Objectives of this trial are to:

Evaluate the kinetics and magnitude of the CMV-specific immune response post-Towne challenge (3000 pfu) in healthy CMV-seronegative volunteers who receive VCL CT02 administered (1 mg weekly x 3) 3 months previously compared to randomized controls who do not receive VCL CT02 as measured by:

1. antibody titers for gB;
2. T-cell IFN-g ELISPOT;
3. T-cell proliferation assays for IE1, pp65, and/or gB; and
4. cytokine and phenotypic flow cytometry responses to pp65, IE1, and/or gB.

Evaluate the safety safety of Towne challenge in healthy CMV-seronegative adult subjects who have previously been immunized with a trivalent pDNA CMV vaccine (VCL-CT02) administered intramuscularly.

Our hypothesis is that the immune response to Towne vaccine 3000 pfu challenge after VLC-CT02 priming will be greater than that after Towne vaccination alone.

This is a Phase 1, single-center, randomized, open-label trial of the live, attenuated Towne CMV vaccine administered as a "challenge" to healthy, CMV-seronegative, adult subjects who previously receive the CMV immunotherapeutic trivalent pDNA-based vaccine, VCL-CT02, given by intramuscular route at Days 1, 7 and 14 or who receive no VCL-CT02.

Up to 12 healthy, CMV-seronegative subjects will be enrolled. If a subject consents and meets all eligibility criteria, the subject will be randomized to the VCL CT02 (N=6)or control (N=6) groups. VCL CT02-assigned subjects will receive VCL CT02 (1 mg weekly x 3) and then on Day 77 will received Towne vacine (3000 pfu subcutaneously). Control-assigned subjects will receive Towne alone. Safety will be monitored and both antibody to CMV gB and T-cell responses to CMV antigens will be measured at specified intervals for 252 days post Towne challenge.

Inclusion Criteria:

• 18 to 45 years of age
• Normal lab values at study entry
• Good general health
• Negative CMV IgG antibody test

Exclusion Criteria:

• CMV seropositive
• Recent vaccination(s)
• Immunodeficiency
• Vaccination with investigational CMV vaccine(s)
• Pregnant or breast-feeding