Detection of cytomegalovirus in clinical specimens by virus isolation and by a monoclonal antibody against the early nuclear antigen

Long-term oral ganciclovir prophylaxis for prevention of cytomegalovirus infection and disease in cytomegalovirus high-risk renal transplant recipients

BACKGROUND

Although specific therapy is available with ganciclovir, cytomegalovirus (CMV) disease remains a major problem after renal transplantation especially in CMV seronegative recipients of organs of seropositive donors (D+R-).

METHODS

In an open-labeled prospective controlled trial we evaluated the effect of long-term oral ganciclovir prophylaxis (3 g/day for 3 months posttransplantation) in a cohort of 31 CMV-high risk (D+R-) renal transplant recipients (GC) compared with a cohort of 28 high-risk patients with targeted CMV prophylaxis (CO) receiving i.v. ganciclovir during antirejection therapy. Primary end-points were CMV infection, diagnosed by pp65 antigenemia assay or serologic method, and CMV disease. Additionally severity of CMV disease quantified by a scoring system was evaluated.

RESULTS

CMV prophylaxis significantly reduced the incidence of CMV infection (CO: 75%, GC: 45%; P<.05) and CMV disease (CO: 60%, GC: 29%; P<.05) without relevant side effects and without any clinical suspicion of ganciclovir resistance. Severity of CMV disease as quantified by a scoring system was reduced from 8.3+/-6.7 points in controls to 3.3+/-2.6 points in ganciclovir-treated patients (P<.05). Mortality did not differ significantly between the two groups (CO: n=3, GC: n=1; NS). However, there was one lethal CMV disease and a second death possibly attributable to CMV disease in the control group, whereas in ganciclovir-treated patients there was no CMV-associated fatal outcome.

CONCLUSION

Long-term oral ganciclovir prophylaxis is effective and safe in CMV high-risk renal transplant recipients.

Diagnosis of cytomegalovirus infections by shell vial assay and conventional cell culture during antiviral prophylaxis

A total of 3,552 specimens for conventional cytomegalovirus (CMV) culture and shell vial assay for CMV immediate-early antigen were obtained during a prospective randomized trial for prophylaxis of CMV disease after liver transplantation. Prophylaxis with ganciclovir for 2 weeks and then high-dose acyclovir for 2.5 months was compared with high-dose acyclovir alone for 3 months. During the first 12 weeks after transplantation, when the patients were on prophylaxis, there were significantly more clinical samples positive by the shell vial assay and negative by standard culture in comparison with the number of samples obtained from weeks 13 to 24, after prophylaxis was discontinued, that were positive by the shell vial assay and negative by standard culture. In contrast, significantly fewer samples were positive by both the shell vial assay and standard culture during the first 12 weeks compared with the number obtained 13 to 24 weeks after transplantation that were positive by both methods. Samples positive by the shell vial assay only were obtained significantly more frequently from patients with asymptomatic than symptomatic CMV infections, while samples positive by both methods were obtained significantly more often from patients with symptomatic CMV infection. It was concluded that antiviral prophylaxis with high-dose acyclovir or ganciclovir and then high-dose acyclovir and asymptomatic CMV infection are associated with a decrease in the level of CMV isolation by standard cell culture in comparison with that by the shell vial assay.

Identification of human cytomegalovirus strain with immediate-early (IE) antigen-specific monoclonal antibody is prevented by point mutation in IE gene

In an AIDS patient with a disseminated human cytomegalovirus (HCMV) infection, presence of HCMV in blood was repeatedly excluded by the shell vial culture method with the HCMV immediate-early (IE) antigen-specific monoclonal antibody (MAb) 5D2 currently employed for rapid HCMV identification, whereas it was repeatedly confirmed by all other assays (conventional virus isolation from blood, antigenemia, and DNAemia). Sequence analysis of the HCMV strain revealed a point mutation in exon 2 of the IE gene, which led to a serine-to-proline substitution at position 20 of the corresponding protein. Cloning and expression of a region of the IE gene containing the mutation showed that this was responsible for the lack of reactivity of MAb 5D2. A pool of IE antigen-reactive MAbs instead of a single MAb must be used for rapid HCMV identification to detect all viral strains.

