A combinatorial CRISPR-Cas12a attack on HIV DNA

What's in a cure: designing a broad-spectrum HIV gene therapy

PURPOSE OF REVIEW

The leading gene editing strategy for a human immunodeficiency virus type 1 (HIV-1) cure involves the delivery of SaCas9 and two guide RNAs (gRNAs) in an adeno-associated viral (AAV) vector. As a dual-component system, CRISPR is targeted to a genetic locus through the choice of a Cas effector and gRNA protospacer design pair. As CRISPR research has expanded in recent years, these components have been investigated for utilization in cure strategies, which will be discussed in this article.

RECENT FINDINGS

Type II SpCas9 and SaCas9 have been the leading Cas effectors across gene editing therapeutics to date. Additionally, extensive research has expanded the potential to multiplex gRNAs and target them effectively to the highly genetically diverse HIV-1 provirus. More recently, the Type V family of Cas12 effectors opens a new opportunity to use a smaller Cas protein for packaging into an AAV vector with multiplexed gRNAs.

SUMMARY

In understanding the individual components of a CRISPR/Cas therapeutic cure for HIV-1, it is important to know that the currently used strategies can be improved upon. Future areas will include alternative smaller Cas effectors, multiplexed gRNAs designs, and/or alternative delivery modalities.

Gaining momentum: stem cell therapies for HIV cure

PURPOSE OF REVIEW

Durable HIV-1 remission has been reported in a person who received allogeneic stem cell transplants (SCTs) involving CCR5 Δ32/Δ32 donor cells. Much of the reduction in HIV-1 burden following allogeneic SCT with or without donor cells inherently resistant to HIV-1 infection is likely due to cytotoxic graft-versus-host effects on residual recipient immune cells. Nonetheless, there has been growing momentum to develop and implement stem cell therapies that lead to durable long-term antiretroviral therapy (ART)-free remission without the need for SCT.

RECENT FINDINGS

Most current research leverages gene editing techniques to modify hematopoietic stem cells which differentiate into immune cells capable of harboring HIV-1. Approaches include targeting genes that encode HIV-1 co-receptors using Zinc Finger Nucleases (ZFN) or CRISPR-Cas-9 to render a pool of adult or progenitor cells resistant to de-novo infection. Other strategies involve harnessing multipotent mesenchymal stromal cells to foster immune environments that can more efficiently recognize and target HIV-1 while promoting tissue homeostasis.

SUMMARY

Many of these strategies are currently in a state of infancy or adolescence; nonetheless, promising preclinical and first-in-human studies have been performed, providing further rationale to focus resources on stem cell therapies.

Computational analysis of cas proteins unlocks new potential in HIV-1 targeted gene therapy

Introduction: The human immunodeficiency virus type 1 (HIV-1) pandemic has been slowed with the advent of anti-retroviral therapy (ART). However, ART is not a cure and as such has pushed the disease into a chronic infection. One potential cure strategy that has shown promise is the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas gene editing system. It has recently been shown to successfully edit and/or excise the integrated provirus from infected cells and inhibit HIV-1 in vitro, ex vivo, and in vivo. These studies have primarily been conducted with SpCas9 or SaCas9. However, additional Cas proteins are discovered regularly and modifications to these known proteins are being engineered. The alternative Cas molecules have different requirements for protospacer adjacent motifs (PAMs) which impact the possible targetable regions of HIV-1. Other modifications to the Cas protein or gRNA handle impact the tolerance for mismatches between gRNA and the target. While reducing off-target risk, this impacts the ability to fully account for HIV-1 genetic variability. Methods: This manuscript strives to examine these parameter choices using a computational approach for surveying the suitability of a Cas editor for HIV-1 gene editing. The Nominate, Diversify, Narrow, Filter (NDNF) pipeline measures the safety, broadness, and effectiveness of a pool of potential gRNAs for any PAM. This technique was used to evaluate 46 different potential Cas editors for their HIV therapeutic potential. Results: Our examination revealed that broader PAMs that improve the targeting potential of editors like SaCas9 and LbCas12a have larger pools of useful gRNAs, while broader PAMs reduced the pool of useful SpCas9 gRNAs yet increased the breadth of targetable locations. Investigation of the mismatch tolerance of Cas editors indicates a 2-missmatch tolerance is an ideal balance between on-target sensitivity and off-target specificity. Of all of the Cas editors examined, SpCas-NG and SPRY-Cas9 had the highest number of overall safe, broad, and effective gRNAs against HIV. Discussion: Currently, larger proteins and wider PAMs lead to better targeting capacity. This implies that research should either be targeted towards delivering longer payloads or towards increasing the breadth of currently available small Cas editors. With the discovery and adoption of additional Cas editors, it is important for researchers in the HIV-1 gene editing field to explore the wider world of Cas editors.

