EHV2 Chapter 11 Slide Presentation PDF

CHAPTER 11 HUMAN IMMUNODEFICIENCY VIRUS Essential Human Virology, 2nd Edition  Learning Objectives Following completion of this chapter, students should be able to: 1. Recall important events in the early years of HIV/AIDS, including how each...

CHAPTER 11 HUMAN IMMUNODEFICIENCY VIRUS Essential Human Virology, 2nd Edition  Learning Objectives Following completion of this chapter, students should be able to: 1. Recall important events in the early years of HIV/AIDS, including how each was discovered and the importance of medical advances against the virus; 2. Relay the taxonomy, groups, and subtypes of HIV viruses; 3. Explain the origin of HIV-1 and HIV-2; 4. Worldwide and in the United States, examine the prevalence of HIV/AIDS in different regions, age groups, sexes, and demographic groups; 5. Describe the transmission of HIV and the clinical course of infection; 6. Identify the function of each HIV protein that was discussed and outline how the virus accomplishes each stage of the viral replication cycle.  Lecture Outline History of HIV infection Taxonomy and origins of HIV Epidemiology of HIV/AIDS Clinical progression of HIV/AIDS Molecular virology and replication of HIV-1  History of HIV Infection June 5, 1981: Morbidity and Mortality Weekly Report (MMWR) publishes a case study that documents five uncommon cases of pneumonia caused by the fungus Pneumocystis carinii (now known as Pneumocystis jirovecii) in young, previously healthy gay men Within days, additional cases were being reported to the CDC Also in 1981, cases of Kaposi’s sarcoma -- a rare skin cancer generally only seen in older men -- were being reported in previously healthy, young gay men in New York and California 270 cases of this severe immunodeficiency had been reported by the end of the year Later determined to be AIDS  History of HIV Infection 1982: CDC establishes the name “acquired immune deficiency syndrome” (AIDS) to replace what had been referred to as “gay- related immune deficiency” (GRID) in an effort not to misclassify the disease Had also received reports of AIDS in: people who had received blood transfusions heterosexual partners of individuals with AIDS hemophiliacs: people who lack clotting factor VII as a result of a gene deficiency and must receive it through intravenous injections of clotting factor concentrates derived from human plasma About half of all people with hemophilia and 90% of those with severe hemophilia became infected with HIV through contaminated factor VIII  History of HIV Infection 1983: CDC had identified all major routes of transmission Figure 11.1 CDC Blood and blood products Sexual intercourse Congenital transmission Not from: respiratory secretions food/water air personal contact Despite this, fears of contracting this deadly disease lead to discrimination, violence, and stigma for those infected  History of HIV Infection 1983: First major breakthrough against the disease Pasteur Institute researchers Françoise Barré-Sinoussi and Luc Montagnier isolated a retrovirus, which they name lymphadenopathy-associated virus (LAV), from the lymph node of an individual with AIDS They shared the 2008 Nobel Prize in Physiology or Medicine for this discovery In the same issue of the scientific journal Science, National Cancer Institute researcher Robert Gallo described a retrovirus that he named the third of the human T-lymphotropic viruses, HTLV-III The following year, Montagnier and Gallo held a joint press conference to announce the two viruses were in fact the same virus and likely the cause of AIDS International Committee on the Taxonomy of Viruses officially named the retrovirus “human immunodeficiency virus” in 1986  History of HIV Infection Slow but steady progress -- both Figure 11.1 scientifically and socially -- occurred over the following 10+ years 1985: Blood test for HIV developed 1987: First antiretroviral drug, zidovudine (AZT), approved 1987: AIDS quilt went on display with 1920 panels 1994: Highly-active antiretroviral therapy (HAART), a cocktail of several antiviral drugs together, began being used as the standard treatment Also known as combination antiretroviral therapy (cART) 1996: Number of new AIDS cases declined for the first time Cindy Smith  History of HIV Infection 2022 – nearly 40 years after the discovery of HIV: 1.5 million people still infected each year globally No HIV/AIDS vaccine yet exists  Lecture Outline History of HIV infection Taxonomy and origins of HIV Epidemiology of HIV/AIDS Clinical progression of HIV/AIDS Molecular virology and replication of HIV-1  Taxonomy and Origins of HIV Two types (species) of HIV HIV-1 HIV-2 Family: Retroviridae Subfamily: Orthoretrovirinae Genera: Lentivirus Species: Human immunodeficiency virus 1 Human immunodeficiency virus 2 The