Patrick A. J. Haslett

Activation of HIV-1 specific CD4 and CD8 T cells by human dendritic cells : Roles for cross-presentation and non-infectious HIV-1 virus

BackgroundThe CD4 T cells in mucosal subepithelia are the first cells to become infected during sexual transmission of HIV-1. Dendritic cells (DC) are located in the same area and are known to play a central role in antiviral immune responses. However, extensive viral replication, syncytia formation and cell death follows the interaction between T cells and DC previously exposed to HIV-1. Despite this, anti-HIV responses are generated that control viremia following acute infection. ObjectiveThe anti-HIV-1 cellular immune responses observed may be activated by sources other than productively infected DC. HIV-1 induces apoptosis both in cells it infects and in bystander cells. Furthermore, retroviral replication typically generates a predominance of defective particles. We tested whether DC exposed to antigen from either of these sources could elicit anti-HIV specific immune responses. Design and methodsApoptotic or necrotic monocytes infected with vaccinia virus vectors encoding HIV antigens, a cell line with integrated HIV-1 and apoptotic CD4 T cells pulsed with non-infectious or infectious HIV-1 virus were used as sources of antigens to assess cross presentation by DC. Furthermore, direct DC presentation of antigen from non-infectious and infectious HIV-1 was examined. ResultsWe find that dead cells expressing HIV-1 antigens as well as non-infectious HIV-1 particles can be acquired and processed by DC, leading to the activation, differentiation and expansion of viral antigen-specific CD4 and CD8 T cells from seropositive individuals. ConclusionsThese sources of antigens may be critical for the generation and maintenance of anti-HIV-1 immunity by DC.

Inhibition of Antigen-Specific T Cell Proliferation and Cytokine Production by Protein Kinase A Type I

cAMP inhibits biochemical events leading to T cell activation by triggering of an inhibitory protein kinase A (PKA)-C-terminal Src kinase pathway assembled in lipid rafts. In this study, we demonstrate that activation of PKA type I by Sp-8-bromo-cAMPS (a cAMP agonist) has profound inhibitory effects on Ag-specific immune responses in peripheral effector T cells. Activation of PKA type I inhibits both cytokine production and proliferative responses in both CD4+ and CD8+ T cells in a concentration-dependent manner. The observed effects of cAMP appeared to occur endogenously in T cells and were not dependent on APC. The inhibition of responses was not due to apoptosis of specific T cells and was reversible by a PKA type I-selective cAMP antagonist. This supports the notion of PKA type I as a key enzyme in the negative regulation of immune responses and a potential target for inhibiting autoreactive T cells.

Human Immunodeficiency Virus Type 1- and Cytomegalovirus-Specific Cytotoxic T Lymphocytes Can Persist at High Frequency for Prolonged Periods in the Absence of Circulating Peripheral CD4+ T Cells

ABSTRACT CD4+ T cells are thought to be critical in the maintenance of virus-specific CD8+ cytotoxic T-cell (CTL) responses. In human immunodeficiency virus type 1 (HIV-1) infection, a selective decline in HIV-1-specific CTL as the CD4+ T-cell count decreases has been reported. Using HLA-peptide tetrameric complexes, we show the presence at high frequency of HIV-1- and cytomegalovirus-specific CD8+ T cells when the peripheral CD4+ T-cell count was low or zero in three HIV-1-infected patients. No direct virus-specific CD8+-mediated effector activity was seen in these subjects, suggesting antigen unresponsiveness, although tetramer-sorted cells could be expanded in vitro in the presence of interleukin-2 into responsive effector cells. Thus, virus-specific CD8+ T cells can be maintained in the peripheral circulation at high frequency in the absence of circulating peripheral CD4+ T cells, but these cells may lack direct effector activity. Strategies designed to overcome this antigen unresponsiveness may be of value in therapies for the treatment of AIDS.

