Expression of CD24 on CD19- CD79a+ early B-cell progenitors in human bone marrow

Bipotential B-neutrophil progenitors are present in human and mouse bone marrow and emerge in the periphery upon stress hematopoiesis

Hematopoiesis is a tightly regulated process that gets skewed toward myelopoiesis. This restrains lymphopoiesis, but the role of lymphocytes in this process is not well defined. To unravel the intricacies of neutrophil responses in COVID-19, we performed bulk RNAseq on neutrophils from healthy controls and COVID-19 patients. Principal component analysis revealed distinguishing neutrophil gene expression alterations in COVID-19 patients. ICU and ward patients displayed substantial transcriptional changes, with ICU patients exhibiting a more pronounced response. Intriguingly, neutrophils from COVID-19 patients, notably ICU patients, exhibited an enrichment of immunoglobulin (Ig) and B cell lineage-associated genes, suggesting potential lineage plasticity. We validated our RNAseq findings in a larger cohort. Moreover, by reanalyzing single-cell RNA sequencing (scRNAseq) data on human bone marrow (BM) granulocytes, we identified the cluster of granulocyte-monocyte progenitors (GMP) enriched with Ig and B cell lineage-associated genes. These cells with lineage plasticity may serve as a resource depending on the host's needs during severe systemic infection. This distinct B cell subset may play a pivotal role in promoting myelopoiesis in response to infection. The scRNAseq analysis of BM neutrophils in infected mice further supported our observations in humans. Finally, our studies using an animal model of acute infection implicate IL-7/GM-CSF in influencing neutrophil and B cell dynamics. Elevated GM-CSF and reduced IL-7 receptor expression in COVID-19 patients imply altered hematopoiesis favoring myeloid cells over B cells. Our findings provide novel insights into the relationship between the B-neutrophil lineages during severe infection, hinting at potential implications for disease pathogenesis.

IMPORTANCE

This study investigates the dynamics of hematopoiesis in COVID-19, focusing on neutrophil responses. Through RNA sequencing of neutrophils from healthy controls and COVID-19 patients, distinct gene expression alterations are identified, particularly in ICU patients. Notably, neutrophils from COVID-19 patients, especially in the ICU, exhibit enrichment of immunoglobulin and B cell lineage-associated genes, suggesting potential lineage plasticity. Validation in a larger patient cohort and single-cell analysis of bone marrow granulocytes support the presence of granulocyte-monocyte progenitors with B cell lineage-associated genes. The findings propose a link between B-neutrophil lineages during severe infection, implicating a potential role for these cells in altered hematopoiesis favoring myeloid cells over B cells. Elevated GM-CSF and reduced IL-7 receptor expression in stress hematopoiesis suggest cytokine involvement in these dynamics, providing novel insights into disease pathogenesis.

CD24 blockade as a novel strategy for cancer treatment

The CD24 protein is a heat-stable protein with a small core that undergoes extensive glycosylation. It is expressed on the surface of various normal cells, including lymphocytes, epithelial cells, and inflammatory cells. CD24 exerts its function by binding to different ligands. Numerous studies have demonstrated the close association of CD24 with tumor occurrence and progression. CD24 not only facilitates tumor cell proliferation, metastasis, and immune evasion but also plays a role in tumor initiation, thus, serving as a marker on the surface of cancer stem cells (CSCs). Additionally, CD24 induces drug resistance in various tumor cells following chemotherapy. To counteract the tumor-promoting effects of CD24, several treatment strategies targeting CD24 have been explored, such as the use of CD24 monoclonal antibodies (mAb) alone, the combination of CD24 and chemotoxic drugs, or the combination of these drugs with other targeted immunotherapeutic techniques. Regardless of the approach, targeting CD24 has demonstrated significant anti-tumor effects. Therefore, the present study focuses on anti-tumor therapy and provides a comprehensive review of the structure and fundamental physiological function of CD24 and its impact on tumor development, and suggests that targeting CD24 may represent an effective strategy for treating malignant tumors.

