Protective Immune Responses to a Recombinant Adenovirus Type 35 Tuberculosis Vaccine in Two Mouse Strains: CD4 and CD8 T-Cell Epitope Mapping and Role of Gamma Interferon

Abstract

There is an urgent need for an efficacious vaccine against tuberculosis (TB). Cellular immune responses are key to an effective protective response against TB. Recombinant adenovirus (rAd) vectors are especially suited to the induction of strong T-cell immunity and thus represent promising vaccine vehicles for the prevention of TB. We have previously reported on rAd vector serotype 35, the serotype of choice due to low preexisting immunity worldwide, which expresses a unique fusion protein of Mycobacterium tuberculosis antigens Ag85A, Ag85B, and TB10.4 (Ad35-TBS). Here, we demonstrate that Ad35-TBS confers protection against M. tuberculosis when administered to mice through either an intranasal or an intramuscular route. Histological evaluation of lung tissue corroborated the protection and, in addition, demonstrated differences between two mouse strains, with diffuse inflammation in BALB/c mice and distinct granuloma formation in C57BL/6 mice. Epitope mapping analysis in these mouse strains showed that the major T-cell epitopes are conserved in the artificial fusion protein, while three novel CD8 peptides were discovered. Using a defined set of T-cell epitopes, we reveal differences between the two mouse strains in the type of protective immune response, demonstrating that different antigen-specific gamma interferon (IFN-␥)-producing T cells can provide protection against M. tuberculosis challenge. While in BALB/c (H-2 d ) mice, a dominant CD8 T-cell response was detected, in C57BL/6 (H-2 b ) mice, more balanced CD4/CD8 T-cell responses were observed, with a more pronounced CD4 response in the lungs. These results unify conflicting reports on the relative importance of CD4 versus CD8 T-cell responses in protection and emphasize the key role of IFN-␥. Tuberculosis (TB), an airborne disease caused by Mycobacterium tuberculosis, is responsible for 2 million deaths each year, with more than 90% of cases occurring in developing countries. It has been estimated that one-third of the world population is infected with M. tuberculosis, and about 5 to 10% of the infected individuals will develop TB during their lifetime. The increasing global impact of TB has been linked to growing poverty, increased emigration, deterioration of public health care, the spread of human immunodeficiency virus, and the development of multidrug-resistant strains of M. tuberculosis. Bacille Calmette-Guérin (BCG), a live and attenuated strain of Mycobacterium bovis, is the only available vaccine against TB to date and has been used for the vaccination of newborns for decades. The vaccine is effective in preventing serious complications of childhood TB, but its efficacy wanes over a period of 10 to 15 years, rendering adolescents increasingly susceptible to pulmonary TB. Significant efforts are being made to generate a more effective TB vaccine (3,24,50), and vaccination regimens aimed to improve BCG-induced protection are currently the most favorable approach (4,14,19,21,29,36). The most promising antigens for vaccine generation include protei...

Impact of Recombinant Adenovirus Serotype 35 Priming versus Boosting of aPlasmodium falciparumProtein: Characterization of T- and B-Cell Responses to Liver-Stage Antigen 1

“…In the ICS assay, the CD4 responses were relatively low compared to the CD8 responses, while by the ELISPOT assay the difference was less pronounced (data not shown), confirming a previously published observation of the high sensitivity of the ELISPOT assay relative to that of the ICS for the detection of antigen-specific CD4 responses (41).…”

“…A possible explanation of our results is that the LSA-1 protein expression and the antigen processing upon immunization are not optimal for the induction of T-helper cells required to trigger anti-LSA-1 antibody responses, probably due to the modified sequence of the protein (24). In line with this hypothesis, it is noteworthy that a relatively high dose of rAd35 (10 10 VP) was required to induce significant T-cell responses, in contrast to our previous results with other rAd35 vectors where a 1-log-lower dose (10 9 VP) was sufficient to induce an optimal T-cell response (37,38,41). The heterologous vaccination regimens elicited a level of anti-LSA-1 IgG responses comparable to that seen for the protein vaccinations.…”

“…T-cell epitope mapping was performed 2 weeks after the last immunization as described elsewhere (41). For epitope mapping, splenocytes from mice immunized with rAd35.LSA-1 (five per group) or Ad35.Empty (three per group) were pooled and stimulated with different pools of overlapping 15-mer peptides covering the whole sequence of the LSA-1 recombinant protein.…”

“…Identification of CD4 ϩ and CD8 ϩ T-cell epitopes was performed for BALB/c (H-2 d ) mice 2 weeks after immunization with rAd35.LSA-1 and using 15-mer peptides arranged in a matrix as described previously (6,41). The different steps involved in the epitope mapping are depicted in Fig.…”

Genetic immunization in the lung induces potent local and systemic immune responses

“…delivery (13). We found that rAd35 is highly immunogenic in the lungs when given by aerosol to rhesus macaques (Fig.…”