Immunological and virological changes associated with decline in CD4/CD8 ratios in lymphoid organs of SIV-infected macaques

Modeling aging in HIV infection in nonhuman primates to address an emerging challenge of the post-ART era

The advent of antiretroviral therapy (ART) has dramatically improved both quality and length of life for subjects infected with human immunodeficiency virus (HIV), delaying or preventing progression to acquired immunodeficiency syndrome (AIDS). However, the virus induces aging-related changes to the immune system which confound treatment. Additionally, the normal physiologic events that occur during aging lead to deficiencies in immunity which not only exacerbate HIV pathogenesis but also trigger a variety of comorbidities. Here, the synergistic linkage between aging and HIV infection is examined in regard to the immunological and pathological mechanisms that drive both senescence and disease progression. The use of NHPs to investigate potential therapeutic strategies to control the deleterious consequences of aging with HIV infection is also reviewed.

The role of the tumor microenvironment in HIV-associated lymphomas

There has been considerable interest in the role of the lymphoma microenvironment. Despite the use of highly active antiretroviral therapy (HAART), AIDS-related diffuse large-B-cell lymphoma remains common and HIV-relatedHIV-associated classical Hodgkin's lymphoma is increasing in incidence. Less is known about the impact HIV and HAART have on the lymphoma microenvironment. AIDS-related diffuse large B-cell lymphoma is highly angiogenic, demonstrates increased lymphoblastic histology, proliferation, increased activated cytotoxic T cells, reduced CD4(+) and FOXP3(+) T cells, but no differences in tumor-associated macrophages. Early initiation of HAART improves immunosurveillance, but cases without viral antigens appear able to avoid immunologic reaction. Increased T cell infiltrates seen with HAART treatment in HIV-related classical Hodgkin's lymphoma may contribute to malignant cell growth.

The microenvironment of AIDS-related diffuse large B-cell lymphoma provides insight into the pathophysiology and indicates possible therapeutic strategies

Despite the use of highly active antiretroviral therapy (HAART), AIDS-related lymphoma remains common. We investigated the tumor, microenvironment, and viral components in 41 AIDS-related diffuse large B-cell lymphomas (AR-DLBCLs) in the pre- and post-HAART era. The outcome has improved and the frequency of the prognostically unfavorable immunoblastic histology has decreased after HAART. Compared with sporadic cases, AR-DLBCL demonstrated increased hyperproliferation (P < .001) and c-Myc rearrangements, reduced CD4(+) (P < .001) and FOXP3(+) T cells (P < .001), increased activated cytotoxic cells (P < .001), but no difference in tumor-associated macrophages. Our analysis showed that AR-DLBCL is highly angiogenic with higher blood-vessel density than sporadic cases (P < .001) and highlighted the role of Epstein-Barr virus in angiogenesis. We recognized viral profiles and as a second step examined the reactive cytotoxic cell infiltrates. Our observation of markedly higher numbers of cytotoxic cells in AR-DLBCL with LMP1 and/or p24 compared with cases lacking viral antigens (P < .001) has important clinical implications, implicitly linked to the immunosurveillance theory. Whereas early initiation of HAART should improve immunosurveillance and reduce the incidence of LMP1-positive AR-DLBCL, cases without viral antigens appear able to avoid immunologic reaction and likely require additional strategies to improve surveillance.

Abnormal activation and cytokine spectra in lymph nodes of people chronically infected with HIV-1

There is growing recognition that HIV-1 infection leads to an activation of the immune system that includes perturbations of cytokine expression, redistribution of lymphocyte subpopulations, cell dysfunction, and cell death. Here, we explored the relationships between HIV-1 infection and immune activation in chronically HIV-1-infected human lymph nodes. In addition to CD4 T-cell depletion, we found increased effector T-cell frequencies associated with profound up-regulation of an activation marker CD38 in naive, central memory, and effector CD4(+) and CD8(+) T cells. Likewise, Fas death receptor (CD95) was more frequently detectable on T cells from HIV-1 nodes. Dendritic cell (DC) depletion was dramatic, with plasmacytoid DCs (PDCs) 40-fold and myeloid DCs (MDCs) 20-fold less frequent in HIV(+) nodes than in control nodes. Cytokine dysregulation was evident, with IL-2 and IL-15 as much as 2 or 3 logs greater in infected nodes than in control nodes. Thus, activated effector cells are inappropriately attracted and/or retained in lymphoid tissue in chronic HIV-1 infection. High-level cytokine expression in turn activates and retains more cells at these sites, leading to lymphadenopathy and massive bystander activation that characterizes HIV-1 infection. Strategies targeting these activation pathways may lead to new therapies.

