In vivo migration and function of transferred HIV-1-specific cytotoxic T cells

Cytolytic CD8+ T cells infiltrate germinal centers to limit ongoing HIV replication in spontaneous controller lymph nodes

Follicular CD8⁺ T cells (fCD8) mediate surveillance in lymph node (LN) germinal centers against lymphotropic infections and cancers, but the precise mechanisms by which these cells mediate immune control remain incompletely resolved. To address this, we investigated functionality, clonotypic compartmentalization, spatial localization, phenotypic characteristics, and transcriptional profiles of LN-resident virus-specific CD8⁺ T cells in persons who control HIV without medications. Antigen-induced proliferative and cytolytic potential consistently distinguished spontaneous controllers from noncontrollers. T cell receptor analysis revealed complete clonotypic overlap between peripheral and LN-resident HIV-specific CD8⁺ T cells. Transcriptional analysis of LN CD8⁺ T cells revealed gene signatures of inflammatory chemotaxis and antigen-induced effector function. In HIV controllers, the cytotoxic effectors perforin and granzyme B were elevated among virus-specific CXCR5⁺ fCD8s proximate to foci of HIV RNA within germinal centers. These results provide evidence consistent with cytolytic control of lymphotropic infection supported by inflammatory recruitment, antigen-specific proliferation, and cytotoxicity of fCD8s.

Reprogramming dysfunctional CD8+ T cells to promote properties associated with natural HIV control

Virus-specific CD8+ T cells play a central role in HIV-1 natural controllers to maintain suppressed viremia in the absence of antiretroviral therapy. These cells display a memory program that confers them stemness properties, high survival, polyfunctionality, proliferative capacity, metabolic plasticity, and antiviral potential. The development and maintenance of such qualities by memory CD8+ T cells appear crucial to achieving natural HIV-1 control. Here, we show that targeting the signaling pathways Wnt/transcription factor T cell factor 1 (Wnt/TCF-1) and mTORC through GSK3 inhibition to reprogram HIV-specific CD8+ T cells from noncontrollers promoted functional capacities associated with natural control of infection. Features of such reprogrammed cells included enrichment in TCF-1+ less-differentiated subsets, a superior response to antigen, enhanced survival, polyfunctionality, metabolic plasticity, less mTORC1 dependency, an improved response to γ-chain cytokines, and a stronger HIV-suppressive capacity. Thus, such CD8+ T cell reprogramming, combined with other available immunomodulators, might represent a promising strategy for adoptive cell therapy in the search for an HIV-1 cure.

Therapeutic roles of CAR T cells in infectious diseases: Clinical lessons learnt from cancer

Cancer immunotherapy has made improvements due to the advances in chimaeric antigen receptor (CAR) T cell development, offering a promising treatment option for patients who have failed to respond to traditional treatments. In light of the successful use of adoptive CAR T cell therapy for cancer, researchers have been inspired to develop CARs for the treatment of other diseases beyond cancers such as viral infectious diseases. Nonetheless, various obstacles limit the efficacy of CAR T cell therapies and prevent their widespread usage. Severe toxicities, poor in vivo persistence, antigen escape, and heterogeneity, as well as off-target effect, are key challenges that must all be addressed to broaden the application of CAR T cells to a wider spectrum of diseases. The key advances in CAR T cell treatment for cancer and viral infections are reviewed in this article. We will also discuss revolutionary CAR T cell products developed to improve and enhance the therapeutic advantages of these treatments.

Immune inactivation of anti-simian immunodeficiency virus chimeric antigen receptor T cells in rhesus macaques

Chimeric antigen receptor (CAR) T cell therapies are being investigated as potential HIV cures and designed to target HIV reservoirs. Monoclonal antibodies (mAbs) targeting the simian immunodeficiency virus (SIV) envelope allowed us to investigate the potency of single-chain variable fragment (scFv)-based anti-SIV CAR T cells. In vitro, CAR T cells expressing the scFv to both the variable loop 1 (V1) or V3 of the SIV envelope were highly potent at eliminating SIV-infected T cells. However, in preclinical studies, in vivo infusion of these CAR T cells in rhesus macaques (RMs) resulted in lack of expansion and no detectable in vivo antiviral activity. Injection of envelope-expressing antigen-presenting cells (APCs) 1 week post-CAR T cell infusion also failed to stimulate CAR T cell expansion in vivo. To investigate this in vitro versus in vivo discrepancy, we examined host immune responses directed at CAR T cells. A humoral immune response against the CAR scFv was detected post-infusion of the anti-SIV CAR T cells; anti-SIV IgG antibodies present in plasma of SIV-infected animals were associated with inhibited CAR T cell effector functions. These data indicate that lack of in vivo expansion and efficacy of CAR T cells might be due to antibodies blocking the interaction between the CAR scFv and its epitope.

Robust expansion of HIV CAR T cells following antigen boosting in ART-suppressed nonhuman primates

Chimeric antigen receptor (CAR) T cells targeting CD19+ hematologic malignancies have rapidly emerged as a promising, novel therapy. In contrast, results from the few CAR T-cell studies for infectious diseases such as HIV-1 have been less convincing. These challenges are likely due to the low level of antigen present in antiretroviral therapy (ART)-suppressed patients in contrast to those with hematologic malignancies. Using our well-established nonhuman primate model of ART-suppressed HIV-1 infection, we tested strategies to overcome these limitations and challenges. We first optimized CAR T-cell production to maintain central memory subsets, consistent with current clinical paradigms. We hypothesized that additional exogenous antigen might be required in an ART-suppressed setting to aid expansion and persistence of CAR T cells. Thus, we studied 4 simian/HIV-infected, ART-suppressed rhesus macaques infused with virus-specific CD4CAR T cells, followed by supplemental infusion of cell-associated HIV-1 envelope (Env). Env boosting led to significant and unprecedented expansion of virus-specific CAR+ T cells in vivo; after ART treatment interruption, viral rebound was significantly delayed compared with controls (P = .014). In 2 animals with declining CAR T cells, rhesusized anti-programmed cell death protein 1 (PD-1) antibody was administered to reverse PD-1-dependent immune exhaustion. Immune checkpoint blockade triggered expansion of exhausted CAR T cells and concordantly lowered viral loads to undetectable levels. These results show that supplemental cell-associated antigen enables robust expansion of CAR T cells in an antigen-sparse environment. To our knowledge, this is the first study to show expansion of virus-specific CAR T cells in infected, suppressed hosts, and delay/control of viral recrudescence.

HIV-1 cure strategies: why CRISPR?

INTRODUCTION

Antiretroviral therapy (ART) has transformed prognoses for HIV-1-infected individuals but requires lifelong adherence to prevent viral resurgence. Targeted elimination or permanent deactivation of the latently infected reservoir harboring integrated proviral DNA, which drives viral rebound, is a major focus of HIV-1 research.

AREAS COVERED

This review covers the current approaches to developing curative strategies for HIV-1 that target the latent reservoir. Discussed herein are shock and kill, broadly neutralizing antibodies (bNAbs), block and lock, Chimeric antigen receptor (CAR) T cells, immune checkpoint modulation, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) coreceptor ablation, and CRISPR/Cas9 proviral excision. Emphasis is placed on CRISPR/Cas9 proviral excision/inactivation. Recent advances and future directions toward discovery and translation of HIV-1 therapeutics are discussed.

