Persistant immunodominant anti-gag SLYNTVATL responses in HIV-patients with up to 7 years of HAART.

We analyzed Gag-specific CD8+ T-cells in HIV-patients on long-term HAART and in untreated chronically-infected patients by using iTAg MHC class I tetramers (HLA-A*0201) specific for SLYNTVATL. Gag SLYNTVATL-specific CD8+ T-cells were detectable in 18 of 26 treated patients (median 5.2 years of HAART) and in 10 of 14 untreated patients. Median percentage of Gag SLYNTVATL-specific CD8+ T-cells in treated patients was 0.10 (range 0.00-0.70%). Median number of Gag SLYNTVATL-specific CD8+ T-cells per 50,000 CD8+ T-cells was 56.0 cells (range 2.0-344.0 cells) and was not significantly different compared with untreated patients (p = 0.978). Numbers of Gag SLYNTVATL-specific CD8+ T-cells were inversely correlated with the duration of undetectable plasma viremia (p = 0.02, Rho = -0.430). Chronically-infected HIV-patients on HAART (for up to 7.7 years) maintained a stable subpopulation of Gag SLYNTVATL-specific CD8+ T-cells. This finding is relevant for the analysis of treatment-induced immune reconstitution and, possibly, for future therapeutic strategies in HIV-disease.

[MHC tetramers: tracking specific immunity]. / MHC-tetrameri: na tragu specificnoj imunosti.

In an adaptive immune response, antigen is recognized by two distinct sets of highly variable receptor molecules: (1) immunoglobulins, that serve as antigen receptors on B cells and (2) the antigen-specific receptors on T cells. T cells play important role in the control of infection and in the development of protective immunity. These cells can also mediate anti-tumor effects and, in case of autoimmune syndromes, contribute to the development and pathology of disease. The specificity of T cells is determined by T cell receptors (TCR). Understanding of the success of immune responses requires the direct measurement of antigen-specific T lymphocytes. Cell with major histocompatibility complex (MHC) class I molecules are able to present antigens to antigen-specific CD8+ cytotoxic T lymphocytes. MHC class I molecules present small peptides (epitopes) processed from intracellular antigens such as viruses and intracellular bacteria. MHC class I molecules in humans are designated as human leukocyte antigen (HLA) class I and divided into HLA-A, -B and -C. CD8+ T cells recognize MHC class I molecules and after activation produce proteins that destroy infected cells. MHC class II molecules receive their peptides mainly from extracellular and soluble antigens and present them to the CD4+ T helper cells. A recently described technique that can be used in flow cytometry enables us to quantify ex vivo antigen-specific T cells by binding of soluble tetramer MHC-peptide complexes attached to fluorochrome. Quantitative analyses of antigen-specific T cell populations provide important information on the natural course of immune responses. The interaction of T cell receptors on T lymphocytes with tetrameric MHC-peptide complexes mimics the situation on the cell surface, and allows for reliable binding. Tetramers consist of four biotinylated HLA-peptide epitope complexes bound to streptavidin conjugated with fluorescent dye. Tetramer technology has sensitivity of detection as little as 0.02% of total cytotoxic T cell pool or T helper cell pool (i.e. approximately 1 in 50.000 lymphocytes). The combination of this technology with intracellular cytokine staining methods opens up significantly better ways of studying these cells than previously possible, allowing immunologists to look at their life cycle (activation and proliferation), manner of death (aging and apoptosis) and effector function (cytotoxic potential and cytokine production). MHC tetramers class I have yielded useful insights into in vivo dynamic and function of antigen-specific CD8+ T cells in viral infections, parasitic infections, cancer, autoimmune disease and transplantation. This knowledge is of special interest for immunotherapy, diagnostic monitoring of T cell mediated immunity, and the development of new vaccination strategies. There is some possibility for cell therapy with antigen-specific CD8+ T cells for various diseases including cancer and viral infections. Targeted immunotherapy of selective deletion of auto--or alloreactive T cells with MHC tetramers may be important for the treatment of autoimmune disease, or to prevent the rejection of transplanted organs. The utility of this technique for the immunotherapy in vivo needs to be confirmed and modified in further research. Understanding how antigen-specific cells develop and function in different circumstances and pathologies will be the key to unravelling the secrets of cellular immune system.

Naive and memory B cells respond differentially to T-dependent signaling but display an equal potential for differentiation toward the centroblast-restricted CD77/globotriaosylceramide phenotype.

Resting (CD38(low)) tonsillar B cells differentiate to express the centroblast-restricted CD77/globotriaosylceramide antigen on high-level engagement of CD154. As the CD38(low) population comprises both naive and memory subsets, we wished to compare the propensity of each to develop this germinal center phenotype; particularly as the capacity of memory B cells to re-enter afollicular reaction remains unclear. Resting B lymphocytes were therefore separated into CD27(-)IgA(-)IgG(-) and IgD(-) fractions to generate subsets enriched for naive and memory cells, respectively. Following stimulation via BCR and/or CD40 - surrogate signals for B cells engaged in T-dependent signaling - differences between the two subsets were seen in the kinetics and/or magnitude of responses such as entry into DNA synthesis, induction of the costimulatory molecules CD80 and CD86; up-regulation of CD23, and changes in BCL-6 mRNA expression. Nevertheless, naive and memory cells revealed a nigh identical capacity for acquiring CD77: both appeared equally sensitive in this regard, with high-level CD40 engagement via cell-bound CD154 being required for both subsets to achieve the hallmark centroblast phenotype. These findings suggest that, provided with the opportunity to encounter cell membrane CD154 in abundance, both naive and memory B cells display the potential to be diverted towards a germinal center pathway of differentiation.