two types cause clinically indistinguishable conditions Viral loads tend to be lower during HIV-2 infection, HIV-2 is less easily transmitted, and progression to AIDS is much slower  Taxonomy and Origins of HIV HIV-1 and HIV-2 are further subdivided into genetically distinct groups HIV-1: Group M (main/major) Group O (outlier) Group N (non-M, non-O) Group P (newest group) Figure 11.2  Taxonomy and Origins of HIV HIV-1 Group M is further divided into nine distinct subtypes/clades Map image reprinted with permission of Wolters Kluwer Health, Inc., from Hemelaar et al., Figure 11.3 Global trends in molecular epidemiology of HIV-1 during 2000-2007. AIDS 2011: 25(5), 679-689. HIV-1 group M viruses are the cause of the worldwide pandemic Subtype C is responsible for ∼50% of infections worldwide Subtype B is most prevalent in Europe and Americas  Taxonomy and Origins of HIV HIV-1 and HIV-2 are further subdivided into genetically distinct groups HIV-1: Group M (main/major) Worldwide pandemic Group O (outlier) 50% of HIV-infected individuals develop severe flu-like symptoms: Fever Swollen lymph nodes Sore throat Arthralgia (joint pain) Myalgia (muscle pain) Headache Fatigue Weight loss Sometimes a rash Viral loads reach very high levels Person seroconverts (produces antibodies against the virus) as symptoms resolve Generally lasts 2-8 weeks  Clinical Progression of HIV/AIDS 2. Asymptomatic Phase (Clinical Latency Stage) Symptoms are absent or limited HIV slowly replicates, causing the gradual depletion of CD4 T cells Lasts an average of 10 years without antiretroviral therapy (ART) Rapid progressors take 2-3 years to progress through this stage (10-15%) Long-term nonprogressors (LTNPs) maintain normal CD4 T cell counts and low HIV titers without ART (5%) A subset known as elite controllers even maintain undetectable viral loads Reasons may include genetic factors, the type of immune response that is elicited, and differences in the HIV-1 strains Activation of cytotoxic T lymphocytes, rather than antibody production, correlates with protection Progression to AIDS can and does occur in the LTNP population, even after decades of stable infection  Clinical Progression of HIV/AIDS 2. Asymptomatic Phase (Clinical Latency Stage) CD4 T cells are progressively depleted as the virus causes direct and indirect damage to the cells Uninfected person: 500-1500 CD4 T cells/µL of blood When the CD4 T cell level falls below 500 cells/µL of blood, opportunistic infections occur: infections caused by pathogens that are normally cleared by the immune system but cause disease when an individual’s immune system becomes impaired  Clinical Progression of HIV/AIDS 3. Acquired Immune Deficiency Syndrome (AIDS) A person is classified as progressed to AIDS when he/she develops one or more opportunistic infections or has a CD4 T cell count below 200 cells/µL of blood At serious risk of developing a life-threatening opportunistic disease Person diagnosed with AIDS lives around 3 years or 1 year if an opportunistic infection is acquired Fungi Bacteria Viruses Parasites  Clinical Progression of HIV/AIDS Figure 11.7 Candida albicans Kaposi’s sarcoma Kaposi’s sarcoma with Cysts of Pneumocystis jiroveci, Candida albicans formerly known as Pneumocystis carinii courtesy of the CDC and (B and C) Sol Silverman, Jr., D.D.S.; (D) Dr. Edwin P. Ewing, Jr.  Clinical Progression of HIV/AIDS 3. Acquired Immune Deficiency Syndrome (AIDS) Other disease complications Kidney disease, due to: the infection of kidney cells by HIV immune complexes, antigen-antibody complexes that become lodged in the kidneys a side effect of antiretroviral drugs Neurological manifestations (>50% of HIV+ individuals) Cognitive issues HIV-associated dementia Encephalitis: inflammation of the brain Meningitis: inflammation of the meninges  Clinical Progression of HIV/AIDS Ultimately, why does the immune system fail to fight off HIV? End-stage progression is characterized by a reduction in the number of HIV- specific cytotoxic T lymphocytes With the increased diversity of the HIV population due to mutation, and the reduction of CD4 T cell help in activating B cells and cytotoxic T lymphocytes, the immune system becomes overwhelmed Progression of HIV-1 infection to AIDS can be predicted based upon the viral load and the CD4 T cell counts in an individual Currently, ART is the only way to reduced HIV replication and slow T cell decline Pre-exposure prophylaxis (PrEP) prevents infection in high-risk HIV-negative people Antiretroviral drugs target several stages of replication  Clinical Progression of HIV/AIDS Progression of HIV-1 infection to AIDS can be predicted based upon the viral load and the CD4 T cell counts in an individual Currently, ART is the only way to reduced HIV replication and slow T cell decline 40% of the 37 