human cases have been in close contact with infected flocks
and there is no known example of a human-to-human
transmission of the current H5N1 bird flu. However, it
is the largest and most severe influenza epidemic ever
registered among birds; since 2003, it has spread rapidly
to poultry in many countries in Asia and most recently it
seems to have established itself in Turkey. The size of this
virus repertoire has caused concerns that re-assortment or
mutations of influenza genes occurring in bird populations,
or in infected humans, eventually will generate a virus that
can be transmitted from person to person causing a highly
contagious, and potentially devastating, pandemic [3].
The primary port of entry of the influenza virus is the
mucosa of the respiratory tract. The adaptive immune system
can provide immune protection against mucosal pathogens
through secretory IgA and IgM immunoglobulins, which
can effectively prevent the virus from infecting its target
cells. Vaccination using inactivated influenza virus preparations
remains the primary method of prevention. However,
the virus attempts to escape neutralizing antibodies through
constantly changing the composition of its surface antigens.
This complicates the development of cross-protective
immunity, i.e. the ability to cover several different isolates;
rather, influenza vaccines must regularly be updated to match
existing seasonal epidemic flu isolates. Current vaccine technology
is likely to be too slow, and also of too low capacity,
to produce enough vaccine against a new emerging flu isolate
in time to prevent a true pandemic. Thus, the development
of faster and more efficient vaccine technologies capable of
delivering new, safe, efficacious and easy-managed protective
influenza vaccines is of high priority.
It is known that CD8+ T cell responses