Protection of Macaques against pathogenic simian/human immunodeficiency virus 89.6PD by passive transfer of neutralizing antibodies

The role of antibody in protection against human immunodeficiency virus (HIV-1) has been difficult to study in animal models because most primary HIV-1 strains do not infect nonhuman primates. Using a chimeric simian/human immunodeficiency virus (SHIV) based on the envelope of a primary isolate (HIV-89.6), we performed passive-transfer experiments in rhesus macaques to study the role of anti-envelope antibodies in protection. Based on prior in vitro data showing neutralization synergy by antibody combinations, we evaluated HIV immune globulin (HIVIG), and human monoclonal antibodies (MAbs) 2F5 and 2G12 given alone, compared with the double combination 2F5/2G12 and the triple combination HIVIG/2F5/2G12. Antibodies were administered 24 h prior to intravenous challenge with the pathogenic SHIV-89.6PD. Six control monkeys displayed high plasma viremia, rapid CD4(+)-cell decline, and clinical AIDS within 14 weeks. Of six animals given HIVIG/2F5/2G12, three were completely protected; the remaining three animals became SHIV infected but displayed reduced plasma viremia and near normal CD4(+)-cell counts. One of three monkeys given 2F5/2G12 exhibited only transient evidence of infection; the other two had marked reductions in viral load. All monkeys that received HIVIG, 2F5, or 2G12 alone became infected and developed high-level plasma viremia. However, compared to controls, monkeys that received HIVIG or MAb 2G12 displayed a less profound drop in CD4(+) T cells and a more benign clinical course. These data indicate a general correlation between in vitro neutralization and protection and suggest that a vaccine that elicits neutralizing antibody should have a protective effect against HIV-1 infection or disease.

The importance of lymphocyte trafficking in regulating blood lymphocyte levels during HIV and SIV infections

In humans, blood is commonly monitored to provide surrogates of disease progression and assess immune status. However, the varied, rapid and atypical alterations in lymphocyte subsets which may occur in blood in response to pathogens, are not predictive of changes in the bulk of the immune system. A hallmark of human and simian immunodeficiency virus (SIV) infections is the profound loss of blood CD4(+) lymphocytes, a feature widely accepted as being a consequence of direct or indirect viral killing of CD4(+) cells throughout the body. However, in recording declining CD4 counts and CD4/8 ratios in the blood, little attention has been paid to migratory behaviour or the composition and tissue distribution of various lymphocyte subsets. This article compares the lymphocyte subsets in blood and various tissues in normal and virus-infected individuals prior to and following drug treatment and indicates an absence of selective CD4(+) cell decreases or increases, highlighting the importance of lymphocyte trafficking and compartmentalization in regulating blood T cell levels and suggesting a reevaluation of the currently favoured paradigm.

Live attenuated, multiply deleted simian immunodeficiency virus causes AIDS in infant and adult macaques

A substantial risk in using live attenuated, multiply deleted viruses as vaccines against AIDS is their potential to induce AIDS. A mutant of the simian immunodeficiency virus (SIV) with large deletions in nef and vpr and in the negative regulatory element induced AIDS in six of eight infant macaques vaccinated orally or intravenously. Early signs of immune dysfunction were seen in the remaining two offspring. Prolonged follow-up of sixteen vaccinated adult macaques also showed resurgence of chronic viremia in four animals: two of these developed early signs of disease and one died of AIDS. We conclude that this multiply deleted SIV is pathogenic and that human AIDS vaccines built on similar prototypes may cause AIDS.

