Research Area:	Immunology
Technology Exchange:	Cellular immunology and Vaccine production and evaluation
Keywords:	vaccine, T cell, immunology, malaria, tuberculosis and influenza

For more than ten years we have been making and testing vaccines designed to induce T cell responses to the antigens we encode, chiefly using antigens from malaria and tuberculosis. We have had most success with heterologous prime-boost regimes using either a DNA vaccine or recombinant fowlpox or adenovirus to prime a response and recombinant MVA to boost it. Several of the vaccines we have developed have progressed into clinical trials. We continue to work on finding the most efficient way to induce a protective T cell response by vaccination and are exploring a number of novel ways to do this.

Recombinant adenoviruses for clinical trials can now be produced to GMP by the University's Clinical Biomanufacturing Facility. Staff at the CNF work closely with academics to prepare batches of new vaccines for clinical trials.

In 2008 clinical trials of a new 'flu vaccine began in Oxford. Most adults already have memory T cell responses to 'flu antigens, but over time these fall below protective levels. The new vaccine, MVA-NP+M1 boosts these low level responses to very high levels. The next stage will be to test if these t cell responses can prvent people from being infected with 'flu.

Name	Institution	Country
Prof. Adrian Hill	University of Oxford	UK
Dr. Alfredo Nicosia	Okairos	Italy
Dr. Glyn Hewinson	Veterinary Laboratories Agency	UK

Vordermeier HM, Rhodes SG, Dean G, Goonetilleke N, Huygen K, Hill AV, Hewinson RG, Gilbert SC. 2004. Cellular immune responses induced in cattle by heterologous prime-boost vaccination using recombinant viruses and bacille Calmette-Guérin. Immunology, 112 (3), pp. 461-70. Read abstract | View on PubMed

The development of novel vaccine strategies to replace or supplement bacille Calmette-Guérin (BCG) is urgently required. Here we study, in cattle, the use of heterologous prime-boost strategies based on vaccination with BCG and the mycobacterial mycolyl transferase Ag85A (Rv3804c) expressed either in recombinant modified vaccinia virus Ankara (MVA85A) or attenuated fowlpox strain FP9 (FP85A). Five different vaccination schedules were tested in the first experiment: MVA85A followed by BCG (group 1); BCG followed by MVA85A (group 2); BCG followed by FP85A and then MVA85A (group 3); MVA85A followed by MVA85A and then FP85A (group 4); and FP85A followed by FP85A and then MVA85A (group 5). Vaccine-induced levels of cellular immunity were assessed by determining interferon-gamma (IFN-gamma) responses in vitro. Prime-boost protocols, using recombinant MVA and BCG in combination (groups 1-3), resulted in significantly higher frequencies of Ag85-specific IFN-gamma-secreting cells than the two viral vectors used in combination (P=0.0055), or BCG used alone (groups 2 and 3, P=0.04). The T-cell repertoires of the calves in all five groups were significantly broader following heterologous booster immunizations than after the primary immunization. In a second experiment, the effects of BCG\MVA85A heterologous prime-boost vaccination were compared with BCG\BCG homologous revaccination. The results suggested a higher Ag85A-specific response with a wider T-cell repertoire in the MVA85A-boosted calves than in the BCG\BCG-vaccinated calves. In conclusion therefore, the present report demonstrates the effectiveness of heterologous prime-boost strategies based on recombinant MVA and BCG to induce strong cellular immune responses in cattle and prioritise such vaccination strategies for rapid assessment of protective efficacy in this natural target species of tuberculosis. Hide abstract

Taracha EL, Bishop R, Musoke AJ, Hill AV, Gilbert SC. 2003. Heterologous priming-boosting immunization of cattle with Mycobacterium tuberculosis 85A induces antigen-specific T-cell responses. Infection and immunity, 71 (12), pp. 6906-14. Read abstract | View on PubMed

