifically killed both E7 peptide-pulsed, and whole E7 gene-transfected tumour target cells; and (iv) in vivo protection against an E7 gene-transfected tumour cell inoculum. These findings have implications for the design of vaccines to stimulate immune responses to endogenously processed target antigens (e.g. tumour-associated antigens) without the unwanted side effects of oil-based adjuvants. In addition they support the case for a E7-targeted therapeutic vaccine for HPV-associated human cervical cancer.

A helper T-cell epitope of the E7 protein of human papillomavirus type 16 in BALB/c mice

The helper T-cell response to the E7 protein of human papillomavirus type 16 (HPV16) was studied using BALB/c (H-2d) mice. Twenty-two overlapping synthetic peptides spanning the HPV16 E7 protein were split into 6 groups. Mice were sensitized using mixtures of synthetic peptides corresponding to each of the groups. Lymph node cell suspensions were cultured with the corresponding mixture of synthetic peptides that was used for sensitization. Two mixtures induced a proliferative response. Analysis of the individual peptides from these mixtures showed that two (overlapping) peptides induced a proliferative response. This response was mediated by CD4+ cells. The common region of the two peptides was found to be a single epitope, and a minimal epitope was demonstrated (AHYNIVTFCCK). In conclusion, in contrast to others, we demonstrated a helper T-cell response in BALB/c mice. This may be due to the fact that we used synthetic peptides as immunizing agent. The helper T-cell epitopes in HPV16 E7 demonstrated previously are partly overlapping with the (minimal) epitope demonstrated here, underlining the 'public' nature of the epitope.

Antibodies to human papillomavirus type 16 E7 related to clinicopathological data in patients with cervical carcinoma

AIMS

To investigate the correlation between antibodies to the transforming protein E7 of human papillomavirus (HPV) type 16 and clinicopathological indices in women with cervical squamous carcinoma.

METHODS

A synthetic peptide of the HPV type 16 E7 protein (amino acids 6 to 35) was used to screen sera from 29 children, 130 women with cervical intraepithelial neoplasia, 443 women with cervical cancer, and 222 controls, for antibodies against this viral antigen. Bivariate and multivariate analyses were used to investigate the correlation between the serological status in the pretreatment sera and clinicopathological indices (size of the lesions, histological grade, stomal infiltration, vascular invasion, and nodal spread). Survival analysis was done using the Cox regression model for all FIGO stages and stages IB and ILA.

RESULTS

Cervical carcinoma patients had a significantly higher prevalence of antibodies to synthetic peptide E7/6-35 than women with cervical intraepithelial neoplasia (17.7% v 7%, p < 0.005) or controls (17.7% v 11%, p < 0.05). Bivariate analysis of the data on the presence of anti-E7/6-35 antibodies in the pretreatment sera from these patients and clinicopathological indices showed a significant correlation between the presence of anti-E7/6-35 antibodies and the size of the lesion (p = 0.0009), histological grade (p = 0.0031), and lymph node metastasis (p = 0.01). 0.011). In addition, the Cox regression model, analysing four risk factors which can be determined before treatment, showed a significant correlation between the presence of anti-E7/6-35 antibodies and a worse prognosis (p = 0.003). Survival analysis revealed that both for all FIGO stages (p = 0.0005) and for stages IB and IIA alone (p = 0.0021), anti-E7/6-35 positive patients before treatment had a significantly shorter life expectancy.

CONCLUSIONS

The presence of antibodies against E7/6-35 in pretreatment sera from patients with cervical carcinoma correlates with the size of the lesions, lymph node involvement, and a worse prognosis.

Follow-up of antibody responses to human papillomavirus type 16 E7 in patients treated for cervical carcinoma

A synthetic peptide comprising amino acids 6-35 of HPV-16 E7 was used in an ELISA to screen sera taken from 31 cervical carcinoma patients. Sera obtained before and during treatment, and in follow-up, were tested for the presence of antibodies to this peptide. Sixteen patients with negative pretreatment serum determination remained negative during treatment and follow-up. Of the 15 patients with positive pretreatment sera, 12 showed a decrease in anti-E7 6-35 antibody level during treatment. During follow-up an increase in anti-E7/6-35 antibody level was observed in 6 out of 7 patients with progressive or recurrent disease, whereas all patients who remained in complete remission showed stable or further decreasing antibody levels. During the course of disease of the 15 seropositive patients, serum anti-E7/6-35 antibody levels were compared with serum squamous cell carcinoma antigen (SCC-Ag) profiles, a clinically useful tumor marker in the management of cervical cancer patients. Similar patterns were observed in 10 out of 15 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies to the E4, E6, and E7 proteins of human papillomavirus (HPV) type 16 in patients with HPV-associated diseases and in the normal population

