SCIENCE REVIEW


‘High-risk types 16 and 18 are the most common human papillomavirus types found in cervical carcinomas worldwide’


results proved an important milestone in HPV genotype epidemiology. In conclusion, the authors suggested


that if HPV testing were used as part of a screening algorithm then preliminary HPV genotyping studies that facilitate multiple type detection should be performed to determine the impact of high-risk HPV types other than 16 and 18 in a given population.


Immune response and HPV Human papillomavirus has a number of genotypes subdivided into low-risk and high-risk types, the latter resulting in a predisposition to cancerous transformation. The HPV16 and HPV18 subtypes are high- risk types because they express the oncoproteins E6 and E7 in target cells, and these contribute to cellular proliferation, differentiation and genomic instability, inducing malignant transformation. Infection occurs when the capsid proteins


L1 and L2 join the receptors of the target cell, followed by amplification of the viral genome by a previral replication complex during the S phase of the cell cycle. The L1 and L2 proteins are responsible for the assembly of the virion and packaging of DNA. Release of the virus occurs at the end of the life of the host cell, and the life cycle of the virus is directly related to the process of cellular differentiation of the host cell. The immune response, whether innate


or acquired, plays a complex role against infection by HPV. However, innate immunity acts directly or indirectly against infectious agents through the activation of natural killer (NK) cells in the tissue. The cytotoxicity of NK cells is regulated through the participation of two classes of receptor on the cell surface: activation receptors, which cause lysis of the target cells, and inhibitory receptors that transmit signals to block the action of NK cells. Inhibitory receptors recognise human


leucocyte antigen (HLA) class I molecules on target cells. The HLA-C allele contains dimorphisms that determine the functional specificity of the link; thus, HLA-C1 encodes HLA-Cw1, Cw3, Cw7, Cw8, Cw12, Cw13 and Cw14; and HLA-C2 encodes HLA-Cw2, Cw4, Cw5, Cw6, Cw15 and Cw17. With decrease of HLA class I molecule expression as a result of tumour transformation or viral infection, the NK cells are activated through receptors that override the inhibitory effect, allowing lysis of the affected cells. Activity of NK cells is controlled by


interactions between killer immunoglobulin- like receptor (KIR) genes expressed in NK cells and their HLA class I ligands expressed


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between the presence or absence of these genes and the occurrence of viral and bacterial infection and autoimmune. diseases. It is suggested that the presence of KIR2DL2 hinders the cellular response against viral infection, and in the Portuguese study the presence of this gene showed a significant association with HPV infection. Therefore, the presence of KIR2DL2may be a risk factor for HPV infection.


Human papillomavirus, a ubiquitous human pathogen.


in target cells. The KIRgenes are a family of 15 genes located on chromosome 19q13.4 that encode inhibitory and activating receptors expressed by NK cells. The different KIR receptors are classified according to the nomenclature of extracellular and intracellular structures, such as the number of immunoglobulin domains (KIR2D and KIR3D) that form the binding element. The inhibitory receptors have a long


cytoplasmic tail (L), generating signals across immunoreceptor tyrosine-based inhibitory motif (ITIM) domains that are part of the protein structure of these receptors. Activating receptors have a short cytoplasmic tail (S), do not generate signalling and are associated with adapter molecules that have ITAM domains. Three KIRgenes (3DL3, 2DL4 and 3DL2)


and a pseudogene (3DP1) are common to all KIR haplotypes, and are referred to as framework genes. The KIR haplotypes are divided into two groups, A and B. Haplotype A comprises nine KIRgenes, six of which are inhibitory, two pseudogenes and one activating gene (KIR 2DS4). Haplotype B contains more than one activating KIRgene. In a study of Portuguese students (Pereira


A, Prata E, Nunes R. Understanding how HLA and KIRgene combinations can influence HPV infection. The Biomedical Scientist 2012 August; 56 [8]: 472–7) the authors aimed to verify the relevance of KIR gene and HLA type in HPV infection, and to clarify whether the absence of HLA ligand for the inhibitory KIR and/or the presence of several activating KIR may contribute to protection against infection. Their results suggest that the HLA Cw4 ligand is associated with a lower number of infected individuals, and absence of the ligand is associated with higher frequency of infection. The study of KIRgenes has enabled researchers to establish an association


Genomics applications: an HPV trio Available clinical HPV diagnostics for head and neck cancer have limited sensitivity and/or fail to define the HPV genotype, Common HPV genotyping assays are costly and labour-intensive and thus a group working in the Maryland, USA (Ambulos NP Jr, Schumaker LM, Mathias TJ et al. Next-generation sequencing-based HPV genotyping assay validated in formalin-fixed, paraffin-embedded oropharyngeal and cervical cancer specimens. J Biomol Tech 2016 Mar 7. pii: jbt.16-2702-004 [Epub ahead of print]), has sought to develop a next-generation sequencing (NGS)-based HPV genotyping assay that is sensitive enough to work on formalin-fixed paraffin wax-embedded (FFPE) samples. This involves an ion torrent NGS HPV genotyping assay using barcoded HPV polymerase chain reaction (PCR) broad-spectrum general primers (BSGP) 5+/6+. To validate genotype specificity and use in


archived FFPE tumour samples, they compared NGS HPV genotyping at two sequencing centres with typing by a linear array (LA) assay in 42 oropharyngeal and cervical cancer specimens representing 10 HPV genotypes, as well as HPV-negative cases. To demonstrate the detection of a broad range of HPV genotypes, the group genotyped a cohort of 266 cervical cancers. A comparison of NGS genotyping of FFPE cancer specimens with genotyping by LA showed concordant results in 34/37 samples (92%) at sequencing site 1 and 39/42 samples (93%) at sequencing site 2. Concordance between sites was 92%. According to the authors, this new NGS assay provides a sensitive and specific high- throughput method to detect and genotype HPV in a range of clinical specimens derived from FFPE. In France a cervical screening campaign


using HR-HPV self-sampling including 22,702 women aged 35-69 years living in low socioeconomic districts of Marseille was organised (Tamalet C, Halfon P, Retraite LL


‘Activity of NK cells is controlled by interactions between KIR genes expressed in NK cells and their HLA class I ligands expressed in target cells’


MAY 2016 THE BIOMEDICAL SCIENTIST


National Cancer Institute; Laboratory of Tumor Virus Biology


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