Mechanisms of alloimmunization in sickle cell disease:

RHCE and Kell genotyping and alloimmunization profile in patients with sickle cell disease in the Federal District of Brazil

INTRODUCTION

Sickle cell disease (SCD) is the most important hemoglobinopathy worldwide. The treatment often requires phenotype-matched red blood cell (RBC) transfusions, but alloimmunization to non-ABO antigens may occur in a part of the SCD patients. The genotyping has been used for RBC antigen prediction, reducing the possibility of the alloimmunization.

OBJECTIVE AND METHOD

In this study we performed the genotyping for the Kell and RHCE blood groups in samples from 77 phenotyped Brazilian SCD patients, whose alloimmunization profiles were also assessed.

RESULTS

Discrepancies between genotyping and phenotyping for the RHCE and Kell blood groups systems were observed in 22.07% (17/77) of the SCD patients. We found C/c and E/e discrepancies in 11.68% and 9.09% of patients, respectively; one SCD patient (1.3%) presented a discrepancy in the Kell group. Two SCD patients with discrepancies between genotype and phenotype were alloimmunized. In total, twenty-eight patients (36.4%) developed alloantibodies, of which 55.17% were directed against antigens in the Rh system, 8.62% were directed against antigens in the Kell system and 36.20%, against other groups. Finally, the frequency of discrepancies is significantly higher in non-alloimmunized patients (30.61%), compared to alloimmunized patients (7.14%) (p = 0.0217).

CONCLUSION

In part, the alloimmunization of the SCD patients may have been triggered by these discrepancies, indicating that the integration of serological and molecular tests in the immunohematology routine could help to increase the transfusion safety. However, the higher number of alloimmunized patients without discrepancies showed that reasons other than the discrepancies appear to have influenced more strongly the alloimmunization in the SCD patients in this study.

Proinflammatory state promotes red blood cell alloimmunization in pediatric patients with sickle cell disease

We examined risk factors for red blood cell (RBC) alloimmunization in pediatric patients with sickle cell disease, focusing on the recipients' inflammatory state at the time of transfusion and anti-inflammatory role of hydroxyurea (HU). Among 471 participants, 55 (11.70%) participants were alloimmunized and formed 59 alloantibodies and 17 autoantibodies with an alloimmunization rate of 0.36 alloantibodies per 100 units. Analysis of 27 participants in whom alloantibodies were formed with specificities showed 23.8% (30/126) of units transfused during a proinflammatory event resulting in alloantibody formation compared with 2.8% (27/952) of units transfused at steady state. Therefore, transfusion during proinflammatory events increased the risk for alloimmunization (odds ratio [OR], 4.22; 95% confidence interval [CI], 1.64-10.85; P = .003). Further analysis of all the 471 participants showed that alloimmunization of patients who received episodic transfusion, mostly during proinflammatory events, was not reduced with HU therapy (OR, 6.52; 95% CI, 0.85-49.77; P = .071), HU therapy duration (OR, 1.13; 95% CI, 0.997-1.28; P = .056), or HU dose (OR, 1.06; 95% CI, 0.96-1.16; P = .242). The analysis also identified high transfusion burden (OR, 1.02; 95% CI, 1.003-1.04; P = .020) and hemoglobin S (HbSS) and HbSβ0-thalassemia genotypes (OR, 11.22, 95% CI, 1.51-83.38; P = .018) as additional risk factors for alloimmunization. In conclusion, the inflammatory state of transfusion recipients affects the risk of RBC alloimmunization, which is not modified by HU therapy. Judicious use of transfusion during proinflammatory events is critical for preventing alloimmunization.

Storage differentially impacts alloimmunization to distinct red cell antigens following transfusion in mice

INTRODUCTION

The impact of blood storage on red blood cell (RBC) alloimmunization remains controversial, with some studies suggesting enhancement of RBC-induced alloantibody production and others failing to observe any impact of storage on alloantibody formation. Since evaluation of storage on RBC alloimmunization in patients has examined antibody formation against a broad range of alloantigens, it remains possible that different clinical outcomes reflect a variable impact of storage on alloimmunization to specific antigens.

METHODS

RBCs expressing two distinct model antigens, HEL-OVA-Duffy (HOD) and KEL, separately or together (HOD × KEL), were stored for 0, 8, or 14 days, followed by detection of antigen levels prior to transfusion. Transfused donor RBC survival was assessed within 24 h of transfusion, while IgM and IgG antibody production were assessed 5 and 14 days after transfusion.

RESULTS

Stored HOD or KEL RBCs retained similar HEL or KEL antigen levels, respectively, as fresh RBCs, but did exhibit enhanced RBC clearance with increased storage age. Storage enhanced IgG antibody formation against HOD, while the oppositive outcome occurred following transfusion of stored KEL RBCs. The distinct impact of storage on HOD or KEL alloimmunization did not appear to reflect intrinsic differences between HOD or KEL RBCs, as transfusion of stored HOD × KEL RBCs resulted in increased IgG anti-HOD antibody development and reduced IgG anti-KEL antibody formation.

CONCLUSIONS

These data demonstrate a dichotomous impact of storage on immunization to distinct RBC antigens, offering a possible explanation for inconsistent clinical experience and the need for additional studies on the relationship between RBC storage and alloimmunization.

