Effect of foscarnet induction treatment on quantitation of human cytomegalovirus (HCMV) DNA in peripheral blood polymorphonuclear leukocytes and aqueous humor of AIDS patients with HCMV retinitis. The Italian Foscarnet Study Group

Quantitative PCR for human herpesviruses 6 and 7

A quantitative PCR assay for the detection of human herpesvirus 6 (HHV-6) (variants A and B) and HHV-7 DNAs in clinical samples was developed. The assay uses a nonhomologous internal standard (IS) for each virus that is coamplified with the wild-type target sequence in the same vial and with the same pair of primers. This method allows for a correction of the variability of efficiency of the PCR technique. A standard curve is constructed for each experiment by coamplification of known quantities of the cloned HHV-6 or HHV-7 target templates with the respective IS. Absolute quantitation of the test samples is then achieved by determining the viral target/IS ratio of the hybridization signals of the amplification products and plotting this value against the standard curve. Using this assay, we quantitated the amount of HHV-6 or HHV-7 DNA in infected cell cultures and demonstrated an inhibitory effect of phosphonoformic acid on the replication of HHV-6 and HHV-7 in vitro. As the first clinical application of this procedure, we performed preliminary measurements of the loads of HHV-6 and HHV-7 in lymph nodes from patients with Hodgkin's disease and AIDS. Application of this quantitative PCR method should be helpful for elucidating the pathogenic roles of HHV-6 and HHV-7.

Intracellular expression of antibody fragments directed against HIV reverse transcriptase prevents HIV infection in vitro

We have tested a novel strategy of intracellular immunization to block human immunodeficiency virus (HIV) infection. The expression of a specific antibody within a cell was achieved by transduction of genes that encode for immunoglobulin chains with specificity to viral reverse transcriptase. We demonstrated that inhibition of this enzyme makes cells resistant to HIV infection by blocking an early stage of viral replication. If high efficiency transduction with a stable vector into lymphohaematopoietic stem cells or mature lymphocytes can be achieved, gene transfer-mediated intracellular immunization might be a feasible treatment strategy in AIDS.

Quantitation of human cytomegalovirus glycoprotein H gene in cells using competitive PCR and a rapid fluorescence-based detection system

A technique is described for quantitation of the human cytomegalovirus (HCMV) glycoprotein H (gH) gene in cells using a quantitative-competitive polymerase chain reaction (QC-PCR). Two recombinant DNA molecules, differing in size due to a 92-bp deletion within the HCMV gH sequence, were used in co-amplification studies to construct a standard curve from which the copy number of the gH gene present in clinical samples could be interpolated. The use of primers labeled with a fluorescent dye allowed direct detection of the amplified products by measuring the amount of fluorescence emitted by each specific PCR fragment with an automated DNA sequencer coupled to a software program. This system was validated subsequently using bronchoalveolar lavage cells obtained from immunocompromised patients and found to be highly sensitive and reproducible over a range of 5-50,000 HCMV gH copies. This rapid procedure could easily be applied to study the pathogenesis of HCMV infection, identify the patients at high risk of developing HCMV disease, and monitor the effects of antiviral therapy at the molecular level.

Comparative quantitation of human cytomegalovirus DNA in blood leukocytes and plasma of transplant and AIDS patients

A new method for the quantitation of human cytomegalovirus (HCMV) DNA was used to determine the levels of viral DNA in parallel in 120 blood leukocyte (leukoDNAemia) and plasma (plasmaDNAemia) samples from 8 heart or heart-lung transplant patients and 17 AIDS patients with disseminated HCMV infection. PlasmaDNAemia was consistently associated with leukoDNAemia in both groups of patients. However, at least in the transplant patients, plasmaDNAemia was not necessarily associated with clinical symptoms, appearing later and disappearing earlier than leukoDNAemia during the course of infection. Quantitative mean levels of leukoDNAemia were mostly higher than those of plasmaDNAemia in both transplant and AIDS patients. However, in the absence of antiviral treatment, plasmaDNAemia levels were significantly higher in AIDS patients than in transplant recipients, whereas leukoDNAemia levels were not significantly different between the two groups of patients. A significant correlation was found between leukoDNAemia and plasmaDNAemia in AIDS patients, as well as in transplant recipients, although to a lesser degree. However, from a diagnostic standpoint, quantitative determination of plasmaDNAemia appears to represent a much less sensitive parameter than that of leukoDNAemia (or antigenemia) for monitoring HCMV infections and antiviral treatment.

Foscarnet. A reappraisal of its antiviral activity, pharmacokinetic properties and therapeutic use in immunocompromised patients with viral infections

The DNA polymerase of human herpes viruses, including cytomegalovirus (CMV), and the reverse transcriptase of human immunodeficiency virus (HIV) are selectively inhibited in vitro by the pyrophosphate analogue foscarnet. Inhibition is reversible on withdrawal of foscarnet and additive or synergistic effects have been demonstrated in vitro with other antiviral drugs, including ganciclovir and zidovudine. Foscarnet appears to have negligible effects on host enzymes and cells. Complete or partial clinical resolution of ocular symptoms is obtained in more than 89% of patients with acquired immunodeficiency syndrome (AIDS) and CMV retinitis during foscarnet induction therapy, but relapse occurs soon after ceasing treatment. Maintenance treatment given daily can extend the period of remission considerably. Foscarnet and ganciclovir monotherapy had similar efficacy in the treatment of CMV retinitis in patients with AIDS in several studies, and have been used concomitantly in immunocompromised patients with recalcitrant CMV infections. In 1 trial, patients receiving foscarnet survived for significantly longer than those receiving ganciclovir. Foscarnet has been used successfully in the treatment of limited numbers of immunocompromised patients with CMV-associated gastrointestinal (improvement in over 67% of patients) and other infections. Aciclovir-resistant herpes simplex infections in immunocompromised patients have also been treated successfully with foscarnet. Almost 90% of a foscarnet dose is excreted in the urine. Reversible nephrotoxicity is common during foscarnet therapy, but may be reduced by dosage adjustment and adequate hydration. Anaemia, nausea and vomiting, disturbances in electrolyte levels and genital ulceration have also been associated with administration of the drug. The different tolerability profiles of foscarnet and zidovudine facilitate the use of these agents in combination in patients with AIDS and CMV infection; whereas ganciclovir, like zidovudine, is associated with dose-limiting haematological toxicity. The apparent survival benefits seen in these patients when receiving foscarnet and zidovudine (possibly linked to synergy between zidovudine and foscarnet and/or the inherent anti-HIV activity of foscarnet), appear to offer potentially important advantages for foscarnet over ganciclovir in the treatment of selected patients with AIDS and CMV infections.

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.