T and B cells in B-chronic lymphocytic leukaemia: Faust, Mephistopheles and the pact with the Devil.

A large number of human malignancies are associated with decreased numbers of circulating T cells. B-CLL, in this regard, represents an anomaly since there is not only high numbers of circulating B cells, characteristic of the malignancy, but also a massive expansion of both CD4 and CD8 T cells. These T cells for the most part may probably not represent a leukaemia-specific TCR-dependent expansion. On the contrary, these T cells, especially the CD4 subset, might support a "microenvironment" sustaining the growth of the leukaemic B cell clone. Conversely, the leukaemic B cells may produce membrane-bound as well as soluble factors that stimulate the proliferation of these T cells in an antigen independent manner. In addition to these T cells lacking anti-leukaemic reactivity, there exist spontaneously occurring leukaemia-specific T cells recognizing several leukaemia-associated antigens, e.g. the tumour derived idiotype, survivin and telomerase. Both CD4 and CD8 leukaemia-specific T cells have been identified using proliferation and gamma-IFN assays. These reactive T cells can lyse autologous tumour cells in an MHC class I and II restricted manner. Spontaneously occurring leukaemia-specific T cells are more frequently noted at an indolent stage rather than in progressive disease. Preliminary results from vaccination trials using whole tumour cell preparations as vaccine have demonstrated that vaccination may induce a leukaemia-specific T cell response, which might be associated with clinical benefits. Extended clinical trials are required to establish the therapeutic effects of vaccination in B-CLL. Studies in our laboratory as well as those of others indicate that whole tumour cell antigen in the form of apoptotic bodies or RNA loaded on to dendritic cells may be a suitable vaccine candidate. Patients with low stage disease may maximally benefit from this form of therapy.