Adenoviral/Retroviral Hybrid Vector Construction

Gene therapy utilizes the delivery of DNA into cells, which can be accomplished by several methods. Adenoviral (Ad) vectors have become attractive gene transfer vectors because of their wide host range, strong infectivity and high purity. However, it is not integrated into the host genome, so gene expression is short, which requires repeated administration. Although retroviral (RV) vectors of type C can be stably integrated into the genome of host cells, this characteristic is limited by their inability to infect non-isolated cells, relatively low titer and smaller packaging capacity. At present, Creative Biolabs has proposed a new method to combine the advantages of high titer and infectivity of Ad vector with the comprehensive characteristics of RV vector in order to establish long-term sustained expression.

Ad/RV Hybrid Vector for Gene Therapy

In the practical application of human gene therapy, one of the most important obstacles is the lack of a single vector system capable of effectively transmitting and stably integrating therapeutic genes in vivo. Viral vectors are often used in gene therapy. The ultimate goal of viral vectors is to treat various diseases in the fields of neurology, neurodegeneration, metabolic diseases and cancer.

Limitations of Conventional Vector Systems

A combination of Ad vector and RV vector has been developed to transfer marker genes to target cells. The most common method is to use mouse leukemia virus (MLV)-based replication-competent retrovirus (RCR) as a vector to construct a hybrid by introducing a long terminal repeat of MLV (two loxP recognition sites on both sides) into an Ad vector. Thus, MLV structural genes (gag, pol and env) are introduced into cultured cells. This vector and method can transplant new production cells into patients for continuous gene transfer. Therefore, the system produces a vector that combines two attractive features of adenovirus and retrovirus, and is suitable for a variety of clinical gene therapy applications, such as experimental human gene therapy.

Figure 1. Vectors in gene therapy.¹

Bridging the Gap Between Transient Expression and Stable Integration

Gene therapy researchers often face a critical challenge: selecting a viral vector that balances efficient gene delivery with long-term, stable expression. Traditional vector systems typically excel in only one of these aspects, forcing compromises in therapeutic design. Adenoviral/Retroviral (Ad/RV) Hybrid Vectors overcome this limitation by integrating the strengths of both systems into a single, highly efficient platform

Comparison of Vector Systems and Our Capabilities

Our Services for Ad/RV Hybrid Vector Development

RCR vector based on MLV mediates effective, selective and persistent tumor transduction, and has significant therapeutic effects in various cancer models. In order to further improve the efficiency of this strategy, relying on the world-class expertise in virus vector technology, Creative Biolabs developed a method of transmitting adenovirus by encoding RCR vector (AdRCR). Therefore, tumor cells transduced by Ad vector instantly become cells producing RCR vector. As expected, compared with the original RCR vector itself, the high titer of AdRCR obtained significantly higher initial transduction levels in human cancer cells in vitro and in vivo. In a pre-established in vivo tumor model, compared with a single RCR, it can not only accelerate the proliferation of subsequent vectors and the progressive transduction of tumors, but also improve the efficacy of gene therapy with high titer AdRCR precursor drug activator in a dose-dependent manner.

• Custom cargo design – Promoter engineering (CMV, EF1α, PGK, CAG, tissue-specific), codon optimization, fluorescent reporters (GFP, Luciferase), shRNA/miRNA expression, and CRISPR elements.
• Hybrid vector backbone selection – Choose from serotype 5 (Ad5), Ad26, Ad35 for tropism modification; fiber knob modifications available (RGD, polylysine) for enhanced transduction of target cells.
• Retroviral integration module – MMLV integrase (preferred for dividing cells) or HIV-1 integrase (low-level transduction of non-dividing cells).
• Production & Purification – Triple transfection in HEK293-ERV producer cells, followed by CsCl gradient or HPLC purification. Final formulation in PBS/glycerol or custom buffer.
• Quality control release – Titer by qPCR (physical) and functional titration on HeLa/NIH3T3, sterility, mycoplasma, endotoxin (<1 EU/mL), RCA testing (passage 5).
• Stability & integration analysis – We can perform integration site analysis (LM-PCR or targeted locus amplification) as an add-on.

