A favorable clinical trend is associated with CD8 T-cell immune responses to the human papillomavirus type 16 e6 antigens in women being studied for abnormal pap smear results

Review of the Standard and Advanced Screening, Staging Systems and Treatment Modalities for Cervical Cancer

Simple Summary

This review discusses the timeline and development of the recommended screening tests, diagnosis system, and therapeutics implemented in clinics for precancer and cancer of the uterine cervix. The incorporation of the latest automation, machine learning modules, and state-of-the-art technologies into these aspects are also discussed.

Abstract

Cancer arising from the uterine cervix is the fourth most common cause of cancer death among women worldwide. Almost 90% of cervical cancer mortality has occurred in low- and middle-income countries. One of the major aetiologies contributing to cervical cancer is the persistent infection by the cancer-causing types of the human papillomavirus. The disease is preventable if the premalignant lesion is detected early and managed effectively. In this review, we outlined the standard guidelines that have been introduced and implemented worldwide for decades, including the cytology, the HPV detection and genotyping, and the immunostaining of surrogate markers. In addition, the staging system used to classify the premalignancy and malignancy of the uterine cervix, as well as the safety and efficacy of the various treatment modalities in clinical trials for cervical cancers, are also discussed. In this millennial world, the advancements in computer-aided technology, including robotic modules and artificial intelligence (AI), are also incorporated into the screening, diagnostic, and treatment platforms. These innovations reduce the dependence on specialists and technologists, as well as the work burden and time incurred for sample processing. However, concerns over the practicality of these advancements remain, due to the high cost, lack of flexibility, and the judgment of a trained professional that is currently not replaceable by a machine.

Depletion of Human Papilloma Virus E6- and E7-Oncoprotein-Specific T-Cell Responses in Women Living With HIV

Background

Cervical cancer - caused by persistent High Risk Human Papilloma Virus (HR HPV) infections - is the second most common cancer affecting women globally. HIV infection increases the risk for HPV persistence, associated disease progression and malignant cell transformation. We therefore hypothesized that this risk increase is directly linked to HIV infection associated dysfunction or depletion of HPV-oncoprotein-specific T-cell responses.

Methods

The 2H study specifically included HIV+ and HIV- women with and without cervical lesions and cancer to analyze HPV oncogene-specific T cell responses in relation to HPV infection, cervical lesion status and HIV status. Oncoprotein E6 and E7 specific T-cell responses were quantified for the most relevant types HPV16, 18 and 45 and control antigens (CMV-pp65) and M.tb-PPD in 373 women, using fresh peripheral blood mononuclear cells in an IFN-γ release ELISpot assay.

Results

Overall, systemic E6- and E7-oncoprotein-specific T-cell responses were infrequent and of low magnitude, when compared to CMV-pp65 and M.tb-PPD (p < 0.001 for all HR HPV types). Within HIV negative women infected with either HPV16, 18 or 45, HPV16 infected women had lowest frequency of autologous-type-E6/E7-specific T-cell responses (33%, 16/49), as compared to HPV18 (46% (6/13), p = 0.516) and HPV45 (69% (9/13), p = 0.026) infected women. Prevalent HPV18 and 45, but not HPV16 infections were linked to detectable oncoprotein-specific T-cell responses, and for these infections, HIV infection significantly diminished T-cell responses targeting the autologous infecting genotype. Within women living with HIV, low CD4 T-cell counts, detectable HIV viremia as well as cancerous and precancerous lesions were significantly associated with depletion of HPV oncoprotein-specific T-cell responses.

Discussion

Depletion of HPV-oncoprotein-specific T-cell responses likely contributes to the increased risk for HR HPV persistence and associated cancerogenesis in women living with HIV. The low inherent immunogenicity of HPV16 oncoproteins may contribute to the exceptional potential for cancerogenesis associated with HPV16 infections.

HPV16 E6-specific T cell response and HLA-A alleles are related to the prognosis of patients with cervical cancer

BACKGROUND

T cell epitopes are polypeptide fragments presented to T cell receptors by MHC molecules encoded by human leukocyte antigen (HLA) genes after antigen-presenting cell processing, which is the basis for the study of antigen immune mechanism and multi-epitope vaccine. This study investigated T cell response to HPV16 E6 and E7 in patients with cervical squamous cell carcinoma (CSCC). Also, the HLA-A allele distribution was compared among patients and evaluated as a factor to predict prognosis in these patients.

