The current approaches used for immune reconstitution in our ongoing clinical trials involves the adoptive transfer of T cells harvested from patients with metastatic or recurrent sarcomas. The T cells are harvested prior to the initiation of cytotoxic chemotherapy and are contaminated with circulating tumor cells in 30-50% of cases. Although it remains unknown whether such contaminated products can cause tumor recurrence, there is a great deal of concern about this potential and any approach to eradicate residual tumor from these products would be welcomed by patients, their families and their caregivers. During the past two years, we developed a collaboration with Dr. Nai-Kong Cheung of Memorial Sloan Kettering Cancer Center to study the use of monoclonal antibody 8H9 in purging these products. The results of this work were published (Merino ME, Navid F, Christensen BL, Toretsky JA, Helman LJ, Cheung NV and Mackall CL. Immunomagnetic purging of Ewing's sarcoma from blood and bone marrow: quantitation using real-time PCR. Journal of Clinical Oncology, 2001;19:3649-3659) this year. In summary, we developed a quantitative real-time PCR approach to quantitate the level of tumor contamination based upon monitoring of the chromosomal translocation found in Ewing's sarcoma. By utilizing nest PCR, we had a level of sensitivity of 1 tumor cell in 10e6 cells. Using immunomagnetic bead selection, we could lower the level of contamination by 2-4 logs. We then went on to show that clinical samples which are contaminated show levels of contamination of approximately 1 cell in 10e5-10e6 cells. Therefore, using this technique, we anticipated that 8H9 based purging along will reduce contamination below detectable levels. Furthermore, when combined with CD34 selection for autologous BMT, we anticipate an approxiamte 5 log reduction in contaminating tumor. The next phase of this project is the development of clinical trials to test purging in the context of immune reconstitution for pediatric sarcomas and in the context of autologous BMT for pediatric sarcomas. To this end, we have developed an CRADA with Memorial Sloan Kettering Cancer Center to allow the production of clinical grade moab 8H9 in sufficient quantities to undertake clinical purging protocols. We have also developed collaborations with the University of Minnesota and Memorial Sloan Kettering to collaborate on these trials. We are currently in the process of finalizing the trials themselves and submitting information for the FDA for and IND so that 8H9 may be used in this context. It is anticipated that ongoing preclinical work will take approximately one year before initiation of these trials.
