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Microbes & Immunity Genetic therapy with HSV-1 vectors

These attenuated viruses are often used as therapeutic (1) After the cells infected with the virus showed lesions
vectors for gene delivery. Attenuated HSV-1 vectors such as swelling, rounding, and cell fusion, the cells
have been applied to live viral vaccines as oncolytic and supernatants were collected;
viruses and gene therapy vectors to deliver genes into (2) Cells were repeatedly frozen and thawed at −70°C and
nerve cells. The toxicity of many HSV-1 non-essential 37°C to lyse the cells;
genes is reduced in animal models. Among them, (3) Centrifuge at low speed to collect the supernatants;
thymidine kinase (TK), ribonucleoside reductase (RR), (4) Centrifuge at 22,000 rpm for 1 h to remove the
viral host shutoff protein Vhs (encoded by UL41), supernatants;
and ICP34.5 have been widely studied. TK genes are (5) The mixture was resuspended in TBS (200 mM NaCl,
involved in nucleotide metabolism for viral growth and 2.6 mM KCl, 10 mM Tris-HCl [pH 7. , 20 mM MgCl ,
5
2
efficient replication in neurons. RR is required for the and 1.8 mM CaCl ), added to different concentrations
2
conversion of rNTPs to dNTPs in neuronal cells and of sucrose (30%, 40%, and 50%), and gradiently
viral DNA synthesis. Vhs destabilize host mRNAs centrifuged at 20,000 rpm for 2 h;
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and limit cellular protein synthesis, thereby providing (6) Fluids with sucrose concentrations ranging from
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favorable conditions for viral protein synthesis. During 40 to 50% were collected, centrifuged again, and
lytic infection, Vhs also leads to viral mRNA instability resuspended in TBS;
and prevents the overexpression of IE and E proteins. (7) Store in a −80°C refrigerator or liquid nitrogen tank
ICP34.5 acts as a neurotoxic factor and is involved for future use.
in HSV-1 pathogenicity. It is involved in multiple
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periods of viral replication and is multifunctional, one 4.4.2. Viral particle titration
of which is preventing cytokine-induced restriction With respect to the titration of virions, plaque formation
of viral growth. ICP34.5 recruits protein phosphatase assays are often employed and are capable of detecting
Ia and phosphorylates eIF2α again to ensure smooth infection-competent viruses. In general, monolayers of
protein translation as well as viral replication. The PKR Vero or other host cells are infected with a range of virion
pathway is often disrupted in tumor cells, and eIF2α dilutions. The virus will multiply in infected cells, eventually
levels increase, allowing the ICP34.5 deletion virus to causing cytotoxic effects and release. The released virus
replicate as well. 53,54 In non-permissive cells, deletion will infect neighboring cells. The whole process is repeated
of ICP34.5 leaves the nucleocapsid in the nucleus, and continuously, eventually leading to the formation of plaques.
viral replication does not persist. To stop the spread of the virus to other areas of the cell and
Newly developed attenuated vectors, in addition to the start a new plaque formation process, a layer of soft agar is
deletion of these viral genes, also insert genes encoding spread over the surface of the cell after completing the initial
various cytokines, such as interleukin (IL)-4, IL-12, IL-10, infection. Its operation steps are briefly described as follows:
granulocyte/macrophage stimulating factor (GM-CSF) or (1) Vero cells were plated in 96-well plates until they were
the costimulatory factor B7-1, thereby maximizing tumor overgrown;
immunogenicity. 28,55-57 (2) The virus was diluted in a medium gradient. EP tubes
can be used for virus dilution, generally with three
With attenuated HSV-1 as a vector, in addition to replicates for each concentration;
genetic stability factors, many safety factors, such as viral (3) The culture medium in the 96-well plate was removed,
latency, reactivation, or recombination with virulent wild- and 100 µL of virus mixture was added to each well;
type viruses, are worth exploring.
(4) After 1 –o1.5 h, the virus mixture was removed, and
4.4. Purification and quantification of HSV-1 virus the tip was changed each time. Another 200 µL of
particles complete medium (containing 2% fetal bovine serum)
was supplemented and cultured for 24 – 48 h. Close
4.4.1. Purification of virions observation was performed until the number of
Amplicon vectors are packaged into infection-competent plaques that appeared at the lowest concentration no
pseudoviruses with the help of helper viruses. As with the longer increased;
virions amplified from the other two derived viral vectors (5) The medium was discarded, 30 µL (5% crystal violet +
(replication-deficient and replication-attenuated), wild- 70% alcohol) was added to each well, and after 2 min
type HSV-1 was purified and quantified. To obtain higher of incubation, the wells were repeatedly washed with
titers and pure virions, sucrose gradient centrifugation is double-distilled water.
usually employed to enrich and purify virions effectively. 58,59 (6) After drying, the plaques were counted, and the titer
Its operation steps are briefly described as follows: was calculated.

Volume 2 Issue 2 (2025) 24 doi: 10.36922/mi.7947