| ADOPTIVE T CELL THERAPY FOR
PROSTATE CANCER
Dr Steven P. Lee, Dr N. M. Steven et al University of Birmingham, Cancer Research UK |
This report describes work carried out since the initiation of this project 13 months ago exploring the use of adoptive T cell therapy for advanced prostate cancer. The grant has supported a grade 500 research technician Ms Anne-Marie Hewitt.
Progress has been made in the following areas:
1. Good Clinical Practice.
A significant amount of time and effort has been spent updating our existing procedures, facilities and quality control measures to comply with new regulations covering Good Clinical Practice (GCP) including Good Clinical Laboratory Practice (GCLP). This work has been essential to the present project because without it we would not be able to conduct the proposed infusions of T cells. Indeed, these regulations have necessitated an overhaul of procedures and laboratory facilities for all clinical trials work within the Institute. During this process we have consulted with the Medicines and Healthcare products Regulatory Agency (MHRA) and with staff at Cancer Research UK with expertise in this area. Towards the end of last year the Institute successfully underwent a GCP audit by the MHRA.
2. Reactivation and infusion of T cells specific for prostate antigens
In the first instance we synthesised peptides representing several defined HLA class I- and HLA class II-restricted target epitopes within prostate cancer antigens. These were then used in an attempt to reactivate in vitro CD8+ and CD4+ T cells respectively. To date we have recruited three patients with advanced prostate cancer who were leukapheresed to provide sufficient numbers of dendritic cells. The dendritic cells were pulsed with peptide epitopes and then used to reactivate specific T cell responses. In a single case we successfully generated a CD4+ T cell clone specific for a defined epitope in Prostase (Kallikrein-4). The prostate-specific CD4+ T cell clone was not only capable of secreting interferon-gamma following antigenic stimulation but also displayed cytolytic function when tested in a conventional chromium release assay against peptide-pulsed targets. Having expanded the clone in vitro to large cell numbers using the Rapid Expansion Protocol it was subjected to extensive safety and specificity testing. It was then infused into the patient on three occasions. The first infusion of 6.4 x 107 cells was followed 14 days later by a second infusion of 4 x 108 cells, and after another 14 days the third and final infusion comprising 9.2 x 108 cells was given. All infusions were well tolerated. From serial blood samples taken before, during and after the treatment period we were able to monitor the infused clone using an Elispot assay for interferon-gamma release. Prior to treatment there were no T cells detectable in this assay that responded to the prostase-derived epitope. Following the first infusion a low frequency of specific cells was detected in the blood, and this increased dramatically following the second and third infusions. Cells were clearly detectable at least 24 hrs after infusion but could not be detected in the blood seven days later. This may be due to the cells homing to tissue sites, but perhaps more likely is that the cells were incapable of persisting long-term in vivo. Possible strategies that we are considering to improve persistence include co-administration of low dose interleukin-2 and/or conditioning patients prior to infusion. Unexpectedly, PSA levels, which were slowly increasing before treatment, doubled after the first infusion but then returned to pre-infusion levels and remained relatively stable during the 6 week treatment period. No clinical responses were observed and PSA levels have gradually risen since the treatment period ended. To our knowledge this is the first prostate cancer patient to be treated using this approach and represents an important first-step in the rational development of T cell-based therapies for this disease.
Our attempts to treat further patients have been hampered for two reasons. Firstly, as described above, we have needed to comply with new regulations governing GCP and GCLP (i.e. the analyses of samples for clinical trials) and secondly, because we have been unable to gain access to the leukapheresis facility within the Queen Elizabeth Hospital due to a substantial increase in work-load for this facility combined with staff shortages. Access to these facilities should improve in the near future but in the meantime we have sought alternative facilities and have recently agreed an arrangement with Heartlands Hospital in East Birmingham. We are now in the process of recruiting further patients whom we plan to treat in the remaining months of this project.
An alternative strategy to treating patients with prostate antigen-specific T cells is to clone the gene encoding the receptor on such T cells and to transfer it into the patient’s T cells. This has the advantage that tumour-antigen specificity can be conferred upon T cells from all patients and cells for therapeutic use would be available within hours/days rather than weeks/months. Therefore, given the hiatus in recruiting patients, we attempted to reactivate T cells specific for prostate cancer antigens from buffy coat cells derived from healthy HLA A2-positive blood donors. Two such donors were tested and in both cases we succeeded in cloning specific T cells. These clones targeted defined HLA A2-restricted epitopes within Prostate Specific Membrane Antigen (PSMA), Prostate Stem Cell Antigen (PSCA) or Prostatic Acid Phosphatase (PAP).
3. Further Funding
Funding through this project has provided essential support for our work seeking to develop T cell-based therapies for human cancer. It has also provided important preliminary data which have very recently helped secure funding from Cancer Research UK to address several of the obstacles to T cell therapy becoming an established treatment. This future work will focus on developing T cell therapy for Nasopharyngeal Carcinoma, a virus associated tumour, and using this as a model to expand the treatment to Prostate Cancer (which, as a non-virus-associated tumour, is representative of the next step in the development of T cell therapy for human malignancies).
Research summary, 11 February 2005
Project G2002/19.