In a cross-sectional study, titers of antibodies to the E4 and E7 proteins of human papillomavirus (HPV) type 16 were measured by peptide-based enzyme-linked immunosorbent assay in 1707 sera. Sera were obtained from healthy individuals (ages 1 to 95 years), from patients with HPV-associated infection (cervical intraepithelial neoplasia and cervical cancer), and from patients who were at high risk for HPV infection (attending a sexually transmitted disease clinic or referred to a colposcopist because of an abnormal Papanicolaou smear). The prevalence of anti-E7 antibodies increased with age, although the overall prevalence in the adult population was low (10.36%) compared to the frequent detection of HPV 16 DNA in the population. This suggests that only a fraction of patients infected with HPV 16 develop an anti-E7 response. The age distribution of anti-E4 antibodies showed a different pattern, i.e., the prevalence was low in the adult population (1.14%) but exceeded 20% in children and teenagers. As the specificity of the anti-E4 reaction was supported by a highly significant association with anti-E6 positivity in children's sera (p = 0.002), it was assumed that infection with HPV 16 can occur frequently early in life. As compared to healthy controls, patients at high risk for HPV infection had a significantly higher frequency (p < 0.001) of antibodies to the HPV 16 E4 protein (but not to the E6 or the E7 protein) in their sera. Therefore, we conclude that in adults E4-specific antibodies may be a marker for virus replication.

Serum antibody against unfused recombinant E7 protein of human papillomavirus type 16 in cervical cancer patients

Sera were examined for the presence of antibody against E7 protein of human papillomavirus type 16 (HPV-16) by Western blot analysis using the bacterially derived unfused protein. The occurrence rates of anti-E7 antibody against HPV-16 were 14.1% (10/71) in cervical cancer patients, 0% (0/48) in cervical intraepithelial neoplasia patients, and 0% (0/41) in female non-malignant patients. Three patients (one with endometrial cancer, one with breast cancer, and one male patient with colon polyp) out of 115 patients with tumors in organs other than the cervix, had antibody against E7 protein of HPV-16. The serum antibody, once positive, could be detected for a long time after surgical removal of the cancers in all cases that could be followed up. HPV-16 DNA could be detected in 50% (13/26) of cervical cancer patients. Sixty-nine percent (9/13) of patients with HPV-16 DNA in cancers had the antibody and all the patients with stages II, III, and IV cervical cancer (8/8) harboring HPV-16 DNA showed the presence of the antibody against E7 protein of HPV-16. In contrast, only 20% (1/5) of cervical cancer patients with stage Ia or Ib harboring HPV-16 DNA showed positive for the anti-E7 antibody in sera. These findings suggest that the presence of anti-E7 antibody in serum depends on the staging of cervical cancer and extent of HPV infection.

A prospective study of antibody responses to defined epitopes of human papillomavirus (HPV) type 16 in relationship to genital and anorectal presence of HPV DNA

The aim of this study was to investigate whether antibody responses against synthetic peptides derived from genital human papillomavirus (HPV) proteins are associated with laboratory-proven genital and anorectal HPV infection. In this study, 158 heterosexual patients (110 women and 48 men) were followed prospectively. At each visit we collected serum samples as well as specimens from several sites in the anogenital area for detection of HPV type 6/11 (HPV-6/11), -16, -18, and -33 DNAs by PCR. Immunoglobulin A (IgA) and IgG responses against disrupted bovine papilloma virions and eight different synthetic peptides derived from HPV-6/11, -16, and -18 were determined for serum samples from the first and the last visits. The subjects attended the Municipal Sexually Transmitted Disease Clinic in Amsterdam, The Netherlands, two to seven times (mean, four times) at approximately 4-month intervals. Women were monitored over a period of 155 person-years, and men were monitored over 65 person-years. The magnitudes of the IgA responses against HPV-16 late protein epitopes L1:13, L1:31, and L2:49 were significantly higher in the sera from the last visit among the currently HPV DNA-positive participants than in HPV DNA-negative persons (P = 0.02). When the persons positive for any HPV type at any time during the follow-up period were compared with those who were negative at all times during the follow-up period, we also found a significant elevation of IgA responses against L1:31 and L2:49 (P = 0.04 and 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic significance of serum antibodies to human papillomavirus-16 E4 and E7 peptides in cervical cancer

BACKGROUND

The objective of this study was to investigate the prognostic significance of serum antibodies to human papillomavirus (HPV)-16 peptides in patients with squamous cell cervical cancer.