million people living with HIV/AIDS are accessing HAART/cART Antiretroviral drugs target several stages of replication The use of HAART has led to significant increases in the life expectancy of an HIV+ individual: In 2000-2002, a 20-year-old with HIV on HAART was expected to live until age 56 In 2016, a 20-year-old with HIV on HAART was expected to live until age 78.4 (6.8 years less than HIV-infected individuals) ART has turned a death sentence into a chronic condition  Lecture Outline History of HIV infection Taxonomy and origins of HIV Epidemiology of HIV/AIDS Clinical progression of HIV/AIDS Molecular virology and replication of HIV-1  Molecular Virology HIV is an enveloped retrovirus possessing a cone- or bullet-shaped capsid CDC / Maureen Metcalfe and Tom Hodge Figure 11.8  Molecular Virology Capsid built from a single protein, the capsid protein (CA) Two complete copies of the +ssRNA genome Considered pseudodiploid because only 1 of the 2 copies is used for reverse transcription +ssRNA genome possesses a 5’ cap and 3’ poly(A) tail, but it is not infectious Figure 11.8  Molecular Virology Within the core: Nucleocapsid protein (NC) that coats the viral RNA Three enzymes: Reverse transcriptase (RT) Integrase (RT) Protease (PR) Vpr, an accessory protein that is involved in the Figure 11.8 transport of cDNA into the nucleus  Molecular Virology The envelope surrounds the core to create a virion 100-120 nm in diameter Matrix protein (MA) attaches to the inner surface of the envelope Trimers of the envelope glycoproteins (Env) are found on the surface Consist of gp120 (surface subunit, SU) and gp41 (transmembrane subunit, TM) Figure 11.8 gp120 and gp41 are cleaved from gp160 during replication but remain non-covalently associated with each other  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription The Env glycoprotein trimer mediates adsorption of the virion to the cell surface receptor, CD4, found on helper T cells (below) and a population of macrophages and dendritic cells Figure 11.9 Seth Pincus, Elizabeth Fischer, and Austin Athman, National Institute of Allergy and Infectious Diseases  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription Before contacting CD4 T cells, the virus gains entry into the body through the bloodstream or by exposure of the virus to genital or intestinal mucosal epithelial surfaces HIV crosses through the tight junctions that attach cells of the epithelium together or penetrates through small tears in the epithelium that occur during sexual activity or as a result of other pathogens In the tissue, HIV comes into contact with macrophages and dendritic cells Macrophages with CD4 can be infected by CCR5-tropic strains  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription On dendritic cells, HIV is able to bind a receptor known as DC-SIGN Triggers endocytosis of HIV into vesicles Dendritic cell travels to lymph node Figure 11.10  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription When the dendritic cell makes contact with a CD4 T cell in the lymph node, a virological synapse is formed where exocytosed HIV virions come into contact with CD4 T cells HIV uses the dendritic cells as “Trojan horses” for transport of virions from the lymph node to the tissue Figure 11.10  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription HIV gp120 binds CD4 and one of two co- receptors, either CCR5 or CXCR4 Variations in the gp120 molecule determine the tropism for CCR5 or CXCR4 CCR5 is the primary co-receptor used during initial infection, and CCR5 strains display tropism for macrophages and a subset of mucosal-associated memory CD4 T cells Known as R5 or M-tropic isolates CXCR4 strains (X4 or T-tropic isolates) arise later during infection and preferentially infect naïve T cells, which express CXCR4 Co-receptor switching from CCR5 to CXCR4 is associated with accelerated disease Figure 11.11 progression  IN-DEPTH LOOK: INDIVIDUALS WITH CCR5 MUTATIONS Within the Caucasian population, some individuals have a 32- base-pair deletion in CCR5 (termed CCR532) Causes a frameshift mutation in CCR5 that leads to a shortened, nonfunctional receptor that cannot be used for HIV for entry 10-15% of Caucasians are heterozygous; only 1% are homozygous Homozygotes are more resistant to infection with R5 strains of HIV-1 (although still susceptible to R4 strains) Heterozygotes display delayed progression to AIDS 32 allele has not been found in people of African, East Asian, or Native American descent  IN-DEPTH LOOK: INDIVIDUALS WITH CCR5 MUTATIONS In 2005, an HIV-infected man with leukemia (a cancer of white blood cells) underwent myeloablative therapy for his cancer Uses radiation or chemotherapy to eliminate the leukemia cells but kills off all immune system cells in the process Followed by hematopoietic