Tuberculosis specific responses following therapy for TB: Impact of HIV co-infection.

Characterizing perturbations in the immune response to tuberculosis in HIV can develop insights into the pathogenesis of coinfection. HIV+ TB+ and TB monoinfected (TB+) subjects recruited from clinics in Bamako prior to initiation of TB treatment were evaluated at time-points following initiation of therapy. Flow cytometry assessed CD4+/CD8+ T cell subsets and activation markers CD38/HLA-DR. Antigen specific responses to TB proteins were assessed by intracellular cytokine detection and proliferation. HIV+ TB+ subjects had significantly higher markers of immune activation in the CD4+ and CD8+ T cells compared to TB+ subjects. HIV+ TB+ had lower numbers of TB-specific CD4+ T cells at baseline. Plasma IFNγ levels were similar between HIV+ TB+ and TB+ subjects. No differences were observed in in-vitro proliferative capacity to TB antigens between HIV+ TB+ and TB+ subjects. Subjects with HIV+ TB+ coinfection demonstrate in vivo expansion of TB-specific CD4+ T cells. Immunodeficiency associated with CD4+ T cell depletion may be less significant compared to immunosuppression associated with HIV viremia or untreated TB infection.

Interleukin-2 induced immune effects in human immunodeficiency virus-infected patients receiving intermittent interleukin-2 immunotherapy.

To characterize the immunological effects of intermittent IL-2 therapy, which leads to selective increases in CD4+ T lymphocytes in HIV-infected patients, 11 patients underwent extensive immunological evaluation. While IL-2 induced changes in both CD4+ and CD8+ cell number acutely, only CD4+ cells showed sustained increases following discontinuation of IL-2. Transient increases in expression of the activation markers CD38 and HLA-DR were seen on both CD4+ and CD8+ cells, but CD25 (a chain of the IL-2 receptor) increased exclusively on CD4+ cells. This increase in CD25 expression was sustained for months following discontinuation of IL-2, and was seen in naive as well as memory cells. IL-2 induced cell proliferation, but tachyphylaxis to these proliferative effects developed after 1 week despite continued IL-2 administration. It thus appears that sustained CD25 expression selectively on CD4+ cells is a critical component of the immunological response to IL-2, and that intermittent administration of IL-2 is necessary to overcome the tachyphylaxis to IL-2-induced proliferation.

Cd4+ T cells programmed to traffic to lymph nodes account for increases in numbers of cd4+ T cells up to 1 year after the initiation of highly active antiretroviral therapy for human immunodeficiency virus type 1 infection.

Cells programmed to traffic through lymph nodes dominate initial increases in total CD4(+) T cell numbers after highly active antiretroviral therapy (HAART) is begun for human immunodeficiency virus type 1 (HIV-1) infection. However, it is unknown whether this dominance continues throughout the first year of treatment. To examine this question, 10 subjects who had a positive response to HAART for 1 year were selected from a cohort of 20 who were receiving this treatment. Flow cytometry, which was used to characterize CD4(+) T cell subsets by immunophenotype, demonstrated that cells programmed to traffic through lymph nodes, irrespective of their memory or naive phenotype, continued to best account for increases in CD4(+) T cells, even 1 year after starting HAART. This suggests that, although this pool is preferentially depleted during HIV-1 infection, HAART allows for reaccumulation of these cells for at least 1 year. Furthermore, it suggests that phenotypic differences based on markers of lymphocyte trafficking may be more relevant for understanding HIV-1 pathogenesis than are naive and memory markers alone.

CCR5 and CXCR4 expression on memory and naive T cells in HIV-1 infection and response to highly active antiretroviral therapy.

OBJECTIVE: To measure CCR5 and CXCR4 chemokine receptor expression on CD4 and CD8 T cells in HIV-1 infection and to relate levels to the distribution of CD45RO memory and CD45RA-naive subsets, measures of disease activity, and response to highly active antiretroviral therapy (HAART). DESIGN: Fourteen untreated HIV-1-infected patients, 18 patients at 3-to 4-weeks after beginning HAART, and 35 uninfected control subjects were studied. METHODS: Four-color cytofluorometry with appropriate conjugated monoclonal antibodies (mAbs) was performed to define CD45RA and CD45RO subsets of CD4 and CD8 T cells and measure their expression of CCR5, CXCR4, and CD38. RESULTS: HIV-1-infected patients had higher CCR5 levels and lower CXCR4 levels on CD4 and CD8 T cells and their CD45RO/CD45RA subsets than control subjects did. However, CCR5 elevation was statistically significant only for CD4 T cells and their subsets, and CXCR4 depression was significant for CD8 T cells and their subsets (and for CD4:CD45RO cells). The elevation of CCR5 and depression of CXCR4 were not due to shifts in CD45RO/CD45RA subset proportions but to upregulation or downregulation within the subsets. CCR5 elevation on CD4 T cells was significantly restored toward normal by HAART, but the CXCR4 depression was not. CCR5 expression but not CXCR4 expression correlated with other measures of immunodeficiency (CD4 T-cell levels), active infection (viral load), and cellular activation (CD38). CONCLUSIONS: CCR5 elevation is a concomitant of immune activation and viral replication that occurs in HIV-1 infection, but the relation of CXCR4 depression to severity of infection, disease progression, and response to therapy remains undefined.

An update on the use of flow cytometry in HIV infection and AIDS.

