Background: Pre- and perinatal human cytomegalovirus (HCMV) infection remains one of the major causes of mental defects and sensineural hearing loss in children. In addition, it is a prominent infectious complication in immunosuppressed individuals such as AIDS patients or transplant recipients. Therefore, the development of an HCMV vaccine has been given top priority by health care institutions.
Study design: Defective subviral particles of HCMV, termed Dense Bodies (DB) contain the dominant target antigens for humoral and cellular immune responses elicited during natural infection. These enveloped particles are released from infected culture cells and can be purified by gradient centrifugation. DB were analyzed for their ability to induce virus neutralizing antibodies and cytotoxic T cells (CTL) after immunization of mice.
Results: Purified DB entered human and murine hematopoetic and fibroblast cells very efficiently, thereby delivering their protein content into the cytoplasm. The cellular uptake was abrogated after sonication and freeze-thawing of the particles, indicating that the integrity of the viral envelope was important for this process. DB immunization of HLA-A2.K(b) transgenic mice induced significant CTL responses in the absence of viral gene expression and without the use of adjuvant. Induction of cytolytic cells by DB was sensitive to sonication and freeze-thawing as determined by CD3epsilon -redirected lysis analysis. In accordance with that, induction of virus neutralizing antibodies was much more effective when untreated DB were used as immunogen.
Conclusions: DB provide a promising basis for the development of a subunit vaccine against HCMV infection. The ability to genetically engineer HCMV provides a rationale to optimize such a vaccine and to develop concepts for future multicomponent vaccines.