Thrombosis risk with haemoglobin C trait and haemoglobin C disease: A systematic review

The thrombotic risk with haemoglobin C trait (HbAC) or haemoglobin C disease (HbCC) is unclear. However, individuals with HbCC have demonstrated chronic haemolysis, higher blood viscosity and altered rheology when compared to individuals with wild-type haemoglobin (HbAA). These physiological alterations may theoretically translate to increased risk of thrombosis; therefore, a systematic literature review was performed to investigate the possible association between HbAC and/or HbCC and thrombosis. Twenty-two studies met inclusion criteria representing 782 individuals with HbAC (n = 694) or HbCC (n = 88). Fifteen studies described the presence/absence of venous thromboembolism (VTE) in patients with HbAC (n = 685) or HbCC (n = 79), while seven studies described patients with HbAC (n = 9) or HbCC (n = 9) and arterial thrombosis. Most (n = 20) studies were case reports or case series; however, two studies suggested a potential increased VTE risk with HbAC compared to HbAA in (i) all patients (OR 2.2, 95% CI: 0.9-5.5) and in (ii) pregnant individuals (RR 3.7, 95% CI 0.9-16). This review is the largest assessment of patients with HbC trait or disease and thrombosis to date; despite its limitations, the findings suggest HbC may be a predisposing risk factor to thrombosis. Prospective cohort studies are warranted to definitively elucidate the risk of thrombosis in this population.

Cost-effectiveness of rapid vs. in-house vs. send-out ADAMTS13 testing for immune thrombotic thrombocytopenic purpura

While awaiting confirmatory results, empiric therapy for patients suspected to have immune thrombotic thrombocytopenic purpura (iTTP) provides benefits and also accrues risks and costs. Rapid assays for ADAMTS13 may be able to avoid the cost and risk exposure associated with empiric treatment. We conducted the first cost-effectiveness evaluation of testing strategies with rapid versus traditional ADAMTS13 assays in patients with intermediate to high-risk PLASMIC scores, with and without caplacizumab use. We built a Markov cohort simulation with four clinical base-case analyses: 1) Intermediate-risk PLASMIC score with caplacizumab, 2) Intermediate-risk PLASMIC score without caplacizumab, 3) High-risk PLASMIC score with caplacizumab, 4) High-risk PLASMIC score without caplacizumab. Each of these evaluated three testing strategies: 1) rapid assay (<1-hour turnaround), 2) in-house FRET-based assay (24-hour turnaround), and 3) send-out FRET-based assay (72-hour turnaround). The primary outcome was the incremental net monetary benefit (iNMB) reported over a 3-day time horizon and across accepted willingness-to-pay thresholds in USD per quality-adjusted life-year (QALY). While accruing the same amount of QALYs, the rapid assay strategy saved up to $46,820 (95% CI $41,961-$52,486) per-patient-tested. No parameter variation changed the outcome. In probabilistic sensitivity analyses, the rapid assay strategy was favored in 100% (three base-cases and scenario analyses) and 99% (one base-case and scenario analysis) across 100,000 Monte Carlo iterations within each. Rapid ADAMTS13 testing for patients with intermediate- or high-risk PLASMIC scores yields significant per-patient cost savings, achieved by reducing the costs associated with unnecessary therapeutic plasma exchange and caplacizumab therapy in patients without iTTP.

Heidenhain variant of Creutzfeldt-Jakob disease masquerading as neuromyelitis optica spectrum disorder: recognizing when apheresis is not the answer

The Heidenhain variant of Creutzfeld-Jakob disease (CJD) is a rare form that initially presents with visual disturbances. In early stages, the presentation can mimic neuromyelitis optica spectrum disorders (NMOSD) and lead to unnecessary treatment modalities. Herein, we describe a case of a 66-year-old man who presented with bilateral vision loss and retro-orbital discomfort. In addition to immunosuppressive therapy, he received 4 rounds of therapeutic plasma exchange after his preliminary diagnosis of NMOSD. We were surprised to note that his condition did not show improvement but deteriorated, with severe neurocognitive symptoms. Eventually, CJD was suspected, and real-time quaking-induced conversion (RT-QuIC) was performed. By the time the diagnosis of Heidenhain variant of CJD was confirmed, the patient was discharged to hospice care and died shortly after.

Assessing Recommendations for Determining Fetal Risk in Alloimmunized Pregnancies in the United States: Is It Time to Update a Decades-Old Practice?

The current recommended testing algorithm for assessing the alloimmunized pregnancy utilized by many obstetricians in the United States (US) fails to consider the most recent evidence, placing fetuses, and mothers at unnecessary risk of poor outcome or death. This narrative review of the current landscape of fetal red blood cell (RBC) antigen testing evaluates the history of hemolytic disease of the fetus and newborn (HDFN) and how its discovery has continued to influence practices in the US today. We compare current US-based HDFN practice guidelines with those in Europe. We also provide transfusion medicine and hematology perspectives and recommendations addressing the limitations of US practice, particularly regarding paternal RBC antigen testing, and discuss the most valuable alternatives based on decades of data and evidence-based recommendations from Europe.

Botulism mimicking Guillain-Barre syndrome: The question of plasma exchange in an unusual case of acute paralysis

Guillain-Barré syndrome (GBS) is an immune-mediated polyradiculoneuropathy and the most common cause of acute flaccid paralysis worldwide. GBS classically presents with acute, progressive, ascending weakness, reduced to absent reflexes, and albuminocytological dissociation on cerebrospinal fluid (CSF) analysis. Botulism is a neurotoxin-mediated acute descending flaccid paralysis with cranial nerve palsies and dysautonomia. Botulism in adults is caused by ingestion/inhalation of botulinum toxin or wound infection with Clostridium botulinum. Both GBS and botulism can rapidly precipitate respiratory failure; thus, prompt diagnosis and treatment are crucial to mitigate poor outcomes. Herein, we describe a case of botulism initially diagnosed as GBS given classic laboratory features, and describe the importance of careful consideration of the most appropriate therapeutic modalities in cases of acute flaccid paralysis, particularly regarding empiric administration of botulinum antitoxin and use of intravenous immune globulin in lieu of plasma exchange for potential GBS to prevent removal of antitoxin.

Warm autoantibodies mimicking alloantibodies: Three cases of autoantibodies with unusual antigenic specificity

OBJECTIVES

We describe 3 cases of red blood cell (RBC) autoantibodies with unusual apparent antigenic specificity and discuss the testing methodology and implications of these findings.

