Since its creation, the Unit has focused on the study of CD4+ T cells and of two cytokines, interleukin-2 (IL-2) and interleukin-7 (IL-7) which play complementary roles on these lymphocytes.
All of our knowledge is directed at understanding HIV pathogenesis.
The roles played by defects of the IL-2/IL-2-receptor and of the IL-7/IL-7-receptor systems are under investigation.
Our starting hypothesis is that abnormal activation of the immune system in HIV-infected patients pushes the CD4+ T lymphocytes towards a refractory state, partially characterized by the non-responsiveness to IL-2 and IL-7.
This might contribute to mechanisms behind CD4+ T cell anergy and lymphopenia, the hallmarks of the immunodeficiency of HIV patients.
From 2007 to 2011, our research has been centered around two main subjects:

1. Interleukin-2 Receptor and Interleukin-7 Receptor signaling mechanisms

(Pascal Bochet - Blanche Tamarit - Marie-Christine Cumont - Thierry Rose)
We have shown that the three IL-2 receptor chains are pre-assembled at the surface of  CD4+ T lymphocytes and that signal transduction is initiated by conformational changes induced by IL-2.

We have demonstrated that the IL-7 signaling complex is composed of more than two hundred proteins, among which 124 have been identified. A high percentage of these proteins are components of lipid microdomains and of the cytoskeleton. We have described that after IL-7 binding, IL‑7 receptor complexes migrate into lipid rafts and bind to microtubules.
The phosphorylation of the tyrosine kinases Jak1 and Jak3 occurs in the lipid rafts and is followed by the phosphorylation of the transcription factor STAT5. We showed that phosphorylated STAT5 is then carried into the nucleus by molecular motors bound to radial microtubules linking the rafts to the nucleus.  
Schema signalisation IL-7  
Sequential steps:

- Il-7 binds to the IL-7 receptor and triggers its migration to lipid microdomains. 
- IL-7 triggers the growth of radial microtubules from the microdomains to the nucleus.
- Non-phosphorylated STAT5 attaches to the radial microtubules with molecular motors and migrates to the receptor microdomain.
- The activated IL-7 receptors bind and phosphorylate intracellular Jak which, in turn, phosphorylates STAT5.
- Phosphorylated STAT5 forms dimers which migrate to the nucleus along the microtubule. 
- Phosphorylated STAT5 dimers enter the nucleus through the Nuclear Pore Complex.
- In the nucleus, phospho-STAT5 activates the expression of the IL-7 specific genetic program

2. Sensitivity or resistance to the immunological disease following chronic HIV infection

(Thierry Rose - Florence Bugault - Marie-Christine Cumont - Jacques Thèze)
Defects in the IL-7 system in HIV infected patients:

In HIV infected patients, abnormal activation of the immune system induces a refractory state in CD4+ T cells and they do not respond to physiological signals.
In this context, we have investigated the effect of IL-7 on CD4+ T lymphocytes from non-treated HIV patients. Although only a very small proportion (less than 0.5%) of CD4+ T lymphocytes are infected, all are in a refractory state. These CD4+ T lymphocytes do not display their normal, proliferative response to IL-7 and therefore do not display the expansion or proliferation needed for maintaining normal CD4+ T cell counts. Using super resolution (STED) microscopy and proteomics (2D electrophoresis and Mass Spectrometry) we have characterized the refractory state of chronically activated CD4+ T cells in non-treated patients.  We are using advanced high resolution microscopy methods to investigate the cause and origin of these defects.
HIV controllers:
HIV Controllers are rare patients (less than 0.5% of HIV patients) who maintain CD4+ T cell homeostasis and spontaneously control HIV replication in the absence of any treatment.

The CD4+ T cell compartment of “HIV Controllers” is characterized by a high numbers of central memory CD4+ T lymphocytes. Central memory CD4+ T cells from HIV Controllers keep a strong ability to secrete IL-2, their autocrine growth factor; to respond to IL-7; and to divide actively.
They express high levels of the lymph node homing chemokine receptor CCR7 and therefore migrate very efficiently to sites of infection.
We found that central memory CD4+ T lymphocytes and their effector counterparts have high avidity for HIV peptides, making them reactive to low amounts of virus.
Taken together, these parameters contribute to maintaining long term and effective anti-viral responses in HIV controller patients in the absence of any treatment.

Specific properties of central memory CD4+ T lymphocytes from HIV controllers:

- increased production of IL-2, the autocrine growth factor for CD4+ T lymphocytes. 
- increased multiplication of the cells over their lifetime. 
- increased expression of the CCR7 homing receptor and increased migration to the lymph nodes.
- increased production of cytokines which activate B lymphocytes and cytotoxic CD8+ T lymphocytes,
therefore triggering effective antiviral activity.
- high avidity specific T cell receptors for HIV antigen. Stimulation of these high avidity receptors triggers the activation of CD4+ T lymphocyte at a very low concentration of the virus.

3. New Projects (Jacques Thèze)

In collaboration with Claudine Duvivier and Olivier Lortholary (Centre Médical Pasteur, Hopital Necker), Olivier Lambotte and Jean Francois Delfraissy (Hopital Bicêtre) and the Centre International de Recherches Chantal Biya (Yaoundé, Cameroun). 
New projects represent the continuation of work done since 2007. Two clinical investigations will be initiated.
One project will build on our knowledge regarding IL-7 and HIV-controller status to launch an assay aimed at treating patients under anti-retroviral therapy by IL-7 cycles. We hope to induce high avidity CD4+ T lymphocytes to induce a status similar to HIV-controllers. This may allow us to interrupt or to definitively stop anti-retroviral therapy.
Another project is aimed at characterizing pediatric HIV-controller patients in Cameroon. We would like to define the mechanism of spontaneous survival of children infected by HIV at birth and also provide an opportunity to undertake new immunological and genetic studies.