EXPERT OPINION

CRISPR/Cas9 proviral targeting fills a niche amongst HIV-1 cure strategies by directly targeting the integrated provirus without the necessity of an innate or adaptive immune response. Each strategy discussed in this review has shown promising results with the potential to yield curative or adjuvant therapies. CRISPR/Cas9 is singular among these in that it addresses the root of the problem, integrated proviral DNA, with the capacity to permanently remove or deactivate the source of HIV-1 recrudescence.

A participant-derived xenograft model of HIV enables long-term evaluation of autologous immunotherapies

HIV-specific CD8⁺ T cells partially control viral replication and delay disease progression, but they rarely provide lasting protection, largely due to immune escape. Here, we show that engrafting mice with memory CD4⁺ T cells from HIV⁺ donors uniquely allows for the in vivo evaluation of autologous T cell responses while avoiding graft-versus-host disease and the need for human fetal tissues that limit other models. Treating HIV-infected mice with clinically relevant HIV-specific T cell products resulted in substantial reductions in viremia. In vivo activity was significantly enhanced when T cells were engineered with surface-conjugated nanogels carrying an IL-15 superagonist, but it was ultimately limited by the pervasive selection of a diverse array of escape mutations, recapitulating patterns seen in humans. By applying mathematical modeling, we show that the kinetics of the CD8⁺ T cell response have a profound impact on the emergence and persistence of escape mutations. This “participant-derived xenograft” model of HIV provides a powerful tool for studying HIV-specific immunological responses and facilitating the development of effective cell-based therapies.

CAR T cells: Living HIV drugs

Human immunodeficiency virus type 1 (HIV-1), the virus that causes AIDS (acquired immunodeficiency syndrome), is a major global public health issue. Although the advent of combined antiretroviral therapy (ART) has made significant progress in inhibiting HIV replication in patients, HIV-infected cells remain the principal cellular reservoir of HIV, this allows HIV to rebound immediately upon stopping ART, which is considered the major obstacle to curing HIV infection. Chimeric antigen receptor (CAR) cell therapy has provided new opportunities for HIV treatment. Engineering T cells or hematopoietic stem cells (HSCs) to generate CAR T cells is a rapidly growing approach to develop an efficient immune cell to fight HIV. Herein, we review preclinical and clinical data available for the development of CAR T cells. Further, the advantages and disadvantages of clinical application of anti-HIV CAR T cells will be discussed.

Virus-Specific T Cell Therapies for HIV: Lessons Learned From Hematopoietic Stem Cell Transplantation

Human immunodeficiency virus (HIV) has caused millions of deaths and continues to threaten the health of millions of people worldwide. Despite anti-retroviral therapy (ART) substantially alleviating severity and limiting transmission, HIV has not been eradicated and its persistence can lead to other health concerns such as cancer. The only two cases of HIV cure to date are HIV⁺ cancer patients receiving an allogeneic hematopoietic stem cell transplantation (allo-HSCT) from a donor with the CCR5 Δ32 mutation. While this approach has not led to such success in other patients and is not applicable to HIV⁺ individuals without cancer, the encouraging results may point toward a breakthrough in developing a cure strategy for HIV. Adoptive transfer of virus-specific T cells (VSTs) post HSCT has been effectively used to treat and prevent reactivation of latent viral infections such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV), making VSTs an attractive therapeutic to control HIV rebound. Here we will discuss the potential of using adoptive T cell therapies in combination with other treatments such as HSCT and latency reversing agents (LRAs) to achieve a functional cure for HIV.

TNIK signaling imprints CD8+ T cell memory formation early after priming

Co-stimulatory signals, cytokines and transcription factors regulate the balance between effector and memory cell differentiation during T cell activation. Here, we analyse the role of the TRAF2-/NCK-interacting kinase (TNIK), a signaling molecule downstream of the tumor necrosis factor superfamily receptors such as CD27, in the regulation of CD8⁺ T cell fate during acute infection with lymphocytic choriomeningitis virus. Priming of CD8⁺ T cells induces a TNIK-dependent nuclear translocation of β-catenin with consecutive Wnt pathway activation. TNIK-deficiency during T cell activation results in enhanced differentiation towards effector cells, glycolysis and apoptosis. TNIK signaling enriches for memory precursors by favouring symmetric over asymmetric cell division. This enlarges the pool of memory CD8⁺ T cells and increases their capacity to expand after re-infection in serial re-transplantation experiments. These findings reveal that TNIK is an important regulator of effector and memory T cell differentiation and induces a population of stem cell-like memory T cells.

Coordinate expression of multiple factors play critical roles in the regulation between effector and memory CD8⁺ T cell differentiation. Here the authors show upon acute viral infection TNIK is critically required as a regulator of effector and memory T cell differentiation.

Advances in Developing CAR T-Cell Therapy for HIV Cure

Acquired immune deficiency syndrome (AIDS), which is caused by HIV infection, is an epidemic disease that has killed millions of people in the last several decades. Although combination antiretroviral therapy (cART) has enabled tremendous progress in suppressing HIV replication, it fails to eliminate HIV latently infected cells, and infected individuals remain HIV positive for life. Lifelong antiretroviral therapy is required to maintain control of virus replication, which may result in significant problems, including long-term toxicity, high cost, and stigma. Therefore, novel therapeutic strategies are urgently needed to eliminate the viral reservoir in the host for HIV cure. In this review, we compare several potential strategies regarding HIV cure and focus on how we might utilize chimeric antigen receptor-modified T cells (CAR T) as a therapy to cure HIV infection.

Pathways towards human immunodeficiency virus elimination

Antiretroviral therapy (ART) suppresses human immunodeficiency virus (HIV) infection. Research seeking to transform viral suppression into elimination has generated novel immune, chemical and molecular antiviral agents. However, none, to date, have excised latent integrated proviral DNA or removed infected cells from infected persons. These efforts included, but are not limited to, broadly neutralizing antibodies, "shock" and "kill" latency-reversing agents, innate immune regulators, and sequential long-acting antiretroviral nanoformulated prodrugs and CRISPR-Cas9 gene editing. While, the latter, enabled the complete excision of latent HIV-1 from the host genome success was so far limited. We contend that improvements in antiretroviral delivery, potency, agent specificity, or combinatorial therapies can provide a pathway towards complete HIV elimination.

Generation of MR1-Restricted T Cell Clones by Limiting Dilution Cloning of MR1 Tetramer+ Cells

Tetramers are a powerful tool for identification of T cell subsets that are restricted by specific antigen presenting molecules and their cognate antigens. The generation of T cell clones from specific T cell subsets allows for further investigation of the phenotype and function of these cells. Here, we describe a method for sorting and cloning of MR1-restricted T cells using the MR1/5-OP-RU tetramer. This protocol can be easily modified to enrich for expansion of specific or unique subsets of MR1-restricted T cell clones from any tissue to further characterize the phenotype and function of those cells.

