XVIII International AIDS Conference, July 19, 2010

1. HIV Pathogenesis Update 2010: Immune Activation & InflammationRichard JefferysCoordinator, Michael Palm Basic Science, Vaccines & Prevention Project, Treatment Action Grouprichard.jefferys@treatmentactiongroup.org XVIII International AIDS Conference, July 19, 2010 XVIII International AIDS Conference, 7/19/2010

2. What is Immune Activation? Immunologists have different definitions, but everyone has experienced the physical symptoms during acute infections like the flu, measles, mono: fever, swollen lymph nodes, fatigue Normally short-lived: these signs of immune activation happen, but only for a week or so Infection is then cleared or controlled, and activation subsides back to baseline After acute HIV infection, activation subsides, but not back to baseline XVIII International AIDS Conference, 7/19/2010

3. T-Cell Development • T cells are produced in the bone marrow then travel to an organ called the thymus that’s just behind the breastbone. • In the thymus, the T-cell acquires a “CD” surface marker that governs what type of T-cell it will be. • The two major T-cell types are: • CD4 helper T-cell. • CD8 T-cells, including cytotoxic T-lymphocytes (CTLs) or killer T-cells. XVIII International AIDS Conference, 7/19/2010

4. T-Cell Development Both CD4 and CD8 T-cells have a docking bay type structure called a "T-cell receptor" (TCR) that can dock with protein fragments called epitopes (from pathogens or other sources) TCRs are generated in the thymus in a sort of slot machine process that gives each T-cell one out of 25 million or so possible TCRs. A newly made T-cell leaves the thymus to patrol around the body looking for an epitope that fits its TCR. At this stage the T-cell is called “naïve.” XVIII International AIDS Conference, 7/19/2010

5. The Immune Response to Infection • On first exposure to a virus, incoming particles are taken up by the sentries of the immune system, dendritic cells (DC) • DCs can recognize pathogen-associated molecular patterns (PAMPs) shared by many different types of pathogens via toll-like receptors (TLRs) • DCs become activated (switched on) which causes them to migrate from the site of exposure to lymph nodes XVIII International AIDS Conference, 7/19/2010

6. The Immune Response to Infection • DCs break the pathogen down into protein fragments (called epitopes) which are then displayed on the outer surface by specialized molecules • Class II HLA (also known as MHC) molecules present epitopes to CD4 T cells • Class I HLA molecules present epitopes to CD8 T cells • In both cases recognition occurs via the docking bay structure on the outside of the cell, the T cell receptor (TCR) XVIII International AIDS Conference, 7/19/2010

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8. The Immune Response to Infection • T cells travel through lymph nodes on string-like pathways made of fibroblastic reticular cells (FRC), these pathways form a complex traffic system with crossroads, junctions and dead ends • DCs hang out at crossroads like salesmen trying to interest T cells in the epitopes they have on offer XVIII International AIDS Conference, 7/19/2010

9. Getting Activated • A passing naïve T cell that recognizes an epitope will engage in a prolonged embrace with the DC and eventually become activated Video of DC (green) and T cell (red) interactions in a mouse lymph node, before and after injection of an antigen. Note how the red T cells only contact DC briefly until antigen is present, then prolonged contacts can be seen. Celli et al. Immunity. 27:625-634 XVIII International AIDS Conference, 7/19/2010

10. Getting Activated • Activated T cells divide >15 times, generating a swarm of T cells specific for the same pathogen epitope • Dividing T cells switch on genes for making important signaling and antiviral proteins (chemokines & cytokines) • Inflammatory cyokines and rapid T cell expansion contribute to the symptoms during acute infection (fever, malaise, swollen lymph nodes) XVIII International AIDS Conference, 7/19/2010

11. T Cell Subsets • Different T cell subsets engage in different tasks, typically defined by production of particular cytokines • CD4 T cells • Type 1 (Th1): help CD8 T cells kill infected cells • Type 2 (Th2): support production of antibodies by B cells • Regulatory (Treg): release immune-suppressive cytokines to dampen the immune response • Th17: Recently discovered subset involved in responses to extracellular bacteria and autoimmunity XVIII International AIDS Conference, 7/19/2010

