Subsequent malignant neoplasms in the Childhood Cancer Survivor Study: Occurrence of cancer types in which human papillomavirus is an established etiologic risk factor.

BACKGROUND: Human papillomavirus (HPV)-associated subsequent malignant neoplasms (SMNHPV ) in childhood cancer survivors are poorly understood. METHODS: The cumulative risk of SMNHPV was assessed among 24,363 Childhood Cancer Survivor Study participants. Standardized incidence ratios (SIRs) and absolute excess risk were calculated using age-matched, sex-matched, and calendar year rates from the Surveillance, Epidemiology, and End Results program. Poisson regression models identified SMNHPV risk factors, evaluating relative SIRs (rSIR) and 95% confidence intervals (95% CIs). RESULTS: In total, 46 survivors developed an SMNHPV (median age, 31 years [range, 10-56 years]; median time from primary cancer, 21 years [range, 9-35 years]). SMNHPV sites included oropharynx (N = 44), anorectum (N = 6), uterine cervix (N = 2), and vulva (N = 2). The 33-year cumulative incidence was 0.3% (95% CI, 0.2%-0.4%), and the SIR was nearly 3-fold that of the general population (SIR, 2.86; 95% CI, 2.05-4.00). Female survivors were not at increased risk of cervical or vulvar cancers compared with the general population. All survivors had an elevated risk of oropharyngeal SMNHPV (males: SIR, 4.06; 95% CI, 2.37-6.97; females: SIR, 8.44; 95% CI 4.88-14.61) and anorectal SMNHPV (males: SIR, 13.56; 95% CI, 5.09-36.13; females: SIR, 9.15; 95% CI, 2.29-36.61). Males (vs females: rSIR, 1.99; 95% CI, 1.00-3.94); head, neck, and pelvic radiotherapy doses >3000 centigray (vs none: rSIR, 2.35; 95% CI, 1.11-4.97); and cisplatin-equivalent doses >400 mg/m2 (vs none: rSIR, 4.51; 95% CI, 1.78-11.43) were associated with increased SMNHPV SIRs in multivariable analysis. CONCLUSIONS: Childhood cancer survivors are at increased risk for SMN in sites susceptible to HPV-associated malignancies. Further research examining HPV in the etiology of SMN and the promotion of HPV vaccination and surveillance guidelines for SMNHPV in cancer survivors is warranted.

Answers to common questions about COVID-19 vaccines in children with cancer.

BACKGROUND: The SARS-CoV-2 outbreak in 2020 evolved into a global pandemic, and COVID-19 vaccines became rapidly available, including for pediatric patients. However, questions emerged that challenged vaccine acceptance and use. We aimed to answer these questions and give recommendations applicable for use in pediatric patients with cancer by healthcare professionals and the public. METHODS: A 12-member global COVID-19 Vaccine in Pediatric Oncology Working Group made up of physicians and nurses from all world regions met weekly from March to July 2021. We used a modified Delphi method to select the top questions. The Working Group, in four-member subgroups, answered assigned questions by providing brief recommendations, followed by a discussion of the rationale for each answer. All Working Group members voted on each recommendation using a scale of 1 to 10, 10 being complete agreement. A "pass" recommendation corresponded to an agreement ≥7.5. RESULTS: We selected 15 questions from 173 suggested questions. Based on existing published information, we generated answers for each question as recommendations. The overall average agreement for the 24 recommendations was 9.5 (95% CI 9.4-9.6). CONCLUSION: Top COVID-19 vaccine-related questions could be answered using available information. Reports on COVID-19 vaccination and related topics have been published at record speed, aided by available technology and the priority imposed by the pandemic; however, all efforts were made to incorporate emerging information throughout our project. Recommendations will be periodically updated on a dedicated website.

Repeated Blood Cultures in Pediatric Febrile Neutropenia: Would Following the Guidelines Alter the Outcome?

