Rituxan

Rituximab as a single agent is an experimental form of treatment in CLL (as opposed to low grade non-Hodgkin's lymphoma) with a very low response rate. The original Pivotal study showed a 13% response rate for SLL/CLL, though higher doses did produce higher responses, and there is some experimental evidence that responses cam be enhanced by activating the effector cells with growth factors.

However, response were defined in the classical way for medical oncology, and there is no doubt that a lot of patients had minor responses judged on softer criteria.

Theoretically there is no reason that repeated responses should not be obtainable with rituximab. Loss of CD20 from the surface of CLL cells is possible, but very rare.

There is some experimental evidence that effector mechanisms may become refractory after rituximab treatment. This is believed to occur because the Fc gamma IIb receptor on macrophages is upregulated, and this is inhibitory to the effect of macrophages. If this is true then intermittent rituximab every few months might be a successful strategy. However, there is no clinical trial evidence to help us here. Some people think that Neupogen might enhance the effect of rituximab, but other think that it induces a "TH2 field" that inhibits macrophage ADCC. Because of these uncertainties it is impossible to predict what effect maintenance rituximab might have.