Rachel Lubong Sabado

Evidence of dysregulation of dendritic cells in primary HIV infection

Myeloid and plasmacytoid dendritic cells (DCs) are important mediators of both innate and adaptive immunity against pathogens such as HIV. During the course of HIV infection, blood DC numbers fall substantially. In the present study, we sought to determine how early in HIV infection the reduction occurs and whether the remaining DC subsets maintain functional capacity. We find that both myeloid DC and plasmacytoid DC levels decline very early during acute HIV infection. Despite the initial reduction in numbers, those DCs that remain in circulation retain their function and are able to stimulate allogeneic T-cell responses, and up-regulate maturation markers plus produce cytokines/chemokines in response to stimulation with TLR7/8 agonists. Notably, DCs from HIV-infected subjects produced significantly higher levels of cytokines/chemokines in response to stimulation with TLR7/8 agonists than DCs from uninfected controls. Further examination of gene expression profiles indicated in vivo activation, either directly or indirectly, of DCs during HIV infection. Taken together, our data demonstrate that despite the reduction in circulating DC numbers, those that remain in the blood display hyperfunctionality and implicates a possible role for DCs in promoting chronic immune activation.

Spatiotemporal trafficking of HIV in human plasmacytoid dendritic cells defines a persistently IFN-α–producing and partially matured phenotype

Plasmacytoid DCs (pDCs) are innate immune cells that are specialized to produce IFN-α and to activate adaptive immune responses. Although IFN-α inhibits HIV-1 replication in vitro, the production of IFN-α by HIV-activated pDCs in vivo may contribute more to HIV pathogenesis than to protection. We have now shown that HIV-stimulated human pDCs allow for persistent IFN-α production upon repeated stimulation, express low levels of maturation molecules, and stimulate weak T cell responses. Persistent IFN-α production by HIV-stimulated pDCs correlated with increased levels of IRF7 and was dependent upon the autocrine IFN-α/β receptor feedback loop. Because it has been shown that early endosomal trafficking of TLR9 agonists causes strong activation of the IFN-α pathway but weak activation of the NF-κB pathway, we sought to investigate whether early endosomal trafficking of HIV, a TLR7 agonist, leads to the IFN-α-producing phenotype we observed. We demonstrated that HIV preferentially traffics to the early endosome in human pDCs and therefore skews pDCs toward a partially matured, persistently IFN-α-secreting phenotype.

Directing dendritic cell immunotherapy towards successful cancer treatment

The use of dendritic cells (DCs) for tumor immunotherapy represents a powerful approach for harnessing the patients own immune system to eliminate tumor cells. However, suboptimal conditions for generating potent immunostimulatory DCs, as well as the induction of tolerance and suppression mediated by the tumors and its microenvironment have contributed to limited success. Combining DC vaccines with new approaches that enhance immunogenicity and overcome the regulatory mechanisms underlying peripheral tolerance may be the key to achieving effective and durable anti-tumor immune responses that translate to better clinical outcomes.

Dendritic cell-based immunotherapy

Immunotherapy using dendritic cell (DC)-based vaccination is an approved approach for harnessing the potential of a patients own immune system to eliminate tumor cells in metastatic hormone-refractory cancer. Overall, although many DC vaccines have been tested in the clinic and proven to be immunogenic, and in some cases associated with clinical outcome, there remains no consensus on how to manufacture DC vaccines. In this review we will discuss what has been learned thus far about human DC biology from clinical studies, and how current approaches to apply DC vaccines in the clinic could be improved to enhance anti-tumor immunity.

In vitro priming recapitulates in vivo HIV-1 specific T cell responses, revealing rapid loss of virus reactive CD4+ T cells in acute HIV-1 infection

Background The requirements for priming of HIV-specific T cell responses initially seen in infected individuals remain to be defined. Activation of T cell responses in lymph nodes requires cell-cell contact between T cells and DCs, which can give concurrent activation of T cells and HIV transmission. Methodology The study aim was to establish whether DCs pulsed with HIV-1 could prime HIV-specific T cell responses and to characterize these responses. Both infectious and aldrithiol-2 inactivated noninfectious HIV-1 were compared to establish efficiencies in priming and the type of responses elicited. Findings Our findings show that both infectious and inactivated HIV-1 pulsed DCs can prime HIV-specific responses from naïve T cells. Responses included several CD4+ and CD8+ T cell epitopes shown to be recognized in vivo by acutely and chronically infected individuals and some CD4+ T cell epitopes not identified previously. Follow up studies of acute and recent HIV infected samples revealed that these latter epitopes are among the earliest recognized in vivo, but the responses are lost rapidly, presumably through activation-induced general CD4+ T cell depletion which renders the newly activated HIV-specific CD4+ T cells prime targets for elimination. Conclusion Our studies highlight the ability of DCs to efficiently prime naïve T cells and induce a broad repertoire of HIV-specific responses and also provide valuable insights to the pathogenesis of HIV-1 infection in vivo.