MATERIALS AND METHODS

This study recruited a total of 76 patients with International Federation of Gynaecology and Obstetrics (FIGO) stage IIB-IIIB CSCC. Mononuclear cells were isolated from the peripheral blood before any treatment and then enzyme-linked immunosorbent spot (ELISpot) assay was employed to measure the E6 and E7-specific T cell response. HLA-A alleles were typed using Sanger sequencing-based typing techniques with DNA extracted from the peripheral blood. The correlation between the T cell responses, HLA-A allele distribution and patient prognosis were analysed using the Kaplan-Meier method, univariate and multivariate Cox proportional hazard models.

RESULTS

The frequency of HPV E6-specific T cell responses in patients with pelvic lymph node metastasis was lower than that in patients without metastasis (P = 0.022). The 5-year overall survival (OS) rates of patients were 87.5% for those responding to multiple overlapping peptides, 72.7% for those responding to 1-2 overlapping peptides and 47.7% for non-responders (P = 0.032). Cox regression analysis indicated that the presence of HLA*A02:07 was independently associated with worse OS (hazard ratio [HR] 3.042; 95% confidence interval [CI] 1.348-6.862; P = 0.007), while concurrent chemoradiation therapy (CCRT) was independently associated with better OS (HR 0.475; 95% CI 0.232-0.975; P = 0.042).

CONCLUSION

The results of our study demonstrated that the level of HPV16 E6-specific T cell response and HLA*A02:07 were correlated with prognosis in patients with advanced CSCC.

The Immune Microenvironment in Human Papilloma Virus-Induced Cervical Lesions-Evidence for Estrogen as an Immunomodulator

Globally, human papilloma virus (HPV) infection is a common sexually transmitted disease. However, most of the HPV infections eventually resolve aided by the body’s efficient cell-mediated immune responses. In the vast majority of the small group of patients who develop overt disease too, it is the immune response that culminates in regression of lesions. It is therefore a rarity that persistent infection by high-risk genotypes of HPV compounded by other risk factors progresses through precancer (various grades of cervical intraepithelial neoplasia—CIN) to cervical cancer (CxCa). Hence, although CxCa is a rare culmination of HPV infection, the latter is nevertheless causally linked to >90% of cancer. The three ‘Es’ of cancer immunoediting viz. elimination, equilibrium, and escape come into vogue during the gradual evolution of CIN 1 to CxCa. Both cell-intrinsic and extrinsic mechanisms operate to eliminate virally infected cells: cell-extrinsic players are anti-tumor/antiviral effectors like Th1 subset of CD4+ T cells, CD8+ cytotoxic T cells, Natural Killer cells, etc. and pro-tumorigenic/immunosuppressive cells like regulatory T cells (Tregs), Myeloid-Derived Suppressor Cells (MDSCs), type 2 macrophages, etc. And accordingly, when immunosuppressive cells overpower the effectors e.g., in high-grade lesions like CIN 2 or 3, the scale is tilted towards immune escape and the disease progresses to cancer. Estradiol has long been considered as a co-factor in cervical carcinogenesis. In addition to the gonads, the Peyer’s patches in the gut synthesize estradiol. Over and above local production of the hormone in the tissues, estradiol metabolism by the gut microbiome: estrobolome versus tryptophan non-metabolizing microbiome, regulates free estradiol levels in the intestine and extraintestinal mucosal sites. Elevated tissue levels of the hormone serve more than one purpose: besides a direct growth-promoting action on cervical epithelial cells, estradiol acting genomically via Estrogen Receptor-α also boosts the function of the stromal and infiltrating immunosuppressive cells viz. Tregs, MDSCs, and carcinoma-associated fibroblasts. Hence as a corollary, therapeutic repurposing of Selective Estrogen Receptor Disruptors or aromatase inhibitors could be useful for modulating immune function in cervical precancer/cancer. The immunomodulatory role of estradiol in HPV-mediated cervical lesions is reviewed.

