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Background: Adult recipients of hematopoietic cell transplantation (HCT) are at a very high risk of adverse outcomes after COVID-19 (Sharma A, Bhatt NS, et al. Clinical characteristics and outcomes of COVID-19 in haematopoietic stem-cell transplantation recipients: an observational cohort study. The Lancet Haematology. 2021 Mar 1;8(3): e185-93). While children are known to have better outcomes after COVID-19 compared to adults in general, data on risk factors and outcomes of COVID-19 among pediatric recipients of HCT are lacking. Methods: Using the data reported to the Center for International Blood and Marrow Transplant Research (CIBMTR) between March 2020 and May 2021, we describe characteristics, severity, treatment approaches, and outcomes of pediatric HCT recipients who were ≤21 years of age at COVID-19 diagnosis. All diagnoses, donor choice/graft sources, and conditioning regimens were included. Patient, disease, and HCT-related factors were described as frequency for categorical variables and median, range, and interquartile range (IQR) for continuous variables. The probability of overall survival after COVID-19 was calculated using the Kaplan Meier estimator. Additionally, an analysis was performed in the subset of allogeneic HCT COVID-19 cases from the United States (US) to identify risk factors for developing COVID-19. COVID-19 cases were compared with a cohort of all pediatric allogeneic HCT recipients without COVID-19 matched by the transplant center. Impact of hematopoietic cell transplant comorbidity index (HCT-CI), HCT indication, donor type, conditioning intensity, graft vs. host disease (GVHD) prophylaxis, and occurrence of acute and chronic GVHD on development of COVID-19 was examined using Cox proportional hazards model. Hazard ratio (HR) and 95% confidence intervals (CI) were provided. Cumulative incidence of COVID-19 among the US centers reporting at least 1 COVID-19 infection was also calculated, using death from any cause as a competing risk. P value Results: A total of 167 pediatric HCT recipients (allogeneic, allo: 135 and autologous, auto: 32) met study inclusion criteria. Median age at COVID-19 diagnosis for allo and auto HCT recipients were 15 years (range Conclusions: This is the largest series to date summarizing the cumulative incidence, risk factors, and outcomes of pediatric HCT recipients with COVID-19. Patients with pre-HCT comorbidities were more likely to develop COVID-19. However, the overall disease severity and mortality after COVID-19 were low in this patient cohort. Figure 1 Figure 1. Disclosures Bhatt: Rite Aid Corporation: Divested equity in a private or publicly-traded company in the past 24 months; Pfizer Inc.: Divested equity in a private or publicly-traded company in the past 24 months; Moderna, Inc.: Divested equity in a private or publicly-traded company in the past 24 months; Johnson & Johnson: Divested equity in a private or publicly-traded company in the past 24 months. Sharma: Medexus Inc: Consultancy; Spotlight Therapeutics: Consultancy; Vindico Medical Education: Honoraria; CRISPR Therapeutics: Other, Research Funding; Novartis: Other: Salary support paid to institution; Vertex Pharmaceuticals/CRISPR Therapeutics: Other: Salary support paid to institution. Riches: ATARA Biotherapeutics: Other: Payment; Jazz Pharmaceuticals: Other: Payment; BioIntelect: Membership on an entity's Board of Directors or advisory committees. Dandoy: Omeros: Other: Consulted and received Honorarium.

