Evolving Strategies to Eliminate the CD4 T Cells HIV Viral Reservoir via CAR T Cell Immunotherapy

Recent advances on anti-HIV chimeric antigen receptor-T-cell treatment to provide sustained HIV remission

PURPOSE OF REVIEW

Successful sustained remission of HIV infection has been achieved after CCR5Δ32/Δ32 allogeneic hematopoietic stem cell transplantation for treatment of leukemia in a small cohort of people living with HIV (PLWH). This breakthrough demonstrated that the goal of curing HIV was achievable. However, the high morbidity and mortality associated with bone marrow transplantation limits the routine application of this approach and provides a strong rationale for pursuing alternative strategies for sustained long-term antiretroviral therapy (ART)-free HIV remission. Notably, long-term immune-mediated control of HIV replication observed in elite controllers and posttreatment controllers suggests that potent HIV-specific immune responses could provide sustained ART-free remission in PLWH. The capacity of chimeric antigen receptor (CAR)-T cells engineered to target malignant cells to induce remission and cure in cancer patients made this an attractive approach to provide PLWH with a potent HIV-specific immune response. Here, we review the recent advances in the design and application of anti-HIV CAR-T-cell therapy to provide a functional HIV cure.

RECENT FINDINGS

HIV reservoirs are established days after infection and persist through clonal expansion of infected cells. The continuous interaction between latently infected cells and the immune system shapes the landscape of HIV latency and likely contributes to ART-free viral control in elite controllers. CAR-T cells can exhibit superior antiviral activity as compared with native HIV-specific T cells, particularly because they can be engineered to have multiple HIV specificities, resistance to HIV infection, dual costimulatory signaling, immune checkpoint inhibitors, stem cell derivation, CMV TCR coexpression, and tissue homing ligands. These modifications can significantly improve the capacities of anti-HIV CAR-T cells to prevent viral escape, resist HIV infection, and enhance cytotoxicity, persistence, and tissue penetration. Collectively, these novel modifications of anti-HIV CAR-T cell design have increased their capacity to control HIV infection.

SUMMARY

Anti-HIV CAR-T cells can be engineered to provide potent and sustained in-vitro and in-vivo antiviral function. The combination of anti-HIV CAR-T cells with other immunotherapeutics may contribute to long-term HIV remission in PLWH.

ACE2 decoy Fc-fusions and bi-specific killer engager (BiKEs) require Fc engagement for in vivo efficacy against SARS-CoV-2

SARS-CoV-2 virus has continued to evolve over time necessitating the adaptation of vaccines to maintain efficacy. Monoclonal antibodies (mAbs) against SARS-CoV-2 were a key line of defense for unvaccinated or immunocompromised individuals. However, these mAbs are now ineffective against current SARS-CoV-2 variants. Here, we tested three aspects of αSARS-CoV-2 therapeutics. First, we tested whether Fc engagement is necessary for in vivo clearance of SARS-CoV-2. Secondly, we tested bi-specific killer engagers (BiKEs) that simultaneously engage SARS-CoV-2 and a specific Fc receptor. Benefits of these engagers include the ease of manufacturing, stability, more cell-specific targeting, and high affinity binding to Fc receptors. Using both mAbs and BiKEs, we found that both neutralization and Fc receptor engagement were necessary for effective SARS-CoV-2 clearance. Thirdly, due to ACE2 being necessary for viral entry, ACE2 will maintain binding to SARS-CoV-2 despite viral evolution. Therefore, we used an ACE2 decoy Fc-fusion or BiKE, instead of an anti-SARS-CoV-2 antibody sequence, as a potential therapeutic that would withstand viral evolution. We found that the ACE2 decoy approach also required Fc receptor engagement and, unlike traditional neutralizing antibodies against specific variants, enabled the clearance of two distinct SARS-CoV-2 variants. These data show the importance of Fc engagement for mAbs, the utility of BiKEs as therapies for infectious disease, and the in vivo effectiveness of the ACE2 decoy approach. With further studies, we predict combining neutralization, the cellular response, and this ACE2 decoy approach will benefit individuals with ineffective antibody levels.

Abbreviations

ACE2, scFv, mAb, BiKE, COVID-19, Fc, CD16, CD32b, CD64, d.p.i.