METHODS

All immunohematologic testing, including ABO and RhD typing, antibody detection and identification, RBC antigen phenotyping and genotyping, direct antiglobulin tests, and elution studies were performed using standardized and validated methods and reagents.

RESULTS

Three patients were found to have autoantibodies, which were originally presumed to be alloantibodies. Case 1 was a 60-year-old man with autoanti-Jka following babesiosis; case 2 was a 79-year-old woman with an autoanti-f; and case 3 was a 28-year-old pregnant woman with an autoanti-S. Cases 1 and 2 required RBC transfusions, which were performed with Jka-negative and f-positive RBC units, respectively. No transfusion reactions were reported, and the hemoglobin responded appropriately in both cases.

CONCLUSIONS

These 3 cases complement the minimal literature regarding warm autoantibodies with unusual antigenic specificity and their potential to mediate clinically significant hemolysis. There are only rare reports of warm autoantibodies with specificity for non-Rh antigens, and prior authors have suggested that autoantibodies with mimicking specificity are usually detected only serologically; in contrast, 2 of the 3 patients herein experienced autoimmune hemolytic anemia.

Immunity in the balance: Fatal disseminated adenovirus infection in a patient undergoing plasma exchange and immunosuppressive chemotherapy for anti-glomerular basement membrane disease

Anti-glomerular basement membrane (anti-GBM) disease (formerly known as Goodpasture's syndrome) is a rare autoinflammatory condition that affects the renal and/or pulmonary capillaries. The standard therapeutic regimen for anti-GBM disease involves therapeutic plasma exchange (TPE), cyclophosphamide, and corticosteroids to rapidly remove and inhibit autoantibody production and reduce organ inflammation. Herein we report an 82-year-old female who developed anti-GBM disease but expired despite therapy, secondary to multi-organ failure in the setting of disseminated adenovirus disease. We discuss the utility and potential adverse effect of daily TPE for a protracted course (ie, 10-14 days), the recommended TPE intensity in the 2023 American Society for Apheresis guidelines, updated from every-other-day TPE in the 2019 guidelines, despite no new data. We also highlight the potential for unusual infections to occur in these patients due to the profound immunosuppression, and discuss the importance of balancing immunosuppression to treat the disease with close surveillance of any potential opportunistic infections.

Passive transfer of alloantibodies through breast milk as a mediator of hemolytic anemia

BACKGROUND

Hemolytic disease of the fetus and newborn (HDFN) is characterized by destruction of fetal/neonatal red blood cells (RBCs) secondary to maternally derived antibodies, which are typically thought to be passively acquired via placental transfer. Few cases have examined the possibility of HDFN mediated by maternal antibodies passively transferred via breast milk.

METHODS

We describe two cases of persistent HDFN in infants potentially mediated by passively acquired antibodies via maternal breast milk. We discuss supporting and refuting evidence that may account for this possibility and describe testing methodology illustrating how maternal alloantibodies can be detected in breast milk.

RESULTS

In both cases, anti-D antibodies were detected in maternal breast milk. One patient experienced a significant decrease in anti-D plasma titer from 64 to 4 dilutions following 2 weeks of breastfeeding cessation. The other patient experienced a resolution of anemia without breastfeeding cessation.

CONCLUSION

There is a paucity of data regarding the lifespan of passively acquired RBC antibodies in neonatal circulation, with significant variation noted between passively acquired IgG based on studies utilizing intravenous immunoglobulin compared to studies of maternally-acquired antiviral IgG antibodies. While our data do not definitively implicate passive transfer of alloantibodies in breast milk as a mediator of HDFN, they do illustrate the need for further investigation into the mechanisms and kinetics of passively acquired antibodies in neonatal circulation.

Epidemiological and clinical features, therapeutic strategies and outcomes in patients with hyperhaemolysis: A systematic review

Hyperhaemolysis syndrome (HHS), a severe form of delayed haemolytic transfusion reaction most commonly described in patients with sickle cell disease (SCD), involves destruction of both donor and recipient red blood cells (RBCs). As the epidemiology and underlying pathophysiology have yet to be definitively elucidated, recognition can be challenging. We systematically reviewed PubMed and EMBASE to identify all cases of post-transfusion hyperhaemolysis and characterized the epidemiological, clinical and immunohaematological characteristics and treatments of HHS. We identified 51 patients (33 females and 18 males), including 31 patients with SCD (HbSS, HbSC and HbS/β-thalassaemia). The median haemoglobin nadir (3.9 g/dL) occurred a median of 10 days post-transfusion. 32.6% and 45.7% of patients had a negative indirect anti-globulin test and a negative direct anti-globulin test, respectively. The most common therapies included corticosteroids and intravenous immune globulin. 66.0% of patients received ≥1 supportive transfusion, which was associated with a longer median hospital stay/time to recovery (23 days vs. 15 days; p = 0.015) compared to no supportive transfusion. These findings illustrate that HHS that often results in marked anaemia 10 days post-transfusion is not restricted to patients with haemoglobinopathies, and additional transfused RBCs may be associated with a longer time-to-recovery.

Optimizing Donor Chimerism Threshold for Next Generation Sequencing Monitoring of Measurable Residual Disease Post-Allogeneic Stem Cell Transplant for Myeloid Neoplasms

BACKGROUND

Next-Generation Sequencing (NGS) is used to monitor genetically-measurable residual disease (gMRD) following allogeneic stem cell transplant (aSCT). It is unknown whether an upper limit of chimerism exists such that gMRD NGS testing can be safely forgone.

METHODS

We reviewed 61 AML and 24 MDS patients between 2016-2020 with at least 1 NGS panel before and after aSCT. Donor chimerism was quantified. Logistic regression characterized which factors predicted gMRD. Receiver operator curves (ROC) determined the optimal chimerism threshold for which gMRD would not be detected. Data from an additional 22 patients with follow-up NGS testing in 2022, was also analyzed to validate our proposed threshold.

RESULTS

Donor chimerism (OR= 0.38, 95% CI[0.10,0.62], p=0.02), as expected, was a significant predictor of gMRD. Age, gender, conditioning regimen, presence of a related donor, and diagnosis were not associated with gMRD. A chimerism threshold of 92.5% optimized sensitivity (97.7) and specificity (95.4) such that values >92.5% strongly predicted absence of gMRD (AUC= .986). The validation cohort demonstrated similar strongly predictive capability (AUC= .974) with appropriate sensitivity (100%) and specificity (90.9%).

