Toxoplasma qPCR kinetics to guide pre-emptive treatment of toxoplasmosis after allogeneic hematopoietic stem cell transplantation.

Background: Recent ECIL-guidelines recommend a quantitative PCR (qPCR) guided pre-emptive treatment approach to toxoplasmosis in seropositive recipients of allogeneic hematopoietic cell transplantation (allo-HCT). While qPCR might serve as a sensitive tool for early Toxoplasma detection, its role in treatment follow-up remains unknown.

Methods: We analyzed the qPCR kinetics of allo-HCT recipients experiencing either Toxoplasma infection (TI, n=71) or disease (TD, n=14) in relation to different parameters. We included 85 patients with available qPCR values expressed as quantitative cycle (Cq) from four large hematological centers from 2009 to 2023, and kinetic analysis was performed in a selection of 74 patients screened at least weekly with blood qPCR. Day 0 (D0) was the day of anti-Toxoplasma treatment start or (when untreated) day of diagnosis.

Results: Time to qPCR negativity was inversely proportional to the Cq value at D0 (p=0.0063). Not reaching negativity at D10 was associated with a significantly higher mortality at D30 (p=0.023). Patients with a high D0-parasitic load and patients with TD showed slower clearance (p<0.001, p=0.032). Time to negativity was not significantly different for patients started on prophylactic vs curative doses as first-line treatment regimen (p=0.16).

Conclusions: This study underscores the predictive value of qPCR kinetics monitoring in allo-HCT patients with toxoplasmosis. With the aforementioned risk factors, clinicians can identify patients at high-risk for worse outcome. Our results support to consider a therapeutic change or reinforcement if the parasitic load does not decrease after 10 days, supplementing existing clinical guidelines.