Rituximab May Be Effective in Purging in Vivo Autografts for Indolent Lymphoma

BALTIMORE—The monoclonal antibody rituximab (Rituxan) may be effective in purging in vivo autografts for indolent lymphoma, and post-transplant may serve as adjuvant immunotherapy, according to research presented at the ASH meeting.

A study from Johns Hopkins Oncology Center in Baltimore suggests that rituximab, already approved for the treatment of relapsed or refractory low-grade or follicular, CD20-positive B-cell non-Hodgkin’s lymphoma, may have broader applicability in hematologic malignancies.

Two Years’ Experience

For about 2 years, rituximab has been used at Johns Hopkins for in vivo purging of peripheral blood stem cells (PBSC) before autologous transplant for non-Hodgkin’s lymphoma. This approach is based on rituximab’s activity in patients with low-grade lymphoma and its ability to deplete peripheral blood of lymphocytes “and theoretically also of lymphoma cells,” explained Ian W. Flinn, MD, Assistant Professor of Oncology there.

Tumor contamination of the PBSC graft was measured with lymphoma colony formation and/or polymerase chain reaction (PCR). Dr. Flinn said that using rituximab as a purge has cleared peripheral blood of all detectable lymphoma cells by PCR assay in a small series of patients.

“We were looking for a new purging method,” he said. “It seemed that by giving the patient the antibody rather than by treating the graft after the cells were collected, you could prevent the mobilization of tumor cells.”

Results from Two Trials

Dr. Flinn presented the combined results from two trials involving 51 patients, most with follicular lymphoma. The trials were similar in design, except in the second trial, a number of patients were CD34-selected for tumor depletion if at least 5 x 106 CD34+ cells/kg (twice the number needed for transplant) were collected. In these 19 patients, the investigators were able to determine purging efficacy with and without the additional CD34-selection, he explained.

“The logic is that with positive and negative selection, you are better able to purge the graft. However, with ex vivo technique many CD34 cells are lost and transplantation may not be possible,” he pointed out. Rituximab does not interfere with stem cell mobilization and thus there are more stem cells available for CD34 selection.

High-volume Apheresis

Patients received 375 mg/m² of rituximab on day 1 of mobilization, followed by cyclophosphamide (Cytoxan, Neosar) 2.5 g/m² on day 4, and either G-CSF 10 µ/kg starting on day 5 or GM-CSF 10 µ/kg on days 5 to 11 and G-CSF 10 µ/kg starting on day 10 through the last day of apheresis. Stem cells were collected using a high-volume apheresis procedure.

The preparative regimen consisted of either cyclophosphamide and total body irradiation or busulfan (Myleran) and cyclophosphamide in patients with prior radiotherapy. Post-transplant, patients in the first study received one dose of rituximab and patients in the second study received four doses.

Successfully Mobilized

Forty-six of the 51 patients were successfully mobilized (median 10.6 x 106 CD34+/kg, range of 2.24 x 106 to 59.5 x 106 CD34+/kg), and most of these required only one high-volume apheresis.

“We found that the majority of patients undergoing in vivo purging were free of lymphoma by colony forming assay, but there was an incremental increase in these numbers [depleted] after CD34 selection,” Dr. Flinn reported.

Thirteen of 19 patients were lymphoma-free before CD34 selection, and 17 of 19 after CD34 selection. Seven patients whose lymphomas were positive for either t(11;14) or t(14;18) received grafts that were not CD34 selected. Only one of these grafts was PCR-positive for lymphoma.

“So far it looks as if the use of both techniques is the best,” Dr. Flinn noted. “But there are still several questions: are we giving the optimal dose of rituximab before stem cell mobilization to get the best purge possible prior to transplant? You might give three to four doses of Rituxan prior to mobilization, and this might produce a better purge and CD34 selection might not be needed,” he proposed.

CD34 selection is labor intensive and expensive.

“Furthermore, some studies have found that there are a population of CD34 cells that are positive for t(14;18). Therefore, grafts that are only CD34 selective may still contain neoplastic cells,” Dr. Flinn said.