Production of CD8+ T cell nonlytic suppressive factors by CD28, CD38, and HLA-DR subpopulations

The CD8+ T Cell Noncytotoxic Antiviral Responses

The CD8+ T cell noncytotoxic antiviral response (CNAR) was discovered during studies of asymptomatic HIV-infected subjects more than 30 years ago. In contrast to CD8+ T cell cytotoxic lymphocyte (CTL) activity, CNAR suppresses HIV replication without target cell killing. This activity has characteristics of innate immunity: it acts on all retroviruses and thus is neither epitope specific nor HLA restricted. The HIV-associated CNAR does not affect other virus families. It is mediated, at least in part, by a CD8+ T cell antiviral factor (CAF) that blocks HIV transcription. A variety of assays used to measure CNAR/CAF and the effects on other retrovirus infections are described. Notably, CD8+ T cell noncytotoxic antiviral responses have now been observed with other virus families but are mediated by different cytokines. Characterizing the protein structure of CAF has been challenging despite many biologic, immunologic, and molecular studies. It represents a low-abundance protein that may be identified by future next-generation sequencing approaches. Since CNAR/CAF is a natural noncytotoxic activity, it could provide promising strategies for HIV/AIDS therapy, cure, and prevention.

Differential gene expression of soluble CD8+ T-cell mediated suppression of HIV replication in three older children

Suppression of human immunodeficiency virus (HIV) replication by CD8+ T-cells (CD8 suppression) contributes to survival in adults and children <1 year. Soluble CD8 suppression can also be seen in some older children with AIDS. The factor responsible, CD8-derived antiviral factor (CAF), acts at the level of HIV RNA transcription. Differential gene expression techniques have been used to define the gene(s) mediating this phenomenon in adults. Recently, CAF has been linked to exosomes secreted by CD8+ T-cells. To compare the gene expression profiles from pediatric patients with each other, with those reported in 2 previous studies in adults and in those reportedly related to exosomes, we used differential gene expression to study three older children with HIV infection, one who did demonstrate soluble CD-8 suppression and two who did not. Eighteen differentially expressed genes were also seen in one adult study (P = 0.002, χ(2) test), and 38 such genes (P < 0.0001, χ(2) test) in a second adult study. In addition, two exosome components and some RNA's related to exosomal proteins were also differentially expressed. In children with HIV infection, we found significant differentially expressed genes that correlated to those previously reported in two studies in adults. Our data also lends some support to the recent identification of CAF with exosomes secreted by CD8+ T-cells.

Phenotypic differences between healthy effector CTL and leukemic LGL cells support the notion of antigen-triggered clonal transformation in T-LGL leukemia

T cell large granular lymphocyte leukemia (T-LGL) is a chronic clonal lymphoproliferation of CTL. In many ways, T-LGL clones resemble terminal effector CTL, including down-modulation of CD28 and overexpression of perforin, granzymes, and CD57. We studied the transcriptome of T-LGL clones and compared it with healthy CD8+CD57+ effector cells as well as CD8+CD57- populations. T-LGL clones were sorted based on their TCR variable beta-chain restriction, and controls were obtained by pooling cell populations from 14 donors. Here, we focus our analysis on immunological networks, as immune mechanisms play a prominent role in the etiology of bone marrow failure in T-LGL. Informative genes identified by expression arrays were studied further in an independent cohort of patients using Taqman PCR, ELISA assays, and FACS analysis. Despite a strikingly similar gene expression profile between T-LGL clones and their healthy counterparts, important phenotypic differences were identified, including up-modulation of TNFRS9, myeloid cell leukemia sequence 1, IFN-gamma, and IFN-gamma-related genes, and several integrins/adhesion molecules. In addition, T-LGL clones were characterized by an overexpression of chemokines and chemokine receptors that are typically associated with viral infections (CXCL2, Hepatitis A virus cellular receptor 1, IL-18, CCR2). Our studies suggest that immunodominant LGL clones, although phenotypically similar to effector CTL, show significantly altered expression of a number of genes, including those associated with an ongoing viral infection or chronic, antigen-driven immune response.

Effects of highly active antiretroviral therapy and immune recovery on CD8+ T-cell-mediated inhibition of HIV-1 transcription

SUMMARY

: To date, the relation between the CD8 antiviral factor (CAF) and clinical indicators of disease progression in HIV-1 infection (CD4 T-cell counts and viral load [VL]) is inconclusive. Particularly, the effect of antiretroviral therapy and immune recovery on CAF production remains unclear. Using a transient transfection assay and a reporter gene activated by the HIV-1 long terminal repeat (LTR), we analyzed CAF production in CD8 T cells of HIV-1-positive individuals divided into 3 groups: patients on protease inhibitor (PI)-based therapy, patients on nonnucleoside reverse transcriptase inhibitor (NNRTI)-based therapy, and patients receiving no therapy. We found that within the untreated group, CAF activity inversely correlated with VL and high CAF was associated with lower VLs over a period of 0.5 to 3 years. Furthermore, patients who were drug-naive demonstrated significantly higher CAF than untreated patients who had previously undergone antiretroviral therapy. CAF activity in treated patients was similar to CAF in drug-naive patients and higher than in off-treatment patients. There seemed to be a trend toward higher CAF in patients on NNRTI-based therapy compared with those on PI-based therapy. These results suggest that immune recovery after highly active antiretroviral therapy (HAART) contributes to the normalization of CAF levels in HIV-1-positive individuals. Furthermore, we have distinguished between CD8 T-cell-mediated suppression of HIV-1 replication and gene transcription.

Antigen-specific beta-chemokine production and CD8 T-cell noncytotoxic antiviral activity in HIV-2-infected individuals

Human immunodeficiency virus-2 (HIV-2) is less pathogenic than HIV-1, and the disease progression in HIV-2-infected individuals seems to be similar to that seen in HIV-1-infected long-term nonprogressors. Cell-mediated immune responses and the production of noncytotoxic CD8+ T-cell antiviral factors (CAF) and beta-chemokines have been correlated to protection against HIV-1 and associated with asymptomatic infection and slower disease progression. We investigated the antigen-induced beta-chemokine production in HIV-2-infected patients living in Sweden and in Guinea-Bissau. We also compared in vitro CD8+ T-cell-mediated noncytotoxic antiviral activity against beta-chemokine-sensitive R5 virus (HIV-1Bal) and beta-chemokine-insensitive X4 virus (HIV-1IIIB) in HIV-2-infected patients with that in HIV-1-infected patients. HIV-2-specific beta-chemokine production was demonstrated in a majority of the HIV-2-infected subjects. CD8+ T cells of both HIV-1 and HIV-2-infected individuals suppressed R5 virus replication in vitro in a similar manner, while the inhibition of X4 virus replication seemed to be more frequent and of a higher magnitude among HIV-2-infected patients compared to HIV-1-infected subjects. Taken together, our results indicate that the production of CD8+ T-cell noncytotoxic antiviral factors may contribute to the low transmission of the virus and slower disease progression in HIV-2-infected patients.