Cutaneous dendritic cells promote replication of immunodeficiency viruses

The frequency of α₄β₇(high) memory CD4⁺ T cells correlates with susceptibility to rectal simian immunodeficiency virus infection

BACKGROUND

Integrin α₄β₇(high) (α₄β₇(high)) mediates the homing of CD4⁺ T cells to gut-associated lymphoid tissues, which constitute a highly favorable environment for HIV expansion and dissemination. HIV and simian immunodeficiency virus (SIV) envelope proteins bind to and signal through α₄β₇(high) and during acute infection SIV preferentially infects α₄β₇(high) CD4⁺ T cells. We postulated that the availability of these cells at the time of challenge could influence mucosal SIV transmission and acute viral load (VL).

METHODS

We challenged 17 rhesus macaques with 3000 TCID50 of SIVmac239 rectally and followed the subsets of α₄β₇(high) T cells and dendritic cells (DCs) by flow cytometry in blood and tissues, before and after challenge.

RESULTS

We found that the frequency of memory CD4⁺ T cells that expressed high levels of α₄β₇(high) (α₄β₇(high) memory CD4⁺ T cells) in blood before challenge correlated strongly with susceptibility to infection and acute VL. Notably, not only at the time of challenge but also their frequency 3 weeks before challenge correlated with infection. This association extended to the rectal tissue as we observed a strong direct correlation between the frequency of α₄β₇(high) memory CD4⁺ T cells in blood and rectum before and after challenge. The frequency of α4β7 myeloid DCs and α₄β₇(high) CD80⁺ DCs also correlated with infection and acute VL, whereas blood CCR5⁺ and CD69⁺ CD4⁺ T cells could not be associated with infection.

CONCLUSIONS

Our results suggest that animals with higher frequency of α₄β₇(high) CD4⁺ T cells in circulation and in rectal tissue could be more susceptible to SIV rectal transmission.

HIV impairment of immune responses in dendritic cells

Dendritic cells and their subsets are diverse populations of immune cells in the skin and mucous membranes that possess the ability to sense the presence of microbes and orchestrate an efficient and adapted immune response. Dendritic cells (DC) have the unique ability to act as a bridge between the innate and adaptive immune responses. These cells are composed of a number of subsets behaving with preferential and specific features depending on their location and surrounding environment. Langerhans cells (LC) or dermal DC (dDC) are readily present in mucosal areas. Other DC subsets such as plasmacytoid DC (pDC), myeloid DC (myDC), or monocyte-derived DC (MDDC) are thought to be recruited or differentiated in sites of pathogenic challenge. Upon HIV infection, DC and their subsets are likely among the very first immune cells to encounter incoming pathogens and initiate innate and adaptive immune responses. However, as evidenced during HIV infection, some pathogens have evolved subtle strategies to hijack key cellular machineries essential to generate efficient antiviral responses and subvert immune responses for spread and survival.In this chapter, we review recent research aimed at investigating the involvement of DC subtypes in HIV transmission at mucosal sites, concentrating on HIV impact on cellular signalling and trafficking pathways in DC leading to DC-mediated immune response alterations and viral immune evasion. We also address some aspects of DC functions during the chronic immune pathogenesis and conclude with an overview of the current and novel therapeutic and prophylactic strategies aimed at improving DC-mediated immune responses, thus to potentially tackle the early events of mucosal HIV infection and spread.

Topical/mucosal delivery of sub-unit vaccines that stimulate the ocular mucosal immune system

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although ocular mucosal immunity is highly beneficial for achieving protective immunity, the induction of ocular mucosal immunity against ocular infectious pathogens, particularly herpes simplex virus type 1 (HSV-1), which is the leading cause of infectious corneal blindness, remains difficult. Recent developments in cellular and molecular immunology of the ocular mucosal immune system (OMIS) may help in the design of more effective and optimal immunization strategies against ocular pathogens. In this review, we highlight ocular mucosal immunoprophylactic and immunotherapeutic vaccine strategies that have been evaluated to control the many pathogens that attack the surface of the eye. Next, we describe the current understandings of the OMIS and elucidate the structure and the function of the humoral and cellular immune system that protects the surface of the eye. Results from our recent experiments using topical ocular delivery of peptides-CpG and lipopeptide-based vaccines against HSV-1 infection are presented. The future challenges and issues related to the ocular mucosal delivery of molecularly defined sub-unit vaccines are discussed.

Amplification of low-frequency antiviral CD8 T cell responses using autologous dendritic cells

OBJECTIVE

To utilize the potent antigen-presenting capacity of mature dendritic cells (MDC) in order to develop a rapid, sensitive method for quantifying antigen-specific CD8 T cells present at low frequency in peripheral blood.

DESIGN

Peripheral blood mononuclear cells (PBMC) were obtained from seven HIV-1-positive individuals with low to moderate CD8 T cell responses, including five on highly active antiretroviral therapy (HAART). IFN-gamma ELISPOT assays were performed using either monocytes or MDC to present antigens expressed by recombinant vaccinia viruses (r-VV).

METHODS

Peripheral blood-derived monocytes were cultured for 5-6 days in the presence of IL-4 and granulocyte macrophage colony-stimulating factor, then matured in monocyte-conditioned medium. MDC were infected with r-VV and co-cultured in an ELISPOT assay with autologous monocyte-depleted PBMC.

RESULTS

Relative to autologous monocytes, MDC amplified detection of antigen-specific CD8 T cells by 2-30-fold in response to antigens from HIV-1, Epstein-Barr virus and cytomegalovirus. Furthermore, antigenic specificities were revealed that had not been detected using standard ELISPOT of PBMC.

CONCLUSION

This assay will prove useful for the detection of memory T cells present at low frequency, and may be of interest for identifying subdominant cytotoxic T lymphocyte epitopes. This method may have broad applications for the detection of antiviral CD8 T cell responses in patient populations in whom such responses have been difficult to detect, including HIV-1-seropositive individuals with advanced disease or undergoing HAART.

Viral persistence: mechanisms and consequences

Recent research has brought additional information on how virus products interfere with host cell antigen processing in vitro, new information on the interaction of virus with dendritic cells as a mechanism for alteration of immune responses - especially immunosuppression, and a preliminary proposal that nonretroviral RNA viruses might persist by utilizing host-cell reverse transcriptase to enter a DNA phase of replication.