Host Defense: Vaccine, Interferon, Antiviral Drugs

Combating Infectious Diseases Prevention by Public Health: –Epidemiology –Control –Education –Vaccines Treatment by Medical Science: –Supportive –Corrective –Drugs Which is preferred? More cost effective?

Vaccination and Immunity The process of using inactivated or attenuated pathogen (or portion) to induce immune response in individual prior to exposure of pathogen Humoral Immunity (antibody, complement) Cell-Mediated Immunity (macrophage, T lymphocytes)

Killed-Virus Vaccine Virulent wild type virus Made noninfectious by chemical treatment (formalin, betapropiolactone) Salk inactivated poliovirus (IPV)

Salk Inactivated Poliovirus Vaccine (IPV) Efficacy – High Route – Intramuscular injection Dose / Cost – High Antibody – IgG CMI – Poor Heat labile – No Interference by other viruses – No Revert to virulence - No Use in immune compromised patient - Yes

Live-Virus Vaccine Avirulent – mild or no disease –Vaccinia virus (cowpox?) Attenuated – mutated wild type virus no longer pathogenic –Sabin oral poliovirus (OPV), not able to get into CNS

Live - Sabin Oral Poliovirus Vaccine (OPV) Efficacy – High Route – Oral (natural transmission, infection) Dose / Cost – Low Antibody – IgG, IgA CMI – Good Heat labile – Yes Interference by other viruses – Yes (other Enterovirus infections) Revert to virulence – Yes (rare, 1/300,000 doses) Use in immune compromised patient - No

Subunit Vaccine A viral protein or glycoprotein that elicits protective immunity May be isolated from virion –Influenza vaccine (HA, NA), grow virus in chick embryo, isolate viral proteins May be made in recombinant expression vector –HBV vaccine (HB s Ag glycoprotein), grow vector in yeast cells

Experimental Recombinant Vaccine Recombinant Virus – introduce viral gene into another virus by gene recombination i.e., HIV gp120 gene into Vaccinia virus

Experimental DNA Vaccine Direct intramuscular injection of viral DNA gene Gene expression and viral protein synthesis

Experimental Plant Vaccine Insert viral gene into plants (potato, tomato, banana) Oral vaccine ingested, elicit immune response

Experimental HIV Vaccine: Neutralizing (Blocking) Ab

Interferon: Cell Antiviral Defense 1957 – Isaacs & Lindenmann studying influenza virus in chick embryo Identify soluble substance in allantoic fluid that blocks influenza virus infection in chick embryo Inhibitor termed “interferon” Now known to be a cell cytokine (signal transducer)

Properties of Interferon Species specific Induced soon (hours) following virus infection Inhibits various viruses Acts indirectly – induces antiviral effector molecules (AVEM) Inhibits cell division Activates immune system Induces fever

Classes of Interferon (IFN) IFN-α made by leukocytes IFN-β made by fibroblasts IFN-γ made by T lymphocytes

Inducers of Interferon RNA viruses dsRNA (synthetic poly I-C) Intracellular MO’s (protozoa, rickettsia) Bacterial endotoxin

Activity of Interferon IFN made and secreted from virus infected cell Binds to specific cell receptor that triggers a signal transduction cascade Prepares the cell to combat virus infection by expressing three proenzymes termed antiviral effector molecules (AVEM)

Antiviral State In Cell (AVEM): Three Proenzymes 1) 2’,5’-oligoA synthetase (OAS) 2) dsRNA- dependent protein kinase (PKR) 3) RNAse-L Proenzymes, when activated, inhibit viral replication

OAS-Activated Cell Viral infection (dsRNA) activates the proenzyme OAS 2’,5’-oligoA is maded 2’,5’-oligoA activates proenzyme RNAse-L, which cleaves mRNA No mRNA, translation STOPPED

PKR-Activated Cell Viral infection (dsRNA) activates the proenzyme PKR Ribosome translation initiation factor (eIF2) is phosphorylated by activated PKR No ribosome initiation complex No ribosome formation, translation & protein synthesis STOPPED

