Generation of PSA-reactive effector cells after vaccination with a PSA-based vaccine in patients with prostate cancer

BACKGROUND. JET 1001 is a vaccine used for therapy of prostate cancer (CA), which consists of recombinant prostate-specific antigen (PSA) with lipid A formulated in liposomes. Patients with prostate CA were vaccinated with JE T 1001 emulsified in mineral oil (n = 5) or with the vaccine in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF) administere d locally at the site of vaccination (n = 5). Frequency of PSA-reactive T c ells was measured in peripheral blood mononuclear cells (PBMC) before and a fter immunization, using an interferon-gamma (IFT-gamma) enzyme-linked immu nospot (ELISPOT) assay with autologous dendritic cells (DC) as antigen-pres enting cells. The hypothesis tested was that PSA-based vaccines induce T ce ll responses to human PSA. METHODS. In order to expand precursor cells, in vitro sensitization (NS) wa s performed. Microcultures of peripheral blood lymphocytes (PBL) (1 x 10(5) /well) in medium supplemented with interleukin-2 (IL-2) (10 IU/ml) and inte rleukin-7 (IL-7) (10 ng / ml) were stimulated twice (day 0 and day 7) with monocyte-derived autologous DC, generated by culture with interleukin-4 (IL -4) and GM-CSF and pulsed with PSA (10 mu g/ml) at sin effector to stimulat or ratio of 10:1. ELISPOT assays were performed on day 14 of culture. In ad dition, PBMC were separated on immunobeads into CD4(+) and CD8(+) subsets f ur ELISPOT assays performed without IVS. RESULTS. Two patients had PSA-reactive responses before vaccination (freque ncy range, 1/700-1/4,400). After vaccination, 8/10 patients had measurable PSA-reactive T-cell frequencies, ranging from 1/200-1/1900, using IVS. In c ontrast, without IVS, but after immunoselection to enrich in CD8(+) and CD4 (+) T cells, only 2/10 patients had detectable PSA-reactive T cells after v accination, at a frequency ranging from 1/2,600-1/4,000. CONCLUSIONS. Vaccination with PSA formulated into liposomes induced T-cell responses in 8/10 patients with prostate carcinoma. The frequency of PSA-re active precursor T cells was relatively low in the blood of these patients, and TVS, leading to amplification of the precursor cells prior to ELISPOT, was necessary for quantification of the PSA-responding T cells. Cellular r esponses to PSA were predominantly mediated by CD4(+) T lymphocytes. (C) 20 00 Wiley-Liss, Inc.