Detection and pharmacokinetics of a cytomegalovirus (CMV) DNA plasmid in human plasma during a clinical trial of an intramuscular CMV vaccine in hematopoietic stem cell transplant recipients.

Cytomegalovirus (CMV) causes significant morbidity and mortality in solid organ and bone marrow transplant recipients. DNA vaccines can provide both humoral and cellular immunity without exposing immune-compromised persons to replication-competent CMV. We studied the kinetics of CMV vaccine DNA in plasma. The samples were obtained from vaccine recipients who were enrolled in a double-blinded, placebo-controlled clinical trial of an intramuscular, plasmid-based, bivalent DNA vaccine for CMV in stem cell transplant recipients. Residual specimens on patients enrolled in the vaccine trial were saved until the trial was unblinded and published. Quantitative real-time polymerase chain reaction (PCR) was used to detect and quantify CMV glycoprotein B (gB) DNA in plasma from 4 recipients of the vaccine. The melting temperature of the vaccine gB amplicon was 62.4°C, compared to 68.8°C, which is seen with the wild-type virus. Sequence analysis revealed that there were 3 mismatches between the fluorescent resonance energy transfer probe and the vaccine DNA sequence. Because preemptive treatment of CMV disease in stem cell transplant patients is based on quantitative PCR analysis of viral sequences in plasma, it is important that vaccine sequences not be confused with those in wild-type virus. Confusion could lead to treatment with toxic medications, potentially compromising the transplant. Effects of PCR target choice and amplicon detection techniques on patient management and vaccine trials are discussed.