CRISPR-Cas attack of HIV-1 proviral DNA can cause unintended deletion of surrounding cellular DNA

IMPORTANCE

Although HIV replication can be effectively inhibited by antiretroviral therapy, this does not result in a cure as the available drugs do not inactivate the integrated HIV-1 DNA in infected cells. Consequently, HIV-infected individuals need lifelong therapy to prevent viral rebound. Several preclinical studies indicate that CRISPR-Cas gene-editing systems can be used to achieve permanent inactivation of the viral DNA. It was previously shown that this inactivation was due to small inactivating mutations at the targeted sites in the HIV genome and to excision or inversion of the viral DNA fragment between two target sites. We, here, demonstrate that CRISPR-Cas treatment also causes large unintended deletions, which can include surrounding chromosomal sequences. As the loss of chromosomal sequences may cause oncogenic transformation of the cell, such unintended large deletions form a potential safety risk in clinical application of this antiviral application and possibly all CRISPR-Cas gene-editing approaches.

Killing two birds with one stone: CRISPR/Cas9 CCR5 knockout hematopoietic stem cells transplantation to treat patients with HIV infection and hematological malignancies concurrently

Human immunodeficiency virus (HIV) is known to cause hematological malignancy. Hematopoietic stem cell transplantation (HPSCT) is an advanced treatment for that. Currently, there are three successful HIV-eliminated cases, and two received HPSCT from CCR5-absent donors. It is well established that the CCR5 protein on the cell surface assists human immunodeficiency virus entry. Preliminary studies have revealed that knocking out CCR5 and/or CXCR4 may inhibit the viral entry of HIV, which may prove promising in the further development of HIV treatment options. Herein, we suggest performing autologous or allogeneic HSCT with CCR5 KO hematopoietic stem cells in patients who suffer from complicated HIV conditions, particularly drug-resistant HIV or a concurrent diagnosis of HIV with lymphoma/leukemia, to achieve complete HIV remission. Nevertheless, at the clinical forefront of CRISPR-HIV technology, more efforts should be directed to advance nonhuman primate (NHP) models for studies of HIV pathogenesis and off-target assessments within this system. CRISPR-Cas9 knock out of host HSCT-expressing CCR5 or CXCR4 may confer HIV-resistance, which when applied to bedside therapeutics in an allogeneic or autologous manner can warrant a permanent and effective treatment outcome.

In-house ELISA protocols for capsid p24 detection of diverse HIV isolates

BACKGROUND

The capsid p24 (CA-p24) antigen is a component of the viral capsid of human immunodeficiency virus (HIV) that has been commonly used for clinical diagnosis and monitoring of HIV infections in Enzyme-linked Immunosorbent Assays (ELISAs). Commercial CA-p24 ELISAs are widely used in research settings, but these kits are costly and have limited breadth for detecting diverse HIV isolates.

METHODS

Commercial CA-p24 antibodies were used as capture and detection antibodies. Specific CA-p24 ELISAs were established with these antibodies and tested for the detection of HIV-1 isolates with the aim of developing in-house protocols to recognize HIV-1 infections in vitro for research purposes.

RESULTS

Here we present four protocols for in-house ELISAs to detect HIV CA-p24 using commercial antibodies. The assays were able to detect the CA-p24 antigen of different HIV-1 isolates tested. Comparison between the protocols showed that these in-house ELISAs exhibit high specificity, sensitivity, and reproducibility for CA-p24 quantitation but their reactivity varied per HIV-1 isolate and subtype.

CONCLUSIONS

These optimized ELISA protocols represent valuable tools to investigate HIV-1 infections in research facilities at a lower price than commercial CA-p24 kits.

CRISPR-Cas12b enables a highly efficient attack on HIV proviral DNA in T cell cultures

BACKGROUND

The novel endonuclease Cas12b was engineered for targeted genome editing in mammalian cells and is a promising tool for certain applications because of its small size, high sequence specificity and ability to generate relatively large deletions. We previously reported inhibition of the human immunodeficiency virus (HIV) in cell culture infections upon attack of the integrated viral DNA genome by spCas9 and Cas12a.

METHODS

We now tested the ability of the Cas12b endonuclease to suppress a spreading HIV infection in cell culture with anti-HIV gRNAs. Virus inhibition was tested in long-term HIV replication studies, which allowed us to test for viral escape and the potential for reaching a CURE of the infected T cells.

