CD200: A Novel Therapeutic Target for Chronic Lymphocytic Leukemia

The ability of cancer cells to escape anti-tumor immune responses is acknowledged as one of the hallmarks of cancer. Overexpression of immunoregulatory molecules is one mechanism responsible for the immunsuppressive network that is characteristic of the tumor microenvironment. In this thesis, we investigated the role of CD200, a potent immunoregulatory molecule, in Chronic Lymphocytic Leukemia. We showed that functional blockade of CD200 on lymphoma cells or primary CLL cells, both of which express CD200 at high levels, augmented cytotoxic killing of these cells by effector CD8+ T cells in vitro. We also identified and characterized a previously unrecognized soluble form of CD200, sCD200, present in elevated levels in CLL plasma when compared to plasma from controls. The data reported show that patients with high sCD200 levels have more aggressive disease, inferring that sCD200 may be a novel prognostic marker for CLL. The in vivo function of sCD200 was investigated for its ability to support engraftment of CLL splenocytes in NOD.SCID mice. Infusion of sCD200hi CLL plasma, but not sCD200lo normal plasma, enhanced engraftment of CLL-splenocytes in vivo, an effect which was abrogated by depletion of sCD200 from CLL plasma. The prolonged engraftment of CLL cells seen in this model (>6 months) suggests these mice represent a useful pre-clinical model for drug screening. The effect of CD200 blockade was tested in this model, and was found to be as effective in eliminating engrafted CLL cells as rituximab. Investigation of the mechanisms leading to the release of sCD200 from CLL cells showed that sCD200 was produced following ectodomain shedding by ADAM proteases and MMPs. Results from studies reported in this thesis support the hypothesis that CD200 plays a major role in CLL biology, and suggests it may represent a novel therapeutic target for CLL.

Department dc:contributor.department

Medical Science

Year dc:date.issued

2013

Author dc:creator

• Wong, Karrie

Advisor dc:contributor.advisor

• Gorczynski, Reginald M.

• CD200
• CLL
• immunotherapy

Language dc:language.iso

en_ca

Handle dc:identifier.uri

http://hdl.handle.net/1807/34969

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/34969