First-in-Human Phase I Clinical Trial of an SFV-Based RNA Replicon Cancer Vaccine against HPV-Induced Cancers

A first-in-human phase I trial of Vvax001, an alphavirus-based therapeutic cancer vaccine against human papillomavirus (HPV)-induced cancers was performed assessing immunological activity, safety, and tolerability. Vvax001 consists of replication-incompetent Semliki Forest virus replicon particles encoding HPV16-derived antigens E6 and E7. Twelve participants with a history of cervical intraepithelial neoplasia were included. Four cohorts of three participants were treated per dose level, ranging from 5 × 10⁵ to 2.5 × 10⁸ infectious particles per immunization. The participants received three immunizations with a 3-week interval. For immune monitoring, blood was drawn before immunization and 1 week after the second and third immunization. Immunization with Vvax001 was safe and well tolerated, with only mild injection site reactions, and resulted in both CD4⁺ and CD8⁺ T cell responses against E6 and E7 antigens. Even the lowest dose of 5 × 10⁵ infectious particles elicited E6/E7-specific interferon (IFN)-γ responses in all three participants in this cohort. Overall, immunization resulted in positive vaccine-induced immune responses in 12 of 12 participants in one or more assays performed. In conclusion, Vvax001 was safe and induced immune responses in all participants. These data strongly support further clinical evaluation of Vvax001 as a therapeutic vaccine in patients with HPV-related malignancies.

Therapeutic Vaccines for HPV-Associated Malignancies

Human papillomavirus (HPV)-related malignancies are responsible for almost all cases of cervical cancer in women, and over 50% of all cases of head and neck carcinoma. Worldwide, HPV-positive malignancies account for 4.5% of the global cancer burden, or over 600,000 cases per year. HPV infection is a pressing public health issue, as more than 80% of all individuals have been exposed to HPV by age 50, representing an important target for vaccine development to reduce the incidence of cancer and the economic cost of HPV-related health issues. The approval of Gardasil^® as a prophylactic vaccine for high-risk HPV 16 and 18 and low-risk HPV6 and 11 for people aged 11-26 in 2006, and of Cervarix^® in 2009, revolutionized the field and has since reduced HPV infection in young populations. Unfortunately, prophylactic vaccination does not induce immunity in those with established HPV infections or HPV-induced neoplasms, and there are currently no therapeutic HPV vaccines approved by the US Food and Drug Administration. This comprehensive review will detail the progress made in the development of therapeutic vaccines against high-risk HPV types, and potential combinations with other immunotherapeutic agents for more efficient and rational designs of combination treatments for HPV-associated malignancies.

The promise of combining cancer vaccine and checkpoint blockade for treating HPV-related cancer

Human papillomavirus (HPV)-associated intraepithelial neoplasia or cancers are ideal candidates for cancer immunotherapy since HPV oncoproteins, such as E6 and E7 proteins of high-risk HPVs, could be utilized as foreign antigens. In HPV-associated cancers as well as nonviral cancers, the cancer cells may evade host immunity through the expression of immune checkpoint molecules, downregulation of human leukocyte antigen, and activation of immune regulatory cells. Because of these immune suppressive mechanisms, HPV therapeutic vaccines have shown little efficacy against HPV-associated cancers, although they have shown efficacy in treating HPV-associated intraepithelial neoplasias. Recently, checkpoint blockade emerged as a promising new treatment for solid cancers; however, these therapies have shown only modest efficacy against HPV-associated cancers. Here we reviewed literature analyzing a combinatory therapy using an immune checkpoint inhibitor and an HPV therapeutic vaccine for treating HPV-associated cancers to compensate for shortfalls of each monotherapy. Complimentary modes of T cell activation would be deployed; as vaccines would directly stimulate the T cells, while checkpoint inhibitors would do so by releasing inhibition. Some promising studies using animal models and early human clinical trials raised a possibility that such combinations may be efficacious in regressing HPV-associated cancers. Epitope spreading (the phenomenon in which non-targeted antigens become new targets of immune response) may play a critical role mechanistically. Currently ongoing studies will shed light as to whether such combination therapy would indeed be a promising new treatment paradigm. Current and future studies must also determine the adverse effect profile of such a combination treatment.

