Levels of antigen processing machinery components in dendritic cells generated for vaccination of HIV-1+ subjects

Programming T cell Killers for an HIV Cure: Teach the New Dogs New Tricks and Let the Sleeping Dogs Lie

Despite the success of combination antiretroviral therapy (cART), a latent viral reservoir persists in HIV-1-infected persons. Unfortunately, endogenous cytotoxic T lymphocytes (CTLs) are unable to control viral rebound when patients are removed from cART. A "kick and kill" strategy has been proposed to eradicate this reservoir, whereby infected T cells are induced to express viral proteins via latency-inducing drugs followed by their elimination by CTLs. It has yet to be determined if stimulation of existing HIV-1-specific CTL will be sufficient, or if new CTLs should be primed from naïve T cells. In this review, we propose that dendritic cells (DCs), the most potent antigen presenting cells, act as dog trainers and can induce T cells (the dogs) to do magnificent tricks. We propose the hypothesis that an HIV-1 cure will require targeting of naïve T cells and will necessitate "teaching new dogs new tricks" while avoiding activation of potentially dysfunctional endogenous memory CTLs (letting the sleeping dogs lie).

Dendritic cells restore CD8+ T cell reactivity to autologous HIV-1

Recall T cell responses to HIV-1 antigens are used as a surrogate for endogenous cellular immune responses generated during infection. Current methods of identifying antigen-specific T cell reactivity in HIV-1 infection use bulk peripheral blood mononuclear cells (PBMC) yet ignore professional antigen-presenting cells (APC) that could reveal otherwise hidden responses. In the present study, peptides representing autologous variants of major histocompatibility complex (MHC) class I-restricted epitopes from HIV-1 Gag and Env were used as antigens in gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) and polyfunctional cytokine assays. Here we show that dendritic cells (DC) enhanced T cell reactivity at all stages of disease progression but specifically restored T cell reactivity after combination antiretroviral therapy (cART) to early infection levels. Type 1 cytokine secretion was also enhanced by DC and was most apparent late post-cART. We additionally show that DC reveal polyfunctional T cell responses after many years of treatment, when potential immunotherapies would be implemented. These data underscore the potential efficacy of DC immunotherapy that aims to awaken a dormant, autologous, HIV-1-specific CD8+ T cell response.

IMPORTANCE

Assessment of endogenous HIV-1-specific T cell responses is critical for generating immunotherapies for subjects on cART. Current assays ignore the ability of dendritic cells to reveal these responses and may therefore underestimate the breadth and magnitude of T cell reactivity. As DC do not prime new responses in these assays, it can be assumed that the observed responses are not detected without appropriate stimulation. This is important because dogma states that HIV-1 mutates to evade host recognition and that CD8+ cytotoxic T lymphocyte (CTL) failure is due to the inability of T cells to recognize the autologous virus. The results presented here indicate that responses to autologous virus are generated during infection but may need additional stimulation to be effective. Detecting the breadth and magnitude of HIV-1-specific T cell reactivity generated in vivo is of the utmost importance for generating effective DC immunotherapies.

Generation and immunosuppressive functions of p53-induced human adaptive regulatory T cells

Inducible regulatory T cells (iTregs, also called Tr1 cells) are generated in the periphery (circulation or tissue) of cancer patients upon the encounter of naïve CD4⁺ T cells with tumor-associated antigens. As p53 is often inactivated by genetic or epigenetic events during oncogenesis, p53-induced Tr1 cells might play a key role in establishing immunosuppressive networks in cancer patients. Tr1 cells were generated by co-culturing circulating CD4⁺CD25⁻ T cells with autologous immature dendritic cells pulsed with a wild-type (WT) p53-derived peptide or an unrelated peptide derived from mucin 1 (MUC1). The Tr1 phenotype and the specificity for p53 of these cells were confirmed by multicolor flow cytometry. Moreover, the Tr1 cell-mediated suppression of T-cell proliferation was evaluated by CFSE-based flow cytometry, while their ability to alter the T-cell cytokine profile by ELISA and Luminex assays. The capacity of p53-induced Tr1 cells to suppress the generation and function of cytotoxic T lymphcoytes (CTLs) was assessed by flow cytometry and ELISPOT. Of note, low doses of the p53-derived peptide (p53_low) induced greater numbers of Tr1 cells than the same peptide employed at high doses (p53_high). Moreover, Tr1/p53_low cells not secreted higher levels of interleukin-10 and transforming growth factor β1, but also mediated more robust suppressive effects on CTL proliferation than Tr1/p53_high cells. Tr1/p53_low cells, Tr1/p53_high cells, as well as Tr1 cells generated with low doses of an unrelated MUC1-derived peptide were equally effective in suppressing the expansion and antitumor activity of p53-reactive CTLs. p53_low induced the expansion of highly suppressive p53-reactive Tr1 cells. However, the capacity of these Tr1 cells to suppress the generation and function of p53-reactive CTLs was independent of their antigen-specificity.

