Six immunocompetent patients with human herpesvirus 6 (HHV-6) chromosomal integration had HHV-6 and ␤-globin DNA quantified in various samples by PCR. The mean HHV-6 DNA concentration (log 10 copies/milliliter) in blood was 7.0 (>1 HHV-6 DNA copies/leukocyte), and in serum it was 5.3 (>1 HHV-6 DNA copies/lysed cell). The mean HHV-6 DNA load (log 10 copies)/hair follicle was 4.2 (>1 copies/hair follicle cell), demonstrating that viral integration is not confined to blood cells. The characteristically high HHV-6 DNA levels in chromosomal integration may confound laboratory diagnosis of HHV-6 infection and should be given due consideration.

Fluorescent in situ hybridization (FISH) was used to investigate the chromosomal integration sites of human herpesvirus 6 (HHV-6) in phytohemagglutinin-stimulated leukocytes and B lymphocytes from Epstein-Barr virus transformed lymphoblastoid cell lines (LCLs). Five different chromosomal integration sites were found in nine individuals. Only one site was identified in each individual, each site was in the vicinity of the telomeric region and was on either the p or q arm of only one of the two chromosome homologues. The sites were 9q34.3, 10q26.3, 11p15.5, 17p13.3, and 19q 13.4, of which three have not been previously identified. For 9q34.3 the site of integration was further mapped using a locus-specific probe for 9q34.3 together with a pan-telomeric probe and both co-localized with the HHV-6 signal. Similarly an arm-specific telomeric probe for 19q co-localized with the HHV-6 signal. It was therefore concluded that the site of integration is actually within the telomere. The number of viral DNA copies/cell was calculated in blood, LCL cells and hair follicles and was one or more in every case for each of the nine individuals. This result was confirmed by FISH where 100% of cells gave an HHV-6 signal. These findings add to previous reports suggesting that integrated HHV-6 DNA is found in every cell in the body and transmitted vertically. Finally, including our data, worldwide seven different chromosomal sites of HHV-6 integration have now been identified. Large epidemiological studies of chromosomal integration are required to identify further telomeric sites, geographical or racial variation and possible clinical consequences.

The expression of the chimeric BCR/ABL1 fusion gene resulting from t(9;22)(q34;q11) in chronic myelogenous leukemia (CML) is necessary for malignant transformation, but not sufficient to maintain disease progression. The appearance of various chromosomal and molecular alterations in the accelerated and terminal phase of CML is well documented, but evidence for causal relationship is largely lacking. We carried out a genome wide screening at a resolution of 1 Mb of 54 samples at different stages of CML together with 12 CML cell lines and found that disease progression is accompanied by a spectrum of recurrent genome imbalances. Among the most frequent are losses at 1p36, 5q21, 9p21, and 9q34 and gains at 1q, 8q24, 9q34, 16p, and 22q11, all of which were located with higher precision within the genome than previously possible. These genome imbalances are unique to CML cases with clinically manifested or suspected accelerated/blast stage alike, but not seen in chronic phase samples. Previously unrecognized cryptic imbalances occurring within the Ph-chromosome were also detected, although further scrutiny is required to pin-point gene involvement and seek association with disease features. Importantly, some of these imbalances were seen in the CD34(+) cells but not in the whole BM samples of patients in accelerated phase. Taken together, these findings highlight the potential of screening CD34(+) cells for genome wide imbalances associated with disease progression. Finally, the numerous single copy number variations recorded, many unique to this cohort of patients, raise the possible association of genome polymorphism and CML.