Immune recovery in HIV disease: role of the thymus and T cell expansion in immune reconstitution strategies

Signal joint T-cell receptor excision circle assay in miniature swine

OBJECTIVE

Assays for T cell receptor excision circles (TREC) have been utilized in human, primate, and mouse models as a measure of thymic activity, but no comparable assay has been described in artiodactyls. We describe the development of the porcine signal joint (sj) TREC assay, and provide a likely reason for previous difficulties in its identification in artiodactyls.

DESIGN AND METHODS

Utilizing the homology between the known genomic sequences in sjTREC in human and mouse, polymerase chain reaction (PCR) primers were derived for the putative porcine sjTREC. Primers from the ψJα side of the sjTREC were derived from the known porcine sequence.

RESULTS

The sjTREC in two artiodactyls, swine and sheep, was identified using forward primers from the ψJα region, and reverse primers from the putative δ-rec region. Unlike in the detection of primate TRECs, initially the use of similar primers close to the δ-rec failed to yield the sjTREC product. Marching about 800 basepairs into δ-rec, primers derived from a homology region between human and mouse led to the detection of sjTREC. Comparing sjTREC amongst the species revealed highest homology between the two artiodactyls. A quantitative PCR (QPCR) assay of porcine sjTREC was also developed.

CONCLUSION

Identification and analysis of the sjTREC sequences in two artiodactyls suggested why previous attempts at cloning the pig TREC using known sjTREC sequences were unsuccessful. The development of the porcine signal joint TREC assay should enable a more direct quantification of thymic activity in porcine models of transplant biology.

Cocaine reduces thymic endocrine function: another mechanism for accelerated HIV disease progression

Thymulin is a thymic peptide important for the maturation and differentiation of immature thymocytes, which have been found to be depressed in patients with low-level CD4(+) cell recovery despite viral control. Substance use is associated with faster progression of HIV disease, which has been ascribed to poor adherence to antiretroviral medication. Recent findings of an association between cocaine use and decline in CD4(+) cell counts independent of antiretroviral adherence indicate alternative mechanisms for disease progression. We evaluated the relationship between thymulin activity, CD4(+) and CD8(+) cell counts and the CD4(+)/CD8(+) ratio, and the covariate effects of substance use cross-sectionally in 80 HIV(+) active substance users and over 12 months in 40 participants. Thymulin activity was analyzed in plasma using a modification of the sheep rosette bioassay. Thymulin activity was negatively associated with cocaine use (β = -0.908,95% CI: -1.704, -0.112; p = 0.026). Compared to those who do not use cocaine, cocaine users were 37% less likely to have detectable thymulin activity (RR = 0.634, 95% CI: 0.406, 0.989 p = 0.045) and were 75 times more likely to show a decrease in thymulin activity (OR = 74.7, 95% CI: 1.59, 3519.74; p = 0.028) over time. CD4(+) cell count was positively associated with thymulin activity (β = 0.127, 95% CI: 0.048,0.205; p = 0.002), detectable thymulin activity was 2.32 times more likely in those with a CD4 cell count ≥200 cells/μl (RR = 2.324, 95% CI: 1.196, 4.513, p = 0.013), and those with an increase in CD4 cell counts were more likely to show an increase in thymulin activity (OR = 1.02, 95% CI: 1.00, 1.034; p = 0.041) over time. Thymulin activity is predictive of HIV disease progression and is depressed in cocaine users independent of antiretroviral treatment (ART) and HIV viral load. Understanding the mechanisms for accelerated HIV disease progression provides opportunities to find alternative strategies to counteract immunosuppression.

The reconstitution of the thymus in immunosuppressed individuals restores CD4-specific cellular and humoral immune responses

Infection with HIV-1 frequently results in the loss of specific cellular immune responses and an associated lack of antibodies. Recombinant growth hormone (rGH) administration reconstitutes thymic tissue and boosts the levels of peripheral T cells, so rGH therapy may be an effective adjuvant through promoting the recovery of lost cellular and T-cell-dependent humoral immune responses in immunosuppressed individuals. To test this concept, we administered rGH to a clinically defined group of HIV-1-infected subjects with defective cellular and serological immune responses to at least one of three commonly employed vaccines (hepatitis A, hepatitis B or tetanus toxoid). Of the original 278 HIV-1-infected patients entering the trial, only 20 conformed to these immunological criteria and were randomized into three groups: Group A (n = 8) receiving rGH and challenged with the same vaccine to which they were unresponsive and Groups B (n = 5) and C (n = 7) who received either rGH or vaccination alone, respectively. Of the eight subjects in Group A, five recovered CD4 cellular responses to vaccine antigen and four of these produced the corresponding antibodies. In the controls, three of the five in group B recovered cellular responses with two producing antibodies, whereas three of the seven in Group C recovered CD4 responses, with only two producing antibodies. Significantly, whereas seven of ten patients receiving rGH treatment in Group A (six patients) and B (one patient) recovered T-cell responses to HIVp24, only two of six in Group C responded similarly. In conclusion, reconstitution of the thymus in immunosuppressed adults through rGH hormone treatment restored both specific antibody and CD4 T-cell responses.