Challenges in dendritic cells-based therapeutic vaccination in HIV-1 infection Workshop in dendritic cell-based vaccine clinical trials in HIV-1

Therapeutic immunization has been proposed as an approach that might help limit the need for lifelong combined antiretroviral therapy (cART). One approach for therapeutic vaccination which has been explored during the last few years is the administration of autologous monocyte-derived DCs (MD-DCs) loaded ex vivo with a variety of antigens. It has been shown in experimental murine models as well as in cancer patients and in patients with chronic infections that this approach can induce and potentiate antigen-specific T-cell response (and to induce a potent protective immunity). Contrary to the wide experience with this strategy in cancer, in HIV-1 infection the experience is limited and the design of the clinical trials varies greatly between groups. This variability affects all the steps of the process, from preparation of immunogen and DCs to clinical trial design and immune monitoring. Although both the study designs and the DC preparation (the maturation stimuli and the identity and source of HIV-1 antigens used to pulse DCs) varied in most of the studies that were published so far, overall the results indicate that DC immunotherapy elicits some degree of immunological response. To address this situation and to allow comparison between trials a panel of experts working in DC-based clinical trials in HIV-1 infection met in Barcelona at the end of 2010. During this meeting, the participants shared the data of their current research activities in this field in order to unify criteria for the future. This report summarizes the present situation of the field and the discussions and conclusions of this meeting.

Production of a dendritic cell-based vaccine containing inactivated autologous virus for therapy of patients with chronic human immunodeficiency virus type 1 infection

In preparation for a pilot clinical trial in patients with chronic human immunodeficiency virus type 1 (HIV-1) infection, a novel dendritic cell (DC)-based vaccine is being manufactured. The trial will test the hypothesis that isolated endogenous virus presented by DCs serves as a potent immunogen for activation of CD8(+) and CD4(+) T cells specific for a broad range of autologous HIV-1 antigens. Production of the vaccine under good manufacture practice conditions involves (i) autologous virus isolation; (ii) superinfection of CD4(+) T cells with the virus; (iii) inactivation of the virus in CD4(+) T cells, T-cell apoptosis, and coincubation of T cells with autologous DCs; and (iv) product testing and release. Endogenous virus was isolated from peripheral blood-derived CD4(+) T cells of three HIV-1-positive subjects by coincubation with autologous OKT-3-stimulated CD4(+) T cells. CD4(+) T-cell supernatants were tested for p24 levels by enzyme-linked immunosorbent assay (>25 ng/ml) and for the 50% tissue culture infective doses (TCID(50); which ranged from 4,642 to 46,416/ml on day 19 of culture). Autologous CD4(+) T cells that were separated on immunobeads (>95% purity) and superinfected with virus-expressed p24 (28 to 54%) had TCID(50) of >400/ml on days 5 to 10. Virus inactivation with psoralen (20 microg/ml) and UVB irradiation (312 nm) reduced the TCID(50) of the supernatants from 199,986 to 11/ml (>99%). 7-Amino-actinomycin D-positive, annexin V-positive CD4(+) T cells were fed to autologous DCs generated by using the Elutra cell separation system and the Aastrom system. Flow analysis showed that DC loading was complete in 24 h. On the basis of these translational results and experience with the generation of DCs from HIV-1-infected patients in a previous clinical trial, the Investigational New Drug application for clinical vaccination was submitted and approved by the FDA (application no. BB-IND-13137).

