T cells in patients with B-cell chronic lymphocytic leukemia (B-CLL) and multiple myeloma (MM) : an immunological study

Abstract

There are several lines of evidence that T cells in patients with Multiple Myeloma (MM) and B-cell Chronic Lymphocytic Leukemia (B-CLL) are phenotypically aberrant. The overall aim of this thesis was to study T cells with a focus on TCR-signaling pathways in these two B-cell malignancies. The role of T-cells in B-CLL etiology was also examined.

In the first study the expression of the TCR a b , CD28, CD152, CD154 and the signal transduction molecules CD3 z , Lck , Fyn , ZAP-70 and PI3-kinase was studied. In addition, the cytokines IFN- g , IL-4 and IL-2 in unstimulated and superantigen-stimulated T cells of MM patients at different stages of the disease was examined by intracellular staining and flow cytometry. The results of this study demonstrated multiple abnormalities both in freshly isolated T cells and following in vitro activation. The CD3 z -chain, Lck , Fyn and ZAP-70 were all generally downregulated and did not respond normally to a TCR-activating signal. The aberrations increased with advancing disease stage and tumor burden.

The second study was undertaken to examine the TCR-signaling components as well as cytokine production in T cells of CLL patients with indolent or progressive disease. The cumulative data of this study suggest that several but not all T cell signaling molecules may be normal or even overexpressed in B-CLL patients in comparison to normal T cells. This observation was especially true in patients with indolent CLL. In addition, the expressions of CD3- z chain and ZAP-70, which are key molecules in the initiating of intracellular TCR signaling pathway, as well as IFN- g and IL-4 were overexpressed to a greater extent in indolent patients than in progressive patients. The overall impression collected from these results suggest that the T cells in B-CLL demonstrate a state of chronic stimulation although this activation does not result in spontaneous anti-leukemic effector activity.

Fludarabine is a purine analogue and alemtuzumab a humanized anti-CD52 monoclonal Ab that are used for treatment of B-CLL. Treatment with either of these agents results in significant reduction of T cells and inhibition of cell mediated immunity. In the next study we investigated the expression of signaling molecules and cytokine production by T-cells of B-CLL patients who were in long-term unmaintained remission/plateau phase following fludarabine or alemtuzumab treatment. T-cell function was assessed after stimulation with the recall antigen, tuberculin purified protein derivative (PPD) or the polyclonal mitogen phytohemagglutinin (PHA). The results of this study demonstrated that T-cell functions might be relatively well preserved long-term after treatment with fludarabine and alemtuzumab.

In the fourth work we have analyzed global gene expression profiles of T cells from the blood of indolent B-CLL patients in an attempt to delineate T cell factors that may potentially influence the malignant B-CLL cells. We have also attempted to identify genes that may contribute to expansion and aberrant functions of T-cells in B-CLL patients. The results of this study demonstrate the expression of a large number (356) of genes that are involved in different cellular pathways and activities including signaling, proliferation control, apoptosis, metabolism, immune response, and cytoskeleton formation are dysregulated. Three genes that demonstrated the greatest upregulation were the chemokines XCL1, XCL2, and the cytokine IFN- g. CCL4 and CCL5 are two other important chemokines that also was found to be specifically upregulated in T cells of B-CLL patients.

Collectively, our results indicate that T cells of MM and B-CLL patients exhibit a variety of anomalies and aberrations in their phenotype and function, which are exacerbated with progressive disease. The preservation of T cell function observed in patients on long term follow up following treatment with these agents may be due to a small population of noncycling memory T cells that remain relatively unaffected by the treatment. The results of the microarray analysis demonstrate that T-cells in B-CLL potentially produce several factors that may have a supportive and antiapoptotic function on the leukemic clone giving credence to the hypothesis that T cells in B-CLL may contribute to the etiology of the malignancy. The therapeutic potential of agents like fludarabine and alemtuzumab may partially be attributable to their ability towards reducing these abnormal T cells.