PBMC were collected by unmobilized peripheral blood leukapheresis and cryopreserved in aliquots. After thawing, monocytes were enriched by adherence to plastic culture vessels and differentiated into DC with 50 ng/mL IL-4 and 100 ng/mL GM-CSF in serum-free medium for 5 days. DC maturation was induced with 20 ng/mL TNFa and 1 lg/mL Prostaglandin-E2 for 2 days. After maturation, DC were split into 3 aliquots. PSCA (patients 1-6) or CPP- PSCA peptide (patients 7-11), a mixture of the 3 PSA peptides, and HIV-gag peptide were added at a concentration of 10 lg/mL to a separate aliquot in 10 mL PBS each for 2 hours at 37°C. After- wards, DCs were washed twice and resuspended in 1 mL PBS.
Patients were immunized 4 times with PSA-, PSCA- and HIV- gag-loaded DCs in biweekly intervals. Each DC aliquot was injected subcutaneously at a separate site into the thigh. Responses were assessed 2 weeks after the 4th vaccination and three-monthly thereafter. Patients without progressive disease were offered continued vaccination in monthly intervals until progression. To assess the immune status of the patients, hepatitis B vaccinations were administered on day 1 and 43, followed by testing for anti-HBs antibodies 2 weeks later.
Cellular immune responses
No patient developed a positive delayed type hypersensitivity (DTH) reaction to unloaded DC. Five patients developed a positive DTH reaction to one or several antigens during the vaccination: Two patients developed DTH to PSCA only, 2 patients to PSA and PSCA, and 1 patient to PSA, PSCA and HIV. A positive DTH was observed in 4 of 6 patients with SD during vaccination, whereas only 1 of the 4 evaluable patients with progressive disease due to rising PSA levels had apositive DTH (patient 10). Interestingly, this patient had a mixed response with complete regression of a retrovesical lymph node despite PSA increase.
Toxicity and clinical response
There was no evidence of any immediate or delayed toxicity in any of the patients. With respect to tumor progression, 6 patients had stable disease (SD) and 5 of these received a median of 2 additional vaccinations until progression. Two of 3 patients (patients 4 and 9) experienced a marked improvement of bone pain. Two patients (patients 5 and 7) received only 3 vaccinations because of early PD, and 4 patients had PD after 4 vaccinations. One of these (patient 10) had a complete regression of a retrovesical lymph node, but was counted as PD because of a rising PSA.
The median survival of patients with documented DTH responses was 22 months, which was significantly superior to the overall survival of the remaining patients (8.0 months).
Vaccination with PSA/PSCA peptide-loaded, autologous DCs may induce cellular responses primarily in immunocompetent patients, which appear to be associated with clinical benefit. Testing of DC-based vaccination is warranted for patients at earlier stages of prostate cancer.
Article Reference link: click here
Scientific article publishing date: 9/26/2006
Immucura identifier BSC22_379EN