Heterologous priming-boosting vaccination regimens involving priming with plasmid DNA antigen constructs and inoculating (boosting) with the same recombinant antigen expressed in replication-attenuated poxviruses have recently been demonstrated to induce immunity, based on CD4(+)- and CD8(+)-T-cell responses, against several diseases in both rodents and primates. We show that similar priming-boosting vaccination strategies using the 85A antigen of Mycobacterium tuberculosis are effective in inducing antigen-specific gamma interferon-secreting CD4(+) and CD8(+) T cells, detected by a bovine enzyme-linked immunospot assay, in Bos indicus cattle. T-cell responses induced by priming with either plasmid DNA or fowlpox virus 85A constructs were enhanced by boosting with modified vaccinia virus Ankara expressing the same antigen administered intradermally. On the basis of the data, it appears that intradermal priming was more effective than intramuscular delivery of the priming dose for boosting with the modified vaccinia virus Ankara strain in cattle. Using either fowlpox virus or DNA priming, there was a significant bias toward induction of CD4(+)- rather than CD8(+)-T-cell responses. These data illustrate the general applicability of priming-boosting vaccination strategies for induction of antigen-specific T-cell responses and suggest that the method may be useful for development of veterinary vaccines. Hide abstract

Robinson HL. 2003. Prime boost vaccines power up in people. Nature medicine, 9 (6), pp. 642-3. View on PubMed

Andrews L, Andersen RF, Webster D, Dunachie S, Walther RM, Bejon P, Hunt-Cooke A, Bergson G, Sanderson F, Hill AV, Gilbert SC. 2005. Quantitative real-time polymerase chain reaction for malaria diagnosis and its use in malaria vaccine clinical trials. The American journal of tropical medicine and hygiene, 73 (1), pp. 191-8. Read abstract | View on PubMed

The demand for an effective malaria vaccine is high, with millions of people being affected by the disease every year. A large variety of potential vaccines are under investigation worldwide, and when tested in clinical trials, researchers need to extract as much data as possible from every vaccinated and control volunteer. The use of quantitative real-time polymerase chain reaction (PCR), carried out in real-time during the clinical trials of vaccines designed to act against the liver stage of the parasite's life cycle, provides more information than the gold standard method of microscopy alone and increases both safety and accuracy. PCR can detect malaria parasites in the blood up to 5 days before experienced microscopists see parasites on blood films, with a sensitivity of 20 parasites/mL blood. This PCR method has so far been used to follow 137 vaccinee and control volunteers in Phase IIa trials in Oxford and on 220 volunteer samples during a Phase IIb field trial in The Gambia. Hide abstract

Gilbert SC, Moorthy VS, Andrews L, Pathan AA, McConkey SJ, Vuola JM, Keating SM, Berthoud T, Webster D, McShane H, Hill AV. 2006. Synergistic DNA-MVA prime-boost vaccination regimes for malaria and tuberculosis. Vaccine, 24 (21), pp. 4554-61. Read abstract | View on PubMed

T-cell-mediated responses against the liver-stage of Plasmodium falciparum are critical for protection in the human irradiated sporozoite model and several animal models. Heterologous prime-boost approaches, employing plasmid DNA and viral vector delivery of malarial DNA sequences, have proved particularly promising for maximising T-cell-mediated protection in animal models. The T-cell responses induced by this prime-boost regime, in animals and humans, are substantially greater than the sum of the responses induced by DNA or MVA vaccines used alone, leading to the term introduced here of "synergistic" prime-boost immunisation. The insert in our first generation clinical constructs is known as multiple epitope-thrombospondin-related adhesion protein (ME-TRAP). We have performed an extensive series of phase I/II trials evaluating various prime-boost combination regimens for delivery of ME-TRAP in over 500 malaria-naïve and malaria-exposed individuals. The three delivery vectors are DNA, modified vaccinia virus Ankara (MVA) and, more recently, fowlpox strain 9 (FP9). Administration was intra-epidermal and intramuscular for DNA and intradermal for MVA and FP9. Doses of DNA ranged from 4 microg to 2mg. Doses of MVA were up to 1.5 x 10(8) plaque forming units (pfu) and of FP9, up to 1.0 x 10(8)pfu. Further trials employing bacille Calmette-Guérin (BCG) as the priming agent and MVA expressing antigen 85A of Mycobacterium tuberculosis as the boosting agent has extended the scope of synergistic prime-boost vaccination. In this review we summarise the safety, immunogenicity and efficacy results from these malaria and tuberculosis vaccine clinical trials. Hide abstract

McShane H, Brookes R, Gilbert SC, Hill AV. 2001. Enhanced immunogenicity of CD4(+) t-cell responses and protective efficacy of a DNA-modified vaccinia virus Ankara prime-boost vaccination regimen for murine tuberculosis. Infection and immunity, 69 (2), pp. 681-6. Read abstract | View on PubMed

