Human fibroblasts transfected with cytomegalovirus immediate-early genes show increased MHC class I expression and are targets for natural killer cell-mediated cytotoxicity

Deletion mutant of human cytomegalovirus lacking US2-US6 and US11 maintains MHC class I expression and antigen presentation by infected dendritic cells

A HCMV mutant of endothelial- and DC-tropic strain TB40/E lacking the described MHC downregulating genes US2-6 and US11 (RVTB40/E(4)ΔUS11) was generated. We analyzed the susceptibility of DC to RVTB40/E(4)ΔUS11 and subsequently studied antigen presentation and T-cell stimulation. Wildtype TB40/E- and RVTB40/E(4)ΔUS11 showed no significant difference in the efficiency of infection of DC. Whereas infection with TB40/E induced downregulation of MHC I, no significant MHC I downregulation was observed on RVTB40/E(4)ΔUS11-infected DC, indicating that the US2-6, US11 region encodes for the major genes relevant for MHC I downregulation. However, both viruses induced downregulation of MHC II, as well as CD40, CD80, CD86 and CD83 to the same levels. Stimulation of IFN-γ production by HCMV-specific CD8+ T-cells by infected autologous DC correlated with the modulation of MHC expression. While TB40/E-infected DC did not efficiently stimulate IFN-γ production, RVTB40/E(4)ΔUS11-infected DC efficiently stimulated CD8+ T-cells to produce IFN-γ.

Cytomegalovirus seropositivity is significantly associated with mycosis fungoides and Sézary syndrome

Although mycosis fungoides (MF) may arise through persistent antigen stimulation, cytomegalovirus (CMV) is not a known risk factor. To study the incidence of seropositivity to viral infections, we compared MF and Sézary Syndrome (SS) patients to healthy bone marrow donors and other historical control groups. Baseline screening serologies at baseline were performed on 116 biopsy-proven MF/SS patients at MD Anderson Cancer Center from 1992 to 2001 and on healthy bone marrow donors evaluated by the transplant service from 1988 to 2001. Antibodies to HTLV-I/II, HIV-1, EBV, and CMV were measured using standard enzyme-linked immunosorbent (ELISA) and membrane enzyme immunoassay (MEIA) assays. One hundred thirteen (97.4%) of all MF/SS patients had positive CMV IgG serologies at initial presentation. Early- and late-stage patients' seropositivity rates were significantly higher than healthy bone marrow donor controls (chi(2).05(df=1) = 71.79). By stage, 98.1% of early-stage MF patients (IA, IB, IIA; 52/53) and 96.8% of late-stage MF and SS patients (IIB-IVB; 61/63) were seropositive compared with healthy bone marrow donors whose seropositivity rate was 57.3% (757/1322). Because the rate of CMV seropositivity increases with age, a subset of cutaneous T-cell lymphoma (CTCL) patients 55 years or younger were compared to age-matched healthy donor controls; their seropositivity rate for CMV was also significantly higher (chi(2).05 05(df=1) = 20.4). EBV titers were positive by serology in 13 patients who were examined prospectively. CMV seropositivity is highly associated with MF and SS, even in the earliest stages of the disease, and is significantly higher than that of healthy and immunocompromised controls.

NK cell activity during human cytomegalovirus infection is dominated by US2-11-mediated HLA class I down-regulation

A highly attractive approach to investigate the influence and hierarchical organization of viral proteins on cellular immune responses is to employ mutant viruses carrying deletions of various virus-encoded, immune-modulating genes. Here, we introduce a novel set of deletion mutants of the human CMV (HCMV) lacking the UL40 region either alone or on the background of a deletion mutant devoid of the entire US2-11 region. Deletion of UL40 had no significant effect on lysis of infected cells by NK cells, indicating that the expected enhancement of HLA-E expression by specific peptides derived from HCMV-encoded gpUL40 leader sequences was insufficient to confer target cell protection. Moreover, the kinetics of MHC class I down-regulation by US2-11 genes observed at early and late phases postinfection with wild-type virus correlated with increased susceptibility to NK lysis. Thus, the influence of HCMV genes on NK reactivity follows a hierarchy dominated by the US2-11 region, which encodes all viral genes capable of down-modulating expression of classical and non-classical MHC class I molecules. The insights gained from studies of such virus mutants may impact on future therapeutic strategies and vaccine development and incorporate NK cells in the line of defense mechanisms against HCMV infection.