Key points

With equal dosing, both neutralization and Fc engagement are necessary for the optimal efficacy of in vivo antibodies and bi-specific killer engagers (BiKEs) against SARS-CoV-2. BiKEs can clear SARS-CoV-2 virus and protect against severe infection in the hACE2-K18 mouse model. ACE2 decoys as part of Fc-fusions or BiKEs provide in vivo clearance of two disparate SARS-CoV-2 variants.

Pharmacological approaches to promote cell death of latent HIV reservoirs

PURPOSE OF REVIEW

HIV requires lifelong antiviral treatment due to the persistence of a reservoir of latently infected cells. Multiple strategies have been pursued to promote the death of infected cells.

RECENT FINDINGS

Several groups have focused on multipronged approaches to induce apoptosis of infected cells. One approach is to combine latency reversal agents with proapoptotic compounds and cytotoxic T cells to first reactivate and then clear infected cells. Other strategies include using natural killer cells or chimeric antigen receptor cells to decrease the size of the reservoir.A novel strategy is to promote cell death by pyroptosis. This mechanism relies on the activation of the caspase recruitment domain-containing protein 8 (CARD8) inflammasome by the HIV protease and can be potentiated by nonnucleoside reverse transcriptase inhibitors.

SUMMARY

The achievement of a clinically significant reduction in the size of the reservoir will likely require a combination strategy since none of the approaches pursued so far has been successful on its own in clinical trials. This discrepancy between promising in vitro findings and modest in vivo results highlights the hurdles of identifying a universally effective strategy given the wide heterogeneity of the HIV reservoirs in terms of tissue location, capability to undergo latency reversal and susceptibility to cell death.

More than the Infinite Monkey Theorem: NHP Models in the Development of a Pediatric HIV Cure

PURPOSE OF REVIEW

An HIV cure that eliminates the viral reservoir or provides viral control without antiretroviral therapy (ART) is an urgent need in children as they face unique challenges, including lifelong ART adherence and the deleterious effects of chronic immune activation. This review highlights the importance of nonhuman primate (NHP) models in developing an HIV cure for children as these models recapitulate the viral pathogenesis and persistence.

RECENT FINDINGS

Several cure approaches have been explored in infant NHPs, although knowledge gaps remain. Broadly neutralizing antibodies (bNAbs) show promise for controlling viremia and delaying viral rebound after ART interruption but face administration challenges. Adeno-associated virus (AAV) vectors hold the potential for sustained bNAb expression. Therapeutic vaccination induces immune responses against simian retroviruses but has yet to impact the viral reservoir. Combining immunotherapies with latency reversal agents (LRAs) that enhance viral antigen expression should be explored. Current and future cure approaches will require adaptation for the pediatric immune system and unique features of virus persistence, for which NHP models are fundamental to assess their efficacy.

Generation of Anti-HIV CAR-T Cells for Preclinical Research

The inability of people living with HIV (PLWH) to eradicate human immunodeficiency virus (HIV) infection is due in part to the inadequate HIV-specific cellular immune response. The antiviral function of cytotoxic CD8+ T cells, which are crucial for HIV control, is impaired during chronic viral infection because of viral escape mutations, immune exhaustion, HIV antigen downregulation, inflammation, and apoptosis. In addition, some HIV-infected cells either localize to tissue sanctuaries inaccessible to CD8+ T cells or are intrinsically resistant to CD8+ T cell killing. The novel design of synthetic chimeric antigen receptors (CARs) that enable T cells to target specific antigens has led to the development of potent and effective CAR-T cell therapies. While initial clinical trials using anti-HIV CAR-T cells performed over 20 years ago showed limited anti-HIV effects, the improved CAR-T cell design, which enabled its success in treating cancer, has reinstated CAR-T cell therapy as a strategy for HIV cure with notable progress being made in the recent decade.Effective CAR-T cell therapy against HIV infection requires the generation of anti-HIV CAR-T cells with potent in vivo activity against HIV-infected cells. Preclinical evaluation of anti-HIV efficacy of CAR-T cells and their safety is fundamental for supporting the initiation of subsequent clinical trials in PLWH. For these preclinical studies, we developed a novel humanized mouse model supporting in vivo HIV infection, the development of viremia, and the evaluation of novel HIV therapeutics. Preclinical assessment of anti-HIV CAR-T cells using this mouse model involves a multistep process including peripheral blood mononuclear cells (PBMCs) harvested from human donors, T cell purification, ex vivo T cell activation, transduction with lentiviral vectors encoding an anti-HIV CAR, CAR-T cell expansion and infusion in mice intrasplenically injected with autologous PBMCs followed by the determination of CAR-T cell capacity for HIV suppression. Each of the steps described in the following protocol were optimized in the lab to maximize the quantity and quality of the final anti-HIV CAR-T cell products.