CD19 negative and dim precursor B-lineage acute lymphoblastic leukemias: real-world challenges in a targeted-immunotherapy era

Flow cytometric diagnosis and minimal residual disease (MRD) assessment of precursor B-lineage acute lymphoblastic leukemia (B-ALL) are heavily dependent on CD19 based gating strategies. However, this approach is not optimal in the diagnosis and follow-up of CD19 negative or dim B-ALLs. Though CD19 negative B-ALLs are rare, in the current era of CD19 targeted immuno-therapy, CD19 negative B-ALL relapses are frequent. We have presented our cohort of 14 de novo CD19 negative and dim B-ALLs and have highlighted the difficulties faced during diagnosis and MRD assessment of these patients. We have also discussed the need to identify alternative B-lineage gating markers and strategies to deal with such scenarios.

Amplification of the CD24 Gene Is an Independent Predictor for Poor Prognosis of Breast Cancer

CD24 is a glycosyl-phosphatidyl-inositol linked glycoprotein expressed in a broad range of cell types including cancer cells. Although it is overexpressed in nearly 70% of human cancers, copy number variation of the CD24 locus has not been reported for any cancer. Here, we analyzed the genomics, transcriptomics, and clinical data of 1082 breast cancer (BRCA) samples and other cancer samples from the clinically annotated genomic database, The Cancer Genome Atlas (TCGA). The GISTIC2 method was applied to stratify the CD24 copy number, and Cox regression was performed to compare hazard ratio (HR) of CD24 overexpression, amplification and other traditional prognosis features for overall survival (OS). Our data demonstrated that CD24 amplification strongly correlated with its mRNA overexpression as well as TP53 mutant, cancer proliferation and metastasis features. In particular, CD24 amplification was enriched in basal-like subtype samples and associated with poor clinical outcome. Surprisingly, based on the univariate Cox regression analysis, CD24 overexpression (HR = 1.62, P = 0.010) and copy number amplification (HR = 1.79, P = 0.022) was more relevant to OS than TP53 mutant, mutation counts, diagnosis age, and BRCA subtypes. And based on multivariate survival analysis, CD24 amplification remained the most significant and independent predictor for worse OS (HR = 1.88, P = 0.015).

Colorectal tumors are enriched with regulatory plasmablasts with capacity in suppressing T cell inflammation

Inflammation plays a critical role in the initiation of colorectal cancer but is also required to mediate antitumor immunity in established tumors. Therefore, identifying the cellular and molecular components in colorectal tumors is necessary for the understanding of tumor progression and the development of novel treatment strategies. In this study, we demonstrated that a specific subtype of regulatory B cells, the CD19^loCD27^hi plasmablasts, was enriched in the colorectal tumor microenvironment. This CD19^loCD27^hi plasmablast subset presented high interleukin 10 (IL-10) expression but not transforming growth factor-β (TGF-β) secretion. Phenotypically, the tumor-infiltrating IL-10⁺ CD19^loCD27^hi plasmablasts presented lower CD24, CD38, and IgA, and higher Tim-1 and IgG expression compared to the IL-10^- CD19^loCD27^hi plasmablasts. The tumor-infiltrating IL-10⁺ CD19^loCD27^hi plasmablasts were found to be gut-homing due to their higher expression of α4β7 while peripheral blood B cells did not show the same characteristic. When cocultured with autologous T cells, CD19^loCD27^hi plasmablasts demonstrated potent activity in suppressing interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) expression but did not promote Foxp3 expression. Overall, this study demonstrate that in colorectal cancer, CD19^loCD27^hi plasmablasts make up a large percentage in tumor-infiltrating lymphocytes and possess potent immunoregulatory functions, and thus could be utilized in future therapeutic strategies.

CD24 Is Not Required for Tumor Initiation and Growth in Murine Breast and Prostate Cancer Models

