A Noninvasive Oral Neutrophil Assay To Monitor Engraftment, Neutrophil Function and Susceptibility to Infection Following Bone Marrow Transplantation (BMT) in Children and Adolescents.

BACKGROUND: A major problem in the post-BMT setting is the determination of neutrophil levels and function that are protective against life threatening infections. Conventional definitions of engraftment by circulating neutrophil counts are unreliable. Identifying successful engraftment of protective neutrophils earlier may negate the need for invasive marrow testing and help predict which patients need empirical antibacterial or antifungal therapy. Monitoring the timing of tissue delivery of neutrophils may serve as an indicator of neutrophil functionality and competence in these acutely neutropenic patients. Past findings suggest that neutrophil quantification in oral rinses can be a useful and practical method to monitor engraftment in adult patients undergoing BMT. The utility of this method in children has not been previously determined.

METHODS: Subjects between 6 and 18 years of age undergoing BMT were asked to perform timed mouth-wash specimens prior to initiating conditioning therapy and then every 1–2 days until they were discharged from the hospital. Oral neutrophil numbers were determined from the rinse samples using fluorescent staining methods and a hemacytometer. These levels were compared to circulating neutrophil levels and clinical outcome measures. In the current BMT setting, engraftment is defined by an absolute neutrophil count of 0.5 x10⁹/L or more for three consecutive days. We defined oral neutrophil engraftment as the day neutrophils reappeared in the oral cavity and were detected during analysis of the oral rinse samples collected from the patients post-BMT. This corresponds to a minimum oral neutrophil count of 0.25 x10⁴/L in the original patient rinse samples.

RESULTS: The patient population consisted of 22 patients (N=22) with either bone marrow failures or malignancies. Oral neutrophils reappeared and returned to a stable level 5.7±3.9SD days earlier in the mouth than in the blood following BMT, thus enabling to successfully predict engraftment much sooner than it was evident in their blood counts as per the conventional definition of engraftment. Furthermore, the time gap between oral and blood neutrophil engraftment was inversely related to the total number of febrile episodes that a patient endured following blood neutrophil engraftment (F _1,15 = 7.81 P = 0.0136). This implies that the timing of neutrophil tissue delivery can be a good indicator of neutrophil functionality and infection susceptibility in the post-BMT setting. Moreover, among patients with oral mucositis, severity declined sharply over the days following oral engraftment. We conclude that monitoring oral neutrophils can be useful in evaluating clinical outcomes in the post-BMT setting. Lastly, it is noteworthy that one of our patients developed severe graft vs. host disease soon after BMT. Although neutrophils were detected in his oral rinses, they were outnumbered by abnormal T cells (CD3+) which are normally not present in oral samples.