Preclinical development of T-cell receptor-engineered T-cell therapy targeting the 5T4 tumor antigen on renal cell carcinoma

5T4 (trophoblast glycoprotein, TPBG) is a transmembrane tumor antigen expressed on more than 90% of primary renal cell carcinomas (RCC) and a wide range of human carcinomas but not on most somatic adult tissues. The favorable expression pattern has encouraged the development and clinical testing of 5T4-targeted antibody and vaccine therapies. 5T4 also represents a compelling and unexplored target for T-cell receptor (TCR)-engineered T-cell therapy. Our group has previously isolated high-avidity CD8⁺ T-cell clones specific for an HLA-A2-restricted 5T4 epitope (residues 17-25; 5T4_p17). In this report, targeted single-cell RNA sequencing was performed on 5T4_p17-specific T-cell clones to sequence the highly variable complementarity-determining region 3 (CDR3) of T-cell receptor α chain (TRA) and β chain (TRB) genes. Full-length TRA and TRB sequences were cloned into lentiviral vectors and transduced into CD8⁺ T-cells from healthy donors. Redirected effector T-cell function against 5T4_p17 was measured by cytotoxicity and cytokine release assays. Seven unique TRA-TRB pairs were identified. All seven TCRs exhibited high expression on CD8⁺ T-cells with transduction efficiencies from 59 to 89%. TCR-transduced CD8⁺ T-cells demonstrated redirected cytotoxicity and cytokine release in response to 5T4_p17 on target-cells and killed 5T4⁺/HLA-A2⁺ kidney-, breast-, and colorectal-tumor cell lines as well as primary RCC tumor cells in vitro. TCR-transduced CD8⁺ T-cells also detected presentation of 5T4_p17 in TAP1/2-deficient T2 target-cells. TCR-transduced T-cells redirected to recognize the 5T4_p17 epitope from a broadly shared tumor antigen are of interest for future testing as a cellular immunotherapy strategy for HLA-A2⁺ subjects with 5T4⁺ tumors.

Adoptive lymphocyte transfer to an HIV-infected progressor from an elite controller

BACKGROUNDHIV-infected patients with poor virologic control and multidrug-resistant virus have limited therapeutic options. The current study was undertaken to evaluate the safety, immunologic effects, and antiviral activity of peripheral lymphocytes transferred from an elite controller, whose immune system is able to control viral replication without antiretroviral medications, to an HLA-B*2705-matched progressor.METHODSApproximately 22 billion cells were collected from an elite controller by lymphapheresis and infused within 6 hours into a recipient with a preinfusion CD4+ T cell count of 10 cells/μL (1%) and HIV plasma viral load of 114,993 copies/mL.RESULTSDonor cells were cleared from the recipient's peripheral blood by day 8. A transient decrease in viral load to 58,421 (day 3) was followed by a rebound to 702,972 (day 6) before returning to baseline values by day 8. The decreased viral load was temporally associated with peak levels of donor T cells, including CD8+ T cells that had high levels of expression of Ki67, perforin, and granzyme B. Notably, recipient CD8+ T cells also showed increased expression of these markers, especially in HIV-specific tetramer-positive cells.CONCLUSIONThese results suggest that the adoptive transfer of lymphocytes from an HIV-infected elite controller to an HIV-infected patient with progressive disease may be able to perturb the immune system of the recipient in both positive and negative ways.TRIAL REGISTRATIONClinicalTrials.gov NCT00559416.FUNDINGIntramural Research Programs of the US NIH Clinical Center and the National Institute of Allergy and Infectious Diseases (NIAID); the National Cancer Institute.

CD8+ T-Cell Response to HIV Infection in the Era of Antiretroviral Therapy

Although the combined antiretroviral therapy (cART) has decreased the deaths associated with the immune deficiency acquired syndrome (AIDS), non-AIDS conditions have emerged as an important cause of morbidity and mortality in HIV-infected patients under suppressive cART. Since these conditions are associated with a persistent inflammatory and immune activation state, major efforts are currently made to improve the immune reconstitution. CD8⁺ T-cells are critical in the natural and cART-induced control of viral replication; however, CD8⁺ T-cells are highly affected by the persistent immune activation and exhaustion state driven by the increased antigenic and inflammatory burden during HIV infection, inducing phenotypic and functional alterations, and hampering their antiviral response. Several CD8⁺ T-cell subsets, such as interleukin-17-producing and follicular CXCR5⁺ CD8⁺ T-cells, could play a particular role during HIV infection by promoting the gut barrier integrity, and exerting viral control in lymphoid follicles, respectively. Here, we discuss the role of CD8⁺ T-cells and some of their subpopulations during HIV infection in the context of cART-induced viral suppression, focusing on current challenges and alternatives for reaching complete reconstitution of CD8⁺ T-cells antiviral function. We also address the potential usefulness of CD8⁺ T-cell features to identify patients who will reach immune reconstitution or have a higher risk for developing non-AIDS conditions. Finally, we examine the therapeutic potential of CD8⁺ T-cells for HIV cure strategies.

Chimeric antigen receptor T-cell approaches to HIV cure

PURPOSE OF REVIEW

Combination antiretroviral therapy (ART) has enabled tremendous progress in suppressing HIV replication in infected patients. However, ART alone cannot eradicate HIV and its latent, persisting reservoirs. Novel approaches are needed to eradicate the virus or achieve functional cure in the absence of ART.

RECENT FINDINGS

Adoptive T-cell therapies were initially tested in HIV-infected individuals with limited efficiency. Benefiting from new and improved methodologies, an increasing array of CAR T-cell therapies has been successfully developed in the cancer immunotherapy field, demonstrating promising new avenues that could be applied to HIV. Numerous studies have characterized various HIV-specific CAR constructs, types of cytolytic effector cells, and CAR-expressing cells' trafficking to the reservoir compartments, warranting further in-vivo efforts. Notably, the ability of CAR cells to persist and function in low-antigen environments in vivo, that is, in ART-suppressed patients, remains unclear.

SUMMARY

Despite promising results in preclinical studies, only a handful of clinical trials have been initiated worldwide. Several obstacles remain prior to successful application of HIV-specific CAR T-cell therapies in patients. In this review, we survey the current state of the field, and address paths towards realizing the goal of an efficacious HIV CAR T-cell product.

HIV-1 is more dependent on the K182 capsid residue than HIV-2 for interactions with CPSF6

The HIV-1 capsid (CA) utilizes CPSF6 for nuclear entry and integration site targeting. Previous studies demonstrated that the HIV-1 CA C-terminal domain (CTD) contains a highly conserved K182 residue involved in interaction with CPSF6. In contrast, certain HIV-2 strains possess a substitution at this residue (K182R). To assess whether CA-CPSF6 interaction via the CA CTD is conserved among primate lentiviruses, we examined resistance of several HIV-1- and HIV-2-lineage viruses to a truncated form of CPSF6, CPSF6-358. The results demonstrated that viruses belonging to the HIV-2-lineage maintain interaction with CPSF6 regardless of the presence of the K182R substitution, in contrast to the case with HIV-1-lineage viruses. Our structure-guided mutagenesis indicated that the differential requirement for CA-CPSF6 interaction is regulated in part by residues near the 182nd amino acid of CA. These results demonstrate a previously unrecognized distinction between HIV-1 and HIV-2, which may reflect differences in their evolutionary histories.

Restoring antiviral immunity with adoptive transfer of ex-vivo generated T cells

PURPOSE OF REVIEW

Latent viruses such as cytomegalovirus (CMV), Epstein-Barr virus (EBV) and adenovirus (ADV) often reactivate in immunocompromised patients, contributing to poor clinical outcomes. A rapid reconstitution of antiviral responses via adoptive transfer of virus-specific T cells (VSTs) can prevent or eradicate even refractory infections. Here, we evaluate this strategy and the associated methodological, manufacturing and clinical advances.

RECENT FINDINGS

From the early pioneering but cumbersome efforts to isolate CMV-specific T cell clones, new approaches and techniques have been developed to provide quicker, safer and broader-aimed ex-vivo antigen-specific cells. New manufacturing strategies, such as the use of G-Rex flasks or 'priming' with a library of overlapping viral peptides, allow for culturing greater numbers of cells that could be patient-specific or stored in cell banks for off-the-shelf applications. Rapid isolation of T cells using major histocompatibility complex tetramer or cytokine capture approaches, or genetic reprogramming of cells to target viral antigens can accelerate the generation of potent cellular products.