Targeting the HIV reservoir: chimeric antigen receptor therapy for HIV cure

ABSTRACT

Although antiretroviral therapy (ART) can reduce the viral load in the plasma to undetectable levels in human immunodeficiency virus (HIV)-infected individuals, ART alone cannot completely eliminate HIV due to its integration into the host cell genome to form viral reservoirs. To achieve a functional cure for HIV infection, numerous preclinical and clinical studies are underway to develop innovative immunotherapies to eliminate HIV reservoirs in the absence of ART. Early studies have tested adoptive T-cell therapies in HIV-infected individuals, but their effectiveness was limited. In recent years, with the technological progress and great success of chimeric antigen receptor (CAR) therapy in the treatment of hematological malignancies, CAR therapy has gradually shown its advantages in the field of HIV infection. Many studies have identified a variety of HIV-specific CAR structures and types of cytolytic effector cells. Therefore, CAR therapy may be beneficial for enhancing HIV immunity, achieving HIV control, and eliminating HIV reservoirs, gradually becoming a promising strategy for achieving a functional HIV cure. In this review, we provide an overview of the design of anti-HIV CAR proteins, the cell types of anti-HIV CAR (including CAR T cells, CAR natural killer cells, and CAR-encoding hematopoietic stem/progenitor cells), the clinical application of CAR therapy in HIV infection, and the prospects and challenges in anti-HIV CAR therapy for maintaining viral suppression and eliminating HIV reservoirs.

Targeting and eradicating latent CNS reservoirs of HIV-1: original strategies and new models

Nowadays, combination antiretroviral therapy (cART) is the standard treatment for all people with human immunodeficiency virus (HIV-1). Although cART is effective in treating productive infection, it does not eliminate latent reservoirs of the virus. This leads to lifelong treatment associated with the occurrence of side effects and the development of drug-resistant HIV-1. Suppression of viral latency is therefore the major hurdle to HIV-1 eradication. Multiple mechanisms exist to regulate viral gene expression and drive the transcriptional and post-transcriptional establishment of latency. Epigenetic processes are amongst the most studied mechanisms influencing both productive and latent infection states. The central nervous system (CNS) represents a key anatomical sanctuary for HIV and is the focal point of considerable research efforts. However, limited and difficult access to CNS compartments makes understanding the HIV-1 infection state in latent brain cells such as microglial cells, astrocytes, and perivascular macrophages challenging. This review examines the latest advances on epigenetic transformations involved in CNS viral latency and targeting of brain reservoirs. Evidence from clinical studies as well as in vivo and in vitro models of HIV-1 persistence in the CNS will be discussed, with a special focus on recent 3D in vitro models such as human brain organoids. Finally, the review will address therapeutic considerations for targeting latent CNS reservoirs.

Opportunities for CAR-T Cell Immunotherapy in HIV Cure

Chimeric antigen receptor (CAR) technology is having a huge impact in the blood malignancy field and is becoming a well-established therapy for many types of leukaemia. In recent decades, efforts have been made to demonstrate that CAR-T cells have potential as a therapy to achieve a sterilizing cure for human immunodeficiency virus (HIV) infection. However, translation of this technology to the HIV scenario has not been easy, as many challenges have appeared along the way that hinder the consolidation of CAR-T cells as a putative therapy. Here, we review the origin and development of CAR-T cells, describe the advantages of CAR-T cell therapy in comparison with other therapies, and describe the major obstacles currently faced regarding application of this technology in the HIV field, specifically, viral escape, CAR-T cell infectivity, and accessibility to hidden reservoirs. Nonetheless, promising results in successfully tackling some of these issues that have been obtained in clinical trials suggest a bright future for CAR-T cells as a consolidated therapy.

