Gamma delta T cell reconstitution is associated with fewer infections and improved event-free survival after hematopoietic stem cell transplantation for pediatric leukemia.

After hematopoietic stem cell transplantation (HSCT), successful engraftment and immune recovery is necessary to protect the patient from relapse and infection. Many studies highlight the importance of conventional αß T cell recovery after HSCT, but the impact of γδ T cell recovery has not been well described. Here, we investigate the recovery of γδ T cells in 102 pediatric patients with acute leukemia in first clinical remission who underwent allogeneic HSCT at St. Jude Children's Research Hospital from 1996 to 2011. Mean patient age was 10.5 ± 5.9 years (range, .6 to 25.2), and mean survivor follow-up was 2.7 ± 1.8 years (range, .12 to 6.0). Diagnoses included 59% patients with acute lymphoblastic leukemia and 41% patients with acute myelogenous leukemia. Multivariate analysis demonstrated significant impact of the maximum number of CD3(+), CD4(+), and CD8(+) T cells and donor source on the γδ T cell recovery (P < .0001, P < .0001, P < .0001, and P < .004, respectively). Univariate and multivariate models found the number of γδ T cells after HSCT to be associated with infections (P = .026 and P = .02, respectively). We found the probability of infections for patients with an elevated number of γδ T cells was significantly lower compared with patients with low or normal γδ T cells after HSCT (18% versus 54%; P = .025). Bacterial infections were not observed in patients with elevated γδ T cells. Finally, event-free survival was significantly higher in patients with enhanced γδ T cell reconstitution compared with patients with low/normal γδ T cell reconstitution after HSCT (91% versus 55%; P = .04). Thus, γδ T cells may play an important role in immune reconstitution after HSCT.

Pseudometastasis secondary to histoplasmosis infection: false-positive PET/CT findings.

Positron emission computed tomography (PET)/CT is a common modality used in the workup of neoplastic conditions. However, false-positive results may be produced by underlying infectious processes. We report two cases of false-positive PET/CT studies secondary to histoplasmosis infections in both a pediatric and a young adult patient. After the diagnoses, one patient was observed with no therapy and the other received a complete course of itraconazole. In both cases biopsy results were positive for fungal elements consistent with histoplasmosis. Both patients were successfully managed and have had follow-up histoplasmosis titers that reveal resolving infections.