Detection of human cytomegalovirus in urine samples by cell culture, early antigen assay and polymerase chain reaction

With the advent of effective therapy rapid, sensitive and reliable assays for diagnosis of human cytomegalovirus (HCMV) infections are required. In a total of 1,928 urine samples, detection of HCMV-immediate early antigen in a spin amplified microplate culture by a monoclonal antibody and immunoperoxidase staining (EA-assay) was compared with virus isolation in cell culture. Sensitivity of the EA assay was 85.5% and specificity was 99.5% compared with virus isolation. Overall agreement of both assays was 97.8%. In addition, in 235/1,928 urine samples amplification of HCMV-DNA was performed by means of polymerase chain reaction (PCR) using primers from the immediate early (IE1) gene region and 141/1,928 using primers from the late region (LA). The sensitivity of PCR compared with virus isolation was 67.8% for IE1 primers and 94.1% for LA primers (statistical significance: p < 0.01, Chi-square-test). Overall agreement between virus isolation and PCR was 88.5% for IE1-PCR and 84.4% for LA-PCR. Discordant results were more often found in adults with acute infection and immunocompromised patients than in infants.

Comparison of two Cobas Core enzyme immunoassays with other test systems for the detection of cytomegalovirus-specific IgG and IgM antibodies

The new Cobas Core CMV IGM and IgG enzyme immunoassays (Roche Diagnostic Systems, Basle, Switzerland) were evaluated for their ability to detect cytomegalovirus (CMV)-specific IgM and IgG antibodies. Therefore, both were compared with some other commercially available and already established serological tests used in the laboratory diagnosis of CMV infection. These included the Abbott IMx CMV IgM and IgG assays, the Abbott CMV-M EIA, the Gull CMV IgM and IgG immunofluorescence tests, the medac CMV-IgM-ELA, and the Enzygnost anti-cytomegalovirus assay (Behringwerke). A total of 572 serum samples of various categories were examined and the results showed high concordances between all methods, ranging from 84.5% to 94.9%.. In a follow-up on renal transplant patients, the times of first detection of seroconversions were compared. Since a high overall agreement between the Cobas Core CMV IgM and IgG enzyme immunoassays and the other test systems were observed, these new assays represent useful and reliable tools for clinical CMV diagnosis.

Physical and chemical methods for enhancing rapid detection of viruses and other agents

Viral replication events can be enhanced by physical, chemical, or heat treatment of cells. The centrifugation of cells can stimulate them to proliferate, reduce their generation times, and activate gene expression. Human endothelial cells can be activated to release cyclo-oxygenase metabolites after rocking for 5 min, and mechanical stress can stimulate endothelial cells to proliferate. Centrifugation of virus-infected cultures can increase cytopathic effects (CPE), enhance the number of infected cells, increase viral yields, and reduce viral detection times and may increase viral isolation rates. The rolling of virus-infected cells also has an effect similar to that of centrifugation. The continuous rolling of virus-infected cultures at < or = 2.0 rpm can enhance enterovirus, rhinovirus, reovirus, rotavirus, paramyxovirus, herpesvirus, and vaccinia virus CPE or yields or both. For some viruses, the continuous rolling of infected cell cultures at 96 rpm (1.9 x g) is superior to rolling at 2.0 rpm for viral replication or CPE production. In addition to centrifugation and rolling, the treatment of cells with chemicals or heat can also enhance viral yields or CPE. For example, the treatment of virus-infected cells with dimethyl sulfoxide can enhance viral transformation, increase plaque numbers and plaque size, increase the number of cells producing antigens, and increase viral yields. The infectivity of fowl plague virus is increased by 80-fold when 4% dimethyl sulfoxide is added to culture medium immediately after infection. The heat shocking of virus-infected cells also has been shown to have a stimulatory effect on the replication events of cytomegalovirus, Epstein-Barr virus, and human immunodeficiency virus. The effects of motion, chemicals, or heat treatments on viral replication are not well understood. These treatments apparently activate cells to make them more permissive to viral infection and viral replication. Perhaps heat shock proteins or stress proteins are a common factor for this enhancement phenomenon. The utility of these treatments alone or in combination with other methods for enhancing viral isolation and replication in a diagnostic setting needs further investigation.

