Chronic Lymphocytic Leukemia Cells Produce a Soluble Factor(s) That Can Induce CD14+ Blood Mononuclear Cells To Assume Properties of Nurselike Cells In Vitro

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Blood (ASH Annual Meeting Abstracts) 2007 110: Abstract 1136

Chronic Lymphocytic Leukemia Cells Produce a Soluble Factor(s) That Can Induce

CD14+ Blood Mononuclear Cells To Assume Properties of Nurselike Cells In Vitro.

Davorka Messmer, PhD1, Hsu-Hsiang Chang1,*, Tomoyuki Endo, M.D.1 and J.

Kipps, M.D., Ph.D.1

1 s Cancer Center, University of California San Diego, La Jolla, CA, USA.

Abstract

CD14+ blood mononuclear cells co-cultured with chronic lymphocytic leukemia

(CLL) B cells can differentiate into large, round, adherent cells that can

attract and support survival of CLL cells in vitro. These cells, called

nurselike cells (NLC), have distinctive high-level expression of CD68, a

property also shared by lymphoma-associated macrophages (LAM), which are found

in the secondary lymphoid tissues of patients with follicular lymphoma and

appear more prevalent in lymph nodes of patients with therapy-resistant disease.

We found that NLC express significantly higher levels of B-cell activating

factor belonging to the tumor necrosis factor family (BAFF) than common

macrophages, which also can differentiate from CD14+ blood mononuclear cells in

vitro. BAFF can induce activation of NF-kB in CLL cells and enhance

leukemia-cell survival. To investigate the influence of CLL cells on the

differentiation of NLC in vitro, we cultured purified CLL cells for 24h in to

generate conditioned media. When CD14+ blood mononuclear cells of healthy donors

were cultured for 7 days in the conditioned media, the cells assumed the

morphology of NLC and acquired high-level expression of BAFF. In contrast, CD14+

blood mononuclear cells cultured in non-conditioned media did not acquire such

changes. Serial dilutions of condition media into non-conditioned media revealed

a dose-response relationship between the relative-concentration of the condition

media and the capacity of the media to induce NLC-changes in the CD14+ blood

mononuclear cells. Although the CLL cells from each patient examined (n=6) could

generate conditioned media that was effective in inducing NLC-changes in CD14+

blood mononuclear cells, initial experiments suggest that conditioned media

derived from CLL cells with features associated with more aggressive disease

(e.g. expression of unmutated IgVH and ZAP-70) showed a higher BAFF-inducing

activity compared to condition media derived from CLL cells that expressed

mutated IgVH and lacked expression of ZAP-70. Condition media was generated

under identical culture condition in all cases. Although IL-10 and TNF-a have

been shown to increase BAFF expression in other systems, we did not observe

increase in BAFF protein expression on monocytes cultured with increasing

amounts with either of these cytokine alone. These studies reveal that CLL cells

elaborate a factor(s) that can induce CD14+ blood mononuclear cells to assume

properties of NLC, which apparently are similar to the LAM also identified in

the tissues of patients with follicular lymphoma. Preliminary biochemical

characterization suggests that these factor(s) are heat- and nuclease resistant.

The results show a previously unrecognized symbiosis between CLL cells and their

microenvironment. Because the survival of neoplastic B cells might depend upon

NLC and other such cells in the microenvironment of lymphoid tissues,

identification of this factor(s), and development of agents that can block its

capacity to induce maturation of CD14+ blood mononuclear cells into NLC, could

provide a novel target for therapy of CLL and other indolent B-cell lymphomas.