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Immune reconstitution Anjie Zhen, PhD

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Presentation on theme: "Immune reconstitution Anjie Zhen, PhD"— Presentation transcript:

1 Immune reconstitution Anjie Zhen, PhD

2 Overview of HIV life cycle
Binding and Fusion Entry Reverse transcription Integration Viral RNA and protein expression Assembly and budding Maturation HIV target cells: CD4T cells, Macrohpages, Dendritic cells

3 Anti-retroviral therapy
HAART: Highly active anti-retroviral therapy Usually combine several drugs that target different stages of HIV replication Classes: Entry inhibitors (Maraviroc/enfuvirtide) Nucleoside reverse transcriptase inhibitors (NRTI) and nucleotide reverse transcriptase inhibitors (NtRTI) (tenofovir, deoxythymidine, zidovudine, etc) Non-nucleoside reverse transcriptase inhibitors (NNRTI) (nevirapine, etc) Integrase inhibitors (Raltegravir) Protease inhibitors (Indinavir, Nelfinavir etc)

4 Overview of HIV life cycle
X HIV life cycle: Binding and Fusion Entry Reverse transcription Integration Viral RNA and protein expression Assembly and budding Maturation HIV target cells: CD4T cells, Macrohpages, Dendritic cells X X X

5 Effect of HAART in US

6 HIV disease progression – clinical latency
Levels (Separate Scales) CD4+ T cell HIV viral load CD8+ T cell Neutralizing Antibodies Years AIDS and Death Acute Asymptomatic (clinical latency) 4 – 8 weeks Primary infection

7 T cell homeostasis

8 Immune reconstitution during HAART
Phase 1: Sudden halt in viral production provokes a rapid increase in CD4 T cells in the first three months Phase 2: Slow recovery over several years, results mostly from regeneration of naïve CD4 T cells population. Figure 1. Kinetics and mechanisms of CD4 T cell reconstitution after HAART initiation. The sudden halt in virus production after HAART initiation provokes a large rapid increase in CD4 T cells (+200 cells mm−3 year−1) during the first three months, which corresponds with a redistribution of memory CD4 T cells together with reduced inflammation, activation markers on CD4 and CD8+ T cells, and activation-induced cell death [21]. The middle slope (+80 cells mm−3 year−1) reflects regeneration of the pool of naïve CD4 T cells. The lowest slope (+20 cells mm−3 year−1) shows normalization of naïve and memory CD4 cell compartments and cellular activation parameters. The slopes are calculated from [3].

9 Immune reconstitution during HAART
Restoration of pathogen and HIV-specific T lymphocytes Pathogen-specific memory CD4 and CD8 T cells are recovered from the pre-existing residual memory CD4 T cell pool during the first phase of immune reconstitution [4]. Recovery is somewhat independent of CD4 T cell numbers and disease stage at the time when HAART is initiated, but does require tight control of HIV [32]. Antigen-specific proliferation of memory CD4 T cells is highly sensitive to HIV, as shown by restored proliferation of CD4 T cells from untreated progressors when HIV production is blocked by anti-HIV siRNA [33]. Thus, the functional defects in CD4 T cells observed before HAART reflect a dynamic process that results more from the loss of antigen-activated CD4 T cells caused by virus infection rather than from cell anergy. Nonetheless, inhibition of abnormal immune activation by HAART is certainly another major factor reducing memory CD4 T cell apoptosis and anergy. Together, these mechanisms contribute to the restoration of memory CD4 T cell function 34 and 35, as well as to cell surface re-expression of molecules, such as CD28, that are required for cross-talk between CD4 T helper or dendritic cells and B or CD8 T cells. HAART leads to reconstitution of antigen-specific CD8 T cell and B cell responses to opportunistic pathogens [36], despite the persistence of some abnormalities, which might include hyperglobulinaemia, abnormal serum paraproteins or some B cell lymphoproliferation 37 and 38. This functional recovery continues as long as virus production is suppressed and leads to increased numbers of antigen-specific CD4 and CD8 T cells, which is illustrated by the expansion of memory cytomegalovirus (CMV)-specific CD4 and CD8 seen in patients with CMV retinitis, which persists for several years after HAART initiation [36]. It is only years after the acute CMV infection is controlled that the clonal contraction of CMV-specific T cells finally occurs [36]. As soon as CD4 T cell counts reach 100 or 200 mm−3, the preventive therapies that had been required before HAART initiation to protect against opportunistic agents such as CMV, Mycobacterium avium complex [39] or others, can be terminated. The ability of the patient's immune system to control these pathogens 40 and 41 illustrates the functionality of the immune reconstitution.

