Directex vivo analysis reveals distinct phenotypic patterns of HIV-specific CD8+ T lymphocyte activation in response to therapeutic manipulation of virus load

Abstract

Therapeutic intervention with antiretroviral therapy (ART) enables the modulation of HIV virus load and hence provides a unique opportunity to study the consequences of varying antigen load onthe phenotype of virus‐specific CD8+ T lymphocytes in a persistent human viral infection. The recent advent of tetrameric peptide / HLA class I complexes has enabled the direct phenotypic characterization of antigen‐specific T cell populations ex vivo. Here, we use this technology to examine directly ex vivo the consequences of therapeutic manipulation of HIV virus load on the phenotype of HIV‐specific CTL. Our observations show that: (1) distinct sequential activation patterns of CD8+ T cells are associated with increasing virus load; (2) T cell receptor (TCR) down‐regulation without apoptosis represents an early event during the generation of a T cell response in a natural infection and precedes the emergence of two distinct antigen‐specific CD8+ T cell populations which differ in TCR and CD8 expression levels. Clear differences in surface Annexin V staining were observed between these populations. The observation that CTL activation, demonstrated by TCR and CD8 down‐regulation, in response to rising levels of virus load, co‐segregates with apoptosis only during later stages of the response indicates that antigen‐associated cell death is restricted to distinct subpopulations of CTL.

Dynamics of T Cell Responses in HIV Infection

“…The activation state of the cells correlated with the levels of TCR expression, as measured by the brightness of tetramer staining: activated cells displayed slightly lower tetramer staining than when resting (Fig. 2B), as described recently (22,23). Ki67 is an intracellular marker of proliferation; expression is restricted to cells in cycle.…”

“…This susceptibility to apoptosis is closely related to the activation status of the cells, and therefore also to the Ag load present in the patient. When viral rebound occurs, HIVspecific CD8 ϩ T cells again exhibit high CD38 levels (22) 5 and also reduced Bcl-2 expression (data not shown). Our observations of the activation state of virus-specific cells were not directly influenced by the use of ART, but more closely followed the viral load, as a similar phenotype was seen in both treated and untreated patients (Fig.…”

Expansion of highly differentiated CD8+ T-cells or NK-cells in patients treated with dasatinib is associated with cytomegalovirus reactivation

“…A similar phenotypic dichotomy (CD8 high vs CD8 low ) has been described previously for HIV-specific CD8 þ T-cells, both during the initiation and discontinuation of antiretroviral therapy. 38 Thus, dynamic perturbations of viral load can elicit such phenotypic patterns within the cognate CD8 þ T-cell population. Consistent with this explanation, both the CD8 high and CD8 low NLVPMVATVspecific CD8 þ T-cell populations were phenotypically and clonotypically similar within individuals, thereby indicating that Table 3 Phenotypic features of NK-cells (either gated on CD16 + or CD56 + first) in patients with T, NK or T+NK LGL expansion the same antigen-specific clonotypes can exist in different states of activation during dasatinib-associated LGL expansion.…”

Human Immunodeficiency Virus-Specific CD8+T-Cell Responses Do Not Predict Viral Growth and Clearance Rates during Structured Intermittent Antiretroviral Therapy

“…For analysis of HIV-specific CD8 ϩ T-cell frequencies, peripheral blood lymphocytes (PBL) were stimulated directly ex vivo with synthetic peptides corresponding to previously described HLA class I-restricted optimal CTL epitopes at a concentration of 2 M in gamma interferon (IFN-␥) ELI-SPOT assays (25,26). Results are expressed as spot-forming cells (SFC) per 10 6 PBL; background values were subtracted from the specific response before normalization to 10 6 PBL.…”