METHODS

Pretreatment sera from 78 patients and 198 control women were tested by an enzyme-linked immunosorbent assay technique for reactivity with HPV-16 E4 (E401p) and E7 (E701p) synthetic peptides. The presence and serum level of these antibodies were correlated with tumor stage, histologic features, and prognostic parameters.

RESULTS

The median follow-up was 65 months (range, 6-97 months). Antibodies to E401p peptide were found in 5 of the 198 (3%) control subjects, 4 of the 43 (9%) patients with low tumor stage (International Federation of Gynecology and Obstetrics [FIGO] Ia, Ib, IIa), and 7 of the 35 (20%) patients with advanced tumor stage (FIGO IIb, III, IVa). Antibodies to E701p were found in 25 (13%), 11 (26%), and 11 (31%) women, respectively. The differences between patients and control subjects were significant (P < 0.002). Seropositivity against these peptides showed no correlation with tumor stage. Antibody levels to both peptides were significantly higher in patients compared with control subjects (P < 0.05). Furthermore, antibody levels to E401p were higher in patients with advanced tumor stage versus patients with low tumor stage (P = 0.0097). Such a relation was not found for anti-E701p antibodies. In the univariate analysis, a high level of anti-E701p antibodies was associated with a shorter disease free interval (P = 0.012) and poor survival (P = 0.049). However, this variable possessed no prognostic value after adjusting for FIGO stage and tumor size.

CONCLUSIONS

The authors' findings indicate that the prognostic significance of serum antibodies to the HPV-16 E4 and E7 peptides used in this study of patients with cervical cancer is limited.

Immunology of the human papilloma virus in relation to cancer

Human papillomaviruses (HPVs) have been associated with benign and malignant epithelial proliferations in either skin or mucosa. Two HPV oncogenic proteins, E6 and E7, are important in the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Therefore, vaccines targeted to these proteins may provide an opportunity to prevent and treat HPV-associated malignancies. The encouraging results from recent experimental vaccination systems in animal models suggest that continued exploration in these systems might lead to trials on human subjects and might allow us to prevent HPV infection or control its potentially life-threatening consequences.

Antibodies against linear and conformational epitopes of the human papillomavirus (HPV) type 16 E6 and E7 oncoproteins in sera of cervical cancer patients

Sera obtained from 137 cervical cancer patients were analysed for the presence of antibodies to the human papillomavirus (HPV) type 16 proteins E6 and E7 by the aid of different assays, i.e. ELISA using as antigen either synthetic peptides or the complete E7 protein and radio-immunoprecipitation (RIPA) which uses the viral protein made by in vitro transcription/translation. In agreement with previous reports, reactivity to the E7 protein was found more frequently than to the E6 protein (31.4% vs. 16.8%) when the sera were assayed by peptide-based ELISA. In contrast, when RIPA was employed, reactivity to either protein was obtained at similar frequency (38.7% vs 46.7%). When the protein was denatured prior to immuno-precipitation the reactivity was lost in all sera tested for E6-specific antibodies but only in a few samples in the E7-RIPA. Therefore it was concluded that the increased sensitivity of the E6-RIPA as compared to the E6 peptide-ELISA is due to the detection of antibodies to conformational epitopes which are presented by the in vitro product but not by the synthetic peptides. Eighty-two sera from healthy donors were tested by HPV 16E6- and E7-RIPA and also by ELISA using the HPV 16E7 protein which was produced in the fission yeast Schizosaccharomyces pombe. One sample reacted each in the E6- and E7-RIPA indicating a high specificity of these assays. The E7 protein-ELISA proved to be less sensitive for the detection of antibodies in cervical cancer patients' sera (22.6% positive) as compared to peptide-based ELISA or RIPA.