Evaluation of immune responses induced by a novel human papillomavirus type 16 E7 peptide-based vaccine with Candida skin test reagent as an adjuvant in C57BL/6 mice

Cell mediated immune (CMI) responses are crucial for the clearance of human papillomavirus (HPV) infection and HPV-associated lesions. Activated CD8 T cells are critical effector cells in recognizing and killing HPV-infected or HPV-transformed cells. CD4 T cells provide help for priming the generation and maintenance of CD8 T cells as well as for tumors immunity. An ideal therapeutic HPV peptide-based vaccine should induce both a robust CD8 T-cell response as well as a CD4 T-cell response for ensuring their efficiency. Candida skin test reagent was demonstrated to be able to induce the secretion of IL-12 by Langerhans cells and T-cell proliferation in vitro by our group, which indicated the potential of Candida to enhance CMI response. In this current study, we designed a novel HPV peptide-based vaccine which includes HPV16 E7 peptides and Candida as an adjuvant. The immune responses induced by the vaccine were comprehensively evaluated. The results showed that the vaccine induced significant HPV-specific CD8 T-cell and Th1 CD4 T-cell responses as well as humoral immune response. It is interesting that Candida alone induced a significant polarization of Th1 response an production of IFN-γ, which indicated Candida alone may be used as a potential immunotherapeutic reagent not only for HPV-associated lesions but also for other viral infection or even cancers.

Integration of Oncogenes via Sleeping Beauty as a Mouse Model of HPV16+ Oral Tumors and Immunologic Control

Human papillomavirus type 16 (HPV16) is the etiologic factor for cervical cancer and a subset of oropharyngeal cancers. Although several prophylactic HPV vaccines are available, no effective therapeutic strategies to control active HPV diseases exist. Tumor implantation models are traditionally used to study HPV-associated buccal tumors. However, they fail to address precancerous phases of disease progression and display tumor microenvironments distinct from those observed in patients. Previously, K14-E6/E7 transgenic mouse models have been used to generate spontaneous tumors. However, the rate of tumor formation is inconsistent, and the host often develops immune tolerance to the viral oncoproteins. We developed a preclinical, spontaneous, HPV16⁺ buccal tumor model using submucosal injection of oncogenic plasmids expressing HPV16-E6/E7, NRas ^G12V , luciferase, and sleeping beauty (SB) transposase, followed by electroporation in the buccal mucosa. We evaluated responses to immunization with a pNGVL4a-CRT/E7(detox) therapeutic HPV DNA vaccine and tumor cell migration to distant locations. Mice transfected with plasmids encoding HPV16-E6/E7, NRas ^G12V , luciferase, and SB transposase developed tumors within 3 weeks. We also found transient anti-CD3 administration is required to generate tumors in immunocompetent mice. Bioluminescence signals from luciferase correlated strongly with tumor growth, and tumors expressed HPV16-associated markers. We showed that pNGVL4a-CRT/E7(detox) administration resulted in antitumor immunity in tumor-bearing mice. Lastly, we demonstrated that the generated tumor could migrate to tumor-draining lymph nodes. Our model provides an efficient method to induce spontaneous HPV⁺ tumor formation, which can be used to identify effective therapeutic interventions, analyze tumor migration, and conduct tumor biology research. Cancer Immunol Res; 6(3); 305-19. ©2018 AACR.

A phase I dose-escalation clinical trial of a peptide-based human papillomavirus therapeutic vaccine with Candida skin test reagent as a novel vaccine adjuvant for treating women with biopsy-proven cervical intraepithelial neoplasia 2/3

PURPOSE: Non-surgical treatments for cervical intraepithelial neoplasia 2/3 (CIN2/3) are needed as surgical treatments have been shown to double preterm delivery rate. The goal of this study was to demonstrate safety of a human papillomavirus (HPV) therapeutic vaccine called PepCan, which consists of four current good-manufacturing production-grade peptides covering the HPV type 16 E6 protein and Candida skin test reagent as a novel adjuvant. PATIENTS AND METHODS: The study was a single-arm, single-institution, dose-escalation phase I clinical trial, and the patients (n = 24) were women with biopsy-proven CIN2/3. Four injections were administered intradermally every 3 weeks in limbs. Loop electrical excision procedure (LEEP) was performed 12 weeks after the last injection for treatment and histological analysis. Six subjects each were enrolled (50, 100, 250, and 500 μg per peptide). RESULTS: The most common adverse events (AEs) were injection site reactions, and none of the patients experienced dose-limiting toxicities. The best histological response was seen at the 50 μg dose level with a regression rate of 83% (n = 6), and the overall rate was 52% (n = 23). Vaccine-induced immune responses to E6 were detected in 65% of recipients (significantly in 43%). Systemic T-helper type 1 (Th1) cells were significantly increased after four vaccinations (P = 0.02). CONCLUSION: This study demonstrated that PepCan is safe. A significantly increased systemic level of Th1 cells suggests that Candida, which induces interleukin-12 (IL-12) in vitro, may have a Th1 promoting effect. A phase II clinical trial to assess the full effect of this vaccine is warranted.