Immunological dysfunction in HIV-1-infected individuals caused by impairment of adenosine deaminase-induced costimulation of T-cell activation

The cell surface association between CD26 and adenosine deaminase (ADA) has a costimulatory function during T-cell activation. Several studies have revealed correlations among CD4(+) CD26(+) T-cell depletion, increased serum levels of ADA, and the evolution of human immunodeficiency virus (HIV) infection, implicating CD26 and ADA in HIV disease progression. In this context, we aimed to determine whether ADA costimulation could be altered during HIV infection. ADA costimulation was investigated in cells from HIV-infected patients (n = 36) in terms of proliferation and cytokine secretion. An effect of ADA on T-cell proliferation was found in HIV-1-infected patients and correlated positively with the CD4(+) percentage and the nadir CD4 count and negatively with viral load, demonstrating that the response depends on the immunological status of the patient. The robust ADA-induced increase in cytokine production [interferon (IFN)-gamma, interleukin (IL)-6 and IL-10] was markedly reduced in T cells from HIV-1-infected subjects. To eliminate some of the variables associated with immunological defects in HIV-1-infected patients, anti-CD3 plus ADA assays with T cells from healthy volunteers were performed in the presence of recombinant glycoprotein 120 (gp120). It was found that gp120 was responsible for the impairment of the ADA-CD26 interaction and consequently of the ADA-induced effect on both costimulation and cytokine production. The gp120-mediated disruption of the CD26-ADA interaction is a novel mechanism that might explain, at least in part, the altered immunological features observed in HIV-1-infected patients and may have significant relevance in AIDS pathogenesis.

Doxycycline enhances the Ras-MAPK signaling and proliferation of mouse thymic epithelial cells

Depletion of T-cell-dependent immunity is a major consideration for patients suffering from infections of human immunodeficiency virus (HIV), those undergoing organ transplantation, and those receiving anti-cancer chemotherapy and/or radiotherapy. In general, T-cell regeneration occurs in the thymus through thymopoiesis. We have found that doxycycline (Dox), a tetracycline derivative, enhances the proliferation of mouse thymic epithelial cells, which are unique in their capacity to support positive selection and are essential throughout the development of thymocytes. Cell cycle analysis indicates that the increased cell proliferation is due to a shortened G(0)/G(1) phase. To reveal the underlying mechanisms, we examined the expression of an array of molecules that regulate the cell cycle. The results show that in mouse thymic medullary-type epithelial cell line 1 (MTEC1) Dox leads to elevated levels of H-Ras, phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), cyclin E, cyclin dependent kinase 4/2 (CDK4/CDK2), E2F3, and c-myc. These data, and the observation that the proliferation-enhancing effect is largely abolished following treatment with an ERK inhibitor support an active role of the Ras-ERK/mitogen-activated protein kinase (MAPK) signaling pathway. In conclusion, the present study reveals a new activity of an old family of antibiotics. The in vivo effect of Dox on immune reconstitution warrants further exploration.

Low and undetectable breast milk interleukin-7 concentrations are associated with reduced risk of postnatal HIV transmission

OBJECTIVE

To investigate if breast milk interleukin [IL]-7 concentrations are associated with postnatal HIV transmission.

DESIGN

A case-control study nested within a cohort of women recruited in Lusaka, Zambia.

METHODS

IL-7 breast milk concentrations were measured in samples from 24 HIV-infected breast-feeding women who transmitted HIV to their child after the neonatal period and from 47 women who did not transmit. Samples were frequency-matched by the time of sample collection (1 week and 1 month postpartum). Logistic regression was used to adjust for possible confounders. For comparison, samples from 18 HIV-uninfected women from the same community were included in the analysis, and plasma IL-7 was determined.

RESULTS

Breast milk IL-7 concentrations were significantly higher than plasma IL-7 concentrations in all 3 groups. In contrast to levels among transmitters and HIV-uninfected women, breast milk IL-7 concentrations exhibited a bimodal distribution among nontransmitters. Breast milk IL-7 concentrations undetectable or less than 30 pg/mL were significantly associated with less HIV transmission (odds ratio = 0.13, 95% confidence interval: 0.03 to 0.64). The association remained strong after adjustment for breast milk viral load and sodium, maternal CD4 cell counts, parity, and time of sample collection.

