Cytotoxic activity of gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia correlates with the expression of protein kinase Syk.

Acute myeloid leukemia (AML) cells express the cell surface antigen CD33 that, upon ligation with a monoclonal antibody (mAb), is a downregulator of cell growth in a Syk-dependent manner. An anti-CD33 mAb coupled to a toxin, gemtuzumab ozogamicin (GO), is used for the treatment of AML (Mylotarg). Therefore, we investigated whether the response of AML cells to GO treatment also depends on Syk expression. Forty primary AML samples (25 Syk-positive and 15 Syk-negative) were tested for their response to the anti-proliferative effects of GO and unmodified anti-CD33 mAb. A correlation between Syk expression and the response of leukemia cells to GO and anti-CD33 mAb was found. 'Blocking' of Syk by small interfering RNA resulted in unresponsiveness of AML cells to both GO and anti-CD33 mAb-mediated cytotoxicity. Syk upregulation by the de-methylating agent 5-azacytidine (5-aza) induced re-expression of Syk in some cases, resulting in enhanced GO and anti-CD33-mediated inhibition of leukemia cell growth. Thus, the cytotoxicity of both GO and anti-CD33 in primary AML samples was associated with Syk expression. 5-Aza restored Syk and increased the sensitivity of originally Syk-negative, non-responsive cells to CD33 ligation to levels of Syk-positive cells. These data have clinical significance for predicting response to GO and designing clinical trials.

Direct effect of bispecific anti-CD33 x anti-CD64 antibody on proliferation and signaling in myeloid cells.

Bispecific anti-CD33 x anti-CD64 antibody (BsAb) directly inhibited proliferation and colony formation of human acute myeloid leukemia cell lines, without affecting the function of normal monocytes. Addition of BsAb to normal monocytes induced tyrosine phosphorylation of Cbl and Vav, association of these molecules with CD33, and downstream signaling. In leukemia cells that were insensitive to BsAb treatment, Vav and Cbl were constitutively phosphorylated and, therefore, constitutively associated with CD33. Direct growth inhibition is an additional mechanism by which BsAb may be useful in the therapy of AML.

The human neural cell adhesion molecule L1 functions as a costimulatory molecule in T cell activation.

L1 is a neural cell adhesion molecule (CAM) known to be important for normal neurological development. Despite being described as a neural CAM, we have documented L1 expression by antigen-presenting cells of myelomonocytic origin. Here we demonstrate that L1 can function as a costimulatory molecule in T cell activation. A monoclonal antibody that abrogates L1-L1 homophilic binding significantly reduced mixed leukocyte responses initiated by allogeneic L1+ dendritic cells. Autologous T cell activation in response to phytohemagglutinin was also inhibited by blockade of L1. In accordance with these results, transfection of human L1 into a murine myeloma cell line significantly increased the capacity of these cells to stimulate xenogeneic T cell responses. As a costimulatory ligand L1 could represent a novel target for immunotherapeutic intervention and may act as an important intermediary in neuroimmunological processes and disease.

[Human oncogene expression in the normal state and in various blood system diseases]. / Ekspressiia onkogenov v norme i pri razlichnykh zabolevaniiakh sistemy krovi u cheloveka.

A study was made of the expression of the cellular oncogens c--myc, c--sis and c--abl in mononuclears from normal donors and patients with different patterns of leukemia and hemopoietic dysplasia using spot hybridization on nitrocellulose filters with virus homologs of the given oncogens. Altogether 43 persons were examined. No specific expression of the oncogens indicated was established whatever the pattern of leukemia. The relationship between the expression of these oncogens and the efficacy of the treatment of acute myeloblastic leukemia was demonstrated. However, in the given investigations, no differences were identified in the expression of oncogens in the leukemic and normal cells stimulated with PHA and phorbolic ether. Enhanced expression of cellular oncogens myc, sis and abl occurred in acute leukemia.

[Therapy of patients with myeloid leukemia with small doses of cytosine arabinoside]. / Terapiia bol'nykh mieloidnymi leikozami malymi dozami tsitozinarabinozida.

A total of 45 patients were given cytosar and daunorubicin therapy at small doses. Of them 23 patients were with acute nonlymphoblastic leukemia, 12--with hemopoietic dysplasia, and 10--with chronic myeloid leukemia. Cytosar was injected subcutaneously every 12 h at a dose of 10 mg/m2 for 10-25 days, daunorubicin was injected intravenously by drop infusion at a dose of 5 mg/m2. Clinicohematological remission was obtained in 13 patients, clinicohematological improvement in 16. Thus, a positive effect was achieved in 29 patients (64%). The authors provided some data on the influence of small doses of cytosar and daunorubicin on cell maturation in vitro.