12. T Cell Subsets • CD8 T cells • Recognize infected cells displaying pathogen fragments on their surface • Release cell-killing substances (perforin, granzyme B) that puncture the cell wall and destroy the infected cell The CD8 T cell is the smaller cell at the bottom of the image that punctures a larger influenza virus-infected cell and destroys it. XVIII International AIDS Conference, 7/19/2010

13. B Cells • Reside in lymph nodes and bone marrow • Factories for the production of antibodies that can stick onto pathogens and prevent them infecting new cells • Signals from CD4 T cells help them make antibodies that are more and more effective (“affinity maturation”) • Recognize pathogen epitopes via B cell receptor (BCR) XVIII International AIDS Conference, 7/19/2010

14. Resolution & Memory When the infection is controlled, most of the newly-produced pathogen-specific “effector” T cells are no longer needed and die in a process called activation-induced cell death (AICD) Importantly, a subset of pathogen-specific T cell and B cells survive and these are described as “memory” cells Memory cells have enhanced functionality compared to naive cells and are often able prevent re-infection (with cleared pathogens) or control a pathogen that remains in the body (e.g. CMV, EBV, herpes zoster) End result is a team of memory CD4 T cells, CD8 T cells and B cells all targeting the same pathogen XVIII International AIDS Conference, 7/19/2010

15. Wherry & Ahmed, J. Virology, 78;11:5535-5545 XVIII International AIDS Conference, 7/19/2010

16. T-Cell Pools Memory T-cell pool size = ~200-300 billion Naïve T-cell pool size = ~100 billion The thymus produces around ~10-100 million new naïve T-cells every day (declines steadily with age) Naïve T cells that meet a matching antigen leave a legacy of memory cells which join the memory pool Naïve T-cells that hadn’t responded to anything die to make room for the fresh naïve T-cells XVIII International AIDS Conference, 7/19/2010

17. Acute HIV infection Transient (typically) loss of CD4 T cells from blood, significant loss of CD4 T cells from gut High viral load High levels of immune activation Increased CD8 T cell counts & skewing of CD4:CD8 ratio (normally around 2:1) XVIII International AIDS Conference, 7/19/2010

18. Acute HIV infection HIV-specific immune responses become detectable in 2-3 weeks Decline in viral load occurs in parallel with emergence of HIV-specific memory CD8 T cell response but is rarely fully controlled HIV infects the CD4 T cells that are responding to it Evidence of HIV-specific memory T cell dysfunction emerges very early Neutralizing antibodies are not generated for several months and are rarely able to neutralize contemporaneous virus XVIII International AIDS Conference, 7/19/2010

19. HIV Infects Developing Memory CD4 T Cells CD127 aka IL-7R is a marker for T cells destined to become long-term memory cells Zaunders et al J. Virology, 80:20:10162-10172 XVIII International AIDS Conference, 7/19/2010

20. Chronic HIV Infection • Immune activation does not fully resolve • Immune responses to HIV become progressively more diverse • as the virus replicates, mutant forms arise and these induce new immune responses (from the naïve T cell and B cell pools) • effective immune responses pressure the virus to mutate in ways that prevent recognition, somewhat similar to the way HIV mutations can impair drug effectiveness (“immune escape”) XVIII International AIDS Conference, 7/19/2010

21. Immune Activation & Disease Progression Immune activation measured by a marker called CD38 on memory CD8 T cells is the strongest predictor of the speed of disease progression Significant link between immune activation and disease progression documented in every infected population, across all age groups and in every geographic location studied Immune activation correlated with progressive loss of naïve T cells and B cells (decreased response to new vaccinations) XVIII International AIDS Conference, 7/19/2010

22. Memory Cells Get Worn Out • Memory T cells become exhausted & senescent • lose the capacity to proliferate (copy themselves) • sequential loss of cytokine production capacity: IL-2>TNFalpha>interferon gamma • Express exhaustion markers (PD-1, Tim-3) • lose the CD28 co-stimulatory molecule, leading to an accumulation of CD28- T cells (also seen in aging) • Shortened telomeres • Dysfunctional HIV-specific CD4 and CD8 T cells accumulate • Memory B cell exhaustion also documented XVIII International AIDS Conference, 7/19/2010