Flow cytometry has played an invaluable role in recent advances made against HIV and AIDS, and there is every reason to expect it will continue to do so. Newer-generation machines, using three- and four-color panels, make measurements of lymphocyte subsets ever more accurate and potentially cost-effective. Similarly, recent single-platform techniques promise even more efficiencies, freeing CD4 enumeration from parallel determination of the CBC. In other developments, quantitative reporting of immunophenotype may well change the way subsets traditionally defined by qualitative determinations are viewed. The most promising initial candidates for such changes are surrogates of immune activation, such as CD38 expression on CD8 cells. But technical demonstration of reproducibility and reliability, and clinical trial evidence of utility--especially as measured against such established laboratory parameters as CD4 cell and HIV RNA determinations--are needed before a change from qualitative to quantitative immunophenotype measurement can be widely accepted. Although too soon to tell if they will emerge from the research arena into the clinical arena, tetramer binding, intracellular cytokine detection, and assays of cell division are rapidly advancing understanding of HIV-disease, and indeed understanding of all of human immunology. Some of these assays provide often subtly different information, and together they will help determine the most important surrogate measures of clinical immunity. Identifying such surrogates is critical to developing a rational HIV vaccine. The power of flow cytometry is its ability simultaneously to analyze data in four, five, six, or more dimensions. For longitudinal experiments, time adds yet another dimension. Humans struggle to think past three dimensions; interpreting results from experimental permutations and combinations that expand geometrically with each additional parameter studied requires considerable effort. Ultimately computer programs might come to our aid, but for now we have to live with the information overload if we hope to gain insight into the workings of complex biologic systems. In a world of limited resources, and with limited capacity to conceptualize in multiple dimensions, insight, inspiration, and perhaps a little luck are needed to ask the right questions and use the right assays if the recent string of advances against AIDS is to continue.

Markers of lymphocyte homing distinguish CD4 T cell subsets that turn over in response to HIV-1 infection in humans.

In HIV-1 infection, the abrupt rise in CD4 T cells after effective antiretroviral therapy has been viewed as a measure of HIV-1-related CD4 T cell turnover in the steady state. The early (2-4 wk) response is reportedly dominated by CD4 T cells with a memory (CD45RO) phenotype. It is controversial whether the measurement of steady-state kinetics identifies cells that otherwise would have been recruited into a short-lived, virus-producing pool or reflects lymphoid redistribution/sequestration. We performed detailed phenotypic and kinetic analysis of CD4 T cell subsets in 14 patients. Turnover occurs in memory (CD45RO) as well as naive (CD45RA) cells, if the latter are present at baseline. Most of the turnover occurs in those memory (CD45RO) and naive (CD45RA) cells that are programmed for recirculation through lymphoid organs (CD62L+ and CD44low), whereas very little turnover occurs in memory cells (CD45RO) destined for recirculation from blood to tissue (CD62L- and CD44high). Turnover occurs in both activated (CD25+ and HLA-DR+) and nonactivated populations, although it is restricted to CD38-positive cells, indicating that turnover does not measure cells that are already infected. More likely, turnover occurs in cells that replace infected cells or are on their way to becoming infected. Taken together, markers of lymphocyte trafficking better describe cell turnover related to virus replication than do naive and memory markers per se, and lymph organs, not tissue-destined cells or peripheral blood cells, appear to be the important site of virus replication and CD4 T cell turnover, destruction, and redistribution.

Lymphocyte kinetics and precursor frequency-dependent recovery of CD4(+)CD45RA(+)CD62L(+) naive T cells following triple-drug therapy for HIV type 1 infection.

New therapeutic regimens have dramatically altered morbidity and mortality attributed to HIV-1 infection. Changes in lymphocyte subsets after treatment may mirror salutary clinical changes. Over 4 months we analyzed lymphocyte subsets in 20 patients starting new HIV-1 therapy. Absolute numbers of lymphocytes, CD4+ T cells, CD8+ T cells, and B cells increased significantly by 4 months, but CD8+ T cell and B cell increases were restricted to late-stage patients. Subset analysis revealed that the magnitude of recovering naive-phenotype CD4+ T cells (slope) correlated with the number of these cells present at baseline, equaling or exceeding the memory-phenotype slope within days if these naive cells were abundant at baseline. Five of 10 patients in whom naive-phenotype CD4+ T cells were absent at baseline partially repopulated these cells by 4 months. These findings have important implications for the origin and mechanisms of renewal of naive-phenotype CD4+ T cells following effective treatment for HIV-1 infection.

Neutralizing antibody and perinatal transmission of human immunodeficiency virus type 1. New York City Perinatal HIV Transmission Collaborative Study Group.

The major immunologic determinants for perinatal transmission of human immunodeficiency virus type 1 (HIV-1) remain largely unknown. The presence of maternal neutralizing antibodies has been proposed as an explanation for why the majority of infants born to untreated HIV-1-infected women do not become infected. Using maternal and infant specimens collected as part of a longitudinal cohort study of perinatal transmission in New York City between 1991 and 1995, we successfully obtained primary viral isolates from 10 of 20 perinatally nontransmitting (NTR) women, 14 of 20 perinatally transmitting (TR) women, and 13 of 13 of their HIV-1-infected infants. Neutralizing antibody titers were then determined using a titer reduction assay. TR and NTR women did not differ in their ability to neutralize autologous virus or laboratory strains LAI and MN. Infant viruses were not less sensitive to neutralization by maternal sera than autologous viruses. Similarly, TR and NTR isolates were neutralized equally well using a reference serum with broad neutralizing ability. Finally, a heteroduplex tracking assay (HTA) was used to analyze the degree of viral homology within 13 TR maternal-infant pairs. In eight pairs, maternal and infant isolates were highly homologous. In five pairs, lesser degrees of homology were observed, consistent with perinatal transmission of a minor species. However, these isolates were no more or less resistant to maternal sera than were homologous isolates. Thus we found no association between the presence of neutralizing antibody in maternal sera as measured by a titer reduction neutralization (inactivation) assay and perinatal transmission of HIV-1.