Next, to judge any matrix effects, we measured the HPV18 E6 concentration of cervical cell lysates from women with negative cytology with the 7D2 icELISA. develop a highly specific and sensitive indirect competitive ELISA (icELISA). The production of hybridomas secreting HPV18 E6 mAbs was carried out through a combined tolerization and immunization strategy, in order to avoid cross-reactivity with the E6 protein from low-risk HPV types 6 and 11. We selected the 7D2 hybridoma clone, which recognized HPV18 E6 and showed some cross-reactivity against the HR HPV45 E6 oncoprotein. The 7D2 mAb enabled the development of a sensitive, reliable and reproducible icELISA to detect and quantify small amounts of HPV18 E6 biomarker for cervical cancer progression. The present study establishes a valid 7D2-based icELISA that constitutes a promising bioanalytical method for the early detection and quantification of HPV18 E6 oncoprotein in cervical swab samples and cancer prevention. == Introduction == Human papillomavirus (HPV) is a non-enveloped double-stranded circular DNA virus and the most common sexually-transmitted infection [1]. HPVs are classified into five genera (alpha, beta, gamma, mu and nu), based on tissue tropism and subsequent host pathology [2]. The alpha-papillomavirus genera, which infects cutaneous and mucosal epithelia, contains members that are further classified into low-risk (LR) or high-risk (HR) types, depending on their oncogenic ability. The LR viral infections result in benign lesions, and are commonly caused by HPV6 and HPV11; while the HR HPV types are the etiological agents of anogenital and head-and-neck cancers [3]. From these, 14 types have been described (HPV16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66 and 68), with HPV16 and HPV18 being responsible for 75% of the worlds cervical cancer burden [4,5]. Cervical cancer is the fourth worlds most common female malignancy, with the vast majority of cases diagnosed in low resource regions, such as South-Eastern Asia, sub-Saharan Africa and Latin America [6]. The most important risk factor for cervical carcinogenesis is persistent infection with HR HPV types [7]. HR HPV DNA is detected in >99% of all tumors of the uterine cervix [8,9]. Efficient screening tests are the key to decreasing mortality associated with this disease. Since HPV cannot be cultured from clinical specimens in the laboratory, diagnosis relies on cytologic and molecular methods [1]. Cervical cytology using Papanicolaou (Pap) stained smears has been the standard screening method for detection of premalignant lesions and cervical cancer. Pap tests have successfully reduced cervical cancer Umeclidinium bromide incidence and mortality in developing countries, yet they carry a high false-negative rate as well as inter-operator and inter-observer variability [1,4,10]. The finding that persistent HR HPV infection has a causal role in the establishment of cervical cancer led to the development of HPV molecular tests. These molecular methods show greater sensitivity and negative predictive value than cytology screening; however, a lower specificity and Umeclidinium bromide positive predicted value have also been reported, particularly in young women in whom HPV infection is usually transient [4,11,12]. Therefore, detection of HPV DNA through molecular tests do not necessary indicate cervical dysplasia or cancer. In this scenario, the HR HPV early protein E6 becomes an interesting candidate for the development of cervical cancer screening methods. E6 is a small Umeclidinium bromide (~150 amino acids) homodimeric oncoprotein [13], which is overexpressed following HPV invasion into the host cervical cells as episomal DNA or through viral integration into the hosts genome [14]. E6 from HR HPV types are functionally different from LR HPV types as they target a plethora of cellular factors, leading to cell cycle progression, evasion of apoptosis, DNA damage and suppression of the hosts immune response [3,14,15]. Thus, considering that elevated expression of HR HPV E6 is a necessary step for oncogenic transformation of cervical epithelial cells, an assay capable of detecting E6 protein from HR HPV types in cervical swab samples will show a high positive predictive value, serving to accurately identify women at increased risk of cancer progression. For this reason, we TRIM13 aimed at developing an indirect competitive ELISA (icELISA) for the detection of the E6 oncoprotein from one of the most prevalent HR HPV types worldwide: Umeclidinium bromide HPV18. In order to obtain highly specific monoclonal antibodies (mAbs) against HPV18 E6 that would not cross-react with the E6 protein from LR HPV types, we have carried out a tolerization procedure with HPV6 and HPV11 E6 proteins before the immunization scheme. With this strategy, we have developed and characterized two mAbs, named 7D2 and 9E2, which bind to HPV18 E6. The 7D2 mAb also shows some cross-reactivity against the HR HPV45 E6 oncoprotein. Using.