Annual influenza A infections affect 5-15% of the population, causing an estimate half million deaths per year worldwide, with the majority of the severe diseases in infants, elderly and immunocompromised individuals. Influenza viruses infect the epithelium of the upper and lower respiratory tracts, typically resulting in an abrupt onset of illness, that usually includes fever, myalgias, upper respiratory tract congestion and pharyngytis. These symptoms persist for approximately one week; pneumonia is a frequent manifestation of more severe infection, while myocarditis, encephalitis and other extra respiratory tract disease occur more ralely. Influenza viruses belongs to Orthomixoviridae family, are enveloped negative single stranded RNA virus able to infect a wide range of avian and mammalian species. The genome of influenza A virus is composed of eight segments that encode for at least ten proteins. Influenza A viruses are subdivided further into subtypes based on their two surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), and currently, 16 known types of HA and 9 known types of NA have been isolated from aquatic birds, the natural reservoir for all influenza viruses. Haemagglutinin (HA) and neuraminidase (NA) are the primary targets of influenza vaccines but also the viral surface glycoproteins that accumulate the highest number of mutations. Haemagglutinin, the most abundant surface glycoprotein, directs binding and viral entry into host cells whereas neuraminidase, the second most abundant surface glycoprotein, cleaves sialic acid and plays important roles in viral entry and release. Influenza vaccination is the most effective method for preventing influenza virus infection and its potentially severe complications. Natural infection and vaccination elicit long lasting protective responses, nevertheless influenza vaccines are modified yearly due to the high propensity of the virus to mutate. Minor mutations, antigenic drift, occur continuously due to the low fidelity of the RNA polymerase and support the need for yearly changes in vaccine strains. Major modifications in the virus, antigenic shift, arise from viral re-assortments, occur more rarely, but represent a major challenge for public health since they can give rise to novel viruses for which the human population has little or no immunity. The latter scenario creates the risk of a pandemic infection similar to the Spanish flu pandemic (1918-1920) resulting in more than 40 million deaths worldwide and to the Asian flu (1957) and the Hong Kong Flu (1968) resulting in 1-4 million deaths. Occasionally, avian influenza A virus cross the species barrier into human and a pandemic may arise if such viruses have the ability to spread efficiently from human to human. In 1997, the increase in outbreaks of highly pathogenic avian influenza (HPAI) in poultry and the occasional transmission of these viruses to humans has caused great concern for the emergence of a new influenza A virus pandemics. Since then HPAI H5N1 viruses have continued to circulate in Asia and 400 human cases have been reported with a fatal outcome of 60%. Protection from avian H5N1 influenza virus could be achieved by vaccines capable of eliciting sustained and broadly cross-reactive immune responses. All clinical studies so far have shown the need for two doses of adjuvanted pre-pandemic flu vaccines to achieve potentially protective neutralizing antibody titers against avian H5N1 Vietnam. Two doses of avian influenza vaccines formulated with a strong adjuvant such as MF59 are required to induce potentially protective titers of neutralizing antibodies broadly reactive to drifted H5 strains. In addition all clinical studies have shown in influenza a limited efficacy of alum compared to oil in water emulsions, such as MF59, an adjuvant with excellent safety record licensed from more than a decade for seasonal flu vaccines in Europe. Those studies also showed that years after priming even if antibodies become undetectable the immune-response can be efficiently boosted in subjects that received a successful priming regimen. Such considerations support a prime boost strategy based on 1 or 2 immunizations for “pre pandemic vaccination” followed by a “booster dose” at the start of the pandemic outbreak. A drawback to this strategy is the lack of early markers capable of predicting the proportion of the population that develops a memory response after pre pandemic vaccination, information currently deduced only post hoc based on the response to the booster dose. To identify an early marker of effective pre pandemic priming we analyzed both the antibody and cell mediated responses in a prime boost clinical trial. We conducted a phase II study wherein healthy adults received 2 doses of a subunit H5N1 A/Vietnam/1194/2004 vaccine as “pre pandemic vaccination”, followed at 6 months by a 3rd booster dose. The vaccine was either plain (Non Adj 15) or adjuvanted with MF59 (MF59 H5N1), an oil/water proprietary adjuvant used in seasonal flu vaccines since 1997. We found that one dose of MF59 H5N1 vaccine is sufficient to expand CD4+ T lymphocytes with a Th1-prone effector/memory phenotype; whereas 2 doses are required to expand the pool of H5N1 memory B cells and to elicit high titers of neutralizing antibodies. Strikingly, a 3 fold increase in total H5 specific CD4+ T cells after the 1st dose predicts the rise of MN antibodies to titers ≥80 after booster immunization and their persistence at 6 months with 75% and 85% accuracy, respectively. We suggest that, if confirmed on a larger number of subjects, CD4+ T cell priming can be used as early measure of vaccine efficacy and can help screen different pre-pandemic vaccine formulations for their ability to induce immune-memory.
(2009). Profiling human cell-mediated immune response to pre-pandemic vaccination.. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2009).
VANONI, MARCO ERCOLE
|Data di pubblicazione:||15-dic-2009|
|Titolo:||Profiling human cell-mediated immune response to pre-pandemic vaccination.|
|Settore Scientifico Disciplinare:||BIO/10 - BIOCHIMICA|
|Scuola di dottorato:||Scuola di dottorato di Scienze|
|Corso di dottorato:||BIOTECNOLOGIE INDUSTRIALI - 15R|
|Citazione:||(2009). Profiling human cell-mediated immune response to pre-pandemic vaccination.. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2009).|
|Parole Chiave:||H5N1 influenza vaccine, MF59 adjuvant prepandemic vaccination, immune memory, protection|
|Appare nelle tipologie:||07 - Tesi di dottorato Bicocca post 2009|