A Spread-Deficient Cytomegalovirus for Assessment of First-Target Cells in Vaccination

Abstract

Human cytomegalovirus (HCMV) is a human pathogen that causes severe disease primarily in the immunocompromised or immunologically immature individual. To date, no vaccine is available. We describe use of a spread-deficient murine CMV (MCMV) as a novel approach for betaherpesvirus vaccination. To generate a spread-deficient MCMV, the conserved, essential gene M94 was deleted. Immunization with MCMV-⌬M94 is apathogenic and protective against wild-type challenge even in highly susceptible IFN␣␤R ؊/؊ mice. MCMV-⌬M94 was able to induce a robust CD4؉ and CD8 ؉ T-cell response as well as a neutralizing antibody response comparable to that induced by wild-type infection. Endothelial cells were identified as activators of CD8 ؉ T cells in vivo. Thus, the vaccination with a spread-deficient betaherpesvirus is a safe and protective strategy and allows the linkage between cell tropism and immunogenicity. Furthermore, genomes of MCMV-⌬M94 were present in lungs 12 months after infection, revealing first-target cells as sites of genome maintenance.

Recombinant mouse cytomegalovirus expressing a ligand for the NKG2D receptor is attenuated and has improved vaccine properties

“…The vaccination potential of CMV mutants lacking nonessential viral genes has already been proven (33,34). Also, spread-deficient MCMV lacking the essential gene M94 induced a virus-specific immune response and proved to be safe in an immunodeficient host (31). The approach of the present study was to generate an experimental vaccine expressing NKG2D ligand, which is therefore attenuated due to strong immune control and, at the same time, resistant to viral immunoevasion of this signaling pathway.…”

“…Still, a live, attenuated vaccine approach has several characteristics that render it attractive. Unlike subunit vaccines, which induce cellular or humoral immune response to selected antigens only, live vaccines induce a much broader immunity that may mimic protection acquired following natural infection (31,33,(66)(67)(68)(69). Cellular immunity against CMV follows unique kinetics characterized by maintenance or even expansion of the virus-specific CD8 + T cell response over time (70,71).…”

“…A number of subunit vaccine strategies and live, attenuated CMV vaccines have been developed (27)(28)(29)(30)(31). Recently, a phase II clinical trial was described that suggested a protective capacity against maternal infection by use of recombinant monovalent gB HCMV vaccine (32).…”

“…Their use, however, carries the risk of CMV disease caused by the vaccine strain or reactivation in the immunocompromised state, unless the vaccine virus is efficiently controlled by residual immunity. One approach to generating such an immunogenic, yet safe live vaccine is deletion of viral genes that subvert the host immune response (33,34) or essential genes resulting in spread-deficient virus (31). The other approach is the insertion of a ligand recognized by the activating receptor on immune cells into the CMV genome.…”

Cytomegalovirus pp65 limits dissemination but is dispensable for persistence

“…Since primary infection with RhCMV 68-1 (the parental strain of ΔUS2-11gag) does not result in robust viremia (see below), direct measurements of viral loads were unlikely to be informative. Instead, we used the development of anti-CMV antibodies as a surrogate for CMV antigen load, because it was shown previously in the murine model that reduced viral spread correlates with reduced antibody responses but does not affect T cell responses (47). However, when lysates Genome copy numbers in tissue samples are given per 10 7 cell equivalents, whereas genome copies in urine and plasma are shown per ml.…”