CD44 standard and CD44v10 isoform expression on leukemia cells distinctly influences niche embedding of hematopoietic stem cells

Abstract

BackgroundA blockade of CD44 is considered a therapeutic option for the elimination of leukemia initiating cells. However, anti-panCD44 can interfere with hematopoiesis. Therefore we explored, whether a CD44 variant isoform (CD44v)-specific antibody can inhibit leukemia growth without attacking hematopoiesis. As a model we used CD44v10 transfected EL4 thymoma cells (EL4-v10).MethodsThe therapeutic efficacy of anti-panCD44 and anti-CD44v10 was evaluated after intravenous application of EL4/EL4-v10. Ex vivo and in vitro studies evaluated the impact of anti-panCD44 and anti-CD44v10 as well as of EL4 and EL4-v10 on hematopoietic stem cells (HSC) in cocultures with bone marrow stroma cells with a focus on adhesion, migration, cell cycle progression and apoptosis resistance.ResultsIntravenously injected EL4-v10 grow in bone marrow and spleen. Anti-panCD44 and, more pronounced anti-CD44v10 prolong the survival time. The higher efficacy of anti-CD44v10 compared to anti-panCD44 does not rely on stronger antibody-dependent cellular cytotoxicity or on promoting EL4-v10 apoptosis. Instead, EL4 compete with HSC niche embedding. This has consequences on quiescence and apoptosis-protecting signals provided by the stroma. Anti-panCD44, too, more efficiently affected embedding of HSC than of EL4 in the bone marrow stroma. EL4-v10, by catching osteopontin, migrated on bone marrow stroma and did not or weakly interfere with HSC adhesion. Anti-CD44v10, too, did not affect the HSC – bone marrow stroma crosstalk.ConclusionThe therapeutic effect of anti-panCD44 and anti-CD44v10 is based on stimulation of antibody-dependent cellular cytotoxicity. The superiority of anti-CD44v10 is partly due to blocking CD44v10-stimulated osteopontin expression that could drive HSC out of the niche. However, the main reason for the superiority of anti-CD44v10 relies on neither EL4-v10 nor anti-CD44v10 severely interfering with HSC – stroma cell interactions that, on the other hand, are affected by EL4 and anti-panCD44. Anti-panCD44 disturbing HSC embedding in the osteogenic niche weakens its therapeutic effect towards EL4. Thus, as far as leukemic cells express CD44v isoforms, the therapeutic use of anti-panCD44 should be avoided in favor of CD44v-specific antibodies.

<p>High Expression of CD44 Predicts a Poor Prognosis in Glioblastomas</p>

“…27 CD44 standard isoforms (CD44s) were expressed in primary gliomas, while CD44 variant isoforms (CD44v) were expressed in intracranial metastatic tumors and participated in inflammatory response. 28,29 We encourage more studies to be done on expression of different CD44 subtypes in tumor tissues. In addition, some studies found that CD44 expressed in different types of cells, including stromal cells, cancer cells, and cancer stem cells.…”

The bone marrow microenvironment in health and disease at a glance

“…The second approach of targeting leukemia cell intrinsic pathways (partly reviewed in Krause and Scadden, 2015) includes the inhibition of Axl and its interaction with Gas6 in AML (Ben-Batalla et al, 2013), for instance with the compound MYD1-72 (Kariolis et al, 2017), or the inhibition of CCL3 (Frisch et al, 2012;Schepers et al, 2013), placental growth factor (PlGF; Schmidt et al, 2011), IL-6 (Welner et al, 2015) and Jak2 in myeloproliferative neoplasia (MPN) (Meyer et al, 2015) and AML (Karjalainen et al, 2017). Other possible therapeutic strategies are inhibition of NF-κB, which lies downstream of the vascular cell adhesion molecule (VCAM)-1-integrin-β1 signaling axis, of various cytokines or their receptors (Jacamo et al, 2014) or targeting of CD44 (Erb et al, 2014;Singh et al, 2013). Other forms of treatment are the Bruton tyrosine kinase (BTK) inhibitor PCI-32765 in CLL (Byrd et al, 2013), or inhibition of the 'moulding' of the niche, for instance through the inhibition of exosome formation with carboxyamidotrizole-orotate (OTC) (Corrado et al, 2012) or that of nanotubes, resulting in a block in the delivery of the leukemia-promoting 'cargo' these tubes carry.…”

The role of CD44 in epithelial&ndash;mesenchymal transition and cancer development

“… 2 Transcripts for the CD44 gene undergo complex alternative splicing, which results in many functionally distinct isoforms, such as CD44 standard isoform (CD44s) and CD44 variant isoform (CD44v). 3 The smallest CD44s is encoded by constant exons 1–5 and 16–20 and translated into a polypeptide of a molecular mass of 80–85 kDa ( Figure 1 ). 4 Exon 1 is an N-terminal signal sequence, exons 2 and 3 are a link module that binds to hyaluronic acid (HA), exons 4, 5, 16, and 17 compose a stem region, exon 18 makes up a single-pass transmembrane domain, and exon 20 forms a cytoplasmic domain.…”