*Purpose: Cytomegalovirus (CMV) in solid organ transplant (SOT) is associated with negative graft and patient outcomes. Prophylactic agents of choice have substantial cytotoxicity, and patients may be switched from universal prophylaxis (PPX) to the preemptive monitoring (PEM) approach. However, viral load (VL) associated with initiation of preemptive treatment (PET) is debated. The primary objective is to describe the experience of PEM in a group of patients converted from universal PPX to PEM. The secondary objective is to determine the utility of a PET threshold.

*Methods: Patients enrolled in our PEM program were followed from 9/1-11/11/19. “Positive” CMV PCR was defined as a PCR greater than the lower limit of quantification (LLOQ) based on local lab testing. A CMV PCR of >500 IU/mL was chosen as the PET threshold. All patients received valganciclovir (VGC) for PET.

*Results: 33 patients were followed. Most patients (94%) were transplanted in 2019 and received lymphocyte depleting induction (88%). Most patients (79%) were kidney transplant recipients (KTRs), followed by pancreas (18%) and liver (3%). All patients initially received universal PPX per center specific protocol, but required conversion due to complications, with 90% converted due to leukopenia. Mean WBC at time of enrollment was 1.6±0.85. In our study population, 85% were seropositive at transplant (R+) and 15% were considered high-risk (D+/R-). Of the seropositive group, 54% were with potential strain variation (D+/R+). CMV viremia occurred in 21% of our PEM patients. Mean enrollment WBC in this group was 1.1±0.8; WBC at initiation of PET was 2.7±1.2. Most patients who developed CMV viremia were KTRs (85%), 100% were R+, and 43% were with potential strain variation (D+/R+). Time from PEM enrollment to PET was 70±26 days. Median VL at first detection was 792 IU/mL (range 70-15,240 IU/mL). Median peak CMV VL was 3,010 IU/mL (range 687-15,240 IU/mL). Two patients (29%) presented with a VL <500 IU/mL at first detection, but both subsequently increased to >500 IU/mL on PCR #2 with a mean delta log of 0.7. Mean duration of PET was 20±7 days. Mean change in WBC in response to PET was -0.2. Immunosuppression (IS) was adjusted in 57% of patients receiving PET, three due to leukopenia, and one due to stalled viral clearance. No patients in our PET group developed symptoms of CMV syndrome or disease.

*Conclusions: In our population of PEM patients, converted from universal PPX to PEM due to leukopenia after receiving lymphocyte depleting induction, incidence of PET was similar to previous literature described rates. All patients with detectable viremia required PET, which resulted in further WBC reduction. Concerningly, most patients required IS adjustment due to myelosuppression while receiving PET. Institution of a PET threshold did not prevent utilization of VGC in any patient and clinically significant viral replication occurred between PCRs 1 and 2, suggesting treatment at first detectable VL in this patient population.

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