23. T-Cell Pools Revisited Memory T-cell pool becomes less diverse, more dysfunctional Naïve T-cells decreased Declining thymus production Persistent activation and recruitment of naïve cells into the memory pool XVIII International AIDS Conference, 7/19/2010

24. Parallels with Aging Decreased thymic output Decreased naive CD4 and CD8 T cell numbers Decreased response to vaccinations Skewed CD4:CD8 ratio Narrowing of the T cell repertoire, particularly in CMV+ (memory pool gets crowded) Increased numbers of CD28- CD8 T cells (associated with morbidity & mortality) Increased levels of inflammatory cytokines (“inflammaging”) XVIII International AIDS Conference, 7/19/2010

25. Causes of Immune Activation • Ongoing HIV replication: production of viral antigens and possibly also via viral HIV RNA stimulating toll-like receptors 7 & 8 • Microbial translocation - leaking of normally harmless bacteria from the gut into the circulation, leading to increased levels of bacterial DNA and LPS in the bloodstream XVIII International AIDS Conference, 7/19/2010

26. Causes of Immune Activation • Co-infections • hepatitis C co-infection associated with increased CD8 T cell activation • CMV: treatment with anti-CMV drug valganciclovir reduced CD8 T cell activation but did not increase CD4 T cell counts • Other herpesviruses (Epstein-Barr Virus, Herpes Simplex Virus types 1+2) • helminth infections • Loss of T cells leads to “homeostatic” proliferation XVIII International AIDS Conference, 7/19/2010

27. Immune Activation Linked to Inflammation Ongoing activation of immune cells causes release of inflammation-promoting cytokines e.g. interleukin-6, tumor necrosis factor (TNF)-alpha, type 1 interferons Inflammatory damage to lymph nodes (fibrosis) Additional biological markers of inflammation such as C-reactive protein (CRP), fibrinogen and D-dimer can be elevated XVIII International AIDS Conference, 7/19/2010

28. Inflammatory Markers are Higher in HIV Infection Compared to Uninfected Controls Participants 45-76 years of age Neuhaus J, et al. CROI 2009. Abstract O-140. From SG Deeks, MD, at Atlanta, GA: March 2, 2010, IAS–USA. XVIII International AIDS Conference, 7/19/2010

29. Impact of Virus Suppression Immune activation declines rapidly CD4 T cell increases: redistribution of cells trapped in lymph tissue, proliferation of functional cells, production of new naive T cells from the thymus (slowest aspect of recovery) CD8 T cell numbers decrease Memory T cell responses to opportunistic pathogens improve Memory T cell repertoire diversity improves XVIII International AIDS Conference, 7/19/2010

30. Antiretroviral Therapy Does Not Always Lower Immune Activation to Normal Levels Steve Deeks, IBT Workshop 2/20/2010 XVIII International AIDS Conference, 7/19/2010

31. Inflammatory Markers Linked to Poor Health Outcomes IL-6, D-dimer & CRP associated with illness, frailty & mortality in the elderly (“inflammaging”) IL-6 & D-dimer levels strongly associated with mortality and non-fatal cardiovascular disease in the Strategies for the Management of AntiRetroviral Therapy (SMART) Trial (Kuller PLoS Med 2008) IL-6 & CRP strongly associated with opportunistic disease in SMART (Rodger J Infect Dis. 2009) Elevated levels of fibrinogen and CRP strong independent predictors or mortality in the FRAM study (922 HIV+ men & women from 16 US centers) (Tien CROI 2010) XVIII International AIDS Conference, 7/19/2010

32. Persistent Inflammation and Lack of Complete Immune Restoration May Contribute to Increased Risk of Aging-Associated Diseases in HIV • Cardiovascular disease • Cancer (non-AIDS) • Bone fractures/osteopenia • Liver disease • Kidney disease • Cognitive decline • Frailty Multiple factors likely explain this increased risk, including co-morbid conditions and antiretroviral drug toxicity From SG Deeks, MD, at Atlanta, GA: March 2, 2010, IAS–USA. XVIII International AIDS Conference, 7/19/2010

33. Research Issues Anti-inflammatory approaches (similar to those being studied in the elderly) Addressing other potential contributors e.g. stress, smoking, diet, lack of exercise Therapies to promote immune restoration Safer antiretrovirals Curing HIV infection XVIII International AIDS Conference, 7/19/2010