New approaches in the immunotherapy of haematological malignancies.

Advances in the management of haematological malignancies have allowed to obtain improved remission rates. Nonetheless, relapses impair these results and justify the search for novel therapeutic strategies. Clinical data demonstrate that the immune system plays an important role in the control of haematological malignancies. An increased frequency of haematological malignancies is observed in immunodeficiency states. Reversal of the immunosuppression is sometimes sufficient to induce tumour regression (withdrawal of cyclosporine in post-transplant lymphoproliferations, highly active anti-retroviral treatment in human immunodeficiency virus related Kaposi's disease). Another line of evidence for the involvement of the immune system in the anti-tumour response comes from the observation of spontaneous anti-tumour responses that parallel the occurrence of paraneoplastic immune-mediated syndromes. Finally, the efficiency of allogeneic transplantation in the haematological field has been clearly demonstrated to depend on the immune-mediated graft vs. leukaemia effect. Nonetheless, tumours develop in immune competent patients because of various tumour escape mechanisms, such as loss of human leucocyte antigen class I antigens, absence of target recognition by deficient adhesion/co-stimulatory molecule expression, tumour cell counterattack against immune effectors, direct (contact-dependent) or indirect (cytokine-mediated) impairment of T-lymphocyte activation. Novel immunotherapy approaches are now orientated in a convergent direction, i.e. the reversal of immune escape mechanisms either via the correction of deficient phases of the immune response or by the amplification of physiological mechanisms.