A Human Papillomavirus Type 16 E6 52-62 CD4 T-Cell Epitope Restricted by the HLA-DR11 Molecule Described in an Epitope Hotspot

Cell-mediated immune responses to the human papillomavirus type 16 (HPV 16) E6 protein have been shown to be important in viral clearance and in regression of cervical lesions. Here, detailed analyses of a novel HPV 16 E6 CD4 T-cell epitope from a subject with cervical intraepithelial neoplasia 1 are described. This subject had demonstrated HPV 16 CD4 T-cell responses to multiple regions within the E6 protein. Isolation and cloning of CD4 T-cells were performed by magnetic selection of interferon-γ secreting cells and limiting dilution. A single HPV 16-specific T-cell clone isolated was shown to have a specificity to HPV 16 E6 52-62 restricted by the HLA-DR11 molecule. Homologous sequences (≥70% amino acid homology) were identified for HPV types 31, 33, 45, 58, 73, but cross-recognition was demonstrated only for HPV 45. Based on work performed by our group and others, it is known that this short peptide contains multiple CD4 and CD8 T-cell HPV epitopes and would be an ideal region to incorporate into a design of vaccines and immunotherapies against HPV-associated malignancies.

Immunologic treatments for precancerous lesions and uterine cervical cancer

Development of HPV-associated cancers not only depends on efficient negative regulation of cell cycle control that supports the accumulation of genetic damage, but also relies on immune evasion that enable the virus to go undetected for long periods of time. In this way, HPV-related tumors usually present MHC class I down-regulation, impaired antigen-processing ability, avoidance of T-cell mediated killing, increased immunosuppression due to Treg infiltration and secrete immunosuppressive cytokines. Thus, these are the main obstacles that immunotherapy has to face in the treatment of HPV-related pathologies where a number of different strategies have been developed to overcome them including new adjuvants. Although antigen-specific immunotherapy induced by therapeutic HPV vaccines was proved extremely efficacious in pre-clinical models, its progression through clinical trials suffered poor responses in the initial trials. Later attempts seem to have been more promising, particularly against the well-defined precursors of cervical, anal or vulvar cancer, where the local immunosuppressive milieu is less active. This review focuses on the advances made in these fields, highlighting several new technologies (such as mRNA vaccine, plant-derived vaccine). The most promising immunotherapies used in clinical trials are also summarized, along with integrated strategies, particularly promising in controlling tumor metastasis and in eliminating cancer cells altogether.

After the early promising clinical results, the development of therapeutic HPV vaccines need to be implemented and applied to the users in order to eradicate HPV-associated malignancies, eradicating existing perception (after the effectiveness of commercial preventive vaccines) that we have already solved the problem.

Control of HPV-associated tumors by innovative therapeutic HPV DNA vaccine in the absence of CD4+ T cells