SUMMARY

Advances in the ex-vivo generation of VSTs in academic medical centres and as off-the-shelf blood bank-based or commercially produced reagents are likely to result in broader accessibility and possible manufacturing cost reduction of these cell products, and will open new therapeutic prospects for vulnerable and critically ill immunocompromised patients.

HIV-Specific, Ex Vivo Expanded T Cell Therapy: Feasibility, Safety, and Efficacy in ART-Suppressed HIV-Infected Individuals

Adoptive T cell therapy has had dramatic successes in the treatment of virus-related malignancies and infections following hematopoietic stem cell transplantation. We adapted this method to produce ex vivo expanded HIV-specific T cells (HXTCs), with the long-term goal of using HXTCs as part of strategies to clear persistent HIV infection. In this phase 1 proof-of-concept study (NCT02208167), we administered HXTCs to antiretroviral therapy (ART)-suppressed, HIV-infected participants. Participants received two infusions of 2 × 107 cells/m2 HXTCs at a 2-week interval. Leukapheresis was performed at baseline and 12 weeks post-infusion to measure the frequency of resting cell infection by the quantitative viral outgrowth assay (QVOA). Overall, participants tolerated HXTCs, with only grade 1 adverse events (AEs) related to HXTCs. Two of six participants exhibited a detectable increase in CD8 T cell-mediated antiviral activity following the two infusions in some, but not all, assays. As expected, however, in the absence of a latency reversing agent, no meaningful decline in the frequency of resting CD4 T cell infection was detected. HXTC therapy in ART-suppressed, HIV-infected individuals appears safe and well tolerated, without any clinical signs of immune activation, likely due to the low residual HIV antigen burden present during ART.

Long-Term Persistence of Anti-HIV Broadly Neutralizing Antibody-Secreting Hematopoietic Cells in Humanized Mice

Broadly neutralizing antibodies (bNAbs) are among the most promising strategies to achieve long-term control of HIV-1 in the absence of combination antiretroviral therapy. Passive administration of such antibodies in patients efficiently decreases HIV-1 viremia, but is limited by the serum half-life of the protein. Here, we investigated whether antibody-secreting hematopoietic cells could overcome this problem. We genetically modified human CD34⁺ hematopoietic stem and progenitor cells (HSPCs) to secrete bNAbs and transplanted them into immunodeficient mice. We found that the gene-modified cells engraft and stably secrete antibodies in the peripheral blood of the animals for the 9 months of the study. Antibodies were predominantly expressed by human HSPC-derived T- and B cells. Importantly, we found that secreted PGT128 was able to delay HIV-1 viremia in vivo and also prevent a decline in CD4⁺ cells. Gene-modified cells were maintained in bone marrow and were also detected in spleen, thymus, lymph nodes, and gut-associated lymphoid tissue. These data indicate that the bNAb secretion from HSPC-derived cells in mice is functional and can affect viral infection and CD4⁺ cell maintenance. This study paves the way for potential applications to other diseases requiring long-lasting protein or antibody delivery.

CRISPR therapeutic tools for complex genetic disorders and cancer (Review)

One of the fundamental discoveries in the field of biology is the ability to modulate the genome and to monitor the functional outputs derived from genomic alterations. In order to unravel new therapeutic options, scientists had initially focused on inducing genetic alterations in primary cells, in established cancer cell lines and mouse models using either RNA interference or cDNA overexpression or various programmable nucleases [zinc finger nucleases (ZNF), transcription activator-like effector nucleases (TALEN)]. Even though a huge volume of data was produced, its use was neither cheap nor accurate. Therefore, the clustered regularly interspaced short palindromic repeats (CRISPR) system was evidenced to be the next step in genome engineering tools. CRISPR-associated protein 9 (Cas9)-mediated genetic perturbation is simple, precise and highly efficient, empowering researchers to apply this method to immortalized cancerous cell lines, primary cells derived from mouse and human origins, xenografts, induced pluripotent stem cells, organoid cultures, as well as the generation of genetically engineered animal models. In this review, we assess the development of the CRISPR system and its therapeutic applications to a wide range of complex diseases (particularly distinct tumors), aiming at personalized therapy. Special emphasis is given to organoids and CRISPR screens in the design of innovative therapeutic approaches. Overall, the CRISPR system is regarded as an eminent genome engineering tool in therapeutics. We envision a new era in cancer biology during which the CRISPR-based genome engineering toolbox will serve as the fundamental conduit between the bench and the bedside; nonetheless, certain obstacles need to be addressed, such as the eradication of side-effects, maximization of efficiency, the assurance of delivery and the elimination of immunogenicity.

The Use of the Humanized Mouse Model in Gene Therapy and Immunotherapy for HIV and Cancer

HIV and cancer remain prevailing sources of morbidity and mortality worldwide. There are current efforts to discover novel therapeutic strategies for the treatment or cure of these diseases. Humanized mouse models provide the investigative tool to study the interaction between HIV or cancer and the human immune system in vivo. These humanized models consist of immunodeficient mice transplanted with human cells, tissues, or hematopoietic stem cells that result in reconstitution with a nearly full human immune system. In this review, we discuss preclinical studies evaluating therapeutic approaches in stem cell-based gene therapy and T cell-based immunotherapies for HIV and cancer using a humanized mouse model and some recent advances in using checkpoint inhibitors to improve antiviral or antitumor responses.

Accumulation of follicular CD8+ T cells in pathogenic SIV infection

LN follicles constitute major reservoir sites for HIV/SIV persistence. Cure strategies could benefit from the characterization of CD8+ T cells able to access and eliminate HIV-infected cells from these areas. In this study, we provide a comprehensive analysis of the phenotype, frequency, localization, and functionality of follicular CD8+ T cells (fCD8+) in SIV-infected nonhuman primates. Although disorganization of follicles was a major factor, significant accumulation of fCD8+ cells during chronic SIV infection was also observed in intact follicles, but only in pathogenic SIV infection. In line with this, tissue inflammatory mediators were strongly associated with the accumulation of fCD8+ cells, pointing to tissue inflammation as a major factor in this process. These fCD8+ cells have cytolytic potential and can be redirected to target and kill HIV-infected cells using bispecific antibodies. Altogether, our data support the use of SIV infection to better understand the dynamics of fCD8+ cells and to develop bispecific antibodies as a strategy for virus eradication.

Reprint of: Virus-Specific T Cells: Broadening Applicability

Virus infection remains an appreciable cause of morbidity and mortality after hematopoietic stem cell transplantation (HSCT). Although pharmacotherapy and/or antibody therapy may help prevent or treat viral disease, these drugs are expensive, toxic, and often ineffective due to primary or secondary resistance. Further, effective treatments are limited for many infections (eg, adenovirus, BK virus), which are increasingly detected after alternative donor transplants. These deficiencies in conventional therapeutics have increased interest in an immunotherapeutic approach to viral disorders, leading to adoptive transfer of virus-specific cytotoxic T lymphocytes (VSTs), which can rapidly reconstitute antiviral immunity post-transplantation without causing graft-versus-host disease. This review will explore how the VST field has improved outcomes for many patients with life-threatening viral infections after HSCT, and how to broaden applicability beyond the "patient-specific" products, as well as extending to other viral diseases even outside the context of HSCT.

