Siglec-15 Is a Novel Immunomodulatory Protein and Therapeutic Target in Acute Lymphoblastic Leukemia

Abstract Immunotherapies have recently shown efficacy in treatment of aggressive, refractory pediatric B cell acute lymphoblastic leukemia (B-ALL), which remains one of the leading causes of cancer-related death in children. The immune evasion mechanisms of B-ALL are still being explored to discover new therapeutic targets and improve patient outcomes. Recent reports have implicated a role for the molecule Siglec-15 (Sig15) in regulating immune response in solid tumor-infiltrating macrophages. Our lab has found higher expression of SIGLEC15 at the RNA level in primary pediatric B-ALL as compared to healthy donor controls, as well as at the RNA and protein levels across a panel of B-ALL, T cell acute lymphoblastic leukemia (T-ALL), and diffuse large B cell lymphoma (DLBCL) cell lines compared to healthy donor PBMCs. Higher expression of SIGLEC15 in pediatric B-ALL samples from the TARGET database correlates with markers of PKC and NFκB activation known to drive B-ALL leukemogenesis, which we have demonstrated to regulate Sig15 RNA and protein expression in vitro. Knockout of Siglec15 expression in a BCR-ABL1 + murine model of B-ALL engrafted in immunocompetent and Rag1 -/- immunodeficient recipients resulted in leukemia clearance in immunocompetent, but not immunodeficient, recipients and 100% survival (Figure A, p=0.01 Sig15 KO into WT vs. Rag1 -/-). Further study indicates that Siglec15 expression on these leukemia cells suppresses T cell effector and memory population expansion at 7 days post-engraftment (Figure B) and correlates with higher levels of IL-10 and lower levels of CCL17 present in the bone marrow, representing a more immunosuppressive bone marrow milieu. These data suggest a prominent role for Sig15 in the suppression of adaptive immune response to B-ALL as well as other hematological malignancies. We have also reported for the first time the release of a soluble form of Sig15 (sSig15), which we have demonstrated to circulate at higher levels in the plasma of pediatric B-ALL patients compared to healthy donors (Figure C, ****P≤0.0001). Detection of this sSig15 negatively correlated with circulating levels of IL-12 and IL-1α/β (Figure D, depicting correlations of cytokines using Pearson's r), suggesting sSig15 levels correspond to a systemically immunosuppressive phenotype. Flow cytometry of fresh pediatric B ALL cells demonstrates expression of surface Sig15 in a subset of cases. Thus, Sig15 has the capacity to promote immunosuppressive effects at both marrow-localized and systemic levels. Together, these results suggest Siglec-15 is a novel, potent immunosuppressive molecule active in leukemia progression that may be targeted therapeutically to activate T lymphocytes against leukemia cells. Figure 1 Figure 1. Disclosures Abukharma: NextCure Inc.: Current Employment. Liu: NextCure: Current Employment, Current holder of stock options in a privately-held company.

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Siglec-15 Is a Novel Immunomodulatory Protein and Therapeutic Target in Childhood Leukemia

Blood ◽

10.1182/blood-2020-142833 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 6-7

Author(s):

Claire E. Pillsbury ◽

Jairo A. Fonseca ◽

Jodi Dougan ◽

Hasan Abukharma ◽

Linda N. Liu ◽

...

Keyword(s):

Acute Lymphoblastic Leukemia ◽

B Cell ◽

Healthy Donor ◽

Childhood Leukemia ◽

Lymphoblastic Leukemia ◽

B Cell Lymphoma ◽

Myelogenous Leukemia ◽

Soluble Form ◽

Pediatric Leukemia ◽

Cell Acute Lymphoblastic Leukemia

Despite advances that have greatly improved the overall survival of pediatric B cell acute lymphoblastic leukemia (B-ALL), it remains one of the leading causes of cancer-related death in children. Immunotherapy has shown efficacy in treatment of refractory disease, highlighting the need for greater understanding of the immune evasion mechanisms underlying this disease so that additional immune modulating therapeutic strategies can be developed. Siglec-15 (Sig15) was recently reported to have immune modulatory functions in the context of solid tumors. We have found that SIGLEC15 is overexpressed at the RNA level in primary B cell acute lymphoblastic leukemia (B-ALL), acute myelogenous leukemia (AML), and diffuse large B cell lymphoma as compared to healthy donor controls. As compared to healthy donor PBMCs, we have confirmed higher expression of Sig15 at the RNA and protein levels through RT-qPCR, immunoblotting, and flow cytometry across a panel of human B-ALL, AML, DLBCL, and T cell acute lymphoblastic leukemia (T-ALL) cell lines. Knockout of Sig15 expression in a BCR-ABL1+ murine model of B-ALL engrafted in immunocompetent and Rag1-/- immunodeficient recipients resulted in leukemia clearance in immunocompetent, but not immunodeficient, recipients and 100% survival (Figure 1). These data suggest a prominent role for Sig15 in the suppression of adaptive immune response to B-ALL as well as other hematological malignancies. Additional studies suggest that SIGLEC15 expression is positively regulated by NFκB signaling, which is known to be constitutively activated in certain B-ALL subsets. Importantly, we have observed release of a soluble form of Sig15 (sSig15) from B-ALL cells, which is regulated by PKC and calcineurin-mediated signaling. To discover translational application, we measured sSig15 in the plasma of both healthy and pediatric leukemia patients and found significantly higher levels of sSig15 as compared to healthy individuals (Figure 2; LLD = 5 pg/ml; **P<0.01). Together, these results suggest Siglec-15 is a novel and potent immunosuppressive molecule active in leukemia that may be targeted therapeutically to activate lymphocytes against leukemia cells. Disclosures Abukharma: NextCure, Inc.: Current Employment. Liu:NextCure, Inc.: Current Employment.