Background: Patients with B-cell lymphoma have poor clinical outcomes to SARS-CoV-2 infection (COVID-19) and are also more likely to have suboptimal responses to immunization. An understanding of which lymphoma patients are at greatest risk of poor COVID-19 vaccine response and what aspects of immunity are most impaired is critical for developing strategies to protect these patients from a potentially fatal infection. Methods: We enrolled 149 participants, including 129 with lymphoma and 20 age-matched controls, who received a complete COVID-19 vaccination series to assess how B- and T-cell vaccine responses vary among clinically relevant subgroups and over time. This cohort included 99 patients with prior anti-CD20 treatment, ranging from 1 week to 17 years prior, allowing us to assess relationships between timing and intensity of anti-CD20 exposure and vaccine response. The cohort also included 18 patients who began treatment with an anti-CD20-containing regimen after being fully vaccinated, in whom we are assessing the potential efficacy of a pre-therapy vaccination strategy. Peripheral blood samples were taken on average 28 days and 4 months after last vaccine dose. B-cell responses are being profiled by measuring anti-Spike serum IgG, RBD-ACE2 blocking activity, and spike-specific memory B cells. T cell assessments include quantitation of spike-specific activation and cytokine production via interferon-gamma ELISPOTs and multiparameter flow cytometry. Results: The 129 participants with lymphoma had a median age of 68, were 59% male, and 70% had either diffuse large B-cell lymphoma (DLBCL) or follicular lymphoma (FL). Thirteen percent had no therapy prior to vaccination, half had not been treated in the past six months and 36% had been treated recently or were currently being treated. Ninety-three percent received an mRNA COVID-19 vaccine. Although we did not detect a statistically significant difference in vaccine response between previously untreated lymphoma patients and controls, 3/17 were negative for blocking antibodies post-vaccine, compared to 0/20 controls (Fishers exact test p=0.09, Figure 1A). Lymphoma patients with any history of treatment had impaired serologic responses to the vaccine compared to previously untreated patients (p=0.01). Responses did not vary by specific lymphoma histology. Blocking antibodies were evident in only 45% and 3% of patients recently/currently treated with a BTK inhibitor or an anti-CD20 antibody, respectively (Figure 1A). Closely evaluating all patients who had ever received anti-CD20 antibody therapy, we found a strong linear correlation between time since last anti-CD20 treatment and RBD-ACE2 binding inhibition (p Conclusions: Treatment with anti-CD20 antibodies significantly impaired COVID-19 vaccine-induced humoral responses in patients with lymphoma in a manner dependent on the time elapsed since last anti-CD20 treatment. Vaccination at least six months after anti-CD20 treatment, likely co-incident with recovery of the B-cell compartment, was associated with positive blocking antibody titers. These data suggest that booster vaccination strategies are more likely to succeed in lymphoma patients who have not received anti-CD20 treatment for at least 6 months and that those patients with recent anti-CD20 treatment may benefit most from passive immunization strategies. Forthcoming results from the pre-therapy vaccination cohort will also help inform sequencing of additional vaccine doses, passive immunization, and anti-cancer treatments. Figure 1 Figure 1. Disclosures Shree: Gilead: Other: Spouse's employment. Beygi: Kite/Gilead: Current Employment. Advani: Astellas/Agensys: Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Bristol Myer Squibb: Membership on an entity's Board of Directors or advisory committees; Cell Medica: Membership on an entity's Board of Directors or advisory committees; Forty Seven: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genetech Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Janssen Pharmaceutical: Research Funding; Juno: Membership on an entity's Board of Directors or advisory committees; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; Kura: Research Funding; Kyowa: Membership on an entity's Board of Directors or advisory committees; Merck: Research Funding; Millenium: Research Funding; Pharmacyclics: Consultancy, Research Funding; Portola Pharmaceuticals: Consultancy; Regeneron: Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees. Khodadoust: CRISPR Therapeutics, Nutcracker Therapeutics: Research Funding; Myeloid Therapeutics: Membership on an entity's Board of Directors or advisory committees; Alexion, AstraZeneca Rare Disease: Other: Study investigator. Kurtz: Roche: Consultancy; Foresight Diagnostics: Consultancy, Current holder of stock options in a privately-held company; Genentech: Consultancy. Alizadeh: Bristol Myers Squibb: Research Funding; Gilead: Consultancy; Celgene: Consultancy, Research Funding; Janssen Oncology: Honoraria; Roche: Consultancy, Honoraria; Foresight Diagnostics: Consultancy, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company; Forty Seven: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company; CAPP Medical: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company; Cibermed: Consultancy, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Levy: GigaGen: Membership on an entity's Board of Directors or advisory committees; Teneobio: Membership on an entity's Board of Directors or advisory committees; Nurix: Membership on an entity's Board of Directors or advisory committees; Dragonfly: Membership on an entity's Board of Directors or advisory committees; Apexigen: Membership on an entity's Board of Directors or advisory committees; Viracta: Membership on an entity's Board of Directors or advisory committees; Spotlight: Membership on an entity's Board of Directors or advisory committees; Immunocore: Membership on an entity's Board of Directors or advisory committees; Walking Fish: Membership on an entity's Board of Directors or advisory committees; Kira: Membership on an entity's Board of Directors or advisory committees; Abintus Bio: Membership on an entity's Board of Directors or advisory committees; Khloris: Membership on an entity's Board of Directors or advisory committees; Virsti: Membership on an entity's Board of Directors or advisory committees; BiolineRx: Membership on an entity's Board of Directors or advisory committees; BeiGene: Membership on an entity's Board of Directors or advisory committees; Quadriga: Membership on an entity's Board of Directors or advisory committees.

