Therapeutic vaccination against malignant gliomas based on allorecognition and syngeneic tumor antigens: proof of principle in two strains of rat.

In the present study we investigated whether allogeneic glioma cells can be utilized to evoke prophylactic or therapeutic immune-mediated elimination of syngeneic glioma in two rat strains. Fisher 344 and Sprague-Dawley (SD) rats were injected with two syngeneic glioma cell lines, 9L and C6, respectively, resulting in progressive tumor growth. 9L is syngeneic to the Fisher 344 and allogeneic to the SD rats, while C6 cells are syngeneic to SD rats and allogeneic to Fisher 344 rats. Both rat strains were subcutaneously injected with their respective allogeneic tumor cells, which proved unable to grow progressively. The allogeneic cells were either rejected immediately in SD rats or within 25 days in Fisher rats, after limited tumor outgrowth. Both rat strains were subsequently challenged with their respective syngeneic glioma tumor cells and once more 10 days later with a fivefold higher dose. SD rats, even after reinjection with five times the original dosage of C6 cells, remained tumor free for at least 360 days. Similarly, Fisher rats, after initially rejecting allogeneic tumors, failed to develop syngeneic tumors. To determine anti-tumor immunity against established glioma tumors under more demanding therapeutic conditions, rats were first injected subcutaneously with their respective syngeneic tumor and vaccinated once or repeatedly (at 5-day intervals) with a mixture of the allogeneic or xenogeneic cells, with or without a lysate from the same syngeneic tumor, which served as a therapeutic vaccine preparations. The control group received either no treatment or syngeneic instead of allogeneic cells. In both strains of rats, we demonstrated that the therapeutically vaccinated groups were able to significantly reduce tumor growth, while complete rejection of tumors was noted in the SD rats. Immunization with syngeneic tumor cells alone failed to evoke anti-tumor immunity. We conclude that therapeutic immunization with a combination of allogeneic cells and syngeneic lysates induces rejection of malignant gliomas and offers a protective effect against challenge with syngeneic tumor cells. This immunization approach may prove useful as a post-surgery adjuvant therapy in future cancer treatment protocols, or even as a stand-alone therapeutic tumor vaccination.

Pre-emptive immunotherapy with CD8-depleted donor lymphocytes after CD34-selected allogeneic peripheral blood stem cell transplantation.

BACKGROUND AND OBJECTIVES: To maximize graft-versus-leukemia (GVL) effects while minimizing the risk of graft-versus-host disease (GVHD), we undertook a study of allogeneic CD34-selected peripheral blood stem cell (PBSC) transplantation followed by CD8-depleted donor lymphocyte infusion (DLI). DESIGN AND METHODS: Twenty-four patients with advanced hematologic malignancies were included. PBSC were collected in matched (N=16) or one-mismatch (N=8) related donors and CD34-selected. On day 60, donors donated lymphocytes that were CD8-depleted and separated into 3 aliquots containing 2 x 10(6), 1 x 10(7) and 5 x 10(7) CD3+ cells/kg (patients 1-13) or into 2 aliquots containing 1 x 10(7) and 5 x 10(7) CD3+ cells/kg (patients 14-24). The 1st aliquot was infused on day 60 and the other 1 (2) cryopreserved and infused on days 100 (and 140). RESULTS: An average of 100%, 100% and 84% of the scheduled dose could be administered in DLI 1, 2 and 3, respectively. Although the study group was at very high risk of GVHD, the actuarial incidence of grade II-IV acute GVHD was 28% (13% for HLA-identical siblings) with only 1 patient developing grade III-IV GVHD (after DLI). The actuarial 2-year probability of extensive chronic GVHD was similarly low (13% for all patients and 0% for HLA-identical siblings). Individual cases as well as a 30% relapse rate (0% for standard-risk patients versus 55% for high-risk patients) indicated preservation of the GVL effect. INTERPRETATION AND CONCLUSIONS: We conclude that allogeneic transplantation of CD34-selected PBSC followed by pre-emptive CD8-depleted DLI is feasible with rapid engraftment and minimizes the risk of severe GVHD. Large prospective trials are required to prove that it preserves the GVL effect fully.