10 HAART effects on immune response
Increase CD4 cell number and function Increase memory and naïve CD4 and CD8 cells Decrease markers of cellular activation Normalize distortion in CD4 repertoire Reconstitution of antigen-specific CD8 T cell and B cell responses to opportunistic pathogens

11 Viral Latency The latent viral pool persists in everyone following Highly Active Anti-Retroviral Therapy (HAART) Is established soon after infection T1/2 of replication competent virus is ~44 months therefore eradication could take up to 60 years. After initiation of HAART, the plasma viral load undergoes a multiphasic decay, with an initial rapid decline (t1/2 ~ days) stemming from the elimination of short-lived infected cells (mostly activated CD4+ lymphocytes) by virus- and immune-mediated mechanisms (8). This is followed by a second phase of slower decline (t1/2 ~ weeks) thought to reflect the loss of infected macrophages, which are more resistant to virus-induced cytopathic effects, and possibly the attrition of other viral sanctuaries (8). Viremia then stabilizes often below the detection limit of current tests (<50 copies of viral RNA per ml of plasma). Occasional viral blips under therapy and the rapid return of high-level viremia whenever HAART is interrupted, however, demonstrate that the virus is not eradicated (8). Although incomplete inhibition of viral replication is likely to contribute to this phenomenon in a subset of individuals, the heart of the problem lays in the early establishment of a stable reservoir of latently infected cells that is not sensitive to current treatments. Low amounts of viral replication seem to contribute to HIV persistence particularly in individuals displaying immune activation in organs such as the gastrointestinal tract (5, 9). Although more potent or penetrating antiviral drugs might succeed in suppressing residual viral replication in this and other anatomical sites such as the central nervous system and the genital tract, they will not affect individual latently infected cells. It is estimated that an HIV-infected individual with no detectable viremia can harbor up to 107 latently infected cells, mostly CD4+ memory T lymphocytes (10). This reservoir is established from the earliest times of infection and is maintained in part by homeostatic proliferation (11–13). Although its size may be reduced when HAART is initiated very early, mathematical models predict that viral eradication could take up to several decades under conditions of complete viral suppression (14). This has led to the proposal of combining HAART with “purging regimens,” that is, therapeutic approaches aimed at forcing viral expression by latently infected cells to induce their destruction by virus- or immune-mediated mechanisms. A good comprehension of the molecular mechanisms of HIV latency is necessary to understand the rationale and evaluate the prospects of such therapeutic interventions.

12 Evidence of Viral Reservoirs
Primary Infection Viral Rebound Viral Setpoint Cessation Of HAART Plasma Viral RNA HAART 50 copies Infection

13 Model for establishment and maintenance of HIV-1 reservoirs
Death Activation: antigen Activated T-cell Quiescent T-cell Activated T-cell and renewed viral replication

14 HIV T cell dynamic on and off HAART
HIV–T cells dynamics, on and off HAART. (A) During acute infection, HIV replication is partially controlled by T cell responses, and depletion of the CD4+ T cell compartment is limited. Because of viral cytopathic effects or immune mediated killing, productively infected activated T cells do not generally survive for long enough to revert to a memory state. A small pool of latently infected memory CD4+ T cells harboring integrated HIV DNA, however, is established. (B) HAART initiation during the acute phase generally results in the normalization of CD4+ T cell counts and the preservation of memory T cell responses, which can subsequently contribute to the control of viral replication upon reactivation from stable reservoirs. (C) Chronic infection is accompanied by depletion of the CD4+ compartment and exhaustion of HIV-specific T cells, leading to uncontrolled viral production. (D) HAART initiation during the chronic phase of the disease generally abrogates viral replication, but CD4+ T cell reconstitution is limited. This is associated with hyperimmune activation of T cells of diverse specificities even in the absence of their cognate antigen. The profound depletion of memory CD4+ T cells along with the exhaustion of HIV-specific CD8+ T cells result in the incapacity of the immune system to control sporadic reactivation events. Although viral dissemination is limited by HAART, de novo infection can occur and may contribute to HIV persistence.

15 Factors influencing immune restoration with antiretroviral therapies
The reason why the drastic reduction in viral load does not always result in the normalization of the CD4+ T-cell count may be multifactorial. It is of major importance to understand these various factors at work if we want to establish an etiologic diagnosis and propose an appropriate therapy. Two main mechanisms may result in a suboptimal rise in CD4 count: insufficient production of CD4+ T cells and excessive CD4+ T-cell destruction. Excessive CD4+ T-cell destruction may be the consequence of HIV pathogenesis, immune activation, and/or genetically determined increase in the programmed cell death of lymphocytes Blood, 2011

16 Therapeutic possibilities to improve immune reconstitution

17 Targeting HIV latent reservoir

18 Q&A What is HAART? Can virus be cleared by HAART and why?
What are the two phase of immune reconstitution after initiation of anti-retroviral therapy?

19 Q&A What is HAART? HAART stands for Highly Active Antiretroviral Therapy. The usual HAART regiment combines three or more different drugs. Can virus be cleared by HAART and why? HAART regiments can reduce the amount of active virus and in some case can lower the number of virus until it is undetectable by current blood testing techniques. However, usual HAART treatment cannot clear HIV infection due to the fact that virus can establish latent infection in the patient. What are the two phase of immune reconstitution after initiation of anti-retroviral therapy? First a rapid initial rise of CD4 T cell counts in the first few months, primarily due to increase in memory T cells, and followed by a slow, steady increase in naïve T cell counts that can continue for years with sustained suppressive ART.

20 Strategies targeting latent reservoirs
How to reactivate latently infected cells? How to improve immune responses to eliminate infected cells?

21 Kick and kill HAART Enhanced CTLs Via engineered Immunity
Active infection HAART Enhanced CTLs Via engineered Immunity Broad neutralizing antibodies Kill Activators Latency

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