MIC 115 Lecture 13: Viral Vectors

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Questions and Answers

What is the primary advantage of pseudotyping retroviral vectors with VSV-G?

It increases the package size of retroviral RNA.

It allows for broader cell type targeting by improving receptor interaction. (correct)

It enables integration of the viral DNA into the host genome.

It enhances the transgene expression levels in target cells.

Which of the following statements is true regarding adenoviral vectors?

Adenoviruses remain as episomes within the nucleus. (correct)

Adenoviral vectors are typically used for their high transgene expression levels.

They are limited to transducing small DNA fragments effectively.

Adenoviruses integrate into the host genome.

What is a key limitation of retroviral vectors in gene transfer?

They cannot transduce DNA fragments larger than 10 kb. (correct)

They require specific protein receptors for cell entry.

They cannot be used for non-dividing cells.

They can only package dsDNA genomes.

What is a defining characteristic of adeno-associated viruses (AAVs)?

They have a small ssDNA genome of 4.7 kb. Signup and view all the answers

In what scenario would retroviral transduction not be the preferred method?

When transfecting cells effectively. Signup and view all the answers

What is a primary characteristic that differentiates lentiviruses from retroviruses?

Lentiviruses can infect both mitotically active and non-dividing cells. Signup and view all the answers

Which type of viral vector is specifically known for being used in gene delivery without undergoing genomic integration?

Adeno-associated viral vectors Signup and view all the answers

Why is it important to use only extensively studied viral vectors for gene therapy?

To confirm their safety for use in humans. Signup and view all the answers

What containment level is necessary to perform viral transduction in a laboratory setting?

BSL-2 Signup and view all the answers

What is the primary role of viral vectors in gene therapy?

To deliver DNA or RNA directly into cells. Signup and view all the answers

What type of genetic material do adenoviruses carry?

Double-stranded DNA Signup and view all the answers

From which component does the ability of retroviral vectors to integrate into the host genome primarily arise?

The presence of integrase enzymes. Signup and view all the answers

Which statement about adeno-associated viruses is accurate?

They have a single-stranded DNA genome and are generally small. Signup and view all the answers

What is the primary requirement for the integration process of proviral DNA?

Presence of LTRs Signup and view all the answers

Why do most retroviruses require mitosis for productive infection?

Because the pre-integration complex cannot pass through nuclear pores Signup and view all the answers

What role does the y sequence play in the lentiviral packaging system?

It is essential for viral particle packaging Signup and view all the answers

What is the primary outcome of transduction in retroviral vectors?

The insertion of DNA into the host genome Signup and view all the answers

What happens if the y sequence is moved from the transfer plasmid to other plasmids?

Transgenes cannot be packaged Signup and view all the answers

Which gene in the retroviral genome is primarily responsible for reverse transcription?

POL gene Signup and view all the answers

Which viral genes are typically removed to create replication-incompetent viral vectors?

All genes related to virulence Signup and view all the answers

What is a distinguishing factor between stable transfection and transient transfection when using retroviral vectors?

Stable transfection results in longer-lasting gene expression Signup and view all the answers

What role does the LTR sequence serve in the retroviral genome?

Facilitates the integration of proviral DNA Signup and view all the answers

What characterizes the life cycle of retroviruses?

Integration into a host genome Signup and view all the answers

Which of the following components is supplied through separate plasmids in the Recombinant Lentiviral Packaging System?

Viral structural proteins Signup and view all the answers

What is the function of the packaging signal (y) in retroviruses?

It is required for viral packaging Signup and view all the answers

What is the primary function of lentiviral vectors in gene therapy?

To introduce recombinant DNA into vertebrate cells Signup and view all the answers

What determines the viral tropism of retroviruses?

The interaction between envelope glycoprotein and host receptors Signup and view all the answers

What percentage of the human genome is estimated to consist of endogenous retroviruses?

5% Signup and view all the answers

Which structural component encapsulates the core of the retrovirus?

Nucleocapsid Signup and view all the answers

Study Notes

Viral Vectors Overview

Viral vectors are used for gene delivery and gene therapy.
Viruses naturally deliver DNA or RNA into cells.
Viral vectors are vehicles to deliver DNA or RNA directly into cells.
Viral vectors are derived from viruses, but all viral genes are removed and modified to only deliver the desired DNA or RNA.
Only extensively studied and determined safe for humans are used.
Biosafety level 2 (BSL-2) facility needed for viral transduction in a lab

Retrovirus and Lentivirus

Retroviruses and lentiviruses have single-stranded RNA genomes.
Retroviruses integrate into the host genome as proviruses.
Retroviral vectors utilize the integration machinery of naturally occurring retroviruses.
Retroviruses are used for stable and efficient gene transfer into cells.
Lentiviruses can infect non-dividing cells as well as dividing cells.

Retroviral and Lentiviral Vectors

Retroviral vectors are developed using retroviruses, including human immunodeficiency virus (HIV).
Retroviral and lentiviral genomes have long terminal repeats (LTRs).
LTRs are crucial for integration into host genome and viral replication.
The packaging signal sequence (ψ) is required for viral packaging.

Adenoviral Vectors

Adenoviruses have double-stranded DNA genomes.
Adenoviruses do not undergo genomic integration.
Adenoviruses are large.
Adenovirus vectors are widely used for vaccines and in vivo gene therapies.

Adeno-Associated Viral Vectors (AAV)

Adeno-associated viruses have single-stranded DNA genomes.
AAVs are small.
AAVs do not integrate into the host genome.
AAV vectors are stably maintained in non-dividing cells (e.g., liver, nerve cells).
AAVs are popular tools for in vivo gene therapies.

Viral Vector Life Cycle

Viral vectors use the host cell's machinery for replication and transgene expression.
Retroviruses use reverse transcription to convert RNA to DNA for integration.
Viral tropism describes the ability of a virus to infect specific cell types.
Integration is the process where viral material combines into the host genome.
Retroviruses often require mitosis for effective infection as their integration process relies on cell division.

Stable Transfection vs. Lentiviral Transduction

Stable transfection doesn't involve integration into host genome whereas lentiviral transduction does.
The expression pattern for stable transfection differs from lentiviral.
Different viral vectors used for diverse applications, considering various factors like stability, integration, and target cells.

Pseudotyping Retroviral Vectors

Retroviral vectors can be modified to target different cell types by replacing the viral envelope protein (Env) with another protein.
The Vesicular Stomatitis Virus Glycoprotein (VSV-G) is one common replacement that expands vector cell types which can target cells lacking receptors for the original viral envelope.

Limitations of Retroviral Vectors

Retroviral vectors have limited capacity for carrying large DNA fragments.
Retroviruses are most effective in cells capable of division.
Retroviral transduction may not be ideal for high transgene expression or efficient transfection.

Adenovirus and AAV Considerations

Adenoviruses and AAVs do not integrate their genetic material into the host genome; hence, the viral DNA resides independently (episome).
This characteristic makes them suitable for situations where stable integration is not needed.

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Description

This quiz covers the fundamentals of viral vectors, their use in gene therapy, and specific types such as retroviruses and lentiviruses. It explores how these vectors function, their safety considerations, and their application in gene delivery. Test your understanding of these essential tools in modern genetic research.