CONCLUSION

NGS monitoring of gMRD is redundant at chimerism values greater than a more conservative threshold of 92.5% after stem cell transplant.

Hemolytic disease of the fetus and newborn mediated by anti-Dia in a U.S. hospital

Di^a is one of the most clinically significant low-prevalence antigens in the Diego blood group system, since antibodies to Di^a have, albeit rarely, been implicated in hemolytic transfusion reactions and hemolytic disease of the fetus and newborn (HDFN). Given the geographical association, most anti-Di^a HDFN cases have been reported in Japan, China, and Poland. We describe a case of HDFN in a neonate born to a 36-year-old G4P2012 woman of self-identified Hispanic ethnicity and of South American descent with multiple negative antibody detection tests in a U.S. hospital. Upon delivery, a cord blood direct antiglobulin test was positive (3+ reactivity), and neonatal bilirubin levels were moderately elevated, but phototherapy and transfusion were not required. This case highlights a rare, unexpected cause of HDFN in the United States secondary to anti-Di^a, given the near-universal absence of this antigen and antibody in most U.S. patient populations. The case also demonstrates the need for awareness of antibodies to antigens that are considered "low-prevalence" in most populations but that might be encountered more frequently in specific racial or ethnic groups and may require more extensive testing.

Quantitative Risk for Single-Positive Lupus Anticoagulant Results With Different Anticoagulants

OBJECTIVES

Clinical experts recommend against testing for lupus anticoagulant (LAC) during anticoagulation.

METHODS

We quantitated the risk of a single-positive dilute Russell viper venom time (dRVVT) result or partial thromboplastin time-based phospholipid neutralization (PN) result on anticoagulation.

RESULTS

Any anticoagulation led to a fourfold greater likelihood of single-positive results, primarily by rivaroxaban (odds ratio [OR] = 8.6) and warfarin (OR = 6.6), resulting in a positive dRVVT test with a normal PN test. Heparin and apixaban were twofold more likely to show single-positive results, but enoxaparin did not show significant single positivity.

CONCLUSIONS

Our results quantitatively support experts' avoidance of LAC testing during anticoagulation.

Alloimmunization following antigen-negative red blood cell transfusion

BACKGROUND

Red blood cell (RBC) alloimmunization can occur secondary to transfusion or pregnancy. It is observed most frequently among patients with hemoglobinopathies and myeloid neoplasms. Although previous antigen exposure is generally required for alloimmunization, some alloantibodies may develop naturally without prior exposure. Other alloantibodies may become evanescent, only to reemerge at a detectable titer following a stimulatory event. In a minute fraction of cases, 'non-naturally occurring' alloantibodies may appear without a known antigenic stimulus.

METHODS AND MATERIALS

All testing (antibody detection tests and identification, antigen phenotyping, and crossmatching) was performed using the same method and reagents, but occurred at two hospitals within the Yale New Haven Hospital delivery network, and was performed by technologists utilizing different instruments and reagent lots.

RESULTS

We present two cases of seemingly de novo alloimmunization (anti-E and anti-K), and one case of re-emergence of a known, previously evanescent alloantibody (anti-K) following transfusion of RBCs that were antigen-negative for the corresponding antibodies.

CONCLUSION

While the exact mechanism underlying the development and/or re-emergence of RBC alloantibodies in the absence of antigenic stimulation remains unclear, these cases highlight this unusual phenomenon, underscoring the general immunogenicity, as well as the potential consequences, of RBC transfusion and reiterates the importance of concluding an alloantibody specificity, even in the absence of known transfusion of RBCs with a particular antigen.

Warm autoimmune hemolytic anemia with anti-Jka specificity following babesiosis masquerading as a delayed hemolytic transfusion reaction

BACKGROUND

Warm autoimmune hemolytic anemia (WAIHA) is characterized by the development of autoantibodies that react with red blood cells (RBCs) optimally at physiologic temperature, classically resulting in a positive direct antiglobulin test (DAT) for IgG and a panreactive eluate. Babesiosis has been described as a potentiator of WAIHA, and all cases have shown classic blood bank findings. Only rare reports have described autoantibodies, both secondary to babesiosis and overall, with specificity for Kidd antigens.

METHODS

Antibody detection and identification were performed using IgG-specific column agglutination technology. Jk^a antigen phenotyping was assessed using monoclonal reagents and genotypic analysis was performed at an immunohematology reference laboratory. DATs were performed via standard tube methods. The elution was performed using the ELUclear glycine acid red cell elution kit.

RESULTS

We report a case of WAIHA induced by Babesia microti infection with an autoantibody with Jk^a specificity, originally believed to be a delayed hemolytic transfusion reaction, given the detection of an RBC antibody in close proximity to numerous RBC transfusions. Determination of autoantibody status with anti-Jk^a -like reactivity was only confirmed after Kidd antigen genotyping predicted expression of the Jk^a antigen.

DISCUSSION

Healthcare providers should be cognizant of the potential for babesiosis-induced WAIHA, particularly in individuals who continue to hemolyze despite undetectable parasitemia. Furthermore, this case highlights the possibility for warm autoantibodies to demonstrate Kidd antigen specificity. Though Kidd antigen variants are rare, antigen genotyping may be beneficial, particularly in the context of recent RBC transfusions, which typically preclude accurate serological phenotypic assessment.

Incidental Discovery of a Patient with the Bombay Phenotype

Bombay phenotype, an exceptionally rare blood type in individuals outside of Southeast Asia, occurs in approximately 1 in 1,000,000 individuals in Europe. This blood phenotype is characterized by the absence of the H antigen on red blood cells (RBCs) and in secretions. As the H antigen is the structure on which the ABO system is built, individuals lacking this antigen are unable to produce A or B antigens and appear as type O on routine ABO phenotyping. H deficiency does not cause ill effect; however, these individuals produce an anti-H alloantibody capable of causing severe acute hemolytic transfusion reactions when exposed to RBCs that express the H antigen. In this case study, we highlight the incidental discovery of a patient with Bombay phenotype in a North American hospital system, expected test results, the immunologic and genetic basis underlying the Bombay and para-Bombay phenotypes, and methods to ensure availability of compatible blood.