Human papillomavirus (HPV) infections are particularly problematic for HIV + and solid organ transplant patients with compromised CD4+ T cell-dependent immunity as they produce more severe and progressive disease compared to healthy individuals. There are no specific treatments for chronic HPV infection, resulting in an urgent unmet need for a modality that is safe and effective for both immunocompromised and otherwise normal patients with recalcitrant disease. DNA vaccination is attractive because it avoids the risks of administration of live vectors to immunocompromised patients, and can induce potent HPV-specific cytotoxic T cell responses. We have developed a DNA vaccine (pNGVL4a-hCRTE6E7L2) encoding calreticulin (CRT) fused to E6, E7 and L2 proteins of HPV-16, the genotype associated with approximately 90% vaginal, vulvar, anal, penile and oropharyngeal HPV-associated cancers and the majority of cervical cancers. Administration of the DNA vaccine by intramuscular (IM) injection followed by electroporation induced significantly greater HPV-specific immune responses compared to IM injection alone or mixed with alum. Furthermore, pNGVL4a-hCRTE6E7L2 DNA vaccination via electroporation of mice carrying an intravaginal HPV-16 E6/E7-expressing syngeneic tumor demonstrated more potent therapeutic effects than IM vaccination alone. Of note, administration of the DNA vaccine by IM injection followed by electroporation elicited potent E6 and E7-specific CD8+ T cell responses and antitumor effects despite CD4+ T cell-depletion, although no antibody response was detected. While CD4+ T cell-depletion did reduce the E6 and E7-specific CD8+ T cell response, it remained sufficient to prevent subcutaneous tumor growth and to eliminate circulating tumor cells in a model of metastatic HPV-16+ cancer. Thus, the antibody response was CD4-dependent, whereas CD4+ T cell help enhanced the E6/E7-specific CD8+ T cell immunity, but was not required. Taken together, our data suggest that pNGVL4a-hCRTE6E7L2 DNA vaccination via electroporation warrants testing in otherwise healthy patients and those with compromised CD4+ T cell immunity to treat HPV-16-associated anogenital disease and cancer.

Candida skin test reagent as a novel adjuvant for a human papillomavirus peptide-based therapeutic vaccine

A vaccine adjuvant that can effectively promote cell-mediated immunity is currently not available. Because of the ability of a Candida skin test reagent injection to induce common wart regression, our group is using it as a novel adjuvant in a clinical trial of a peptide-based human papillomavirus therapeutic vaccine. The goal of this current study was to investigate the mechanisms of how Candida enhances the vaccine immune responses. Maturation effects on Langerhans cells, capacity to proliferate T-cells, expression of cytokines and pattern recognition receptors by Langerhans cells, and ability to induce Th1, Th2, and Th17 responses were investigated in healthy subjects. The vaccine, human papillomavirus peptides with Candida, demonstrated partial maturation effects on Langerhans cells indicated by significantly up-regulated CD40 (p=0.00007) and CD80 (p<0.00001) levels, and showed T-cell proliferative capacity (p<0.00001) when presented by Langerhans cells in vitro. Interestingly, the maturation effects were due to the peptides while Candida was responsible for the T-cell proliferation. The cytokine profile (IL-1β, IL-6, IL-8, IL-10, IL-12p40, IL-23Ap19, IFN-γ and TNF-α) of Langerhans cells treated with the vaccine or Candida alone showed that IL-12p40 mRNA was most frequently induced, and IL-12p70 protein was detected in the supernatants. The presence of pattern recognition receptors known to associate with Candida albicans (DC-SIGN, dectin-1, dectin-2, galectin-3, mincle, mannose receptor, Toll-like receptors-1, 2, 4, 6 and 9) were demonstrated in all subjects. On the other hand, the induction of Th1 response demonstrated by IFN-γ secretion by CD4 cells stimulated with the vaccine or Candida pulsed Langerhans cells was demonstrated only in one subject. In summary, the Langerhans cell maturation effects of the vaccine were due to the peptides while the T-cell proliferative capacity was derived from Candida, and the most frequently induced cytokine was IL-12.

Therapeutic Human Papillomavirus (HPV) Vaccines: A Novel Approach

Cervical cancer is the second largest cause of cancer-related death in women worldwide, and it occurs following persistent infection, sometimes for decades, with a specific subset of human papillomavirus (HPV) types; the approximately 13 oncogenic subtypes. Prophylactic vaccines against HPV infections hold promise for cost-effective reductions in the incidence of cervical cancer, but this may not be enough. Two prophylactic HPV vaccines are presently available and both contain L1 virus-like particles (VLPs) derived from the HPV subtypes most frequently associated with cervical cancer, HPV-16 and -18. Since the L1-VLP vaccines can only effectively prevent infection by the specific HPV subtype against which the vaccine was developed, cervical cancers caused by high-risk HPV subtypes other than HPV-16 and -18 may still occur in recipients of the current HPV vaccines. Furthermore, HPV vaccination coverage for adolescents is insufficient in most countries and therefore even HPV-16 and -18 infections are unlikely to be fully eradicated using the existing strategies. The development of HPV therapeutic vaccines remains essential. Many therapeutic vaccines aimed at clearing HPV-related cervical lesions have been developed and tested in patients with HPV16-positive cervical intraepithelial lesions (CIN) or cervical cancers. To date, definitive clinical efficacy and appropriate immunological responses have never been demonstrated for cervical neoplasia although promising results have been reported in patients with vulvar intraepithelial neoplasia. Here we discuss shortcomings of previous HPV therapeutic vaccine candidates and propose a novel vaccination strategy that leverages newly gained knowledge about mucosal immunity and the induction of mucosal immune responses.

