Integration of adeno-associated virus (AAV) into the genomes of most Thai and Mongolian liver cancer patients does not induce oncogenesis.

BACKGROUND: Engineered versions of adeno-associated virus (AAV) are commonly used in gene therapy but evidence revealing a potential oncogenic role of natural AAV in hepatocellular carcinoma (HCC) has raised concerns. The frequency of potentially oncogenic integrations has been reported in only a few populations. AAV infection and host genome integration in another type of liver cancer, cholangiocarcinoma (CCA), has been studied only in one cohort. All reported oncogenic AAV integrations in HCC come from strains resembling the fully sequenced AAV2 and partly sequenced AAV13. When AAV integration occurs, only a fragment of the AAV genome is detectable in later DNA or RNA sequencing. The integrated fragment is typically from the 3' end of the AAV genome, and this positional bias has been only partly explained. Three research groups searched for evidence of AAV integration in HCC RNAseq samples in the Cancer Genome Atlas (TCGA) but reported conflicting results. RESULTS: We collected and analyzed whole transcriptome and viral capture DNA sequencing in paired tumor and non-tumor samples from two liver cancer Asian cohorts from Thailand (N = 147, 47 HCC and 100 intrahepatic cholangiocarcinoma (iCCA)) and Mongolia (N = 70, all HCC). We found only one HCC patient with a potentially oncogenic integration of AAV, in contrast to higher frequency reported in European patients. There were no oncogenic AAV integrations in iCCA patients. AAV genomic segments are present preferentially in the non-tumor samples of Thai patients. By analyzing the AAV genome positions of oncogenic and non-oncogenic integrated fragments, we found that almost all the putative oncogenic integrations overlap the X gene, which is present and functional only in the strain AAV2 among all fully sequenced strains. This gene content difference could explain why putative oncogenic integrations from other AAV strains have not been reported. We resolved the discrepancies in previous analyses of AAV presence in TCGA HCC samples and extended it to CCA. There are 12 TCGA samples with an AAV segment and none are in Asian patients. AAV segments are present in preferentially in TCGA non-tumor samples, like what we observed in the Thai patients. CONCLUSIONS: Our findings suggest a minimal AAV risk of hepatocarcinogenesis in Asian liver cancer patients. The partial genome presence and positional bias of AAV integrations into the human genome has complicated analysis of possible roles of AAV in liver cancer.

miR-451 limits CD4+ T cell proliferative responses to infection in mice.

MicroRNAs (miRNAs) are major regulators of cell responses, particularly in stressed cell states and host immune responses. Some miRNAs have a role in pathogen defense, including regulation of immune responses to Plasmodium parasite infection. Using a nonlethal mouse model of blood stage malaria infection, we have found that miR-451-/- mice infected with Plasmodium yoelii XNL cleared infection at a faster rate than did wild-type (WT) mice. MiR-451-/- mice had an increased leukocyte response to infection, with the protective phenotype primarily driven by CD4+ T cells. WT and miR-451-/- CD4+ T cells had similar activation responses, but miR-451-/- CD4+ cells had significantly increased proliferation, both in vitro and in vivo. Myc is a miR-451 target with a central role in cell cycle progression and cell proliferation. CD4+ T cells from miR-451-/- mice had increased postactivation Myc expression. RNA-Seq analysis of CD4+ cells demonstrated over 5000 differentially expressed genes in miR-451-/- mice postinfection, many of which are directly or indirectly Myc regulated. This study demonstrates that miR-451 regulates T cell proliferative responses in part via a Myc-dependent mechanism.