Although chemotherapy can induce complete responses in patients with chronic lymphocytic leukemia (CLL), it is not considered curative. Treated patients generally develop recurrent disease requiring additional therapy, which can cause worsening immune dysfunction, myelosuppression, and selection for chemotherapyresistant leukemia-cell subclones. Cellular immune therapy promises to mitigate these complications and potentially provide for curative treatment. Most experience with this is in the use of allogeneic hematopoietic stem-cell transplantation (allo-HSCT), in which graft-versus-leukemia (GVL) effects can be observed and shown responsible for long-term disease-free survival. However, use of allo-HSCT for CLL is limited because of the lack of suitable donors and the treatment-related morbidity/mortality for elderly patients, who constitute the majority at risk for developing this disease. The GVL effect, however, suggests there are specific CLL-associated antigens that could be targeted in autologous cellular immune therapy. Effective strategies for this will have to overcome the disease-related acquired immune deficiency and the capacity of the leukemia-cell to induce T-cell tolerance, thereby compromising the activity of even conventional vaccines in patients with this disease. We will discuss the different strategies being developed to overcome these limitations that might provide for effective cellular immune therapy of CLL.
IntroductionChronic lymphocytic leukemia (CLL) is a CD5 ϩ B-cell malignancy that is considered incurable. Historically, the first-line treatment consisted of alkylating agents, which resulted in response rates in up to 70% of patients, but did not improve survival. 1 Treatment regimens with the nucleoside (purine) analogs, such as fludarabine monophosphate (F-ara-A) or pentostatin, were found to yield higher response rates and to provide for longer progression-free survival, 2 especially in combination with cyclophosphamide. 3 However, despite effecting increased complete response rates, treatment with purine analogs alone does not appear to improve survival. 2 Newer treatment combinations have incorporated use of monoclonal antibodies to chemotherapy. 4,5 Although treatment with such combinations might provide for a first-time-observed survival benefit, 6 such therapy still is not considered curative.Although most patients initially respond to these chemotherapeutic approaches, many develop therapy-resistant disease with repeated therapy. Patients with refractory disease more frequently have leukemia cells that harbor deletions in the short arm of chromosome 17 (17pϪ), which often is associated with loss of functional p53, or in the long arm of chromosome 11 (11qϪ) in and/or around the gene encoding the ataxia telangectasia (ATM), which is a kinase required for p53 function. 7,8 Moreover, many chemotherapy-refractory patients have leukemia cells that have lost functional p53. Because the cytoreductive activity of most chemotherapy agents requires functional p53, 9,10 loss of p53 is ...