Consolidation and Maintenance Immunotherapy with Rituximab Improve Progression Free Survival within ZAP-70 Positive Chronic Lymphocytic Leukemia (CLL).

Clinical studies of monoclonal antibodies combined with chemotherapy have attained more complete responses and longer duration of responses in CLL because this approach reduces disease burden to levels detectable only by immunological or molecular methods. Recent literature data indicate that V_H genes, CD38, ZAP-70 protein, and cytogenetic status have a major impact on CLL prognosis. We performed a phase II study that added rituximab sequentially to fludarabine (Flu) as initial therapy for symptomatic, untreated CLL in order to evaluate both the clinical response and outcome. Remission status was also assessed by a multiparametric flow cytometric method based on the detection of CD19+CD5+CD79b− residual B-CLL lymphocytes. V_H mutational status, CD38 and cytogenetics were obtained in all pts before treatment. ZAP-70 protein was performed by flow cytometry using an anti-ZAP-70 Alexa Fluor 488 conjugated antibody. Seventy-five CLL pts, median age 60 years, received six monthly courses of Flu (25 mg/m² for 5 days) and four weekly doses of rituximab (375 mg/m²) starting on an average of thirty days after completion of Flu therapy. According to modified Rai stages, 6 pts had a low stage, 66 an intermediate stage and 3 a high stage. Based on NCI criteria, 61/75 (81%) pts achieved a complete remission (CR), 10/75 (13%) a partial remission (PR) and 4/75 (5%) no response. Three pts presented grade 3 (WHO) infective lung toxicity and 1 patient acute fatal B hepatitis.

Hematologic toxicity included neutropenia (grade 3 and/or 4 in 38 pts) and thrombocytopenia (grade 3 and/or 4 in 4 pts). Twenty eight pts, either with CD5+CD19+CD79b− (MRD) bone marrow (BM) cells >1% (n=17 pts) or with CD19+CD5+CD79b− (MRD) peripheral blood lymphocytes (PBL) >1000/microl (n=11 pts) within six months after completion of the induction treatment, underwent consolidation/maintenance therapy with four monthly cycles of rituximab at 375 mg/m² followed by twelve monthly doses of rituximab at 150 mg/m². The median follow-up duration was 37 months. Noteworthy, all pts experienced a long progression-free survival (PFS) from treatment (67% at 5 years). Nevertheless, CLL pts that underwent consolidation therapy (n=28) showed a significant longer duration of response (75% vs 27% at 5 years, P=0.002) in comparison with the subset of not consolidated and BM or PBL MRD positive (n=18) CLL pts. Interestingly, BM and PBL MRD negative pts (n=26) showed a duration of response similar to that of the consolidated pts. Moreover, a significant shorter PFS was observed within CD38+ pts (29% vs 79% at 5 years, P=0.005), unmutated pts (0% vs 92% at 2 years, P=0.001), ZAP-70+ pts (29% vs 92% at 5 years; P=0.00003) and within the “poor risk” [trisomy 12 or del 11q or del 17p] cytogenetic subset (0% vs 79% at 2 years, P=0.03). Interestingly, within the ZAP-70+ subset (n=35), the consolidated pts (n=12) showed a longer duration of response (68% vs 0% at 2.6 years, P=0.007) in comparison with the unconsolidated pts (n=11). Therefore, the addition of a consolidation/maintenance therapy with rituximab prolongs significantly the duration of response allowing a better outcome. Moreover, rituximab improves significantly PFS of pts notoriously at worse prognosis, such as ZAP-70+ B-CLL.