Background: Post-allogeneic hematopoietic cell transplant (HCT) work status is an important indicator of survivors' health recovery and social and economic well-being. However, current literature lacks data on work status, missed time at work, work performance, and quality of life (QOL) of long-term survivors of childhood HCT. Methods: A cross-sectional web-based survey study of ≥1-year survivors of childhood allogeneic HCT (performed between 1985-2010 at Children's Wisconsin, Milwaukee, WI) who were Results: Out of 99 allogeneic HCT recipients who met the selection criteria, 47 initiated the survey and 44 completed it (44% response rate). At the time of survey, 73% (n=32) of the respondents were working, 23% (n=10) were unemployed, and 4% (n=2) were students. Median age at HCT and survey were 11.1 years (interquartile range [IQR] 7.0-13.5) and 30.0 years (IQR 26.5-34.0), respectively. Median follow-up from HCT was 22 years (range 9-32). Fifty two percent were females and 75% received HCT for malignant diseases (acute lymphoblastic leukemia 45%). Compared to unemployed survivors, employed survivors reported less pain interference and sleep disturbance (Figure 1). History of acute graft vs. host disease (GVHD) was associated with worse physical function. Median absolute absenteeism and presenteeism scores were 0 hours (IQR [-1.5]-16) and 83 (IQR 73-92), respectively. Higher absolute presenteeism was associated with less pain interference and more satisfaction with social roles and activities and physical function. Higher relative presenteeism was associated with less cognitive concerns. Higher absolute absenteeism was associated with less depression and higher relative absenteeism with less fatigue (Table 1). Conclusions: Nearly a quarter of the survivors reported being unemployed at the time of the survey. Significant associations between survivors' work status, work performance, and QOL were identified. Our findings provide an important insight on the implications of work outcomes on HCT survivors' physical, mental, and social health and emphasizes the importance of routine longitudinal assessment of work status, performance and QOL in this population. These results also have the potential to help develop effective communication strategies with employers to balance work expectations of survivors in order to achieve better work productivity and in turn, good QOL. Figure 1 Figure 1. Disclosures Bhatt: Johnson & Johnson: Divested equity in a private or publicly-traded company in the past 24 months; Moderna, Inc.: Divested equity in a private or publicly-traded company in the past 24 months; Pfizer Inc.: Divested equity in a private or publicly-traded company in the past 24 months; Rite Aid Corporation: Divested equity in a private or publicly-traded company in the past 24 months. Phelan: Amgen Pharmaceuticals: Research Funding. Shaw: mallinkrodt: Other: payments; Orca bio: Consultancy.