BACKGROUND: The Infectious Diseases Society of America (IDSA) guidelines recommend collecting blood cultures for the first 3 days of febrile neutropenia (FN) in the clinically stable oncology patient with persistent fevers. Nonetheless, many physicians send daily blood cultures beyond 3 days, and the impact of that practice is uncertain. PROCEDURE: We reviewed pediatric FN episodes from July 2009 to May 2014 at University of Chicago Comer Children's Hospital. For each positive culture, we determined if it was a pathogen or a contaminant. We reviewed episode and patient demographics to identify risk factors for subsequent positive blood cultures in the setting of an initially negative culture. RESULTS: We identified 381 episodes of FN in 162 patients. Of those, 87 had a positive blood culture on day 1 (21.0% incidence of bacteremia). Of 294 episodes with a negative blood culture on day 1, six (2.04%, 95% confidence interval [CI] 0.42-3.67) had a positive culture after day 3. Of those, three were pathogens (1.02%, 95%CI -0.14 to 2.18), and only one was found in a hemodynamically stable patient (0.34%, 95%CI -0.33 to 1.01) with new mucositis. In the other two patients, Escherichia coli was isolated from blood cultures after day 10 in the setting of significant hemodynamic changes. Risk factor analysis performed in stable patients yielded nonsignificant results. CONCLUSIONS: Of 294 FN episodes with an initial negative blood culture, only one episode of bacteremia occurred without hemodynamic changes past day 3, supporting the IDSA guidelines to discontinue blood cultures in stable FN patients after day 3.

Taxi Drivers: A Target Population for the Prevention of Transmissible Disease?

We set out to assess the feasibility and uptake of an on-site influenza vaccination campaign targeting taxi drivers in airport taxicab lots in Chicago, Illinois. Influenza vaccine was provided by the Chicago Department of Public Health as this event aligned with ongoing efforts to provide influenza vaccinations throughout the city. Clinicians and clinic support staff were volunteers recruited from the University of Chicago Medicine and incorporated nursing staff, physicians, physician residents, and administrative support. Together, this allowed for a cost-effective approach to provide free influenza vaccines to the primarily uninsured taxi driver population. During these events, 545 taxi drivers received influenza vaccine in 2012 while 354 drivers were immunized in 2013. Nearly all drivers reported uninsured or under-insured status. The ability to use volunteers and healthcare organization's desires to meet the needs of the community, in collaboration with often under-staffed but highly dedicated local health departments have the potential to offer valuable public health services to underserved members of the community. Educational initiatives targeting vaccine hesitancy and misinformation may be necessary to improve immunization coverage among this population.

CD24 Expression Dampens the Basal Antiviral State in Human Neuroblastoma Cells and Enhances Permissivity to Zika Virus Infection.

Zika virus (ZIKV) exhibits distinct selectivity for infection of various cells and tissues, but how host cellular factors modulate varying permissivity remains largely unknown. Previous studies showed that the neuroblastoma cell line SK-N-AS (expressing low levels of cellular protein CD24) was highly restricted for ZIKV infection, and that this restriction was relieved by ectopic expression of CD24. We tested the hypothesis that CD24 expression allowed ZIKV replication by suppression of the antiviral response. SK-N-AS cells expressing an empty vector (termed CD24-low cells) showed elevated basal levels of phosphorylated STAT1, IRF-1, IKKE, and NFκB. In response to exogenously added type I interferon (IFN-I), CD24-low cells had higher-level induction of antiviral genes and activity against two IFN-I-sensitive viruses (VSV and PIV5-P/V) compared to SK-N-AS cells with ectopic CD24 expression (termed CD24-high cells). Media-transfer experiments showed that the inherent antiviral state of CD24-low cells was not dependent on a secreted factor such as IFN-I. Transcriptomics analysis revealed that CD24 expression decreased expression of genes involved in intracellular antiviral pathways, including IFN-I, NFκB, and Ras. Our findings that CD24 expression in neuroblastoma cells represses intracellular antiviral pathways support the proposal that CD24 may represent a novel biomarker in cancer cells for susceptibility to oncolytic viruses.

High potency silencing by single-stranded boranophosphate siRNA.

In RNA interference (RNAi), double-stranded short interfering RNA (ds-siRNA) inhibits expression from complementary mRNAs. Recently, it was demonstrated that short, single-stranded antisense RNA (ss-siRNA) can also induce RNAi. While ss-siRNA may offer several advantages in both clinical and research applications, its overall poor activity compared with ds-siRNA has prevented its widespread use. In contrast to the poor gene silencing activity of native ss-siRNA, we found that the silencing activity of boranophosphate-modified ss-siRNA is comparable with that of unmodified ds-siRNA. Boranophosphate ss-siRNA has excellent maximum silencing activity and is highly effective at low concentrations. The silencing activity of boranophosphate ss-siRNA is also durable, with significant silencing up to 1 week after transfection. Thus, we have demonstrated that boranophosphate-modified ss-siRNA can silence gene expression as well as native ds-siRNA, suggesting that boranophosphate-modified ss-siRNAs should be investigated as a potential new class of therapeutic agents.

