EXPRESSION OF ILT3 RECEPTOR IN CHRONIC LYMPHOCYTIC LEUKEMIA Tyrone Reid HCS 2007 Mentor: Dr. Adrianna Colovai Columbia University Medical Center ( CUMC)

INTRODUCTION Chronic lymphocytic leukemia (CLL) is the most frequent form of leukemia in adults of the Western world. CLL is characterized by the accumulation of cancerous B lymphocytes in bone marrow, blood, and lymph nodes (1,2). Patients with CLL have different types of the disease: some have slowly progressive (low-risk) disease, do not require anti-cancer treatment and live longer, while others have aggressive or rapidly progressing (high-risk) disease, require treatment and have shorter survival. Therefore, the correct decision regarding the treatment and follow-up of patients with CLL can be only made if patients with rapidly progressive disease can be distinguished from those with stable disease at the time of diagnosis. For this, laboratory tests may be very useful.

In the present study, we attempted to identify a protein that is displayed only on the surface of cancer B cells from patients with aggressive form of CLL, and not on the surface of normal B cells or B cells from patients with slowly progressing CLL. The screening of almost 100 different proteins led us to the discovery of a protein receptor, ILT3 (immunoglobulin-like transcript 3), which is only expressed by cancer B cells from patients with aggressive CLL.

MATERIAL AND METHODS Human specimens Forty-seven patients with CLL and 25 normal volunteers were enrolled in this study, in accordance to an existing IRB protocol. Flow cytometry Cell surface staining of ILT3 protein was performed using anti-ILT3 PC5 mAb (Beckman Coulter). Cells were run and analyzed on a FACSCalibur (BD Biosciences) using CellQuestPro software. Statistical analysis Statistical analysis was performed using Student’s t-test of significance and two-tailed Fisher exact test. Bonferroni criteria were applied.

RESULTS  ILT3 receptor is not expressed by normal B cells.  ILT3 was expressed by CLL B cells in 23 out of 47 patients.

NORMAL BLOODHIGH-RISK CLL

Table 1. Clinical data and ILT3 expression in CLL patients Group variable All patients ILT3 positive patients ILT3 negative patientsp value (>10% of CD19+CD5+ cells) (<10% of CD19+CD5+ cells) No. of patients Patient age (n=47)696870NS No. of male patients311813NS No. of female patients16511 Lymph node involvement (n=23) Yes15114p=0.009 No817 WBC/10 -9 L (n=46) NS LDT, months (n=25) NS

CONCLUSIONS  ILT3 protein is present on B cells from patients with high-risk CLL, but it is absent on normal B cells or B cells from patients with low-risk CLL. Thus, detection of ILT3 by flow cytometry may be used as a laboratory test to identify patients with high- risk CLL, and select the appropriate treatment for these patients.  This study opens new avenues in cancer research. We next plan to explore the role of ILT3 protein in CLL, and identify the cellular mechanisms leading to its expression in high-risk CLL.  This study also opens new possibilities for the treatment of CLL. Since ILT3 is only present on B cells from high-risk CLL patients, new drugs that target ILT3 positive B cells may be designed. Such drugs may specifically bind to ILT3 on the cell surface of cancer B cells, and kill these cells.

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Acknowledgment Dr. Adrianna Colovai Staff at CUMC Dr. Sat Staff at HCS