A microneutralization enzyme immunoassay for antibody to human cytomegalovirus

We have developed a relatively rapid, sensitive and quantitative microneutralization assay for antibody to human cytomegalovirus (HCMV). Cell monolayers in 96-well microtiter plates inoculated with pre-incubated virus-antibody mixtures were fixed after 3 days. Infectious foci were stained with peroxidase-labeled human monoclonal antibody to a 64 kDa immediate early antigen of HCMV, and the plates were read at OD450. The 50% neutralization titer of the antibody was calculated. A study with 20 human sera and a human monoclonal antibody which neutralizes virus showed that this microneutralization enzyme immunoassay is more sensitive than, and as quantitative as, the conventional plaque reduction assay for antibody to HCMV. The neutralizing antibody titers of each sample measured by these two methods showed good correlation (n = 19, r = 0.884). Thus, this new assay is a useful and valid alternative to the conventional method for mass screening of sera and hybridoma fluids, and considerably more rapid.

New monoclonal antibodies for the detection of immediate early antigens of cytomegalovirus

Two new monoclonal antibodies, CIE-1 and CIE-2, were developed for the rapid detection of human cytomegalovirus (HCMV) infection. They were found to be reactive with immediate early protein of HCMV in the nuclei of infected fibroblasts, as early as 3 hours post-infection. By radioimmunoprecipitation, CIE-1 was found to react with a protein with an apparent molecular weight of 70,000, whereas CIE-2 precipitated 2 proteins of 70,000 and 72,000 daltons, respectively. Both monoclonal antibodies recognized three prototype strains of HCMV: AD-169, Towne, and Davis, and did not cross-react with other human herpesviruses. CIE-1 and CIE-2 were compared with four commercial anti-HCMV monoclonal antibodies (Clonab, Dupont, Sera-Lab and Syva) by testing 88 clinical isolates. Culture confirmation tests and shell vial assays showed that CIE-1 and CIE-2 were more sensitive than several of these reagents and equally sensitive to the Dupont reagent. Moreover, CIE-1 and CIE-2 produced a bright, sharp staining of the nuclei of infected cells. These monoclonal antibodies should thus be valuable in rapid diagnosis of HCMV.

Rapid diagnosis of cytomegalovirus infections by direct immunoperoxidase staining with human monoclonal antibody against an immediate-early antigen

Direct immunoperoxidase technique using a horseradish peroxidase (HRP)-conjugated Fab' fragment of human monoclonal antibody (humab C7), designated HRP-C7, was evaluated as a rapid diagnosis of cytomegalovirus (CMV) infection. A total of 138 clinical specimens consisting of 124 urine samples and 14 oral swabs were examined for CMV by the direct HRP-C7 staining in comparison with conventional virus isolation. The number of CMV-positive samples by each method was 40 (29.0%) for the former and 37 (26.8%) for the latter, respectively. By HRP-C7 staining, CMV was identifiable within 24 hr after inoculation. By conventional isolation method, an average of 10.3 days had passed before cytopathic effect characteristic of CMV appeared in the cell culture. Some false-positive and false-negative cases were discussed in relation to toxicity of urine samples, storage of the samples, and amount of CMV in the sample. The sensitivity and specificity of HRP-C7 method against conventional isolation method were 89.2% and 93.1%, respectively. Thus, HRP-C7 staining is useful for a rapid diagnosis of CMV infections.

Demonstration of antigenic variation among isolates of human cytomegalovirus using monoclonal antibodies and indirect ELISA

An indirect ELISA was developed for the detection of antigenic differences between isolates of human cytomegalovirus (HCMV) using a monoclonal antibody to an early (67 kDa) antigen. Antibody binding curves were analyzed using a microcomputer program (LISACRV) based on a nonlinear logistical model. The derivation of values for the average intrinsic association constant for seven isolates of HCMV and the prototype AD169 strain revealed significant differences between them. Because of the importance of HCMV as a pathogen, especially in immunosuppressed and AIDS patients, further investigation of the biological significance of differences between isolates of HCMV is clearly warranted.

