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. 2019 Mar 21;93(7):e02183-18.
doi: 10.1128/JVI.02183-18. Print 2019 Apr 1.

Reduction of Kaposi's Sarcoma-Associated Herpesvirus Latency Using CRISPR-Cas9 To Edit the Latency-Associated Nuclear Antigen Gene

Affiliations

Reduction of Kaposi's Sarcoma-Associated Herpesvirus Latency Using CRISPR-Cas9 To Edit the Latency-Associated Nuclear Antigen Gene

For Yue Tso et al. J Virol. .

Abstract

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of Kaposi's sarcoma (KS), an AIDS-defining cancer in HIV-1-infected individuals or immune-suppressed transplant patients. The prevalence for both KSHV and KS are highest in sub-Saharan Africa where HIV-1 infection is also epidemic. There is no effective treatment for advanced KS; therefore, the survival rate is low. Similar to other herpesviruses, KSHV's ability to establish latent infection in the host presents a major challenge to KS treatment or prevention. Strategies to reduce KSHV episomal persistence in latently infected cells might lead to approaches to prevent KS development. The CRISPR-Cas9 system is a gene editing technique that has been used to specifically manipulate the HIV-1 genome but also Epstein-Barr virus (EBV) which, similar to KSHV, belongs to the Gammaherpesvirus family. Among KSHV gene products, the latency-associated nuclear antigen (LANA) is absolutely required in the maintenance, replication, and segregation of KSHV episomes during mitosis, which makes LANA an ideal target for CRISPR-Cas9 editing. In this study, we designed a replication-incompetent adenovirus type 5 to deliver a LANA-specific Cas9 system (Ad-CC9-LANA) into various KSHV latent target cells. We showed that KSHV latently infected epithelial and endothelial cells transduced with Ad-CC9-LANA underwent significant reductions in the KSHV episome burden, LANA RNA and protein expression over time, but this effect is less profound in BC3 cells due to the low infection efficiency of adenovirus type 5 for B cells. The use of an adenovirus vector might confer potential in vivo applications of LANA-specific Cas9 against KSHV infection and KS.IMPORTANCE The ability for Kaposi's sarcoma-associated herpesvirus (KSHV), the causative agent of Kaposi's sarcoma (KS), to establish and maintain latency has been a major challenge to clearing infection and preventing KS development. This is the first study to demonstrate the feasibility of using a KSHV LANA-targeted CRISPR-Cas9 and adenoviral delivery system to disrupt KSHV latency in infected epithelial and endothelial cell lines. Our system significantly reduced the KSHV episomal burden over time. Given the safety record of adenovirus as vaccine or delivery vectors, this approach to limit KSHV latency may also represent a viable strategy against other tumorigenic viruses and may have potential benefits in developing countries where the viral cancer burden is high.

Keywords: CRISPR-Cas9; Kaposi’s sarcoma-associated herpesvirus; LANA; latency.

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Figures

FIG 1
FIG 1
Illustrations of the replication-incompetent adenovirus vector and KSHV episome copy number analysis using droplet digital PCR (ddPCR). All diagrams are not drawn to scale. (A) Schematic showing the LANA-specific guide RNA and Cas9 expression cassette (CC9-LANA) in the replication-incompetent adenovirus type 5 vector. (B) Relative locations of the ddPCR amplification primers and probes within KSHV LANA and ORF26 genes. (C) The effects of a functional CC9-LANA might have on KSHV episome are presented as three hypothetical scenarios. Predicted ddPCR detectability of the respective probes are shown in tables below each scenario. (D) Example patterns of KSHV episome copy number/cell based on ddPCR analysis that reflects each hypothetical scenarios are shown.
FIG 2
FIG 2
KSHV episome copy number in Vero219 cells transduced with Ad-CC9-LANA or Ad-iCC9-LANA at 10, 50, and 100 MOI over 11 days, as determined by ddPCR. (A) Cells transduced with active CC9-LANA. (B) Cells transduced with inactive CC9-LANA. Statistical significance relative to respective mock is shown by vertical *** (P value, <0.0001), vertical ** (P value, 0.0003), and vertical * (P value, 0.0002). Error bars reflect mean with standard deviation (SD).
FIG 3
FIG 3
KSHV episome copy number in different cell lines transduced with 100 MOI of Ad-CC9-LANA or Ad-iCC9-LANA over 32 days, as determined by ddPCR. (A) Vero219 transduced with active CC9-LANA. Statistical significance relative to respective mock is shown by vertical * (P value, <0.0001). (B) Vero219 transduced with inactive CC9-LANA. (C) L1T2 transduced with active CC9-LANA. Statistical significance relative to respective mock is shown by vertical * (P value, <0.0001). (D) L1T2 transduced with inactive CC9-LANA. Error bars reflect mean with SD.
FIG 4
FIG 4
Growth kinetics of different cell lines in 32 days adenovirus transduction with 100 MOI of Ad-CC9-LANA or Ad-iCC9-LANA. (A) Vero. (B) Vero219. (C) L1T2.
FIG 5
FIG 5
LANA, Cas9, ORF50, and ORF71 transcript levels in Vero219 and L1T2 cells transduced with 100 MOI of Ad-CC9-LANA or Ad-iCC9-LANA over 32 days. (A) LANA. (B) Cas9. (C) ORF50. (D) ORF71. Transcript level was relative to the mock transduced from each respective time point. Error bars reflect mean with SD.
FIG 6
FIG 6
Cells from 32 days postransduction by 100 MOI of Ad-CC9-LANA or Ad-iCC9-LANA were seeded into chamber slides and allowed to grow for 2 days before detection of KSHV LANA by immunohistochemistry. (A) Negative controls of Vero cells stained with normal rat IgG or rat anti-LANA antibody. (B) Vero219 transduced with either mock or inactive or active CC9-LANA. (C) L1T2 transduced with either mock or inactive or active CC9-LANA. Five times 5 fields of pictures (i.e., 25 pictures) were taken at ×40 magnification and digitally stitched for each culture. Red arrows showed examples of LANA+ cells, as indicated by the brown punctate staining within the nuclear boundary. A magnified view was shown at the left lower corner of Vero219 and L1T2 mock transduced to demonstrate the brown punctate staining of LANA within the nucleus. (D) Western blot showing LANA protein expression in mock, active CC9-LANA, and inactive CC9-LANA transduced cells from day 32 samples. KSHV negative Vero cells were used as control. Green color indicates the main LANA isoforms (indicated by yellow arrows). Red color indicates the protein ladder.
FIG 7
FIG 7
LANA mutations in cells from 4 days postransduction by 100 MOI of Ad-CC9-LANA. (A) Nucleotide sequences alignment of the wild-type LANA with those derived from Ad-CC9-LANA-transduced culture. The Cas9 targeted site at the N terminus of LANA gene is highlighted by the red box. (B) Amino acid sequence alignment of the wild-type LANA with those derived from Ad-CC9-LANA-transduced culture. Sequences above the horizontal lines are wild type and below are mutated sequences. The Cas9 targeted site at the N terminus of LANA gene is highlighted by the red box. *, stop codon.
FIG 8
FIG 8
KSHV episome copy number in BC3 cells transduced with Ad-CC9-LANA or Ad-iCC9-LANA at 10, 50, and 100 MOI over 11 days, as determined by ddPCR. (A) Cells transduced with active CC9-LANA. (B) Cells transduced with inactive CC9-LANA.

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