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  • AIDS is a disease caused by a virus, A RETROVIRUS. Much of our knowledge about the disease and our attempts to counter it are based on this fact We know more about this virus than any other virus Yet despite our burgeoning knowledge base, the way in which the virus participates in disease seems more and more complicated, leading to more and more complicated anti-viral strategies It was very early in the development of the AIDS pandemic that the involvement of an infectious agent became clear and, to see why, we must go back to the very beginning of the epidemic. To the late 1970’s
  • Before the AIDS pandemic, Kaposi’s sarcoma was found primarily in elderly Jewish men and immuno-compromised patients
  • It was originally suggested that there was an immuno-suppressive factor in semen Now we know this disease as AIDS
  • The clusters of infected patients showed that the disease was in groups of sexual partners
  • But HIV was difficult to grow from the infected patients blood. It killed the cells on which it grows and it could not be grown on ordinary cultured T4 cells
  • Although the obvious agent was a virus, it was difficult to grow. It did not grow on cultured T4 cells, the only cells at that time that were know to be infected by HIV. Cultured T4 cells are resting, unactivated T4 cells. The great step forward made by Gallo and his collaborators was to use interleukin 2 to activate T4 cells. Then they could support HIV replication Gall showed that cells could support the replication of virus but there was no long term production. The assay was reverse transcriptase. Gallo had discovered HTLV-1 and know that it could give a similar cellular picture: Leukemia in some patients and immuno-suppression in others. This immuno-suppression was the result also of the specific loss of T4 cells. Feline leukemia virus also shows immuno-suppression in many cats. Gal also showed that there was reverse transcriptase in the blood of infected patients, suggesting infection by a retrovirus It was clear from the start that it is a major characteristic of HIV that it causes a fall in the number of T4 cells. WHEREVER AIDS OCCURS, HIV PRECEDES IT
  • This time course of HIV infection applies to persons not receiving chemotherapy.
  • HIV is now NOT replicating in resting T4 cells and most are resting in the peripheral circulation. At this time most replication is in lymph nodes in macrophages and dendritic cells. Symptoms are ‘flu or mononucleosis-like.There is a cellular immune response within weeks. Antiviral antibodies and cytotoxic T cells rise to high levels and persist for years. They are very effective at keeping the virus in the circulation at low levels. The CD8 cells rises transiently while CD4 cells fall but5 again recover (almost at least). The loss of these CD4 cells may result from DIRECT INFECTION of T cells in the circulation. Although antibodies lower HIV in blood, infection persists in the lymph nodes and in macrophages
  • Persistent infection with no or minor symptoms: Night sweats, generalized lymphadenopathy, diarrhea Virus persists as provirus in resting memory T cells. Reactivation of cells occurs contributing to overall viral load but this does not at this stage significantly affect CD4 cell number. Nevertheless, CD4 cells drop in number throughout infection
  • Also neuroplogical manifestations, lymphoid neoplasms Opportunistic infects occur when CD4 cells drop below 300 cells per cu mm Mechanism of this loss is still uncertain
  • Clinically most Kaposi’s is indolent and many infected individuals die of other causes. The AIDS-associated form is much more progressive involving many sites (skin, lymph, lungs, intestine) Human herpes virus-8 or Kaposi’s sarcoma-associated herpes virus found in many AIDS patients. In AIDS anti-HHV-8 antibodies are found only in those that have Kaposi’s or will get Kaposi’s. Blood from hemophiliacs with HIV infection does not show antibodies against the herpes virus
  • Clearly there are cases of immuno-suppression without HIV – that is to be expected, diseases of different etiology. Clearly for other diseases such as Kaposi’s, HIV is a cofactor rather than a cause. The data argue for a specific sexually transmitted agent of Kaposi’s in which immune suppression is a DOMINANT COFACTOR
  • The establishment that the disease is caused by a virus and therefore the ability to produce antibodies against viral antigens led to the first tests for HIV, the ELIZA and Western blot tests. However, there is a 1 to 2 month time lag before antibodies are produced. This can be overcome by using a test that identifies viral RNA rather than antibodies produced against viral protein e.g PCR. The very fact that we can use an antibody test shows us that there is a good immune response and it is neutralizing antibody which gives hope for a vaccine . But the virus is not completely neutralized which argues that a vaccine may be difficult to develop. The virus goes underground within the cells and because it is a retrovirus , is prone to genetic drift . As it changes it overcomes the immune system. As we shall see retroviral vaccines pose special problems and HIV is more complicated than other retroviruses
  • The size of the HIV genome is similar to that of other retroviruses but it is more complex. There is no oncogene but there are extra open reading frames which do code for protein. In all 15 proteins are encoded in HIV and they are made because antibodies to them can be found in patients. These extra open reading frames are not typical of retroviruses such as RSV. These extra open reading frames give a clue to the complex lifestyle of HIV. Note that some of them are encoded in two or more exons so there will have to be multiple splice events to make the final RNA. Could these be a site for intervention in the replication of the virus?