Quantification of human cytomegalovirus viremia by using monoclonal antibodies to different viral proteins

Human cytomegalovirus (HCMV) viremia in peripheral blood polymorphonuclear leukocytes (PMNLs) from 187 immunosuppressed patients (79 heart transplant recipients and 108 patients with acquired immunodeficiency syndrome [AIDS]) was investigated. Five mouse monoclonal antibodies (MAbs), one specifically reactive to HCMV immediate-early antigen (IEA) in PMNLs, two specifically reactive to IEA in infected cell cultures, and two specifically reactive to late antigens, were used in immunofluorescence and/or immunoperoxidase test systems for (i) detection of HCMV IEA in human embryonic lung fibroblast (HELF) cell cultures inoculated with PMNL samples, (ii) direct detection of HCMV IEA in PMNL nuclei of cytospin preparations, and (iii) identification of HCMV isolates from PMNL samples in HELF cells. Quantification of viremia was achieved by counting the number of infected PMNLs per 2 x 10(5) cells examined directly on cytospin preparations as well as by counting the number of IEA-positive HELF cells inoculated with 2 x 10(5) PMNLs. A significant correlation was found between the number of infected PMNLs and the number of infected HELF cells. When the number of infected PMNLs per 2 x 10(5) cells was greater than 10, both methods (PMNL IEA and HELF IEA) gave concordant results; when it was greater than 80/2 x 10(5) cells, clinical symptoms were consistently associated with HCMV viremia. Ten patients with heart transplants and three patients with AIDS who had high or increasing levels of HCMV viremia underwent antiviral treatment with ganciclovir. Treatment was discontinued only after disappearance of IEA-positive PMNLs from blood (the last marker of infection to become negative). On the other hand, in the presence of low levels of viremia (less than 10 infected PMNLs per 2 x 10(5) cells), different methods often provided discordant results and overt clinical symptoms were never observed. IEA-negative results with PMNL samples or HELF cells in the presence of positive virus isolation could never be attributed to the inability of IEA MAbs to recognize individual HCMV strains, since all of the relevant viral isolates were recognized by IEA MAbs. In addition, all five MAbs used in the study were capable of identifying all 135 conventional HCMV isolates obtained from the study population. It was concluded that (i) maximal sensitivity in diagnosing HCMV viremia may be achieved by combining different techniques; (ii) direct detection of HCMV IEA in PMNLs, yielding results on the day of blood collection, is a very rapid and sensitive technique, and thus one can rely on it for clinical management of HCMV infections; and (iii) low levels of viremia are clinically irrelevant, whereas high levels are associated with clinical symptoms.

Early detection of cytomegalovirus in cell culture by a new monoclonal antibody, CCH2

A CMV monoclonal antibody, CCH2, produced in this laboratory was evaluated for rapid detection of CMV. Two staining procedures, immunofluorescence and an immunoenzymatic technique using biotin-streptavidin peroxidase, were compared. The CCH2 monoclonal antibody was used to demonstrate early CMV antigen in cell culture 24 h after inoculation of 598 urine samples from kidney transplanted patients by indirect immunofluorescence in comparison with virus isolation. One hundred and sixty of the specimens were stained additionally by an immunoenzymatic technique and the results were compared. CMV was isolated from 170 out of 598 specimens within 6 weeks. Early CMV antigen was demonstrated in 114 of these specimens by immunofluorescence giving a sensitivity of 67% and a specificity of 95%. In the comparison with the immunoenzymatic staining procedure the results for all three tests agreed for 81% (130/160) of the specimens. After resolving discordant results into true positives and true negatives, the sensitivity was 87, 85 and 70%, respectively for virus isolation, immunoenzymatic staining and immunofluorescence and the specificity 100, 96 and 99%. The CCH2 monoclonal antibody proved to be useful for rapid detection of CMV in urine specimens and using immunoenzymatic staining with biotin-streptavidin a sensitivity comparable to that of virus isolation was found.

