Dendritic cell maturation with poly(I:C)-based versus PGE2-based cytokine combinations results in differential functional characteristics relevant to clinical application.

In vitro maturation of dendritic cells (DCs) for cancer immunotherapy may be accomplished by cytokine cocktails containing prostaglandin E2 (PGE2). More recently, a poly(I:C)-based protocol has been proposed as a potentially superior alternative because of a strong induction of interleukin (IL)-12 secretion by resulting DCs. As optimal DC maturation represents a crucial issue for cancer vaccination trials, we performed a systematic and comprehensive comparison of both protocols with respect to important indicators of DC function. Although both methods yielded phenotypically mature DCs, transcriptional profiling revealed a substantially higher number of differentially regulated genes after poly(I:C)-based than PGE2-based maturation. Several of these are involved in immunologic processes, indicating that both DC types exhibit subtle, but distinct, molecular properties. Up-regulation of genes encoding the T-cell-attracting chemokines CXCL9, 10, and 11 in poly(I:C)-DC but not PGE2-DC was confirmed on a protein level. Although poly(I:C)-based maturation induced substantial IL-12p70 secretion, poly(I:C)-DC also secreted low levels of IL-10 and showed a significantly higher expression of functionally active indoleamine-2,3-dioxygenase than PGE2-DC, which might mediate immune inhibitory functions. Nonetheless, the number of peptide-specific T cells tended to be higher after in vitro priming with poly(I:C)-DC compared with PGE2-DC. Finally, PGE2-DC displayed superior migratory abilities, which are essential for in vivo applications. In summary, we have identified previously unrecognized shared and distinct molecular features of DCs matured by 2 commonly used protocols that lead to subtle, but significant, immunologic features of the resulting cells relevant to clinical applications.

Vaccination of advanced prostate cancer patients with PSCA and PSA peptide-loaded dendritic cells induces DTH responses that correlate with superior overall survival.

Prostate stem cell antigen (PSCA) and prostate-specific antigen (PSA) are overexpressed in most prostate cancers. PSCA- and PSA-derived, HLA-A2 binding peptides are specific targets for T-cell responses in vitro. A phase I/II trial was performed to demonstrate feasibility, safety and induction of antigen-specific immunity by vaccination with dendritic cells (DC) presenting PSCA and PSA peptides in patients with hormone- and chemotherapy-refractory prostate cancer. Patients received 4 vaccinations with a median of 2.7 x 10(7) peptide-loaded mature DC s.c. in biweekly intervals. Clinical responses were assessed 2 weeks after the 4th vaccination. Immune monitoring was performed by DTH and HLA multimer analysis. Twelve patients completed vaccination without relevant toxicities. Six patients had stable disease after 4 vaccinations. One patient had a complete disappearance of lymphadenopathy despite rising PSA. Four patients with SD and 1 progressor developed a positive DTH after the 4th vaccination. With a median survival of all patients of 13.4 months, DTH-positivity was associated with significantly superior survival (p = 0.003). HLA tetramer analysis detected high frequencies of peptide-specific T cells after 2 vaccinations in 1 patient who was also the sole responder to concomitant hepatitis B vaccination as an indicator of immune competence and survived 27 months after start of vaccination. 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.