Poly-ADP-ribose polymerase inhibitors (PARPi) are currently in clinical trial to determine their therapeutic efficacy for the treatment of acute myeloid leukemia (AML). We have shown that vitamin C (VitC), an essential micronutrient and co-factor of Ten-Eleven translocation (TET) proteins, enhances AML sensitivity to PARPi, potentially due to an increased dependency on base-excision repair (BER) enzymes needed to remove TET-catalyzed oxidized methylcytosine bases via active DNA demethylation. TET2 is the most frequently mutated TET gene in patients with AML, and vitamin C treatment can mimic genetic restoration of TET2 function, leading to DNA demethylation, differentiation, and leukemia cell death. Whether vitamin C efficacy in combination with PARPi depends on the level of TET2 functional alleles is not yet known and may stratify whether TET2 wild-type or mutant patients should be targeted by vitamin C adjuvant therapy. We have generated primary murine AML-ETO9a+ and MLL-AF9+ leukemia models with Tet2 +/+, Tet2 +/- and Tet2 -/- alleles to determine the Tet2-dependent efficacy of PARPi treatment when combined with vitamin C. Furthermore, we have performed CRISPR gene knockout and drug library screening in human AML cell lines in combination with vitamin C treatment, and tested a panel of 10 AML cell lines with titrating concentrations of PARPi (Olaparib, Talazoparib, Veliparib and Rucaparib) alone or in combination with vitamin C (L-ascorbic acid) mimicking physiological to pharmacological in vivo doses. Primary murine AML cells and human cell lines were assayed for colony-forming capacity, differentiation, cell cycling, viability and effects on DNA methylation, levels of oxidized 5-mC and gene expression upon combination treatment in vitro and in vivo. TET2 mutant PDX and primary murine AMLs treated in vivo with L-ascorbate (4g/kg) and Olaparib (50mg/kg) by daily IP injection were also monitored for disease burden, cellular differentiation and survival. Vitamin C is known to drive the TET-catalyzed iterative oxidation of 5-methylcytosine (5-mC) leading to the formation of 5-hydroxymethylcytosine (5-hmC), 5-formylcytosine (5-fC) and 5-carboxylcytosine (5-caC). We show that VitC-PARPi combination treatment causes an accumulation of oxidized 5-mC intermediates in the AML genome that correlates with increased yH2AX formation in mid-S phase and cell cycle stalling. Vitamin C reduces the IC 50 of Olaparib and Talazoparib by greater than 10-fold in human AML cells lines and primary murine leukemia cells, and treatment in combination promotes myeloid differentiation and blocks colony-forming capacity greater than either alone. In both our in vitro and in vivo studies, Tet2 +/- AML cells exhibit increased sensitivity to vitamin C treatment alone or in combination with PARPi compared to either Tet2 +/+ or Tet2 -/- cells, suggesting that patients with TET2 haploinsufficiency, which represents the majority of TET2 mutant cases, could benefit the most from combined treatment. Our findings confirm that vitamin C can act synergistically with PARPi to block AML cell viability, reduce colony-forming capacity, and decrease leukemia burden in PDX and primary murine leukemia models in a TET2 allelic dose-dependent manner. The combinatorial effect works at clinically relevant concentrations of PARPi, and low-pharmacological doses of vitamin C. These studies suggest that vitamin C can be used as a non-toxic therapeutic adjuvant to PARPi therapy for the treatment of AML. Disclosures Neel: Northern Biologics, LTD: Current equity holder in publicly-traded company, Other: Co- Founder; SAB: Other: Co-Founder; Navire Pharma: Consultancy, Current equity holder in publicly-traded company; Jengu Therapeutics: Consultancy, Current equity holder in publicly-traded company, Other: Co-Founder; Arvinas, Inc: Consultancy, Current equity holder in publicly-traded company; Recursion Pharma: Current equity holder in publicly-traded company.

