A recent study by a group of researchers in Japan suggests that a tetrameric glycoprotein complex gH/GL/gQ1/gQ2, can be used to make the first ever vaccine to prevent human herpes virus 6B (HHV6B) infection.
HHV 6 is a group of various viruses belonging to the herpes virus family. HHV-6B causes a disease called exanthema subitum or roseola infantum in children and infants and is one of the most common causes of emergency hospitalisation in children up to 3 years of age.
The study was published in the peer-reviewed journal PLOS Pathogens.
HHV6B infection is a highly common condition that affects infants between the age of 6 and 18 months when their maternal antibodies start to decline. Primary infection of HHV6B or exanthem subitum shows up as fever and skin rashes.
Since there is no cure for this infection, children are mostly given supportive treatment to manage symptoms – antipyretics for fever reduction for example. However, the condition can be severe in immunocompromised (those with a weak immune system) children and hence they need treatment including antiviral medications.
Also, like every herpes virus, HHV6B becomes latent in the body after the primary infection. The virus stays in the body of the person forever but does not cause disease even if it is somehow reactivated. But, in immunocompromised people or those undergoing organ transplantation, this reactivation may lead to viremia (high viral levels in blood) and encephalitis.
HHV6B tetramer or gH/GL/gQ1/gQ2 is a protein on the surface of the HHV6 virus that interacts with the human CD134 (a protein present on T cells) to gain entry into host cells. As viruses are intracellular parasites, they need a living cell to survive.
The researchers created a soluble version (one not present on the virus surface) of this tetramer to make a vaccine against HHV6B. They then injected this tetramer into mice along with aluminium or CpG oligodeoxynucleotide adjuvant. Adjuvants are substances that can increase the immunogenicity (the ability to stimulate an immune response) of a vaccine.
It was found that a certain amount of the tetramer (about 40 mcg in mice) along with about 302 mcg of alum induced high antibody levels. Reducing the concentration of either alum or the tetramer reduced antibody levels. However, the study pointed out that alum can only improve humoral immunity (antibody formation), it does not do much when it comes to T cell production. T cells are immune system cells that fight against viruses. They destroy the infected cells and help clear viral infections. Hence, CpG oligodeoxynucleotide was also added as adjuvant to increase T cell response to the tetramer. CpG oligodeoxynucleotide is a short stretch of DNA.
To check if humans produce natural antibodies against the tetramer when the get HHV6B infection, the researchers took the sera (blood without clotting factors) of 14 patients with drug-induced hypersensitivity syndrome, which is highly related to HHV6B infection, and five healthy people. It was noted that the sera did contain antibodies that reacted with the tetramer in a similar manner as they would to HHV6B infected cells.
It is important to note that though the vaccine is only shown to be effective in mice so far, it may be one of the first steps towards HHV6 prevention.
For more information on the process of vaccine development, read our article on How are vaccines made
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