Knockout of the M33 Chemokine Receptor Gene in Murine Cytomegalovirus is Associated with Decreased Levels of Cardiac Allograft Vasculopathy in a Murine Aortic Transplant Model

Objectives: Cytomegalovirus (CMV) infection after heart transplantation is considered as risk factor for the development of cardiac allograft vasculopathy (CAV), a serious long-term complication after heart transplantation. In previous work we could show that murine CMV infection (MCMV) leads to increased levels of CAV. MCMV genome encodes the G protein-coupled receptor (GPCR) M33 which is associated with virus latency and replication in the host. Therefore we analyzed if M33 knockout could prevent CMV induced CAV development.

Methods: A M33 deleted murine CMV (delM33) was created via homologous recombination. Following abdominal aortic transplantation in MHC-I mismatched mice, animals were infected with 1x10⁶ pfu delM33 or wildtype (wt). 30 days after infection grafts were recovered and histologically analyzed for neointima formation. A second group of grafts was recovered after 14 days for qPCR analysis of cytokine expression.

Results: In vivo imaging using luciferase ensured successful infection of wt and delM33 virus within treated mice. Measurement of aortic lumen obliteration caused by neointima development revealed that infection with wildtype MCMV significantly increased vessel occlusion compared with uninfected controls [41.71% ± 9.06% vs. 24.33% ± 11.70%; p < 0.05, n = 6]. Infection with M33 deleted MCMV also resulted in elevated neointima proliferation compared with controls, but this was significantly reduced as compared with wildtype infected grafts (32.19% ± 7.26% vs. 41.71% ± 9.06%; p < 0.05, n = 6).

Conclusion: Deletion of the M33 receptor gene reduces MCMV promoted development of CAV after abdominal aortic transplantation in mice. Further investigations are under progress regarding the human (HCMV) US28 homologue of M33 in a genetically modified mouse model.