Emma Welch

Introduction: HIV continues to be a major public health issue in the United States. In 2015, there were 39,513 new case of HIV diagnosed in the US, with African American MSM being disproportionately affected.[1] HIV, which infects and kills CD4 cells, weakens the immune system over time, making patients susceptible to opportunistic infections like TB, candidiasis, and recurrent pneumonia.[2] Since the advent of highly successful antiretroviral therapy (ART) in the 1990s, HIV can now be treated much like a chronic disease. However, ART cannot eradicate latent viral reservoirs, and thus novel treatments are still needed to try and cure HIV.[3] One such therapy is genome editing, specifically the use of Transcription Activator-Like Effector Nucleases, or TALENs. The use of TALEN technology to treat HIV latency is still in its initial stages, however three studies have examined its use in targeting different HIV proviral genes. Methods: Two studies used TALENs to disrupt the LTR region of HIV proviral DNA. In one case, T cells were infected with HIV and then transfected with mRNAs encoding TAR TALENs.[4]  In the other study, A TALEN pair was created to target 3’ and 5’ HIV LTR sequences, and endonuclease activity was tested on HIV PCR product fragments. The TALEN protein pair was then tested in vivo, and function was assessed based on GFP expression of transfected cells.[5] A final study examined an alternative target, the HIV Gag p17 gene. Here, two different TALENs were constructed to target the HIV Gag p17 gene. Jurkat T cells were infected with HIV followed by transfection with TALENs via electroporation.[6]  Results:  All three studies showed that TALENs are effective at cleaving their targeted regions in HIV proviral DNA, resulting in mutated DNA incapable of producing gene expression.^4,5,6  Conclusions: Studies have indicated that TALENs are a possible strategy for disrupting HIV proviral DNA, and therefore treating HIV latency. However, more research is necessary to find effective methods for TALEN delivery in vivo.

[1] Basic statistics. Centers for Disease Control and Prevention Web site. https://www.cdc.gov/hiv/basics/statistics.html. Updated 2016. Accessed March 24, 2017.

[2] Coffin JM, Hughes SH, Varmus HE. Course of infection with HIV and SIV. Cold Spring Harbor Laboratory Press; 1997.

[3] Alexaki A, Liu Y, Wigdahl B. Cellular reservoirs of HIV-1 and their role in viral persistence. Curr HIV Res. 2008;6(5):388-400.

[4] Ebina H, Kanemura Y, Misawa N, et al. A high excision potential of TALENs for integrated DNA of HIV-based lentiviral vector. PLoS ONE. 2015;10(3):e0120047.

[5] Strong CL, Guerra HP, Mathew KR, Roy N, Simpson LR, Schiller MR. Damaging the integrated HIV proviral DNA with TALENs. PLoS ONE. 2015;10(5):e0125652.

[6] Kishida T, Ejima A, Mazda O. Specific destruction of HIV proviral p17 gene in T lymphoid cells achieved by the genome editing technology. Front Microbiol. 2016;7:1001.