Exosomes are secreted cellular vesicles that can be internalized by dendritic cells (DCs), contributing to antigen-specific naive CD4+ T-cell activation. Here, we demonstrate that human immunodeficiency virus type 1 (HIV-1) can exploit this exosome antigen-dissemination pathway intrinsic to mature DCs (mDCs) for mediating trans-infection of T lymphocytes. Capture of HIV-1, HIV-1 Gag-enhanced green fluorescent protein (eGFP) viral-like particles (VLPs), and exosomes by DCs was up-regulated upon maturation, resulting in localization within a CD81+ compartment. Uptake of VLPs or exosomes could be inhibited by a challenge with either particle, suggesting that the expression of common determinant(s) on VLP or exosome surface is necessary for internalization by mDCs. Capture by mDCs was insensitive to proteolysis but blocked when virus, VLPs, or exosomes were produced from cells treated with sphingolipid biosynthesis inhibitors that modulate the lipid composition of the budding particles. Finally, VLPs and exosomes captured by mDCs were transmitted to T lymphocytes in an envelope glycoprotein-independent manner, underscoring a new potential viral dissemination pathway.

Exosomes are secreted cellular vesicles that can induce specific CD4⁺ T cell responses in vivo when they interact with competent antigen-presenting cells like mature dendritic cells (mDCs). The Trojan exosome hypothesis proposes that retroviruses can take advantage of the cell-encoded intercellular vesicle traffic and exosome exchange pathway, moving between cells in the absence of fusion events in search of adequate target cells. Here, we discuss recent data supporting this hypothesis, which further explains how DCs can capture and internalize retroviruses like HIV-1 in the absence of fusion events, leading to the productive infection of interacting CD4⁺ T cells and contributing to viral spread through a mechanism known as trans-infection. We suggest that HIV-1 can exploit an exosome antigen-dissemination pathway intrinsic to mDCs, allowing viral internalization and final trans-infection of CD4⁺ T cells. In contrast to previous reports that focus on the ability of immature DCs to capture HIV in the mucosa, this review emphasizes the outstanding role that mature DCs could have promoting trans-infection in the lymph node, underscoring a new potential viral dissemination pathway.

Background: The use of tolerogenic DCs is a promising therapeutic strategy for transplantation and autoimmune disorders. Immunomodulatory DCs are primarily generated from monocytes (MDDCs) forin vitroexperiments following protocols that fail to fulfil the strict regulatory rules of clinically applicable products. Here, we compared the efficacy of three different tolerance-inducing agents, dexamethasone, rapamycin and vitamin D3, on DC biology using GMP (Good Manufacturing Practice) or clinical grade reagents with the aim of defining their use for human cell therapy.Methods: Tolerogenic MDDCs were generated by adding tolerogenic agents prior to the induction of maturation using TNF-α, IL-β and PGE2. We evaluated the effects of each agent on viability, efficiency of differentiation, phenotype, cytokine secretion and stability, the stimulatory capacity of tol-DCs and the T-cell profiles induced.Results: Differences relevant to therapeutic applicability were observed with the cellular products that were obtained. VitD3-induced tol-DCs exhibited a slightly reduced viability and yield compared to Dexa-and Rapa-tol-DCs. Phenotypically, while Dexa-and VitD3-tol-DCs were similar to immature DCs, Rapa-tol-DCs were not distinguishable from mature DCs. In addition, only Dexa-and moderately VitD3-tol-DCs exhibited IL-10 production. Interestingly, in all cases, the cytokine secretion profiles of tol-DCs were not modified by a subsequent TLR stimulation with LPS, indicating that all products had stable phenotypes. Functionally, clearly reduced alloantigen T cell proliferation was induced by tol-DCs obtained using any of these agent. Also, total interferon-gamma (IFN-γ) secretion by T cells stimulated with allogeneic tol-DCs was reduced in all three cases, but only T cells co-cultured with Rapa-tol-DCs showed impaired intracellular IFN-γ production. In addition, Rapa-DCs promoted CD4+ CD127 low/negative CD25high and Foxp3+ T cells.Conclusions: Our results demonstrate contrasting influences of different clinical-grade pharmacological agents on human tol-DC generation. This should be taken into account for decisions on the use of a specific agent for the appropriate cellular therapy in the context of a particular disease.

Dendritic cells (DCs) are specialized antigen-presenting cells. However, DCs exposed to human immunodeficiency virus type 1 (HIV-1) are also able to transmit a vigorous cytopathic infection to CD4 ⁺ T cells, a process that has been frequently related to the ability of DC-SIGN to bind HIV-1 envelope glycoproteins. The maturation of DCs can increase the efficiency of HIV-1 transmission through trans infection. We aimed to comparatively study the effect of maturation in monocyte-derived DCs (MDDCs) and blood-derived myeloid DCs during the HIV-1 capture process. In vitro capture and transmission of envelope-pseudotyped HIV-1 and its homologous replication-competent virus to susceptible target cells were assessed by p24 ^gag detection, luciferase activity, and both confocal and electron microscopy. Maturation of MDDCs or myeloid DCs enhanced the active capture of HIV-1 in a DC-SIGN- and viral envelope glycoprotein-independent manner, increasing the life span of trapped virus. Moreover, higher viral transmission of mature DCs to CD4 ⁺ T cells was highly dependent on active viral capture, a process mediated through cholesterol-enriched domains. Mature DCs concentrated captured virus in a single large vesicle staining for CD81 and CD63 tetraspanins, while immature DCs lacked these structures, suggesting different intracellular trafficking processes. These observations help to explain the greater ability of mature DCs to transfer HIV-1 to T lymphocytes, a process that can potentially contribute to the viral dissemination at lymph nodes in vivo, where viral replication takes place and there is a continuous interaction between susceptible T cells and mature DCs.

Multiple sclerosis (MS) is a chronic demyelinating autoimmune disease of the central nervous system. Current therapies decrease the frequency of relapses and limit, to some extent, but do not prevent disease progression. Hence, new therapeutic approaches that modify the natural course of MSneed to be identified. Tolerance induction to self‐antigens using monocyte‐derived dendritic cells (MDDCs) is a promising therapeutic strategy in autoimmunity. In this work, we sought to generate and characterize tolerogenic MDDCs (tolDCs) from relapsing‐remitting (RR) MSpatients, loaded with myelin peptides as specific antigen, with the aim of developing immunotherapeutics for MS. MDDCs were generated from both healthy‐blood donors and RR‐MSpatients, and MDDCmaturation was induced with a proinflammatory cytokine cocktail in the absence or presence of 1α,25‐dihydroxyvitamin‐D₃, a tolerogenicity‐inducing agent. tolDCs were generated from monocytes of RR‐MSpatients as efficiently as from monocytes of healthy subjects. The RR‐MStolDCs expressed a stable semimature phenotype and an antiinflammatory profile as compared with untreated MDDCs. Importantly, myelin peptide‐loaded tolDCs induced stable antigen‐specific hyporesponsiveness in myelin‐reactive T cells from RR‐MS patients. These results suggest that myelin peptide‐loaded tolDCs may be a powerful tool for inducing myelin‐specific tolerance in RR‐MS patients.