With the rapid development of anti-tumor cellular immunotherapy technology in the world, there is an increasing number of anti-tumor cellular immunotherapy and research at home and abroad. As the most ideal carrier for cellular immunotherapy-viral vectors, it is used in cellular immunotherapy for tumor diseases. The application has entered the clinical application stage. Currently, the most widely used viral vectors in the world are the three major viral vectors: Adenovirus (Ad), Retrovirus (RV) and Adeno-associated virus (AAV). The safest of these is the adeno-associated virus.
Advantages and disadvantages of viral vectors
A variety of viral vectors have been developed, such as Adenovirus (Ad), Adeno-associated virus (AAV), Lentivirus, Retrovirus (RV), Herpes virus (Herpes virus) ), Poxviridae, etc., their respective advantages and disadvantages:
1. Adenovirus (Adenovirus, Ad) vector: It is the earliest and most widely used viral vector. It is characterized by easy preparation and can infect a variety of host cells. The disadvantage is that Ad is a pathogenic virus, which mainly invades and causes diseases such as the respiratory system, and easily causes inflammatory reactions and other adverse reactions. At the same time, after infection of host cells, the expression of the target gene is relatively short, which is not conducive to immunotherapy that requires continuous expression of the target gene.
2. Adeno-associated virus (Adeno-associated virus, AAV) vector: a single-stranded linear DNA virus without envelope, with high safety, low immunogenicity, and long expression cycle. AVV is currently known as the most suitable for in vivo A powerful tool for studying (invivo) gene function. The disadvantage is that the host can produce infectious AAV with the assistance of helper viruses such as adenovirus or herpes virus, so it is called adeno-associated virus.
3. Lentivirus vector: Lentivirus vector is basically derived from immunodeficiency virus (HIV), so it is still a retroviral vector. However, it has the characteristics of infecting quiescent cells and dividing cells, can stably integrate into the host chromosome and continuously express the target gene. The disadvantage is that it not only has strong immunogenicity itself, which is not conducive to immune cell therapy, but also the uncertainty of entering the host chromosome can easily lead to gene mutations and potentially infect laboratory workers.
4. Poxvirus (Poxviridae) and Herpes virus (Herpes virus) vectors: Its characteristic is that it can infect nerve cells. However, both have strong immunogenicity, easily cause inflammatory reactions and other adverse reactions, and have potential pathogenicity, and are not suitable for cellular immunotherapy.
5. Retrovirus (RV) vector: It is a highly efficient gene transduction viral vector, which can integrate the target gene into the host chromosome to obtain stable expression. However, it has similar shortcomings as lentiviral vectors, and it has the risk of potential tumorigenicity.
Application of virus vector in cellular immunotherapy
Based on domestic and foreign research reports, the application of recombinant adenovirus or retrovirus to infect dendritic cells (DC) requires multiple doses of repeated infections to achieve the purpose of effectively stimulating DC. Figure 1 shows the comparison of the time required for the three recombinant viruses carrying antigen genes to infect DCs to prepare Cytotoxic T lymphocytes (CTL).

 
Figure one

In the previous process of cellular immunotherapy, it took about 3-8 weeks from cell culture to reinfusion to tumor patients, which could not meet the demand for continuous treatment of tumor patients, especially those with severe disease.
To address the problem of too long cell culture time. ACTL targeted anti-tumor cellular immunity technology (abbreviated as ACTL technology) has greatly improved the virus production process. The recombinant adeno-associated virus (rAAV) product prepared has high titer, high activity, No bovine serum albumin or other miscellaneous proteins, no wild-type adenovirus pollution. With only one dose, rAAV can efficiently infect and stimulate DC. It only takes 12-18 days from cell culture to reinfusion to the patient, which fully meets the frequency required for clinical treatment.
The principle of ACTL technology is to transform a non-pathogenic adeno-associated virus (AAV) into a recombinant adeno-associated virus (rAAV) carrying specific tumor-associated determinant genes through genetic recombination technology. Infected patients' peripheral blood mononuclear cells (Monocytes, Mo), induced by cytokines, the monocytes transform into dendritic cells (DC) with powerful antigen presentation function. The obtained DC can stimulate the production of Cytotoxic T ilmphocytes (CTL), which are effective in killing tumor cells, and the generated CTL has tumor antigen specificity, that is, targeting. CTL stimulated by rAAV-infected DCs only have a killing effect on certain or several tumor-associated antigen-positive tumor cells, and have no effect on antigen-negative cells.
From the principle of ACTL technology, it can be seen that the viral vector used is rAAV, which will not cause any physiological or pathological changes after infecting the human body. The experimental results shown in Figure 2 show that rAAV can effectively infect and stimulate DC with only one dose. rAAV has an up-regulating effect on the function of DCs, which can ensure that DCs exert their antigen presentation (stimulation) function to the greatest extent, which leads to powerful DCs.
 

Figure II

Secondly, as shown in the experimental results of Figure 3: rAAV-infected DC and lymphocytes are mixed to promote the production of CD8+ T cells, thereby obtaining more CTLs that kill tumor cells.
 

Figure three

Summary: As can be seen from the above content, rAAV, as a viral vector, has a high infection efficiency and a wide range, can be stably expressed in host cells and the antigen expressed is closer to natural. And it can be large-scaled, standardized preparation or production, which is convenient for the clinical application of cellular immunotherapy, and has advantages that other methods can't compare. It is one of the most ideal carriers for cellular immunotherapy.