Demographics of first-time donors returning for donation during the pandemic: COVID-19 convalescent plasma versus standard blood product donors

BACKGROUND

Previous studies have demonstrated low first-time donor return rates (DRR) following catastrophic events. Little is known, however, about the influence of demographic factors on the DRR of first-time donors during the COVID-19 pandemic, including the unique motivation of COVID-19 convalescent plasma (CCP) donors as compared to non-CCP donors.

STUDY DESIGN AND METHODS

Thirteen blood collection organizations submitted deidentified data from first-time CCP and non-CCP donors returning for regular (non-CCP) donations during the pandemic. DRR was calculated as frequencies. Demographic factors associated with returning donors: race/ethnicity, gender, and generation (Gen Z: 19-24, Millennial: 25-40, Gen X: 41-56, and Boomer: ≥57 years old), within the CCP and non-CCP first-time cohorts were compared using chi-square test at p < .05 statistical significance.

RESULTS

From March 2020 through December 2021, there were a total of 44,274 first-time CCP and 980,201 first-time non-CCP donors. DRR were 14.6% (range 11.9%-43.3%) and 46.6% (range 10.0%-76.9%) for CCP and non-CCP cohorts, respectively. Age over 40 years (Gen X and Boomers), female gender, and White race were each associated with higher return in both donor cohorts (p < .001). For the non-CCP return donor cohort, the Millennial and Boomers were comparable.

CONCLUSION

The findings demonstrate differences in returning donor trends between the two donor cohorts. The motivation of a first-time CCP donor may be different than that of a non-CCP donor. Further study to improve first-time donor engagement would be worthwhile to expand the donor base with a focus on blood donor diversity emphasizing engagement of underrepresented minorities and younger donors.

How do I initiate and maintain a mobile apheresis service in the era of cellular therapy

BACKGROUND

Mobile delivery of apheresis services is an increasingly important component of health care equity, as patients should not have to transfer care providers or travel far distances to receive critical therapeutic apheresis procedures or cell therapy-based treatments. Therefore, the availability of such services should be expanded.

STUDY DESIGN AND METHODS

In this "How Do I" article, we provide a detailed overview of the elements necessary to initiate and maintain a successful mobile apheresis service, including challenges and potential solutions.

RESULTS

Safe and efficient operation of a mobile apheresis service must consider acquisition of physical assets, such as apheresis sites, personnel, equipment and supplies, communication devices, and transportation vehicles, and optimize organizational aspects, such as staff responsibilities, service partnerships, logistics management, case scheduling and triage, and billing. In the era of cellular therapy, additional critical considerations include regulatory compliance and facility accreditation.

DISCUSSION

To our knowledge, no previous publication provides the extensive details described herein to set up and maintain a successful mobile apheresis service, and thus will be very helpful to those facilities wishing to initiate or expand mobile apheresis services.

Access to and safety of COVID-19 convalescent plasma in the United States Expanded Access Program: A national registry study

BACKGROUND

The United States (US) Expanded Access Program (EAP) to coronavirus disease 2019 (COVID-19) convalescent plasma was initiated in response to the rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19. While randomized clinical trials were in various stages of development and enrollment, there was an urgent need for widespread access to potential therapeutic agents. The objective of this study is to report on the demographic, geographical, and chronological characteristics of patients in the EAP, and key safety metrics following transfusion of COVID-19 convalescent plasma.

METHODS AND FINDINGS

Mayo Clinic served as the central institutional review board for all participating facilities, and any US physician could participate as a local physician-principal investigator. Eligible patients were hospitalized, were aged 18 years or older, and had-or were at risk of progression to-severe or life-threatening COVID-19; eligible patients were enrolled through the EAP central website. Blood collection facilities rapidly implemented programs to collect convalescent plasma for hospitalized patients with COVID-19. Demographic and clinical characteristics of all enrolled patients in the EAP were summarized. Temporal patterns in access to COVID-19 convalescent plasma were investigated by comparing daily and weekly changes in EAP enrollment in response to changes in infection rate at the state level. Geographical analyses on access to convalescent plasma included assessing EAP enrollment in all national hospital referral regions, as well as assessing enrollment in metropolitan areas and less populated areas that did not have access to COVID-19 clinical trials. From April 3 to August 23, 2020, 105,717 hospitalized patients with severe or life-threatening COVID-19 were enrolled in the EAP. The majority of patients were 60 years of age or older (57.8%), were male (58.4%), and had overweight or obesity (83.8%). There was substantial inclusion of minorities and underserved populations: 46.4% of patients were of a race other than white, and 37.2% of patients were of Hispanic ethnicity. Chronologically and geographically, increases in the number of both enrollments and transfusions in the EAP closely followed confirmed infections across all 50 states. Nearly all national hospital referral regions enrolled and transfused patients in the EAP, including both in metropolitan and in less populated areas. The incidence of serious adverse events was objectively low (<1%), and the overall crude 30-day mortality rate was 25.2% (95% CI, 25.0% to 25.5%). This registry study was limited by the observational and pragmatic study design that did not include a control or comparator group; thus, the data should not be used to infer definitive treatment effects.

CONCLUSIONS

These results suggest that the EAP provided widespread access to COVID-19 convalescent plasma in all 50 states, including for underserved racial and ethnic minority populations. The study design of the EAP may serve as a model for future efforts when broad access to a treatment is needed in response to an emerging infectious disease.

TRIAL REGISTRATION

ClinicalTrials.gov NCT#: NCT04338360.

Transfusion Practices in Pediatric Cardiac Surgery Requiring Cardiopulmonary Bypass: A Secondary Analysis of a Clinical Database

OBJECTIVES

To describe blood component usage in transfused children with congenital heart disease undergoing cardiopulmonary bypass surgery across perioperative settings and diagnostic categories.

DESIGN

Datasets from U.S. hospitals participating in the National Heart, Lung, and Blood Institute Recipient Epidemiology and Donor Evaluation Study-III were analyzed.

SETTING

Inpatient admissions from three U.S. hospitals from 2013 to 2016.

PATIENTS

Transfused children with congenital heart disease undergoing single ventricular, biventricular surgery, extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Eight hundred eighty-two transfused patients were included. Most of the 185 children with single ventricular surgery received multiple blood products: 81% RBCs, 79% platelets, 86% plasma, and 56% cryoprecipitate. In the 678 patients undergoing biventricular surgery, 85% were transfused plasma, 75% platelets, 74% RBCs, and 48% cryoprecipitate. All 19 patients on extracorporeal membrane oxygenation were transfused RBCs, plasma, and cryoprecipitate, and 18 were transfused platelets. Intraoperatively, patients commonly received all three components, while postoperative transfusions were predominantly single blood components. Pretransfusion hemoglobin values were normal/low-normal for age for all phases of care for single ventricular surgery (median hemoglobin 13.2-13.5 g/dL). Pretransfusion hemoglobin values for biventricular surgeries were higher intraoperatively compared with other timing (12.2 g/dL vs 11.2 preoperative and postoperative; p < 0.0001). Plasma transfusions for all patients were associated with a near normal international normalized ratio: single ventricular surgeries median international normalized ratio was 1.3 postoperative versus 1.8 intraoperative and biventricular surgeries median international normalized ratio was 1.1 intraoperative versus 1.7 postoperative. Intraoperative platelet transfusions with biventricular surgeries had higher median platelet count compared with postoperative pretransfusion platelet count (244 × 109/L intraoperative vs 69 × 109/L postoperative).