Background: Oral corticosteroids (CS) are often the first line of therapy for immune thrombocytopenia (ITP). Recent guidelines recommend against prolonged CS use (>6 weeks) for adults with ITP and suggest switching to second-line treatments for non-responsive or CS-dependent patients. The duration and potential overuse of CS among newly treated with CS adult ITP patients has yet to be described in a real-world setting. This study quantified the real-world duration of CS use among adult ITP patients newly treated with CS and assessed the clinical and economic consequences of prolonged CS use. Objectives: 1) To describe treatment patterns, bleeding events, and side effects of CS among patients with ITP; 2) To describe healthcare resource utilization (HRU) and costs among patients with ITP treated with CS. Methods: A retrospective observational cohort study was conducted using claims contained in the IBM® MarketScan® Commercial and Medicare Databases. Adult patients with an ITP diagnosis between January 1, 2013 and June 30, 2018 were selected for the study. Patients were required to be newly treated with CS (prednisone, dexamethasone, methylprednisolone) (first CS claim=index date) with at least 12 months of continuous enrollment prior to and 12 months following index. Patients with a diagnosis for any other thrombocytopenia and evidence of causes of secondary thrombocytopenia were excluded. Patients were categorized into cohorts based on CS duration during the follow-up period: CS days' supply ≤6 weeks, >6 weeks to 8 weeks, or >8 weeks. Discontinuation was defined as a gap of >30 days of the index CS following the run-off date of the last observed claim. Bleeding events, incidence of CS side effects (defined as new events occurring during the follow-up period only), HRU and costs (2018 USD), and treatment patterns were described during the follow-up period. Results: Among 1,720 patients who met study inclusion criteria, 65% had ≤6 weeks of CS use, 6% had >6-8 weeks, and 29% had >8 weeks. Median age among all patients was 48 years and majority were female (61%). About three quarters (71%) of patients started on prednisone as the index CS treatment, 16% on methylprednisolone, and 13% on dexamethasone. Patients with higher CS duration of use (>6-8 and >8 week) had a shorter time to CS treatment start following ITP diagnosis (mean 69 and 92 days, respectively; median 5 days for both) compared to the ≤6 week cohort (mean 306, median 152 days). All but one patient discontinued their index CS therapy. Patients with >8 weeks of CS had higher CS restart rates following discontinuation (49%) compared to patients with ≤6 weeks (23%). Among patients who switched therapies following CS discontinuation, those in the ≤6 week cohort had higher utilization of second line ITP agents compared to the >8 week cohort, including eltrombopag (16% vs. 11%) and romiplostim (23% vs. 11%). Patients in the >8 week cohort had higher rates of switching to splenectomy (15%) and rituximab (33%) following CS discontinuation compared to the ≤6 cohort (6% and 26%). About a fifth (19%) of patients experienced a bleeding event during the follow-up period. Bleeding event rates were higher for those with >8 weeks of CS than those with ≤6 weeks (23% vs. 17%). Nearly 40% of all patients experienced a CS side effect and rates were similar among the three cohorts. Patients with greater use of CS (>8 weeks) had higher rates of inpatient admissions (34%) compared to the ≤6 week (22%) and >6-8 week (32%) cohorts. Mean annual all-cause costs were $24,800, $42,706, and $51,896 for the ≤6 week, >6-8 week, and >8 week cohorts, respectively. Conclusions: Patients with ≤6 weeks of CS had the shortest switch time to a non-CS ITP treatment, with higher utilization of thrombopoietin receptor agonists, as compared to patients with greater CS use. Patients with a higher duration of CS use had significantly higher inpatient and outpatient HRU and more than double the healthcare costs compared to patients with ≤6 weeks of CS. The rate of bleeding events was lowest among patients with ≤6 weeks of CS use. Approximately 35% of patients in this study were treated with >6 weeks of CS, indicating a need for earlier intervention with more effective ITP therapies that may reduce CS use and risk of bleeding events, and subsequently decrease the economic burden incurred by patients with prolonged CS exposure. Further study is needed to assess the clinical and economic outcomes related to duration of CS use. Figure Disclosures Hatfield: Amgen Inc.: Current Employment. Manjelievskaia:Amgen Inc.: Consultancy; IBM Watson Health: Current Employment. Evans:Amgen Inc.: Consultancy; IBM Watson Health: Current Employment. Chan:Amgen Inc.: Consultancy; IBM Watson Health: Current Employment. Shah:Amgen Inc.: Current Employment. Saad:Amgen Inc: Current Employment.

