Immune Responses and Protective Efficacy of a Multi-subunit Tuberculosis Vaccine Delivered as Naked DNA or Recombinant Protein.

Yasir A.W. Skeiky, Mark R. Alderson, Lise Brandt, Jeffrey A. Guderian1, Pamela J. Ovendale1, Antonio Campos-Neto, Yves Lobet, Wilfried Dalemans, Ian M. Orme, and Steven G. Reed

Corixa Corporation and The Infectious Disease Research Institute, 1124 Columbia St, Suite 200, Seattle, WA98104; Colorado State University, Fort Collins, Co 80523; and GlaxoSmithKline Biologicals, Rixensart, Belgium.

e-mail: yskeiky@aol.com

A subset of Mycobacterium tuberculosis (Mtb) antigens initially identified in the context of host response to infection were prioritized for the development of a multi-valent subunit vaccine against tuberculosis (TB). Our lead candidate, Mtb72F, comprising “three” components and coding for a 72kDa poly-protein was generated by linking in tandem the open reading frames of Mtb32C, Mtb39 and Mtb32N (with N- and C- referring to the amino and carboxyl portions of Mtb32 respectively). The immune responses and protective efficacy of Mtb72F were evaluated in C57BL/6 mice delivered either as naked DNA or as recombinant protein formulated in two proprietary (GlaxoSmithKline) adjuvant systems, AS01B and AS02A. The outcome of the immune response was found to be influenced by the way in which Mtb72F was delivered. Immunization of C57BL/6 mice with Mtb72f delivered as naked DNA resulted in the elicitation of IFN-γ response directed against the first two components of the poly-protein and a strong CD8⁺ response directed exclusively against Mtb32C. In contrast, immunization of mice with rMtb72F formulated in the adjuvant AS02A resulted in the elicitation of a good IFN- γ response directed primarily against the Mtb39 portion, antibody responses (of both igG1 and IgG2a specificity) against all three components of the molecule but a weak to undetectable CD8 response. However, immunization of mice with a formulation of rMtb72F in AS01B adjuvant generated a comprehensive and robust immune response resulting in the elicitation of strong IFN- γ and antibody responses comprising all three components of the vaccine and as well, a strong CD8⁺ CTL response. All three forms of Mtb72F immunizations resulted in the protection of C57BL/6 mice against aerosol challenge with a virulent strain of Mtb. Most importantly, immunization of guinea pigs with Mtb72F delivered either as DNA or as a recombinant antigen based vaccine prolonged the survival of the animals against tuberculosis challenge to an extent comparable to those seen with BCG vaccination. While our primary aim is to pursue the development of an adjuvant formulated recombinant antigen based vaccine for a Phase I clinical trial, we have also explored prime-boost vaccination strategies.