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Preconditioning with fetal cord blood facilitates engraftment of primary childhood T-cell acute lymphoblastic leukemia in immunodeficient mice

Blood ◽

10.1182/blood.v97.10.3218 ◽

2001 ◽

Vol 97 (10) ◽

pp. 3218-3225 ◽

Cited By ~ 15

Author(s):

Deno P. Dialynas ◽

Mi-Jeong Lee ◽

Daniel P. Gold ◽

Li-en Shao ◽

Alice L. Yu ◽

...

Keyword(s):

Bone Marrow ◽

Acute Lymphoblastic Leukemia ◽

T Cell ◽

Cord Blood ◽

Lymphoblastic Leukemia ◽

Leukemia Cells ◽

Mouse Bone Marrow ◽

Human Leukemia ◽

Immunodeficient Mice ◽

Cell Acute Lymphoblastic Leukemia

Abstract Childhood T-cell acute lymphoblastic leukemia (T-ALL) is one of the most common childhood cancers. It is reported that preconditioning sublethally irradiated immunodeficient NOD/SCID (nonobese diabetic/X-linked severe combined immunodeficient) mice with human cord blood mononuclear cells facilitates the engraftment, expansion, and dissemination in these mice of primary T-ALL cells obtained from patients at the time of diagnosis. Cells recovered from mouse bone marrow or spleen resembled the original leukemia cells from patients with respect to surface lineage markers and T-cell receptor Vβ gene rearrangements. Moreover, the pattern of leukemia dissemination in mouse tissues, resulting in universally fatal leukemia, is reminiscent of the human clinical disease. In addition, the fidelity of the model to the human disease is documented with regard to the presence of morphologically identifiable human leukemia cells in mouse bone marrow and blood and the maintenance of leukemia-initiating capacity within the leukemia-engrafted mouse. Therefore, several lines of independent approaches are used to suggest that the engrafted cells are of human leukemia origin and are not derived from cord blood. The in vivo model described here should enable the study of the growth properties of primary T-ALL cells obtained from patients and should prove useful in evaluating the potential efficacy of therapeutic strategies directed toward T-ALL.

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Intravenous Forodesine (BCX-1777), a Novel Purine Nucleoside Phosphorylase (PNP) Inhibitor, Demonstrates Clinical Activity in Phase I/II Studies in Patients with B-Cell Acute Lymphoblastic Leukemia.

Blood ◽

10.1182/blood.v104.11.2743.2743 ◽

2004 ◽

Vol 104 (11) ◽

pp. 2743-2743 ◽

Cited By ~ 7

Author(s):

Richard R. Furman ◽

Varsha V. Gandhi ◽

J. Claude Bennett ◽

Shanta Bantia ◽

J. Michael Kilpatrick

Keyword(s):

