Rituximab immunotherapy results in the induction of a lymphoma idiotype-specific T-cell response in patients with follicular lymphoma: support for a "vaccinal effect" of rituximab.

The incorporation of rituximab, a chimeric anti-CD20 monoclonal antibody, into the therapeutic armamentarium for patients with follicular lymphoma (FL) has significantly improved treatment outcome for such patients. Despite the almost universal application of this therapy, however, its exact mechanism of action has not been completely defined. One proposed mechanism is that of a "vaccinal" effect, whereby FL cell kill by rituximab results in the elicitation of an FL-specific T-cell response. The demonstration that rituximab can even elicit such a response in patients has, to our knowledge, never been shown. We analyzed the response against the immunoglobulin expressed by the FL before and after rituximab monotherapy in 5 FL patients and found an increase in FL idiotype-specific T cells after rituximab in 4 of 5 patients. Our data thus provide "proof of principle" for the ability of passive immunotherapy with rituximab to elicit an active FL-specific cellular response.