681. HIV-1 Mediated Insertional Activation of STAT5B and BACH2 Promotes the Formation of a Viral Reservoir in T Regulatory Cells

Abstract

Since its identification, HIV-1 remains a global health threat responsible for a world-wide pandemic. The introduction of Anti-Retroviral Therapy (ART) greatly extended patients survival; however ART can control but not cure HIV infection. 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 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 peripheral blood mononuclear cells (PBMC) from 54 HIV-1 infected patients under ART, BACH2 and STAT5B were targeted by a significantly higher number of integrations and with the same orientation of gene transcription compared to other lentiviral integration (LV) datasets (p<0.0001). Furthermore, 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 were found in PBMC of 34% (30/87) of HIV-1 patients under ART. Tracking the expression of HIV-1/STAT5B and HIV/BACH2 transcripts by droplet digital PCR in T cell subpopulations purified from the blood of patients under ART (N=6), we found a significant enrichment (higher than 10 fold) of the chimeric mRNAs in T-regulatory cells in all patients tested. The absence of any reported cases of T cell leukemia induced by HIV insertions in patients (despite several years of infection) and the role of these transcription factors suggest that cell clones harboring this type of activating insertions acquire a selective advantage possibly by altering the T-cell identity and/or homeostasis rather than triggering cell transformation. In vitro experiments performed on T regulatory cells purified from healthy donors demonstrated that the LV-mediated expression of these transcription factors significantly increased their proliferation ability (p<0.001) without impacting on their immune-suppressive function. Overall, our findings provide novel evidences that HIV-1 takes advantage of insertional mutagenesis to favor its persistence in the host by activating STAT5B and BACH2. Indeed, the HIV-mediated deregulation of these transcription factors could confer a selective advantage to T regulatory cells, which being able to diminish the immune surveillance against infected cells contribute to promote 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.