  • Syncytia are only possible if fusion occurs at ambient pH, this is very important as the formation of syncytia between infected and uninfected cells can allow spread of the virus without having to travel between cells. This must be borne in mind when thinking about vaccine strategies since humoral antibody will have no effect on this kind of spread. A vaccine must, clearly, be effective against INFECTED CELLS as well as virions. How fusion occurs is not known but involves the fusogen, gp41 which undergoes a conformational change But there is something more than just binding to CD4 antigen for infection. Early on it was known that if we transfect a MOUSE cell with the gene for CD4 antigen, it is NOT infected. Something else exists in a HUMAN cell, that allows infection
  • Human HeLa cells are not infected by HIV because they do not have CD4 antigen. When CD4 gene was transfected into the HeLa cells, they became able to bind HIV and were infected.
  • What is extra to CD4 in human cells are the chemokine CO-RECEPTORS. It was discovered that infection of human cells could be blocked with high concentrations of chemokines, proteins that are secreted by CD8 cells in many inflammatory responses.
  • In long term non-progressors the CD4 cells fall after infection but recover to near normal and remain there, so far for more than 15 years
  • A chemokine receptor may be one reason why these people remain healthy. What part this co-receptor plays in the biology of HIV we shall see later. The T cells or macrophages of non-progressors are very resistant to HIV because they have a mutant chemokine receptor. In some rather rare mutations of CCR5 (macrophage co-receptor), it is virtually impossible for the virus to enter the cell. Other long term non-progressors appear to make high levels of chemokines that block the chemokine receptor and therefore block binding of HIV to the cell.
  • Because of their work, these women are repeatedly exposed to HIV (remember that their clients are probably infected at a rate of 25% or more). Yet they show no sign of disease after more than 15 years. All of us can present a large number of antigen peptides in association with our class I MHC antigens…but not all peptides can be presented by all people so the antigens to which we can raise an immune response is limited albeit large. All of us can raise antibodies or induce a T cell response to HIV but the actual antigen peptide recognized differs. If an individual is lucky enough to present an HIV peptide than cannot undergo mutation in the virus without loss of viral infectivity, that individual produces an immune response from which the virus cannot escape
  • Protease is necessary for cutting up proteins in viral maturation … could be site of chemotherapeutic intervention
  • Thus we have a very complex life cycle. In some cells the virus goes latent while in others such as macrophages, it seems not to. Why such a complex life cycle? What is the molecular basis of this?