DNA vaccines whose DNA encodes a variety of antigens from Mycobacterium tuberculosis have been evaluated for immunogenicity and protective efficacy. CD8(+) T-cell responses and protection achieved in other infectious disease models have been optimized by using a DNA immunization to prime the immune system and a recombinant virus encoding the same antigen(s) to boost the response. A DNA vaccine (D) and recombinant modified vaccinia virus Ankara (M) in which the DNA encodes early secreted antigenic target 6 and mycobacterial protein tuberculosis 63 synthesized, and each was found to generate specific gamma interferon (IFN-gamma)-secreting CD4(+) T cells. Enhanced CD4(+) IFN-gamma T-cell responses were produced by both D-M and M-D immunization regimens. Significantly higher levels of IFN-gamma were seen with a D-D-D-M immunization regimen. The most immunogenic regimens were assessed in a challenge study and found to produce protection equivalent to that produced by Mycobacterium bovis BCG. Thus, heterologous prime-boost regimens boost CD4(+) as well as CD8(+) T-cell responses, and the use of heterologous constructs encoding the same antigen(s) may improve the immunogenicity and protective efficacy of DNA vaccines against tuberculosis and other diseases. Hide abstract

Gilbert SC, Schneider J, Hannan CM, Hu JT, Plebanski M, Sinden R, Hill AV. 2002. Enhanced CD8 T cell immunogenicity and protective efficacy in a mouse malaria model using a recombinant adenoviral vaccine in heterologous prime-boost immunisation regimes. Vaccine, 20 (7-8), pp. 1039-45. Read abstract | View on PubMed

Recombinant replication-defective adenovirus expressing the CS gene from Plasmodium berghei (Ad-PbCS) was found to induce a strong CD8(+) T cell response after intra-dermal or -muscular immunisation. Boosting of an adenovirus-primed immune response with the replication-impaired poxvirus, modified vaccinia virus Ankara (MVA) led to enhanced immunogenicity and substantial protective efficacy. The recombinant adenoviral vaccine was capable of boosting to protective levels a CD8(+) T cell response primed by either a plasmid DNA vaccine, a recombinant Ty virus-like particle vaccine or recombinant MVA each expressing the same epitope or antigen. Complete protective efficacy after intradermal immunisation was observed with the adenovirus prime-MVA boost regime. This study identifies recombinant replication-defective adenovirus as an alternative to recombinant replication-defective poxviruses as boosting agents for the induction of strong protective CD8(+) T cell responses. Hide abstract

Keating SM, Bejon P, Berthoud T, Vuola JM, Todryk S, Webster DP, Dunachie SJ, Moorthy VS, McConkey SJ, Gilbert SC, Hill AV. 2005. Durable human memory T cells quantifiable by cultured enzyme-linked immunospot assays are induced by heterologous prime boost immunization and correlate with protection against malaria. Journal of immunology (Baltimore, Md. : 1950), 175 (9), pp. 5675-80. Read abstract | View on PubMed

Immunological memory is a required component of protective antimalarial responses raised by T cell-inducing vaccines. The magnitude of ex vivo IFN-gamma T cell responses is widely used to identify immunogenic vaccines although this response usually wanes and may disappear within weeks. However, protection in the field is likely to depend on durable central memory T cells that are not detected by this assay. To identify longer-lived memory T cells, PBMC from malaria-naive vaccinated volunteers who had received prime boost vaccinations with a combination of DNA and/or viral vectors encoding the multiepitope string-thrombospondin-related adhesion protein Ag were cultured in vitro with Ag for 10 days before the ELISPOT assay. Ex vivo T cell responses peaked at 7 days after the final immunization and declined substantially over 6 mo, but responses identified after T cell culture increased over the 6-mo period after the final immunization. Moreover, individual cultured ELISPOT responses at the day of challenge time point correlated significantly with degree of protection against malaria sporozoite challenge, whereas ex vivo responses did not, despite a correlation between the peak ex vivo response and magnitude of memory responses 6 mo later. This cultured assay identifies long-lasting protective T cell responses and therefore offers an attractive option for assessments of vaccine immunogenicity. Hide abstract

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