Strong Human Immunodeficiency Virus (HIV)-Specific CD4+ T Cell Responses in a Cohort of Chronically Infected Patients Are Associated with Interruptions in Anti-HIV Chemotherapy

Virus-specific CD4+ T-helper cell function is important in controlling human immunodeficiency virus (HIV) infection but is impaired in patients with progressive HIV disease. It has been reported that after highly active antiretroviral therapy (HAART), HIV-specific lymphoproliferative responses remain absent, whereas responses to non-HIV microbial antigens are restored. However, in analyzing immune responses in a cohort of chronically infected adults on HAART, we observed strong HIV-specific CD4+ T cell responses of Th-1 phenotype in 11 of 22 patients. The magnitude and frequency of HIV-specific lymphoproliferative responses was strongly associated with previous interruptions in HAART (P=.001). In contrast, the magnitude of CD8+ T cell responses to HIV Gag, Pol, Env, and Nef was similar in patients who had and those who had not interrupted HAART. We conclude that (1) a significant proportion of chronically HIV-infected patients on HAART can generate strong HIV-specific CD4+ and CD8+ T cell immunity and (2) transient interruptions in antiviral treatment may prime or boost HIV-specific CD4+ T-helper responses.

Thalidomide for the Treatment of AIDS-Associated Wasting

A double-blind, placebo-controlled trial of efficacy and safety of thalidomide in AIDS-associated wasting was carried out. Ninety-nine of 103 male patients had at least one on-study measurement (intent-to-treat [ITT] cohort). Patients were randomized to thalidomide at 100 mg/day (T100) or 200 mg/day (T200), or placebo for 8 weeks. By ITT analysis, the mean change in body weight of the placebo, T100, and T200 treatment groups was 0.3 kg (0.4%), 2.0 kg (3.0%), and 0.9 kg (1.4%), respectively (p = 0.021 for T100 versus placebo; p = 0.53 for T200 versus placebo). Of the 64 patients who completed the 8 weeks of study treatment, significant weight gain was observed in both the T100 group (2.2 kg, [33%]; p = 0.008 versus placebo) and the T200 group (1.5 kg [2.5%]; p = 0.019 versus placebo). Approximately half the weight gain was fat-free mass (bioimpedance analysis). Patients in the T100 or T200 groups had no significant change in CD4+ cell counts, neutrophil counts, or TNF-alpha levels, compared with placebo. HIV viral load measured as log10 copies/ml decreased by a median of 0.07 in the placebo group, and increased by a median of 0.29 (T100 group) and 0.23 (T200 group) (p = 0.024 andp = 0.018 versus placebo, respectively). Thalidomide therapy was associated with mild to moderate rashes and fevers, but not peripheral neuropathy. Although the anabolic benefits of high-dose thalidomide are limited by drug intolerance, 8 weeks of low-dose thalidomide results in significant weight gain in patients with AIDS-associated wasting.

Thalidomide stimulates T cell responses and interleukin 12 production in HIV-infected patients.

We performed a placebo-controlled study to evaluate the effects of immunomodulatory treatment with thalidomide on HIV levels, TNF-alpha levels, and immune status of 31 HIV-infected individuals, after temporary suppression of viral replication with antiretroviral drugs. Treatment with a combination of zidovudine and lamivudine (ZDV/LMV) for 14 days resulted in a median decline in plasma viremia of 1.94 log10 RNA equivalents/ml. After discontinuation of ZDV/LMV, thalidomide therapy (200 mg/day for 4 weeks) did not retard the prompt return of HIV titers to the pretreatment levels, and had no effect on plasma levels of TNF-alpha. In contrast, thalidomide treatment resulted in significant immune stimulation. We observed increased levels of plasma soluble IL-2 receptor, soluble CD8 antigen, and IL-12 (p < 0.01 for all parameters), as well as increased cutaneous delayed-type hypersensitivity reactions to recall antigens (p < 0.01) in thalidomide-treated patients. These changes were associated with a median increase in HIV titer of 0.2 log10 RNA equivalents/ml in the thalidomide-treated group (p < 0.05), which resolved after stopping the drug. Further studies were performed in vitro to elucidate the mechanism of thalidomide-induced immune stimulation. When purified T cells from HIV-infected individuals were stimulated by immobilized anti-CD3 in the presence of thalidomide, a costimulatory effect of the drug was observed, resulting in increased production of IL-2 and IFN-gamma, and increased T cell-proliferative responses. Further experiments showed that thalidomide increased IL-12 production by antigen-presenting cells in a T cell-dependent manner. Our findings suggest a potential application for thalidomide as a novel immune adjuvant in HIV disease.

