DNA vaccines expressing glycoprotein complex II antigens gM and gN elicited neutralizing antibodies against multiple human cytomegalovirus (HCMV) isolates

Human cytomegalovirus (HCMV) glycoprotein complex II (gcII) consists of two glycoproteins, gM and gN. Although gcII specific IgG purified from HCMV positive patient sera can neutralize HCMV, there has been no report describing the generation of virus-neutralizing antibodies by immunization with individual recombinant gM or gN antigens. In the current study, gM and gN antigens were expressed by the mammalian expression vector pJW4303 and used as DNA vaccines to determine the immunogenicity of these proteins. Sera from mice or rabbits immunized with individual or combinations of gM and gN DNA vaccines contained gM and gN specific antibodies as confirmed by ELISA and Western blot analyses. The combined gM and gN antigens induced the strongest antibody responses that recognized both gM and gcII complex while gM DNA vaccine alone could only elicit antibody specific for gM antigen. When given alone, the gN DNA vaccine did not induce detectable gcII specific antibody even though in vitro gN expression was confirmed by the formation of gM/gN complex in FSK cells using a gN-specific monoclonal antibody 14-16A. The neutralizing antibody titer of anti-gM/gN sera (1:128) was higher than that of anti-gM sera (1:32) against the autologous virus, HCMV AD169. Heterologous HCMV strains including Towne and Davis could also be neutralized by the anti-gM/gN antisera. Our data supported the rationale for the use of the HCMV gM/gN protein complex as protective antigens for subunit based HCMV vaccine development. DNA vaccination is an effective approach to express the gM/gN antigen complex in vivo without the need to express and purify these highly insoluble and structurally complicated antigens.