CONCLUSION

Breast milk IL-7 may be necessary for effective HIV transmission.

T cell receptor excision circles (TRECs) analysis during acute intrarectal infection of cynomolgus monkeys with pathogenic chimeric simian human immunodeficiency virus

Several studies have shown the importance of evaluating Recent Thymic Emigrants (RTEs) by quantification of T cell receptor-rearrangement excision circles (TRECs), as a measure of de novo T cell generation during human immunodeficiency virus-1 (HIV-1) infection. To determine whether acute viral infection may have an impact on TRECs, cynomolgus monkeys (Macaca fascicularis) were infected intrarectally with simian human immunodeficiency virus (SHIV) 89.6P(cy11) and the number of signal-joint (sj) TRECs was determined in purified CD4+ and CD8+ populations for up to 28 weeks post-infection. Four weeks after infection, TRECs levels significantly decreased in both CD3+ CD4+ and in CD3+ CD8+ T lymphocytes of infected monkeys, whereas they remained unchanged in uninfected animals. This reduction was followed by a progressive TRECs number recovery in CD3+ CD4+ T lymphocytes that positively correlated with changes in the levels of circulating CD3+ CD4+ T cells. In the CD3+ CD8+ T cell subset, TRECs number remained significantly low and inversely correlated with the increase in the percentages of CD3+ CD8+ T cells. These data suggest that SHIV89.6P(cy11) intrarectal infection of cynomolgus monkeys differently affects TRECs content in CD3+ CD4+ and CD3+ CD8+ T cell subsets.

Immunopathogenesis of feline immunodeficiency virus infection in the fetal and neonatal cat

The global incidence of pediatric HIV infection is estimated at 2.3 million children, most acquiring the infection from their mothers in utero, peripartum, or postpartum. Pediatric HIV infection typically causes a rapidly progressive disease when compared with adult infection, due in part to the profound susceptibility of the neonatal thymus to productive infection or degenerative changes. Failed production of naive T-lymphocytes further limits the success of antiviral therapy to restore immunologic function. In this review, we explore the use of feline immunodeficiency virus (FIV) infection of domestic cats as an animal model for pediatric HIV infection. Cats infected with FIV represent the smallest host of a naturally occurring lentivirus, and the immunodeficiency syndrome elicited by FIV infection is similar to that of HIV-AIDS. The feline-FIV model uniquely reproduces several key aspects of immunosuppressive lentivirus infection of the thymus, allowing investigators to define viral determinants of pathogenicity, influence of host age on disease outcome, and therapeutic strategies to restore thymus function.

HIV infection of primary CD4+ Th2 cells, defined by expression of the chemoattractant receptor-homologous (CRTH2), induces a Th0 phenotype

The association between HIV, cytokine profile, and disease progression is controversial. In this study, we evaluated whether HIV infection of a primary T helper-like type 2 cytokine (Th2) cell subset augments their cytokine profile. We utilized the CRTH2 (chemoattractant receptor-homologous) marker to identify CD4+ Th2 cells. Approximately 2-4% of CD4+ T cells are CRTH2+. CRTH2+ expression is confirmed to delineate a Th2 subset as indicated by robust inducible IL-4 response. CD4+ CRTH2+ T cells were also more inherently activated than their CRTH2-negative counterpart as indicated by a higher percent expression of CD69, CD45RO, CD95, CD25, and HLA-DR. CD4+CRTH2+ T cells were not terminally differentiated as indicated by expression of CD27 and CD28. In vitro HIV infection of primary human CD4 CRTH2T cells, independent of chemokine coreceptor usage, potently upregulated IFN-gamma production while still maintaining robust IL-4 expression. This Th0 (IFNgamma+ IL-4+) phenotype was upregulated in CD4+CRTH2+ T cells post-HIV infection by 18-fold, demonstrating a shift to a Th0 phenotype. Ex vivo studies also demonstrated that HIV+ patients exhibited a decline in CD4+CRTH2+ cells and a shift of this population toward cells that express both IFN-gamma and IL-4. Collectively, these data indicate that HIV replication in Th2 cells induces a Th0 phenotype. This phenomenon may be a deliberate viral escape mechanism to prevent the skewing of the immune response toward Th1 or Th2.

