Single-agent rituximab in treatment-refractory or poor prognosis patients with chronic lymphocytic leukemia

Long-Term Response and Possible Cure of Patients With B-Cell Malignancies With Dose-Escalated Rituximab

Rituximab (R), a chimeric monoclonal antibody targeting CD20 antigen on B-cells, has become a standard of care in the treatment of B-cell malignancies, most often in conjunction with cytotoxic chemotherapy. Activity has been demonstrated in many subtypes of B-cell lymphoma, including diffuse large cell lymphoma, follicular lymphoma (FL), mantle cell lymphoma (MCL), chronic lymphocytic leukemia (CLL), lymphocyte-predominant Hodgkin lymphoma, and Waldenström macroglobulinemia (WM). Additionally, dose escalation of R as a single agent has demonstrated improved activity in previously treated/poor prognosis CLL. We present 4 cases of B-cell malignancy (2 CLL variants/MCL, 1 FL, 1 WM) who received dose-escalated R as a single agent and achieved complete response (3 patients) and stable disease/partial response (1 patient) of 6.5+ to 15+ years duration. They have been off treatment for 6.5+ to 15+ years. Toxicity was minimal, with initial infusion reactions similar to those observed with standard dose infusions. There were no serious treatment-related adverse events or infections. Dose escalated R as a single agent may possibly be curative for some patients with B-cell malignancies, unlike the standard empiric dose of 375 mg/m², and deserves further study.

Maintenance in CLL

In this issue of Blood, Abrisqueta and colleagues report on the outcomes of a phase 2 clinical trial evaluating rituximab maintenance therapy in chronic lymphocytic leukemia (CLL) patients after treatment with rituximab, fludarabine, cyclophosphamide, and mitoxantrone (R-FCM).

Intraclonal complexity in chronic lymphocytic leukemia: fractions enriched in recently born/divided and older/quiescent cells

The failure of chemotherapeutic regimens to eradicate cancers often results from the outgrowth of minor subclones with more dangerous genomic abnormalities or with self-renewing capacity. To explore such intratumor complexities in B-cell chronic lymphocytic leukemia (CLL), we measured B-cell kinetics in vivo by quantifying deuterium ((2)H)-labeled cells as an indicator of a cell that had divided. Separating CLL clones on the basis of reciprocal densities of chemokine (C-X-C motif) receptor 4 (CXCR4) and cluster designation 5 (CD5) revealed that the CXCR4(dim)CD5(bright) (proliferative) fraction contained more (2)H-labeled DNA and hence divided cells than the CXCR4(bright)CD5(dim) (resting) fraction. This enrichment was confirmed by the relative expression of two cell cycle-associated molecules in the same fractions, Ki-67 and minichromosome maintenance protein 6 (MCM6). Comparisons of global gene expression between the CXCR4(dim)CD5(bright) and CXCR4(bright)CD5(dim) fractions indicated higher levels of pro-proliferation and antiapoptotic genes and genes involved in oxidative injury in the proliferative fraction. An extended immunophenotype was also defined, providing a wider range of surface molecules characteristic of each fraction. These intraclonal analyses suggest a model of CLL cell biology in which the leukemic clone contains a spectrum of cells from the proliferative fraction, enriched in recently divided robust cells that are lymphoid tissue emigrants, to the resting fraction enriched in older, less vital cells that need to immigrate to lymphoid tissue or die. The model also suggests several targets preferentially expressed in the two populations amenable for therapeutic attack. Finally, the study lays the groundwork for future analyses that might provide a more robust understanding of the development and clonal evolution of this currently incurable disease.