Regulation of antigen presentation machinery in human dendritic cells by recombinant adenovirus

Recombinant adenoviral vectors (AdV) are potent vehicles for antigen engineering of dendritic cells (DC). DC engineered with AdV to express full length tumor antigens are capable stimulators of antigen-specific polyclonal CD8+ and CD4+ T cells. To determine the impact of AdV on the HLA class I antigen presentation pathway, we investigated the effects of AdV transduction on antigen processing machinery (APM) components in human DC. Interactions among AdV transduction, maturation, APM regulation and T cell activation were investigated. The phenotype and cytokine profile of DC transduced with AdV was intermediate, between immature (iDC) and matured DC (mDC). Statistically significant increases in expression were observed for peptide transporters TAP-1 and TAP-2, and HLA class I peptide-loading chaperone ERp57, as well as co-stimulatory surface molecule CD86 due to AdV transduction. AdV transduction enhanced the expression of APM components and surface markers on mDC, and these changes were further modulated by the timing of DC maturation. Engineering of matured DC to express a tumor-associated antigen stimulated a broader repertoire of CD8+ T cells, capable of recognizing immunodominant and subdominant epitopes. These data identify molecular changes in AdV-transduced DC (AdV/DC) that could influence T cell priming and should be considered in design of cancer vaccines.

Dendritic cell-based human immunodeficiency virus vaccine

Dendritic cells (DC) have profound abilities to induce and coordinate T-cell immunity. This makes them ideal biological agents for use in immunotherapeutic strategies to augment T-cell immunity to HIV infection. Current clinical trials are administering DC-HIV antigen preparations carried out ex vivo as proof of principle that DC immunotherapy is safe and efficacious in HIV-infected patients. These trials are largely dependent on preclinical studies that will provide knowledge and guidance about the types of DC, form of HIV antigen, method of DC maturation, route of DC administration, measures of anti-HIV immune function and ultimately control of HIV replication. Additionally, promising immunotherapy approaches are being developed based on targeting of DC with HIV antigens in vivo. The objective is to define a safe and effective strategy for enhancing control of HIV infection in patients undergoing antiretroviral therapy.

Therapeutic immunization with human immunodeficiency virus type 1 (HIV-1) peptide-loaded dendritic cells is safe and induces immunogenicity in HIV-1-infected individuals

Treatments for human immunodeficiency virus type 1 (HIV-1)-positive individuals that augment HIV-1 suppression and have potential for achieving long-term control of HIV-1 viremia in the absence of antiretroviral therapy (ART) are urgently needed. We therefore conducted a phase I, clinical safety trial of a dendritic cell (DC)-based vaccination strategy as immunotherapy for HIV-1-positive individuals on ART. We studied 18 HIV-1-positive subjects on ART who underwent leukapheresis to obtain peripheral blood mononuclear cells for DC generation from monocytes cultured with cytokines. Mature DC were pulsed with three HIV-1 HLA*A0201 Gag, Env, and Pol peptides and one influenza A virus matrix protein peptide. The vaccine was administered to donors randomized to receive two vaccinations, either intravenously or subcutaneously. The primary end points were safety and tolerability of two doses of peptide-DC vaccine (3 million versus 10 million). Secondary end points included gamma interferon (IFN-gamma) enzyme-linked immunospot assay responses and clinical correlates of an immune response to vaccination. Autologous DC-peptide vaccine was safe, well tolerated, and feasible for use in all participants. Adverse events were rare. Although the trial was not powered to assess an immunologic response, a significantly increased frequency of HIV-1 peptide-specific IFN-gamma-positive cells was observed 2 weeks following the second vaccine, with three individuals responding to all four peptides. DC vaccination was safe, was feasible, and showed promise of immunogenicity in ART-treated, HIV-1-positive individuals. Additional studies of DC immunization strategies for HIV-1 infection are warranted.