Detection of cytomegalovirus by the early-antigen immunofluorescence test versus conventional tissue culture

The two methods commonly used to diagnose cytomegalovirus (CMV) infections, conventional tissue culture and detection of early CMV nuclear antigen by immunofluorescence from cell culture, were performed in parallel on 597 clinical specimens. CMV was detected by the early-antigen test in 108 samples, of which 102 (94%) were detected 1 to 3 days after inoculation. Of these 108 CMV-positive specimens, seven were negative on conventional culture. Two samples negative in the early-antigen test were positive on conventional culture. Thus, CMV was detected in 110 specimens. A cytopathic effect in conventional tissue culture occurred 9 to 42 days after inoculation. The diagnosis of CMV infection was possible by the conventional method 29.6 +/- 12.7 days and by early-antigen immunofluorescence 1.9 +/- 1.5 days after obtaining the specimen. The rapid early-antigen test was slightly more sensitive than culture, and fewer samples were lost due to bacterial or fungal infections during incubation. Detection of CMV by conventional culture usually requires several weeks and provides a diagnosis only retrospectively. The main advantage of the early-antigen test is that a virologically proven diagnosis of CMV infection is available at an early stage.

Rapid diagnosis of cytomegalovirus by indirect immunofluorescence assay with monoclonal antibody F6b in a commercially available kit

Anti-human cytomegalovirus (CMV) monoclonal antibody (MAb) F6b produced by clone 95/12 was used for the rapid diagnosis (16 to 24 h) of CMV isolates in 308 clinical specimens and compared with classic isolation. MAb F6b gave 100% correlation with isolation. When this MAb was used for direct diagnosis with 212 urine and bronchoalveolar specimens, detection of CMV varied from 50 to 75% compared with viral isolation.

Detection of cytomegalovirus DNA in short term cultures

Detection of human cytomegalovirus (CMV) by in situ DNA hybridisation six days after incubation of human diploid fibroblasts (ISDH-6) was evaluated prospectively in 205 urine samples, obtained from 57 kidney transplant and 17 bone marrow transplant recipients. The results were compared to those of conventional virus isolation (CVI) and the detection of CMV early antigens after one day of cultivation (EA-1). Of 42 samples positive for CMV by at least one of these methods, 40 (95%) were detected with ISDH-6. Thirty-five (83%) and 34 (81%) positive samples were found with CVI and EA-1, respectively. These data indicate that ISDH-6 is a sensitive method for detection of CMV. It can be used as a rapid and sensitive alternative to CVI in combination with EA-1.

Correlation of urine pH with the detection of cytomegalovirus by the shell vial technique

The influence of the pH of urine on the detection of cytomegalovirus (CMV) by the shell vial assay was evaluated. The pH values of 295 urine specimens ranged from 4.7 to 8.5 (mean 6.3) and were not significantly different in culture-positive versus culture-negative samples. None of the urine specimens appeared to be toxic for the cells used in the shell vial assay. We recommend inoculation of urine specimens into shell vials without adjustment of pH.

Potential of in situ hybridization for early diagnosis of productive cytomegalovirus infection

In situ hybridization with a probe specific for immediate-early genes was used for detection of cytomegalovirus (CMV) transcripts in peripheral blood mononuclear cells, and the potential use of this technique as a diagnostic tool was assessed. The results were compared with those obtained with conventional assay systems. In 8 of 18 continually observed patients who developed a productive CMV infection, a high number of hybridization-positive cells were observed 1 to 2 weeks before the conventional tests yielded positive results. Thus, quantitative evaluation of hybridization results provided an early and specific marker for beginning CMV infection or reactivation. In three cases, quantitative in situ hybridization assays provided the only laboratory marker indicating CMV infection or reactivation. It was also found that a probe specific for immediate-early genes was superior to a probe specific for late genes for diagnosis of productive infections.