Curing HIV: lessons from cancer therapy

HIV cure: Are we going to make history?

BACKGROUND

At present, combination antiretroviral therapy (cART) is the mainstay for the treatment of people living with HIV/AIDS. cART can suppress the viral load to a minimal level; however, the possibility of the emergence of full-blown AIDS is always there. In the latter part of the first decade of the 21st century, an HIV-positive person received stem cell transplantation (SCT) for treatment of his haematological malignancy. The patient was able to achieve remission of the haematological condition as well as of HIV following SCT. Thorough investigations of various samples including blood and biopsy could not detect the virus in the person's body. The person was declared to be the first cured case of HIV.

LITERATURE SEARCH

Over the next decade, a few more similar cases were observed and have recently been declared cured of the infection. A comprehensive search was performed in PubMed, Cochrane library and Google Scholar. Four such additional cases were found in literature.

DESCRIPTION & DISCUSSION

These cases all share a common proposed mechanism for the HIV cure, that is, transplantation of stem cells from donors carrying a homozygous mutation in a gene encoding for CCR5 (receptor utilized by HIV for entry into the host cell), denoted as CCR5△32. This mutation makes the host immune cells devoid of CCR5, causing the host to acquire resistance against HIV. To the best of our knowledge, this is the first review to look at relevant and updated information of all cured cases of HIV as well as the related landmarks in history and discusses the underlying mechanism(s).

Identifying a Minor Histocompatibility Antigen in Mauritian Cynomolgus Macaques Encoded by APOBEC3C

Allogeneic hematopoietic stem cell transplants can lead to dramatic reductions in human immunodeficiency virus (HIV) reservoirs. This effect is partially mediated by donor T cells recognizing lymphocyte-expressed minor histocompatibility antigens (mHAgs). The potential to mark malignant and latently infected cells for destruction makes mHAgs attractive targets for cellular immunotherapies. However, testing such HIV reservoir reduction strategies will likely require preclinical studies in non-human primates (NHPs). In this study, we used a combination of alloimmunization, whole exome sequencing, and bioinformatics to identify an mHAg in Mauritian cynomolgus macaques (MCMs). We mapped the minimal optimal epitope to a 10-mer peptide (SW10) in apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 3C (APOBEC3C) and determined the major histocompatibility complex class I restriction element as Mafa-A1∗063, which is expressed in almost 90% of MCMs. APOBEC3C SW10-specific CD8+ T cells recognized immortalized B cells but not fibroblasts from an mHAg-positive MCM. These results provide a framework for identifying mHAgs in a non-transplant setting and suggest that APOBEC3C SW10 could be used as a model antigen to test mHAg-targeted therapies in NHPs.

Lessons Learned From Failures and Success Stories of HIV Breakthroughs: Are We Getting Closer to an HIV Cure?

There is a continuous search for an HIV cure as the success of ART in blocking HIV replication and the role of CD4+ T cells in HIV pathogenesis and immunity do not entirely eradicate HIV. The Berlin patient, who is virus-free, serves as the best model for a 'sterilizing cure' and many experts are trying to mimic this approach in other patients. Although failures were reported among Boston and Essen patients, the setbacks have provided valuable lessons to strengthen cure strategies. Following the Berlin patient, two more patients known as London and Düsseldorf patients might be the second and third person to be cured of HIV. In all the cases, the patients underwent chemotherapy regimen due to malignancy and hematopoietic stem cell transplantation (HSCT) which required matching donors for CCR5Δ32 mutation - an approach that may not always be feasible. The emergence of newer technologies, such as long-acting slow-effective release ART (LASER ART) and CRISPR/Cas9 could potentially overcome the barriers due to HIV latency and persistency and eliminate the need for CCR5Δ32 mutation donor. Appreciating the failure and success stories learned from these HIV breakthroughs would provide some insight for future HIV eradication and cure strategies.

Leveraging Cancer Therapeutics for the HIV Cure Agenda: Current Status and Future Directions

Despite effective antiretroviral therapy (ART) and undetectable HIV RNA in the plasma, latent replication-competent HIV persists indefinitely in long-lived cells. Cessation of ART results in rebound of HIV from these persistent reservoirs. While this was thought to be an insurmountable obstacle to viral eradication, recent cases suggest otherwise. To date one patient has been "cured" of HIV and several others have been able to interrupt ART without viral rebound for prolonged periods. These events have sparked renewed interest in developing strategies that will allow eradication of HIV in infected individuals. We review the current knowledge of HIV latency and the viral reservoir, describe the potential utility of emerging cancer therapeutics in HIV cure research with an emphasis on pathways implicated in reservoir persistence, and outline opportunities and challenges in the context of the current clinical trial and regulatory environment.

Towards an HIV cure based on targeted killing of infected cells: different approaches against acute versus chronic infection

PURPOSE OF REVIEW

Current regimens of combination antiretroviral therapy (cART) offer effective control of HIV infection, with maintenance of immune health and near-normal life expectancy. What will it take to progress beyond the status quo, whereby infectious virus can be eradicated (a 'sterilizing cure') or fully controlled without the need for ongoing cART (a 'functional cure')?

RECENT FINDINGS

On the basis of therapeutic advances in the cancer field, we propose that targeted cytotoxic therapy to kill HIV-infected cells represents a logical complement to cART for achieving an HIV cure. This concept is based on the fact that cART effectively blocks replication of the virus, but does not eliminate cells that are already infected; targeted cytotoxic therapy would contribute precisely this missing component. We suggest that different modalities are suited for curing primary acute versus established chronic infection. For acute infection, relatively short-acting potent agents such as recombinant immunotoxins might prove sufficient for HIV eradication, whereas for chronic infection, a long-lasting (lifelong?) modality is required to maintain full virus control, as might be achieved with genetically modified autologous T cells.