Paediatricians' attitudes and practices towards HPV vaccination.

AIM: In June 2006, the human papillomavirus (HPV) vaccine, Gardasil, was licensed for use in the United States. We examined whether paediatricians would recommend the vaccine, obstacles they encountered and characteristics associated with not recommending the HPV vaccine to all eligible patients. METHODS: Four hundred fifty general paediatricians, 200 members of the section of infectious diseases and 200 members of the section of adolescent medicine of the American Academy of Pediatrics web-based directory were surveyed. RESULTS: Of 752 eligible paediatricians, 373 (50%) responded. Eighty-eight percent (292 of 332) of respondents stated that they would give the vaccine to all, 36 (11%) would give it to some and 4 (1%) would give it to none of their eligible patients. The main obstacles were cost and safety; a minority expressed concern about the vaccine's potential impact on adolescent sexual activity. Physicians who would not recommend HPV vaccination to all eligible patients were more likely to be generalists, have higher intrinsic religiosity, self-describe as conservative, report later adoption of new drugs/vaccines, and would not encourage vaccinating their own daughter or the daughter of a close friend. CONCLUSION: Although paediatricians are highly supportive of the HPV vaccine, certain characteristics may predict reluctance to immunize.

Pediatricians are more supportive of the human papillomavirus vaccine than the general public.

OBJECTIVE: The purpose of this study was to determine pediatricians' attitudes about the human papillomavirus (HPV) vaccine and to compare their attitudes with those expressed by the general public. METHODS: Eight-hundred and fifty pediatricians from the American Academy of Pediatrics were surveyed, including general pediatricians (n = 450), and members of the sections of adolescent medicine (n = 200) and infectious diseases (n = 200). Pediatricians were asked to answer four items that had been included on a Wall Street Journal (WSJ) poll of the general public shortly after the HPV vaccine was approved by the Food and Drug Administration. RESULTS: Of 752 eligible pediatricians, 373 (50%) responded. Compared to the general public, pediatricians were less likely to agree that routine Papanicolaou smears are a better strategy for preventing cervical cancer than HPV vaccination (12% vs 45%, P < 0.001), that abstinence programs are a better strategy for preventing the spread of HPV (17% vs 44%, P < 0.001), and that HPV vaccination may encourage sexual activity (4% vs 27%, P < 0.001). Pediatricians were more likely to support HPV vaccination without parental permission (77% vs 47%, P < 0.001). There were no differences between pediatricians based on gender. General pediatricians were more likely than pediatricians affiliated with the sections of infectious diseases and adolescent medicine to endorse abstinence programs over HPV vaccination (22% vs 16% and 8%, respectively, P = 0.01). CONCLUSION: Pediatricians are much more supportive of HPV vaccination than the general public. Pediatricians should be aware of these differences when counseling patients and their families.

Zika virus as an oncolytic treatment of human neuroblastoma cells requires CD24.

Neuroblastoma is the second most common childhood tumor. Survival is poor even with intensive therapy. In a search for therapies to neuroblastoma, we assessed the oncolytic potential of Zika virus. Zika virus is an emerging mosquito-borne pathogen unique among flaviviruses because of its association with congenital defects. Recent studies have shown that neuronal progenitor cells are likely the human target of Zika virus. Neuroblastoma has been shown to be responsive to infection. In this study, we show that neuroblastoma cells are widely permissive to Zika infection, revealing extensive cytopathic effects (CPE) and producing high titers of virus. However, a single cell line appeared poorly responsive to infection, producing undetectable levels of non-structural protein 1 (NS1), limited CPE, and low virus titers. A comparison of these poorly permissive cells to highly permissive neuroblastoma cells revealed a dramatic loss in the expression of the cell surface glycoprotein CD24 in poorly permissive cells. Complementation of CD24 expression in these cells led to the production of detectable levels of NS1 expression after infection with Zika, as well as dramatic increases in viral titers and CPE. Complementary studies using the Zika virus index strain and a north African isolate confirmed these phenotypes. These results suggest a possible role for CD24 in host cell specificity by Zika virus and offer a potential therapeutic target for its treatment. In addition, Zika viral therapy can serve as an adjunctive treatment for neuroblastoma by targeting tumor cells that can lead to recurrent disease and treatment failure.

RNA interference using boranophosphate siRNAs: structure-activity relationships.