Optimization of culture and storage conditions for an in vitro system to evaluate thymocyte phenotype and function

Studies on thymopoiesis are critical to the understanding of T-cell homeostasis as well as the host response to T-cell depletion. Various in vitro culture systems have been used in the study of thymocyte development; however it is unclear if current co-culture methods have been fully optimized. In this study in vitro suspension cultures have been re-evaluated and the optimal storage conditions for thymocytes have been established by evaluating various methods of storing/isolating thymic tissue and isolated thymocytes as well as the source of thymic epithelial cells (TEC). It was determined that thymocytes must be freshly isolated from whole thymic tissue and ideally stored at 4 degrees C prior to co-culture. Co-culture with either autologous or allogeneic TEC results in similar thymocyte subset distribution as well as interleukin-7 receptor-alpha (CD127) expression on these subsets. To evaluate the influence of the source of TEC on one aspect of thymocyte function the effect of IL-7 stimulation on the expression of CD127 was evaluated. IL-7 stimulation resulted in a downregulation of the expression of CD127 on all thymic subsets similar to that observed in circulating CD8+ T-cells. The effect of this was the same whether TEC were autologous or allogeneic. Optimizing culture techniques and facilitating the study of individual thymocyte subsets will lead to a better understanding of thymic function and development. It could also lead to therapeutic approaches that enhance immune recovery after T-cell depletion in HIV infection, bone marrow transplantation or following chemotherapy.

Evaluation of the impact of highly active antiretroviral therapy on immune recovery in antiretroviral naive patients

OBJECTIVES

To examine the extent of immune reconstitution in treatment-naive patients with CD4 T-cell counts <500 cells/microL following 48 weeks of highly active antiretroviral therapy (HAART).

METHODS

Thirteen antiretroviral naive patients were evaluated longitudinally for 48 weeks on HAART utilizing immune functional and lymphocyte phenotyping assays, including lymphocyte proliferation assay, flow cytometric evaluation of cell surface markers, and delayed type hypersensitivity skin tests. Virologic responses were monitored using commercially available viral load assays and gag/pol mRNA quantification using simultaneous immunophenotyping/UltraSensitive fluorescence in situ hybridization (ViroTect In Cell HIV-1 Detection Kit; Invirion, Frankfort, MI). Thymic function was evaluated for a subset of four patients using real-time polymerase chain reaction (PCR) for T-cell receptor excision circle (TREC) quantification and thymic scans using computerized axial tomography (CT) of the thymus.

RESULTS

HAART initiation resulted in a significant decline in plasma viremia and percentage of infected peripheral blood cells, and a rise in CD4 T cells from a baseline median of 207 cells/microL to a week-48 median of 617 cells/microL. The rise was predominately in CD4 memory cells. Naive T cells also increased in number, but at a slower rate. Activated (HLA-DR CD38) CD4 and CD8 T cells were elevated at baseline (24 and 62%, respectively) and declined by week 48 (17 and 36%, respectively) but did not reach normal levels. The number of Fas CD4 T cells increased from a baseline median of 169 to 381 cells/microL at week 48. Both soluble interleukin (IL)-2 and tumour necrosis factor (TNF) II receptors declined by week 48. HIV p24 lymphocyte proliferation assay responses were transiently detected in three patients. TREC values increased from a median 6400 copies/microg at baseline to a week-48 median value of 26 697 copies/microg.

CONCLUSION

Immune functional reconstitution was not achieved in these HAART naive patients.

Differential effects of interleukin-7 and interleukin-15 on NK cell anti-human immunodeficiency virus activity

The ability of interleukin-7 (IL-7) and IL-15 to expand and/or augment effector cell functions may be of therapeutic benefit to human immunodeficiency virus (HIV)-infected patients. The functional effects of these cytokines on innate HIV-specific immunity and their impact on cells harboring HIV are unknown. We demonstrate that both IL-7 and IL-15 augment natural killer (NK) function by using cells (CD3(-) CD16(+) CD56(+)) from both HIV-positive and -negative donors. Whereas IL-7 enhances NK function through upregulation of Fas ligand, the effect of IL-15 is mediated through upregulation of tumor necrosis factor-related apoptosis-inducing ligand. The difference in these effector mechanisms is reflected by the ability of IL-15-treated but not IL-7-treated NK cells to reduce the burden of replication-competent HIV in autologous peripheral blood mononuclear cells (PBMC) (infectious units per million for control NK cells, 6.79; for IL-7-treated NK cells, 236.17; for IL-15-treated cells, 1.01; P = 0.01 versus control). In addition, the treatment of PBMC with IL-15-treated but not IL-7-treated NK cells causes undetectable HIV p24 (five of five cases), HIV RNA (five of five cases), or HIV DNA (three of five cases). These results support the concept of adjuvant immunotherapy of HIV infection with either IL-7 or IL-15 but suggest that the NK-mediated antiviral effect of IL-15 may be superior.