Pediatric Post Transplant Neutrophil Function

Allogeneic stem cell transplant (ASCT) is a life saving procedure for children with diverse malignant and non-malignant conditions. The conditioning regimen renders the patient very susceptible to infection until neutrophil (PMN) engraftment occurs. In pediatric patients is not known if these newly engrafted PMN's function normally, nor is it known how long they take to become fully functional. We hypothesize that pediatric patients, like their adult counterparts, demonstrate PMN dysfunction at the time of engraftment and beyond, which will be influenced by, the conditioning regimen, stem cell source and level of GVHD, and may predispose these children to serious bacterial and fungal infections. Peripheral blood specimens were collected from pediatric patients at Children's Hospital Colorado at 1, 2, 3, and 6 and 12 months post ASCT. PMN's were isolated using standard technique of ficoll gradient, followed by hypotonic lysis. PMN activity was assessed looking at 1) superoxide (0₂^- ) production (luminescence); 2) azurophilic granule release (colorimetric assay for elastase); 3) secondary granule production (lactoferrin ELISA); 4) CD11b surface expression (flow cytometry), and; 5) phagocytosis (Phagotest^TM-a flow cytometry assay). Results: To date 22 patients have been enrolled; and over 50 samples obtained out to the 6 month post ASCT, with many approaching 12 months post ASCT. Mean age of the participants is 10.8 years, and 65% are male. Engraftment period has averaged 24 days. Transplant types include eleven cord bloods, six matched-related bone marrow donors, and three matched-unrelated bone marrow donors. PMN function appears to be relatively intact with no significant differences noted between healthy controls and sample specimens at all time points in relation to 0₂^- production, phagocytosis, CD11b surface expression and lactoferrin. The lone exception is with elastase release which is significantly decreased at all time points versus controls (p<0.05); with a slow improvement seen over time (Figure 1).  Subgroup analysis did not show a preferential difference in elastase release in relation to specific stem cell source or conditioning regimen.  We conclude that similar to adults, pediatric patients have PMN dysfunction which appears to be restricted to elastase release and continues 6 months post ASCT. A defect of this type is somewhat similar to Chediak-Higashi and may put patients at higher risk for serious bacterial infections, particularly staphylococcus and streptococcus.