stem cell transplantation (HSCT), the transfer of bone marrow stem cells to reconstitute the immune system cells Received bone marrow from a CCR532 homozygote Result: HIV loads became undetectable The “Berlin patient” was able to discontinue HAART and is still HIV-free to this day Only two other individuals, the “Düsseldorf patient” and the “London patient,” have had success after similar treatments  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription 1. Binding of gp120 to CD4 causes a conformation change in the molecule that reveals the binding site for the co-receptor 2. Binding of gp120 to the co-receptor modifies the heterodimer, revealing a fusion peptide within gp41 that is inserted into the plasma membrane 3. gp41 refolds to create a fusion pore (likely after internalization of the virion into an endosome through clathrin-mediated endocytosis) 4. The core (nucleocapsid) is released through the pore into the cytoplasm Fig. 11.11  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription Much remains to be learned about HIV uncoating The viral capsid influences reverse transcription Reverse transcription occurs within the capsid The capsid must dissociate at least partially to allow access to cellular factors (e.g. nucleotides)  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription Reverse Transcriptase Heterodimer of two polypeptide chains, Subunit 2 (p66) p51 and p66 in green, blue, and gray Performs several enzymatic functions: 1. RNA-dependent DNA polymerase 2. DNA-dependent DNA polymerase 3. RNase H (able to degrade the RNA portion of an RNA-DNA duplex) Does not have proofreading ability Subunit 1 (p51) in orange Figure 4.14 Beilhartz et al., Viruses 2010, 2: 900-926.  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription The retrovirus genome has several different domains that are of importance during viral replication Only 1 of the 2 +ssRNA genome strands serves as a template for reverse transcription A tRNA obtained from the previous cell -- usually specific for lysine or proline -- acts as a primer to start reverse transcription tRNA primer R R Redundant Redundant sequence sequence Unique 5’ Unique 3’ domain domain Reverse Transcription occurs in cytoplasm carried out by reverse transcriptase (Follow along with handout) Figure 4.12 Image used with permission from Elsevier/Academic Press: Alan J. Cann, Principles of Molecular Virology 4th edition, 2005.  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription Result of reverse transcription: complementary DNA (cDNA) Long terminal Long terminal repeat repeat Resulting LTRs in cDNA are important for integration  Replication of HIV-1 Attachment, Penetration, Uncoating, and Reverse Transcription Core protects reverse transcribed cDNA until it enters the nucleus Most retroviruses must wait until the nuclear envelope dissolves during mitosis in order to gain entry into the nucleus As a lentivirus, HIV cDNA is able to cross nuclear pores The pre-integration complex (PIC) is the term for the HIV cDNA and proteins -- both of viral and cellular origin -- that facilitate entry of the cDNA into the nucleus HIV proteins involved: CA, NC, MA, RT, IN, Vpr Interact with nucleoporin proteins that constitute the nuclear pore complex Figure 11.11  Replication of HIV-1 Integration and Replication Carried out by integrase enzyme Integrated cDNA is known as proviral DNA; in its integrated state, HIV is known as a provirus Integration is not directed to any site, although it usually occurs in an area of active transcription Figure 4.13 Image used with permission from Elsevier/Academic Press: Alan J. Cann, Principles of Molecular Virology 4th edition2005.  Replication of HIV-1 Integration and Replication All retroviruses possess the three major gag, pol, and env genes HIV also encodes several essential and accessory regulatory proteins  Replication of HIV-1 Integration and Replication HIV proviral DNA contains at least 9 open reading frames that encode 15 individual proteins, in total HIV relies upon extensive splicing of viral mRNAs to generate its mature transcripts As with all retroviruses, the LTR contains a viral promoter Figure 11.12  Replication of HIV-1 Integration and Replication Full-length, capped and polyadenylated viral mRNAs are created The mRNAs for Gag and Gag-Pol precursors are unspliced The mRNAs for vif, vpr, vpu, and env are spliced once The mRNAs for tat, rev, and nef are multiply-spliced Figure 11.12  Replication of HIV-1 Integration and Replication Host transcription factors bind to the U3 portion of the LTR and recruit RNA pol II to the proviral DNA Tat (transactivator of transcription) and Rev (regulator of expression of viral proteins) are expressed first Tat binds to the viral mRNAs as they are being transcribed, stabilizing RNA pol II to ensure