  • Although clearly connected with immune deficiency, wasting and brain diseases (dementia) appear to be linked to macrophage infection and are distinct from the severe immuno-suppression caused by T4 cell depletion
  • During infection virus is not totally controlled. This is an inevitable result of being a retrovirus. This is a great problem for a vaccine. During course of the disease, many subtypes arise and the tropism shifts from macrophage to CD4-infecting strains. Also from non-syncytium-inducing to syncytium-inducing. A GREAT PROBLEM FOR A VACCINE
  • Aids2007

    1. 1. HIV and AIDS <ul><li>Acquired Immunodeficiency Syndrome </li></ul><ul><li>Disease caused by an infectious agent: </li></ul><ul><li>a retrovirus </li></ul>
    2. 2. HIV and AIDS History of an infectious agent <ul><li>1979 - 5 cases of Pneumocystis carinii pneumonia </li></ul>All Homosexual Dot-like intracystic bodies of Pneumocystis carinii in lung Cytologic preparation from a bronchoalveolar lavage – Giemsa stain Pneumocystis jiroveci
    3. 3. 107 cases of Pneumocystis carinii pneumonia reported in the United States before the AIDS epidemic AIDS epidemic has resulted in 166,368 cases up to 1999 HIV and AIDS History of an infectious agent Pneumocystis pneumonia
    4. 4. HIV and AIDS With dissemination to extrapulmonary sites, Pneumocystis carinii tends to produce foci with prominent calcification, as seen in the kidney
    5. 5. HIV and AIDS an infectious agent – Kaposi’s Sarcoma Early 1981 MMWR: 5 cases of Kaposi’s sarcoma Hitherto: rare (immunocompromization) Elderly - Non-aggressive <ul><li>1981 - 26 cases of Kaposi’s sarcoma </li></ul><ul><ul><ul><li>Young </li></ul></ul></ul><ul><ul><ul><li>Male </li></ul></ul></ul><ul><ul><ul><li>San Francisco and New York </li></ul></ul></ul><ul><li>All Homosexuals </li></ul>
    6. 6. Before 1981: 40 - 120 cases per year in United States HIV and AIDS an infectious agent – Kaposi’s Sarcoma 1981-1999: 46,684 definite cases in United States
    7. 7. HIV and AIDS Two rare diseases in the gay community linked to IMMUNOSUPPRESSION OPPORTUNISTIC INFECTIONS <ul><li>Gay-Related Immune Deficiency </li></ul><ul><li>Acquired Immune Deficiency Syndrome (AIDS) </li></ul>Also Lymphadenopathy (diffuse, undifferentiated non-Hodgkins lymphoma) 1977- 1980: No cases in the young male (20 - 39 years old) population of the San Francisco area March 1981 - January 1982: four cases within 10 months
    8. 8. HIV and AIDS <ul><li>Little in common but: </li></ul><ul><li>Young </li></ul><ul><li>White </li></ul><ul><li>Male </li></ul><ul><li>Large towns </li></ul><ul><li>Homosexual community </li></ul>But not all gay men got the disease
    9. 9. HIV and AIDS <ul><li>Clusters of infected men </li></ul><ul><li>Apparent concentration within sexually interactive groups </li></ul><ul><li>High numbers of sex partners </li></ul>Distinguishing characteristics Suggests an infectious agent
    10. 10. HIV and AIDS Female sex partners of AIDS-positive IV drug users and hemophiliacs Not just in the Gay community More evidence for an infectious agent Different ways of getting a similar syndrome <ul><li>Blood transfusions </li></ul><ul><li>Intravenous drug use </li></ul><ul><li>Hemophilia (clotting factor) </li></ul>Haitian origin
    11. 11. HIV and AIDS 1983: The 4H Club <ul><li>H omosexuality among males </li></ul><ul><li>H emophilia </li></ul><ul><li>H eroin use (drug use that may involve shared needles) </li></ul><ul><li>H aitian origin </li></ul>
    12. 12. HIV and AIDS Obvious agent: A virus …… that is now in the blood supply Primary route of transmission: Sex AIDS is a sexually-transmitted viral disease
    13. 13. HIV and AIDS The Cellular Picture In advanced disease: the loss of another cell type CD8+ cytotoxic killer cells Loss of one cell type throughout the course of the disease CD4+ T4 helper cells A fall in the CD4+ cells always precedes disease Suggests an infectious agent A virus But initially difficult to grow Rapidly kills cells on which it grows