State of the Evidence: Drug Removal via Apheresis

Therapeutic apheresis refers to a diversity of procedures in which specific hematologic components (e.g., plasma, erythrocytes, leukocytes, etc.) with pathological associations are removed from circulation (with possible replacement) in order to treat a variety of disease processes. As pharmacologic agents also circulate with these components, their removal is sometimes incidental, or in the scenario of drug toxicity, a therapeutic goal. The corpus of published manuscripts on this subject has grown immensely over the past few decades; however, the breadth of diseases, methods, and drugs that co-exist in this space make it challenging to generate generalizable evidence regarding drug removal via apheresis. This review discusses factors worth considering when interpreting literature-reported data on drug removal by apheresis with examples from several notable studies and highlights topics in need of evidential improvement and growth as our palette of therapeutic agents continues to expand.

Assessment of polymicrobial interactions in bacterial isolates from transfused platelet units associated with sepsis

BACKGROUND

In 2019 the Centers for Disease Control and Prevention (CDC) reported a series of 4 transfusion reactions that resulted from contamination of apheresis platelet products. Products involved in all 4 cases were contaminated with Acinetobacter calcoaceticus-baumannii complex (ACBC) and in 3 products Staphylococcus saprophyticus was found as well. CDC investigation found that bacterial isolates from the cases were genetically related and suggested a common source of contamination. The contamination of blood products with ACBC is rare and polymicrobial contamination of blood products even less common. ACBC and S. saprophyticus have been observed to adhere to one another and sediment out of suspension in vitro, a process referred to as coaggregation, and we hypothesized that there was an interaction between the strains from these cases that contributed to their co-contamination of blood products.

STUDY DESIGN AND METHODS

To test the hypothesis of bacterial interaction, we performed coaggregation experiments and observed the growth characteristics of ACBC and S. saprophyticus strains recovered from contaminated blood products involved in a subset of the CDC cases.

RESULTS

An increase in S. saprophyticus CFU concentration was observed after several days of co-culture with ACBC in LB and plasma; however, no other findings suggested coaggregation or augmentative growth interaction between the bacterial strains.

CONCLUSION

Ultimately, an interaction between ACBC and S. saprophyticus that could help explain their co-occurrence and growth in contaminated platelet units was not found; however future studies of potential interactions may be warranted.

Procuring rare (しい)* Japanese red blood cell units for a bleeding patient with anti-K11 requiring a life-saving procedure

Alloimmunization to K11 is an extremely rare event. However, given the potential clinical significance of K11 alloantibodies, allocating antigen-negative red blood cell (RBC) units is a clinical necessity. In brief, we report a 39-year-old woman with multiple comorbidities including a right lower-extremity, below-the-knee amputation, who developed aggressive osteomyelitis associated with continuous bloody oozing, leading to anemia. To address these issues, the patient required extremity amputation. Surgery required addressing the concomitant critical anemia (hemoglobin <5 g/dL). However, with anti-K11 (in addition to anti-Jk^a) identified, no compatible units were immediately on hand and transfusing crossmatch-incompatible, antigen-positive units was deemed too high a risk. After a national search by the American Rare Donor Program (ARDP) was unsuccessful, the ARDP identified 2 irradiated, group O, K₀ (Kell_null), Jk(a-) RBC units in Japan that were predicted to be crossmatch-compatible with the patient's plasma. The units were successfully procured and infused, without evidence of adverse reactions, and the patient was able to safely undergo amputation to save her life. This case report reviews the complexities of anti-K11 detection and confirmation, as well as the processes by which K11- RBC units may be procured, which could help others in the global transfusion community should they be faced with similar challenging cases.

Automated analysers underestimate atypical basophil count in myeloid neoplasms

INTRODUCTION

Recent data suggest basophils can adopt an atypical appearance in myeloid disorders including myeloproliferative neoplasms (MPNs) and myeloproliferative/myelodysplastic disease. We hypothesized that automated analysers may not accurately quantitate basophils in myeloid neoplasms based on scatter properties. This study examined basophil counts and properties in myeloid disorders by automated cell analyser, manual differential, and flow cytometry.

METHODS

Patients with myeloid neoplasms and control patients with no myeloid disorder diagnosis at a tertiary care centre were identified. Basophil percentage was compared for automated analyser counts (Sysmex XN9000), manual differential, and flow cytometry. Basophil scatter properties in MPNs were examined using flow cytometry.

RESULTS

Thirty-one patients with myeloid neoplasms were included: 58% were male, mean age was 70.2 (±20.7) years, 32% had a diagnosis of chronic myeloid leukaemia with the remaining patients divided among various other forms of myeloid disease (including: essential thrombocythemia, polycythemia vera, unclassifiable MPN, myelodysplastic syndromes). For these patients, mean basophil percentage by automated analyser was significantly lower than manual differential (2.7 ± 2.9 vs. 7.1 ± 4.6, respectively, p < 0.001). No significant difference was found between automated versus manual differential for basophils in control subjects (p = 0.373). For myeloid neoplasm patients, mean basophil percentage was not significantly different between manual differential and flow cytometry (p = 0.116); mean basophil percentage by automated analyser was significantly lower than flow cytometry (2.7 ± 2.9 vs. 5.3 ± 3.7, respectively, p = 0.003).

CONCLUSION

Automated analysers underestimate basophil counts in patients with myeloid neoplasms. Manual differential and flow cytometry are recommended for more accurate quantitation and characterization of aberrant basophils.

Efficacy and Safety of COVID-19 Convalescent Plasma in Hospitalized Patients: A Randomized Clinical Trial

IMPORTANCE

There is clinical equipoise for COVID-19 convalescent plasma (CCP) use in patients hospitalized with COVID-19.

OBJECTIVE

To determine the safety and efficacy of CCP compared with placebo in hospitalized patients with COVID-19 receiving noninvasive supplemental oxygen.

DESIGN, SETTING, AND PARTICIPANTS

CONTAIN COVID-19, a randomized, double-blind, placebo-controlled trial of CCP in hospitalized adults with COVID-19, was conducted at 21 US hospitals from April 17, 2020, to March 15, 2021. The trial enrolled 941 participants who were hospitalized for 3 or less days or presented 7 or less days after symptom onset and required noninvasive oxygen supplementation.

INTERVENTIONS

A unit of approximately 250 mL of CCP or equivalent volume of placebo (normal saline).

MAIN OUTCOMES AND MEASURES

The primary outcome was participant scores on the 11-point World Health Organization (WHO) Ordinal Scale for Clinical Improvement on day 14 after randomization; the secondary outcome was WHO scores determined on day 28. Subgroups were analyzed with respect to age, baseline WHO score, concomitant medications, symptom duration, CCP SARS-CoV-2 titer, baseline SARS-CoV-2 serostatus, and enrollment quarter. Outcomes were analyzed using a bayesian proportional cumulative odds model. Efficacy of CCP was defined as a cumulative adjusted odds ratio (cOR) less than 1 and a clinically meaningful effect as cOR less than 0.8.