Retention of functional mitochondria in mature red blood cells from patients with sickle cell disease

Sickle cell disease (SCD) is an inherited blood disorder characterized by sickled red blood cells (RBCs), which are more sensitive to haemolysis and can contribute to disease pathophysiology. Although treatment of SCD can include RBC transfusion, patients with SCD have high rates of alloimmunization. We hypothesized that RBCs from patients with SCD have functionally active mitochondria and can elicit a type 1 interferon response. We evaluated blood samples from more than 100 patients with SCD and found elevated frequencies of mitochondria in reticulocytes and mature RBCs, as compared to healthy blood donors. The presence of mitochondria in mature RBCs was confirmed by flow cytometry, electron microscopy, and proteomic analysis. The mitochondria in mature RBCs were metabolically competent, as determined by enzymatic activities and elevated levels of mitochondria-derived metabolites. Metabolically-active mitochondria in RBCs may increase oxidative stress, which could facilitate and/or exacerbate SCD complications. Coculture of mitochondria-positive RBCs with neutrophils induced production of type 1 interferons, which are known to increase RBC alloimmunization rates. These data demonstrate that mitochondria retained in mature RBCs are functional and can elicit immune responses, suggesting that inappropriate retention of mitochondria in RBCs may play an underappreciated role in SCD complications and be an RBC alloimmunization risk factor.

Alloimmunization in transfused patients with constitutional anemias in Norway

BACKGROUND AND OBJECTIVES

The status of red blood cell alloimmunization in patients with constitutional anemias including hemoglobinopathies is not known in Norway. The study objective was to investigate the impact of a strategy based on phenotype-matching for C, c, E, e, K, Jka, Jkb, Fya, Fyb, S and s on alloimmunization.

MATERIALS AND METHODS

We reviewed transfusions of 40 patients retrospectively using the computerized blood bank management system and medical records; including diagnosis, age at start of transfusion therapy, gender, number and age of packed red blood cell units transfused, follow-up time, phenotypes of the donors and patients, antigen-negative patients exposed to antigen-positive packed red blood cell units, transfusion reactions and alloantibody specificities.

RESULTS

Forty patients received 5402 packed red blood cell units. Alloimmunization frequency was 20 % for the whole group, being 7%, 25 % and 30 % in patients with sickle cell disease (n = 14), thalassemia (n = 16) and other conditions (n = 10), respectively. The alloantibodies detected were anti-E, -c, -C, -Cw, -K, -Jka and -Lua.

CONCLUSION

Good communication between the clinicians and the transfusion services is essential for successful management of patients with constitutional anemias. Providing full phenotype-matched units was not always possible. Extended pheno-/genotyping before the first transfusion and providing antigen-negative units for antigen-negative patients for at least C, c, E and K in every red cell transfusion would probably have reduced the alloimmunization rate. Non-phenotype-matched transfusions seem to be the main reason for alloimmunization. Finding markers for identifying responders prone to alloimmunization will ensure targeted transfusion strategies.

Whole-blood phenotyping to assess alloimmunization status in transfused sickle cell disease patients

It is essential to limit hemolytic transfusion reactions in polytransfused individuals, and the prevention of alloimmunization is a key solution. CD4+ T lymphocyte (TL) markers, particularly follicular T helper (Tfh) cells, may differentiate between responder and nonresponder alloimmunization statuses. We tested this hypothesis by studying the phenotype of CXCR5+PD1+ TLs in whole blood. Our results suggest that high levels of CXCR5+PD1+CD4+ TLs in whole blood may be a characteristic of nonalloimmunized patients. However, these cells did not display the phenotypic characteristics of active Tfh cells. Instead, a decrease in blood quiescent Tfh-cell levels was observed in nonalloimmunized polytransfused patients. High levels of CXCR5+PD1+CD4+ TLs may be associated with inhibitory signaling functions of T cells, as reflected by the low levels of PD1+ICOS+ cells in the nonalloimmunized polytransfused group. The description of these particular phenotypes, and their comparison among groups of patients, responders, and nonresponders, suggests that new immunological components should be considered when trying to understand posttransfusion alloimmunization.

Pilot assessment of omega-3 fatty acids and potassium thiocyanate in sickle cell anemia patients with conditional peak systolic cerebral artery blood velocity

OBJECTIVE

The purpose of this pilot study was to explore the effect of omega-3 fatty acids and potassium thiocyanate on conditional peak systolic cerebral artery blood velocity in children with sickle cell anemia (SCA).

METHODS

Transcranial doppler ultrasonography (TCD) was done on 232 SCA children, and 21 found with conditional peak systolic blood velocity (PSV) of 200-249 cm/s in internal carotid, middle or anterior cerebral arteries. These were randomized to receive omega-3 fatty acids and potassium thiocyanate with standard treatment of SCA (test group, N = 14), or standard treatment only (control group, N = 7). After 3 months of treatment, PSV was measured again.

RESULTS

Right middle cerebral artery PSV was significantly reduced in the test relative to the control groups (p = 0.04). PSV returned to normal in 79% of the test versus 43% of the control group; and increased to abnormal in one member of the control group, but none of the test group.

CONCLUSIONS

The pilot data suggest that in SCA, omega-3 fatty acids and potassium thiocyanate might reduce conditional blood velocity to normal, or prevent progression to abnormal values. A larger, randomized, clinical trial is required to further address the current gap in management of conditional TCD blood velocity.

Transfusion and Cellular Therapy in Pediatric Sickle Cell Disease

Red blood cell (RBC) transfusion is critical in managing acute and chronic complications of sickle cell disease. Alloimmunization and iron overload remain significant complications of transfusion therapy and are minimized with prophylactic Rh and K antigen RBC matching and iron chelation. Matched sibling donor hematopoietic stem cell transplant (HSCT) is a curative therapeutic option. Autologous hematopoietic stem cell (HSC)-based gene therapy has recently shown great promise, for which obtaining sufficient HSCs is essential for success. This article discusses RBC transfusion indications and complications, transfusion support during HSCT, and HSC mobilization and collection for autologous HSCT with gene therapy.