Since
neutralizing antibodies (NAb) targeting the human cytomegalovirus (HCMV) pentamer complex (PC) potently block HCMV host cell entry, anti-PC NAb induction is thought to be important for a
vaccine formulation to prevent HCMV
infection. By developing a
vaccine strategy based on soluble PC
protein and using a previously generated Modified
Vaccinia Ankara vector co-expressing all five PC subunits (MVA-PC), we compared HCMV NAb induction by homologous immunization using prime-boost
vaccine regimen employing only PC
protein or MVA-PC and heterologous immunization using prime-boost combinations of PC
protein and MVA-PC. Utilizing a recently isolated anti-PC NAb, we produced highly pure soluble PC
protein that displayed conformational and linear neutralizing
epitopes, interfered with HCMV entry, and was recognized by
antibodies induced by HCMV during natural
infection. Mice vaccinated by different immunization routes with the purified PC
protein in combination with a clinically approved adjuvant formulation elicited high-titer and durable HCMV NAb. While MVA-PC and soluble PC
protein either alone or in combination elicited robust HCMV NAb, significantly different potencies of these
vaccine approaches were observed in dependence on immunization schedule. Using only two immunizations, vaccination with MVA-PC alone or prime-boost combinations of MVA-PC and PC
protein was significantly more effective in stimulating HCMV NAb than immunization with PC
protein alone. In contrast, with three immunizations, NAb induced by soluble PC
protein either alone or combined with two boosts of MVA-PC increased to levels that exceeded NAb titer stimulated by MVA-PC alone. These results provide insights into the potency of soluble
protein and MVA to elicit NAb by the HCMV PC via homologous and heterologous prime-boost immunization, which may contribute to develop clinically deployable
vaccine strategies to prevent HCMV
infection.