Killing nearly 2 million people a year, TB is one of the leading causes of infectious disease deaths globally. In 2007, there were an estimated 9.27 million cases of TB. Co-infection with HIV and an increase in drug-resistant strains of TB are making the epidemic even more severe and complicated to address. The current TB vaccine, BCG, is almost 90 years old and has been ineffective in saving the millions of lives lost to TB each year. Aeras Global TB Vaccine Foundation is a non-profit Product Development Partnership working in collaboration with leading researchers and scientists from the academic, industry, non-profit and government sectors to develop new and effective vaccine regimens to stop TB. An increasingly well documented defect in the BCG vaccine lies in its inability to escape the phagolysosome of infected macrophages and dendritic cells, which, unlike M. tuberculosis or M. leprae, diverts the immune response to primarily MHC class II antigen presentation and is the likely reason for the CD4 dominant T cell response to vaccination. Loss and gain of function screens using M. tuberculosis and the related avirulent M. kansasii have identified specific genes present in Mtb complex organisms, including BCG, whose gene products function to inhibit apoptosis of infected macrophages. Aeras will create fully cGxP compliant recombinant BCG vaccines incorporating deletions in genes known to inhibit apoptosis to enhance immune responses by cross-priming and will also construct cGxP compliant booster vaccines encoding and expressing high valency CD8+ T cell immunogens to create an optimal tuberculosis vaccine regimen. The booster vaccines will consist of recombinant adenovirus serotype 4 and recombinant human CMV vectors, both of which have been shown to elicit potent CD8+ T cell responses. We will evaluate these regimens in mice and rhesus macaques, models of TB vaccine immunology and efficacy with which we have extensive experience, to expediently select an optimal regimen.
Killing nearly 2 million people a year, TB is one of the leading causes of infectious disease deaths globally. In 2007, there were an estimated 9.27 million cases of TB. Co-infection with HIV and an increase in drug-resistant strains of TB are making the epidemic even more severe and complicated to address. The current TB vaccine, BCG, is almost 90 years old and has been ineffective in saving the millions of lives lost to TB each year. Aeras Global TB Vaccine Foundation is a non-profit Product Development Partnership working in collaboration with leading researchers and scientists from the academic, industry, non-profit and government sectors to develop new and effective vaccine regimens to stop TB. The requested grant will support the preclinical development of second generation tuberculosis (TB) vaccine candidates. Specifically, the aims of the proposed project include the following: 1. Generation of pro-apoptotic recombinant BCGs (rBCGs) and recombinant viral vectors; 2. Evaluation of cross-presentation induced by pro-apoptotic rBCGs expressing SIINFEKL- tagged proteins; 3. Optimization and evaluation of immune responses induced by various combinations of prime and boost regimens;and 4. Assessment of immunogenicity of prime-boost regimens in non-human primates. It is well documented that virulent but not avirulent mycobacteria induce apoptosis of infected macrophages. It has similarly been demonstrated that dendritic cells phagocytose apoptotic bodies from infected macrophages and that this results in the presentation of mycobacterial immunogens and the subsequent activation of antigen specific T cells. Apoptotic bodies created in this cross-priming process have in fact been shown to protect mice against challenge with virulent Mtb. Mtb may inhibit the extrinsic apoptosis pathway by down regulating expression of death receptors including Fas and soluble TNF receptor 2. Similarly Mtb may inhibit the intrinsic apoptosis pathway by upregulating mcl-1 and A or down regulating the expression of Bad, a known pro-apoptotic protein. Loss of function studies using Mtb transposon libraries and gain of function using Mtb genetic libraries expressed in avirulent M. smegmatis or M. kansasii have identified genes involved in the inhibition of apoptosis. nuoG, a subunit of the NADH dehydrogenase-1 complex is one such protein. It is highly conserved among Mtb complex organisms, including BCG, and its role in BCG suppression of apoptosis has also been confirmed. Other proteins, including SecA2, SodA, PknE and TrxA have also been identified as inhibitors of apoptosis. It is noteworthy that most of the factors identified as being of significance in the inhibition of apoptosis are redox mediators, including mediators of the bacterial response to oxidative stress from the infected host cell. It has long been known that mammalian redox proteins are key players in the signaling of apoptosis. Using techniques well established at Aeras, we will construct pro-apoptotic rBCG mutant vaccine strains in the background of our endosome perforating strain AERAS-401. We will use the pro-apoptotic rBCG as backbones for the over expression of key Mtb antigens to be boosted with viral vectors. It has been our personal experience that Adenoviral vectors are potent mediators of CD4+ and CD8+ T cell responses and we will construct a booster using the safe oral adenovirus type 4 as a vector. Further, based on findings in SIV and macaques, we will construct a second booster using an attenuated HCMV vector. From these, we intend to select an optimal regimen through immunization studies in mice and rhesus macaques for advancement into the clinic.
| Hokey, David A (2014) TB Vaccines: The (Human) Challenge Ahead. Mycobact Dis 4:e128 |
