Since the mucosa is often the primary sight of exposure, longterm, localized immune responses against Ebola virus are desirable for providing optimal protection against infection. In this context, T cell mediated immune responses were assessed by ELISPOT from various tissue compartments specific to the route of immunization 45 days after vaccination. The number of activated IFN-c secreting mononuclear cells harvested from splenocytes was significantly reduced by 38 and 59% in mice vaccinated nasally or orally when compared to those immunized by intramuscular injection (p#0.05, Figure 2A ). In contrast, samples obtained from the spleen of animals with pre-existing immunity that were immunized by the I.N. route contained the highest number of activated IFN-c secreting cells (8156190 spot-forming cells (SFC)/ million mononuclear cells (MNCs), Figure 2C ) although this was approximately 30% lower than that seen in naive animals (1,3406146 SFC/million MNCs, Figure 2A ). Pre-existing immunity also significantly reduced the number of these cells produced by animals immunized by the I.M. (210668 SFC/million MNCs) and P.O. routes (71612 SFC/million MNCs) with respect to those seen in naïve animals (2,145612 (I.M.) and 8856168 (P.O.)), p#0.05, Figure 2A) . A very limited number of activated IFN-c secreting mononuclear cells were detected in splenocytes of naïve animals immunized with the AdlacZ vector (50620 SFC/million MNCs, Figure 2A ) and those with pre-existing immunity to the same virus (1261, AdlacZ, Figure 2C ). Significant levels of INF-c positive cells were detected in bronchioalveolar lavage fluid (BAL) after intranasal immunization (146614 SFC/million MNCs, p#0.05, Figure 2B ). This was not significantly compromised by pre-existing immunity to adenovirus (120616 SFC/million MNCs, p#0.06, Figure 2D) . A limited number of INF-c secreting cells were detected in BAL from naïve animals immunized by the I.M. or P.O. routes (462 and 1165 SFC/million MNCs respectively, Figure 2B ) and were similar to that seen in samples obtained from animals given the AdlacZ vector (1261, negative control). Pre-existing immunity to adenovirus reduced these cell populations further to values that were not statistically significant (161 (I.M.), 562 (P.O.) and 261 (AdlacZ) SFC/million MNCs (p = 0.08, Figure 2D) ). INF-c positive cells were found in mesenteric lymph nodes (MLN) and Peyer's Patches (PP) (146611 and 2965 SFC/million MNCs, respectively) only after oral vaccination with Ad-ZGP ( Figure 2B ). Pre-existing immunity, however, reduced production of these cells to 18612 SFC/million MNCs (MLN) and 1662 SFC/million MNCs (PP) ( Figure 2D ).