Pathways utilized by dendritic cells for binding, uptake, processing and presentation of antigens derived from HIV-1

The outcome following HIV infection depends on the nature and durability of the HIV‐specific T cell response induced initially. The activation of protective T cell responses depends upon dendritic cells (DC), antigen‐presenting cells which have the capacity to process and present viral antigens. DC pulsed with aldrithiol‐2‐inactivated HIV and delivered in vivo were reported to induce immune responses and promote virologic control in chronically HIV‐1‐infected subjects. To gain an understanding of this phenomenon, we characterized the steps involved in the presentation of antigens derived from aldrithiol‐2‐treated vs. infectious HIV‐1 by DC. Antigen presentation, on both MHC class I and II, was independent of DC‐specific ICAM‐3‐grabbing integrin, DEC‐205 and macrophage mannose receptor, C‐type lectins expressed by the DC. Inhibitor studies showed that presentation on MHC class I was dependent on viral fusion in a CD4/coreceptor‐dependent manner, both at the cell surface and within endosomes, and access to the classical endosomal processing pathway. MHC class II presentation of HIV‐associated antigens was dependent on active endocytosis, probably receptor‐mediated, and subsequent degradation of virions in acidified endosomes in the DC. Our study brings forth new facts regarding the binding, uptake, and processing of chemically inactivated virions leading to efficient antigen presentation and should aid in the design of more effective HIV vaccines.

HIV-1 impairs in vitro priming of naïve T cells and gives rise to contact-dependent suppressor T cells

Priming of T cells in lymphoid tissues of HIV‐infected individuals occurs in the presence of HIV‐1. DC in this milieu activate T cells and disseminate HIV‐1 to newly activated T cells, the outcome of which may have serious implications in the development of optimal antiviral responses. We investigated the effects of HIV‐1 on DC–naïve T‐cell interactions using an allogeneic in vitro system. Our data demonstrate a dramatic decrease in the primary expansion of naïve T cells when cultured with HIV‐1‐exposed DC. CD4+ and CD8+ T cells showed enhanced expression of PD‐1 and TRAIL, whereas CTLA‐4 expression was observed on CD4+ T cells. It is worth noting that T cells primed in the presence of HIV‐1 suppressed priming of other naïve T cells in a contact‐dependent manner. We identified PD‐1, CTLA‐4, and TRAIL pathways as responsible for this suppresion, as blocking these negative molecules restored T‐cell proliferation to a higher degree. In conclusion, the presence of HIV‐1 during DC priming produced cells with inhibitory effects on T‐cell activation and proliferation, i.e. suppressor T cells, a mechanism that could contribute to the enhancement of HIV‐1 pathogenesis.

Dendritic cell immunotherapy

The U.S. Food and Drug Administrations approval of the first cell‐based immunotherapy has rejuvenated interest in the field. Early clinical trials have established the ability of dendritic cell (DC) immunotherapy to exploit a patients own immune system to induce antitumor immune responses. However, suboptimal conditions for generating potent immunostimulatory DCs, in addition to the suppression mediated by the tumor microenvironment, have contributed to limited clinical success in vivo. Therefore, combining DC vaccines with new approaches that enhance immunogenicity and overcome the regulatory mechanisms underlying peripheral tolerance may be key to achieving effective, durable, antitumor immune responses that translate to better clinical outcomes.

Resiquimod as an Immunologic Adjuvant for NY-ESO-1 Protein Vaccination in Patients with High-Risk Melanoma

Sabado, Pavlick, and colleagues show that NY-ESO-1 protein in Montanide with or without topical resiquimod is safe, well-tolerated, and induces antibody and CD4 T-cell responses in most patients, but the addition of topical resiquimod is not sufficient to induce consistent NY-ESO-1–specific CD8 T-cell responses. The Toll-like receptor (TLR) 7/8 agonist resiquimod has been used as an immune adjuvant in cancer vaccines. We evaluated the safety and immunogenicity of the cancer testis antigen NY-ESO-1 given in combination with Montanide (Seppic) with or without resiquimod in patients with high-risk melanoma. In part I of the study, patients received 100 μg of full-length NY-ESO-1 protein emulsified in 1.25 mL of Montanide (day 1) followed by topical application of 1,000 mg of 0.2% resiquimod gel on days 1 and 3 (cohort 1) versus days 1, 3, and 5 (cohort 2) of a 21-day cycle. In part II, patients were randomized to receive 100-μg NY-ESO-1 protein plus Montanide (day 1) followed by topical application of placebo gel [(arm A; n = 8) or 1,000 mg of 0.2% resiquimod gel (arm B; n = 12)] using the dosing regimen established in part I. The vaccine regimens were generally well tolerated. NY-ESO-1–specific humoral responses were induced or boosted in all patients, many of whom had high titer antibodies. In part II, 16 of 20 patients in both arms had NY-ESO-1–specific CD4+ T-cell responses. CD8+ T-cell responses were only seen in 3 of 12 patients in arm B. Patients with TLR7 SNP rs179008 had a greater likelihood of developing NY-ESO-1–specific CD8+ responses. In conclusion, NY-ESO-1 protein in combination with Montanide with or without topical resiquimod is safe and induces both antibody and CD4+ T-cell responses in the majority of patients; the small proportion of CD8+ T-cell responses suggests that the addition of topical resiquimod to Montanide is not sufficient to induce consistent NY-ESO-1–specific CD8+ T-cell responses. Cancer Immunol Res; 3(3); 278–87. ©2015 AACR.

Cancer immunotherapy: Dendritic-cell vaccines on the move

Vaccines that induce an antitumour immune response are disappointingly ineffective in treating patients with cancer. Pre-conditioning the vaccination site to induce inflammation might provide a way to improve this therapy. See Letter p.366 John Sampson and colleagues report on a small clinical trial in glioblastoma patients that shows that the immune and anti-tumour response to dendritic cell vaccination is increased by pre-conditioning the site of vaccination with tetanus/diptheria toxoid (Td). Experiments in mice showed similar effects and demonstrated that pre-conditioning with Td enhanced migration of dendritic cells to the tumours, at least in part due to the action of the cytokine CCL3. Although the clinical trial reported is small, these findings may pave the way for new ways of improving the efficacy of anti-cancer vaccines.