Rituximab-induced direct inhibition of T-cell activation

BACKGROUND

Rituximab, an anti-CD20 monoclonal antibody, is reported to increase the T-cell-dependent infection risk. The current study was designed to investigate whether rituximab interferes with T-cell activation.

PATIENTS AND METHODS

Patients with non-Hodgkin lymphoma receiving 4-6 courses of 375 mg/m(2) rituximab underwent detailed assessment of T-cell activation pre- and post-rituximab. A similar analysis assessed the in vitro effect of rituximab on T-cell activation in response to allogeneic dendritic cells (allo-DCs) and other stimuli.

RESULTS

Patients receiving rituximab exhibited a significant decline in IL-2 and IFN-γ levels in peripheral blood, most prominent after repeated rituximab courses. Evaluation at 3 months after rituximab therapy showed restoration of inflammatory cytokine production. Similarly, in vitro stimulation of peripheral blood mononuclear cells in the presence of rituximab resulted in a significant decrease in T-cell activation markers, inflammatory cytokine production and proliferative capacity. These effects were also observed using B-cell-depleted T cells (CD3(+)CD25(-)CD19(-)) and were accompanied with disappearance of CD3(+)CD20(dim) T-cell population.

CONCLUSION

Rituximab administration results in transient, dose-dependent T-cell inactivation. This effect is obtained even in B-cell absence and may increase the infection risk.

Unresolved issues in diffuse large B-cell lymphomas

For more than 25 years, the combination of cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) was considered the 'gold standard' for the treatment of aggressive lymphomas, 90% of which are diffuse large B-cell lymphomas (DLBCLs). After the demonstration of rituximab's single-agent activity in DLBCL, a pivotal trial in elderly patients demonstrated that combining rituximab with eight applications of CHOP significantly improved complete remission rates, and event-free and overall survival rates compared with CHOP alone. These positive results have meanwhile been confirmed by two additional randomized trials and have been extended to young patients with good-prognosis DLBCL by a fourth trial and rituximab, in combination with CHOP, has become accepted worldwide as the new standard for all DLBCL. Remaining issues concern biology-based approaches and the guidance of therapy by PET, the definition of the optimal dosage and schedule of rituximab for DLBCL, as well as the optimal chemotherapy regimen partner for rituximab. Finally, patients failing after rituximab-containing immunochemotherapy have a dismal prognosis and the treatment of these patients has become a prime challenge in the rituximab era.

Dose-intensified treatment of advanced-stage diffuse large B-cell lymphomas

The introduction of the CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) regimen 30 years ago was the great breakthrough in the treatment of advanced-stage aggressive lymphomas. About 50% of all patients treated with CHOP achieved complete remission, and about one third experienced long-term disease-free survival and cure. Attempts to improve results by modifications of CHOP using escalated doses, additional drugs, or the alternative use of putatively non-cross-resistant chemotherapy regimens were not confirmed in randomized trials. With the availability of granulocyte colony-stimulating factor (G-CSF) and the tool of autologous stem cell support in the 1990s, dose escalation, dose densification (by interval reduction), or combinations thereof were pursued to increase dose intensity. While dose-escalation strategies, including high-dose approaches necessitating stem cell support, have not been demonstrated unequivocally yet to be superior to a baseline CHOP-21, dose-dense (biweekly) modifications improved the outcome of young and elderly patients with aggressive lymphomas compared to baseline CHOP-21. The challenges in the era of the monoclonal antibody rituximab are the identification of the ideal chemotherapy partner for rituximab both with respect to potential synergistic effects and to the lack of interference with its effector mechanisms. Finally, the issue of intensifying rituximab within such approaches must be addressed by appropriately designed randomized trials.