P341: A NOVEL BISPECIFIC T CELL ENGAGER (UMG2-CD3) IS EFFECTIVE AGAINST CORTICAL-DERIVED ACUTE LYMPHOBLASTIC LEUKEMIA

Abstract

Background: T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy derived by T cell precursors and characterized by poor prognosis.The immunotherapy has revolutionized the outcome of B cell acute lymphoblastic leukemia (B-ALL), but the absence of tumor-specific T cell antigen hampers its efficacy in T-ALL. Therefore, the development of novel immune-therapeutic options for the management of this orphan disease is eagerly awaited. CD1a is a glycoprotein expressed on cortical T-ALL and only on healthy thymocytes and Langerhans cells. Taking into account its safe pattern of expression, CD1a might represent a valuable therapeutic target for thetreatment of T-ALL. Aims: With the aim to provide an effective immune-therapeutic strategy for T-ALL, we developed a bispecific T cell engager (BTCE) derived from a novel UMG2 mAb that recognize a previously uncharacterized CD1a epitope. Methods: To evaluate the specificity of UMG2 binding to CD1a epitope, HEK293T cells which do not express CD1a endogenously, have been used. In this regards, cells were transfected with a plasmid that encode for CD1a or with an empty vector and UMG2 reactivity has been evaluated by flow cytometry. To assess the unicity of UMG2 mAb binding, a competitive binding assay between UMG2 and commercially available CD1a antibodies has been performed. The UMG2 expression profile on peripheral blood cells from healthy donors and on a panel of cortical T-ALL cells has been evaluated. To develop a UMG2-CD3 construct, an asymmetric 2 + 1 UMG2-CD3 bispecific T cellengager (BTCE) has been generated by using knobs into hole technology. UMG2-CD3 T cell-redirected cytotoxicity has been evaluated on HEK293T wild type, on HEK293T-CD1a+ and on patient-derived T-ALL cells, co-cultured with peripheral blood mononuclear cells (PBMCs), CD4/CD8 depleted and CD56 enriched lymphocytes at different E:T ratio.Moreover, T cell activation has been assesed by flow cytometry. UMG2-CD3 anti-tumor activity against a CD1a+ T-ALL cells has been evaluated in vivo. For this purpose,Hu-PBMCs NSG mouse model has been generated and tumor growth has been assessed by fluorescent imaging probe via IVIS system. Results: UMG2 mAb recognizes a novel CD1a epitope and does not compete with any of the commercially available anti-CD1a mAbs with the exception of a partial competition with NA1/34-HLK clone. A strong UMG2 reactivity has been observed on T-ALL cells, while no binding has been found on normal blood cells. A concentration-dependent T cell cytotoxicity on CD1a+ T-ALL cells co-cultured with PBMCs in the presence of UMG2-CD3 has been observed. Minimal UMG2-CD3 residual anti-tumor activity has been observed in CD4/CD8 depleted and CD56 enriched lymphocytes. CD56 depleted and Fc-blocked BMCs were able to induce an anti-T-ALL activity comparable to total PBMCs, demonstrating that UMG2-CD3 could not recruit monocytes and NK cells through Fc-FcyR interaction. Moreover, the concentration-dependent increase of i) T cell proliferation, ii) cytotoxic degranulation marker (CD107a), iii) expression of cell surface activation markers (CD25, CD69),and iv) pro-inflammatory cytokine secretion (IL-2, TNF-α, IFN-γ) has been observed in the presence of UMG2-CD3. Importantly, in an in vivo immune-humanized NSG mice model,UMG2-CD3 was able to significantly inhibit tumor growth and then conferring the survival advantage of treated animals. Summary/Conclusion: All our findings, demonstrated that UMG2-CD3 BTCE represents a promising immune-therapeutic agent against T-ALL to be further investigated for clinical translation.