The B-Cell Follicle in HIV Infection: Barrier to a Cure

The majority of HIV replication occurs in secondary lymphoid organs (SLOs) such as the spleen, lymph nodes, and gut-associated lymphoid tissue. Within SLOs, HIV RNA⁺ cells are concentrated in the B-cell follicle during chronic untreated infection, and emerging data suggest that they are a major source of replication in treated disease as well. The concentration of HIV RNA⁺ cells in the B-cell follicle is mediated by several factors. Follicular CD4⁺ T-cell subsets including T-follicular helper cells and T-follicular regulatory cells are significantly more permissive to HIV than extrafollicular subsets. The B cell follicle also contains a large reservoir of extracellular HIV virions, which accumulate on the surface of follicular dendritic cells (FDCs) in germinal centers. FDC-bound HIV virions remain infectious even in the presence of neutralizing antibodies and can persist for months or even years. Moreover, the B-cell follicle is semi-immune privileged from CTL control. Frequencies of HIV- and SIV-specific CTL are lower in B-cell follicles compared to extrafollicular regions as the majority of CTL do not express the follicular homing receptor CXCR5. Additionally, CTL in the B-cell follicle may be less functional than extrafollicular CTL as many exhibit the recently described CD8 T follicular regulatory phenotype. Other factors may also contribute to the follicular concentration of HIV RNA⁺ cells. Notably, the contribution of NK cells and γδ T cells to control and/or persistence of HIV RNA⁺ cells in secondary lymphoid tissue remains poorly characterized. As HIV research moves increasingly toward the development of cure strategies, a greater understanding of the barriers to control of HIV infection in B-cell follicles is critical. Although no strategy has as of yet proven to be effective, a range of novel therapies to address these barriers are currently being investigated including genetically engineered CTL or chimeric antigen receptor T cells that express the follicular homing molecule CXCR5, treatment with IL-15 or an IL-15 superagonist, use of bispecific antibodies to harness the killing power of the follicular CD8⁺ T cell population, and disruption of the follicle through treatments such as rituximab.

Virus-Specific T Cells: Broadening Applicability

Virus infection remains an appreciable cause of morbidity and mortality after hematopoietic stem cell transplantation (HSCT). Although pharmacotherapy and/or antibody therapy may help prevent or treat viral disease, these drugs are expensive, toxic, and often ineffective due to primary or secondary resistance. Further, effective treatments are limited for many infections (eg, adenovirus, BK virus), which are increasingly detected after alternative donor transplants. These deficiencies in conventional therapeutics have increased interest in an immunotherapeutic approach to viral disorders, leading to adoptive transfer of virus-specific cytotoxic T lymphocytes (VSTs), which can rapidly reconstitute antiviral immunity post-transplantation without causing graft-versus-host disease. This review will explore how the VST field has improved outcomes for many patients with life-threatening viral infections after HSCT, and how to broaden applicability beyond the "patient-specific" products, as well as extending to other viral diseases even outside the context of HSCT.

New approaches for the enhancement of chimeric antigen receptors for the treatment of HIV

HIV infection continues to be a life-long chronic disease in spite of the success of antiretroviral therapy (ART) in controlling viral replication and preventing disease progression. However, because of the high cost of treatment, severe side effects, and inefficiency in curing the disease with ART, there is a call for alternative therapies that will provide a functional cure for HIV. Cytotoxic T lymphocytes (CTLs) are vital in the control and clearance of viral infections and therefore immune-based therapies have attempted to engineer HIV-specific CTLs that would be able to clear the infection from the body. The development of chimeric antigen receptors (CARs) provides an opportunity to engineer superior HIV-specific CTLs that will be independent of the major histocompatibility complex for target recognition. A CD4-based CAR has been previously tested in clinical trials to test the antiviral efficacy of peripheral T cells armed with this CD4-based CAR. The results from these clinical trials showed the safety and feasibility of CAR T cell therapy for HIV infection; however, minimal antiviral efficacy was seen. In this review, we will discuss the various strategies being developed to enhance the therapeutic potency of anti-HIV CARs with the goal of generating superior antiviral responses that will lead to life-long HIV immunity and clearance of the virus from the body.

In Vivo Persistence of Donor Cells following Adoptive Transfer of Allogeneic Dendritic Cells in HIV-Infected Patients

Peripheral blood samples from HIV-seropositive individuals enrolled in a pilot clinical trial investigating the use of allogeneic dendritic cell therapy were evaluated for mixed chimerism. In this study, dendritic cells from HLA-identical, HIV-seronegative siblings were used. Patients received an infusion of dendritic cells pulsed with HIV MN gp160 protein or with peptides from HLA-A2 restricted epitopes of env, gag, and pol proteins every month for 6–9 months. Of the five allogeneic dendritic cell recipients, two showed increases in HIV antigen-specific immune responses. Allele-specific polymorphisms were identified in three sib-pairs that allowed infused donor cells to be detected using sensitive PCR-based molecular methods. Analysis of blood samples from patients showed similar patterns of donor cell persistence after the first infusion, in that cells were detectable for at least 1 week. Also, differences were observed in the kinetics of cell survival between the first and subsequent infusion cycles in all three patients. This suggests variation in HIV-specific immune responses detected among these three patients was not due to differences in persistence of infused donor cells.

Follicular CD8 T cells accumulate in HIV infection and can kill infected cells in vitro via bispecific antibodies

Cytolytic CD8 T cells play a crucial role in the control and elimination of virus-infected cells and are a major focus of HIV cure efforts. However, it has been shown that HIV-specific CD8 T cells are infrequently found within germinal centers (GCs), a predominant site of active and latent HIV infection. We demonstrate that HIV infection induces marked changes in the phenotype, frequency, and localization of CD8 T cells within the lymph node (LN). Significantly increased frequencies of CD8 T cells in the B cell follicles and GCs were found in LNs from treated and untreated HIV-infected individuals. This profile was associated with persistent local immune activation but did not appear to be directly related to local viral replication. Follicular CD8 (fCD8) T cells, despite compromised cytokine polyfunctionality, showed good cytolytic potential characterized by high ex vivo expression of granzyme B and perforin. We used an anti-HIV/anti-CD3 bispecific antibody in a redirected killing assay and found that fCD8 T cells had better killing activity than did non-fCD8 T cells. Our results indicate that CD8 T cells with potent cytolytic activity are recruited to GCs during HIV infection and, if appropriately redirected to kill HIV-infected cells, could be an effective component of an HIV cure strategy.

Tissue Dimensionality Influences the Functional Response of Cytotoxic T Lymphocyte-Mediated Killing of Targets

Cytotoxic T lymphocyte (CTL)-mediated killing of virus infections and tumors occurs over a wide range of conditions. The spatial environments in which CTLs encounter target cells vary from narrow vessels, to two-dimensional epithelial tissues, to densely populated 3-dimensional (3D) T cell areas within lymphoid tissues. How such spatial environments alter the functional response of CTL-mediated killing, i.e., how the killing efficiency depends on cell densities, is unclear. In this study, we perform cellular Potts model simulations in different spatial configurations to investigate how the dimensionality of the space affects the functional response of CTL-mediated killing. Irrespective of the spatial configuration, the function with separate saturation constants for CTL and for target cell densities that we previously proposed can in all cases describe the response, demonstrating its generality. However, the tissue dimensionality determines at which cell densities the killing rate starts to saturate. We show that saturation in a fully 3D environment is stronger than in a "flat" 3D environment, which is largely due to accompanying differences in the CTL-target encounter rates.