CONCLUSIONS

Children with congenital heart disease undergoing cardiopulmonary bypass surgery are transfused many blood components both intraoperatively and postoperatively. Multiple blood components are transfused intraoperatively at seemingly normal/low-normal pretransfusion values. Pediatric evidence guiding blood component transfusion in this population at high risk of bleeding and with limited physiologic reserve is needed to advance safe and effective blood conservation practices.

Convalescent plasma for hospitalized patients with COVID-19: an open-label, randomized controlled trial

The efficacy of convalescent plasma for coronavirus disease 2019 (COVID-19) is unclear. Although most randomized controlled trials have shown negative results, uncontrolled studies have suggested that the antibody content could influence patient outcomes. We conducted an open-label, randomized controlled trial of convalescent plasma for adults with COVID-19 receiving oxygen within 12 d of respiratory symptom onset (NCT04348656). Patients were allocated 2:1 to 500 ml of convalescent plasma or standard of care. The composite primary outcome was intubation or death by 30 d. Exploratory analyses of the effect of convalescent plasma antibodies on the primary outcome was assessed by logistic regression. The trial was terminated at 78% of planned enrollment after meeting stopping criteria for futility. In total, 940 patients were randomized, and 921 patients were included in the intention-to-treat analysis. Intubation or death occurred in 199/614 (32.4%) patients in the convalescent plasma arm and 86/307 (28.0%) patients in the standard of care arm—relative risk (RR) = 1.16 (95% confidence interval (CI) 0.94–1.43, P = 0.18). Patients in the convalescent plasma arm had more serious adverse events (33.4% versus 26.4%; RR = 1.27, 95% CI 1.02–1.57, P = 0.034). The antibody content significantly modulated the therapeutic effect of convalescent plasma. In multivariate analysis, each standardized log increase in neutralization or antibody-dependent cellular cytotoxicity independently reduced the potential harmful effect of plasma (odds ratio (OR) = 0.74, 95% CI 0.57–0.95 and OR = 0.66, 95% CI 0.50–0.87, respectively), whereas IgG against the full transmembrane spike protein increased it (OR = 1.53, 95% CI 1.14–2.05). Convalescent plasma did not reduce the risk of intubation or death at 30 d in hospitalized patients with COVID-19. Transfusion of convalescent plasma with unfavorable antibody profiles could be associated with worse clinical outcomes compared to standard care.

A randomized trial in patients hospitalized with COVID-19 showed no benefit and potentially increased harm associated with the use of convalescent plasma, with subgroup analyses suggesting that the antibody profile in donor plasma is critical in determining clinical outcomes.

Transfusion practices for pediatric oncology and hematopoietic stem cell transplantation patients: Data from the National Heart Lung and Blood Institute Recipient Epidemiology and Donor Evaluation Study-III (REDS-III)

BACKGROUND

To evaluate transfusion practices in pediatric oncology and hematopoietic stem cell transplant (HSCT) patients.

STUDY DESIGN AND METHODS

This is a multicenter retrospective study of children with oncologic diagnoses treated from 2013 to 2016 at hospitals participating in the National Heart Lung and Blood Institute Recipient Epidemiology and Donor Evaluation Study-III. Transfusion practices were evaluated by diagnosis codes and pre-transfusion laboratory values.

RESULTS

A total of 4766 inpatient encounters of oncology and HSCT patients were evaluated, with 39.3% (95% confidence interval [CI]: 37.9%-40.7%) involving a transfusion. Red blood cells (RBCs) were the most commonly transfused component (32.4%; 95% CI: 31.1%-33.8%), followed by platelets (22.7%; 95% CI: 21.5%-23.9%). Patients in the 1 to <6 years of range were most likely to be transfused and HSCT, acute myeloid leukemia, and aplastic anemia were the diagnoses most often associated with transfusion. The median hemoglobin (Hb) prior to RBC transfusion was 7.5 g/dl (10-90th percentile: 6.4-8.8 g/dl), with 45.7% of transfusions being given at 7 to <8 g/dl. The median platelet count prior to platelet transfusion was 20 × 10⁹ /L (10-90th percentile: 8-51 × 10⁹ /L), and 37.9% of transfusions were given at platelet count of >20-50 × 10⁹ /L. The median international normalized ratio (INR) prior to plasma transfusion was 1.7 (10-90th percentile: 1.3-2.7), and 36.3% of plasma transfusions were given at an INR between 1.4 and 1.7.

DISCUSSION

Transfusion of blood components is common in hospitalized pediatric oncology/HSCT patients. Relatively high pre-transfusion Hb and platelet values and relatively low INR values prior to transfusion across the studied diagnoses highlight the need for additional studies in this population.

Variation in Neonatal Transfusion Practice

OBJECTIVE

To estimate the incidence of blood product transfusion, including red blood cells, platelets, and plasma, and characterize pretransfusion hematologic values for infants during their initial hospitalization after birth.

STUDY DESIGN

Retrospective cohort study using data from 7 geographically diverse US academic and community hospitals that participated in the National Heart Lung and Blood Institute Recipient Epidemiology and Donor Evaluation Study-III (REDS-III) from 2013 to 2016. Pretransfusion hematologic values were evaluated closest to each transfusion and no more than 24 hours beforehand.

RESULTS

Data from 60 243 infants were evaluated. The incidence of any transfusion differed by gestational age (P < .0001), with 80% (95% CI 76%-84%) transfused at <27 weeks of gestation (n = 329) and 0.5% (95% CI 0.5%-0.6%) transfused at ≥37 weeks of gestation (n = 53 919). The median pretransfusion hemoglobin was 11.2 g/dL (10th-90th percentile 8.8-14.1) for the entire cohort, ranging from 10.5 g/dL (8.8-12.3) for infants born extremely preterm at <27 weeks of gestation to 13.0 g/dL (10.5-15.5) for infants born at term. The median pretransfusion platelet count (×10⁹/L) was 71 (10th-90th percentile 26-135) for the entire cohort, and was >45 for all gestational age groups examined. The median pretransfusion international normalized ratio for the entire cohort was 1.7 (10th-90th percentile 1.2-2.8).

CONCLUSIONS

There is wide variability in pretransfusion hemoglobin, platelet count, and international normalized ratio values for neonatal transfusions. Our findings suggest that a large proportion of neonatal transfusions in the US are administered at thresholds greater than supported by the best-available evidence and highlight an opportunity for improved patient blood management.

Transfusion practices in a large cohort of hospitalized children

BACKGROUND

While previous studies have described the use of blood components in subsets of children, such as the critically ill, little is known about transfusion practices in hospitalized children across all departments and diagnostic categories. We sought to describe the utilization of red blood cell, platelet, plasma, and cryoprecipitate transfusions across hospital settings and diagnostic categories in a large cohort of hospitalized children.

STUDY DESIGN AND METHODS

The public datasets from 11 US academic and community hospitals that participated in the National Heart Lung and Blood Institute Recipient Epidemiology and Donor Evaluation Study-III (REDS-III) were accessed. All nonbirth inpatient encounters of children 0-18 years of age from 2013 to 2016 were included.

RESULTS

61,770 inpatient encounters from 41,943 unique patients were analyzed. Nine percent of encounters involved the transfusion of at least one blood component. RBC transfusions were most common (7.5%), followed by platelets (3.9%), plasma (2.5%), and cryoprecipitate (0.9%). Children undergoing cardiopulmonary bypass were most likely to be transfused. For the entire cohort, the median (interquartile range) pretransfusion laboratory values were as follows: hemoglobin, 7.9 g/dl (7.1-10.4 g/dl); platelet count, 27 × 10⁹ cells/L (14-54 × 10⁹ cells/L); and international normalized ratio was 1.6 (1.4-2.0). Recipient age differences were observed in the frequency of RBC irradiation (95% in infants, 67% in children, p < .001) and storage duration of RBC transfusions (median storage duration of 12 [8-17] days in infants and 20 [12-29] days in children, p < .001).

