BETHESDA, MdMolecular complete remissions of follicular lymphoma have been achieved with use of a patient-specific vaccine, Maurizio Bendandi, MD, reported at the plenary session of the American Society of Hematology annual meeting.
The vaccine, which must be prepared specifically for each patient, wiped out residual lymphoma cells in eight of 11 patients treated, all of whom were in first complete clinical remission after induction chemotherapy, and this effect correlated with development of cytotoxic T lymphocytes specific for each patients tumor.
Efficacy was measured by a polymerase chain reaction (PCR) assay for cells with the t(14;18) gene translocation marker for lymphoma.
The work was done in the Department of Experimental Transplantation and Immunology, Medicine Branch, at the National Cancer Institute (Bethesda), and in the Department of Pathology, Penn State University (Hershey).
The rationale behind this approach is to modify a tumor cell or tumor-derived antigen, which is then injected back into the patient to induce host antibody and T-cell responses.
At a symposium held in conjunction with ASH, Larry Kwak, MD, PhD, principal investigator, said that the vaccine is used in an attempt to induce an immune response to a self-antigen that has escaped detection, in order to correct an experiment that failed in nature.
Possible tumor vaccine targets include tumor antigens or peptide-pulsed antigen-presenting cells, HLA-matched allogeneic tumor cell lines, or (as in this trial) autologous tumor cells.
To make the follicular lymphoma vaccine, tumor cells from each patient are cultured and induced to secrete immunoglobulin proteins. Surface receptor (M-protein) molecules are purified and conjugated to a carrier protein (keyhole limpet hemocyanin). After patients complete induction chemotherapy, the conjugate is then injected to induce the patients T cells to recognize and kill residual tumor cells.
Although the vaccine must be prepared individually for each patient, Dr. Bendandi said that it fits easily into the conventional treatment regimen. Preparing the vaccine takes about 3 months, which is well within the 6 months required to complete induction chemotherapy, he explained.
Clinical Trial Results
Dr. Bendandi said that the vaccine approach was tested in 20 patients with follicular lymphoma who were in first complete remission following ProMACE chemotherapy. Complete remissions were verified by restaging, including bone marrow examination. Patients were given a 6-month break for immune recovery, then given the vaccine as a series of five monthly 0.5-mg injections, together with GM-CSF as an immune adjuvant.
With a median follow-up of 34+ months after completion of ProMACE (range, 19+ to 42+ months), 18 of 20 patients remain in continuous clinical complete remission.
Ability to Eradicate t(14;18)
Since vaccine therapy was administered when the patients were already in complete remission, standard tumor shrinkage criteria cannot be used to determine efficacy; therefore, we have focused on the potential ability of this therapy to eradicate t(14;18) positive follicular lymphoma cells from peripheral blood mononuclear cells (PBMCs), as detectable by PCR, Dr. Bendandi said.
The researchers analyzed serial PBMC samples with bcl-2 mbr-rearrangement-specific primers in a nested PCR, which can detect one tumor cell in 100,000 cells. All assays were performed by individuals blinded to clinical information in independent laboratories at two separate sites.
Dr. Bendandi said that nearly complete concurrence of results was observed between replicates of individual samples and between the two laboratory sites. All bcl-2 rearrangements were sequenced and found to be unique.
Eleven of the 20 patients had tumors that were mbr positive and thus were available for molecular analysis. All 11 patients were PCR positive in PBMC samples at diagnosis, as well as just before vaccine therapy, despite being in continuous clinical complete remission for 6 to 12 months after chemotherapy. After vaccination therapy, eight of these 11 patients became PCR negative.
This elimination, or at least reduction, of lymphoma cells from the peripheral blood was also sustained over time. All eight patients have maintained PCR negativity in follow-up samples for a median of 11+ months after completion of vaccination (range, 1+ to 27+ months).
The other three patients have remained continuously PCR positive, and one relapsed shortly after completion of vaccination.
These PCR results also correlated with development of cytotoxic T lymphocytes (CTLs) capable of lysing the patients own lymphoma cells and with induction of tumor necrosis factoralpha (TNF-alpha) and other antitumor cytokines, he said. Immunologic studies showed that autologous follicular lymphoma-specific CD8+ T cells were induced in most patients as a result of vaccination.
In response to a question about whether patients in ProMACE induced complete remission might not become PCR negative over time without vaccination, Dr. Bendandi said that the literature would support the persistence of PCR positivity in such patients treated with conventional-dose chemotherapy.
The long-term clinical significance of molecular remissions in patients with follicular lymphoma remains to be determined, he said. However, aside from case reports of isolated tumor regressions, this systematic analysis of molecular response rate provides the first evidence for an anti-tumor effect of lymphoma-specific vaccination.
Dr. Bendandi said that the researchers are not claiming that PCR conversion means complete destruction of the tumor or prolonged patient survival. A randomized trial is now required to assess the potential impact of the vaccine on disease-free survival.