Mouse T-cells restrict replication of human immunodeficiency virus at the level of integration

Both T-cell lines and primary T-cells from mice harbor a severe post-entry defect that is independent of potential species-specTR transactivation. Reverse transcription occurred efficiently following VSV-G-mediated entry of virions into mouse T-cells, and abundant levels of 2-LTR circles indicated successful nuclear import of the pre-integration complex. To probe the next step in the retroviral replication cycle, i.e. the integration of HIV-1 into the host cell genome, we established and validated a nested real-time PCR to specifically quantify HIV-1 integrants exploiting highly repetitive mouse B1 elements. Importantly, we demonstrate that the frequency of integrant formation is diminished 18- to > 305-fold in mouse T-cell lines compared to a human counterpart, resulting in a largely abortive infection. Moreover, differences in transgene expression from residual vector integrants, the transcription off which is cyclin T1-independent, provided evidence for an additional, peri-integrational deficit in certain mouse T-cell lines.In contrast to earlier reports, we find that mouse T-cells efficiently support early replication steps up to and including nuclear import, but restrict HIV-1 at the level of chromosomal integration.Human immunodeficiency virus type 1 (HIV-1) displays a highly restricted host and cell tropism and is only capable of efficient replication in primary and immortalized T-cells and macrophages of human origin. Cells from native mice do not or only inefficiently support various steps of the HIV-1 replication cycle [1-7]. The precise mapping of some of these species-specific barriers has, on one hand, facilitated the identification and molecular characterization of critical host factors, and, on the other hand, highlighted the complexity of the task to develop genetically altered mice that are fully permissive for HIV-1 infection.The by far most prominent category of barriers thus far identified in mouse cell lines appears to be recessive in nature. Bl