Hemoglobin A clearance in children with sickle cell anemia on chronic transfusion therapy

Survival of transfused red blood cells from a donor with alpha-thalassemia trait in a recipient with sickle cell disease

BACKGROUND

Post-transfusion survival of donor red blood cells (RBCs) is important for effective chronic transfusion therapy in conditions including sickle cell disease (SCD). Biotin labeling RBCs allows direct in vivo measurement of multiple donor RBC units simultaneously post-transfusion.

STUDY DESIGN AND METHODS

In an observational trial of patients with SCD receiving monthly chronic transfusion therapy, aliquots of RBCs from one transfusion episode were biotin-labeled and infused along with the unlabeled RBC units. Serial blood samples were obtained to measure RBC survival. Donor units were tested for RBC indices, hemoglobin fractionation, and glucose-6-phosphate dehydrogenase (G6PD) enzyme activity. For microcytic donor RBCs (MCV < 70 fL), HBA1 and HBA2 genetic testing was performed on whole blood.

RESULTS

We present one recipient, a pediatric patient with SCD and splenectomy who received two RBC units with aliquots from each unit labeled at distinct biotin densities (2 and 18 μg/mL biotin). One donor unit was identified to have microcytosis (MCV 68.5 fL after biotinylation); whole blood sample obtained at a subsequent donation showed 2-gene deletion alpha-thalassemia trait (ɑ-3.7kb/ɑ-3.7kb) and normal serum ferritin. G6PD activity was >60% of normal mean for both. The RBCs with alpha-thalassemia RBC had accelerated clearance and increased surface phosphatidylserine post-transfusion, as compared with the normocytic RBC (half life 65 vs. 86 days, respectively).

DISCUSSION

Post-transfusion RBC survival may be lower for units from donors with alpha-thalassemia trait, although the impact of thalassemia trait donors on transfusion efficacy requires further study.

Post-transfusion biotin-labeled red blood cell survival studies in pediatric sickle cell disease with antibodies of uncertain significance

BACKGROUND

Red blood cell (RBC) antibodies are common in multiply transfused patients with sickle cell disease (SCD). Unlike RBC alloantibodies, the potential of autoantibodies to cause post-transfusion hemolysis may be uncertain. Biotin-labeling provides a direct measurement of red cell survival (RCS) over time, thus can be used to assess the clinical significance of RBC antibodies. Antibodies to biotinylated RBC (B-RBC) occasionally are detected after exposure, which may impact B-RBC survival in subsequent RCS studies.

STUDY DESIGN AND METHODS

Pediatric patients with SCD receiving monthly chronic transfusions underwent RCS studies, receiving aliquots of allogeneic RBC labeled at distinct densities of biotin (2-18 μg/mL). B-RBC survival was followed for 4 months post-transfusion, and B-RBC antibody screening for 6 months. Patients with warm autoantibodies (WAA) or B-RBC antibodies are reported here.

RESULTS

RBC antibodies were detected during RCS in four patients: one with WAA, one with WAA followed by B-RBC-specific antibodies, and two with transient B-RBC antibodies within the first 5 weeks of exposure. B-RBC half-lives (T50) ranged 37.6-61.7 days (mean 47.8 days). There was no evidence of increased hemolysis or accelerated B-RBC clearance in the presence of WAA or B-RBC antibodies.

DISCUSSION

Biotinylation of allogenic RBC can be used to assess the possible effects of RBC antibodies on transfusion survival in individual cases, particularly when it is uncertain if the detected antibodies may result in hemolysis. In the cases presented here, neither WAA nor B-RBC antibodies were associated with significant shortening of B-RBC survival in individuals with SCD.

Novel approaches to measure transfusion effectiveness

PURPOSE OF REVIEW

This review encompasses different considerations of transfusion effectiveness based upon clinical scenario and transfusion indication. Tissue oxygenation, cerebral metabolic oxygen use, and red blood cell (RBC) survival are important elements of transfusion effectiveness in individuals with acute and chronic transfusion requirements.

