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 αβ 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 that underwent an allogeneic HSCT at St. Jude Children’s Research Hospital from 1996-2011. The mean age of the patients was 10.5 ± 5.9 years (range, 0.6-25.2) and the mean follow up of the survivors was 2.7±1.8 years (range 0.12-6.0). Diagnoses included 59% patients with ALL and 41% patients with AML. 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<0.0001, P<0.0001, P<0.0001 and P <0.004; respectively). Univariate and multivariate model found the number of γδ T cells after HSCT to be associated with infections (P = 0.026 and P = 0.02, respectively). We found the probability of infections for patients with an elevated number of γδ T cells was significantly lower compared to patients with low or normal γδ T cells after HSCT (18% vs. 54%; P=0.025). Bacterial infections were not observed in patients with elevated γδ T cells. Lastly, event free survival was significantly higher in patients with enhanced γδ T cell reconstitution compared to patients with low/normal γδ T cell reconstitution after HSCT (91% vs. 55%; P=0.04). Thus, γδ T cell may play an important role in immune reconstitution after HSCT.

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12 month median 2729 vs. 12062.5 unique TCR sequences, P ¼ .22). Median lymphocyte counts did not increase between 3 and 12 months in the PD group as in the U+UD group, but the proportion of CD3 + cells within lymphocytes increased in both groups. PD T cell repertoires were less clonal than U+UD samples at 3 months (1-normalized entropy: 0.14 vs. 0.25, P ¼ .09) and 12 months (1-normalized entropy: 0.11 vs. 0.23, P ¼ .95), with more even frequency distribution of TCRs. PD T cell repertoire was more dynamic than the U+UD controls with a significantly decreased T cell clonal persistence between 3 and 12 months (TCR sequence overlap: 8.73% vs. 38.84%, P ¼ .027). Conclusions: Ex vivo dmPGE 2 modulation with dmPGE 2 dominance results in delayed T cell and lymphocyte recovery, but less clonality despite a T cell repertoire restricted by low CD3 + counts. The reduced oligoclonality and rapid T cell turnover may indicate enhanced thymopoiesis. Correlation with TRECs and clinical infectious outcomes is ongoing.

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.

Cord blood (CB) T cells are known to be naïve cells, but can be activated to respond similar to adult peripheral blood (PB) T cells. Reports indicate that culture with aminobisphosphonate (NBP) stimulates CB gamma delta T cell proliferation ex vivo, specifically the TCRγ9δ2 subset, which has been extensively studied in PB gamma delta T cells. As CB gamma delta T cells are not well described, we compared CB gamma delta T cell proliferation, phenotype and genotype to PB gamma delta T cells when culturing cells with the NBP, Zometa (zoledronic acid), and IL-2. Fourteen days in culture resulted in significant fold increase in the proliferation of gamma delta T cells and in the percent of lymphocytes in both sample types. PB gamma delta T cells proliferated more robustly than CB with a 288.60 versus 21.32 fold increase, respectively. Additionally, in freshly isolated samples, CB gamma delta T cells comprised an average of 1.404% of the lymphocyte population, which was similar to PB gamma delta T cells, with an average of 2.319%. However, by day 14, PB gamma delta T cells increased to 70.15% of lymphocytes whereas CB gamma delta T cells increased to 12.49%. Phenotypically, both CB and PB had similar percent of CD45RA+ and CD45RO+ gamma delta T cell memory subsets in freshly isolated samples. Following culture, PB gamma delta T cells were mostly CD45RO+ memory cells, with significantly fewer CD45RA+ naïve cells, whereas more CB gamma delta T cells were of the intermediate CD45RA+CD45RO+ subset. Further phenotypic analysis of the memory subsets indicated that cultured PB gamma delta T cells were either effector memory cells (CD27-CD45RA-) or central memory cells (CD27+CD45RA-), while CB gamma delta T cells were mostly naïve (CD27+CD45RA+). The cytokines secreted by these cells were also assessed and the culture of PB and CB gamma delta T cells resulted in differing cytokine secretion profiles. After 14 days of culture, PB gamma delta T cells secreted more IFNγ and TNFα, while CB gamma delta T cells secreted more IL-10 and RANTES. We also examined TCRγ9 and TCRδ2 phenotypic expression and found that the TCRγ9δ2 was a common clone in freshly isolated PB gamma delta T cells, which predominated after 14 days in culture. However, while the TCRγ9δ2 variant was expressed in CB gamma delta T cells, it was low before and after culture, suggesting that Zometa may not stimulate gamma delta T cells in CB the same as PB. As limited TCRγδ phenotypic reagents are available, we developed a single cell PCR assay for genotypic analysis of the TCRγδ repertoire. PCR analysis suggests that the TCRγδ repertoire is diverse in both samples, yet TCRγ9δ2 is most prevalent. Further analysis of the variant subsets is warranted and may give insight into how each of these receptor pairings affects function. Disclosures No relevant conflicts of interest to declare.