Dendritic Cells, Infected with Vesicular Stomatitis Virus-Pseudotyped HIV-1, Present Viral Antigens to CD4+ and CD8+ T Cells from HIV-1-Infected Individuals

Nonreplicating vectors are being considered in HIV-1 vaccine design. However, nonreplicating viruses are typically weak immunogens, leading to efforts to target the vaccine to mature dendritic cells (DCs). We have studied a single-cycle form of HIV-1, prepared by pseudotyping envelope-defective HIV-1 plasmids with the envelope from vesicular stomatitis virus (VSV) G protein (VSV-G), to which most humans lack preexisting immunity. The nonreplicating, VSV/HIV-1 efficiently infected the immature stage of DC development, in this case represented by monocytes cultured with GM-CSF and IL-4. A majority of the cells reverse transcribed the HIV-1 RNA, and a minority expressed gag protein. The infected populations were further matured with CD40 ligand, leading to strong stimulation of autologous T cells from HIV-1-infected individuals, but not controls. Enriched CD8+ T cells from 12/12 donors released IFN-γ (50–300 enzyme-linked immunospots/200,000 T cells) and proliferated. Macrophages were much less efficient in expanding HIV-1-responsive T cells, and bulk mononuclear cells responded weakly to VSV/HIV-1. CD4+ T cells from at least half of the donors showed strong responses to VSV/HIV-1-infected DCs. Presentation to CD8+ T cells, but not to CD4+, was primarily through an endogenous pathway, because the responses were markedly reduced if envelope-defective virus particles or reverse transcriptase inhibitors were added. Therefore, nonreplicating vaccines can be targeted to immature DCs, which upon further maturation induce combined and robust CD4+ and CD8+ immunity.

Thalidomide-Induced Antigen-Specific Immune Stimulation in Patients with Human Immunodeficiency Virus Type 1 and Tuberculosis

Thalidomide, which inhibits monocyte tumor necrosis factor (TNF)-alpha production and costimulates T cells, was tested for immune modulation in patients with human immunodeficiency virus (HIV) infection and tuberculosis (TB) in a placebo-controlled study. Thalidomide therapy resulted in increased levels of plasma interleukin (IL)-2 receptor, soluble CD8, interferon-gamma, and IL-12, indicating immune stimulation. TNF-alpha levels were not reduced. Thalidomide treatment increased CD4+ and CD8+ T cell counts and lymphocyte proliferation to purified protein derivative. Immune stimulation was not associated with an increase in plasma HIV levels. In vivo, a thalidomide dose-dependent costimulatory effect on T cell proliferation and HIV replication was observed after stimulation with antigens or anti-CD3, respectively. Thalidomide-induced increased viral replication in CD4+ T cells was abrogated by adding back autologous CD8+ T cells. Thus, in the presence of thalidomide, antigen-specific immune responses in vitro and in patients with HIV/TB were enhanced.

Adverse Reactions to Thalidomide in Patients Infected with Human Immunodeficiency Virus

Thalidomide is emerging as a useful agent in the management of several complications of disease due to human immunodeficiency virus (HIV). We conducted three prospective studies of 56 HIV-infected patients who were treated with thalidomide for 14-21 days; 24 (43%) of these patients discontinued therapy owing to adverse reactions. Cutaneous and/or febrile reactions were the most frequent toxicities, arising in 20 (36%) of the patients. These reactions occurred after a mean interval (+/-SD) of 10 +/- 3 days and were associated with significantly lower CD4 T lymphocyte counts in reactors than in nonreactors (median count, 52.5/mm3 vs. 242 cells/mm3, respectively; P = .009). Four of four rechallenged patients experienced accelerated hypersensitivity; hypotension occurred in one case. Although sedation was an almost universal side effect among the patients, it was moderate or severe in only seven (13%); constipation was moderate or severe in five (9%) of the patients. Severe neuropathic symptoms and mood changes were each noted in two (4%) of the 56 patients. We conclude that the increasing use of thalidomide to treat HIV-infected patients must be accompanied by recognition of the drugs increased potential for toxicity in this population.

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-γ 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.