SUMMARY

We present perspectives for complementing cART with targeted cytotoxic therapy, whereby HIV infection is either eradicated or fully controlled, thereby eliminating the need for lifelong cART.

Novel CD4-Based Bispecific Chimeric Antigen Receptor Designed for Enhanced Anti-HIV Potency and Absence of HIV Entry Receptor Activity

Adoptive transfer of CD8 T cells genetically engineered to express "chimeric antigen receptors" (CARs) represents a potential approach toward an HIV infection "functional cure" whereby durable virologic suppression is sustained after discontinuation of antiretroviral therapy. We describe a novel bispecific CAR in which a CD4 segment is linked to a single-chain variable fragment of the 17b human monoclonal antibody recognizing a highly conserved CD4-induced epitope on gp120 involved in coreceptor binding. We compared a standard CD4 CAR with CD4-17b CARs where the polypeptide linker between the CD4 and 17b moieties is sufficiently long (CD4-35-17b CAR) versus too short (CD4-10-17b) to permit simultaneous binding of the two moieties to a single gp120 subunit. When transduced into a peripheral blood mononuclear cell (PBMC) or T cells thereof, all three CD4-based CARs displayed specific functional activities against HIV-1 Env-expressing target cells, including stimulation of gamma interferon (IFN-γ) release, specific target cell killing, and suppression of HIV-1 pseudovirus production. In assays of spreading infection of PBMCs with genetically diverse HIV-1 primary isolates, the CD4-10-17b CAR displayed enhanced potency compared to the CD4 CAR whereas the CD4-35-17b CAR displayed diminished potency. Importantly, both CD4-17b CARs were devoid of a major undesired activity observed with the CD4 CAR, namely, rendering the transduced CD8(+) T cells susceptible to HIV-1 infection. Likely mechanisms for the superior potency of the CD4-10-17b CAR over the CD4-35-17b CAR include the greater potential of the former to engage in the serial antigen binding required for efficient T cell activation and the ability of two CD4-10-17b molecules to simultaneously bind a single gp120 subunit.

IMPORTANCE

HIV research has been energized by prospects for a cure for HIV infection or, at least, for a "functional cure" whereby antiretroviral therapy can be discontinued without virus rebound. This report describes a novel CD4-based "chimeric antigen receptor" (CAR) which, when genetically engineered into T cells, gives them the capability to selectively respond to and kill HIV-infected cells. This CAR displays enhanced features compared to previously described CD4-based CARs, namely, increased potency and avoidance of the undesired rendering of the genetically modified CD8 T cells susceptible to HIV infection. When adoptively transferred back to the individual, the genetically modified T cells will hopefully provide durable killing of infected cells and sustained virus suppression without continued antiretroviral therapy, i.e., a functional cure.

HIV-1 latency: an update of molecular mechanisms and therapeutic strategies

The major obstacle towards HIV-1 eradication is the life-long persistence of the virus in reservoirs of latently infected cells. In these cells the proviral DNA is integrated in the host’s genome but it does not actively replicate, becoming invisible to the host immune system and unaffected by existing antiviral drugs. Rebound of viremia and recovery of systemic infection that follows interruption of therapy, necessitates life-long treatments with problems of compliance, toxicity, and untenable costs, especially in developing countries where the infection hits worst. Extensive research efforts have led to the proposal and preliminary testing of several anti-latency compounds, however, overall, eradication strategies have had, so far, limited clinical success while posing several risks for patients. This review will briefly summarize the more recent advances in the elucidation of mechanisms that regulates the establishment/maintenance of latency and therapeutic strategies currently under evaluation in order to eradicate HIV persistence.

Targeted cytotoxic therapy kills persisting HIV infected cells during ART

Antiretroviral therapy (ART) can reduce HIV levels in plasma to undetectable levels, but rather little is known about the effects of ART outside of the peripheral blood regarding persistent virus production in tissue reservoirs. Understanding the dynamics of ART-induced reductions in viral RNA (vRNA) levels throughout the body is important for the development of strategies to eradicate infectious HIV from patients. Essential to a successful eradication therapy is a component capable of killing persisting HIV infected cells during ART. Therefore, we determined the in vivo efficacy of a targeted cytotoxic therapy to kill infected cells that persist despite long-term ART. For this purpose, we first characterized the impact of ART on HIV RNA levels in multiple organs of bone marrow-liver-thymus (BLT) humanized mice and found that antiretroviral drug penetration and activity was sufficient to reduce, but not eliminate, HIV production in each tissue tested. For targeted cytotoxic killing of these persistent vRNA(+) cells, we treated BLT mice undergoing ART with an HIV-specific immunotoxin. We found that compared to ART alone, this agent profoundly depleted productively infected cells systemically. These results offer proof-of-concept that targeted cytotoxic therapies can be effective components of HIV eradication strategies.

Therapeutics for HIV-1 reactivation from latency

Intensive combined antiretroviral therapy successfully suppresses HIV-1 replication and AIDS disease progression making infection manageable, but it is unable to eradicate the virus that persists in long-lived, drug-insensitive and immune system-insensitive reservoirs thus asking for life-long treatments with problems of compliance, resistance, toxicity and cost. These limitations and recent insights into latency mechanisms have fueled a renewed effort in finding a cure for HIV-1 infection. Proposed eradication strategies involve reactivation of the latent reservoir upon induction of viral transcription followed by the elimination of reactivated virus-producing cells by viral cytopathic effect or host immune response. Several molecules identified by mechanism-directed approaches or in large-scale screenings have been proposed as latency reversing agents. Some of them have already entered clinical testing in humans but with mixed or unsatisfactory results.