Asymptomatic simian immunodeficiency virus infection decreases blood CD4(+) T cells by accumulating recirculating lymphocytes in the lymphoid tissues

Declining blood CD4(+) T-cell counts mark the progress of simian immunodeficiency virus (SIV) disease in macaques and model the consequences of untreated human immunodeficiency virus infection in humans. However, blood lymphocytes are only a fraction of the recirculating lymphocyte pool, and their numbers are affected by cell synthesis, cell depletion, and distribution among blood and lymphoid tissue compartments. Asymptomatic, SIV-infected macaques maintained constant and nearly normal numbers of recirculating lymphocytes despite the decline in CD4(+) T-cell counts. Substantial depletion was detected only when blood CD4(+) T-cell counts fell below 300/microliter. In asymptomatic animals, changes in CD4(+) T-cell distribution were more important than lymphocyte depletion for controlling the blood cell levels.

Phenotypic variability of lymphocyte populations in peripheral blood and lymph nodes from HIV-infected individuals and the impact of antiretroviral therapy. DATRI 003 Study Group. Division of AIDS Treatment Research Initiative

This study presents immunophenotypic variation in lymphocyte populations obtained from peripheral blood and lymph nodes from individuals with early HIV disease who were enrolled in a prospective, open-label study. At baseline, there was a significantly greater percentage of B cells and significantly smaller percentage of CD8+ cells in lymph nodes compared with peripheral blood. Evaluation of lymphocyte phenotypic markers of function, maturation, and activation at baseline revealed a significantly higher percentage of activated CD4+ cells in lymph nodes compared with peripheral blood, whereas the percentages of activated CD8+ cells were similar in both compartments. After an 8-week period of randomly assigned treatment, peripheral blood phenotypic marker changes included (1) a reduced proportion of activated cells (HLA-DR+) in antiretroviral-naive patients who received zidovudine (ZDV), and (2) as increased proportion of "naive" cells (CD45RA+) in individuals, previously administered ZDV alone, who received ZDV and didanosine (ddI) therapy. The lymph node phenotypic marker analysis showed no significant changes over the 8-week treatment period. Overall, the study demonstrates significant differences in lymphocyte subsets from lymph nodes compared with peripheral blood and suggests that further studies be performed to determine the functional significance of these phenotypic subsets.

Enhanced follicular dendritic cell function in lymph nodes of simian immunodeficiency virus-infected macaques: consequences for pathogenesis

HIV and simian immunodeficiency virus (SIV) infections are characterized by several abnormalities in B cell function. Pathogenesis is also associated with marked changes within germinal centers (GC) including hypertrophy and degeneration of follicular dendritic cells (FDC) and accumulation of both viral antigen and activated CD45RO+ CD8+ cells. Since FDC are critical to the generation of antibody-forming cells and specific B cell memory, the simplest assumption is that such B cell defects directly result from virus-induced changes in the GC environment. The present study examined FDC-enriched mesenteric lymph node lymphocyte preparations from early and late stage SIV-infected and uninfected macaques for their ability to support GC reactions in vitro. The results indicate that FDC function as measured by cluster formation, B cell proliferation and SIV-specific antibody production is enhanced in SIV-infected macaques suggesting that, despite FDC atrophy, virus accumulation induces increased FDC-B cell interactions resulting in B cell hyperactivity. The activation and proliferation of CD8+ cells in FDC-enriched cultures further suggest that the infiltrating CD8+ population observed in situ in GC of late-stage SIV/HIV-infected individuals may also benefit from FDC-derived growth signals. Thus, in addition to enhanced B cell proliferation and antibody production, hyperactivity of FDC may potentially promote their own self destruction via the infiltrating CD8+ cells. The increased B cell responsiveness may further exacerbate the disease process due to an overall decrease in the affinity of anti-HIV/SIV antibody, a loss of crucial protective antibodies to other infectious agents and the creation of an environment in which increased trapping of virions facilitates more extensive infection of CD4+ T cells.

Characteristics of the CD8+ lymphocytosis during primary simian immunodeficiency virus infections

OBJECTIVE

To investigate the source of the expanded blood CD8+ subsets during an acute primary simian immunodeficiency virus (SIV) infection of macaques and the potential role of these cells in disease progression.