Clinical Use of Interferon: Antiviral Available in adequate amount since 1980s by recombinant DNA technology Life threatening infections – rabies, hemorrhagic fevers, encephalitis due to arboviruses Persistent chronic infections - hepatitis B hepatitis C, papilloma, herpesvirus, HIV

Clinical Use of Interferon: Anti-Cancer Leukemia / lymphoma Multiple myeloma GI tumors Kidney, Bladder cancer Mesothelioma (lung cancer) AIDS-related Kaposi’s sarcoma (Human Herpes Virus-8)

Interferon: Toxic Side-Effects Fever Chills Headache Nausea & vomiting Anorexia Rash, dry skin CNS – depression, dizziness, confusion

Current Use of Interferon Combination with other antivirals Lipid formulation –Not as readily degraded –Better delivery to target cell –Less toxicity

Antiviral Drugs Virus & host cell replication closely related Antiviral requires –Low toxicity for host cell –Selective toxicity for virus

Testing For Safety of Antiviral Laboratory: Cell culture & animal testing Clinical Trials in Humans: –Phase 1 test for safety –Phase 2 test for efficacy –Phase 3 test for efficacy in a large population

Therapeutic Index (T.I.) for Antiviral Measure tolerated dose (not toxic/lethal) Measure curative dose (decrease disease or death) Therapeutic Index = tolerated dose / curative dose – T. I. = 1/1 = ≤ 1 (toxic) – T. I. = 1/ 1 (safe)

Antivirals: Nucleoside Analogues

Acyclovir & Herpesvirus Nucleoside analogue Target viral enzymes in DNA synthesis Herpesvirus thymidine kinase activates acyclovir Viral DNA polymerase incorporates acyclovir into growing DNA chain DNA synthesis STOPPED due to chain termination

Rimantadine (Flumadine) - Influenza A Virus Synthetic cyclic amine compound Stops virus Uncoating/Maturation Prevents acid pH required for membrane fusion, by blocking viral M2 (ion channel) protein CNS side effects: dizziness, ataxia, insomnia, convulsions

Neuraminidase Inhibitor (Zanamvir) - Influenza Virus A, B Drug blocks neuramindase (NA), virus release STOPPED During budding, virus hemagglutinin (HA) readily binds to neuraminic acid (sialic acid) NA cleaves sialic acid to insure release of virus from cell NA inhibitors are sialic acid analogues Competitive inhibitor of virus NA enzyme

Neuraminidase Inhibitors Oseltamvir (Tamiflu) – oral, pill Zanamivir (Relenza) – nasal, inhaler Need to be given within 48 hr. infection

Antivirals Against HIV Reverse transcriptase (RT) nucleoside inhibitors –Azidothymidine RT non-nucleoside inhibitors –ddC, ddI Protease inhibitors –Saquinavir Entry inhibitors –Enfuvirtide DNA Integrase inhibitor –Raltegravir

Protease Inhibitor This picture shows the HIV protease (purple and green) complexed with the inhibitor (spacefill). This prevents the substrate from reacting with the protease and thus, the polypeptides are not cleaved.

Current Treatment for HIV “Cocktail” – combination of four or more drugs Decease virus load (# progeny virus) in blood Clinical “latency” Prolong life High cost HIV reservoir in lymphoid tissue (replicate in low #)

Experimental Antiviral: Antisense Oligonucleotide ssRNA or ssDNA complimentary to viral mRNA made Will combine with viral mRNA and prevent translation Essential viral protein STOPPED and virus replication stopped

Reading & Questions Chapter 8: Strategies to Protect Against and Combat Viral Infections (omit Question 1)

QUESTIONS???

Class Discussion – Lecture 4 1. How is virus replication stopped in interferon-treated cells? 2. Is a cell treated with interferon able to make interferon if it is infected by a virus? 3. At what steps are current antivirals effective in stopping virus replication? 4. Why is the antiviral drug, acyclovir, more selective for herpesvirus? How does it stop herpesvirus replication?