Key Features of Our Ad/RV Hybrid Vector Service

1. High Transduction Efficiency Across Diverse Cell Types

• Efficient infection of dividing and non-dividing cells
• Particularly effective in:
  • Neurons
  • Hard-to-transfect cell lines

2. Stable and Long-Term Gene Expression

• Retroviral integration enables:
  • Persistent transgene expression
  • Long-term therapeutic effects

3. Large Cargo Capacity

• Adenoviral backbone allows:
  • Delivery of large or complex genetic constructs
  • Multi-gene or regulatory system integration

4. Tumor-Selective Amplification

• In oncology applications:
  • Infected tumor cells produce retroviral vectors
  • Leads to progressive spread within tumor tissue
• Demonstrated improved therapeutic outcomes in tumor models

5. Scalable High-Titer Production

• Efficient viral packaging systems
• High-titer output for in vivo studies

6. Customizable Design

• Promoter selection
• Gene cassette design
• Safety modifications
• Tropism engineering

Our Collaboration Process

At Creative Biolabs, we understand that every gene therapy project is unique and requires a tailored approach. Our collaboration model is designed to provide a seamless, transparent, and efficient experience, guiding clients from initial concept to final delivery.

1. 1. Initial Consultation and Feasibility Assessment

   The collaboration begins with an in-depth consultation to fully understand your scientific objectives, target indications, and experimental requirements. Our experts evaluate the feasibility of the proposed strategy and recommend the most suitable hybrid vector design, including considerations for promoter selection, payload size, target cell tropism, and safety features.

2. 2. Customized Vector Design

   Once the project scope is defined, our scientists proceed with the rational design of the adenoviral/retroviral hybrid vector. We carefully select promoters, regulatory sequences, and therapeutic gene cassettes to optimize expression and specificity. For oncology or tissue-targeted applications, additional customization—such as tumor-specific promoters or envelope engineering—can be incorporated to enhance targeting and therapeutic efficacy.

3. 3. Vector Construction and Sequence Verification

   Following the design phase, the hybrid vector is constructed using advanced molecular cloning techniques. Each construct undergoes rigorous sequence verification to ensure accuracy and integrity. This step guarantees that the final vector precisely matches the approved design, minimizing downstream risks and ensuring reproducibility. Clients receive detailed documentation, including vector maps and sequence confirmation reports.

4. 4. Viral Packaging and High-Titer Production

   After successful construction, the hybrid vector is packaged using optimized production systems. Our team employs well-established packaging cell lines and scalable manufacturing processes to generate high-titer viral stocks. This ensures robust transduction efficiency for both in vitro and in vivo applications. Throughout this stage, production parameters are carefully monitored to maintain consistency and quality.

5. 5. Purification and Comprehensive Quality Control

   To ensure the highest level of reliability, all viral preparations undergo stringent purification and quality control procedures. These include assessments of viral titer, purity, sterility, endotoxin levels, and replication competency. Our comprehensive quality assurance measures provide clients with confidence that the delivered vectors meet rigorous research and preclinical standards. A detailed Certificate of Analysis (COA) accompanies each project.

6. 6. Optional Functional Validation

   For clients seeking additional assurance of vector performance, we offer optional functional validation services. These studies may include in vitro transduction efficiency assays, long-term expression analysis, and evaluation of retroviral integration. In oncology applications, tumor-selective amplification and therapeutic gene expression can also be assessed. The resulting data provide valuable insights that facilitate downstream experimental or translational studies.

7. 7. Delivery and Ongoing Technical Support

   Upon completion, the final viral products are securely packaged and shipped under appropriate conditions to preserve stability and activity. Clients receive comprehensive technical documentation, including handling instructions and experimental protocols. Our commitment extends beyond delivery, with ongoing technical support and consultation available to address any questions or future optimization needs.

What You'll Receive

Frequently Asked Questions (FAQ)

At Creative Biolabs, we don't just build vectors. We partner with you to de-risk your program, shorten development timelines, and deliver vectors that perform reliably from bench to bedside. With end-to-end customization, rigorous quality control, and a track record of >150 successful projects, we are ready to help you turn your gene therapy vision into reality. Don't let vector limitations hold back your science. Choose the hybrid advantage. Contact us today and let's build something that lasts.

Reference

1. From Wikipedia: Peter Znamenskiy, CC0 1.0, https://commons.wikimedia.org/wiki/File:Lentiviral_vector.png.