IL-12 GENE-THERAPY PROTECTS MICE IN LETHAL KLEBSIELLA PNEUMONIA

IL-12 is a proinflammatory cytokine that has recently been shown to ha ve beneficial effects in the setting of acquired host immunity, To det ermine the role of IL-12 in innate immunity against Gram-negative bact erial organisms, CBA/J mice were challenged with 10(2) CFU of Klebsiel la pneomoniae intratracheally (i.t.), resulting in the time-dependent expression of IL-12 mRNA (p35 and p40) and protein within the lung. Pa ssive immunization of animals with anti-IL-12 serum i.p. at the time o f K. pneomoniae inoculation resulted in a 12-fold increase in K. pneum oniae CFU in lung homogenates at 48 h, as compared with animals receiv ing control serum, In addition, treatment of Klebsiella-infected mice with anti-IL-12 Abs significantly decreased both short and long term s urvival, To assess the effect of compartmentalized IL-12 overexpressio n on outcome in Klebsiella pneumonia, animals were treated i.t. with 5 x10(8) PFU of a nonreplicating adenoviral vector containing a human cy tomegalovirus promoter and cDNAs coding for the p35 and p40 subunits o f IL-12 inserted into the E1 and E3 domains (Ad5mlL-12), respectively. In vivo transfection with Ad5mlL-12 resulted in 45% long term surviva l in Klebsiella pneumonia, whereas no animals with Klebsiella pneumoni a receiving control adenovirus survived. Moreover, treatment with anti -IFN-gamma Abs or soluble TNF receptor:lg construct partially and comp letely attenuated survival benefits observed in animals receiving Ad5m lL-12, respectively, In conclusion, endogenous IL-12 is a critical com ponent of antibacterial host defense, and the compartmentalized overex pression of IL-12 using recombinant adenoviral gene therapy represents a safe and effective approach to deliver IL-12 to the lung in the set ting of murine Klebsiella pneumonia.