26. HIV-1 Mediated Insertional Mutagenesis Increase the Persistence of Infected T Cells in Patients Under ART by Triggering Their Differentiation Into Long Lived T-Regulatory and T-Central Memory Cells
Authors: Daniela Cesana, Francesca R. Santoni de Sio, Laura Rudilosso, Pierangela Gallina, Andrea Calabria, Laura Passerini, Silvia Nozza, Elisa Vicenzi, Guido Poli, Giuseppe Tambussi, Eugenio Montini
Journal: Molecular Therapy (2015)

It has been recently suggested that HIV-1 by integrating near cancer-associated genes could promote the expansion and persistence of infected cells in patients under Anti Retroviral Therapy (ART). However, the molecular mechanism/s of insertional mutagenesis used and the physiological impact on the cells harboring these integrations are completely unknown. Here, we found that in the peripheral blood mononuclear cells from 54 HIV-1 infected patients under ART, BACH2 and STAT5B were targeted by a significant number of integrations compared to other lentiviral integration datasets (p<0.0001) and with the same orientation of gene transcription. Furthermore, we observed that in the blood of 34% of HIV-1 patients under ART (30/87) there are cell clones expressing aberrant chimeric transcripts containing viral sequences fused to the first protein coding exon of BACH2 or STAT5B and predicted to encode for unaltered full-length proteins. However, it is unlikely that the ectopic expression of these transcription factors in T cells per se would trigger cell transformation. Indeed, accordingly with their roles in the regulation of T-cell identity and homeostasis, forced expression of STAT5B and BACH2 in naive CD4+ T-cells significantly skewed their differentiation towards functional T-regulatory cells with a marked immunosuppressive potential. Moreover, STAT5B ectopic expression promoted the IL-2 independent proliferation of T-regulatory cells that was however blocked by TGFB treatment, indicating that these cells are able to respond to external differentiating cues. Importantly, tracking the expression of HIV-1/STAT5B transcripts in T cell subpopulations and monocytes purified from the blood of patients under ART, we found that, in all patients tested (N=6), chimeric mRNAs were present only in T-regulatory and T-central memory cells but not in CD8+ T-cells, T naïve, T stem cell memory, T effector memory nor monocytes. Our findings provide novel evidence that HIV-1 takes advantage of insertional mutagenesis to favor its persistence in the host by activating STAT5B and possibly BACH2. However, the selective advantage conferred by these integrations does not involve T-cell transformation but rather their differentiation into functional T-regulatory and T-central memory cells which are long lived, potentially able to diminish the immune surveillance against infected cells thus favoring the escape from the immune system and long-term viral persistence. Hence, new targeted therapies aimed at interfering with BACH2 and STAT5B regulated pathways could provide the general means for the immunological re-sensitization towards HIV-1 infected cells to reduce long lived cellular reservoirs and the eradication of the viral infection in HIV-1 patients.