RESULTS

Of 941 participants randomized (473 to placebo and 468 to CCP), 556 were men (59.1%); median age was 63 years (IQR, 52-73); 373 (39.6%) were Hispanic and 132 (14.0%) were non-Hispanic Black. The cOR for the primary outcome adjusted for site, baseline risk, WHO score, age, sex, and symptom duration was 0.94 (95% credible interval [CrI], 0.75-1.18) with posterior probability (P[cOR<1] = 72%); the cOR for the secondary adjusted outcome was 0.92 (95% CrI, 0.74-1.16; P[cOR<1] = 76%). Exploratory subgroup analyses suggested heterogeneity of treatment effect: at day 28, cORs were 0.72 (95% CrI, 0.46-1.13; P[cOR<1] = 93%) for participants enrolled in April-June 2020 and 0.65 (95% CrI, 0.41 to 1.02; P[cOR<1] = 97%) for those not receiving remdesivir and not receiving corticosteroids at randomization. Median CCP SARS-CoV-2 neutralizing titer used in April to June 2020 was 1:175 (IQR, 76-379). Any adverse events (excluding transfusion reactions) were reported for 39 (8.2%) placebo recipients and 44 (9.4%) CCP recipients (P = .57). Transfusion reactions occurred in 2 (0.4) placebo recipients and 8 (1.7) CCP recipients (P = .06).

CONCLUSIONS AND RELEVANCE

In this trial, CCP did not meet the prespecified primary and secondary outcomes for CCP efficacy. However, high-titer CCP may have benefited participants early in the pandemic when remdesivir and corticosteroids were not in use.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04364737.

Autologous hematopoietic stem cell product contaminated with Salmonella due to occult salmonellosis in an asymptomatic donor

Recent advancements in infectious disease testing methods and pathogen reduction technologies have greatly reduced the incidence of microbial contamination of allogeneic blood products. Despite this significant reduction, contamination of autologous cellular therapy products remains a challenging issue, as many of these mitigation strategies are not feasible for such products. Most microorganisms isolated from cellular therapy products are Gram-positive normal skin flora, and studies have demonstrated that adverse effects are infrequent when these contaminated products are infused. However, no prior report has documented an autologous hematopoietic stem cell (HSC) or other cellular therapy product contaminated with Salmonella bacteria-a pathogenic Gram-negative organism. We present the first known case of Salmonella contaminating an HSC product secondary to occult salmonellosis in the donor, and discuss the implications of this contaminating organism and the therapeutic dilemma posed by this scenario.

Therapeutic plasma exchange for peripheral neuropathy associated with trisulfated heparan disaccharide IgM antibodies: A case series of 17 patients

BACKGROUND

Small fiber neuropathy (SFN) can be associated with autoantibodies, including those of IgM class with specificity for the trisulfated heparan disaccharide (TS-HDS) antigen. We hypothesized that, as an IgM autoantibody-mediated disorder, TS-HDS-associated SFN symptoms may be reduced with therapeutic plasma exchange (TPE).

STUDY METHODS

This was an observational analysis of all patients referred for TPE from 2018 to 2020 following laboratory confirmation of SFN with TS-HDS autoantibodies; a loading course of 3 to 5 procedures over 2 weeks was completed, with some patients returning for monthly procedures. The following data were collected: demographics, symptoms and duration, TS-HDS levels, skin biopsy results, reported responses to TPE, and TPE-associated adverse events.

RESULTS

Of the 17 subjects, 12 (71%) were female and the mean age was 57.5 years (range 27-94). The most common reported symptom was lower extremity paresthesia (88% of subjects). The mean number of TPE procedures completed per subject was 9 (range 3-18), with 71% (12/17) reporting symptomatic improvement or slowed disease progression. About 15% of procedures were associated with an adverse event, with vasovagal reactions being the most common; 53% of patients had at least one adverse event.

CONCLUSIONS

Given a reported symptomatic response rate of more than 70%, TPE may be a treatment option for individuals with autoimmune-mediated SFN associated with increased titers of TS-HDS IgM autoantibodies. Since TPE-associated adverse events appear common in this population, close monitoring during procedures is warranted.

Development of anti-Jk3 associated with silenced Kidd antigen expression and a novel single nucleotide variant of the JK gene

Anti-Jk3 is a rare alloantibody to a high-prevalence antigen primarily seen in individuals of Polynesian descent and is associated with a handful of well-established variants of the SLC14A1 gene. We report a case of the Jk_null phenotype, associated with formation of anti-Jk3, in a patient of non-Polynesian descent. This patient, a 51-year-old woman self-described as of Jamaican and Scottish ancestry, presented to our hospital for oncologic care. The patient's blood sample typed as blood group A, D+. All screening and panel reagent red blood cells showed reactivity, ranging from 2 to 4+; autocontrol and direct antiglobulin test were both negative. Antigen phenotyping revealed Jk(a-b-), leading to suspicion for anti-Jk3, which was subsequently confirmed by our immunohematology reference laboratory. Given her reported familial background, testing of the SLC14A1 gene was performed, revealing that the patient was heterozygous for the single nucleotide variant (SNV) at c.838G>A in exon 8 and therefore carries both JK*01 and JK*02 alleles that encode Jk^a and Jk^b, respectively. However, the patient was found to be heterozygous for several additional SNVs: c.28G>A in exon 3; c.191G>A, c.226G>A, and c.303G>A in exon 4; and c.757T>C in exon 7. The patient's Jk(b-) phenotype can be explained by coinheritance of c.838A with c.191G>A, which defines null allele JK*02N.09. Coinheritance of SNVs c.28G>A and c.838G with rare SNV c.757C that is predicted to cause a non-conservative amino acid change (p.S253P) likely accounts for the complete serologic absence of Jk^a and the ability to form anti-Jk3 in this case. This finding would represent a new JK*01 null allele. This evaluation illustrates the importance of genetic analysis in identifying the factors preventing a high-prevalence antigen from being expressed, particularly when discovered outside of an expected racial or ethnic group.