full-length transcription Rev shuttles unspliced transcripts from the nucleus to the cytoplasm (i.e. gag, gag-pol) Normally any mRNAs with splice sites are retained in the nucleus for splicing  Replication of HIV-1 Integration and Replication Translation of the 3 polyproteins occurs 1. The Gag precursor is cleaved by the viral protease into the MA, CA, NC, and p6 proteins only after the virion is released from the cell 2. During translation of the Gag polyprotein, about 5% of the time the ribosome undergoes a frame shifting event that leads to continued translation, forming the Gag-Pol precursor Autocatalysis cleaves off the Pol portion, which is further cleaved into PR, IN, and the two RT subunits Figure 11.12  Replication of HIV-1 Integration and Replication Translation of the 3 polyproteins occurs 3. The Env precursor p160 is highly glycosylated in the rough ER and a cellular enzyme in the Golgi complex cleaves it into gp120 and gp41 The remaining six HIV proteins are the product of spliced full-length mRNAs and are translated individually Accessory proteins Vif, Vpr, Vpu, and Nef are not essential but increase replication of HIV virions and infectivity Figure 11.12  Replication of HIV-1 Integration and Replication Replication of the genome occurs The viral +ssRNA genome is transcribed by RNA pol II as a full-length, unspliced, capped, and polyadenylated mRNA Transcription starts within the LTR, transcribing the 5’ R and U5 regions, coding sequences, and 3’ U3 and R regions to reconstitute the HIV genome proviral DNA RNA pol II  Replication of HIV-1 Assembly Gag precursor is targeted to the plasma membrane, where the MA portion interacts with the inner side of the plasma membrane The other end of the Gag precursor associates with the viral genome The Env subunits gp120 and gp41 (non-covalently associated) are targeted to the site of assembly gp41 provides the transmembrane domain gp120 associates with gp41 external to the virion envelope Dr. Matthew Gonda / National Cancer Institute Fig 11.13  Replication of HIV-1 Release Assembled virion buds from the surface of the cell, obtaining its envelope in the process Dr. Matthew Gonda / National Cancer Institute Fig 11.13  Replication of HIV-1 Maturation Maturation occurs after budding The viral protease cleaves several sites within Gag and Pol precursors The release of the individual proteins dramatically alters the architecture of the capsid, creating a fully-infectious virion Dr. Matthew Gonda / National Cancer Institute Fig 11.13 Replication of HIV-1  IN-DEPTH LOOK: WHY DOESN’T AN HIV VACCINE EXIST YET? Vaccine efforts began almost immediately following the discovery of HIV in 1983 First clinical trial of an HIV vaccine occurred in 1986 No vaccine has yet shown statistical significance of its efficacy Why haven’t any candidate HIV vaccines been successful? 1. Traditional methods (live attenuated or inactivated virus vaccines) have not been effective in providing protective immunity 2. HIV is a human virus that does not infect typical animal models -- testing for safety and efficacy is a challenge 3. HIV mutates quickly due to the low fidelity of the RT 4. The number of HIV subtypes make it unreasonable to create a “universal vaccine” against them all 5. gp120 is highly glycosylated, preventing antibodies from easily interacting with it 6. How should the immune system be stimulated for protective immunity?? No naturally-infected individuals have succeeded in warding off infection, so we don’t know (although we still hope it is possible)  IN-DEPTH LOOK: WHY DOESN’T AN HIV VACCINE EXIST YET? Candidate vaccines that generated neutralizing antibodies against gp120 were not protective  Vaccine efforts shifted to the cell-mediated response A vaccine using adenovirus to express HIV Gag, Pol, and Nef proteins was highly immunogenic in monkeys but did not prevent infection of humans Most promising so far: a “prime-boost” strategy “Prime” vaccine -- recombinant vector vaccine using canarypox to deliver and express HIV Gag, Pol, and Env peptides Administered SIX times Last two injections included the “boost” vaccine, containing the gp120 protein Vaccine was 31.2% effective in preventing HIV Only 1 of 3 statistical tests showed statistical significance  IN-DEPTH LOOK: WHY DOESN’T AN HIV VACCINE EXIST YET? Broadly neutralizing antibodies (bNAbs) that neutralize a range of HIV isolates have been observed in rare HIV+ individuals Requires someone to have been infected for years Antibodies have mutations that allow the antibody to pass through glycans to interact with conserved regions of gp120 Numerous bNAbs have been identified New vaccine trials are attempting to elicit bNAbs in vaccinated individuals CONCLUSION: HIV VACCINE DEVELOPMENT IS ONE OF THE GREATEST CHALLENGES THAT SCIENTISTS HAVE ENCOUNTERED