In RNA interference (RNAi), short double-stranded RNA (known as siRNA) inhibits expression from homologous genes. Clinical or pre-clinical use of siRNAs is likely to require stabilizing modifications because of the prevalence of intracellular and extracellular nucleases. In order to examine the effect of modification on siRNA efficacy and stability, we developed a new method for synthesizing stereoregular boranophosphate siRNAs. This work demonstrates that boranophosphate siRNAs are consistently more effective than siRNAs with the widely used phosphorothioate modification. Furthermore, boranophosphate siRNAs are frequently more active than native siRNA if the center of the antisense strand is not modified. Boranophosphate modification also increases siRNA potency. The finding that boranophosphate siRNAs are at least ten times more nuclease resistant than unmodified siRNAs may explain some of the positive effects of boranophosphate modification. The biochemical properties of boranophosphate siRNAs make them promising candidates for an RNAi-based therapeutic.

Infections diagnosed in the first year after pediatric stem cell transplantation.

BACKGROUND: Cumulative incidence of infections in the first year posttransplantation in adult patients has been well-described. Such description is less than complete for pediatric stem cell transplantation (SCT) patients. Further among those patients who have been infected, analysis of risk factors for infection has not been well-described for a large cohort of pediatric SCT patients. METHODS: We conducted a retrospective cohort study of infections in the first year after SCT at Duke University Medical Center. We recorded all infections in the first year after transplantation. We determined incidences for 6 categories of infection: gram-negative rods; gram-positive cocci; yeast species; Aspergillus sp.; adenovirus; and cytomegalovirus. We determined incidences based on type of transplant and days post transplantation. We also completed bivariable and multivariable analysis of risk factors [neutropenia, graft vs. host disease (GVHD) and GVHD treatment] for infection type among those children who were infected. RESULTS: We evaluated 510 transplants in 485 children. There were 584 infections in the first year after transplantation. During the first 30 days posttransplantation, type of transplantation did not predict incidence of infection or type of infection. After 30 days children who received unrelated cord blood transplant and matched unrelated donor transplant were at much higher risk of infection than were patients who received autologous, matched sibling or haploidentical transplant (P < 0.001). Patients who received unrelated cord blood or matched unrelated donor transplantation were at higher risk of aspergillosis (P = 0.002), candidiasis (P = 0.005) and adenovirus (P < 0.0001) but not cytomegalovirus (P = 0.18). In analysis of risk factors among those infected, patients with aspergillosis were more likely to have severe GVHD: multivariable 1 year risk ratio, 7.5; 95% confidence interval, 3.0, 18.4. Neutropenia was more strongly associated with gram-negative rod infection than any other type of infection. CONCLUSIONS: The incidence of infection immediately after transplantation did not differ significantly by type of transplant in this pediatric population. Type of transplant predicted increased incidence of infection 30 days posttransplantation and increased incidence of infection with several organisms traditionally associated with a high mortality rate in the transplant population.

Adolescent sexual activity and cancer risk: physicians' duty to inform?

Yearly, 33,000 cancer diagnoses in the US are attributed to human papillomavirus (HPV), with cervical cancer the most common. HPV is transmitted through sexual contact; HPV types 16 and 18 cause the majority of ano-genital cancers in men and women. HPV causes ∼100% of cervical cancers, ∼90% of anal cancers, and ∼50% of vaginal, vulvar, and penile cancers. HPV is also involved in ∼70% of oropharyngeal cancers (OPCs) in the US. The CDC recommends routine administration to all female (bivalent or quadrivalent vaccine) and male (quadrivalent vaccine) patients at 11-12 years of age; the series may be started as early as 9 years of age. Recent evidence suggests physicians do not universally recommend the vaccine to all adolescents. Additionally, parents may refuse the vaccine due to safety concerns as well as religious and moral beliefs related to onset of sexual debut. It has been suggested physicians should consider discussing HPV vaccine as a cancer prevention tool only, with less focus on the fact that transmission is caused by sexual activity. In this commentary we suggest physicians have a duty to warn parents and adolescents that OPCs may be transmitted through oral sex, which is often perceived as not constituting sexual activity.

Challenges to school-located vaccination: lessons learned.