Immune responses against human papillomavirus (HPV) infection and evasion of host defense in cervical cancer

Human papillomavirus (HPV) is the most important etiological factor for cervical cancer. A recent study demonstrated that more than 20 HPV types were thought to be oncogenic for uterine cervical cancer. Notably, more than one-half of women show cervical HPV infections soon after their sexual debut, and about 90 % of such infections are cleared within 3 years. Immunity against HPV might be important for elimination of the virus. The innate immune responses involving macrophages, natural killer cells, and natural killer T cells may play a role in the first line of defense against HPV infection. In the second line of defense, adaptive immunity via cytotoxic T lymphocytes (CTLs) targeting HPV16 E2 and E6 proteins appears to eliminate cells infected with HPV16. However, HPV can evade host immune responses. First, HPV does not kill host cells during viral replication and therefore neither presents viral antigen nor induces inflammation. HPV16 E6 and E7 proteins downregulate the expression of type-1 interferons (IFNs) in host cells. The lack of co-stimulatory signals by inflammatory cytokines including IFNs during antigen recognition may induce immune tolerance rather than the appropriate responses. Moreover, HPV16 E5 protein downregulates the expression of HLA-class 1, and it facilitates evasion of CTL attack. These mechanisms of immune evasion may eventually support the establishment of persistent HPV infection, leading to the induction of cervical cancer. Considering such immunological events, prophylactic HPV16 and 18 vaccine appears to be the best way to prevent cervical cancer in women who are immunized in adolescence.

Use of interferon-γ enzyme-linked immunospot assay to characterize novel T-cell epitopes of human papillomavirus

A protocol has been developed to overcome the difficulties of isolating and characterizing rare T cells specific for pathogens, such as human papillomavirus (HPV), that cause localized infections. The steps involved are identifying region(s) of HPV proteins that contain T-cell epitope(s) from a subject, selecting for the peptide-specific T cells based on interferon-γ (IFN-γ) secretion, and growing and characterizing the T-cell clones (Fig. 1). Subject 1 was a patient who was recently diagnosed with a high-grade squamous intraepithelial lesion by biopsy and underwent loop electrical excision procedure for treatment on the day the T cells were collected(1). A region within the human papillomavirus type 16 (HPV 16) E6 and E7 proteins which contained a T-cell epitope was identified using an IFN- g enzyme-linked immunospot (ELISPOT) assay performed with overlapping synthetic peptides (Fig. 2). The data from this assay were used not only to identify a region containing a T-cell epitope, but also to estimate the number of epitope specific T cells and to isolate them on the basis of IFN- γ secretion using commercially available magnetic beads (CD8 T-cell isolation kit, Miltenyi Biotec, Auburn CA). The selected IFN-γ secreting T cells were diluted and grown singly in the presence of an irradiated feeder cell mixture in order to support the growth of a single T-cell per well. These T-cell clones were screened using an IFN- γ ELISPOT assay in the presence of peptides covering the identified region and autologous Epstein-Barr virus transformed B-lymphoblastoid cells (LCLs, obtained how described by Walls and Crawford)(2) in order to minimize the number of T-cell clone cells needed. Instead of using 1 x 10(5) cells per well typically used in ELISPOT assays(1,3), 1,000 T-cell clone cells in the presence of 1 x 10(5) autologous LCLs were used, dramatically reducing the number of T-cell clone cells needed. The autologous LCLs served not only to present peptide antigens to the T-cell clone cells, but also to keep a high cell density in the wells allowing the epitope-specific T-cell clone cells to secrete IFN-γ. This assures successful performance of IFN-γ ELISPOT assay. Similarly, IFN- γ ELISPOT assays were utilized to characterize the minimal and optimal amino acid sequence of the CD8 T-cell epitope (HPV 16 E6 52-61 FAFRDLCIVY) and its HLA class I restriction element (B58). The IFN- γ ELISPOT assay was also performed using autologous LCLs infected with vaccinia virus expressing HPV 16 E6 or E7 protein. The result demonstrated that the E6 T-cell epitope was endogenously processed. The cross-recognition of homologous T-cell epitope of other high-risk HPV types was shown. This method can also be used to describe CD4 T-cell epitopes(4).

