CRISPR Genome Editing Applied to the Pathogenic Retrovirus HTLV-1

Abstract

CRISPR editing of retroviral proviruses has been limited to HIV-1. We propose human T-cell leukemia virus type 1 (HTLV-1) as an excellent model to advance CRISPR/Cas9 genome editing technologies against actively expressing and latent retroviral proviruses. HTLV-1 is a tumorigenic human retrovirus responsible for the development of both leukemia/lymphoma (ATL) and a neurological disease (HAM/TSP). The virus immortalizes and persists in CD4+ T lymphocytes that survive for the lifetime of the host. The most important drivers of HTLV-1-mediated transformation and proliferation are the tax and hbz viral genes. Tax, transcribed from the plus-sense or genome strand, is essential for de novo infection and cellular immortalization. Hbz, transcribed from the minus-strand, supports proliferation and survival of infected cells in both its protein and mRNA forms. Abrogating the function or expression of tax and/or hbz by genome editing and mutagenic double-strand break repair may disable HTLV-1-infected cell growth/survival and prevent immune modulatory effects and ultimately HTLV-1-associated disease. In addition, the HTLV-1 viral genome is highly conserved with remarkable sequence homogeneity, both within the same host and even among different HTLV isolates. This offers more focused guide RNA targeting. In addition, there are several well-established animal models for studying HTLV-1 infection in vivo as well as cell immortalization in vitro. Therefore, studies with HTLV-1 may provide a better basis to assess and advance in vivo genome editing against retroviral infections.

Targeting Cancer with CRISPR/Cas9-Based Therapy

“…A multitude of other oncogenic viruses have been described and treated using CRISPR/Cas9 gene editing including: Epstein-Barr virus (EBV) causing nasopharyngeal cancer, Burkitt’s lymphoma or Hodgkin’s lymphoma [ 96 , 97 ]; Hepatitis B and C viruses (HBV and HCV respectively) in hepatocellular carcinoma [ 98 , 99 , 100 ] and Human herpesvirus 8 (HHV-8) causing Kaposi’s sarcoma [ 101 , 102 ]. Many more neoplasms caused by oncogenic viral infections still await targeted genetic therapy, for example an adult T-cell leukemia/lymphoma induced by Human T- cell leukemia virus type 1 (HTLV-1) infection [ 103 ], or Merkel cell carcinoma - an aggressive skin cancer caused by Merkel cell polyomavirus (MCV) [ 104 ].…”

Milk Transmission of HTLV-1 and the Need for Innovative Prevention Strategies

“…Currently, clinical studies addressing the impact of ART on the PVL in breast milk of HTLV-1-infected mothers or, vice versa, assessing the use of prophylactic treatment of the suckling, using for example integrase inhibitors, are lacking but might serve as a promising and cost-effective tool to prevent MTCT. Future challenging strategies to get rid of the integrated virus within infected mothers could include excision strategies using HTLV-1-specific recombinases that have already been evolved for HIV ( 96 , 97 ), zinc finger nucleases ( 98 ) or genetic editing strategies using CRISPR/Cas 9 ( 99 ). Hence, it may be easier to prevent de novo infection of the infant.…”

Novel perspectives on antisense transcription in HIV-1, HTLV-1, and HTLV-2

“…Regarding the application of new therapeutic technologies, much discussion has been raised surrounding the use of CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) for antiretroviral therapy (Panfil et al, 2020). Prior to the use of CRISPR systems, zinc finger nucleases (ZFNs) targeting LTR promoters were utilized to inhibit the proliferation of HTLV-1 infected cell lines (Tanaka et al, 2013).…”

“…In this methodology published in 2013, the therapeutic effects of HTLV-1 elimination were supported in vivo, and it was further suggested that zinc finger nucleases could be used to remove HTLV-1 proviral genomes from infected cells for therapeutic benefit (Tanaka et al, 2013). However, with the onset of wider application of CRISPR technologies, multiple factors suggest that CRISPR may be a more optimized alternative to ZFN-based therapies, including greater cost-effectiveness, simplicity, and efficiency (Panfil et al, 2020). Even greater support lies in that such implementation has already been shown to effectively decrease ATLL cell proliferation in vitro (Nakagawa et al, 2018).…”