Biologics: Interferons Study Notes

BIOLOGICS: INTERFERONS
DISCOVERY OF INTERFERONS

  • Year of Discovery: 1957

  • Discoverers: Isaacs & Lindenmann

  • Key Question: What factors block viral infection?

  • Findings:

    • Mediated by a soluble factor identified as the ‘Interfering Protein.’

    • Named Interferon (IFN).

WHAT ARE INTERFERONS?

  • Definition: Interferons are proteins that “interfere” with viral replication.

  • Characteristics:

    • Secreted in response to pathogens.

    • Widely expressed across various cell types.

    • Secreted by all mononuclear cells; some are more prolific than others.

VIRAL CLEARANCE & PROTECTION

  • Mechanism:

    • Virally infected cells secrete Interferons (IFN) that lead to:

    • Activation of immune cells.

    • Increased resistance of uninfected cells to subsequent infections by inhibiting viral protein synthesis, inactivation of viral RNA, and enhancing phagocytic and cytotoxic mechanisms.

    • Interferon Stimulated Genes (ISGs):

    • Examples include PKR, OAS, and MxA.

CLASSIFICATION OF INTERFERONS

Based on:

  • Sequence Homology: Similarities in their ancient evolutionary pathways.

  • Chromosomal Location:

    • Type I on chromosome 9.

    • Type II on chromosome 12.

    • Type III on chromosome 19.

  • Receptor Specificity:

Types of Interferons:

  • Type I IFNs:

    • Include IFN-α (13 sub-types), IFN-β, IFN-ω, IFN-ε, and IFN-κ.

    • Produced mainly by dendritic cells (DCs), especially plasmacytoid DCs (pDCs).

    • Share approximately 30% amino acid sequence homology between IFNα and IFNβ.

    • Signal through IFNAR1 & 2 receptors.

  • Type II IFNs:

    • IFN-γ

    • Also known as immune interferon, activated by IL-12.

    • Released primarily by cytotoxic T (CD8+) cells and T helper (CD4+) cells.

    • Exhibits weak direct anti-viral properties but has significant immuno-modulatory functions:

    • Stimulates macrophage (MØ) oxygen burst.

    • Matures Th1 cells.

    • Increases TLR4 expression.

    • Signals through IFNGR1 & 2.

  • Type III IFNs:

    • Types include IFN-λ1 (IL-29), IFN-λ2 (IL-28A), IFN-λ3 (IL-28B), IFN-λ4.

    • Large quantities produced by DCs and possess anti-viral, anti-proliferative, and anti-tumour activity.

    • Actions similar to the anti-inflammatory IL-10 but distinct as IFN-λ induces ISGs.

    • Signals via IL-10R & IFNλR chains.

CELLULAR RESPONSE TO INTERFERONS

  • Type I IFNs are induced by viruses across virtually all cell types, whereas Type II IFNs are primarily induced by T cells and natural killer (NK) cells, and Type III IFNs have expression restricted to T cells and NK cells.

MECHANISMS OF TYPE I IFN SIGNALING

Activation and Pathways:

  1. Viral Pathogen-Associated Molecular Patterns (PAMPs) stimulate Toll-like Receptors (TLRs) and cytosolic sensors leading to type I IFN expression.

  2. IFNs act in both autocrine and paracrine manners.

  3. Signal Transduction:

    • Interaction with specific receptors activates STAT (signal transducer and activator of transcription) complexes.

    • Each type of IFN activates a unique STAT involved in transcription regulation of immune genes.

    • Classical pathway identified: Janus kinase-STAT (JAK-STAT).

    • Combinations of STAT family members (e.g., STAT-1, -3, -5, -6) form dimers that associate with IFN-gamma activated site (GAS) or ISRE in gene promoters.

TYPE I IFN SIGNALLING PATHWAY

  1. Binding: Type I IFNs bind to heterodimeric IFNAR1/2 receptors.

  2. Activation of JAK/STAT pathway: Activates heterodimeric transcription factor complex ISGF3, comprising phosphoSTAT1, STAT2, and IRF9.

  3. Nuclear Translocation: ISGF3 translocates to the nucleus and binds to ISRE sites in the ISGs' promoters, leading to the anti-viral gene response.

  4. Secondary Pathways:

    • Activation of p38 MAP kinase pathway for anti-proliferative and anti-viral effects.

    • Induction of Retinoic Acid-Inducible Gene G (RIG-G) which inhibits NF-κB and STAT3.

CLINICAL USES OF TYPE I INTERFERONS

Therapeutic Applications:

  1. Anti-Tumour Effects: IFNα used in therapies for certain solid tumors, such as melanoma.

  2. Anti-Viral Effects:

    • IFNα utilized for treating viral infections including Hepatitis C Virus (HCV).

    • Induces proteins with anti-viral effects, such as PKR, OAS, and MxA.

HOW TYPE I IFN WORKS ANTI-VIRALLY:

Protein Kinase R (PKR)

  • Induced by IFN.

  • Activated by viral RNA.

  • Dimerization leads to autophosphorylation and phosphorylation of eIF2a, thus inhibiting protein synthesis of cellular and viral RNA.

MxA Gene

  • Accumulates at cell membranes, binds to viral nucleoproteins, and traffics them for degradation.

2-5 Oligo-Adenylate Synthetase (OAS)

  • Binds double-stranded viral RNA, forms an active tetramer, converts ATP into oligonucleotides, activating RNase L for cellular and viral RNA cleavage.

INFLUENCE ON HCV:

  1. HCV can impede Type I IFN production by decreasing STAT1 and STAT3 expression, which reduces interferon signaling.

  2. Treatment with recombinant IFNα correlates with lower incidences of hepatocellular carcinoma, even though HCV may lead to chronic conditions through persistent liver inflammation resulting in cirrhosis and potential liver cancer.

HIV INFECTION

  • Early Infection: Type I IFNs enhance anti-HIV innate immunity effectively during early infection stages.

  • Chronic HIV/AIDS: Continuing Type I IFN signaling can contribute to T cell exhaustion, resulting in ineffective target cell elimination and cytokine production.

AUTOIMMUNE DISEASE & MULTIPLE SCLEROSIS (MS)

  • Characterization of MS:

    • Autoimmune disease affecting the central nervous system.

    • Affects approximately 2.3 million worldwide with a higher prevalence in women, typically diagnosed around the age of 30.

  • Type I IFNs Role:

    • Type I IFNs (notably IFNβ) are among the first disease-modifying therapies (DMTs) approved for MS treatment.

    • As of March 2020, >580,000 patients treated with intramuscular IFNβ since its approval.

  • Mechanism:

    • IFNβ reduces inflammatory Th1 cytokines and promotes naïve Treg cell proliferation while reducing memory Treg cells to create a stable immune environment.

ANTI-TUMOUR EFFECTS OF TYPE I IFN

  1. Type I IFN has been evaluated in cancer therapies for promoting tumor-associated antigen (TAA) expression.

  2. Possible therapy involves combination treatments or using PRR agonists for therapeutic enhancement.

  3. Challenges exist in predicting the effectiveness of these therapies due to variations in individual immune responses and cancer types.