Melanoma immunotherapy using mature DCs expressing the constitutive proteasome
Jens Dannull, … , Douglas S. Tyler, Scott K. Pruitt
Jens Dannull, … , Douglas S. Tyler, Scott K. Pruitt
Published June 24, 2013
Citation Information: J Clin Invest. 2013;123(7):3135-3145. https://doi.org/10.1172/JCI67544.
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Clinical Research and Public Health Oncology

Melanoma immunotherapy using mature DCs expressing the constitutive proteasome

Abstract

Background. Many cancers, including melanoma, exclusively express constitutive proteasomes (cPs) and are unable to express immunoproteasomes (iPs). In contrast, mature DCs used for immunotherapy exclusively express iPs. Since proteasomes generate peptides presented by HLA class I molecules, we hypothesized that mature melanoma antigen–loaded DCs engineered to process antigens through cPs would be superior inducers of antimelanoma immunity in vivo.

Methods. Subjects with metastatic melanoma were vaccinated with mature DCs transfected with RNAs encoding melanoma antigens MART1, MAGE-3, gp100, and tyrosinase. These DCs were derived from monocytes that were untransfected (Arm A; n = 4), transfected with control siRNA (Arm B; n = 3), or transfected with siRNAs targeting the 3 inducible iP subunits (Arm C; n = 5).

Results. Vaccination stimulated antigen-specific T cell responses in all subjects, which peaked after 3–4 vaccinations, but remained elevated in Arm C subjects. Also in Arm C, circulating melanoma cell levels (as detected by quantitative PCR) fell, and T cell lytic activity against autologous melanoma was induced. In HLA-A2+ subjects, CD8+ T cells that bound tetramers loaded with cP-derived melanoma antigenic peptides were found in the peripheral blood only in Arm C subjects. Of 2 subjects with active disease (both in Arm C), one had a partial clinical response, while the other, who exhibited diffuse dermal and soft tissue metastases, had a complete response.

Conclusion. These results suggest that the efficacy of melanoma DC–based immunotherapy is enhanced when tumor antigen–loaded DCs used for vaccination express cPs.

Trial registration. Clinicaltrials.gov NCT00672542.

Funding. Duke Clinical Research Institute/Duke Translational Medicine Institute, Duke Melanoma Consortium, and Duke University Department of Surgery.

Authors

Jens Dannull, N. Rebecca Haley, Gary Archer, Smita Nair, David Boczkowski, Mark Harper, Nicole De Rosa, Nancy Pickett, Paul J. Mosca, James Burchette, Maria A. Selim, Duane A. Mitchell, John Sampson, Douglas S. Tyler, Scott K. Pruitt

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Figure 1

Rationale for the clinical trial.

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Rationale for the clinical trial. When TAA-loaded DCs undergo maturation...
When TAA-loaded DCs undergo maturation, cPs are no longer expressed; therefore, the TAA-derived peptides presented in the context of HLA class I on the surface of the immunostimulatory mature DCs are exclusively generated by the iP (triangles). CD8+ T cells induced by these DCs will then specifically recognize only iP-generated TAA-derived peptides. In contrast, melanoma cells (as well as other cancer cells) express the cP and not the iP, even when exposed to inflammatory mediators. Therefore, TAA-derived peptides presented in the context of HLA class I on the surface of melanoma cells will be exclusively generated by the cP (squares). T cells induced by the mature TAA–loaded DCs and recognizing iP-generated peptides will then not recognize melanoma cells expressing cP-derived peptides from the same TAA, resulting in a misdirected and suboptimal antimelanoma immune response. By modulating the proteasome of the mature DC from the iP to the cP though transfection of the monocytes from which the DCs were derived with iP siRNA, mature immunostimulatory TAA–loaded DCs then present TAA-derived peptides generated by the cP, stimulating a T cell response that will be appropriately directed against melanoma cells expressing the cP and presenting TAA-derived peptides generated by the cP.