Reactivation of Murine Cytomegalovirus Is Associated with Increased Gvhd Severity in Allogeneic Hematopoietic Cell Transplant Recipients

Background:Graft versus host disease (GVHD) and infectious complications are major limiting factors to the success of allogeneic (allo) hematopoietic cell transplantation (HCT). CMV reactivation and disease lead to morbidity and mortality, and potentially promote GVHD. Primary infection commonly leads to latency, and viral replication can be reactivated in the immunocompromised state. Using a low mortality/low GVHD severity murine HCT model, we assessed for a contributory role of MCMV in GVHD development.

Methods:BALB/c mice were infected with either Smith strain murine CMV (MCMV) (3X10⁴ PFU) or mock and monitored for 24 weeks to establish latency. CMV seropositivity was confirmed and HCT was performed using sublethal TBI (750cGy single dose) followed by i.v. administration of 7x10⁶ bone marrow cells plus 3X10⁶ splenocytes from either syngeneic (syn) BALB/c or allo B10.D2 donors. Recipients were observed for survival and clinical GVHD. At day +100, lung, liver, gut, spleen were collected in surviving animals and analyzed for pathology and cytokine expression; BALF cellularity was assessed. Engraftment of allo donor cells was confirmed by PCR for D2Mit265 gene product size of 139bp (BALB/c) versus 103bp (B10.D2) in recipient’s splenic DNA, all allo recipients being at least 60% donor chimera.

Results: Mortality (26.3 vs. 8.3%) and GVHD severity in allo MCMV preinfected recipients was higher than in allo mock controls. All syn recipients survived without evidence of clinical disease. To assess the contribution of MCMV latency and reactivation to GVHD pathology, allo recipients were stratified by using MCMV IE1 gene expression at time of analysis as an indicator for active replication. Pathologic changes of lung and liver GVHD in IE-1+ recipients were significantly increased compared to mock controls (p<0.01), and were only slightly increased in IE-1- . None of the changes were characteristic of active viral disease. No significant gut injury was seen in allo recipients and no differences in pathology were seen among syn groups. In IE1+ allo recipients, total cell and total CD4+ (but not CD8+) T cell count in BALF were increased (p<0.05) when compared with mock controls, as were protein expression of lung IFN-gamma and liver TNF (p<0.05).

Conclusion: MCMV IE-1 expression indicating replicative CMV reactivation is associated with increased GVHD severity and strengthens the concept of CMV being not only a pathogen of potentially lethal viral disease but also as a driving factor in GVHD development.