    14. 14. <ul><li>AIDS is therefore the end point of an infection that is continuous, progressive and pathogenic </li></ul><ul><li>With the prevalence of HIV in the developing world, HIV and its complications will be with us for generations </li></ul>AIDS Definition <ul><li>AIDS is currently defined as the presence of one of 25 conditions indicative of severe immunosuppression </li></ul><ul><li>OR </li></ul><ul><li>HIV infection in an individual with a CD4+ cell count of <200 cells per cubic mm of blood </li></ul>
    15. 15. <ul><li>Approximately 40,000,000 people in the world are HIV-infected </li></ul><ul><li>Approximately 14,000 new HIV infections occur daily around the world </li></ul><ul><li>Over 90% of these are in developing countries </li></ul><ul><li>1000 are in children less than 15 years of age </li></ul><ul><li>Of adult infections, 48% are in women and 15% in individuals 15-25 years </li></ul>AIDS Statistics
    16. 16. <ul><li>As of December 2005, 984,155 Americans reported with AIDS </li></ul><ul><li>At least 550,394 of them have died (2005 figures) </li></ul><ul><li>9,101 children under 15 </li></ul>AIDS Statistics About ONE MILLION persons in the United States are living with HIV/AIDS
    17. 17. HIV and AIDS
    18. 18. HIV and AIDS AIDS Deaths Prevalaence
    19. 19. HIV and AIDS Black White Hispanic
    20. 20. AIDS Statistics <ul><li>Sub-Saharan Africa </li></ul><ul><li>About 1 million new cases of AIDS per year </li></ul><ul><li>30 million people with HIV infection </li></ul><ul><li>AIDS is responsible for a decrease in life expectancy and increase in child mortality . Child mortality rates in East Africa will double by 2010 and adult life expectancy has declined in that region </li></ul><ul><li>Several countries in sub-Saharan Africa report infection rates of over 25%, especially urban areas </li></ul><ul><li>Zimbabwe: 33.7% of adult population infected </li></ul><ul><li>90% of truck drivers in Zimbabwe are infected </li></ul><ul><li>In Zambia, 1 in 5 urban girls is HIV-positive by the age of 20 </li></ul>
    21. 21. Life Expectancy Sub Saharan Africa
    22. 22. Impact of AIDS on life expectancy in five African countries, 1970–2010 Life expectancy at birth (years) Source: United Nations Population Division (2004). World Population Prospects: The 2004 Revision, database. Botswana South Africa Swaziland Zambia Zimbabwe 1970–1975 1975–1980 1980–1985 1985–1990 1990–1995 1995–2000 2000–2005 2005–2010 70 65 60 55 50 45 40 35 30 25 20 4.1
    23. 23. Botswana Zimbabwe Lesotho Swaziland HIV prevalence (%) in adults in Africa, 2005 2.5
    24. 24. H uman I mmunodeficiency V irus
    25. 25. HIV and AIDS The Virus <ul><li>The virus only grows on T4 cells that are proliferating in response to an immune stimulus -- Therefore difficult to grow in culture </li></ul><ul><li>Reverse transcriptase in activated T4 cells in blood of patients with AIDS </li></ul><ul><li>Robert Gallo : HTLV-3 </li></ul><ul><li>Luc Montagnier: LAV </li></ul>Human immunodeficiency viral particles are seen at medium magnification in this electron micrograph (CDC) Human Immunodeficiency Virus (HIV)
    26. 26. HIV and AIDS The cellular and immunological picture - The course of the disease virus CD4 cells antibody
    27. 27. HIV and AIDS The cellular and immunological picture - The course of the disease CD8 cells
    28. 28. HIV and AIDS The cellular and immunological picture The course of the disease 1. Acute Infection <ul><li>High virus titer </li></ul><ul><li>Mild symptoms </li></ul><ul><li>Fall in CD4+ cells but recovers </li></ul><ul><li>Rise in CD8+ cells but recovers </li></ul><ul><li>A high virus titer (up to 10 million viruses per ml blood) </li></ul><ul><li>Macrophages infected </li></ul>
    29. 29. HIV and AIDS 2. A strong immune response
    30. 30. HIV and AIDS 3. A latent state
    31. 31. HIV and AIDS <ul><li>10 billion HIV particles per day </li></ul><ul><li>Virus half life 5.7 hours </li></ul><ul><li>100-10 million virions per ml blood (set point) </li></ul><ul><li>Small minority of T4 cells are infected </li></ul><ul><li>Virus found in lymph nodes </li></ul>