Anti-Jk3 is a rare alloantibody to a high-prevalence antigen primarily seen in individuals of Polynesian descent and is associated with a handful of well-established variants of the SLC14A1 gene. We report a case of the Jk_null phenotype, associated with formation of anti-Jk3, in a patient of non-Polynesian descent. This patient, a 51-year-old woman self-described as of Jamaican and Scottish ancestry, presented to our hospital for oncologic care. The patient’s blood sample typed as blood group A, D+. All screening and panel reagent red blood cells showed reactivity, ranging from 2 to 4+; autocontrol and direct antiglobulin test were both negative. Antigen phenotyping revealed Jk(a–b–), leading to suspicion for anti-Jk3, which was subsequently confirmed by our immunohematology reference laboratory. Given her reported familial background, testing of the SLC14A1 gene was performed, revealing that the patient was heterozygous for the single nucleotide variant (SNV) at c.838G>A in exon 8 and therefore carries both JK*01 and JK*02 alleles that encode Jk^a and Jk^b, respectively. However, the patient was found to be heterozygous for several additional SNVs: c.28G>A in exon 3; c.191G>A, c.226G>A, and c.303G>A in exon 4; and c.757T>C in exon 7. The patient’s Jk(b–) phenotype can be explained by coinheritance of c.838A with c.191G>A, which defines null allele JK*02N.09. Coinheritance of SNVs c.28G>A and c.838G with rare SNV c.757C that is predicted to cause a non-conservative amino acid change (p.S253P) likely accounts for the complete serologic absence of Jk^a and the ability to form anti-Jk3 in this case. This finding would represent a new JK*01 null allele. This evaluation illustrates the importance of genetic analysis in identifying the factors preventing a high-prevalence antigen from being expressed, particularly when discovered outside of an expected racial or ethnic group.

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.

Early but not late convalescent plasma is associated with better survival in moderate-to-severe COVID-19

BACKGROUND

Limited therapeutic options exist for coronavirus disease 2019 (COVID-19). COVID-19 convalescent plasma (CCP) is a potential therapeutic, but there is limited data for patients with moderate-to-severe disease.

RESEARCH QUESTION

What are outcomes associated with administration of CCP in patients with moderate-to-severe COVID-19 infection?

STUDY DESIGN AND METHODS

We conducted a propensity score-matched analysis of patients with moderate-to-severe COVID-19. The primary endpoints were in-hospital mortality. Secondary endpoints were number of days alive and ventilator-free at 30 days; length of hospital stay; and change in WHO scores from CCP administration (or index date) to discharge. Of 151 patients who received CCP, 132 had complete follow-up data. Patients were transfused after a median of 6 hospital days; thus, we investigated the effect of convalescent plasma before and after this timepoint with 77 early (within 6 days) and 55 late (after 6 days) recipients. Among 3,217 inpatients who did not receive CCP, 2,551 were available for matching.

RESULTS

Early CCP recipients, of whom 31 (40%) were on mechanical ventilation, had lower 14-day (15% vs 23%) and 30-day (38% vs 49%) mortality compared to a matched unexposed cohort, with nearly 50% lower likelihood of in-hospital mortality (HR 0.52, [95% CI 0.28-0.96]; P = 0.036). Early plasma recipients had more days alive and ventilator-free at 30 days (+3.3 days, [95% CI 0.2 to 6.3 days]; P = 0.04) and improved WHO scores at 7 days (-0.8, [95% CI: -1.2 to -0.4]; P = 0.0003) and hospital discharge (-0.9, [95% CI: -1.5 to -0.3]; P = 0.004) compared to the matched unexposed cohort. No clinical differences were observed in late plasma recipients.

INTERPRETATION

Early administration of CCP improves outcomes in patients with moderate-to-severe COVID-19, while improvement was not observed with late CCP administration. The importance of timing of administration should be addressed in specifically designed trials.

Clinical Laboratory Biosafety Gaps: Lessons Learned from Past Outbreaks Reveal a Path to a Safer Future

Patient care and public health require timely, reliable laboratory testing. However, clinical laboratory professionals rarely know whether patient specimens contain infectious agents, making ensuring biosafety while performing testing procedures challenging. The importance of biosafety in clinical laboratories was highlighted during the 2014 Ebola outbreak, where concerns about biosafety resulted in delayed diagnoses and contributed to patient deaths. This review is a collaboration between subject matter experts from large and small laboratories and the federal government to evaluate the capability of clinical laboratories to manage biosafety risks and safely test patient specimens. We discuss the complexity of clinical laboratories, including anatomic pathology, and describe how applying current biosafety guidance may be difficult as these guidelines, largely based on practices in research laboratories, do not always correspond to the unique clinical laboratory environments and their specialized equipment and processes. We retrospectively describe the biosafety gaps and opportunities for improvement in the areas of risk assessment and management; automated and manual laboratory disciplines; specimen collection, processing, and storage; test utilization; equipment and instrumentation safety; disinfection practices; personal protective equipment; waste management; laboratory personnel training and competency assessment; accreditation processes; and ethical guidance. Also addressed are the unique biosafety challenges successfully handled by a Texas community hospital clinical laboratory that performed testing for patients with Ebola without a formal biocontainment unit. The gaps in knowledge and practices identified in previous and ongoing outbreaks demonstrate the need for collaborative, comprehensive solutions to improve clinical laboratory biosafety and to better combat future emerging infectious disease outbreaks.

Behind the scenes with basophils: an emerging therapeutic target

Though basophils were originally viewed as redundant blood ‘mast cells’, the implementation of flow cytometry has established basophils as unique leukocytes with critical immunomodulatory functions. Basophils play an active role in allergic inflammation, autoimmunity, and hematological malignancies. They are distinguishable from other leukocytes by their characteristic metachromatic deep-purple cytoplasmic, round granules. Mature basophils are phenotypically characterized by surface expression of IL-3Rα (CD123); IL-3 drives basophil differentiation, degranulation, and synthesis of inflammatory mediators including type 2 cytokines. Basophil degranulation is the predominant source of histamine in peripheral blood, promoting allergic responses. Basophils serve as a bridge between innate and adaptive immunity by secreting IL-4 which supports eosinophil migration, monocyte differentiation into macrophages, B-cell activation, and CD4 T-cell differentiation into Th2 cells. Further, basophilia is a key phenomenon in myeloid neoplasms, especially chronic myeloid leukemia (CML) for which it is a diagnostic criterion. Increased circulating basophils, often with aberrant immunophenotype, have been detected in patients with CML and other myeloproliferative neoplasms (MPNs). The significance of basophils’ immunoregulatory functions in malignant and non-malignant diseases is an active area of research. Ongoing and future research can inform the development of immunotherapies that target basophils to impact allergic, autoimmune, and malignant disease states. This review article aims to provide an overview of basophil biology, identification strategies, and roles and dysregulation in diseases.

