The present invention relates to the use of the major OprI lipoprotein of Pseudomonas aeruginosa to elicit a Type-1 immune response towards a heterologous antigen. The invention relates specifically to the use of OprI-antigen fusion proteins to elicit the Type-1 response. More particularly, the present invention is directed to pharmaceutical formulations comprising OprI and/or OprI fusion proteins, optionally together with a suitable excipient, to stimulate the Th1 dependent, cellular immune response.