DESIGN AND METHODS

The primary CD8+ lymphocytosis, which occurs at 1-2 weeks following infection with SIVsmm/PBj-14, was examined in rhesus and cynomolgus macaques. Extensive subset analysis of the expanded blood CD8+ cell pool in a rhesus macaque was compared phenotypically with those in thymus, lymph nodes, spleen, ileum and lung washouts obtained at necropsy during blood lymphocytosis. The influence of the primary CD8+ cells expansion on disease progression was assessed at days 175-679 post-infection in long-term PBj-14 survivors staged according to immunological, virological and histopathological changes in their lymphoid organs.

RESULT

The very rapid and transient blood lymphocytosis following infection consisted of two distinct CD45RA(low), CD8+ and CD28-, lymphocyte function-associated antigen (LFA)-1(high), CD45RA(high), CD8+ populations. These populations were present in low levels in thymus, lymph and spleen but were highly represented in mucosal tissues, such as long washout, in which CD28- LFA-1(high) CD45RA(high) CD8+ cells comprised 86% of CD8+ cells, and gut, which was predominantly CD45RA(low) CD28- CD8+ cells. A comparison of progressor and non-progressor PBj-14-infected rhesus and cynomolgus macaques also indicated that the existence or magnitude of a blood CD8+ lymphocytosis during the acute phase of infection did not by itself appear to influence or be predictive of disease progression.

CONCLUSION

The marked blood CD8+ lymphocytosis observed during acute SIV infection did not result from expansion of virus-specific precursors in peripheral lymph node and did not appear to influence the rate of disease progression. The findings provide a novel explanation for the primary CD8+ cell lymphocytosis and invoke a mechanism whereby virus-induced cytokine/chemokine production in mucosal sites initiate the transient migration of a pre-existing CD8+ population into the blood from compartments such as lung and gut. Such results suggest that the magnitude of lymphocytosis may depend on the level of viral replication in mucosal tissues and the presence of other infections, for example, cytomegalovirus.

CD8+ cell-mediated immune responses: relation to disease resistance and susceptibility in lentivirus-infected primates

Immune responses mediated by CD8+ lymphocytes have been correlated with protection from HIV infection and disease progression in humans and nonhuman primates. The CD8+ cell population is heterogeneous in terms of biological function and phenotype. We have undertaken a review of the current state of knowledge of subtypes of CD8+ cells and their role in immune responses directed to HIV and related primate lentiviruses. Differences in the pathogenesis of lentivirus infections in various primate hosts were examined and the possible roles of the various subpopulations of CD8+ lymphocytes in the resistance and/or susceptibility to lentivirus-related disease were compared.

Characterization of gut-associated lymphoid tissue (GALT) of normal rhesus macaques

This study characterizes the gut-associated lymphoid tissue (GALT) of normal healthy rhesus macaques and compares the percentages of T and B cell subsets to those of systemic lymphoid tissue. Lymphocytes from the systemic lymphoid tissue (spleen, axillary, and inguinal lymph nodes), mesenteric lymph nodes (MLN), and intestinal epithelium (IEL) and lamina propria (LPL) of the jejunum, ileum, and colon were examined from both adult and juvenile, normal rhesus macaques. Lymphocytes were analyzed for expression of CD2, CD3, CD4, CD8, CD25, gamma delta TCR, and CD20 by two- or three-color flow cytometric analysis. Sections of jejunum, ileum, and colon were examined for CD3, CD20, and CD103 expression by immunohistochemistry. Peyer's patches were also examined for CD3, CD4, CD8, and CD20 expression by immunohistochemistry. Most IEL and LPL were CD103+, CD3+ T cells with significantly fewer CD20+ B cells. The IEL were predominantly CD3+CD8+ (63-80%), with very few CD4+ cells, whereas CD4:CD8 ratios in the LPL ranged from 0.74 to 1.3. Three to 38% of the IEL were gamma delta TCR positive, but gamma delta expression was rare in the LPL and MLN. gamma delta TCR expression was also higher in the IEL of younger animals. LPL had higher expression of CD25 compared to IEL and systemic tissues, particularly in aged animals. CD4+CD8+, double-positive and CD3+CD4-CD8- double-negative cells were also observed in GALT. These results demonstrate that GALT of rhesus macaques is remarkably similar to that of humans, further justifying the use of these animals as models for various intestinal disorders.