T-cell therapies for HIV: Preclinical successes and current clinical strategies

Although antiretroviral therapy (ART) has been successful in controlling HIV infection, it does not provide a permanent cure, requires lifelong treatment, and HIV-positive individuals are left with social concerns such as stigma. The recent application of T cells to treat cancer and viral reactivations post-transplant offers a potential strategy to control HIV infection. It is known that naturally occurring HIV-specific T cells can inhibit HIV initially, but this response is not sustained in the majority of people living with HIV. Genetically modifying T cells to target HIV, resist infection, and persist in the immunosuppressive environment found in chronically infected HIV-positive individuals might provide a therapeutic solution for HIV. This review focuses on successful preclinical studies and current clinical strategies using T-cell therapy to control HIV infection and mediate a functional cure solution.

B Cells Loaded with Synthetic Particulate Antigens: A Versatile Platform To Generate Antigen-Specific Helper T Cells for Cell Therapy

Adoptive cell therapy represents a promising approach for several chronic diseases. This study describes an innovative strategy for biofunctionalization of nanoparticles, allowing the generation of synthetic particulate antigens (SPAg). SPAg activate polyclonal B cells and vectorize noncognate proteins into their endosomes, generating highly efficient stimulators for ex vivo expansion of antigen-specific CD4+ T cells. This method also allows harnessing the ability of B cells to polarize CD4+ T cells into effectors or regulators.

HIV-specific CD8⁺ T cells and HIV eradication

After the success of combination antiretroviral therapy (cART) to treat HIV infection, the next great frontier is to cure infected persons, a formidable challenge. HIV persists in a quiescent state in resting CD4+ T cells, where the replicative enzymes targeted by cART are not active. Although low levels of HIV transcripts are detectable in these resting cells, little to no viral protein is produced, rendering this reservoir difficult to detect by the host CD8+ T cell response. However, recent advances suggest that this state of latency might be pharmacologically reversed, resulting in viral protein expression without the adverse effects of massive cellular activation. Emerging data suggest that with this approach, infected cells will not die of viral cytopathic effects, but might be eliminated if HIV-specific CD8+ T cells can be effectively harnessed. Here, we address the antiviral properties of HIV-specific CD8+ T cells and how these cells might be harnessed to greater effect toward achieving viral eradication or a functional cure.

Challenges and Opportunities for T-Cell-Mediated Strategies to Eliminate HIV Reservoirs

HIV's ability to establish latent reservoirs of reactivation-competent virus is the major barrier to cure. "Shock and kill" methods consisting of latency-reversing agents (LRAs) followed by elimination of reactivating cells through cytopathic effects are under active development. However, the clinical efficacy of LRAs remains to be established. Moreover, recent studies indicate that reservoirs may not be reduced efficiently by either viral cytopathic or CD8(+) T-cell-mediated mechanisms. In this perspective, we highlight challenges to T-cell-mediated elimination of HIV reservoirs, including characteristics of responding T cells, aspects of the cellular reservoirs, and properties of the latent virus itself. We also discuss potential strategies to overcome these challenges by targeting the antiviral activity of T cells toward appropriate viral antigens following latency.

What do mathematical models tell us about killing rates during HIV-1 infection?

Over the past few decades the extent to which cytotoxic T lymphocytes (CTLs) control human immunodeficiency virus (HIV) replication has been studied extensively, yet their role and mode of action remain controversial. In some studies, CTLs were found to kill a large fraction of the productively infected cells relative to the viral cytopathicity, whereas in others CTLs were suggested to kill only a small fraction of infected cells. In this review, we compile published estimates of CTL-mediated death rates, and examine whether these studies permit determining the rate at which CTLs kill HIV-1 infected cells. We highlight potential misinterpretations of the CTL-killing rates from the escape rates of mutants, and from perturbations of the steady state viral load during chronic infection. Our major conclusion is that CTL-mediated killing rates remain unknown. But contrary to current consensus, we argue that killing rates higher than one per day are perfectly consistent with the experimental data, which would imply that the majority of the productively infected cells could still die from CTL-mediated killing rather than from viral cytopathicity.

Engineering T Cells to Functionally Cure HIV-1 Infection

Despite the ability of antiretroviral therapy to minimize human immunodeficiency virus type 1 (HIV-1) replication and increase the duration and quality of patients' lives, the health consequences and financial burden associated with the lifelong treatment regimen render a permanent cure highly attractive. Although T cells play an important role in controlling virus replication, they are themselves targets of HIV-mediated destruction. Direct genetic manipulation of T cells for adoptive cellular therapies could facilitate a functional cure by generating HIV-1-resistant cells, redirecting HIV-1-specific immune responses, or a combination of the two strategies. In contrast to a vaccine approach, which relies on the production and priming of HIV-1-specific lymphocytes within a patient's own body, adoptive T-cell therapy provides an opportunity to customize the therapeutic T cells prior to administration. However, at present, it is unclear how to best engineer T cells so that sustained control over HIV-1 replication can be achieved in the absence of antiretrovirals. This review focuses on T-cell gene-engineering and gene-editing strategies that have been performed in efforts to inhibit HIV-1 replication and highlights the requirements for a successful gene therapy-mediated functional cure.

Broadly-specific cytotoxic T cells targeting multiple HIV antigens are expanded from HIV+ patients: implications for immunotherapy

Antiretroviral therapy (ART) is unable to eradicate human immunodeficiency virus type 1 (HIV-1) infection. Therefore, there is an urgent need to develop novel therapies for this disease to augment anti-HIV immunity. T cell therapy is appealing in this regard as T cells have the ability to proliferate, migrate, and their antigen specificity reduces the possibility of off-target effects. However, past human studies in HIV-1 infection that administered T cells with limited specificity failed to provide ART-independent, long-term viral control. In this study, we sought to expand functional, broadly-specific cytotoxic T cells (HXTCs) from HIV-infected patients on suppressive ART as a first step toward developing cellular therapies for implementation in future HIV eradication protocols. Blood samples from seven HIV+ patients on suppressive ART were used to derive HXTCs. Multiantigen specificity was achieved by coculturing T cells with antigen-presenting cells pulsed with peptides representing Gag, Pol, and Nef. All but two lines were multispecific for all three antigens. HXTCs demonstrated efficacy as shown by release of proinflammatory cytokines, specific lysis of antigen-pulsed targets, and the ability to suppress HIV replication in vitro. In conclusion, we are able to generate broadly-specific cytotoxic T cell lines that simultaneously target multiple HIV antigens and show robust antiviral function.

Compartmentalization of simian immunodeficiency virus replication within secondary lymphoid tissues of rhesus macaques is linked to disease stage and inversely related to localization of virus-specific CTL

We previously demonstrated that HIV replication is concentrated in lymph node B cell follicles during chronic infection and that HIV-specific CTL fail to accumulate in large numbers at those sites. It is unknown whether these observations can be generalized to other secondary lymphoid tissues or whether virus compartmentalization occurs in the absence of CTL. We evaluated these questions in SIVmac239-infected rhesus macaques by quantifying SIV RNA(+) cells and SIV-specific CTL in situ in spleen, lymph nodes, and intestinal tissues obtained at several stages of infection. During chronic asymptomatic infection prior to simian AIDS, SIV-producing cells were more concentrated in follicular (F) compared with extrafollicular (EF) regions of secondary lymphoid tissues. At day 14 of infection, when CTL have minimal impact on virus replication, there was no compartmentalization of SIV-producing cells. Virus compartmentalization was diminished in animals with simian AIDS, which often have low-frequency CTL responses. SIV-specific CTL were consistently more concentrated within EF regions of lymph node and spleen in chronically infected animals regardless of epitope specificity. Frequencies of SIV-specific CTL within F and EF compartments predicted SIV RNA(+) cells within these compartments in a mixed model. Few SIV-specific CTL expressed the F homing molecule CXCR5 in the absence of the EF retention molecule CCR7, possibly accounting for the paucity of F CTL. These findings bolster the hypothesis that B cell follicles are immune privileged sites and suggest that strategies to augment CTL in B cell follicles could lead to improved viral control and possibly a functional cure for HIV infection.

