Increased prevalence of CMV gB3 in marrow of patients with aplastic anemia

Various infectious agents have been implicated in causing aplastic anemia (AA), either by direct lytic infection or by inducing a pathophysiologic host immune response.1 But little attention has been given to cytomegalovirus (CMV), even though the myelosuppressive potential of this virus, in vivo as well as in vitro, is well established.2-6 Undoubtedly, the relatively high prevalence of this virus has made it an unlikely agent for AA, which is a very rare disease. But CMV has a broad spectrum of pathogenicities and sites of infection. Mechanisms responsible for this heterogeneity are not defined but are hypothesized to include both host and viral differences.

Our past studies indicate that genetically distinct strains of CMV, identified by variations in the gene encoding envelope glycoprotein B (gB), occur at variable frequencies and can be associated with different clinical outcomes.5-8 CMV gB types 1 and 2 were shown to be more frequently associated with survival following marrow transplantation than were types 3 and 4.7 In a second study, types 3 and 4 were specifically associated with death due to persistent neutropenia.5 

Given the strong statistical association between CMV gB3/4 with posttransplantation myelosuppression, we hypothesized that these strains may also contribute to the pathogenesis of AA and, if so, that the virus would be detected more frequently in AA marrow than in marrow from patients with other hematologic diseases and, further, that gB types 3 and/or 4 would be overrepresented.

To test this hypothesis, we measured the incidence of CMV-infected marrow and the distribution of gB types in AA patients compared to patients with other hematologic diseases. Experimental samples consisted of fresh-frozen marrow biopsies obtained from 100 CMV-seropositive AA patients before transplantation. Controls consisted of marrow aspirates from 151 CMV-seropositive non-AA patients harvested at day 28 after allogeneic marrow transplantation. This control population was chosen because it has an increased risk of CMV exposure, reactivation, and disease, thereby raising the background of CMV in the control samples and making our estimate of differences between AA patients and controls more conservative. Patient groups were similar for gender and ethnic background but differed in regard to age, with the AA patient group being much younger. For this reason, the logistic regression analysis was adjusted for age. CMV genotyping was based on sequence variations in the gene encoding gB as detected by restriction analysis of polymerase chain reaction (PCR)–amplified gB DNA.5Table 1 shows that the frequency distribution of CMV gB types differs between AA and control patients, with the control group being comparable to previously reported results. Results shown in Table 2 indicate that the odds of possessing CMV in the marrow, particularly gB type 3, are significantly increased among AA patients. This association, together with previous reports, makes it reasonable to hypothesize a role for CMV in the pathogenesis of aplastic anemia in some patients.