Commentary on Abstract #2833 and #4812

In general, results with autologous stem-cell transplantation for patients with follicular NHL have been disappointing, without the evidence for cure observed in patients with large B-cell NHL (Rohatiner et al: J Clin Oncol 12:1177-1184, 1994; Freedman and Nadler: J Clin Oncol 11:1841-1843, 1993; Freedman et al: Blood 94:3325-3333, 1999). A major problem has been the high rate of recurrence, related, in part, to reinfusion of tumor cells.

In vitro purging with monoclonal antibodies and complement can render the stem cells PCR negative, and patients who become persistently PCR negative may experience a prolongation of disease-free survival (Freedman et al: Blood 94:3325-3333, 1999). Rituximab administered during stem-cell mobilization has been evaluated as a method of in vivo purging to reduce tumor load.

Flinn et al (abstract #2833) described their experience with 51 patients who had a variety of histologies of low-grade NHL and mantle cell lymphoma. A single infusion of rituximab was administered during mobilization, and one or four infusions were given following transplant as an adjuvant. Mobilization was successful in all but five patients, with no additional toxicity noted. No outcome data are yet available.

Buckstein et al (abstract #4812) also administered rituximab both as an in vivo purge and as adjuvant therapy following autologous transplantation. All 14 patients underwent successful stem-cell harvesting. Despite the fact that six of the seven stem-cell products remained positive, all patients subsequently became PCR negative.

Whether there are longer-term consequences of rituximab in vivo purging, such as late infections or graft failure, remains to be determined by longer follow-up. Phase III trials are being planned to evaluate the role of in vivo purging with rituximab.