School-located vaccination (SLV) has a long history in the United States and has successfully contributed to lower morbidity and mortality due to vaccine-preventable diseases.(1) Historically, SLV efforts, which tended to be single-vaccine programs intended to provide catch-up immunization to a defined school-age cohort or were implemented in response to an outbreak, were unfunded, funded by local health department, or were funded by industry or federal grants. The growing palette of vaccines recommended for routine use in adolescents along with limited success of office-based adolescent immunization create a compelling argument for the creation of financially sustainable SLV programs. An arguably significant barrier to both office-based and school-located adolescent immunization is the modest reimbursement rates afforded to immunizers. Because the immunization promotion and consent process is expensive, these costs must be reduced to a minimum to reach financial viability. Although there are challenges to creating a financially sustainable SLV program coordinated by an academic medical center, (AMC), the ability of AMCs to bill private and public insurers, the nonprofit status of medical centers, the allowances for faculty for academic pursuit, and the substantial infrastructure already present make AMCs a potentially practical site for the administration of SLV programs. Alternatively, as health departments throughout the nation continue to explore methods for billing private insurance, we may find health departments to be uniquely suited for coordinating the administration and billing of these services.

A School-Located Vaccination Adolescent Pilot Initiative in Chicago: Lessons Learned.

BACKGROUND: Many adolescents underutilize preventive services and are underimmunized. METHODS: To promote medical homes and increase immunization rates, we conceptualized and implemented a 3-year, 8-school pilot school-located vaccination collaborative program. We sought community, parent, and school nurse input the year prior to implementation. We selected schools with predominantly Medicaid-enrolled or Medicaid-eligible students to receive Vaccines For Children stock vaccines. Nurses employed by a mass immunizer delivered these vaccines at participating schools 3 times a year. RESULTS: Over 3 years, we delivered approximately 1800 vaccines at schools. School administrators, health centers, and neighboring private physicians generally welcomed the program. Parents did not express overt concerns about school-located vaccination. School nurses were not able to participate because of multiple school assignments. Obtaining parental consent via backpack mail was an inefficient process, and classroom incentives did not increase consent form return rate. The influenza vaccine had the most prolific uptake. The optimal time for administering vaccines was during regular school hours. CONCLUSIONS: Although school-located vaccination for adolescents is feasible, this is a paradigm shift for community members and thus accompanies challenges in implementation. High principal or school personnel turnover led to a consequent lack of institutional memory. It was difficult to communicate directly with parents. Because we were uncertain about the proportion of parents who received consent forms, we are exploring Internet-based and back-to-school registration options for making the consent form distribution and return process more rigorous. Securing an immunization champion at each school helped the immunization processes. Identifying a financially sustainable school-located vaccination model is critical for national expansion of school-located vaccination.

Barriers to HPV immunization for African American adolescent females.

PURPOSE: The objective of this study was to identify motivations and barriers to HPV vaccination and culturally relevant and meaningful opportunities for vaccine promotion among African American mothers and adolescent daughters. Qualitative methods were employed to identify barriers to HPV immunization and understand mothers motivations to vaccinate their daughters. We conducted in-depth interviews with 19 mother-daughter pairs focused on 5 key areas: health history, prior vaccine experience, knowledge of HPV and HPV vaccine, relationship with physician, and experience of cervical dysplasia and cervical cancer (CD/CC). RESULTS: Four key factors drive HPV immunization among African-American mothers of adolescent daughters. First, mothers' CD/CC disease experiences motivated a strong commitment to protect daughters from the trauma of CD/CC. Second, limited understanding of HPV and its connection to CD/CC made it difficult for mothers to assess the risk of infection or explain the medical benefits of the vaccine to their daughters. Third, mothers anticipate the sexual debut of adolescent daughters and advocate for healthcare interventions to protect them. Mothers were not deterred by multiple visits to complete the vaccine series; they likened HPV immunization to injectable contraceptives that require a series of injections and offer protection from the unintended consequences of sexual activity. Finally, mothers trusted physicians to initiate discussion of HPV immunization. Physicians who failed to initiate discussion and offer unconditional endorsement generated doubt about the vaccine among mothers and missed opportunities for immunization. CONCLUSIONS: Our initial results indicate that physicians can engage in culturally relevant vaccine promotion in urban, underserved African American communities by initiating discussions of HPV immunization that (1) acknowledge mothers' own CD/CC experiences, (2) support parenting strategies that aim to protect daughters from the unintended consequences of sexual activity, and (3) make explicit the connection between CD/CC and HPV infection, and between prevention of HPV infection and HPV immunization.

HPV-beyond cervical cancer (online resource center).