CONCLUSION

Based on a cohort of patients from 2013 to 2016, the transfusion of blood components is relatively common in the care of hospitalized children. The frequency of transfusion across all pediatric hospital settings, especially in children undergoing cardiopulmonary bypass, highlights the opportunities for the development of institutional transfusion guidelines and patient blood management initiatives.

Convalescent plasma for adults with acute COVID-19 respiratory illness (CONCOR-1): study protocol for an international, multicentre, randomized, open-label trial

BACKGROUND

Convalescent plasma has been used for numerous viral diseases including influenza, severe acute respiratory syndrome, Middle East respiratory syndrome and Ebola virus; however, evidence to support its use is weak. SARS-CoV-2 is a novel coronavirus responsible for the 2019 global pandemic of COVID-19 community acquired pneumonia. We have undertaken a randomized controlled trial to assess the efficacy and safety of COVID-19 convalescent plasma (CCP) in patients with SARS-CoV-2 infection.

METHODS

CONCOR-1 is an open-label, multicentre, randomized trial. Inclusion criteria include the following: patients > 16 years, admitted to hospital with COVID-19 infection, receiving supplemental oxygen for respiratory complications of COVID-19, and availability of blood group compatible CCP. Exclusion criteria are : onset of respiratory symptoms more than 12 days prior to randomization, intubated or imminent plan for intubation, and previous severe reactions to plasma. Consenting patients are randomized 2:1 to receive either approximately 500 mL of CCP or standard of care. CCP is collected from donors who have recovered from COVID-19 and who have detectable anti-SARS-CoV-2 antibodies quantified serologically. The primary outcome is intubation or death at day 30. Secondary outcomes include ventilator-free days, length of stay in intensive care or hospital, transfusion reactions, serious adverse events, and reduction in SARS-CoV-2 viral load. Exploratory analyses include patients who received CCP containing high titre antibodies. A sample size of 1200 patients gives 80% power to detect a 25% relative risk reduction assuming a 30% baseline risk of intubation or death at 30 days (two-sided test; α = 0.05). An interim analysis and sample size re-estimation will be done by an unblinded independent biostatistician after primary outcome data are available for 50% of the target recruitment (n = 600).

DISCUSSION

This trial will determine whether CCP will reduce intubation or death non-intubated adults with COVID-19. The trial will also provide information on the role of and thresholds for SARS-CoV-2 antibody titres and neutralization assays for donor qualification.

TRIAL REGISTRATION

Clinicaltrials.gov NCT04348656 . Registered on 16 April 2020.

Characteristics of coronavirus disease 19 convalescent plasma donors and donations in the New York metropolitan area

Background

Convalescent plasma (CP) is an important initial treatment in pandemics and the New York (NY) metropolitan area is likely to remain a hotspot for collection and distribution of such units. This study reports characteristics of coronavirus disease 19 CP (CCP) donors and their donations to the New York Blood Center (NYBC).

Study design and methods

All CCP data from our first day of collection on March 26th through July 7th, 2020 are included in this retrospective analysis. Donor and donation data were extracted from NYBC electronic databases. SARS‐CoV‐2 antibody testing was initially performed by the NY State Department of Health, and later by NYBC using Ortho and Abbott platforms.

Results

CCP donor age and ABO distributions were consistent with reported lower COVID‐19 susceptibility in O blood types. CCP versus whole blood donors had similar on‐site deferrals, but higher post‐donation deferral rates. CCP versus routine plasmapheresis donations had higher vasovagal reactions but similar product rejection rates. Changes in antibody (Ab) test platforms resulted in significant changes in the percent of donors regarded as antibody positive. Donor correlates with higher anti‐spike total Ig S/CO ratios were Hispanic ethnicity, overweight body mass index, and longer symptom duration; and with higher anti‐nucleocapsid IgG S/CO ratios were male gender, older age, Hispanic ethnicity, and fewer days between symptom onset and first donation.

Discussion

We identify donor characteristics not previously reported to correlate with Ab titer. Our analysis should assist with donor outreach strategies, blood center operating logistics, and recruitment of high titer donors.

Potentially modifiable predictors of cell collection efficiencies and product characteristics of allogeneic hematopoietic progenitor cell collections

BACKGROUND

Hematopoietic progenitor cell (HPC) and immune effector cell (IEC) therapies often require high doses of mononuclear cells (MNCs), whether CD34+ cells, lymphocytes, or monocytes. Cells for IEC can be sourced from HPC products. We thus examined potentially modifiable variables affecting collection efficiencies (CEs) of MNC subsets in HPC collection and also of the typically undesired cell types of platelets, granulocytes, and red cells, which hinder downstream processing. Finally, we sought to confirm previously indeterminate studies of the effect of an adjusted collect flow rate (CFR) on CD34+ CE.

STUDY DESIGN AND METHODS

We performed univariate and multivariate regression analyses of all 135 National Marrow Donor Program (NMDP) HPC collections in 2019 and compared these fixed CFR procedures to previous NMDP collections using adjusted CFRs.

RESULTS

Target cell CEs decreased with increasing peripheral blood (PB) concentration and were associated with different cell type locations within the MNC layer. CEs of undesired cell types varied with standard procedural parameters (inlet flow rate, whole blood processed, etc.). Interestingly, some CEs increased with preapheresis hematocrit. Finally, adjusting the CFR by PB MNC count improved MNC CE but not CD34+ CE.

CONCLUSION

Correlation of target cell CEs with their PB concentration and different cell type locations by depth within the MNC layer indicates the importance of investigating the compensatory fine-tuning of procedure variables to improve CE. Correlation of CEs with PB hematocrit, and CFR adjustment by a modified PB MNC and/or PB CD34 algorithm should be further explored. Adjusting standard procedural parameters may reduce product contamination.

Safety and benefits of automated red cell depletion-exchange compared to standard exchange in patients with sickle cell disease undergoing chronic transfusion

BACKGROUND

The Spectra Optia allows automated performance of red blood cell reduction and isovolemic hemodilution (IHD) prior to standard red cell exchange (RCE), and is primarily intended for patients with sickle cell disease (SCD) undergoing chronic RCE. Data on the safety of inducing transient further anemia and the benefits of IHD-RCE is limited and occasionally contradictory.

STUDY DESIGN AND METHODS

In this retrospective crossover analysis of six patients with SCD who underwent chronic exchange with standard RCE (Cobe Spectra) followed by IHD-RCE (Spectra Optia), we compared safety and benefit outcomes with IHD-RCE vs standard RCE.

RESULTS

There were statistically but not clinically significant drops in blood pressure in the post-IHD phase. With IHD-RCE, there were significant reductions in red blood cell (RBC) usage and/or lower fraction of cells and significant increases in postprocedure hematocrit (Hct) associated with increased preprocedure Hct. There were no differences achieved in the time interval between procedures or in the net RBC gain with IHD-RCE. Overall, there were also no significant differences in pre- and postprocedure percentage of hemoglobin S, reticulocyte count, interval daily hemoglobin A decrement, or postprocedure white blood cell, neutrophil, or platelet counts.

CONCLUSIONS

Our study supports that IHD-RCE can be safely used in patients with stroke risk and compared to standard RCE, results in benefits of lower RBC usage and/or fraction of cells remaining and higher postprocedure Hct associated with higher preprocedure Hct. These findings support wider use of IHD-RCE, especially in the current environment with reduced availability of minority units.