The route of HIV escape from immune response targeting multiple sites is determined by the cost-benefit tradeoff of escape mutations

Cytotoxic T lymphocytes (CTL) are a major factor in the control of HIV replication. CTL arise in acute infection, causing escape mutations to spread rapidly through the population of infected cells. As a result, the virus develops partial resistance to the immune response. The factors controlling the order of mutating epitope sites are currently unknown and would provide a valuable tool for predicting conserved epitopes. In this work, we adapt a well-established mathematical model of HIV evolution under dynamical selection pressure from multiple CTL clones to include partial impairment of CTL recognition, , as well as cost to viral replication, . The process of escape is described in terms of the cost-benefit tradeoff of escape mutations and predicts a trajectory in the cost-benefit plane connecting sequentially escaped sites, which moves from high recognition loss/low fitness cost to low recognition loss/high fitness cost and has a larger slope for early escapes than for late escapes. The slope of the trajectory offers an interpretation of positive correlation between fitness costs and HLA binding impairment to HLA-A molecules and a protective subset of HLA-B molecules that was observed for clinically relevant escape mutations in the Pol gene. We estimate the value of from published experimental studies to be in the range (0.01–0.86) and show that the assumption of complete recognition loss () leads to an overestimate of mutation cost. Our analysis offers a consistent interpretation of the commonly observed pattern of escape, in which several escape mutations are observed transiently in an epitope. This non-nested pattern is a combined effect of temporal changes in selection pressure and partial recognition loss. We conclude that partial recognition loss is as important as fitness loss for predicting the order of escapes and, ultimately, for predicting conserved epitopes that can be targeted by vaccines.

Like many viruses, HIV has evolved mechanisms to evade the host immune response. As early as a few weeks after infection is initiated, mutations appear in the viral genome that reduce the ability of cytotoxic T lymphocytes (CTL) to control virus replication. However, of the many mutations in the viral genome that could potentially mediate viral escape from the CTL response, a specific subset are typically observed. This suggests that some mutations either entail too high a fitness cost for the virus, or are relatively inefficient escape mutations. A successful vaccine would target the CTL response to these regions in such a way that escape would not be possible. We use a computational model of HIV infection in order to study the factors that determine whether a given escape mutation will occur, how long it will be maintained in the population, and how these changes in the viral genome will affect the CTL response. Our analysis highlights the important role of partial recognition loss conferred by a mutation in producing the complex dynamics of escape that are observed during the course of infection.

Expansion of dysfunctional Tim-3-expressing effector memory CD8+ T cells during simian immunodeficiency virus infection in rhesus macaques

The T cell Ig- and mucin domain-containing molecule-3 (Tim-3) negative immune checkpoint receptor demarcates functionally exhausted CD8(+) T cells arising from chronic stimulation in viral infections like HIV. Tim-3 blockade leads to improved antiviral CD8(+) T cell responses in vitro and, therefore, represents a novel intervention strategy to restore T cell function in vivo and protect from disease progression. However, the Tim-3 pathway in the physiologically relevant rhesus macaque SIV model of AIDS remains uncharacterized. We report that Tim-3(+)CD8(+) T cell frequencies are significantly increased in lymph nodes, but not in peripheral blood, in SIV-infected animals. Tim-3(+)PD-1(+)CD8(+) T cells are similarly increased during SIV infection and positively correlate with SIV plasma viremia. Tim-3 expression was found primarily on effector memory CD8(+) T cells in all tissues examined. Tim-3(+)CD8(+) T cells have lower Ki-67 content and minimal cytokine responses to SIV compared with Tim-3(-)CD8(+) T cells. During acute-phase SIV replication, Tim-3 expression peaked on SIV-specific CD8(+) T cells by 2 wk postinfection and then rapidly diminished, irrespective of mutational escape of cognate Ag, suggesting non-TCR-driven mechanisms for Tim-3 expression. Thus, rhesus Tim-3 in SIV infection partially mimics human Tim-3 in HIV infection and may serve as a novel model for targeted studies focused on rejuvenating HIV-specific CD8(+) T cell responses.

Rates of CTL killing in persistent viral infection in vivo

The CD8⁺ cytotoxic T lymphocyte (CTL) response is an important defence against viral invasion. Although CTL-mediated cytotoxicity has been widely studied for many years, the rate at which virus-infected cells are killed in vivo by the CTL response is poorly understood. To date the rate of CTL killing in vivo has been estimated for three virus infections but the estimates differ considerably, and killing of HIV-1-infected cells was unexpectedly low. This raises questions about the typical anti-viral capability of CTL and whether CTL killing is abnormally low in HIV-1. We estimated the rate of killing of infected cells by CD8⁺ T cells in two distinct persistent virus infections: sheep infected with Bovine Leukemia Virus (BLV) and humans infected with Human T Lymphotropic Virus type 1 (HTLV-1) which together with existing data allows us to study a total of five viruses in parallel. Although both BLV and HTLV-1 infection are characterised by large expansions of chronically activated CTL with immediate effector function ex vivo and no evidence of overt immune suppression, our estimates are at the lower end of the reported range. This enables us to put current estimates into perspective and shows that CTL killing of HIV-infected cells may not be atypically low. The estimates at the higher end of the range are obtained in more manipulated systems and may thus represent the potential rather than the realised CTL efficiency.

Virus replication is countered by a range of innate and adaptive host defences. One important and widely studied adaptive defence is the CD8⁺ cytotoxic T lymphocyte (CTL) response. Quantification of the in vivo lytic capability of CTLs is essential for a detailed understanding of the immune response. This includes understanding the balance between viral replication and viral clearance, understanding the rate limiting steps in CTL killing and thus how killing can be increased and understanding the failure of CTL vaccines. However, the typical rate at which virus-infected cells are killed by the CTL response in vivo is poorly understood. Current estimates differ considerably and are especially low for HIV-1-infection. We estimated the rate of killing of infected cells by CD8⁺ T cells in two distinct persistent virus infections which enables us to put current estimates into perspective. We show that CTL killing of HIV-infected cells may not be atypically low. The estimates at the higher end of the range are obtained in more manipulated systems and may thus represent the potential rather than the realised CTL efficiency.

CD4 T-cell immunotherapy for chronic viral infections and cancer

During chronic infections and cancer, T cells progressively lose function and become exhausted. However, effective T-cell responses are necessary to ultimately control viral infections and tumors. Hence, strategies that either restore endogenous immune responses or provide functional T cells by adoptive immunotherapy need to be explored. CD8 T cells play a prominent role in viral infections, as well as cancer, but CD4 T cells are necessary to support CD8 T-cell function. In addition, CD4 T cells exert direct effector functions, induce optimal B-cell responses and orchestrate innate immunity. Therefore, we propose that adoptive transfer strategies should exploit CD4 T cells alone or in combination with CD8 T cells, for the treatment of chronic infections and cancer. Furthermore, since adoptively transferred cells are subject to exhaustion, combining adoptive transfer therapy with immunotherapies that inhibit T-cell exhaustion should maximize the longevity and success rate of responses.