Evaluation of Positive B- and T-Cell Gene Rearrangement Studies in Patients With Negative Morphology, Flow Cytometry, and Immunohistochemistry

CONTEXT.—

The significance of positive immunoglobulin (IG) or T-cell receptor (TCR) gene rearrangement studies in the context of otherwise normal ancillary findings is unknown.

OBJECTIVE.—

To examine long-term hematologic outcomes of individuals with positive gene rearrangement studies with otherwise unremarkable blood or bone marrow studies in parallel.

DESIGN.—

Data from patients who underwent IG or TCR gene rearrangement testing at the authors' affiliated Veterans Affairs Hospital January 1, 2013 to July 6, 2018 were extracted from medical records. Date of testing, specimen source, and morphologic, flow cytometric, immunohistochemical, and cytogenetic characterization of the tissue source were recorded. Gene rearrangement results were categorized as test positive/phenotype positive (T+/P+), test positive/phenotype negative (T+/P-), test negative/phenotype negative (T-/P-), or test negative/phenotype positive (T-/P+) based on comparison to other studies and/or final diagnosis. Patient records were reviewed for subsequent diagnosis of hematologic malignancy for patients with positive gene rearrangements but no other evidence for a disease process.

RESULTS.—

A total of 136 patients with 203 gene rearrangement studies were analyzed. For TCR studies, there were 2 T+/P- and 1 T-/P+ results in 47 peripheral blood assays, as well as 7 T+/P- and 1 T-/P+ results in 54 bone marrow assays. Regarding IG studies, 3 T+/P- and 12 T-/P+ results in 99 bone marrow studies were identified. None of the 12 patients with T+/P- TCR or IG gene rearrangement studies later developed a lymphoproliferative disorder.

CONCLUSIONS.—

Positive IG/TCR gene rearrangement studies in the context of otherwise negative bone marrow or peripheral blood findings are not predictive of lymphoproliferative disorders.

Optimization of repeat plerixafor dosing for autologous peripheral blood stem-cell collection

INTRODUCTION

Peripheral CD34+ cells may be mobilized using filgrastim alone or in combination with chemotherapy. The addition of plerixafor can be efficacious, though guidelines for repeat dosing are lacking.

MATERIAL AND METHODS

This quality improvement project was initiated to generate guidelines for repeat plerixafor dosing after retrospective evaluation of data in adult patients undergoing autologous peripheral blood stem cell mobilization and collection.

RESULTS

Analysis included 195 patients: 119 (61 %) with multiple myeloma and 76 (39 %) with lymphoma. Patients given at least one dose of plerixafor (n = 109) were further divided: Group 1) (A) goal of 3 × 10E6/kg and day 1 peripheral blood CD34+ count < 30 × 10E6/L, vs (B) ≥ 30 × 10 E6/L; Group 2) (A) goal of 6 × 10E6/kg and day 1 peripheral blood CD34+ count < 50 × 10E6/L or < 50 % of collection goal after day 1, vs (B) ≥ 50 % of collection goal after day 1. Ninety five percent of cases in Group 1B and 88 % of cases in Group 2B did not receive additional plerixafor doses and all of them achieved their collection goals. In contrast, those in Groups 1A and 2A required additional plerixafor dosing and some mobilizations/collections were futile.

CONCLUSION

Based on these data, with consideration of collection goal, peripheral blood CD34+ count, and CD34+ cell bag count on collection day 1, we have generated institutional guidelines for collection initiation and repeat plerixafor dosing. Long term, we predict these guidelines will optimize pharmacy, apheresis, and stem cell processing resources while improving the patient experience.

The Development and Implementation of a Novel Electronic Consult System by a Laboratory Medicine Service: Experience From the First 2 Years of Use

CONTEXT.—

A novel electronic consult (e-consult) system for a pathology and laboratory medicine service (PLMS) was implemented in 2015 at a high-complexity Veterans Administration health care facility. Consults were previously made through direct provider communication without documentation in the medical record.

OBJECTIVE.—

To evaluate the utilization trends of the laboratory e-consult system at the Department of Veterans Affairs Connecticut facility during the first 2 years since inception.

DESIGN.—

E-consultation involves pathology and laboratory medicine resident review followed by attending pathologist review and cosignature. E-consults to the pathology and laboratory medicine service from 2015 to 2017 were reviewed to record type of consult, requesting department, patient location, and turnaround time.

RESULTS.—

The pathology and laboratory medicine service received 351 e-consults from 2015 to 2017. The volume varied by subsection: hematology and coagulation (215 of 351; 61%), chemistry (109 of 351; 31%), blood bank (19 of 351; 6%), and microbiology/virology (8 of 351; 2%). Hematology and coagulation consults were entirely for peripheral blood smear review (215 of 215; 100%). Chemistry consults were placed for toxicology/drugs of abuse (81 of 109; 74%), test utilization (17 of 109; 16%), or nontoxicology (11 of 109; 10%). Three services placed the majority of consults: primary care (279 of 351; 80%), hematology/oncology (39 of 351; 11%), and psychiatry (27 of 351; 8%). The median turnaround time for completion of e-consults was 1.2 days. Since e-consult implementation, the mean number of consults increased from 8.6/mo in 2015 to 18.1/mo in 2017, peaking in the last quarter of analysis in 2017 with a mean of 25.3 consults/mo.

CONCLUSIONS.—

This novel e-consult system improved accessibility to and documentation of answers to laboratory questions and increased the visibility of the pathology and laboratory medicine service. Future goals include development of outcomes-based measures to better assess the clinical impact of e-consults.

The utility and limitations of B- and T-cell gene rearrangement studies in evaluating lymphoproliferative disorders

A hallmark of lymphoid malignancies is the presence of a monoclonal lymphocyte population. Monoclonality of B- and T-cell populations can be established through immunoglobulin (IG) or T-cell receptor (TCR) gene rearrangement analysis, respectively. The biological rationale of IG and TCR gene rearrangement analysis is that due to the extensive combinatorial repertoire made possible by V(D)J recombination in lymphocytes, it is unlikely that any substantive lymphocyte population would share the same IG or TCR gene rearrangement pattern unless there is an underlying neoplastic or reactive origin. Modern IG and TCR gene rearrangement analysis is typically performed by polymerase chain reaction (PCR) using commercially available primer sets followed by gel capillary electrophoresis. This process is highly sensitive in the detection of nearly all lymphoid malignancies. Several pitfalls and limitations, both biological and technical, apply to IG/TCR gene rearrangement analysis, but these can be minimised with high quality controls, performance of assays in duplicate, and adherence to strict criteria for interpreting and reporting results. Next generation sequencing (NGS) will likely replace PCR based methods of IG/TCR gene rearrangement analysis but is not yet widespread due to the absence of standardised protocols and multicentre validation.