Bone Marrow ◽

Acute Lymphoblastic Leukemia ◽

T Cell ◽

Phase I ◽

B Cell ◽

Lymphoblastic Leukemia ◽

Clinical Activity ◽

Cell Acute Lymphoblastic Leukemia ◽

Pre Treatment ◽

T Cell Malignancies

Abstract Forodesine is a potent, specific transition-state analog inhibitor of PNP with clinical activity in T-cell malignancies. Pharmacodynamic studies support that this anti-leukemic effect is mediated through the accumulation of plasma 2′-deoxyguanosine (dGuo) and intracellular Dgtp. In vitro studies indicated that B-cell acute lymphoblastic leukemia (B-ALL) cells can also accumulate Dgtp. These preclinical data led to a phase I/II multicenter dose-escalation study to evaluate forodesine in pts with various hematologic malignancies. 15 pts were treated with forodesine, including 6 with B-ALL. Forodesine was given via a 30-min IV infusion followed 24 hrs later by doses every 12 hrs for a total of 9 doses. A second course could be repeated after a 2-week break. Doses were escalated by 50% to pts grouped in cohorts of 3 (starting dose: 40 mg/m2). There was a rapid rise in plasma dGuo and a maximum PNP inhibition was achieved at 40 mg/m2 (Fig 1). 7/15 treated pts (2 T-cell malignancies and 5 B-ALL), including 5/6 treated B-ALL pts, demonstrated a hematologic benefit, defined as a decrease in tumor burden. 3 of the responding B-ALL pts were further treated with 6 courses of forodesine on a compassionate use protocol. One pt treated at 135 mg/m2 demonstrated a complete response with a decrease in bone marrow blast cells from 22% to 5% at the end of therapy. The other 2 pts, treated with 90 mg/m2 and 135 mg/m2 forodesine respectively, showed dramatic improvement in their CBC despite the persistence of bone marrow blasts. The dramatic fall in WBC count was accompanied in each pt by a rise in plasma dGuo (Cmax: 1.9–7.1 μM) and intracellular Dgtp (380–800 pmoles/107 cells vs 25–40 pmoles/107 cells pre-treatment), The response of the pt treated with 90 mg/m2 forodesine is shown in Fig 2. The absolute neutrophil count (ANC) improved from ~0 at pre-treatment to 1800 cells/mm3 at Day 18. To-date forodesine has been safe and well-tolerated at all dose levels tested with no dose-limiting toxicities. Clinical activity has been seen in T- and B-ALL. It is interesting to note the restoration of normal hematopoiesis, indicating the specificity of forodesine for leukemic cell populations and supporting that forodesine represents an important breakthrough in the development of less toxic ALL therapy. This encouraging clinical activity has led to the initiation of a phase II trial in pts with B-ALL. Additional clinical and pharmacodynamic results will be presented.

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Tumor staging in a Beagle dog with concomitant large B-cell lymphoma and T-cell acute lymphoblastic leukemia

Journal of Veterinary Diagnostic Investigation ◽

10.1177/10406387211011024 ◽

2021 ◽

pp. 104063872110110

Author(s):

Alessandro Ferrari ◽

Marzia Cozzi ◽

Luca Aresu ◽

Valeria Martini

Keyword(s):

Bone Marrow ◽

Lymph Node ◽

T Cell ◽

B Cell ◽

Cell Lymphoma ◽

Tumor Staging ◽

Lymphoblastic Leukemia ◽

B Cell Lymphoma ◽

Large B Cell Lymphoma ◽

Cell Acute Lymphoblastic Leukemia

An 8-y-old spayed female Beagle dog was presented with peripheral lymphadenomegaly. Lymph node cytology and flow cytometry led to the diagnosis of large B-cell lymphoma (LBCL). We detected minimal percentages of LBCL cells in peripheral blood and bone marrow samples. However, a monomorphic population of neoplastic cells different from those found in the lymph node was found in the bone marrow. T-cell acute lymphoblastic leukemia was suspected based on flow cytometric immunophenotyping. PCR for antigen receptor rearrangement (PARR) revealed clonal rearrangement of both B-cell and T-cell receptors, and the presence of both neoplastic clones in the lymph node, peripheral blood, and bone marrow. The dog was treated with multi-agent chemotherapy but died 46 d following diagnosis. Tumor staging and patient classification are needed to accurately establish a prognosis and select the most appropriate therapeutic protocol.

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Co-culture model of B-cell acute lymphoblastic leukemia recapitulates a transcription signature of chemotherapy-refractory minimal residual disease

Scientific Reports ◽

10.1038/s41598-021-95039-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Stephanie L. Rellick ◽

Gangqing Hu ◽

Debra Piktel ◽

Karen H. Martin ◽

Werner J. Geldenhuys ◽

...

Keyword(s):

Bone Marrow ◽

Acute Lymphoblastic Leukemia ◽

B Cell ◽

Tumor Cells ◽

Minimal Residual Disease ◽

Residual Disease ◽

Lymphoblastic Leukemia ◽

Adherent Cells ◽

Cell Acute Lymphoblastic Leukemia ◽

Minimal Residual

AbstractB-cell acute lymphoblastic leukemia (ALL) is characterized by accumulation of immature hematopoietic cells in the bone marrow, a well-established sanctuary site for leukemic cell survival during treatment. While standard of care treatment results in remission in most patients, a small population of patients will relapse, due to the presence of minimal residual disease (MRD) consisting of dormant, chemotherapy-resistant tumor cells. To interrogate this clinically relevant population of treatment refractory cells, we developed an in vitro cell model in which human ALL cells are grown in co-culture with human derived bone marrow stromal cells or osteoblasts. Within this co-culture, tumor cells are found in suspension, lightly attached to the top of the adherent cells, or buried under the adherent cells in a population that is phase dim (PD) by light microscopy. PD cells are dormant and chemotherapy-resistant, consistent with the population of cells that underlies MRD. In the current study, we characterized the transcriptional signature of PD cells by RNA-Seq, and these data were compared to a published expression data set derived from human MRD B-cell ALL patients. Our comparative analyses revealed that the PD cell population is markedly similar to the MRD expression patterns from the primary cells isolated from patients. We further identified genes and key signaling pathways that are common between the PD tumor cells from co-culture and patient derived MRD cells as potential therapeutic targets for future studies.

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