Hemin controls T cell polarization in sickle cell alloimmunization

Melanoma tumor growth is accelerated in a mouse model of sickle cell disease

Background

The effect of sickle cell disease (SCD) on tumor growth is unknown. Sickled red blood cells may form aggregates within the microvasculature of hypoxic tumors and reduce blood flow leading to impairment of tumor growth. However, there is a paucity of data related to tumor growth in SCD.

Methods

To investigate the effect of SCD on tumor growth in a melanoma model, we generated SCD and control mice using bone marrow transplantation and inoculated the chest wall with B16-F10 melanoma cells. Tumor growth was monitored and angiogenesis was studied in vivo and in vitro.

Results

From day 1 to 21, tumor growth rate was nearly identical between SCD and WT mice, however from day 22 to day 29 tumor growth was accelerated in SCD mice compared to WT mice. Disparity in tumor size was confirmed at autopsy with an approximate 2-fold increase in tumor weights from SCD mice. Tumors from SCD mice showed increased vascularity and elevated levels of heme oxygenase-1 (HO-1). HO-1 inhibition with zinc protoporphyrin (ZnPP) blocked the angiogenic and tumor growth response to SCD in vivo and the response to hemin in vitro.

Conclusions

Growth of melanoma tumors is potentiated in a mouse model of SCD. Therapies targeting angiogenesis or HO-1 may be useful in SCD patients with malignant tumors.

Mechanisms of sickle cell alloimmunization

Red blood cell (RBC) alloimmunization can be a life-threatening complication for patients with sickle cell disease (SCD) receiving therapeutic transfusions. Despite provision of extended antigen-matched donor RBCs, patients continue to develop antibodies due to high degree of polymorphisms in the immunogenic antigens in individuals of African ancestry. Identification of biomarkers of alloimmunization in this patient population is therefore of great interest and will help to identify in advance patients most likely to make antibodies in response to transfusion. We have recently identified altered T cell responses and innate immune abnormalities in alloimmunized SCD patients. In this paper, we summarize this work and propose our working model of how innate immune abnormalities can contribute to pathogenic T cell responses in alloimmunized SCD patients. We believe that unravelling the basis of such altered interactions at the cellular and molecular level will help future identification of biomarkers of alloimmunization with the goal that this information will ultimately help guide therapy in these patients.

Red blood cell transfusions are associated with HLA class I but not H-Y alloantibodies in children with sickle cell disease

Blood transfusions can induce alloantibodies to antigens on red blood cells (RBCs), white blood cells and platelets, with these alloantibodies affecting transfusion and transplantation. While transfusion-related alloimmunization against RBC antigens and human leucocyte antigens (HLA) have been studied, transfusion-related alloimmunization to minor histocompatibility antigens (mHA), such as H-Y antigens, has not been clinically characterized. We conducted a cross-sectional study of 114 children with sickle cell disease (SCD) and tested for antibodies to 5 H-Y antigens and to HLA class I and class II. Few patients had H-Y antibodies, with no significant differences in the prevalence of any H-Y antibody observed among transfused females (7%), transfused males (6%) and never transfused females (4%). In contrast, HLA class I, but not HLA class II, antibodies were more prevalent among transfused than never transfused patients (class I: 33% vs. 13%, P = 0·046; class II: 7% vs. 8%, P = 0·67). Among transfused patients, RBC alloantibody history but not amount of transfusion exposure was associated with a high (>25%) HLA class I panel reactive antibody (Odds ratio 6·8, 95% confidence interval 2·1-22·3). These results are consistent with immunological responder and non-responder phenotypes, wherein a subset of patients with SCD may be at higher risk for transfusion-related alloimmunization.

Phenotypic differences of CD4(+) T cells in response to red blood cell immunization in transfused sickle cell disease patients

Alloimmunization against red blood cells (RBCs) is the main immunological risk associated with transfusion in patients with sickle cell disease (SCD). However, about 50-70% of SCD patients never get immunized despite frequent transfusion. In murine models, CD4(+) T cells play a key role in RBC alloimmunization. We therefore explored and compared the CD4(+) T-cell phenotypes and functions between a group of SCD patients (n = 11) who never became immunized despite a high transfusion regimen and a group of SCD patients (n = 10) who had become immunized (at least against Kidd antigen b) after a low transfusion regimen. We studied markers of CD4(+) T-cell function, including TLR, that directly control lymphocyte function, and their spontaneous cytokine production. We also tested responders for the cytokine profile in response to Kidd antigen b peptides. Low TLR2/TLR3 expression and, unexpectedly, strong expression of CD40 on CD4(+) T cells were associated with the nonresponder status, whereas spontaneous expression of IL-10 by CD4(+) T cells and weak Tbet expression were associated with the responder status. A Th17 profile was predominant in responders when stimulated by Jb(k) . These findings implicate CD4(+) T cells in alloimmunization in humans and suggest that they may be exploited to differentiate responders from nonresponders.