Purpose

Knowledge about the risk of rejection can be combined with available clinical data to plan additional treatment for your patient.

Rationale

Reactivation of CMV is accompanied by loss of cell-based immunity to the virus. In transplant patients, reactivation leads physicians to lower immunosuppression and start antiviral drugs. This can lead to rejection in some patients or side effects of antiviral drugs in others. CMV can also recur after completion of antiviral drug therapy and can progress to CMV disease. Knowing whether cell-based immunity to CMV is intact or decreased can further guide when to start or stop antiviral drugs or modify immunosuppression.

Intended Use

To measure the level of cell-mediated immunity to CMV.

Procedure

• PlexCMVTM measures functional cell-mediated immunity to CMV.
• A whole blood sample, 3 mL from children and 5 mL from adults, in sodium heparin (green top) tubes. Samples are to be shipped at ambient temperature overnight to Plexision’s reference laboratory.
• CMV-specific T-cells and their subsets, which express the inflammatory marker, CD154, are measured after stimulation with CMV pp65 antigen.
• Simultaneously, recipient T-cell stimulation with mitogen measures general T-cell responsiveness.
• Results are reported within 6 hours after blood samples reach the laboratory.
• Results are reported as frequencies of CMV-specific T-cells.
• For reference, the frequency of CMV-specific T-cells which is associated with freedom from CMV infection is also provided. This threshold frequency has been established from studies in over 140 transplant recipients. The frequency is used to assess whether the patient is protected against CMV infection or not.

Performance

• CMV-specific T-cell frequency of 1.7% or greater was seen in 93% of transplant recipients without CMV infection. Thus, the negative predictive value of this test is 93%.
• In recipients who did not have IgG antibodies to the CMV virus, the incidence of CMV infection was 5% of 1.7% CMV-specific T-cells were present, and 62% of CMV-specific T-cells were less than 1.7% (p=0.004).
• The data was generated by testing 145 samples, of which 19 were known positive and the remainder were known negative. 

Benefits

• Recipient-donor combinations where one or both show no antibody to the CMV virus are administered preventive antiviral medications because they are at high risk to develop CMV infection. These medications can suppress blood cell counts which predisposes to other infections.

• Establishing the level of anti-CMV immunity at baseline and during periods of high dose immunosuppression permits the level of anti-CMV immunity to be assessed in each patient. This can help formulate personalized antiviral therapy or immunosuppressive treatment.