Introduction:Sickle cell disorders were originally found in the African regions, Arabian Peninsula and parts of India. However, in today's age of globalization patients with homozygous or compound heterozygous Sickle cell disorders can be found all over the world. The objective of our study was to assess the distribution and clinical presentation of patients with Sickle homozygous or heterozygous diseases in the Eastern part of India. Methods:Patients who attended the Thalassemia Clinic in our tertiary care center, between 1st January 2018 to 31st May 2020 (2 years and 4 months) were retrospectively analysed and the ones with a component of Sickle haemoglobin(HbS), either in the form of Sickle cell anemia/homozygous Sickle cell disorders(SCA) or compound heterozygous diseases, like Sickle cell/β thalassemia(HbS/β), Sickle cell/Delta thalassemia(HbS/D), Sickle cell Haemoglobin/E thalassemia(HbS/E), were included in the study. People having Sickle cell trait (HbS trait), have also been included. Thorough history of painful crises, blood transfusions, family history and treatment history was elicited and every patient was clinically examined. The patients were diagnosed by High Pressure Liquid Chromatography (HPLC) or Thalassemia Mutation analysis by Polymerase Chain reaction (PCR). Results:A total of 95 patients with a component of HbS were considered as our study cohort, with HbS/β thalassemia patients being the majority (53.7%), followed by SCA (30.5%). Age of the study cohort ranged between 2-50 years age. HbS/β thalassemia patients presented at a later age (median 17.5 years) than SCA patients (median 12 years). Their demographic distribution is depicted in Table 1. The most common clinical presentation was painful crisis (32,33.7%), be it abdominal pain (11,11.6%) or bone pain (13,13.7%). Other presenting complaints were pallor (26,27.4%), jaundice (12,12.6%) and fever (4,4.2%). Some rarer presenting manifestations were fatigue (4,4.2%), splenic infarction (1,1%), convulsions (1,1%), Raynaud's phenomenon (1,1%), headache (1,1%) or itchy skin lesions (1,1%). Few patients (4,4.2%) had recurrent pregnancy loss, and one patient was diagnosed incidentally during an antenatal check-up. Most patients had more than one complaint. Very occasionally patients required hospital admission, the reasons being, chest pain, fever, convulsions or abdominal pain. HbS trait was diagnosed incidentally during evaluation for other illnesses, most commonly during evaluation of pallor (3,60%): one patient was later diagnosed with iron deficiency anemia. Most patients who attended our center were from within the state or neighbouring states. The patients were treated with Hydroxyurea, with/without blood transfusions, chelation therapy with Deferasirox as required and Folic acid supplementation. People with HbS Trait continued to receive Folate supplementation. Discussion and Conclusions:This study highlights the varied distribution of HbS among the population attending a tertiary care center, irrespective of a specific area-based population. Till date most studies conducted in India have highlighted the prevalence of Sickle cell disorders among specific focused populations. HbS/β thalassemia was the most common sickle cell disorder in our study. This is in contrast to most findings in published literature from other countries, where SCA is the commonest. Only one other study conducted in eastern India, has depicted a finding similar to ours. The median age of disease presentation was at a later age in our study, in contrast to findings in published literature from other countries. There is a variation in the severity of disease manifestation in our study cohort. The most common painful crisis was bone pain, followed by abdominal pain. Pallor was also one of the commonest presenting symptoms. Stroke, a common manifestation of SCA in other countries, was rare in our study cohort. Disclosures No relevant conflicts of interest to declare.

Conditional knockout (KO) mouse models are invaluable for elucidating the physiological roles of platelets. The Platelet factor 4-Cre recombinase (Pf4-Cre) transgenic mouse is the current model of choice for generating megakaryocyte/platelet-specific KO mice. Platelets and leukocytes work closely together in a wide range of disease settings, yet the specific contribution of platelets to these processes remains unclear. This is partially a result of the Pf4-Cre transgene being expressed in a variety of leukocyte populations. To overcome this issue, we developed a Gp1ba-Cre transgenic mouse strain in which Cre expression is driven by the endogenous Gp1ba locus. By crossing Gp1ba-Cre and Pf4-Cre mice to the mT/mG dual-fluorescence reporter mouse and performing a head-to-head comparison, we demonstrate more stringent megakaryocyte lineage-specific expression of the Gp1ba-Cre transgene. Broader tissue expression was observed with the Pf4-Cre transgene, leading to recombination in many hematopoietic lineages, including monocytes, macrophages, granulocytes, and dendritic and B and T cells. Direct comparison of phenotypes of Csk, Shp1, or CD148 conditional KO mice generated using either the Gp1ba-Cre or Pf4-Cre strains revealed similar platelet phenotypes. However, additional inflammatory and immunological anomalies were observed in Pf4-Cre-generated KO mice as a result of nonspecific deletion in other hematopoietic lineages. By excluding leukocyte contributions to phenotypes, the Gp1ba-Cre mouse will advance our understanding of the role of platelets in inflammation and other pathophysiological processes in which platelet-leukocyte interactions are involved.