Stimulation of antibody dependent cellular cytotoxicity (ADCC) in SCID mice significantly improves the therapeutic efficacy of an anti-CD7 antibody and immunotoxin directed against human T-cell leukaemia xenografts
Authors: David J. Flavell, Jenny Keeley, Sarah L. Warnes, Armorel Noss, Sopsamorn U. Flavell
Journal: Cancer Research (2005)

4271  A B-cell phenotype occurs in approximately 80-85% of childhood acute lymphoblastic leukemia (ALL). Although the five-year survival rate for pediatric ALL is about 80%, the remaining 20-25% who relapse have a dismal prognosis and their treatment remains controversial (Chessells et al, Br J Haematol, 1998). Few agents have been approved for the treatment of pre-B ALL in the past decade and no novel targeted therapies that deliver drug precisely to the pre-B ALL cell with limited toxicity to normal cells are presently approved therapeutic drugs in childhood ALL. CD22 is an especially promising target, because it is present exclusively on normal B-cells (Tedder et al, Ann Rev Immunol, 1997), 95% of pre-B ALL, and mature B-cell ALL (Perkins, Cairo, Clin Adv Hematol, 2003). Anti-CD22 antibodies in development include epratuzumab, a humanized antibody (hLL2) to CD22, 90Y-DOTA-hLL2, a radiolabeled immunoconjugate, and CMC-544, a humanized anti CD22 IgG4 conjugated to calicheamicin. CD74, an integral membrane protein, is a major histocompatibility complex (MHC) class II chaperone and is also expressed on B-lymphocytes. Furthermore, doxorubicin, when conjugated to anti-CD74, has been shown to be effective in treating B-NHL in a xenograft model (Griffiths et al, Clin Can Res, 2003). In this study, we sought to determine the expression of CD22 and CD74 and antibody dependent cellular cytotoxicity (ADCC) with these antibodies in pre-B ALL cell lines, including poor risk, RS4-11, t(4;11) and SUP-B15, t(9;22), and good risk, REH, t(12;21). The T-cell line Loucy, t(16,20), was used as a negative control and the lymphoma line, RAJI, as a positive control. Antigen expression of CD22 was detected by flow cytometry using a direct staining method with CD3-fluorescein isothiocyanate (FITC), CD19-FITC, CD22-Cy, CD74-FITC, IgG1-phycoerythrin (PE)-cytochrome(Cy)5 and IgG2a-FITC (isotype controls) (BD Biosciences). ADCC using unlabeled anti-CD22 (0.05 mcg/105 cells), anti-CD74 (5 mcg/ml) and peripheral blood mononuclear cells (PBMNC) as the effector cells (10:1 effector: target ratio) was performed by measurement of released europium (Perkin Elmer) in a fluorometer. CD22 expression in RS4-11, SUP-B15 and REH cells was 84.22 ± 2.47%, 93.67 ± 0.76% and 85.75 ± 2.03%, respectively. CD74 expression in RS4-11, SUP-B15 and REH cells was 42.68 ± 1.45%, 56.70 ± 3.86% and 44.87 ± 3.02%, respectively. Results of the cytotoxicity with anti-CD22 and anti-CD74, respectively, are: RS4-11, 66.84 ± 0.04% (p=0.0003), 39.81 ± 0.06% (p=0.3); SUP-B15, 51.97 ± 0.03% (p=0.0008), 66.95 ± 0.03%(p=0.0007); REH, 56.39 ± 0.02% (p=0.04), 59.08 ± 0.03% (p=0.003) vs Loucy 16.37 ± 0.07%, 34.65 ± 0.05%. These two new targets, CD22 and CD74, may offer promising novel strategic approaches for the treatment of relapsed or refractory pre-B ALL with targeted immunotherapy.