Similar abnormalities of idiotype and immunoglobulin light chain expression and of cell-mediated cytotoxicity in HIV-infected humans and simian immunodeficiency virus (SIV)-infected rhesus macaques

The pathogenesis of AIDS in simian immunodeficiency virus (SIV)-infected rhesus macaques models the pathogenesis of human AIDS. We investigated whether certain immunological abnormalities associated with HIV infection and implicated in disease progression also occur in SIV infection. We observed striking parallels between the rhesus macaque humoral immune response to SIV and unusual features of the human humoral immune response to HIV infection. Anti-SIV envelope antibodies from SIV-infected macaques exhibited skewed kappa/lambda L chain usage relative to the ratio of kappa/lambda L chain usage detected on total plasma Ig. In addition, the same idiotope conserved on human anti-HIV gag, pol and env antibodies was detected with a similar distribution pattern on macaque anti-SIV env, gag and pol antibodies. Skewed Ig L chain representation and selection of a highly conserved possible dominant regulatory idiotope on antibodies against key neutralizing antigens raise the possibility that the progressive failure of the humoral immune response to SIV and HIV involves skewed oligoclonal humoral immunity. We also found that SIV-infected macaques, like HIV-infected humans, have elevated levels of CD8+ lymphocyte-mediated cytotoxicity. Cytotoxicity against human B cells was higher in CD8+ effector lymphocytes from SIV-infected macaques than in those from uninfected macaques (P < 0.05). Cell-mediated cytotoxicity against human NK cell targets was not elevated in effector lymphocytes from the SIV-infected macaques, suggesting that CTL activity was selectively elevated. Two out of seven SIV-infected macaques tested had CD8+ cytotoxic lymphocytes that selectively killed activated uninfected CD4+ macaque lymphocytes. Oligoclonal B cell responses and persistently elevated CD8+ lymphocyte-mediated cytotoxicity are consistent features of primate retroviral infections leading to AIDS. Understanding immune predispositions to these features triggered by HIV and SIV may advance new prophylactic and therapeutic strategies.

Toward an understanding of the correlates of protective immunity to HIV infection

Considerable progress has been made recently in understanding the genetic, immunologic and virologic factors in human immunodeficiency virus (HIV)-infected individuals who either rapidly progress or do not progress to acquired immunodeficiency syndrome (AIDS). In addition, detection of HIV-specific immune responses in HIV-negative individuals who have been exposed to the virus multiple times suggests that natural immune responses to HIV may be protective in rare individuals. Understanding the correlates of protective immunity to HIV infection is critical to efforts to develop preventive HIV vaccines as well as to determine the feasibility of treating HIV infection by boosting immunity to HIV.

Viral DNA burden and decline in percentage of CD4-positive cells in the lymphoid compartment of SIV-infected macaques

The decline in CD4+ cells and increased viral DNA and RNA burden in the blood of human immunodeficiency virus (HIV)-infected individuals have been used as closely related correlates of disease progression. However, little is known about levels of total or unintegrated viral DNA in lymphoid tissue of HIV-infected patients and how they relate to CD4+ cell decline or disease progression. Exploiting the similarities between HIV- and simian immunodeficiency virus (SIV)-induced disease, we examined lymphoid organs and peripheral blood from SIV-infected macaques for total (pol) and unintegrated 2-LTR circular viral DNA by polymerase chain reaction (PCR). Two SIV isolates (SIVmac/251 and SIVmne/E11S) that differ markedly in their biological and clinical properties were studied. The results indicate that total viral DNA burdens vary considerably between isolates. There was no strong association between total viral DNA levels and CD4% in lymphoid tissues when isolates were compared and death was not associated with any particular level of viral pol DNA. In contrast, accumulation of unintegrated viral DNA was closely associated with decline in CD4/CD8 ratios in lymphoid organs and AIDS. The appearance of both pol and unintegrated viral DNA in thymus of infected macaques also emerged as one of the single best correlates or possible predictors of advanced disease yet studied. Their roles in pathogenesis are discussed.