How did we rapidly implement a convalescent plasma program?

Since the beginning of the COVID-19 pandemic, the use of convalescent plasma as a possible treatment has been explored. Here we describe our experience as the first U.S. organization creating a COVID-19 convalescent plasma program to support its use through the single-patient emergency investigational new drug, the National Expanded Access Program, and multiple randomized controlled trials. Within weeks, we were able to distribute more than 8000 products, scale up collections to more than 4000 units per week, meet hospital demand, and support randomized controlled trials to evaluate the efficacy of convalescent plasma treatment. This was through strategic planning; redeployment of staff; and active engagement of hospital, community, and public health partners. Our partners helped with donor recruitment, testing, patient advocacy, and patient availability. The program will continue to evolve as we learn more about optimizing the product. Remaining issues to be resolved are antibody titers, dose, and at what stage of disease to transfuse.

Deployment of convalescent plasma for the prevention and treatment of COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), has spurred a global health crisis. To date, there are no proven options for prophylaxis for those who have been exposed to SARS-CoV-2, nor therapy for those who develop COVID-19. Immune (i.e., "convalescent") plasma refers to plasma that is collected from individuals following resolution of infection and development of antibodies. Passive antibody administration through transfusion of convalescent plasma may offer the only short-term strategy for conferring immediate immunity to susceptible individuals. There are numerous examples in which convalescent plasma has been used successfully as postexposure prophylaxis and/or treatment of infectious diseases, including other outbreaks of coronaviruses (e.g., SARS-1, Middle East respiratory syndrome [MERS]). Convalescent plasma has also been used in the COVID-19 pandemic; limited data from China suggest clinical benefit, including radiological resolution, reduction in viral loads, and improved survival. Globally, blood centers have robust infrastructure for undertaking collections and constructing inventories of convalescent plasma to meet the growing demand. Nonetheless, there are nuanced challenges, both regulatory and logistical, spanning donor eligibility, donor recruitment, collections, and transfusion itself. Data from rigorously controlled clinical trials of convalescent plasma are also few, underscoring the need to evaluate its use objectively for a range of indications (e.g., prevention vs. treatment) and patient populations (e.g., age, comorbid disease). We provide an overview of convalescent plasma, including evidence of benefit, regulatory considerations, logistical work flow, and proposed clinical trials, as scale-up is brought underway to mobilize this critical resource.

Validation of simple prediction algorithms to consistently achieve CD3+ and postselection CD34+ targets with leukapheresis

BACKGROUND

Cellular therapies using engineered T cells, haploidentical transplants, and autologous gene therapy are increasing. Specified CD3+ or high CD34+ doses are typically required for subsequent manufacturing, manipulation, or CD34+ selection. Simple, practical, and reliable lymphocyte and hematopoietic progenitor cell (HPC) collection algorithms accounting for subsequent CD34+ selection have not been published.

STUDY DESIGN AND METHODS

In this analysis of 15 haploidentical donors undergoing tandem lymphocyte and HPC collections, we validated one-step, practical prediction algorithms (Appendix S1, available as supporting information in the online version of this paper) that use conservative facility-specific collection efficiencies, CD34+ selection efficiency, and donor-specific peripheral counts to reliably achieve the target CD3+ and CD34+ product doses. These algorithms expand on our previously published work regarding predictive HPC collection algorithms.

RESULTS

Ninety-three percent of lymphocyte and 93% of CD34+ collections achieved the final target CD3+ and CD34+ product dose when our algorithm-calculated process volumes were used. Linear regression analysis of our algorithms for CD3+, preselection CD34+, and postselection CD34+ showed statistically significant models with R² of 0.80 (root mean square error [RMSE], 31.3), 0.72 (RMSE, 385.7), and 0.56 (RMSE, 326.0), respectively, all with p values less than 0.001.

CONCLUSION

Because achievement of CD3+ or CD34+ dose targets may be critical for safety and efficacy of cell therapies, these simple, practical, and reliable prediction algorithms for lymphocyte and HPC collections should be very useful for collection facilities.

Red blood cells donated by smokers: A pilot investigation of recipient transfusion outcomes

BACKGROUND

Current regulations do not require blood collection facilities to ask donors about cigarette smoking, and the prevalence of nicotine and its metabolites in blood products is not well established. Although smokers have higher hemoglobin (Hb) levels, smoking may adversely affect the quality of donated red blood cells through higher carboxyhemoglobin (COHb) content and premature hemolysis.

STUDY DESIGN AND METHODS

Red blood cell (RBC) unit segments from 100 unique donors were tested for nicotine and its metabolite cotinine by mass spectrometry and for COHb spectrophotometrically. Outcomes were evaluated retrospectively in adult non-bleeding patients receiving single RBC units.

RESULTS

Thirteen of 100 RBC segments (13%) were positive for cotinine at levels consistent with current smoking (> 10 ng/mL). The cotinine positive RBCs showed significantly greater COHb content compared to cotinine negative units (median 3.0% vs. 0.8%, p = 0.007). For patients transfused cotinine-positive units, there was no significant change in their vital signs following transfusion and no transfusion reactions were observed. However, patients transfused cotinine-positive units showed significantly reduced hematocrit and hemoglobin increments (median +1.2% and +0.4 g/dL) following transfusion compared to patients receiving cotinine negative units (median +3.6% and +1.4 g/dL) (p = 0.014).

CONCLUSION

Thirteen percent of RBC units tested positive for cotinine at levels consistent with active smoking, accordant with the estimated national smoking rate of 15.5%. Cotinine-positive RBC units had greater COHb content and showed reduced hematocrit and hemoglobin increments following transfusion. These preliminary results should be validated in a larger cohort.

Apheresis to Mitigate Atherosclerotic Vascular Disease

BACKGROUND

Therapeutic apheresis is a term used to describe a group of treatments where blood components are separated in real time, and one component is removed, exchanged, and/or treated to remove pathogenic substances from the circulation. Plasma exchange, which removed all plasma components, and lipid apheresis which selectively removes lipoproteins from circulation, have both been used to treat atherosclerotic vascular diseases.

METHODS

To review the literature regarding the application of therapeutic apheresis for atherosclerotic vascular diseases.

RESULTS

Primarily lipid apheresis is used to treat atherosclerotic vascular diseases, particularly familial hypercholesterolemia, lipoprotein (a) hyperlipoproteinemia and peripheral vascular diseases. Lipid apheresis can be used as first line or second line treatment with a strong evidenced-based recommendation. Its use has decreased atherosclerotic events.

CONCLUSION

Lipid apheresis is an important therapy for the treatment of familial hypercholesterolemia, lipoprotein (a) hyperlipoproteinemia and peripheral vascular diseases. Lipid apheresis does more than remove low-density lipoproteins and other lipoproteins but also decreases inflammatory markers and improves blood flow.

Clinical outcomes in a cohort of patients with heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a thrombotic disorder usually prompting treatment with non-heparin anticoagulants. The benefits and risks of such treatments have not been fully assessed.

METHODS

We analyzed data for 442 patients having a positive heparin-platelet factor 4 antibody test and recent heparin exposure. The primary outcome was a composite endpoint (death, limb amputation/gangrene, or new thrombosis). Secondary outcomes included bleeding and the effect of anticoagulation.

