A Chemo-enzymatically Linked Bispecific Antibody Retargets T Cells to a Sialylated Epitope on CD43 in Acute Myeloid Leukemia

Abstract

Acute myeloid leukemia (AML) is a high-risk disease with a poor prognosis, particularly in elderly patients. Because current AML treatment relies primarily on untargeted therapies with severe side effects that limit patient eligibility, identification of novel therapeutic AML targets is highly desired. We recently described AT1413, an antibody produced by donor B cells of a patient with AML cured after allogeneic hematopoietic stem cell transplantation. AT1413 binds CD43s, a unique sialylated epitope on CD43, which is weakly expressed on normal myeloid cells and overexpressed on AML cells. Because of its selectivity for AML cells, we considered CD43s as a target for a bispecific T-cell-engaging antibody (bTCE) and generated a bTCE by coupling AT1413 to two T-cell-targeting fragments using chemo-enzymatic linkage. In vitro, AT1413 bTCE efficiently induced T-cell-mediated cytotoxicity toward different AML cell lines and patient-derived AML blasts, whereas endothelial cells with low binding capacity for AT1413 remained unaffected. In the presence of AML cells, AT1413 bTCE induced upregulation of T-cell activation markers, cytokine release, and T-cell proliferation. AT1413 bTCE was also effective in vivo. Mice either coinjected with human peripheral blood mononuclear cells or engrafted with human hematopoietic stem cells [human immune system (HIS) mice] were inoculated with an AML cell line or patient-derived primary AML blasts. AT1413 bTCE treatment strongly inhibited tumor growth and, in HIS mice, had minimal effects on normal human hematopoietic cells. Taken together, our results indicate that CD43s is a promising target for T-cell-engaging antibodies and that AT1413 holds therapeutic potential in a bTCE-format. Significance: These findings offer preclinical evidence for the therapeutic potential of a bTCE antibody that targets a sialylated epitope on CD43 in AML.

Genome-scale CRISPR activation screen uncovers tumor-intrinsic modulators of CD3 bispecific antibody efficacy

“…This antibody targeted a sialylated epitope on SPN that was expressed across all AML subtypes, but was not found on healthy monocytes, granulocytes, B cells or T cells. Targeting this unique SPN epitope in a CD3 bsAb format showed anti-tumor efficacy against human AML cell lines in vitro and in vivo while engrafted healthy myeloid cells were unaffected 48 . While discovery and generation of glycoform-specific therapeutics is arduous, it could be an effective way to preferentially inhibit SPN function on tumor cells.…”

Tumour-reactive B cells and antibody responses after allogeneic haematopoietic cell transplantation

“…Despite lowlevel expression of CD43s on non-malignant human haematopoietic progenitor cells, AT1413-bTCE treatment did not affect normal haematopoiesis. 61 As described above, antibodies against the B-cell maturation antigen (BCMA) were found in patients with multiple myeloma after allogeneic HCT. A BCMA-specific antibody has been clinically developed as an antibodyedrug conjugate and shows promising first results in patients, and BCMA-targeting CAR-T cells have shown clinical effect in a phase I study.…”

Immunotherapy-Based Targeting and Elimination of Leukemic Stem Cells in AML and CML

“…Overall, however, little is known about the clinical efficacy and toxicity of the above-mentioned BiTEs, DARTs, and other immune-cell-recruiting agents in AML. A number of additional bispecific and other multi-targeting antibodies with diverse specificities and multiple mechanisms of action are currently being developed in AML, with the hope to target disease-initiating LSC [143,144,145,146,147,148]. Whether these drugs will reach clinical application and help eradicate LSC remains to be determined in preclinical and clinical studies.…”