Background Discharging patients from the intensive care unit (ICU) often requires complex decision making to balance patient needs with available resources. Unplanned return to the ICU (“bounce back”, BB) has been associated with increased resource utilization and worse outcomes but few data on trauma patients are available. The goal of this study was to review ICU BB and define ICU discharge variables that may be predictive of BB. Methods Adults admitted to ICU and discharged alive to a ward from 11/18/04 to 9/01/09 (interval with no changes in coverage) were selected from our trauma registry. Patients with unplanned return to ICU (BB cases) were matched 1:2 with controls on age, ISS and duration of post-ICU stay. Data were collected by chart review then analyzed with univariate and conditional multivariate techniques. Results 1971 of 8835 hospital admissions (22.3%) were discharged alive from ICU to a ward. 88 patients (4.5%) met our criteria for BB (male 75%, mean age 52.9 + 21.9, mean ISS 23.1 + 10.2). Most (71.6%) occurred within 72 hours. Mortality for BB cases was high (19.3%). Regression analysis showed that male gender (Odds Ratio 2.9, p=0.01), GCS<9 (Odds Ratio 22.3, p<0.01), discharge during day shift (Odds Ratio 6.9, p<0.0001) and presence of one (Odds Ratio 3.5, p=0.03), two (Odds Ratio 3.8, p=0.03) or three or more co-morbidities (Odds Ratio 8.4, p<0.001) were predictive of BB. Conclusion In this study, BB rate was 4.8% and associated mortality was 19.3%. At the time of ICU discharge, male gender, a GCS <9, higher FiO2, discharge on day shift and presence of one or more co-morbidities were the strongest predictors of BB. A multi-institutional study is needed to validate and extend these results.

• Tolerance induction after in utero hematopoietic cell transplantation involves both direct and indirect antigen presentation.• Tolerance is achieved by deletion of effector T cells, which results in Treg enrichment without de novo Treg induction.In utero hematopoietic cell transplantation (IUHCTx) is a promising method to induce donor-specific tolerance but the mechanisms of antigen presentation that educate host T cells and the relative importance of deletion vs regulation in this setting are unknown. We studied the roles of direct and indirect antigen presentation (mediated by donorand host-derived antigen-presenting cells [APCs], respectively) in a mouse model of IUHCTx. We found that IUHCTx leads to precocious maturation of neonatal host dendritic cells (DCs) and that there is early differentiation of donor-derived DCs, even after transplantation of a stem cell source without mature APCs. We next performed allogeneic IUHCTx into donor-specific T-cell receptor transgenic mice and confirmed that both direct and indirect antigen presentation lead to clonal deletion of effector T cells in chimeras. Deletion did not persist when chimerism was lost. Importantly, although the percentage of regulatory T cells (Tregs) after IUHCTx increased, there was no expansion in Treg numbers. In wild-type mice, there was a similar deletion of effector cells without expansion of donor-specific Tregs. Thus, tolerance induction after IUHCTx depends on both direct and indirect antigen presentation and is secondary to thymic deletion, without de novo Treg induction. (Blood. 2013;121(22):4595-4602)

Compared to NIHF alone, pregnancies with NIHF and P/PM had a lower risk of IUFD and were at increased risk of PTB (<37 and <34 weeks) and spontaneous PTB. This information may help providers in counseling patients with NIHF and supports the need for close antenatal surveillance.

Introduction In utero hematopoietic cell transplantation (IUHCTx) is a promising strategy to treat congenital disorders as the fetal host can potentially be tolerized to transplanted cells early in gestation. However, levels of engraftment have been low and fetal host conditioning strategies to increase space in hematopoietic niches have not been widely explored. We hypothesized that depletion of fetal host hematopoietic stem cells (HSC) using an antibody against the c-kit receptor (ACK2), a strategy which selectively depletes HSC by disrupting stem cell factor (SCF) signaling, would improve engraftment after HSC transplantation. Methods Fetal C57B6.CD45.2 (B6) mice were injected with increasing doses of ACK2 (2.5-50 µg/fetus) or isotype control antibody on E14.5 and surviving pups were transplanted with congenic B6.CD45.1 fetal liver mononuclear cells (2.5×106 cells/pup) on day of life 1 (P1, 7 days after in utero injection), allowing post-transplantation host monitoring. Host HSC depletion and residual serum ACK2 concentration were examined on P1. Peripheral blood chimerism, defined as donor/(donor+host) CD45 cells, as well as the lineage distribution of chimeric cells, were determined beginning 4 weeks after transplantation. Results Survival to birth among fetuses injected with 2.5, 5, or 10 µg of ACK2 was similar to controls (control: 74%; 2.5 µg: 80%; 5 µg: 71%; 10 µg: 60%, p=0.2 by chi-square test, n≥45/group) but was significantly lower at higher concentrations (20 µg: 37%; 50 µg: 31%, p<0.001 vs. control, n≥70/group). Transient anemia and leukopenia were observed on P1 with doses ≥ 5 µg which resolved by P7 (n=17). Four of 19 pups previously treated with ACK2 (2.5-10 µg) and observed long-term had patchy coat discoloration, possibly a manifestation of disruption of C-kit+ melanocyte migration. In utero ACK2 treatment resulted in significant and dose-dependent depletion of host HSCs (defined as Lin-Sca-1+C-kit+, KLS) in the bone marrow of treated animals by P1 (Figure 1A). There was no depletion of KLS cells in the liver. Residual ACK2 antibody was undetectable in the serum by P1, validating our strategy of in utero depletion and neonatal transplantation. In animals receiving neonatal transplantation, ACK2 depletion resulted in a significant increase in levels of engraftment 4 weeks after transplantation compared to controls (control: 3.3±0.3%; 2.5 µg: 13±1.4%; 5 µg: 10±2.4%; 10 µg: 11±2.0%, p<0.05 for each dose vs control by ANOVA). Accordingly, we detected an increased number total bone marrow KLS cells 7 days after transplantation in ACK2 treated animals compared to controls (412±45.9 vs. 933±112 cells, p=0.01, n≥3/group). Moreover, levels of chimerism increased over time in treated animals (Figure 1B; 12 weeks: 2.5 µg: 190%; 5 µg: 170%; 10 µg: 160%) while they remained unchanged in controls. Overall, levels of chimerism achieved with ACK2 treatment were significantly higher than that observed in animals that received in utero transplantation without ACK2 depletion. Lineage analysis of peripheral blood for granulocytes, B cells, and T cells indicated an equal increase in all lineages, suggesting ACK2 depletes true HSCs and not committed progenitors. Interestingly, ACK2 depletion at doses 2.5-10 µg did not result in engraftment of allogeneic BALB/c cells (n=11), indicating that allogeneic neonatal transplantation, unlike in utero transplantation, is limited by a host immune response which is unaffected by ACK2. Conclusion We have demonstrated that fetal HSC depletion using ACK2 can lead to clinically relevant levels of donor cell engraftment with minimal toxicity. In previous studies with this antibody, host HSC depletion required either immunodeficient animals or concurrent irradiation, whereas we achieved depletion in wild-type fetal hosts, suggesting differences in fetal vs. adult HSC sensitivity to SCF signaling. Future studies should explore this strategy to improve engraftment in large animals models of IUHCTx. Disclosures: Weissman: Amgen, Systemix, Stem cells Inc, Cellerant: Consultancy, Employment, Equity Ownership, Membership on an entity’s Board of Directors or advisory committees.