rBCG Induces Strong Antigen-Specific T Cell Responses in Rhesus Macaques in a Prime-Boost Setting with an Adenovirus 35 Tuberculosis Vaccine Vector

BACKGROUND: BCG vaccination, combined with adenoviral-delivered boosts, represents a reasonable strategy to augment, broaden and prolong immune protection against tuberculosis (TB). We tested BCG (SSI1331) (in 6 animals, delivered intradermally) and a recombinant (rBCG) AFRO-1 expressing perfringolysin (in 6 animals) followed by two boosts (delivered intramuscullary) with non-replicating adenovirus 35 (rAd35) expressing a fusion protein composed of Ag85A, Ag85B and TB10.4, for the capacity to induce antigen-specific cellular immune responses in rhesus macaques (Macaca mulatta). Control animals received diluent (3 animals). METHODS AND FINDINGS: Cellular immune responses were analyzed longitudinally (12 blood draws for each animal) using intracellular cytokine staining (TNF-alpha, IL-2 and IFN-gamma), T cell proliferation was measured in CD4(+), CD8alpha/beta(+), and CD8alpha/alpha(+) T cell subsets and IFN-gamma production was tested in 7 day PBMC cultures (whole blood cell assay, WBA) using Ag85A, Ag85B, TB10.4 recombinant proteins, PPD or BCG as stimuli. Animals primed with AFRO-1 showed i) increased Ag85B-specific IFN-gamma production in the WBA assay (median >400 pg/ml for 6 animals) one week after the first boost with adenoviral-delivered TB-antigens as compared to animals primed with BCG (<200 pg/ml), ii) stronger T cell proliferation in the CD8alpha/alpha(+) T cell subset (proliferative index 17%) as compared to BCG-primed animals (proliferative index 5% in CD8alpha/alpha(+) T cells). Polyfunctional T cells, defined by IFN-gamma, TNF-alpha and IL-2 production were detected in 2/6 animals primed with AFRO-1 directed against Ag85A/b and TB10.4; 4/6 animals primed with BCG showed a Ag85A/b responses, yet only a single animal exhibited Ag85A/b and TB10.4 reactivity. CONCLUSION: AFRO-1 induces qualitatively and quantitatively different cellular immune responses as compared with BCG in rhesus macaques. Increased IFN-gamma-responses and antigen-specific T cell proliferation in the CD8alpha/alpha+ T cell subset represents a valuable marker for vaccine-take in BCG-based TB vaccine trials

Study Timeline and Sampling Schedule.

<p>NHPs were boosted with AERAS-402 fifteen and twenty-seven weeks after the prime with BCG or AFRO-1, Animals in group 1 were primed with BCG, animals in group 2 with the recombinant BCG (AFRO-1) which combines endosomal escape, TB10.4 expression and over-expression of Ag85A and Ag85B. Animals in both groups were boosted with the non-replicating adenovirus 35 AERAS-402 which expresses the Ag85A, Ag85B and TB10.4 fusion protein. Animals in group 3 received the diluent (control group).</p

Prime with BCG or AFRO-1 induces a different IFN-γ production profile in response to <i>Mtb</i> antigen stimulation.

<p>The median of IFN-γ production (measured by ELISA) in whole blood cultures for each group in response to different <i>Mtb</i> antigen stimulation was assessed. Stronger IFN-γ production was seen in animals primed with AFRO-1 in response to Ag85A and Ag85B, as compared to animals primed with BCG one week after the first boost with AERAS-402.</p

Prime with AFRO-1 induces proliferation of Ag85B-specific T cells in CD4⁺ and CD8alpha/alpha⁺ T cells.

<p>The median of the proliferation index (% of blasts in response to antigen stimulation - % of blasts in negative control) in response to <i>Mtb</i> antigens was determined by flow cytometric analysis. Differential expansion of T cell subsets was gauged by gating on T cell subsets, i.e. CD4⁺, CD8alpha/beta⁺ and CD8alpha/alpha⁺. Animals primed with AFRO-1 showed stronger proliferation in response to Ag85B stimulation within CD4⁺ T cells (A) and CD8alpha/alpha⁺ T cells (B) as compared to animals primed with BCG one week after the first boost with AERAS-402. No difference was detectable between animals primed with AFRO-1 or BCG in the CD8alpha/beta⁺ T cell compartment (C).</p

Prime-Boost Vaccination with rBCG/rAd35 Enhances CD8+ Cytolytic T-Cell Responses in Lesions from Mycobacterium Tuberculosis –Infected Primates

To prevent the global spread of tuberculosis (TB) infection, a novel vaccine that triggers potent and long-lived immunity is urgently required. A plasmid-based vaccine has been developed to enhance activation of major histocompatibility complex (MHC) class I–restricted CD8+ cytolytic T cells using a recombinant Bacille Calmette-Guérin (rBCG) expressing a pore-forming toxin and the Mycobacterium tuberculosis (Mtb) antigens Ag85A, 85B and TB10.4 followed by a booster with a nonreplicating adenovirus 35 (rAd35) vaccine vector encoding the same Mtb antigens. Here, the capacity of the rBCG/rAd35 vaccine to induce protective and biologically relevant CD8+ T-cell responses in a nonhuman primate model of TB was investigated. After prime/boost immunizations and challenge with virulent Mtb in rhesus macaques, quantification of immune responses at the single-cell level in cryopreserved tissue specimen from infected organs was performed using in situ computerized image analysis as a technological platform. Significantly elevated levels of CD3+ and CD8+ T cells as well as cells expressing interleukin (IL)-7, perforin and granulysin were found in TB lung lesions and spleen from rBCG/rAd35-vaccinated animals compared with BCG/rAd35-vaccinated or unvaccinated animals. The local increase in CD8+ cytolytic T cells correlated with reduced expression of the Mtb antigen MPT64 and also with prolonged survival after the challenge. Our observations suggest that a protective immune response in rBCG/rAd35-vaccinated nonhuman primates was associated with enhanced MHC class I antigen presentation and activation of CD8+ effector T-cell responses at the local site of infection in Mtb-challenged animals

Four-gene pan-African blood signature predicts progression to tuberculosis

Rationale: Contacts of patients with tuberculosis (TB) constitute an important target population for preventive measures because they are at high risk of infection with Mycobacterium tuberculosis and progression to disease. Objectives: We investigated biosignatures with predictive ability for incident TB. Methods: In a case–control study nested within the Grand Challenges 6-74 longitudinal HIV-negative African cohort of exposed household contacts, we employed RNA sequencing, PCR, and the pair ratio algorithm in a training/test set approach. Overall, 79 progressors who developed TB between 3 and 24 months after diagnosis of index case and 328 matched nonprogressors who remained healthy during 24 months of follow-up were investigated. Measurements and Main Results: A four-transcript signature derived from samples in a South African and Gambian training set predicted progression up to two years before onset of disease in blinded test set samples from South Africa, the Gambia, and Ethiopia with little population-associated variability, and it was also validated in an external cohort of South African adolescents with latent M. tuberculosis infection. By contrast, published diagnostic or prognostic TB signatures were predicted in samples from some but not all three countries, indicating site-specific variability. Post hoc meta-analysis identified a single gene pair, C1QC/TRAV27 (complement C1q C-chain / T-cell receptor-α variable gene 27) that would consistently predict TB progression in household contacts from multiple African sites but not in infected adolescents without known recent exposure events. Conclusions: Collectively, we developed a simple whole blood–based PCR test to predict TB in recently exposed household contacts from diverse African populations. This test has potential for implementation in national TB contact investigation programs