Human naive CD4 T-cell clones specific for HIV envelope persist for years in vivo in the absence of antigenic challenge

Recursion-based depletion of human immunodeficiency virus-specific naive CD4(+) T cells may facilitate persistent viral replication and chronic viraemia leading to acquired immunodeficiency syndrome

Although antiretroviral therapy has made human immunodeficiency virus (HIV) infection a controllable disease, it is still unclear how viral replication persists in untreated patients and causes CD4(+) T-cell depletion leading to acquired immunodeficiency syndrome (AIDS) in several years. Theorists tried to explain it with the diversity threshold theory in which accumulated mutations in the HIV genome make the virus so diverse that the immune system will no longer be able to recognize all the variants and fail to control the viraemia. Although the theory could apply to a number of cases, macaque AIDS models using simian immunodeficiency virus (SIV) have shown that failed viral control at the set point is not always associated with T-cell escape mutations. Moreover, even monkeys without a protective major histocompatibility complex (MHC) allele can contain replication of a super infected SIV following immunization with a live-attenuated SIV vaccine, while those animals are not capable of fighting primary SIV infection. Here we propose a recursion-based virus-specific naive CD4(+) T-cell depletion hypothesis through thinking on what may happen in individuals experiencing primary immunodeficiency virus infection. This could explain the mechanism for impairment of virus-specific immune response in the course of HIV infection.

Evaluation of antigen-specific T-cell responses with a miniaturized and automated method

The evaluation of antigen-specific T-cell responses is helpful for both research and clinical settings. Several techniques can enumerate antigen-responsive T cells or measure their products, but they require remarkable amounts of peripheral blood mononuclear cells (PBMCs). Since screening numerous antigens or testing samples from pediatric or lymphopenic patients is hampered in clinical practice, we refined a miniaturized, high-throughput assay for T-cell immunity. Antigens and cells in 10-microl volumes were dispensed into 1,536-well culture plates precoated with anti-gamma interferon (anti-IFN-gamma) antibodies. After being cultured, the wells were developed by enzyme-linked immunosorbent assay for bound cytokine. Miniaturization and automation allowed quantitation of antigen-specific responses on 10(4) PBMCs. This method was applied for epitope mapping of mycobacterial antigens and was used in the clinic to evaluate T-cell immunity to relevant opportunistic pathogens by using small blood samples. A comparison with conventional methods showed similar sensitivity. Therefore, current flow cytometric methods that provide information on frequency and phenotype of specific T cells can be complemented by this assay that provides extensive information on cytokine concentrations and profiles and requires 20- to 50-fold fewer PBMCs than other analytical methods.

Helper function of cytolytic lymphocytes: Switching roles in the immune response

T helper (Th) cells and cytolytic T lymphocytes (CTL) play defined roles in the cellular immune response. This distinction wavered when Th lymphocytes were shown to kill antigen-presenting cells displaying the relevant antigen. Here we demonstrate that also the opposite can be true: CTL can exert helper functions. We noticed that certain CMV-specific CTL lines grew after antigen activation also without exogenous IL-2. These lines produced their own IL-2, which supported the expansion of other CTL and Th cell lines. High levels of helper cytokines like IL-4, IL-5 and IL-6 were detected in the culture supernatants. Thus, we set up a helper assay to study the functional interactions between T cells (or their supernatants) and B cells. Conditioned media from helper CTL lines induced secretion of antigen-specific antibodies by B cells pulsed with antigen as first signal. We conclude that it is possible to isolate CTL lines that exhibit helper functions for T cells and B cells. If this possibility is proven also in vivo, we should revise some of our views on the pathogenesis of diseases in which CD8 cells are key players, such as in viral infections, graft rejection and GVHD.

Comparative analysis of new innovative vaccine formulations based on the use of procaryotic display systems

A T helper epitope was expressed in three innovative delivery vehicles recently developed in our laboratories and based respectively, on the filamentous bacteriophage fd, the E2 protein from the PDH complex of Bacillus stearothermophilus and the protein CotC of Bacillus subtilis spores. Studies of antigenicity and immunogenicity were performed by using a specific T cell hybridoma and by priming mononuclear cells isolated from the venous blood of human donors. The results indicate that the E2 system is the best suited for inducing a specific immune response towards a CD4 T cell epitope. Importantly, TCR clonal analysis demonstrated the persistence over years of a previously described antigen specific clonotype and its presence correlates with the immunogenic strength of the antigen delivery system.