The human papillomavirus (HPV) causes more than 99% of all cervical cancers (see Am J Med Resource Center: http://supplements.amjmed.com/2011/HPV/). Exposure to HPV infections occurs in a high proportion of the overall population; however, 2 safe and effective vaccines, HPV2 and HPV4, are approved for the prevention of HPV-16 and HPV-18 infection, the most common causes of cervical cancer. Additionally, HPV4 prevents HPV-6 and HPV-11-related genital warts. While prevention of cervical cancer in women has been the initial aim of vaccination programs, it has now become apparent that HPV causes other types of cancer as well, including vulvar and vaginal cancers in women, penile cancer in men, and anal cancer in both sexes. Furthermore, these viruses have been implicated in head and neck cancers in both men and women as well. It is estimated that HPV-related cancers occur in 10,000 American males annually, suggesting that limiting vaccination programs to females may be underserving a significant proportion of the population. The efficacy of the 2 available vaccines against oncogenic HPV is more than 90% for both cervical and anal intraepithelial neoplasia. For those receiving the HPV4 vaccine, efficacy against genital warts is nearly 90%. Adverse effects are few and include episodes of syncope in the period immediately following vaccination. Benefits of vaccinating males include reduction in disease burden in men and enhanced herd immunity to reduce disease burden in women.

Development and cardiac contractility: cardiac troponin T isoforms and cytosolic calcium in rabbit.

Cardiac contractility depends on calcium sensitivity of the myofilaments and cytosolic free calcium concentration ([Ca(2+)](i)) during activation. During development, the cardiac troponin T isoform cTnT(1) is replaced by shorter cTnT isoforms, including cTnT(4), and changes occur in other myofibrillar proteins and in calcium regulation. We expressed rabbit recombinant (r)cTnT(1) and rcTnT(4) in Spodoptera frugiperda cells and determined their effect on calcium binding to TnC in solution and on the calcium sensitivity of myofilaments in skinned rabbit ventricular fibers in vitro. We measured [Ca(2+)](i) and L-type calcium current (I(Ca)) in ventricular myocytes from 3-wk-old and adult rabbits. The dissociation constant (K(d)) of Ca-Tn(cTnT1) in solution was smaller than that of Ca-Tn(cTnT4) (mean +/- SE: 0.52 +/- 0.08 mumol/L versus 0.83 +/- 0.09 mumol/L). The Ca(2+) sensitivity of force development was greater in fibers reconstituted with rcTnT(1) (pCa(50) 6.07 +/- 0.04) than those reconstituted with rcTnT(4) (pCa(50) 5.75 +/- 0.07). Systolic [Ca](i) was lower in 3-wk-old than adult cells (443 +/- 35 nmol/L versus 882 +/- 88 nmol/L) as was I(Ca) (5.8 +/- 0.9 pA/pF versus 14.2 +/- 1.6 pA/pF). The higher calcium sensitivity of Tn-Ca binding and of force development conferred by rcTnT(1) suggest that higher neonatal cTnT(1) expression may partially compensate for the lower systolic [Ca(2+)](i).

Human TATA binding protein inhibits human papillomavirus type 11 DNA replication by antagonizing E1-E2 protein complex formation on the viral origin of replication.

The human papillomavirus (HPV) protein E2 possesses dual roles in the viral life cycle. By interacting directly with host transcription factors in basal keratinocytes, E2 promotes viral transcription. As keratinocyte differentiation progresses, E2 associates with the viral helicase, E1, to activate vegetative viral DNA replication. How E2's major role switches from transcription to replication during keratinocyte differentiation is not understood, but the presence of a TATA site near the viral origin of replication led us to hypothesize that TATA-binding protein (TBP) could affect HPV replication. Here we show that the C-terminal domain of TBP (TBPc) is a potent inhibitor of E2-stimulated HPV DNA replication in vitro (50% inhibitory concentration = 0.56 nM). Increasing the E1 concentration could not overcome TBPc inhibition in replication assays, indicating that TBPc is a noncompetitive inhibitor of E1 binding. While direct E2-TBPc association could be demonstrated, this interaction could not fully account for the mechanism of TBPc-mediated inhibition of viral replication. Because E2 supports sequence-specific binding of E1 to the viral ori, we proposed that TBPc antagonizes E1-ori association indirectly through inhibition of E2-DNA binding. Indeed, TBPc potently antagonized E2 binding to DNA in the absence (K(i) = 0.5 +/- 0.1 nM) and presence (K(i) = 0.6 +/- 0.3 nM) of E1. Since E2 and TBPc cannot be coadjacent on viral sequences, direct DNA-binding competition between TBPc and E2 was responsible for replication inhibition. Given the ability of TBPc to inhibit HPV DNA replication in vitro and data indicating that TBPc antagonized E2-ori association, we propose that transcription factors regulate HPV DNA replication as well as viral transcription.