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Targeting and Depletion of Acute Myeloid Leukemia Blasts By MEN1112, a Novel Humanized Defucosylated Monoclonal Antibodies with Specificity for Bst1/CD157 Antigen

Adriano Venditti, Francesco Buccisano, Luca Maurillo, Maria Ilaria Del Principe, Andrea Coppola, Patrizia Palomba, Anna Aureli, Roberto Arriga, Daniela Bellarosa, Alessandro Bressan, Stefano Manzini, Cecilia Simonelli, Monica Binaschi, Sergio Amadori and Giuseppe Sconocchia

Abstract

MEN1112 is a new humanized, defucosylated, monoclonal antibody (mAb) with high specific affinity for Bst1/CD157 antigen. Bst1/CD157 antigen expression on blood cells of acute myeloid leukemia (AML) patients and healthy donors was investigated by flow cytometry using a PE-labeled MEN1112 mAb. Twenty three patients affected with AML have been tested, 18 at diagnosis, 4 at relapse, 1 resistant. In 16 out of 23 patients both bone marrow (BM) and peripheral blood (PB) specimens were evaluated. PB and BM samples from healthy donors (N=2) were also assessed. In healthy donors and AML patients, PB and BM lymphocytes were Bst1/CD157 antigen negative whereas monocytes and neutrophils showed a distinct pattern of MEN1112 mean fluorescence intensity (MIF), with monocytes having the brightest expression. In the stem cell compartment, an intermediate level of MFI was observed (p<0.001). Prevalence of expression of the antigen on patients’ samples was over 90%. On AML blast cells from each single patient, MEN1112 expression was heterogeneous; indeed the antigen was expressed on 50%±29% and 47% ±39% of blasts in BM and PB, respectively. The anti-leukemia activity of MEN1112 on AML cell lines was tested, in vitro, by a flow cytometry-based cell depletion assay in the presence of lymphokine activated immune effector cells: a strong depletion of leukemia cells was demonstrated suggesting that MEN1112 might exert anti-leukemia activity through antibody dependent cell-mediated cytotoxicty (ADCC). The activity of MEN1112 was also tested ex vivo on whole PB showing that the antibody was able to deplete AML blasts in 9 out of 23 patients (47.4 %) with a percentage of AML blast depletion ranging between 4.3 - 66 %. In whole BM from 2 out of 11 evaluable patients MEN1112 induced 68% and 23% of AML blast depletion. Bst1/CD157 shedding assessment showed that, in the sera from AML samples, the concentration of Bst1/CD157 antigen was comparable to that measured in healthy donors. Moreover, since Fcγ receptor (CD16) genotype might be a factor contributing to the antitumor activity of the antibody, the polymorphism CD16-158Phe/Val was analyzed. Five out of 19 samples were homozygous for CD16-158 Phe; 5 were homozygous for CD16- 158 Val and 9 were heterozygous for CD16-158. MEN1112-induced blast depletion was observed for each genotype. Moreover, in an attempt to identify the determinant of MEN1112 activity, % in PB of blast (antigen positive), NK cells or residual normal cells were evaluated. Altogether, these results are promising suggesting the potential for an ADCC-mediated MEN1112 antileukemic effect and they support the clinical development of MEN1112.

Disclosures Venditti: Menarini Ricerche SpA: Research Funding. Buccisano: Menarini Ricerche SpA: Research Funding. Del Principe: Menarini Ricerche SpA: Research Funding. Coppola: Menarini Ricerche SpA: Research Funding. Palomba: Menarini Ricerche SpA: Research Funding. Aureli: Menarini Ricerche SpA: Research Funding. Arriga: Menarini Ricerche SpA: Research Funding. Bellarosa: Menarini Spa: Employment. Bressan: Menarini Ricerche SpA: Employment. Manzini: Menarini Ricerche SpA: Employment. Simonelli: Menarini Ricerche SpA: Employment. Binaschi: Menarini Ricerche SpA: Employment. Amadori: Menarini Ricerche SpA: Research Funding. Sconocchia: Menarini Ricerche SpA: Research Funding.

  • * Asterisk with author names denotes non-ASH members.