RECENT FINDINGS

Noninvasive measures of tissue and cerebral oxygen extraction include near-infrared spectroscopy (NIRS) and specialized MRI sequences. RBC survival timepoints including 24 h posttransfusion recovery, 50% recovery timepoint, and mean potential lifespan may be accurately measured with biotin-labeling of RBC prior to transfusion. Labeling at different cell surface densities allows survival of multiple RBC populations to be determined.

SUMMARY

Although past trials of optimal transfusion thresholds have focused on Hb as a singular marker for transfusion needs, measures of oxygenation (via NIRS or specialized MRI) and RBC survival (via biotin labeling) provide the opportunity to personalize transfusion decisions to individual patient's acute health needs or chronic transfusion goals.

Optimizing RBC Transfusion Outcomes in Patients with Acute Illness and in the Chronic Transfusion Setting

Red blood cell (RBC) transfusion is a common clinical intervention used to treat patients with acute and chronic anemia. The decision to transfuse RBCs in the acute setting is based on several factors but current clinical studies informing optimal RBC transfusion decision making (TDM) are largely based upon hemoglobin (Hb) level. In contrast to transfusion in acute settings, chronic RBC transfusion therapy has several different purposes and is associated with distinct transfusion risks such as iron overload and RBC alloimmunization. Consequently, RBC TDM in the chronic setting requires optimizing the survival of transfused RBCs in order to reduce transfusion exposure over the lifespan of an individual and the associated transfusion complications mentioned. This review summarizes the current medical literature addressing optimal RBC-TDM in the acute and chronic transfusion settings and discusses the current gaps in knowledge which need to be prioritized in future national and international research initiatives.

Measurement of post-transfusion red blood cell survival kinetics in sickle cell disease and β-Thalassemia: A biotin label approach

BACKGROUND

Red blood cell (RBC) transfusions are an important treatment modality for patients with sickle cell disease (SCD) and β-thalassemia. A subgroup of these patients relies on a chronic RBC transfusion regimen. Little is known about RBC survival (RCS) of the transfused allogeneic RBCs. In this study, we aimed to study the RCS kinetics of transfused RBCs in SCD and β-thalassemia and to investigate factors that determine RCS.

METHODS AND MATERIALS

We performed a prospective cohort study on fourteen adults with SCD and β-thalassemia disease receiving a chronic transfusion regimen. RCS and the influence of donor and patient characteristics on RCS were assessed by simultaneous transfusion of two allogeneic RBCs using RBC biotinylation. Phenotyping of well-known RBC markers over time was performed using flow cytometry.

RESULTS

RCS of the two transfused RBC units was similar in most patients. Although intra-individual variation was small, inter-individual variation in RCS kinetics was observed. Most patients demonstrated a non-linear trend in RCS that was different from the observed linear RCS kinetics in healthy volunteers. After an initial slight increase in the proportion of biotinylated RBCs during the first 24 h, a rapid decrease within the first 10-12 days was followed by a slower clearance rate.

CONCLUSION

These are the first data to demonstrate that patient-related factors largely determine post-transfusion RCS behavior of donor RBC in SCD and β-thalassemia, while donor factors exert a negligible effect. Further assessment and modeling of RCS kinetics and its determinants in SCD and β-thalassemia patients may ultimately improve transfusion therapy.

Glucose-6-phosphate dehydrogenase deficiency is more prevalent in Duffy-null red blood cell transfusion in sickle cell disease

BACKGROUND

Resistance to malaria infection may be conferred by erythrocyte genetic variations including glucose-6-phosphate dehydrogenase (G6PD) deficiency and lack of Duffy antigens. In red blood cell (RBC) transfusion, G6PD deficiency may shorten transfusion survival. Because Duffy-null units are commonly transfused in sickle cell disease (SCD) due to antigen matching protocols, we examined whether Duffy-null donor RBC units have a higher prevalence of G6PD deficiency.

