Search

Patients harboring CRLF2-rearranged B-lineage acute lymphocytic leukemia (B-ALL) face a 5-year survival rate as low as 20%. While significant gains have been made to position targeted therapies for B-ALL treatment, continued efforts are needed to develop therapeutic options with improved duration of response. Here, first we have demonstrated that patients with CRLF2-rearranged Ph-like ALL harbor elevated thymic stromal lymphopoietin receptor (TSLPR) expression, which is comparable with CD19. Then we present and evaluate the anti-tumor characteristics of 1B7/CD3, a novel CD3-redirecting bispecific antibody (BsAb) that co-targets TSLPR. In vitro, 1B7/CD3 exhibits optimal binding to both human and cynomolgus CD3 and TSLPR. Further, 1B7/CD3 was shown to induce potent T cell activation and tumor lytic activity in both cell lines and primary B-ALL patient samples. Using humanized cell- or patient-derived xenograft models, 1B7/CD3 treatment was shown to trigger dose-dependent tumor remission or growth inhibition across donors as well as induce T cell activation and expansion. Pharmacokinetic studies in murine models revealed 1B7/CD3 to exhibit a prolonged half-life. Finally, toxicology studies using cynomolgus monkeys found that the maximum tolerated dose of 1B7/CD3 was ≤1 mg/kg. Overall, our preclinical data provide the framework for the clinical evaluation of 1B7/CD3 in patients with CRLF2-rearranged B-ALL., (© 2023. The Author(s).)

Immunotherapy targeting leukemia-associated antigens has shown promising results. Because of the heterogeneity of leukemia, vaccines with a single peptide have elicited only a limited immune response. Targeting several peptides together elicited peptide-specific cytotoxic T lymphocytes (CTLs) in leukemia patients, and this was associated with clinical responses. Thus, the discovery of novel antigens is essential. In the current study, we investigated cyclin E as a novel target for immunotherapy. Cyclin E1 and cyclin E2 were found to be highly expressed in hematologic malignancies, according to reverse transcription polymerase chain reaction and western blot analysis. We identified two HLA-A*0201 binding nonameric peptides, CCNE1 M from cyclin E1 and CCNE2 L from cyclin E2, which both elicited the peptide-specific CTLs. The peptide-specific CTLs specifically kill leukemia cells. Furthermore, CCNE1 M and CCNE2 L CTLs were increased in leukemia patients who underwent allogeneic hematopoietic stem cell transplantation, and this was associated with desired clinical outcomes. Our findings suggest that cyclin E1 and cyclin E2 are potential targets for immunotherapy in leukemia.

PR1, an HLA-A2-restricted peptide derived from both proteinase 3 and neutrophil elastase, is recognized on myeloid leukemia cells by cytotoxic T lymphocytes (CTLs) that preferentially kill leukemia and contribute to cytogenetic remission. To evaluate safety, immunogenicity and clinical activity of PR1 vaccination, a phase I/II trial was conducted. Sixty-six HLA-A2+ patients with acute myeloid leukemia (AML: 42), chronic myeloid leukemia (CML: 13) or myelodysplastic syndrome (MDS: 11) received three to six PR1 peptide vaccinations, administered subcutaneously every 3 weeks at dose levels of 0.25, 0.5 or 1.0 mg. Patients were randomized to the three dose levels after establishing the safety of the highest dose level. Primary end points were safety and immune response, assessed by doubling of PR1/HLA-A2 tetramer-specific CTL, and the secondary end point was clinical response. Immune responses were noted in 35 of 66 (53%) patients. Of the 53 evaluable patients with active disease, 12 (24%) had objective clinical responses (complete: 8; partial: 1 and hematological improvement: 3). PR1-specific immune response was seen in 9 of 25 clinical responders versus 3 of 28 clinical non-responders (P=0.03). In conclusion, PR1 peptide vaccine induces specific immunity that correlates with clinical responses, including molecular remission, in AML, CML and MDS patients.

The PR1 peptide, derived from the leukemia-associated antigens proteinase 3 and neutrophil elastase, is overexpressed on HLA-A2 in acute myeloid leukemia (AML). We developed a high-affinity T-cell receptor-like murine monoclonal antibody, 8F4, that binds to the PR1/HLA-A2 complex, mediates lysis of AML and inhibits leukemia colony formation. Here, we explored whether 8F4 was active in vivo against chemotherapy-resistant AML, including secondary AML. In a screening model, coincubation of AML with 8F4 ex vivo prevented engraftment of all tested AML subtypes in immunodeficient NSG (NOD scid IL-2 receptor γ-chain knockout) mice. In a treatment model of established human AML, administration of 8F4 significantly reduced or eliminated AML xenografts and extended survival compared with isotype antibody-treated mice. Moreover, in secondary transfer experiments, mice inoculated with bone marrow from 8F4-treated mice showed no evidence of AML engraftment, supporting the possible activity of 8F4 against the subset of AML with self-renewing potential. Our data provide evidence that 8F4 antibody is highly active in AML, including chemotherapy-resistant disease, supporting its potential use as a therapeutic agent in patients with AML.

Antibodies to granulocyte-macrophage colony-stimulating factor (GM-CSF) can be induced when GM-CSF is used as an adjuvant to solid tumor vaccination. Neutralizing anti-GM-CSF IgG has been associated with pulmonary alveolar proteinosis (PAP), and secondary PAP has been linked to myeloid leukemia. We studied 69 patients with acute myeloid leukemia, chronic myeloid leukemia and myelodysplastic syndrome, including 19 patients who received GM-CSF with peptide antigen and incomplete Freund's adjuvant in a vaccine trial for the presence or induction of anti-GM-CSF antibodies. Anti-GM-CSF IgG were present in 36 (52%) patients with myeloid leukemia compared to only 1 of 33 (3%) healthy subjects (P=0.008) and in none of 6 patients with lymphoid leukemia (P=0.0001). Antibody titers were unaffected by vaccination. Anti-GM-CSF IgA and IgM were found in 33 and 20% of patients, respectively; IgA from two patients neutralized GM-CSF. Strikingly, while anti-GM-CSF IgG titers were higher in patients with active disease (n=52) versus those in complete remission (n=14, P=0.0009), GM-CSF expression was not increased in either group. These data are first to show that anti-GM-CSF antibodies of multiple isotypes are present in patients with active myeloid leukemia without PAP and may be useful markers of disease activity.