FINDINGS

Seventy-one patients (16%) had HIT with thrombosis (HIT-T); 284 (64%) had HIT without thrombosis (isolated HIT); 87 (20%) did not have HIT. An intermediate or high "4T" score was found in 85%, 58%, and 8% of the three respective groups. Non-heparin anticoagulation was begun in 80%, 56%, and 45%. The composite endpoint occurred in 48%, 36%, and 17% (P = .01) of which 61%, 38%, and 40% were receiving non-heparin anticoagulation. Compared with the no HIT group, the composite endpoint was significantly more likely in HIT-T [HR 2.48 (1.35-4.55), P = .003)] and marginally more likely in isolated HIT [HR 1.66 (0.96-2.85), P = .071]. Importantly, risk increased (HR 1.77, P = .02) after platelet transfusion. Major bleeding occurred in 48%, 36%, and 16% of the three groups (P = .005). Non-heparin anticoagulation was not associated with a reduction in composite endpoint events in either HIT group.

INTERPRETATION

HIT patients have high risks of death, limb amputation/gangrene, thrombosis, and bleeding. Non-heparin anticoagulant treatment may not benefit all patients and should be considered only after careful assessment of the relative risks of thrombosis and bleeding in individual patients.

Platelet Factor 4 Inhibits and Enhances HIV-1 Infection in a Concentration-Dependent Manner by Modulating Viral Attachment

Platelet factor 4 (PF4) has been recently shown to inhibit infection by a broad range of human immunodeficiency virus type 1 (HIV-1) isolates in vitro. We found that the inhibitory effects of PF4 are limited to a defined concentration range where PF4 exists largely in a monomeric state. Under these conditions, PF4 bound the HIV-1 envelope protein and inhibited HIV-1 attachment to the cell surface. However, as concentrations increased to the point where PF4 exists largely in tetrameric or higher-order forms, viral infection in vitro was enhanced. Enhancement could be inhibited by mutations in PF4 that shift the oligomeric equilibrium toward the monomeric state, or by using soluble glycosaminoglycans (GAGs) to which tetrameric PF4 avidly binds. We conclude that at physiologically relevant concentrations, oligomeric PF4 enhances infection by HIV-1 by interacting with the viral envelope protein as well as cell surface GAGs, enhancing virus attachment to the cell surface. This effect was not specific to HIV-1, as enhancement was seen with some but not all other viruses tested. The biphasic effects of PF4 on HIV-1 infection suggest that native PF4 will not be a useful antiviral agent and that PF4 could contribute to the hematologic abnormalities commonly seen in HIV-infected individuals by enhancing virus infection in the bone marrow.

Therapeutic plasma exchange and immunosuppressive therapy in a patient with anti-GAD antibody-related epilepsy: quantification of the antibody response

Antibodies to glutamic acid decarboxylase (GAD) have been associated with a host of neurological disorders including stiff person syndrome, cerebellar ataxia, limbic encephalitis, and epilepsy. Whether anti-GAD antibodies have an etiological role in these neurological disorders or simply serve as disease markers is unclear. Here, we report a case of a patient with recurrent seizures, poorly responsive to conventional treatment, associated with anti-GAD antibodies. The patient was experiencing near daily seizures at the time of presentation and had marked improvement while receiving immunosuppressive therapy and therapeutic plasma exchange (TPE). We go on to show that the patient had a substantial reduction of her GAD autoantibody burden following this therapy. Using immunostaining, we further demonstrate a progressive loss of GAD reactivity in the patient's sera to neurons and GAD-expressing HELA cells with successive TPEs. Hence, these data support the concept of an immune-mediated pathogenic component to these autoantibody-associated neurological syndromes.

Shared VH1-46 gene usage by pemphigus vulgaris autoantibodies indicates common humoral immune responses among patients

Pemphigus vulgaris (PV) is a potentially fatal blistering disease caused by autoantibodies (autoAbs) against desmoglein 3 (Dsg3). Here, we clone anti-Dsg3 antibodies (Abs) from four PV patients and identify pathogenic VH1-46 autoAbs from all four patients. Unexpectedly, VH1-46 autoAbs had relatively few replacement mutations. We reverted antibody somatic mutations to their germline sequences to determine the requirement of mutations for autoreactivity. Three of five VH1-46 germline-reverted Abs maintain Dsg3 binding, compared with zero of five non-VH1-46 germline-reverted Abs. Site-directed mutagenesis of VH1-46 Abs demonstrates that acidic amino-acid residues introduced by somatic mutation or heavy chain VDJ recombination are necessary and sufficient for Dsg3 binding. Our data suggest that VH1-46 autoantibody gene usage is commonly found in PV because VH1-46 Abs require few to no mutations to acquire Dsg3 autoreactivity, which may favour their early selection. Common VH gene usage indicates common humoral immune responses, even among unrelated patients.

Distinct specificity and single-molecule kinetics characterize the interaction of pathogenic and non-pathogenic antibodies against platelet factor 4-heparin complexes with platelet factor 4

Heparin-induced thrombocytopenia (HIT) is a thrombotic complication of heparin therapy mediated by antibodies to complexes between platelet factor 4 (PF4) and heparin or cellular glycosaminoglycans. However, only a fraction of patients with anti-PF4-heparin antibodies develop HIT, implying that only a subset of these antibodies is pathogenic. The basis for the pathogenic potential of anti-PF4-heparin antibodies remains unclear. To elucidate the intrinsic PF4-binding properties of HIT-like monoclonal antibody (KKO) versus non-pathogenic antibody (RTO) at the single-molecule level, we utilized optical trap-based force spectroscopy to measure the strength and probability of binding of surface-attached antibodies with oligomeric PF4 to simulate interactions on cells. To mimic the effect of heparin in bringing PF4 complexes into proximity, we chemically cross-linked PF4 tetramers using glutaraldehyde. Analysis of the force histograms revealed that KKO-PF4 interactions had ∼10-fold faster on-rates than RTO-PF4, and apparent equilibrium dissociation constants differed ∼10-fold with similar force-free off-rates (k(off) = 0.0031 and 0.0029 s(-1)). Qualitatively similar results were obtained for KKO and RTO interacting with PF4-heparin complexes. In contrast to WT PF4, KKO and RTO showed lower and similar binding probabilities to cross-linked PF4(K50E), which forms few if any oligomers. Thus, formation of stable PF4 polymers results in much stronger interactions with the pathogenic antibody without a significant effect on the binding of the non-pathogenic antibody. These results suggest a fundamental difference in the antigen-binding mechanisms between model pathogenic and non-pathogenic anti-PF4 antibodies that might underlie their distinct pathophysiological behaviors.

Transfusion of 28-day-old leucoreduced or non-leucoreduced stored red blood cells induces an inflammatory response in healthy dogs

BACKGROUND AND OBJECTIVES

Studies in mice suggest that rapid transfusions of red blood cells (RBCs), refrigerator stored for longer durations, induce a pro-inflammatory cytokine response. Studies in human neonates confirm these findings; however, to date, adult human studies have failed to replicate these findings. We used healthy research dogs to begin to examine the factors affecting the cytokine response to transfusion.

MATERIALS AND METHODS

In a prospective study, healthy dogs were randomized for two autologous packed RBC transfusions after 7 (i.e. 'fresh') and 28 (i.e. 'old') days of storage, or after 28 and 7 days of storage, with or without prestorage leucoreduction (LR).

RESULTS

No significant differences were observed between LR and non-LR transfusions for all circulating analytes measured following transfusion. A pro-inflammatory cytokine response, exemplified by monocyte chemoattractant protein-1, was observed 6 h after only old RBC transfusions, irrespective of infusion rate (P < 0·001). This response was accompanied by increased neutrophil counts (P < 0·001) and decreased platelet counts (P < 0·001).

CONCLUSION

In healthy dogs, old RBC transfusions induce inflammation, which is unaffected by infusion rate.

