Nucleic acid amplification technique–based assays are a primary method for the detection of acute hepatitis E virus (HEV) infection, but assay sensitivity can vary widely. To improve interlaboratory results for the detection and quantification of HEV RNA, a candidate World Health Organization (WHO) International Standard (IS) strain was evaluated in a collaborative study involving 23 laboratories from 10 countries. The IS, code number 6329/10, was formulated by using a genotype 3a HEV strain from a blood donation, diluted in pooled human plasma and lyophilized. A Japanese national standard, representing a genotype 3b HEV strain, was prepared and evaluated in parallel. The potencies of the standards were determined by qualitative and quantitative assays. Assay variability was substantially reduced when HEV RNA concentrations were expressed relative to the IS. Thus, WHO has established 6329/10 as the IS for HEV RNA, with a unitage of 250,000 International Units per milliliter.

Quantitative PCR (qPCR) analysis of human T-cell leukemia virus type 1 (HTLV-1) was used to assess the amount of HTLV-1 provirus DNA integrated into the genomic DNA of host blood cells. Accumulating evidence indicates that a high proviral load is one of the risk factors for the development of adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis. However, interlaboratory variability in qPCR results makes it difficult to assess the differences in reported proviral loads between laboratories. To remedy this situation, we attempted to minimize discrepancies between laboratories through standardization of HTLV-1 qPCR in a collaborative study. TL-Om1 cells that harbor the HTLV-1 provirus were serially diluted with peripheral blood mononuclear cells to prepare a candidate standard. By statistically evaluating the proviral loads of the standard and those determined using in-house qPCR methods at each laboratory, we determined the relative ratios of the measured values in the laboratories to the theoretical values of the TL-Om1 standard. The relative ratios of the laboratories ranged from 0.84 to 4.45. Next, we corrected the proviral loads of the clinical samples from HTLV-1 carriers using the relative ratio. As expected, the overall differences between the laboratories were reduced by half, from 7.4-fold to 3.8-fold on average, after applying the correction. HTLV-1 qPCR can be standardized using TL-Om1 cells as a standard and by determining the relative ratio of the measured to the theoretical standard values in each laboratory. Human T-cell leukemia virus type 1 (HTLV-1) is present in certain regions of endemicity, including sub-Saharan Africa, the Caribbean, parts of South America, the Middle East, Melanesia, and southwest Japan (1, 2). HTLV-1 mainly infects vertically from infected mothers to children through breastfeeding and horizontally between adults by sexual intercourse and transmission through transfusions with blood products. Although the majority of infected people live without any symptoms, some HTLV-1 carriers suffer from adult T-cell leukemia (ATL), HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and HTLV-1 uveitis/HTLV-1-associated uveitis after a long period of latency (3).HTLV-1 mainly infects CD4-positive peripheral blood cells, and the provirus is integrated into the host genome. Generally, HTLV-1 infection is determined by serological testing. Detection of proviral DNA in peripheral blood mononuclear cells (PBMCs) by PCR is one of the methods to detect the infection. Quantitation of both the provirus and a cellular gene in PBMCs by TaqMan quantitative PCR (qPCR) enables calculation of the percentages of

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