MATERIALS AND METHODS

Pediatric patients with SCD on chronic transfusion therapy were followed prospectively for multiple transfusions. RBC unit segments were collected to measure G6PD activity and RBC genotyping. The decline in donor hemoglobin (ΔHbA) following transfusion was assessed from immediate posttransfusion estimates and HbA measurements approximately 1 month later.

RESULTS

Of 564 evaluable RBC units, 59 (10.5%) were G6PD deficient (23 severe, 36 moderate deficiency); 202 (37.6%) units were Duffy-null. G6PD deficiency occurred in 40 (19.8%) Duffy-null units versus 15 (4.5%) Duffy-positive units (p < .0001). In univariate analysis, the fraction of Duffy-null RBC units per transfusion was associated with greater decline in HbA (p = .038); however, in multivariate analysis, severe G6PD deficiency (p = .0238) but not Duffy-null RBC (p = .0139) were associated with ΔHbA.

CONCLUSION

Selection of Duffy-null RBC units may result in shorter in vivo survival of transfused RBCs due to a higher likelihood of transfusing units from G6PD deficient donors.

Marginal zone B cells mediate a CD4 T-cell-dependent extrafollicular antibody response following RBC transfusion in mice

Red blood cell (RBC) transfusions can result in alloimmunization toward RBC alloantigens that can increase the probability of complications following subsequent transfusion. An improved understanding of the immune mechanisms that underlie RBC alloimmunization is critical if future strategies capable of preventing or even reducing this process are to be realized. Using the HOD (hen egg lysozyme [HEL] and ovalbumin [OVA] fused with the human RBC antigen Duffy) model system, we aimed to identify initiating immune factors that may govern early anti-HOD alloantibody formation. Our findings demonstrate that HOD RBCs continuously localize to the marginal sinus following transfusion, where they colocalize with marginal zone (MZ) B cells. Depletion of MZ B cells inhibited immunoglobulin M (IgM) and IgG anti-HOD antibody formation, whereas CD4 T-cell depletion only prevented IgG anti-HOD antibody development. HOD-specific CD4 T cells displayed similar proliferation and activation following transfusion of HOD RBCs into wild-type or MZ B-cell-deficient recipients, suggesting that IgG formation is not dependent on MZ B-cell-mediated CD4 T-cell activation. Moreover, depletion of follicular B cells failed to substantially impact the anti-HOD antibody response, and no increase in antigen-specific germinal center B cells was detected following HOD RBC transfusion, suggesting that antibody formation is not dependent on the splenic follicle. Despite this, anti-HOD antibodies persisted for several months following HOD RBC transfusion. Overall, these data suggest that MZ B cells can initiate and then contribute to RBC alloantibody formation, highlighting a unique immune pathway that can be engaged following RBC transfusion.

Antigen density dictates RBC clearance, but not antigen modulation, following incompatible RBC transfusion in mice

Incompatible red blood cell (RBC) transfusion can result in life-threatening transfusion complications that can be challenging to manage in patients with transfusion-dependent anemia. However, not all incompatible RBC transfusions result in significant RBC removal. One factor that may regulate the outcome of incompatible RBC transfusion is the density of the incompatible antigen. Despite the potential influence of target antigen levels during incompatible RBC transfusion, a model system capable of defining the role of antigen density in this process has not been developed. In this study, we describe a novel model system of incompatible transfusion using donor mice that express different levels of the KEL antigen and recipients with varying anti-KEL antibody concentrations. Transfusion of KEL+ RBCs that express high or moderate KEL antigen levels results in rapid antibody-mediated RBC clearance. In contrast, relatively little RBC clearance was observed following the transfusion of KEL RBCs that express low KEL antigen levels. Intriguingly, unlike RBC clearance, loss of the KEL antigen from the transfused RBCs occurred at a similar rate regardless of the KEL antigen density following an incompatible transfusion. In addition to antigen density, anti-KEL antibody levels also regulated RBC removal and KEL antigen loss, suggesting that antigen density and antibody levels dictate incompatible RBC transfusion outcomes. These results demonstrate that antibody-induced antigen loss and RBC clearance can occur at distinct antigen density thresholds, providing important insight into factors that may dictate the outcome of an incompatible RBC transfusion.