FINDINGS

We demonstrate that Cas12b can achieve complete HIV inactivation with only a single gRNA, a result for which Cas9 required two gRNAs. When the Cas12b system is programmed with two antiviral gRNAs, the overall anti-HIV potency is improved and more grossly mutated HIV proviruses are generated as a result of multiple cut-repair actions. Such "hypermutated" HIV proviruses are more likely to be defective due to mutation of multiple essential parts of the HIV genome. We report that the mutational profiles of the Cas9, Cas12a and Cas12b endonucleases differ significantly, which may have an impact on the level of virus inactivation. These combined results make Cas12b the preferred editing system for HIV-inactivation.

INTERPRETATION

These results provide in vitro "proof of concept' for CRISPR-Cas12b mediated HIV-1 inactivation.

Two CRISPR/Cas12a-based methods for fast and accurate detection of single-base mutations

Current single-base mutation detection approaches are time-consuming, labor-intensive, and costly. This highlights the critical need for speedy and accurate technology capable of detecting single-base alterations. Using clustered regularly interspaced short palindromic repeats/associated protein 12a (CRISPR/Cas12a), two fundamental approaches for getting 100% differentiation of single-base mutations have been established, by which fluorescence signals could be detected for variants but not for wild strains. The first method required both polymerase chain reaction (PCR) and CRISPR/Cas12a cleavage: By introducing a mismatched base at the 3' end of the primers and adjusting the PCR settings, the wild strain strand amplifications were completely blocked prior to CRISPR/Cas12a cleavage. The parameters for Method 1 (PCR + CRISPR/Cas12a) could be easily controlled and adjusted to attain a sensitivity of one copy (about 6 copies μL-1). The second method included isothermal recombinase polymerase amplification (RPA) and CRISPR/Cas12a cleavage: By introducing an extra mismatched base adjacent to the single-base mutant site by RPA (IMAS-RPA), the RPA products from the wild strains were rendered incapable of triggering the cleavage activity of CRISPR/Cas12a. Method 2 (IMAS-RPA) was rapid and easy to implement (can be finished within 1 h). Because each method has its own set of advantages, the laboratory environment-appropriate methods can be selected independently. Both approaches are expected to aid in clinical diagnosis to some extent in the near future.

A CRISPR-Cas Cure for HIV/AIDS

Human immunodeficiency virus (HIV) infections and HIV-induced acquired immunodeficiency syndrome (AIDS) continue to represent a global health burden. There is currently no effective vaccine, nor any cure, for HIV infections; existing antiretroviral therapy can suppress viral replication, but only as long as antiviral drugs are taken. HIV infects cells of the host immune system, and it can establish a long-lived viral reservoir, which can be targeted and edited through gene therapy. Gene editing platforms based on the clustered regularly interspaced palindromic repeat-Cas system (CRISPR-Cas) have been recognized as promising tools in the development of gene therapies for HIV infections. In this review, we evaluate the current landscape of CRISPR-Cas-based therapies against HIV, with an emphasis on the infection biology of the virus as well as the activity of host restriction factors. We discuss the potential of a combined CRISPR-Cas approach that targets host and viral genes to activate antiviral host factors and inhibit viral replication simultaneously. Lastly, we focus on the challenges and potential solutions of CRISPR-Cas gene editing approaches in achieving an HIV cure.

Complete and Prolonged Inhibition of Herpes Simplex Virus Type 1 Infection In Vitro by CRISPR/Cas9 and CRISPR/CasX Systems

Almost all people become infected with herpes viruses, including herpes simplex virus type 1 (HSV-1), during their lifetime. Typically, these viruses persist in a latent form that is resistant to all available antiviral medications. Under certain conditions, such as immunosuppression, the latent forms reactivate and cause disease. Moreover, strains of herpesviruses that are drug-resistant have rapidly emerged. Therefore, it is important to develop alternative methods capable of eradicating herpesvirus infections. One promising direction is the development of CRISPR/Cas systems for the therapy of herpesvirus infections. We aimed to design a CRISPR/Cas system for relatively effective long-term and safe control of HSV-1 infection. Here, we show that plasmids encoding the CRISPR/Cas9 system from Streptococcus pyogenes with a single sgRNA targeting the UL30 gene can completely suppress HSV-1 infection of the Vero cell line within 6 days and provide substantial protection within 9 days. For the first time, we show that CRISPR/CasX from Deltaproteobacteria with a single guide RNA against UL30 almost completely suppresses HSV-1 infection of the Vero cell line for 3 days and provides substantial protection for 6 days. We also found that the Cas9 protein without sgRNAs attenuates HSV-1 infection. Our results show that the developed CRISPR/Cas systems are promising therapeutic approaches to control HSV-1 infections.