    32. 32. HIV and AIDS 4. The beginning of disease
    33. 33. HIV and AIDS 5. Advanced disease - AIDS <ul><li>CD8+ cells destroy more CD4+ cells </li></ul><ul><li>CD4 cell loss means virus and infected cells no longer controlled </li></ul><ul><li>As CD4+ cells fall below 200 per cu mm virus titer rises rapidly and remaining immune response collapses </li></ul><ul><li>CD8+ cell number collapses </li></ul><ul><li>Opportunistic infections </li></ul><ul><li>Death in ~2 years without intervention </li></ul>
    34. 34. HIV and AIDS Good correlation between number of HIV particles measured by PCR and progression to disease
    35. 35. HIV and AIDS Viral load predicts survival time
    36. 36. HIV and AIDS CD4 cell count is not a good predictor of progression to disease
    37. 37. Cofactors Not all cases of Kaposi’s are associated with HIV Not all HIV infected persons suffer from Kaposi’s 20% of homosexual HIV+ males get Kaposi’s Few IV drug users or hemophiliacs get Kaposi’s Kaposi’s sarcoma associated herpes virus Human herpes virus-8 HIV and AIDS
    38. 38. HIV and AIDS So far it seems that >50% of HIV-infected persons have progressed to AIDS There is NO strong evidence there is any other infectious agent involved than HIV Three Views of AIDS Gallo : Infection by HIV is sufficient to cause AIDS Montagnier : HIV may be harmless in the absence of other co-factors Duesberg / Mullis : HIV is too silent to be the etiologic agent of AIDS. It is a much maligned by-stander
    39. 39. HIV - The Virus Membrane: host derived Retrovirus Three genes GAG – POL – ENV Three polyproteins
    40. 40. HIV - The Virus vaccine problem Retrovirus ENV gene Two glycoproteins: gp160 gp120 and gp41 gp41 is fusogen that spans the membrane sugars
    41. 41. HIV - The Virus GAG gene Group-Specific Antigens Retrovirus Polyprotein p17: inner surface - myristoylated p24: nucleocapsid p9: nucleocapsid associated with RNA
    42. 42. HIV - The Virus <ul><li>Polymerase (reverse transcriptase – RNA dependent DNA polymerase) </li></ul><ul><li>Integrase </li></ul><ul><li>Protease (cuts polyproteins) </li></ul>Enzymes <ul><li>POL gene </li></ul>Retrovirus Polyprotein
    43. 43. The Genome of HIV Three structural genes LTRs Extra open reading frames are clue to latency These ORFs code for small proteins - antibodies in AIDS patients
    44. 44. HIV - The Virus
    45. 45. HIV - The Virus <ul><li>A retrovirus </li></ul><ul><li>Latency </li></ul><ul><li>Specific destruction of CD4+ cells </li></ul><ul><li>How does the virus enter the cell? </li></ul>Life History
    46. 46. HIV - Life History <ul><li>Fusion at ambient pH </li></ul><ul><li>No need for entry into lysosomes </li></ul><ul><li>Syncytia </li></ul>Profound significance for AIDS progression: Spread from cell to cell Profound significance for therapy: Humoral antibody will not stop spread – need cell-mediated response
    47. 47. HIV - Life History Entry into the cell T4 (CD4+) cells are major target Human HeLa Cell Human HeLa Cell transfected with CD4 antigen NOT INFECTED INFECTED But NOT the whole answer since this does not happen if CD4 is transfected into a MOUSE cell
    48. 48. HIV - Life History Why do CD4-transfected human cells become infected but CD4-transfected mouse cells do not? Human cells must possess a co-factor for infection that mouse cells do not Co-Receptors CD8+ Cells MIP-1 alpha MIP-1 beta RANTES Chemokines Block HIV infection of macrophages
    49. 49. HIV - Life History CD4 CD4 CD4 HIV CCR5 CCR5 chemokine Mutant CCR5 macrophage Chemokine receptors are necessary co-receptors along with CD4 antigen
    50. 50. HIV and AIDS Some people do not get AIDS Long term survivors Exposed uninfected persons The chemokine receptor story
    51. 51. HIV and AIDS <ul><li>Co-receptors and HIV infection </li></ul><ul><li>CCR5 is a chemokine receptor </li></ul><ul><li>Cells with homozygous mutant CCR5 molecules are not infected by HIV </li></ul><ul><li>1 in 100 Caucasians </li></ul><ul><li>No Africans </li></ul><ul><li>Persons with heterozygous mutant CCR5 molecules progress to AIDS more slowly </li></ul>