Investigation of a potential protective mechanism against heparin-induced thrombocytopenia in patients on chronic intermittent hemodialysis

BACKGROUND

Heparin-induced thrombocytopenia (HIT) develops as a result of platelet (PLT) activation by anti-platelet factor 4 (PF4)/heparin complex antibodies. Despite repeated exposure to heparin, patients undergoing chronic intermittent hemodialysis (HD) rarely develop HIT. We investigated the possibility that HD decreases/removes PF4 from PLT surfaces and/or plasma, thereby disfavoring immune complex formation as a mechanism of protection against HIT.

MATERIALS AND METHODS

We enrolled 20 patients undergoing chronic HD at the Penn Presbyterian Medical Center. Blood samples were drawn before, during and after treatment in the presence and absence of heparin. PF4, anti-PF4/heparin antibody, heparin, and P-selectin levels were measured.

RESULTS

No patients demonstrated clinical symptoms of HIT. PLT surface PF4 levels decreased and plasma PF4 levels increased concurrently with the increase in plasma heparin concentration. In the absence of heparin, PLT surface and plasma PF4 levels were unchanged. Anti-PF4/heparin antibodies, which were non-functional by the serotonin release assay, were detectable in 8 patients. PLT surface P-selectin levels did not change during treatment.

CONCLUSIONS

Removal of PLT surface and/or plasma PF4 as a mechanism of protection against HIT in patients undergoing HD is not supported by the results of our study, although the transient decrease in PLT surface PF4 in the presence of large amounts of heparin remains a candidate mechanism. The small sample size, single type of dialyzer membrane, and early sampling time points may have led to the inability to detect changes in PF4 levels. Future studies should explore other potential protective mechanisms.

Low-density lipoprotein apheresis reduces platelet factor 4 on the surface of platelets: a possible protective mechanism against heparin-induced thrombocytopenia and thrombosis

BACKGROUND

Heparin-induced thrombocytopenia and thrombosis (HITT) is characterized by thrombocytopenia due to the formation of antibodies against heparin : platelet factor 4 (PF4) complexes. Despite the exposure to heparin during treatment and predisposition of patients with atherosclerosis to HITT, HITT in patients undergoing low-density lipoprotein (LDL) apheresis is rare. We investigated the possibility that LDL apheresis decreases PF4 on platelet (PLT) surfaces and/or plasma HITT antibody levels, either of which would disfavor HITT.

STUDY DESIGN AND METHODS

We enrolled 25 patients undergoing LDL apheresis at the Hospital of the University of Pennsylvania. Blood samples were drawn before and after treatment. Plasma samples were drawn proximal and distal to the LA-15 treatment column. PF4, HITT antibodies, heparin levels, and P-selectin were measured.

RESULTS

No patient had clinical symptoms of HITT. The LA-15 column was found to efficiently remove PF4. PF4 levels in peripheral blood plasma did not change significantly after LDL apheresis. However, PLT surface PF4 significantly decreased after treatment. HITT antibodies were found in only two patients and were nonfunctional. PLT surface P-selectin did not change during treatment.

CONCLUSIONS

We have demonstrated that LDL apheresis via dextran sulfate absorption removes plasma PF4 and reduces the amount of PF4 on the surface of circulating PLTs. Reduced surface PF4 may decrease antibody formation and/or recognition by HITT antibodies. These data provide a potential explanation for the near lack of HITT in hypercholesterolemic patients undergoing LDL apheresis. They also suggest the possibility that LDL apheresis using dextran sulfate adsorption may have therapeutic value in the treatment of HITT.

Increased risk of citrate reactions in patients with multiple myeloma during peripheral blood stem cell leukapheresis

The citrate based anticoagulant ACD is commonly used in apheresis procedures. Due to its ability to decrease ionized calcium, citrate may cause unpleasant symptoms, such as paresthesias and muscle cramps, in patients undergoing therapeutic and donor apheresis. We noticed that patients with multiple myeloma (MM) undergoing autologous stem cell leukapheresis appeared to have more citrate reactions when compared to other patients undergoing the same procedure. A retrospective chart review was performed to evaluate 139 (of 151) consecutive patients with MM, amyloidosis, hematological and solid malignancies who had autologous peripheral blood stem cell collection between January 2007 and February 2008. Citrate reactions, ranging from mild (e.g., perioral tingling and parasthesias) to severe (e.g., nausea/vomiting and muscle cramps) were noted for 35 patients. Twenty-three of 63 patients with MM had documented citrate reactions, which was significantly higher than those with other hematological and solid malignancies (37% vs. 20%; P < 0.05, Relative Risk (RR) = 1.9). The severities of citrate reactions were the same in both groups; approximately 50% of patients in each group received i.v. calcium gluconate for treatment of hypocalcemia. No correlation between bisphosphonate therapy and citrate reactions were noted in our study group. Examination of available laboratory values related to calcium homeostasis, liver, and renal function failed to reveal a mechanism for the increase in citrate reactions observed. In summary, this single institution retrospective study indicates that patients with MM are more sensitive to citrate-induced hypocalcemia during leukapheresis when compared to patients with other hematological and solid malignancies. Strategies for decreasing citrate reactions (e.g., supplemental calcium and slowing return rates) should be considered for patient safety and comfort, especially in the MM population, on a prophylactic rather than reactive basis.

Evidence-based practice guidelines for plasma transfusion

BACKGROUND

There is little systematically derived evidence-based guidance to inform plasma transfusion decisions. To address this issue, the AABB commissioned the development of clinical practice guidelines to help direct appropriate transfusion of plasma.

STUDY DESIGN AND METHODS

A systematic review (SR) and meta-analysis of randomized and observational studies was performed to quantify known benefits and harms of plasma transfusion in common clinical scenarios (see accompanying article). A multidisciplinary guidelines panel then used the SR and the GRADE methodology to develop evidence-based plasma transfusion guidelines as well as identify areas for future investigation.

RESULTS

Based on evidence ranging primarily from moderate to very low in quality, the panel developed the following guidelines: 1) The panel suggested that plasma be transfused to patients requiring massive transfusion. However, 2) the panel could not recommend for or against transfusion of plasma at a plasma : red blood cell ratio of 1:3 or more during massive transfusion, 3) nor could the panel recommend for or against transfusion of plasma to patients undergoing surgery in the absence of massive transfusion. 4) The panel suggested that plasma be transfused in patients with warfarin therapy-related intracranial hemorrhage, 5) but could not recommend for or against transfusion of plasma to reverse warfarin anticoagulation in patients without intracranial hemorrhage. 6) The panel suggested against plasma transfusion for other selected groups of patients.

CONCLUSION

We have systematically developed evidence-based guidance to inform plasma transfusion decisions in common clinical scenarios. Data from additional randomized studies will be required to establish more comprehensive and definitive guidelines for plasma transfusion.

Elimination of platelet factor 4 (PF4) from platelets reduces atherosclerosis in C57Bl/6 and apoE-/- mice

Activated platelets, which release platelet factor 4 (PF4) are present in patients with atherosclerosis. To date, no direct in-vivo evidence exists for the involvement of PF4 in atherogenesis. In the current study, we tested the hypothesis that PF4 is atherogenic, and that genetic elimination of PF4 would protect mice from atherosclerosis. We have bred PF4(-/-) mice onto two athero-susceptible backgrounds, WT-C57Bl/6(WT) and apoE(-/-) to examine the importance of PF4 in atherogenesis. In order to induce atherosclerosis, WT and PF4(-/-) mice were fed an atherogenic diet for 30 weeks, while apoE(-/-) and apoE(-/-) PF4(-/-) mice were fed a high-fat Western-style diet for 10 weeks. Examination of lesions in the aortic roots of atherogenic diet fed mice demonstrated reduced atherosclerosis in PF4(-/-) (20% compared to WT). Examination of apoE(-/-) mice demonstrated similar changes, with apoE(-/-) PF4(-/-) mice demonstrating 37% of the aortic atherosclerotic burden compared to apoE(-/-) mice. Although we found similar levels of total and non-HDL cholesterol in WT and PF4(-/-) mice, HDL-cholesterol levels were increased in PF4(-/-) on both backgrounds. These data demonstrate, for the first time, that the platelet specific chemokine PF4 promotes atherosclerotic lesion development in vivo.