The impact of pre-existing HLA and red blood cell antibodies on transfusion support and engraftment in sickle cell disease after nonmyeloablative hematopoietic stem cell transplantation from HLA-matched sibling donors: A prospective, single-center, observational study

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is curative for patients with sickle cell disease (SCD). Prior to HSCT, patients with SCD commonly receive RBC transfusions with some becoming RBC or HLA alloimmunized. This alloimmunization may impact post-HSCT transfusion requirements and donor engraftment.

METHODS

The study population included patients with SCD transplanted on a single-center nonmyeloablative, HLA-matched sibling HSCT trial at the National Heart, Lung, and Blood Institute (NHLBI) who had a pre-HSCT sample available for HLA class I antibody testing. We evaluated transfusion requirements and engraftment outcomes comparing patients with and without pre-existing HLA and RBC antibodies.

FINDINGS

Of 36 patients studied, 10 (28%) had HLA class I antibodies and 11 (31%) had a history of RBC alloantibodies. Up to day +45 post-HSCT, patients with HLA antibodies received more platelet transfusions (median 2.5 vs 1, p = 0.042) and those with RBC alloantibodies received more RBC units (median 7 vs 4, p = 0.0059) compared to respective non-alloimmunized patients. HLA alloimmunization was not associated with neutrophil engraftment, donor chimerism, or graft rejection. However, RBC alloimmunization correlated with a decreased donor T cell chimerism at 1 year (median 24% vs 55%, p = 0.035).

INTERPRETATION

Pre-existing HLA and RBC alloantibodies are clinically significant for patients undergoing HLA-matched nonmyeloablative HSCT. Testing for both HLA and RBC antibodies is important to help estimate transfusion needs peri‑HSCT. The association of lower donor T cell chimerism and pre-existing RBC alloantibodies needs further investigation.

FUNDING

NIH Clinical Center and NHLBI Intramural Research Program (Z99 CL999999, HL006007-11) and the Thrasher Research Fund.

Examining the Role of Complement in Predicting, Preventing, and Treating Hemolytic Transfusion Reactions

Red blood cell (RBC) transfusion is a critical component of optimal management for a broad range of conditions. Regardless of the indication, pretransfusion testing is required to appropriately match RBC donors and recipients to provide immunologically compatible blood. Although this approach is effective in the vast majority of situations, occasionally, patients will inadvertently receive an incompatible RBC transfusion, which can result in a hemolytic transfusion reaction (HTR). In addition, patients with life-threatening anemia and a complex alloantibody profile, which precludes rapid procurement of compatible RBCs, may also receive incompatible RBCs, placing them at risk for an HTR. Despite the rarity of these clinical situations, when incompatible blood transfusion results in an HTR, the consequences can be devastating. In this review, we will explore the challenges associated with actively preventing and treating acute HTRs following incompatible RBC transfusion. In doing so, we will focus primarily on the role of complement, not only as a key player in HTRs, but also as a potential target for the prevention and treatment of HTRs.

Challenges in preventing and treating hemolytic complications associated with red blood cell transfusion

Red blood cell (RBC) transfusion support represents a critical component of sickle cell disease (SCD) management. However, as with any therapeutic intervention, RBC transfusion is not without risk. Repeat exposure to allogeneic RBCs can result in the development of RBC alloantibodies that can make it difficult to find compatible RBCs for future transfusions and can directly increase the risk of developing acute or delayed hemolytic transfusion reactions, which can be further complicated by hyperhemolysis. Several prophylactic and treatment strategies have been employed in an effort to reduce or prevent hemolytic transfusion reactions. However, conflicting data exist regarding the efficacy of many of these approaches. We will explore the challenges associated with predicting, preventing and treating different types of hemolytic transfusion reactions in patients with SCD in addition to describing future strategies that may aid in the management of the complex transfusion requirements of SCD patients.