    52. 52. HIV and AIDS <ul><li>Co-receptors </li></ul><ul><li>25% of long term survivors are CCR5 or CCR2 mutants (deletions) </li></ul><ul><li>The same CCR5 mutation (called “delta 32”) is thought to be the mutation that rendered some people immune to the plague in the middle ages </li></ul><ul><li>Many other chemokine receptors </li></ul>
    53. 53. Long term non-progressers <ul><li>People who have been infected with HIV for more than seven years that have stable CD4+ cell counts above 600 per cu mm with no symptoms and no chemotherapy </li></ul><ul><li>Many have produced a very good immune response to the virus </li></ul>HIV and AIDS
    54. 54. HIV and AIDS <ul><li>Nairobi prostitutes </li></ul><ul><li>Client infection rate more than 25% </li></ul><ul><li>Rare HLA antigens </li></ul><ul><li>Associations between resistance to infection and their class I and class II MHC (HLA) haplotypes </li></ul>
    55. 55. HIV - Life History GAG POL ENV HIV is a retrovirus It carries with it: <ul><li>Reverse transcriptase </li></ul><ul><li>Integrase </li></ul><ul><li>Protease </li></ul><ul><li>tRNA primer </li></ul>HIV genes HIV has no oncogene but could still be oncogenic vaccine problem
    56. 56. HIV - Life History HIV infection is not manifested as disease for years During apparent clinical latency, virus is being replicated and cleared Latency – Cellular – The problem of memory T4 cells Only activated T4 cells can replicate virus Most infected T4 cells are rapidly lyzed but are replaced Some T4 cells revert to resting state as memory cells which are long-lived Memory T4 cells cannot replicate the virus unless they become activated Clinical Latency
    57. 57. Dynamics of CD4 T cells in an HIV infection Cell death apoptosis etc Uninfected activated T cell Cell death immune destruction Chronically-infected memory T cells with provirus Return to resting state Reactivation Uninfected unactivated memory T cell pool Infection Long lived! Long lived!
    58. 58. Long term latent HIV T4 resting memory cell It may be impossible to cure the patient of HIV Even if combination therapy stops HIV replication Immune response T4 activated HIV production
    59. 59. Inexorable decline of CD4+ T4 cells Of great importance to therapeutic strategy Why do all of the T4 cells disappear? At early stages of infection only 1 in 10,000 cells is infected Late 1 in 40
    60. 60. But few cells are infected: Early stage of infection 1:10,000 Late 1:40 Why do all T4 cells disappear? 1. PUNCTURED MEMBRANE Virus destroys the cell as a result of budding
    61. 61. Why do all T4 cells disappear? - 2 But syncytia not common Most T4 cells are not HIV+ Could “sweep up” uninfected cells Uninfected CD4 cell Gp120 negative Cells Fuse Killing of CD4 cells 2. Syncytium Formation Infected CD4 cell Gp120 positive
    62. 62. Killing of CD4 cells 3. Cytotoxic T cell-mediated lysis Why do all T4 cells disappear? BUT: Most cells are not infected Cytotoxic T cell
    63. 63. Killing of CD4+ cells 4. Binding of free Gp120 to CD4 antigen makes uninfected T4 cell look like an infected cell Complement-mediated lysis Could account for the loss of uninfected T4 cells
    64. 64. CD8 cell (no CD4 antigen) Macrophage CXCR4 chemokine receptor Why do all T4 cells disappear? Induction of apoptosis Binding to CXCR4 results in expression of TNF-alpha on the cell surface ? G protein signal ? Binding to CXCR4 results in expression of TNF-alpha receptor II HIV gp120 chemokine
    65. 65. CD8 cell Macrophage CXCR4 Why do all T4 cells disappear? Induction of apoptosis Death CD8 T cell apoptotic bodies
    66. 66. Macrophages may be infected by two routes CD4 Fc receptor HIV gp120 binds to macrophage CD4 antigen Virus is opsonized by anti gp120 antibodies which bind to macrophage Fc receptors - an enhancing antibody vaccine problem HIV gp120 HIV Anti-gp120
