Weighing in on the risks and benefits of probiotic use in HIV-infected and immunocompromised populations.

Probiotics are used in the prophylaxis and treatment of several conditions, including irritable bowel syndrome, diarrhoea, necrotising enterocolitis (NEC) and colic in infants. Despite the long history of probiotic use in humans, there is still significant debate about their efficacy and safety, particularly in HIV-infected and immunocompromised individuals. Here, we reviewed the safety and adverse event (AE) reporting from clinical trials that have tested probiotics in at risk populations, including HIV-infected individuals, the terminally ill and elderly, and neonates. Our analysis suggests that the benefits of probiotic therapy outweigh their potential risks in HIV-infected populations, and in the treatment of colic and NEC in low birth weight or premature neonates. Most case reports of severe AEs were in the elderly and terminally ill, or in those with additional severe medical conditions. We conclude that probiotic use, as adjunctive treatment, is effective and safe in the majority of patients including HIV-infected individuals, although special care should be taken in individuals with extreme immunosuppression and severe medical conditions in all ages.

Distinct genital tract HIV-specific antibody profiles associated with tenofovir gel.

The impact of topical antiretrovirals for pre-exposure prophylaxis on humoral responses following HIV infection is unknown. Using a binding antibody multiplex assay, we investigated HIV-specific IgG and IgA responses to envelope glycoproteins, p24 Gag and p66, in the genital tract (GT) and plasma following HIV acquisition in women assigned to tenofovir gel (n=24) and placebo gel (n=24) in the CAPRISA 004 microbicide trial to assess if this topical antiretroviral had an impact on mucosal and systemic antibody responses. Linear mixed effect modeling and partial least squares discriminant analysis was used to identify multivariate antibody signatures associated with tenofovir use. There were significantly higher response rates to gp120 Env (P=0.03), p24 (P=0.002), and p66 (P=0.009) in plasma and GT in women assigned to tenofovir than placebo gel at multiple time points post infection. Notably, p66 IgA titers in the GT and plasma were significantly higher in the tenofovir compared with the placebo arm (P<0.05). Plasma titers for 9 of the 10 HIV-IgG specificities predicted GT levels. Taken together, these data suggest that humoral immune responses are increased in blood and GT of individuals who acquire HIV infection in the presence of tenofovir gel.

CD4 T cell depletion at the cervix during HIV infection is associated with accumulation of terminally differentiated T cells.

In blood, the accumulation of terminally differentiated (TD) T cells during HIV infection is associated with CD4 T cell loss and HIV disease progression. Here, we investigated the maintenance and functional characteristics of memory T cells at the cervix. We found that CD4 T cell depletion at the cervix mirrors CD4 depletion in blood. In all women, depletion of CD4 T cells at the cervix was associated with significant reductions in CD45RA- CCR7+ (central memory [CM]) T cells and the accumulation of CD45RA+ CCR7- (TD T cells). We determined whether inflammation in the genital tract was associated with the local differentiation of T cells at the cervix. In uninfected women, genital tract inflammation was associated with the accumulation of CD45RA- CCR7+ CM CD4 T cells and reduced frequencies of CD45RA+ CCR7- TD cells at the cervix. This finding may reflect the fact that, in the absence of HIV infection, TD T cells may be slowly lost in the presence of genital inflammation, while CD45RA- CCR7+ CM T cells are recruited to replenish the diminishing CD4 T cell pool. Following global stimulation with phorbol myristate acetate (PMA)-ionomycin, we noted a significant interleukin 2 (IL-2) deficit in both cervical and blood CD4 T cells from HIV-infected women compared to uninfected women, while gamma interferon (IFN-γ) production was similar, irrespective of HIV status. Few HIV-infected women had detectable IFN-γ and IL-2 HIV-specific T cell responses at the cervix, and these responses were significantly lower in magnitude than the corresponding responses in blood. These data suggest that CD4 depletion was associated with the accumulation of terminally differentiated T cell phenotypes at the cervical mucosa defective in their ability to produce IL-2. CD4 depletion and compromised immunity at the cervix may be accompanied by progressive decline of central memory-like T cells and development of T cells toward terminally differentiated phenotypes.

The immune response of the Chacma baboon to Bacille Calmette Guerin: development of a primate model for BCG-based vaccine research.

Mycobacterium bovis Bacilli Calmette-Guerin (BCG) is used increasingly as an efficient vector for expression of recombinant proteins to induce a strong cell-mediated immunity. Here, we tested the immune response of Chacma baboons to the Tokyo and Pasteur strains of BCG in order to obtain base-line information on the response of this primate to BCG. While a humoral immune response to BCG was detected only in some vaccinated baboons, a cellular immune response characterized by a PPD-specific delayed hypersensitivity response and BCG-specific IFN-gamma production from PBMC was a consistent finding. These responses were long-lived and could be detected beyond a year after a booster inoculation at 20 weeks. The results thus suggest that the Chacma baboon may be used as a non-human primate for the evaluation of recombinant BCG vaccines.

Granule-dependent cytolysis of Mycobacterium tuberculosis-infected macrophages by human gammadelta+ T cells has no effect on intracellular mycobacterial viability.

One of the most important effector functions of activated gammadelta+ T cells in tuberculosis is their strong cytolytic activity against a variety of target cells, including M. tuberculosis-infected macrophages. In the present study, we investigated the relationship between the mechanism of cytolysis utilized by gammadelta+ CTL and intracellular M. tuberculosis survival using a panel of cytolytic human M. tuberculosis-specific gammadelta+ CTL clones. Cytolysis mediated by the gammadelta+ T-cell clones was found to be Ca2+-dependent, sensitive to Cyclosporin A, and was completely abrogated following Sr2+-induced de-granulation of the gammadelta+ T cell effectors. These data demonstrate that gammadelta+ T-cell-mediated cytoxicity was mediated via the granule exocytosis/perforin pathway. Despite significant cytolytic activity against mycobacteria infected U937 cells, the gammadelta+ CTL clones had no impact on the survival of intracellular M. tuberculosis.

The human macrophage cell line U937 as an in vitro model for selective evaluation of mycobacterial antigen-specific cytotoxic T-cell function.

Despite strong evidence for CD8+ T-cell function in murine mycobacterial infections, their corresponding role in human tuberculosis has proven more difficult to demonstrate. We have evaluated the human macrophage (Mphi) cell line U937 as an in vitro model for human leucocyte antigen (HLA) class I-restricted presentation of mycobacterial antigens, as HLA class I is constitutively expressed at high levels by U937 cells in the absence of detectable HLA class II or CD1 molecules. U937 cells were evaluated for their ability to phagocytose Mycobacterium tuberculosis and for their ability to present mycobacterial antigens to human HLA class I-matched cytotoxic T lymphocytes (CTLs). Differentiated U937 cells were capable of efficient phagocytosis of M. tuberculosis but did not generate a subsequent respiratory burst response, and were permissive for intracellular growth of both bacillus Calmette-Guérin (BCG) and the virulent M. tuberculosis H37Rv strain. CTL activity was restricted to live mycobacterial organisms and was shown to be mediated by M. tuberculosis-specific, HLA class I-matched, purified CD8+ CTL lines and CD8+ T-cell clones. Furthermore, M. tuberculosis-infected U937 targets were more rapidly and strongly lysed by CD8+ CTLs than were infected autologous Mphi. Finally, M. tuberculosis-infected U937 cells simultaneously provided a sensitive indicator for detection of mycobacterial-specific, HLA-unrestricted gammadelta+ CTL activity.