Comparison of peptide enzyme-linked immunosorbent assay and radioimmunoprecipitation assay with in vitro-translated proteins for detection of serum antibodies to human papillomavirus type 16 E6 and E7 proteins

Antibodies to human papilloma virus (HPV) type 16 (HPV-16) E6 and E7 proteins in serum are markers for HPV-associated invasive cervical carcinoma. We compared two assays, a radioimmunoprecipitation assay with in vitro-translated HPV-16 E6 and E7 proteins and an enzyme-linked immunosorbent assay (ELISA) with E6 and E7 synthetic peptides, for their abilities to discriminate serologically between patients with invasive cervical cancer and controls. Among the patients, antibody prevalences were higher by the E6 radioimmunoprecipitation assay (55.7%) than by the E6 peptide ELISA (15.5%), but among the controls, they were lower by the radioimmunoprecipitation assay (1.7%) than by the E6 peptide ELISA (5%). For E7, antibody prevalences among the patients were comparable by the radioimmunoprecipitation assay (43%) and the peptide ELISA (41%), but among the controls they were higher by the E7 peptide ELISA (17.4%) than by the radioimmunoprecipitation assay (4.1%). There was good agreement between the E7 radioimmunoprecipitation assay and the E7 peptide ELISA among patients but not among controls. In tests with representative sera, heat denaturation of the translated proteins resulted in a complete loss of reactivity to the E6 protein and a marked decrease in reactivity to the E7 protein. Our study showed that the radioimmunoprecipitation assay discriminates better than the peptide ELISA between patients with invasive cervical cancer and controls and that this is related to the ability of the radioimmunoprecipitation assay to detect conformational epitopes.

Brief report: antibody response to E6, E7, and L1 proteins of human papillomavirus 16 in an Italian population

The serological response to human papillomavirus type 16 (HPV16) E6, E7, and L1 proteins was investigated in Italian patients with cervical cancer, cervical intraepithelial neoplasia (CIN), flat cervical warts, condylomas, and in healthy individuals. Bacterially expressed beta-galactosidase fusion proteins were purified and used as antigen in Western blot assays. The HPV16 DNA status was also determined in most of the women. The incidence of antibody response to E6 and E7 proteins was higher in cervical cancer than in CIN patients. No variation of antibody titre against E6 was observed in the cervical cancer patients, while one patient in an advanced stage of disease displayed very high levels of E7 antibodies. High seroprevalence to both E6 and L1 was observed in patients with genital condylomas, but this may be due to cross-reactivity between HPV6 or 11 antibodies and the experimental HPV16 antigens. Antibodies to L1 were detected in control women, suggesting that HPV infection is widespread. The data obtained in this study are in agreement with previous findings in other countries.

T-cell response to cottontail rabbit papillomavirus structural proteins in infected rabbits

Cottontail rabbit papillomavirus (CRPV)-induced papillomas progress at a high frequency to carcinomas and thus can serve as a model for high-cancer-risk human papillomavirus infection. Previously, we have shown that antibodies to nonstructural and structural proteins are detected in only a fraction of papilloma-bearing animals. However, the antibody response to structural proteins drastically increases as papillomas progress to carcinoma (Y.-L. Lin, L. A. Borenstein, R. Selvakumar, R. Ahmed, and F. O. Wettstein, J. Virol. 67:382-389, 1993). Here we have monitored the cellular immune response to viral proteins during the course of infection and particularly during progression from papilloma to carcinoma. This was done by measuring the in vitro proliferation response of peripheral blood mononuclear cells (PBMCs) to CRPV structural proteins L1 and L2. The proliferating cells were identified as T cells by selective removal of B or T cells. In general, the T-cell response was low for rabbits at the papilloma stage and none responded to L2. Lymphocytes from animals with carcinomas more frequently and more strongly responded to L1, and more than half also responded to L2. In addition to stimulation of PBMCs, L1- and L2-specific proliferation could also be demonstrated with lymph node and spleen cells. Overall, our data show that progression of papilloma to carcinoma is associated with an increased T-cell response to CRPV structural proteins in addition to an increased humoral response. This greater immune reactivity, however, was not associated with a selectively increased expression of structural proteins, since RNA isolated from papillomas and carcinomas contained similar relative levels of late and early RNA as shown by dot blot analysis. Thus, the heightened immune reactivity seen in carcinoma-bearing rabbits most likely reflects greater stimulation of the immune system owing to dissemination of the tumor. These findings suggest that increased immune responses to papillomavirus proteins may be prognostic of progression to carcinoma and particularly of the development of metastases.