T-Cell Signaling in HIV-1 Infection

HIV exploits the T-cell signaling network to gain access to downstream cellular components, which serves as effective tools to break the cellular barriers. Multiple host factors and their interaction with viral proteins contribute to the complexity of HIV-1 pathogenesis and disease progression. HIV-1 proteins gp120, Nef, Tat and Vpr alter the T-cell signaling pathways by activating multiple transcription factors including NF-ĸB, Sp1 and AP-1. HIV-1 evades the immune system by developing a multi-pronged strategy. Additionally, HIV-1 encoded proteins influence the apoptosis in the host cell favoring or blocking T-cell apoptosis. Thus, T-cell signaling hijacked by viral proteins accounts for both viral persistence and immune suppression during HIV-1 infection. Here, we summarize past and present studies on HIV-1 T-cell signaling with special focus on the possible role of T cells in facilitating viral infection and pathogenesis

HLA-F and MHC-I open conformers cooperate in a MHC-I antigen cross-presentation pathway

Peptides that are presented by MHC class I (MHC-I) are processed from two potential sources, as follows: newly synthesized endogenous proteins for direct presentation on the surface of most nucleated cells and exogenous proteins for cross-presentation typically by professional APCs. In this study, we present data that implicate the nonclassical HLA-F and open conformers of MHC-I expressed on activated cells in a pathway for the presentation of exogenous proteins by MHC-I. This pathway is distinguished from the conventional endogenous pathway by its independence from TAP and tapasin and its sensitivity to inhibitors of lysosomal enzymes, and further distinguished by its dependence on MHC-I allotype-specific epitope recognition for Ag uptake. Thus, our data from in vitro experiments collectively support a previously unrecognized model of Ag cross-presentation mediated by HLA-F and MHC-I open conformers on activated lymphocytes and monocytes, which may significantly contribute to the regulation of immune system functions and the immune defense.

Human Mycobacterium tuberculosis CD8 T Cell Antigens/Epitopes Identified by a Proteomic Peptide Library

Identification of CD8⁺ T cell antigens/epitopes expressed by human pathogens with large genomes is especially challenging, yet necessary for vaccine development. Immunity to tuberculosis, a leading cause of mortality worldwide, requires CD8⁺ T cell immunity, yet the repertoire of CD8 antigens/epitopes remains undefined. We used integrated computational and proteomic approaches to screen 10% of the Mycobacterium tuberculosis (Mtb) proteome for CD8 Mtb antigens. We designed a weighting schema based upon a Multiple Attribute Decision Making:framework to select 10% of the Mtb proteome with a high probability of containing CD8⁺ T cell epitopes. We created a synthetic peptide library consisting of 15-mers overlapping by 11 aa. Using the interferon-γ ELISPOT assay and Mtb-infected dendritic cells as antigen presenting cells, we screened Mtb-specific CD8⁺ T cell clones restricted by classical MHC class I molecules (MHC class Ia molecules), that were isolated from Mtb-infected humans, against this library. Three novel CD8 antigens were unambiguously identified: the EsxJ family (Rv1038c, Rv1197, Rv3620c, Rv2347c, Rv1792), PE9 (Rv1088), and PE_PGRS42 (Rv2487c). The epitopes are B5701-restricted EsxJ_24–34, B3905-restricted PE9_53–67, and B3514-restricted PE_PGRS42_48–56, respectively. The utility of peptide libraries in identifying unknown epitopes recognized by classically restricted CD8⁺ T cells was confirmed, which can be applied to other intracellular pathogens with large size genomes. In addition, we identified three novel Mtb epitopes/antigens that may be evaluated for inclusion in vaccines and/or diagnostics for tuberculosis.

Generation of rejuvenated antigen-specific T cells by reprogramming to pluripotency and redifferentiation

Adoptive immunotherapy with functional T cells is potentially an effective therapeutic strategy for combating many types of cancer and viral infection. However, exhaustion of antigen-specific T cells represents a major challenge to this type of approach. In an effort to overcome this problem, we reprogrammed clonally expanded antigen-specific CD8(+) T cells from an HIV-1-infected patient to pluripotency. The T cell-derived induced pluripotent stem cells were then redifferentiated into CD8(+) T cells that had a high proliferative capacity and elongated telomeres. These "rejuvenated" cells possessed antigen-specific killing activity and exhibited T cell receptor gene-rearrangement patterns identical to those of the original T cell clone from the patient. We also found that this method can be effective for generating specific T cells for other pathology-associated antigens. Thus, this type of approach may have broad applications in the field of adoptive immunotherapy.

Development of CD8+ T cells expressing two distinct receptors specific for MTB and HIV-1 peptides

The immune response in individuals co-infected with Mycobacterium tuberculosis (MTB) and the human immunodeficiency virus (MTB/HIV) gradually deteriorates, particularly in the cellular compartment. Adoptive transfer of functional effector T cells can confer protective immunity to immunodeficient MTB/HIV co-infected recipients. However, few such effector T cells exist in vivo, and their isolation and amplification to sufficient numbers is difficult. Therefore, enhancing immune responses against both pathogens is critical for treating MTB/HIV co-infected patients. One approach is adoptive transfer of T cell receptor (TCR) gene-modified T cells for the treatment of MTB/HIV co-infections because lymphocyte numbers and their functional avidity is significantly increased by TCR gene transfer. To generate bispecific CD8⁺ T cells, MTB Ag85B_199–207 peptide-specific TCRs (MTB/TCR) and HIV-1 Env_120–128 peptide-specific TCRs (HIV/TCR) were isolated and introduced into CD8⁺ T cells simultaneously using a retroviral vector. To avoid mispairing among exogenous and endogenous TCRs, and to improve the function and stability of the introduced TCRs, several strategies were employed, including introducing mutations in the MTB/TCR constant (C) regions, substituting part of the HIV/TCR C regions with CD3ζ, and linking gene segments with three different 2A peptides. Results presented in this report suggest that the engineered T cells possessed peptide-specific specificity resulting in cytokine production and cytotoxic activity. This is the first report describing the generation of engineered T cells specific for two different pathogens and provides new insights into TCR gene therapy for the treatment of immunocompromised MTB/HIV co-infected patients.

Adoptive transfer of lymphocytes isolated from simian immunodeficiency virus SIVmac239Δnef-vaccinated macaques does not affect acute-phase viral loads but may reduce chronic-phase viral loads in major histocompatibility complex-matched recipients

The live attenuated simian immunodeficiency virus (SIV) SIVmac239Δnef is the most effective SIV/human immunodeficiency virus (HIV) vaccine in preclinical testing. An understanding of the mechanisms responsible for protection may provide important insights for the development of HIV vaccines. Leveraging the uniquely restricted genetic diversity of Mauritian cynomolgus macaques, we performed adoptive transfers between major histocompatibility complex (MHC)-matched animals to assess the role of cellular immunity in SIVmac239Δnef protection. We vaccinated and mock vaccinated donor macaques and then harvested between 1.25 × 10(9) and 3.0 × 10(9) mononuclear cells from multiple tissues for transfer into 12 naive recipients, followed by challenge with pathogenic SIVmac239. Fluorescently labeled donor cells were detectable for at least 7 days posttransfer and trafficked to multiple tissues, including lung, lymph nodes, and other mucosal tissues. There was no difference between recipient macaques' peak or postpeak plasma viral loads. A very modest difference in viral loads during the chronic phase between vaccinated animal cell recipients and mock-vaccinated animal cell recipients did not reach significance (P = 0.12). Interestingly, the SIVmac239 challenge virus accumulated escape mutations more rapidly in animals that received cells from vaccinated donors. These results may suggest that adoptive transfers influenced the course of infection despite the lack of significant differences in the viral loads among animals that received cells from vaccinated and mock-vaccinated donor animals.