Extracellular Vesicle-Based SARS-CoV-2 Vaccine

Messenger ribonucleic acid (RNA) vaccines are mainly used as SARS-CoV-2 vaccines. Despite several issues concerning storage, stability, effective period, and side effects, viral vector vaccines are widely used for the prevention and treatment of various diseases. Recently, viral vector-encapsulated extracellular vesicles (EVs) have been suggested as useful tools, owing to their safety and ability to escape from neutral antibodies. Herein, we summarize the possible cellular mechanisms underlying EV-based SARS-CoV-2 vaccines.

Systemic treatment and radiotherapy for patients with non-small cell lung cancer (NSCLC) and HIV infection - A systematic review

Lung cancer is the most common non-AIDS defining cancer among people living with HIV (PLWH), but there is a paucity of data regarding the efficacy and toxicity of radiotherapy and systemic regimens, including immunotherapy, in the treatment of these patients. In order to answer this question, we have performed a systematic search of the literature in Ovid Medline until March 17, 2022. We included 21 publications, enrolling 513 PLWH with non-small cell lung cancer (NSCLC), mostly male (75-100%), (ex-)smokers (75-100%) and with stage III-IV at diagnosis (65-100%). The overall response rate (ORR) to chemotherapy (n = 186 patients, mostly receiving platinum-based regimens) was highly variable (17 %-83 %), with a substantial hematological toxicity. ORR varied between 13 % and 50 % with single-agent immunotherapy (n = 68), with median overall survival between 9 and 11 months and a very acceptable toxicity profile, in line with studies in the HIV non-infected population. All five patients receiving tyrosine kinase inhibitors (TKIs; gefitinib or erlotinib) showed a partial response and long overall survival. Yet, combination of TKIs with antiretroviral therapy using pharmacological boosters, such as ritonavir, should be avoided. Radiotherapy was evaluated among 42 patients, showing high ORR (55 %-100 %), but 18 % of patients had a pneumonitis. This systematic review shows that radiotherapy and systemic therapy are effective and safe among PLWH with controlled infection diagnosed with NSCLC. Nonetheless, most reports were small and heterogeneous and larger studies are needed to confirm these encouraging findings. Moreover, clinical trials should not restrict the inclusion of PLWH, as more data is needed regarding the long-term efficacy and safety of treatments among this underserved population, especially of immunotherapy.

Development of an anti-CAR antibody response in SIV-infected rhesus macaques treated with CD4-MBL CAR/CXCR5 T cells

T cells expressing a simian immunodeficiency (SIV)-specific chimeric antigen receptor (CAR) and the follicular homing molecule, CXCR5, were infused into antiretroviral therapy (ART) suppressed, SIV-infected rhesus macaques to assess their ability to localize to the lymphoid follicle and control the virus upon ART interruption. While the cells showed evidence of functionality, they failed to persist in the animals beyond 28 days. Development of anti-CAR antibodies could be responsible for the lack of persistence. Potential antigenic sites on the anti-SIV CAR used in these studies included domains 1 and 2 of CD4, the carbohydrate recognition domain (CRD) of mannose-binding lectin (MBL), and an extracellular domain of the costimulatory molecule, CD28, along with short linker sequences. Using a flow cytometry based assay and target cells expressing the CAR/CXCR5 construct, we examined the serum of the CD4-MBL CAR/CXCR5-T cell treated animals to determine that the animals had developed an anti-CAR antibody response after infusion. Binding sites for the anti-CAR antibodies were identified by using alternative CARs transduced into target cells and by preincubation of the target cells with a CD4 blocking antibody. All of the treated animals developed antibodies in their serum that bound to CD4-MBL CAR/CXCR5 T cells and the majority were capable of inducing an ADCC response. The CD4 antibody-blocking assay suggests that the dominant immunogenic components of this CAR are the CD4 domains with a possible additional site of the CD28 domain with its linker. This study shows that an anti-drug antibody (ADA) response can occur even when using self-proteins, likely due to novel epitopes created by abridged self-proteins and/or the self-domain of the CAR connection to a small non-self linker. While in our study, there was no statistically significant correlation between the ADA response and the persistence of the CD4-MBL CAR/CXCR5-T cells in rhesus macaques, these findings suggest that the development of an ADA response could impact the long-term persistence of self-based CAR immunotherapies.