CD8 T-cell responses in incident and prevalent human papillomavirus types 16 and 18 infections

CD8 T-cell responses were examined in subjects with incident (new following negative visits) or prevalent (lasting ≥ 4 months) human papillomavirus type 16 (HPV16) or human papillomavirus (HPV18) infection. The groups were chosen from a cohort of women being followed every 4 months with cervical cytology and HPV-DNA testing. Enzyme-linked immunospot (ELISPOT) assay was performed at enrollment (time zero) and one year later. At time zero, 1 (6%) of 17 subjects with incident HPV 16/18 infections had positive ELISPOT results which increased to 6 (35%) at one year. For the subjects with prevalent HPV 16/18 infections, the ELISPOT results were similar at time zero (2 (15%) of 15 subjects positive) and at one year (3 (20%)). While all of the 11 women with prevalent HPV16 infection showed clearance one year later, unexpectedly only 1 (25%) of 4 women with prevalent HPV18 infection demonstrated clearance one year later (P = .009).

CD4+ T-cell response against human papillomavirus type 16 E6 protein is associated with a favorable clinical trend

The association between the CD8+ T-cell responses to human papillomavirus type 16 (HPV-16) E6 protein and a favorable clinical trend has been demonstrated previously. The roles of human papillomavirus (HPV)-specific CD4+ T-cell responses and of regulatory T-cells (Tregs) were examined. Subjects with a recent history of abnormal Papanicolaou smear were eligible, and colposcopy-guided biopsy was performed at enrollment. Interferon-γ enzyme-linked immunospot assay and fluorescent-activated cell sorter analysis to measure the frequencies of Tregs were performed. Subjects with histological diagnoses of cervical intraepithelial neoplasia 1, 2, or 3 were considered to have short-term persistence of cervical abnormality and were called "persistors" (n = 51) while those of normal histology were designated to be "regressors" (n = 33). A significantly higher percentage CD4+ T-cell response was detected in the regressors (15/33 or 45.5%) compared with the persistors (10/51 or 19.6%) (P = .015) for the E6 peptides but not for the E7 peptides. The CD4+ responses to certain E6 regions [E6(16-40), E6(91-115), E6(106-130), and E6(136-158)] were also significantly higher in the regressors. Although there was no difference in the frequencies of Tregs between the two groups, low frequencies of Tregs were significantly associated with positive CD4+ T-cell responses within certain E6 regions [E6(16-40), E6(31-55), E6(76-100), E6(91-115), and E6(106-130)]. The CD4+ and CD8+ T-cell responses to the HPV-16 E6 protein are associated with a favorable clinical trend. The HPV-16 E6 protein should be incorporated in the design of an HPV therapeutic vaccine.

Characterization of gut-derived intraepithelial lymphocyte (IEL) residing in human papillomavirus (HPV)-infected intraepithelial neoplastic lesions

PROBLEM

Mucosal T cells are the most likely direct effectors in host anti-human papillomavirus adaptive immunity and regression of cervical intraepithelial neoplasia (CIN) lesions. There are no studies addressing intraepithelial lymphocytes (IELs) in CIN lesions.

METHOD OF STUDY

Cervical lymphocytes were collected using cytobrushes from patients with CIN and analyzed by FACS analysis. Comparisons were made between populations of cervical T cells in CIN regressors and non-regressors.

RESULTS

A median of 74% of cervical lymphocytes were CD3(+) T cells. Populations of integrin αEβ7(+) IEL in CIN lesions varied markedly among patients (6-57%). Approximately half of integrin β7(+) T cells were CD45RA-negative memory T cells. The number of integrin αEβ7(+) cells among cervical T cells was significantly higher in CIN regressors when compared to non-regressors.

CONCLUSION

Higher cervical IEL numbers are associated with spontaneous regression of CIN. Accumulation of cervical integrin αEβ7(+) IEL may be necessary for local adaptive effector functions.