Genetic diversity, attributable to the low fidelity of reverse transcription, recombination and mutation, is an important feature of infectious retroviruses. Under selective pressure, such as that imposed by superinfection interference, gammaretroviruses commonly adapt their envelope proteins to use alternative receptors to overcome this entry block. The first characterized koala retroviruses KoRV subgroup A (KoRV-A) were remarkable in their absence of envelope genetic variability. Once it was determined that KoRV-A was present in all koalas in US zoos, regardless of their disease status, we sought to isolate a KoRV variant whose presence correlated with neoplastic malignancies. More than a decade after the identification of KoRV-A, we isolated a second subgroup of KoRV, KoRV-B from koalas with lymphomas. The envelope proteins of KoRV-A and KoRV-B are sufficiently divergent to confer the ability to bind and employ distinct receptors for infection. We have now obtained a number of additional KoRV envelope variants. In the present studies we report these variants, and show that they differ from KoRV-A and KoRV-B envelopes in their host range and superinfection interference properties. Thus, there appears to be considerable variation among KoRVs envelope genes suggesting genetic diversity is a factor following the KoRV-A infection process.

Intra-host tumor virus variants may influence the pathogenesis and treatment responses of some virally-associated cancers. However, the intra-host variability of Kaposi sarcoma-associated herpesvirus (KSHV), the etiologic agent of Kaposi sarcoma (KS), has to date been explored with sequencing technologies that possibly introduce more errors than that which occurs in the viral population, and these studies have only studied variable regions. Here, full-length KSHV genomes in tumors and/or oral swabs from 9 Ugandan adults with HIV-associated KS were characterized. Furthermore, we used deep, short-read sequencing using duplex unique molecular identifiers (dUMI)–random double-stranded oligonucleotides that barcode individual DNA molecules before library amplification. This allowed suppression of PCR and sequencing errors to ~10−9/base as well as afforded accurate determination of KSHV genome numbers sequenced in each sample. KSHV genomes were assembled de novo, and rearrangements observed were confirmed by PCR and Sanger sequencing. 131-kb KSHV genome sequences, excluding major repeat regions, were successfully obtained from 23 clinical specimens, averaging 2.3x104 reads/base. Strikingly, KSHV genomes were virtually identical within individuals at the point mutational level. The intra-host heterogeneity that was observed was confined to tumor-associated KSHV mutations and genome rearrangements, all impacting protein-coding sequences. Although it is unclear whether these changes were important to tumorigenesis or occurred as a result of genomic instability in tumors, similar changes were observed across individuals. These included inactivation of the K8.1 gene in tumors of 3 individuals and retention of a region around the first major internal repeat (IR1) in all instances of genomic deletions and rearrangements. Notably, the same breakpoint junctions were found in distinct tumors within single individuals, suggesting metastatic spread of rearranged KSHV genomes. These findings define KSHV intra-host heterogeneity in vivo with greater precision than has been possible in the past and suggest the possibility that aberrant KSHV genomes may contribute to aspects of KS tumorigenesis. Furthermore, study of KSHV with use of dUMI provides a proof of concept for utilizing this technique for detailed study of other virus populations in vivo.

Kaposi sarcoma (KS), a common HIV-associated malignancy, presents a range of clinicopathological features. Kaposi sarcoma-associated herpesvirus (KSHV) is its etiologic agent, but the contribution of viral genomic variation to KS development is poorly understood. To identify potentially influential viral polymorphisms, we characterized KSHV genetic variation in 67 tumors from 1–4 distinct sites from 29 adults with advanced KS in Kampala, Uganda. Whole KSHV genomes were sequenced from 20 tumors with the highest viral load, whereas only polymorphic genes were screened by PCR and sequenced from 47 other tumors. Nine individuals harbored ≥1 tumors with a median 6-fold over-coverage of a region centering on K5 and K6 genes. K8.1 gene was inactivated in 8 individuals, while 5 had mutations in the miR-K10 microRNA coding sequence. Recurring inter-host polymorphisms were detected in K4.2 and K11.2. The K5-K6 region rearrangement breakpoints and K8.1 mutations were all unique, indicating that they arise frequently de novo. Rearrangement breakpoints were associated with potential G-quadruplex and Z-DNA forming sequences. Exploratory evaluations of viral mutations with clinical and tumor traits were conducted by logistic regression without multiple test corrections. K5-K6 over-coverage and K8.1 inactivation were tentatively correlated (p<0.001 and p = 0.005, respectively) with nodular rather than macular tumors, and with individuals that had lesions in ≤4 anatomic areas (both p≤0.01). Additionally, a trend was noted for miR-K10 point mutations and lower survival rates (HR = 4.11, p = 0.053). Two instances were found of distinct tumors within an individual sharing the same viral mutation, suggesting metastases or transmission of the aberrant viruses within the host. To summarize, KSHV genomes in tumors frequently have over-representation of the K5-K6 region, as well as K8.1 and miR-K10 mutations, and each might be associated with clinical phenotypes. Studying their possible effects may be useful for understanding KS tumorigenesis and disease progression.

Intra-host evolved tumor virus variants have provided insights into the risk, pathogenesis and treatment responses of associated cancers. However, the intra-host variability of Kaposi sarcoma-associated herpesvirus (KSHV), the etiologic agent of Kaposi sarcoma (KS), has not been explored at the whole viral genome level. An accurate and detailed description of KSHV intra-host diversity in whole KSHV genomes from matching tumors and oral swabs from Ugandan adults with HIV-associated KS was obtained by deep, short read sequencing, using duplex unique molecular identifiers (dUMI) – random double-stranded oligonucleotides that barcode individual DNA molecules before library amplification. This allowed suppression of PCR and sequencing errors down to ∼10−9/base. KSHV genomes were assembled de novo, and identified rearrangements were confirmed by PCR. 131-kb KSHV genome sequences, excluding major repeat regions and averaging 2.3 × 104 reads/base, were successfully obtained from 23 specimens from 9 individuals, including 7 tumor-oral pairs. Sampling more than 100 viral genomes in at least one specimen per individual showed that KSHV genomes were virtually homogeneous within samples and within individuals at the point mutational level. Heterogeneity, if present, was due to point mutations and genomic rearrangements in tumors. In 2 individuals, the same mutations were found in distinct KS tumors. The K8.1 gene was inactivated in tumors from 3 individuals, and all KSHV genomic aberrations retained the region surrounding the first major internal repeat (IR1). These findings suggest that lytic gene alterations may contribute to KS tumorigenesis or persistence.Author summaryKaposi sarcoma (KS) is a leading cancer in sub-Saharan Africa and in those with HIV co-infection. Infection by Kaposi sarcoma-associated herpesvirus (KSHV) is necessary for KS, yet why only few KSHV infections develop into KS is largely unknown. While strain differences or mutations in other tumor viruses are known to affect the risk and progression of their associated cancers, whether KSHV genetic variation is important to the natural history of KS is unclear. Most studies of KSHV diversity have characterized only ∼4% of its 165-kb genome and may have been impacted by PCR or cloning artifacts. Here, we performed highly sensitive, single-molecule sequencing of whole KSHV genomes in paired KS tumors and oral swabs from 9 individuals with KS. We found that KSHV genomes were virtually identical within individuals, with no evidence of quasispecies formation nor multistrain infection. However, KSHV genome aberrations and inactivating mutations appeared to be a common, tumor-associated phenomenon, with some mutations shared by distinct tumors within an individual. Certain regions of the KSHV genome featured prominently among tumor-associated mutations, suggesting that they are important contributors to the pathogenesis or persistence of KS.