Challenges in the treatment and prevention of delayed hemolytic transfusion reactions with hyperhemolysis in sickle cell disease patients

BACKGROUND

Delayed hemolytic transfusion reactions (DHTRs) are serious complications of RBC transfusion that can occur in previously alloimmunized patients. Patients who require episodic transfusions during heightened inflammatory states, such as patients with sickle cell disease (SCD), are particularly prone to alloimmunization and developing DHTRs with hyperhemolysis. While efforts to mitigate these hemolytic episodes via immunosuppressive drugs can be employed, the relative efficacy of various treatment options remains incompletely understood.

CASE REPORTS

In this study, we explored five patients with SCD and multiple RBC alloantibodies who received various forms of immunosuppressive therapy in an attempt to prevent or treat severe DHTRs.

RESULTS

The clinical course for these five patients provides insight into the difficulty of effectively treating and preventing DHTRs in patients with SCD with currently available immunosuppressive therapies.

CONCLUSION

Based on our experience, and the current literature, it is difficult to predict the potential impact of various immunosuppressive therapies when seeking to prevent or treat DHTRs. Future mechanistic studies are needed to identify the optimal treatment options for DHTRs in the presence or absence of distinct alloantibodies in patients with SCD.

Coexpression network analysis of platelet genes in sickle cell disease

Platelets play important roles in vascular health. Activation of platelet may contribute to coagulation and inflammation. Evidence suggests circulating platelets are chronically activated in sickle cell disease (SCD) patients with steady state and further activated in vaso-occlusive crisis. However, the molecular basis of sickle platelet dysfunction remains obscure. Here, we used weighted gene coexpression network analysis combined with differentially expressed genes (DEGs) analysis to further investigate this basis. We found 57 DEGs were closely related to platelet dysfunction in SCD. Enrichment analysis showed that these 57 genes were mostly related to protein synthesis, adenosine triphosphate (ATP) synthase activity and inflammation, suggesting a hyperactivation status of platelets in SCD. We identified six hub genes from the 57 DEGs according to their Gene Significance value ranking, including CRYM, CCT6P1, SUCNR1, PRKAB2, GSTM3 and FCGR2C. Altogether, our results offered some new insight into platelet activation and identified novel potential targets for antiplatelet therapy in SCD.

Marginal Zone B Cells Induce Alloantibody Formation Following RBC Transfusion

Red blood cell (RBC) alloimmunization represents a significant immunological challenge for some patients. While a variety of immune constituents likely contribute to the initiation and orchestration of alloantibodies to RBC antigens, identification of key immune factors that initiate alloantibody formation may aid in the development of a therapeutic modality to minimize or prevent this process. To define the immune factors that may be important in driving alloimmunization to an RBC antigen, we determined the specific immune compartment and distinct cells that may initially engage transfused RBCs and facilitate subsequent alloimmunization. Our findings demonstrate that the splenic compartment is essential for formation of anti-KEL antibodies following KEL RBC transfusion. Within the spleen, transfused KEL RBCs are found within the marginal sinus, where they appear to specifically co-localize with marginal zone (MZ) B cells. Consistent with this, removal of MZ B cells completely prevented alloantibody formation following KEL RBC transfusion. While MZ B cells can mediate a variety of key downstream immune pathways, depletion of follicular B cells or CD4 T cells failed to similarly impact the anti-KEL antibody response, suggesting that MZ B cells may play a key role in the development of anti-KEL IgM and IgG following KEL RBC transfusion. These findings highlight a key contributor to KEL RBC-induced antibody formation, wherein MZ B cells facilitate antibody formation following RBC transfusion.