The cooperative activity between the carboxyl-terminal TSP1 repeats and the CUB domains of ADAMTS13 is crucial for recognition of von Willebrand factor under flow

ADAMTS13 cleaves von Willebrand factor (VWF) between Tyr(1605) and Met(1606) residues at the central A2 subunit. The amino-terminus of ADAMTS13 protease appears to be sufficient to bind and cleave VWF under static and denatured condition. However, the role of the carboxyl-terminus of ADAMTS13 in substrate recognition remains controversial. Present study demonstrates that ADAMTS13 cleaves VWF in a rotation speed- and protease concentration-dependent manner on a mini vortexer. Removal of the CUB domains (delCUB) or truncation after the spacer domain (MDTCS) significantly impairs its ability to cleave VWF under the same condition. ADAMTS13 and delCUB (but not MDTCS) bind VWF under flow with dissociation constants (K(D)) of about 50 nM and about 274 nM, respectively. The isolated CUB domains are neither sufficient to bind VWF detectably nor capable of inhibiting proteolytic cleavage of VWF by ADAMTS13 under flow. Addition of the TSP1 5-8 (T5-8CUB) or TSP1 2-8 repeats (T2-8CUB) to the CUB domains restores the binding affinity toward VWF and the inhibitory effect on cleavage of VWF by ADAMTS13 under flow. These data demonstrate directly and quantitatively that the cooperative activity between the middle carboxyl-terminal TSP1 repeats and the distal carboxyl-terminal CUB domains may be crucial for recognition and cleavage of VWF under flow.

Chemokines and thrombogenicity

Thrombosis is an important clinical entity, and pathologic thrombosis, in the form of atherosclerosis, is a major cause of morbidity and mortality. Recent research points to the role of chemokines, normally key factors in inflammation, in thrombogenesis. Many recent studies in murine transgenic and knockout models show that chemokines and their receptors are important modulators of the process of thrombus formation, particularly in atherosclerosis. Platelet-released chemokines can potentiate or inhibit thrombosis and inflammation. This review focuses on the role of chemokines in platelet activation and thrombosis, particularly as it relates to atherosclerosis. Further studies to define this complex interaction are underway.

Heparin-induced thrombocytopenia: An autoimmune disorder regulated through dynamic autoantigen assembly/disassembly

Heparin-induced thrombocytopenia (HIT) is the most common drug-induced, antibody-mediated cause of thrombocytopenia and thrombosis. HIT is caused by IgG antibodies that bind to epitopes on platelet factor 4 (PF4) released from activated platelets that develop when it forms complexes with heparin. Anti-PF4/antibodies develop in over 50% of patients undergoing surgery involving cardiopulmonary bypass (CPB), an incidence 20-fold higher than HIT. Why might this occur? Binding of HIT IgG occurs only over a narrow molar ratio of reactants, being optimal at 1 mol PF4 tetramer to 1 mol unfractionated heparin (UFH). At these ratios, PF4 and UFH form ultralarge (>670 kD) complexes that bind multiple IgG molecules/complex, are highly antigenic, and promote platelet activation. Low molecular weight heparin (LMWH), which is less antigenic, forms ultralarge complexes less efficiently and largely at supratherapeutic concentrations. In transgenic mice that vary in expression of human PF4 on their platelets, antigenic complexes form between PF4 and endogenous chondroitin sulfate. Binding of HIT IgG to platelets and induction of thrombocytopenia in vivo is proportional to PF4 expression. Heparin prolongs the duration and exacerbates the severity of the thrombocytopenia. High doses of heparin, as used in CPB, or protamine, which competes with PF4 for heparin, disrupts antigen formation and prevents thrombocytopenia induced by HIT antibody. These studies may help explain the disparity between the incidence of antibody formation and clinical disease and may help identify patients at risk for HIT (high platelet PF4). They also demonstrate that this autoimmune disease can be modulated at the level of autoantigen formation and point to rational means to intervene proximal to thrombin generation.

Prothrombotic factors enhance heparin-induced thrombocytopenia and thrombosis in vivo in a mouse model

BACKGROUND

Heparin-induced thrombocytopenia/thrombosis (HIT/T) is a common cause of life- and limb-threatening thrombosis. The development of antibodies that react with complexes of heparin and platelet factor 4 (PF4) is fundamental to the development of the disease. However, anti-PF4/heparin antibodies are far more common than is HIT/T and there is less understanding of the factors that contribute to thrombosis in only a subset of patients.

OBJECTIVES

Both qualitative and quantitative differences in multiple factors (e.g. antibodies, heparin and platelets) may influence the clinical course of patients who develop anti-PF4/heparin antibodies. We examined the hypothesis that host-specific factors, such as comorbid prothrombotic conditions, would exacerbate the pathologic effects of anti-PF4/heparin antibodies.

METHODS AND RESULTS

A mouse model transgenic for human Fcgamma RIIa and PF4 and null for mouse PF4 was used to study the influence of prothrombotic conditions on the effects of anti-PF4/heparin antibodies in vivo. To simulate a prothrombotic milieu, mice were fed a hypercholesterolemic diet (HD). HD-fed mice had elevated plasma cholesterol, increased platelet reactivity and increased endothelial activation relative to mice fed a standard diet (SD). Age- and sex-matched mice from each diet group were treated with an anti-PF4/heparin antibody and heparin. HD-fed mice developed more severe thrombocytopenia than similarly treated SD-fed mice. Mice with moderate to severe thrombocytopenia had elevated plasma levels of thrombin-antithrombin complexes, indicative of increased thrombin generation in vivo. Platelet-fibrin thrombi were observed in multiple organs of HD-fed mice that developed severe thrombocytopenia.

CONCLUSIONS

Host-specific factors, such as prothrombotic changes in platelet reactivity and/or endothelial activation, may influence the development of thrombosis in a subset of patients who develop anti-PF4/heparin antibodies.

PF4/heparin complexes are T cell-dependent antigens

Heparin-induced thrombocytopenia (HIT) is a life-threatening, thrombotic disorder associated with development of anti-platelet factor 4 (anti-PF4)/heparin autoantibodies. Little is known about the antigenic and cellular requirements that initiate the immune response to these complexes. To begin to delineate mechanisms of autoantibody formation in HIT, we studied the immunizing effects of murine PF4 (mPF4)/heparin in mice with and without thymic function. Euthymic mice were injected with mPF4/heparin complexes, mPF4, heparin, or buffer. Mice injected with mPF4/heparin, but not mPF4 or heparin alone, developed heparin-dependent autoantibodies that shared serologic and functional characteristics of human HIT antibodies, including preferential binding to mPF4/heparin complexes and causing heparin- and FcRgammaIIA-dependent platelet activation. In contrast, athymic mice did not develop HIT-like antibodies. Taken together, these studies establish that PF4/heparin complexes are highly immunogenic and elicit self-reacting anti-PF4/heparin antibodies in a T cell-dependent manner.

