Immature dendritic cells (DCs) capture HIV type 1 (HIV-1) and can transmit captured virus particles to T cells. In this report, we show that HIV-1 particles captured by DCs can be transmitted to T cells by exocytosis without de novo infection. Captured HIV-1 particles were rapidly endocytosed to tetraspan protein (CD9, CD63)-positive endocytic compartments that were reminiscent of multivesicular endosomal bodies. Furthermore, some of the endocytosed virus particles were constitutively released into the extracellular milieu in association with HLA-DR1 ؉ , CD1b ؉ , CD9 ؉ , and CD63 ؉ vesicles (exosomes) and could initiate productive infections of CD4 ؉ target cells. Surprisingly, the exocytosed vesicle-associated HIV-1 particles from DCs were 10-fold more infectious on a perparticle basis than cell-free virus particles. These studies describe a previously undescribed mechanism of DC-mediated HIV-1 transmission and suggest that virus particle trafficking to multivesicular endosomal bodies and subsequent exocytosis can provide HIV-1 particles captured by DCs an avenue for immune escape.

Herpes simplex virus type 1 (HSV-1) infects a wide range of cells, including dendritic cells. Consequently, HSV-1 vectors may be capable of eliciting strong immune responses to vectored antigens. To test this hypothesis, an HSV-1 amplicon plasmid encoding human immunodeficiency virus type 1 gp120 was constructed, and murine immune responses to helper virus-free amplicon preparations derived from this construct were evaluated. Initial studies revealed that a single intramuscular (i.m.) injection of 10 6 infectious units (i.u.) of HSV:gp120 amplicon particles (HSV:gp120) elicited Env-specific cellular and humoral immune responses. A potent, CD8؉ -T-cell-mediated response to an H-2D d -restricted peptide from gp120 (RGPGRAFVTI) was measured by a gamma interferon ELISPOT and was confirmed by standard cytotoxic-T-lymphocyte assays. Immunoglobulin G enzyme-linked immunosorbent assay analysis showed the induction of a strong, Envspecific antibody response. An i.m. or an intradermal administration of HSV:gp120 at the tail base elicited a more potent cellular immune response than did an intraperitoneal (i.p.) inoculation, although an i.p. introduction generated a stronger humoral response. The immune response to HSV:gp120 was durable, with robust cellular and humoral responses persisting at 171 days after a single 10 6 -i.u. inoculation. The immune response to HSV:gp120 was also found to be dose dependent: as few as 10 4 i.u. elicited a strong T-cell response. Finally, HSV:gp120 elicited significant Env-specific cellular immune responses even in animals that had been previously infected with wild-type HSV-1. Taken together, these data strongly support the use of helper-free HSV-1 amplicon particles as vaccine delivery vectors.Genetically engineered herpesviruses have been successfully used for the development of vaccines against important animal diseases, including Aujesky's disease (pseudorabies virus), infectious bovine rhinotracheitis, and swine fever (hog cholera virus) (21,56,57). In addition, attenuated herpesviruses have been used for human vaccination (including the Towne strain of human cytomegalovirus and the Oka strain of varicellazoster virus) (5, 24, 38, 52). Both herpes simplex virus type 1 (HSV-1) and varicella-zoster virus have been used for the expression of foreign genes, since these viruses can accommodate large segments of exogenous DNA with little effect on virus replication (15, 43). Replication-competent and replication-defective gene replacement vectors based on both viruses are being explored as possible human immunodeficiency virus (HIV) vaccine delivery systems (32, 45). The appeal of this approach lies in part in the ability of herpesviruses to (i) elicit strong cytotoxic-T-lymphocyte (CTL) responses; (ii) infect mucosal surfaces; (iii) infect a broad range of cell types, including dendritic cells (1,23,30,40); and (iv) establish a state of persistence in the infected cell. The latter property may conceivably result in more durable immune responses to herpesvirus-based vaccines compared to man...

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