Factor V activity in apheresis platelets: Implications for management of FV deficiency

BACKGROUND

Allogeneic platelet (PLT) infusion is a strategy to raise Factor V (FV) levels in patients with congenital FV deficiency. However, since FV is labile in vitro, we hypothesized that FV activity could be low in PLT units.

STUDY DESIGN AND METHODS

FV activity was tested using a prothrombin time-based platform in the supernatant and platelet lysate (PL) of apheresis PLT units (16 units stored in PLT additive solution with acetate and phosphate [PAS-C] and 10 units stored in plasma only), on post-collection days 3-6. Statistical analysis was performed using Student's t test (P < .05).

RESULTS

FV activity was severely diminished in PAS-C PLTs (N = 16) supernatant (3.70% ± 1.02%) and PL (3.26% ± 1.02%). FV activity in plasma-only PLTs (N = 10) was lower in both supernatant (44.55% ± 6.46%) and lysate (39.67% ± 6.33%) relative to normal plasma levels, but both were significantly higher (P < .0001) compared to PAS-C PLTs. In a separate set of experiments, FV activity in PAS-C PLTs examined serially over storage time (N = 3 for these experiments) showed that FV levels were reduced by day 3 and not significantly different by day 5 of storage (Day 3 supernatant 5.03% ± 1.41%; Day 5 supernatant: 3.10% ± 0.57%; P = .2; Day 3 lysate: 3.89% ± 1.03%; Day 5 lysate: 2.61% ± 0.41%; P = .4).

CONCLUSION

Plasma should be considered over PLTs as first-line therapy for non-complex FV deficiency-associated hemorrhage. If PLTs are considered for transfusion, plasma-only PLT units should be preferentially utilized, as PAS-C PLT have near-absent FV activity.

Monocytic Acute Myeloid Leukemias with KM2TA Translocations to Chromosome 17q that May Clinically Mimic Acute Promyelocytic Leukemia

OBJECTIVE

Acute promyelocytic leukemia (APL) with variant RARA translocation, eg, t(11;17), is not sensitive to all-trans retinoic acid and requires distinct chemotherapy. However, there are some leukemic entities that may mimic aspects of the clinical and/or laboratory picture of APL and cause confusion because of karyotype nomenclature. Therefore, recognition of such entities may be of therapeutic and prognostic significance.

METHODS

We present 2 cases of acute myeloid leukemia (AML) with t(11;17) that were clinically concerning for APL based primarily on clinical presentation but were ultimately diagnosed as AML with monocytic differentiation.

RESULTS

Both leukemias harbored KMT2A translocations, one located near but not involving RARA and the other with SEPT9.

CONCLUSION

In leukemias that clinically and/or immunophenotypically mimic APL, identification of specific gene translocations can lead to the correct diagnosis and may carry therapeutic/prognostic implications.

Immunohematologic aspects of alloimmunization and alloantibody detection: A focus on pregnancy and hemolytic disease of the fetus and newborn

Alloimmunization to non-ABO, red blood cell (RBC) antigens remains one of the most clinically-relevant complexities faced by blood banking practitioners. In the setting of transfusion therapy, these antibodies raise risks for incompatibilities, while for pregnant patients they can mediate deadly forms of hemolytic disease of the fetus and newborn. As such, a thorough understanding of pathways that lead to alloimmunization, as well as the tools used by blood banks to detect alloantibodies, is critical to transfusion practice. In this review, in which alloimmunization in the setting of pregnancy will be emphasized, we will review: 1) the clinical impacts of RBC alloantibodies in the peri-partum period; 2) the current pathophysiologic mechanisms thought to influence non-ABO antigen alloimmunization; 3) the strengths and weaknesses of laboratory tools used in aiding alloimmunization detection; and 4) future directions of the transfusion community related to alloimmunization impacting pregnancy.

Fc Gamma Receptors and Complement Component 3 Facilitate Anti-fVIII Antibody Formation

Anti-factor VIII (fVIII) alloantibodies, which can develop in patients with hemophilia A, limit the therapeutic options and increase morbidity and mortality of these patients. However, the factors that influence anti-fVIII antibody development remain incompletely understood. Recent studies suggest that Fc gamma receptors (FcγRs) may facilitate recognition and uptake of fVIII by recently developed or pre-existing naturally occurring anti-fVIII antibodies, providing a mechanism whereby the immune system may recognize fVIII following infusion. However, the role of FcγRs in anti-fVIII antibody formation remains unknown. In order to define the influence of FcγRs on the development of anti-fVIII antibodies, fVIII was injected into WT or FcγR knockout recipients, followed by evaluation of anti-fVIII antibodies. Anti-fVIII antibodies were readily observed following fVIII injection into FcγR knockouts, with similar anti-fVIII antibody levels occurring in FcγR knockouts as detected in WT mice injected in parallel. As antibodies can also fix complement, providing a potential mechanism whereby anti-fVIII antibodies may influence anti-fVIII antibody formation independent of FcγRs, fVIII was also injected into complement component 3 (C3) knockout recipients in parallel. Similar to FcγR knockouts, C3 knockout recipients developed a robust response to fVIII, which was likewise similar to that observed in WT recipients. As FcγRs or C3 may compensate for each other in recipients only deficient in FcγRs or C3 alone, we generated mice deficient in both FcγRs and C3 to test for potential antibody effector redundancy in anti-fVIII antibody formation. Infusion of fVIII into FcγRs and C3 (FcγR × C3) double knockouts likewise induced anti-fVIII antibodies. However, unlike individual knockouts, anti-fVIII antibodies in FcγRs × C3 knockouts were initially lower than WT recipients, although anti-fVIII antibodies increased to WT levels following additional fVIII exposure. In contrast, infusion of RBCs expressing distinct alloantigens into FcγRs, C3 or FcγR × C3 knockout recipients either failed to change anti-RBC levels when compared to WT recipients or actually increased antibody responses, depending on the target antigen. Taken together, these results suggest FcγRs and C3 can differentially impact antibody formation following exposure to distinct alloantigens and that FcγRs and C3 work in concert to facilitate early anti-fVIII antibody formation.