Long-term effects of LDL apheresis in patients with severe hypercholesterolemia

Familial hypercholesterolemia (FH) is an inherited disorder of lipoprotein metabolism involving mutations in the LDL receptor (LDL-R). Patients with mutation in one (heterozygous) or both (homozygous) genes have markedly elevated LDL cholesterol and are at increased risk for coronary heart disease (CHD). Aggressive lipid lowering is required for homozygous and many heterozygous FH patients. This often involves LDL-apheresis, where LDL and other apo-B containing lipoproteins are selectively removed from the plasma. We have retrospectively studied 34 patients treated with biweekly LDL-apheresis at the Hospital of the University of Pennsylvania. In our patient population, adverse events were uncommon and rarely resulted in shortened treatment time. There was a dramatic decrease in the relative risk of cardiovascular events and cardiovascular interventions in patients treated with LDL-apheresis for an average of 2.5 years. Some but not all patients had long-term reduction in their LDL levels as a result of LDL-apheresis, suggesting that time-averaged reduction in LDL and/or LDL:HDL ratios were responsible for clinical improvement. These data support the use of LDL-apheresis in patients with FH, as well as medication-intolerant patients that have elevated LDL cholesterol despite maximal pharmacological treatment.

Endothelial expression of E-selectin is induced by the platelet-specific chemokine platelet factor 4 through LRP in an NF-kappaB-dependent manner

The involvement of platelets in the pathogenesis of atherosclerosis has recently gained much attention. Platelet factor 4 (PF4), a platelet-specific chemokine released on platelet activation, has been localized to atherosclerotic lesions, including macrophages and endothelium. In this report, we demonstrate that E-selectin, an adhesion molecule involved in atherogenesis, is up-regulated in human umbilical vein endothelial cells exposed to PF4. Induction of E-selectin RNA is time and dose dependent. Surface expression of E-selectin, as measured by flow cytometry, is also increased by PF4. PF4 induces E-selectin expression by activation of transcriptional activity. Activation of nuclear factor-kappaB is critical for PF4-induced E-selectin expression, as demonstrated by promoter activation studies and electrophoretic mobility shift assays. Further, we have identified the low-density lipoprotein receptor-related protein as the cell surface receptor mediating this effect. These results demonstrate that PF4 is able to increase expression of E-selectin by endothelial cells and represents another potential mechanism by which platelets may participate in atherosclerotic lesion progression.

Platelet factor 4 localization in carotid atherosclerotic plaques: correlation with clinical parameters

Emerging evidence supports a role for platelets in the progression of atherosclerosis in addition to an involvement in thrombotic vascular occlusion. Platelet Factor 4 (PF4), a chemokine released by activated platelets, stimulates several pro-atherogenic processes. Therefore, we examined the localization of PF4 and the homologous protein, Neutrophil Activating Protein-2 (NAP-2) in lesions representing the evolution of human atherosclerotic plaques. Carotid plaques from 132 patients with critical carotid stenosis and 6 autopsy specimens were studied. Clinical, histologic and immunohistochemical data were analyzed using a chi(2)-test. PF4 was detected in the cytoplasm of luminal and neovascular endothelium, in macrophages and in regions of plaque calcification. The presence of PF4 in macrophages and neovascular endothelium correlated with lesion grade (p = 0.004; p = 0.044). Staining of macrophages for PF4 correlated with the presence of symptomatic atherosclerotic disease (p = 0.028). In early lesions, PF4 was commonly found in macrophages of early lesions (Grade I/II), whereas NAP-2 was rarely present. In conclusion, correlation between PF4 deposition, lesion severity and symptomatic atherosclerosis suggests that persistent platelet activation may contribute to the evolution of atherosclerotic vascular lesions. These studies support the rationale for the chronic use of anti-platelet therapy in patients at risk for developing symptomatic atherosclerosis.

Ultralarge complexes of PF4 and heparin are central to the pathogenesis of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia and thrombosis (HITT) is a severe complication of heparin therapy caused by antibodies to complexes between unfractionated heparin (UFH) and platelet factor 4 (PF4) that form over a narrow molar range of reactants and initiate antibody-induced platelet activation. We observed that UFH and tetrameric PF4 formed ultralarge (> 670 kDa) complexes (ULCs) only over a narrow molar range with an optimal ratio of PF4 to heparin of approximately 1:1. These ULCs were stable and visible by electron microscopy, but they could be dissociated into smaller complexes upon addition of heparin. ULCs formed inefficiently when PF4 was incubated with low-molecular-weight heparin, and none formed with the pentasaccharide fondaparinux sodium. In addition, mutation studies showed that formation of ULCs depended on the presence of PF4 tetramers. The ULCs were more reactive as determined by their capacity to bind to a HITT-like monoclonal antibody and showed greater capacity to promote platelet activation in an antibody- and FcgammaRIIA-dependent manner than were the smaller complexes. The capacity of PF4 to form ULCs composed of multiple PF4 tetramers arrayed in a lattice with several molecules of UFH may play a fundamental role in autoantibody formation, antibody-dependent platelet activation, and the propensity for thrombosis in patients with HITT.

Interactions of Platelet Factor 4 with the Vessel Wall

Platelet factor 4 (PF4) is a platelet-specific protein that is stored in platelet alpha granules and released following platelet activation. PF4 was the first chemokine that was isolated, but unlike other chemokines, it may not have a clear role in inflammation. Gathering evidence suggests that unlike other chemokines that bind to specific receptors, PF4's biology depends on its unusually high affinity for heparan sulfates and other negatively charged molecules at concentrations attained in the immediate vicinity of activated platelets. There has been one report that PF4 binds to CXCR3B, a chemokine receptor isoform that may be present in some vascular beds, but the biological relevance of this single observation is not clear. We propose that the main biological role of PF4 and the basis for its presence in the alpha granules of all known mammalian platelets is to neutralize surface heparan sulfate side-chains of glycosaminoglycans and to optimize thrombus development at sites of vascular injury. In addition, the binding of PF4 to surface glycosaminoglycans may also underlie its angiostatic and proatherogenic properties. Additionally, PF4 binds to several other proteins that are central to thrombosis, angiogenesis, and atherogenesis. These interactions may also contribute to its biological and pathobiological effects. Certainly, future studies using in vivo models to test biological relevance of each of these proposed mechanisms by which PF4 interacts with the vasculature are needed, as are studies to define the importance of PF4 binding to CXCR3B.

Factor VIII ectopically expressed in platelets: efficacy in hemophilia A treatment

Activated platelets release their granule content in a concentrated fashion at sites of injury. We examined whether ectopically expressed factor VIII in developing megakaryocytes would be stored in alpha-granules and whether its release from circulating platelets would effectively ameliorate bleeding in a factor VIIInull mice model. Using the proximal glycoprotein 1b alpha promoter to drive expression of a human factor VIII cDNA construct, transgenic lines were established. One line had detectable human factor VIII that colocalizes with von Willebrand factor in platelets. These animals had platelet factor VIII levels equivalent to 3% to 9% plasma levels, although there was no concurrent plasma human factor VIII detectable. When crossed onto a factor VIIInull background, whole blood clotting time was partially corrected, equivalent to a 3% correction level. In a cuticular bleeding time study, these animals also had only a partial correction, but in an FeCl3 carotid artery, thrombosis assay correction was equivalent to a 50% to 100% level. These studies show that factor VIII can be expressed and stored in platelet alpha-granules. Our studies also suggest that platelet-released factor VIII is at least as potent as an equivalent plasma level and perhaps even more potent in an arterial thrombosis model.