    67. 67. Macrophages - The Trojan Horse Carry virus into different organs (brain) Non-proliferating mature macrophages sustain HIV production for a long time without being killed by virus Macrophages form a reservoir outside the blood Early HIV isolated during infection are macrophage tropic (have a macrophage chemokine co-receptor (CCR5)) Virus probably infects patient via macrophages in semen etc Infection by HIV leads to altered cytokine production “slim disease” Slim disease very like Visna in sheep - also infects macrophages
    68. 68. Population Polymorphism HIV genome 9749 nucleotides Therefore EVERY new virus has at least one mutation! Every possible single mutation arises daily 1% of all possible double mutations arise daily The HIV that infects a patient is very different from that seen by the time AIDS appears HIV is a retrovirus Retroviruses use host cell RNA polymerase II to replicate their genome vaccine problem Pol II has a high error rate 1:2,000-10,000
    69. 69. Population Polymorphism <ul><li>Initial infecting virus is macrophage-tropic (has CCR5 as co-receptor) </li></ul><ul><li>These are non-syncytium-inducing strains </li></ul><ul><li>(Note: most vaccines have been made against syncytium-inducing T4 cell tropic strains) </li></ul><ul><li>As virus mutates, it changes subtypes of cells that it infects as the ability to bind different co-receptors changes </li></ul>
    70. 70. Population Polymorphism <ul><li>Early in infection: </li></ul><ul><li>Macrophage-tropic </li></ul><ul><li>Non-syncytium-inducing </li></ul><ul><li>Slowly replicating </li></ul><ul><li>Late in infection </li></ul><ul><li>T4 cell tropic </li></ul><ul><li>Syncytium-inducing </li></ul><ul><li>High titer virus </li></ul>vaccine problem
    71. 71. Population Polymorphism <ul><li>The most variable protein is gp120 </li></ul><ul><li>Amino acid sequence within a single patient varies by 1-6% </li></ul><ul><li>Up to 30% in population </li></ul>Co-infection may result in recombination <ul><li>Glycosylation masks conserved sites </li></ul>vaccine problem vaccine problem vaccine problem
    72. 72. Population Polymorphism Polymorphism due to high mutation rate as a result of lack of proof-reading in reverse transcriptase and RNA pol II Sub-populations arise with altered cell tropism drug problem <ul><li>Variation in reverse transcriptase leads to resistance to nucleoside analogs </li></ul><ul><li>Variation in protease leads to resistance to protease inhibitors </li></ul>drug problem
    73. 73. Other cells infected by HIV CD4- <ul><li>Epithelial cells of bowel and vagina </li></ul><ul><li>Endothelial cells of brain </li></ul><ul><li>Brains cells : Astroglia, oligodendroglia </li></ul><ul><li>Galactocerebroside receptor </li></ul>
    74. 74. Anti-HIV Strategies <ul><li>Education </li></ul><ul><li>Sexually transmitted </li></ul><ul><li>Not highly infectious </li></ul><ul><li>Chemotherapy </li></ul><ul><li>Mutation selection Resistance </li></ul><ul><li>but </li></ul><ul><li>Suppress replication No capacity for mutation </li></ul>
    75. 75. Anti-HIV Strategies H ighly A ctive A nti- R etroviral T herapy HAART: Two nucleoside analog RT inhibitors and 1 protease inhibitor Now also: Two nucleoside analog RT inhibitors and 1 non nucleoside
    76. 76. Does HIV Cause AIDS? <ul><li>Gay San Franciscans </li></ul><ul><li>New York I.V. drug users </li></ul><ul><li>African heterosexuals </li></ul><ul><li>Hemophiliacs </li></ul><ul><li>Spouses of hemophiliacs and drug users </li></ul><ul><li>Children of hemophiliacs and drug users </li></ul>Single common factor between:
    77. 77. Does HIV Cause AIDS? <ul><li>HIV precedes AIDS in every population in which AIDS occurs </li></ul><ul><li>Infection by cloned virus </li></ul><ul><li>SIV HIV </li></ul><ul><li>Simian AIDS Human AIDS </li></ul>
    78. 78. Remember! <ul><li>Education led to leveling off of rate of increase in AIDS </li></ul><ul><li>HAART has greatly slowed death rate </li></ul><ul><li>The fact that fewer people are dying per year from the infection means that the number of HIV-infected people in the population is rising ! </li></ul><ul><li>Unless education continues to be successful and unless we can cure infected people of virus, the problem of virus spread is, and will continue to be, with us </li></ul>