CD24 is a small, heavily glycosylated, GPI-linked membrane protein, whose expression has been associated with the tumorigenesis and progression of several types of cancer. Here, we studied the expression of CD24 in tumors of MMTV-PyMT, Apc^1572/T+ and TRAMP genetic mouse models that spontaneously develop mammary or prostate carcinoma, respectively. We found that CD24 is expressed during tumor development in all three models. In MMTV-PyMT and Apc^1572T/+ breast tumors, CD24 was strongly but heterogeneously expressed during early tumorigenesis, but decreased in more advanced stages, and accordingly was increased in poorly differentiated lesions compared with well differentiated lesions. In prostate tumors developing in TRAMP mice, CD24 expression was strong within hyperplastic lesions in comparison with non-hyperplastic regions, and heterogeneous CD24 expression was maintained in advanced prostate carcinomas. To investigate whether CD24 plays a functional role in tumorigenesis in these models, we crossed CD24 deficient mice with MMTV-PyMT, Apc^1572T/+ and TRAMP mice, and assessed the influence of CD24 deficiency on tumor onset and tumor burden. We found that mice negative or positive for CD24 did not significantly differ in terms of tumor initiation and burden in the genetic tumor models tested, with the exception of Apc^1572T/+ mice, in which lack of CD24 reduced the mammary tumor burden slightly but significantly. Together, our data suggest that while CD24 is distinctively expressed during the early development of murine mammary and prostate tumors, it is not essential for the formation of tumors developing in MMTV-PyMT, Apc^1572T/+ and TRAMP mice.

Somatically diversified and proliferating transitional B cells: implications for peripheral B cell homeostasis

The peripheral B cell compartment in mice and humans is maintained by continuous production of transitional B cells in the bone marrow. In other species, however, including rabbits, B lymphopoiesis in the bone marrow abates early in life, and it is unclear how the peripheral B cell compartment is maintained. We identified transitional B cells in rabbits and classified them into T1 (CD24(high)CD21(low)) and T2 (CD24(high)CD21(+)) B cell subsets. By neutralizing B cell-activating factor in vivo, we found an arrest in peripheral B cell development at the T1 B cell stage. Surprisingly, T1 B cells were present in GALT, blood, and spleen of adult rabbits, long after B lymphopoiesis was arrested. T1 B cells were distinct from their counterparts in other species because they are proliferating and the Ig genes are somatically diversified. We designate these newly described cells as T1d B cells and propose a model in which they develop in GALT, self renew, continuously differentiate into mature B cells, and thereby maintain peripheral B cell homeostasis in adults in the absence of B lymphopoiesis.

CD24: from A to Z

As a testament to the importance of CD24, researchers with diverse interests, including adaptive immunity, inflammation, autoimmune diseases and cancer, have encountered CD24. CD24 is overexpressed in many cancers and appears oncogenic. In the adaptive immune response, CD24 is a redundant costimulatory molecule in costimulation-rich lymphoid organs but is essential in selected target organs tested, such as brain and skin. More recent studies suggest it may have a role in discriminating danger and pathogen-associated molecular patterns by dendritic cells. The biology of CD24 is intriguing but poorly understood. Here we summarize the major findings associated with CD24 to stimulate new ideas for further research that may reveal the underlying link among the diverse processes mediated by CD24.

Reduction of phosphoinositide-phospholipase C beta1 methylation predicts the responsiveness to azacitidine in high-risk MDS

Lipid signaling pathways are involved in cell growth, differentiation, and apoptosis, and could have a role in the progression of myelodysplastic syndromes (MDS) into acute myeloid leukemia (AML). Indeed, recent studies showed that phosphoinositide-phospholipase (PI-PL)Cbeta1 mono-allelic deletion correlates with a higher risk of AML evolution. Also, a single patient treated with azacitidine, a DNA methyltransferase inhibitor currently used in MDS, displayed a direct correlation between PI-PLCbeta1 gene expression and drug responsiveness. Consequently, we hypothesized that PI-PLCbeta1 could be a target for demethylating therapy. First, we analyzed the structure of PI-PLCbeta1 gene promoter, then quantified the degree of PI-PLCbeta1 promoter methylation and gene expression in MDS patients at baseline and during azacitidine administration. Indeed, PI-PLCbeta1 mRNA increased in responder patients, along with a reduction of PI-PLCbeta1 promoter methylation. Also, the molecular response correlated to and anticipated the clinical outcome, thus suggesting that PI-PLCbeta1 gene reactivation could predict azacitidine responsiveness. Our results demonstrate not only that PI-PLCbeta1 promoter is hypermethylated in high-risk MDS patients, but also that the amount of PI-PLCbeta1 mRNA could predict the clinical response to azacitidine, therefore indicating a promising new therapeutic approach.