Abstract

Background and Methods: B-cell chronic lymphocytic leukemia (B-CLL) occurs as a result of clonal accumulation of functionally abnormal B cells. Alemtuzumab is a humanized monoclonal antibody specific for the CD52 antigen, which is highly expressed on both B-CLL cells and normal lymphocytes, but not on hematopoietic (CD34) stem cells. Alemtuzumab has been shown to effectively deplete the blood and bone marrow of lymphocytes, including CD4 and CD8 T cells, which may lead to profound immunosuppression and make patients more susceptible to infections. We and others have previously shown that the CD4 T cells in B-CLL patients may be clonally distinct from the normal population in that they present a more clonal pattern of the T-cell receptor (TCR) repertoire (

Rezvany et al,
Blood
2003
;
101
:
1063
–1070
). It is therefore of interest to study the T cell repertoire following alemtuzumab administration as well as factors affecting T cell reconstitution following CD52 targeted therapy. In this study, we evaluated in depth the T-cell receptor-beta-variable sequence (TCR BV) in CD4 and CD8 T cells by real-time PCR, before and repeatedly after/during long term follow-up, in 5 B-CLL patients who had received alemtuzumab as first-line therapy (
Lundin et al,
Blood
2002
;
100
:
768
–773
). Also, an analysis was conducted of CDR3 length polymorphism to describe changes in the clonality pattern.

Results: A decline in most of BV genes either in CD4 or CD8 T cells was observed shortly after alemtuzumab treatment, which was followed by a gradual increase in most of the BV genes during long-term follow up. CDR3 length polymorphism analysis shortly after treatment revealed an even more highly restricted pattern in CD4 T cells compared to baseline with a shift towards a monoclonal/oligoclonal pattern regardless of increased or decreased BV usage. Furthermore, in the analysis of the clonal spectrum that was expressed shortly after alemtuzumab therapy, the number of peaks was significantly reduced in CD4 (P <0.01) but not in CD8 T cells, which was followed by a gradual increase in diversity towards a polyclonal repertoire during long-term follow up.

Conclusions: These results indicate that perturbations in the T cell repertoire following alemtuzumab are complex, and are not reflected by changes in CD4/CD8 T cell numbers only. The restricted CDR3 pattern present prior to therapy became even more restricted after end of treatment, followed by a normalization of CDR3 patterns in CD4 T-cells during long-term follow-up. These results further suggest a regulatory role for T cells in relation to the malignant B cell clone in patients with B-CLL.

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