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Early identification of antigen-specific immune responses in vivo by [18F]-labeled 3'-fluoro-3'-deoxy-thymidine ([18F]FLT) PET imaging.

ABSTRACT: Current biomarkers are unable to adequately predict vaccine-induced immune protection in humans with infectious disease or cancer. However, timely and adequate assessment of antigen-specific immune responses is critical for successful vaccine development. Therefore, we have developed a method for the direct assessment of immune responses in vivo in a clinical setting. Melanoma patients with lymph node (LN) metastases received dendritic cell (DC) vaccine therapy, injected intranodally, followed by [(18)F]-labeled 3'-fluoro-3'-deoxy-thymidine ([(18)F]FLT) PET at varying time points after vaccination. Control LNs received saline or DCs without antigen. De novo immune responses were readily visualized in treated LNs early after the prime vaccination, and these signals persisted for up to 3 wk. This selective [(18)F]FLT uptake was markedly absent in control LNs, although tracer uptake in treated LNs increased profoundly with as little as 4.5 × 10(5) DCs. Immunohistochemical staining confirmed injected DC dispersion to T-cell areas and resultant activation of CD4(+) and CD8(+) T cells. The level of LN tracer uptake significantly correlates to the level of circulating antigen-specific IgG antibodies and antigen-specific proliferation of T cells in peripheral blood. Furthermore, this correlation was not observed with [(18)F]-labeled fluoro-2-deoxy-2-D-glucose. Therefore, [(18)F]FLT PET offers a sensitive tool to study the kinetics, localization, and involvement of lymphocyte subsets in response to vaccination. This technique allows for early discrimination of responding from nonresponding patients in anti-cancer vaccination and aid physicians in individualized decisionmaking.

SUBMITTER: Aarntzen EH

PROVIDER: S-EPMC3215004 | biostudies-literature | 2011 Nov

REPOSITORIES: biostudies-literature

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Early identification of antigen-specific immune responses in vivo by [18F]-labeled 3'-fluoro-3'-deoxy-thymidine ([18F]FLT) PET imaging.

Aarntzen Erik H J G EH Srinivas Mangala M De Wilt Johannes H W JH Jacobs Joannes F M JF Lesterhuis W Joost WJ Windhorst Albert D AD Troost Esther G EG Bonenkamp Johannes J JJ van Rossum Michelle M MM Blokx Willeke A M WA Mus Roel D RD Boerman Otto C OC Punt Cornelis J A CJ Figdor Carl G CG Oyen Wim J G WJ de Vries I Jolanda M IJ

Proceedings of the National Academy of Sciences of the United States of America 20111024 45

Current biomarkers are unable to adequately predict vaccine-induced immune protection in humans with infectious disease or cancer. However, timely and adequate assessment of antigen-specific immune responses is critical for successful vaccine development. Therefore, we have developed a method for the direct assessment of immune responses in vivo in a clinical setting. Melanoma patients with lymph node (LN) metastases received dendritic cell (DC) vaccine therapy, injected intranodally, followed b ...[more]

PMID: 22025695

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Project description:The ability to measure tumor determinants of response to nucleoside analog (NA) chemotherapy agents such as gemcitabine and related compounds could significantly affect the management of several types of cancer. Previously we showed that the accumulation in tumors of the new PET tracer 1-(2'-deoxy-2'-(18)F-fluoro-?-d-arabinofuranosyl)cytosine ((18)F-FAC) is predictive of responses to gemcitabine. (18)F-FAC retention in cells requires deoxycytidine kinase (dCK), a rate-limiting enzyme in the deoxyribonucleoside salvage metabolism and in gemcitabine conversion from an inactive prodrug to a cytotoxic compound. The objectives of the current study were to determine whether (18)F-FAC tumor uptake is also influenced by cytidine deaminase (CDA), a determinant of resistance to gemcitabine; to develop a new PET assay using (18)F-FAC and the related probe 1-(2'-deoxy-2'-(18)F-fluoro-?-l-arabinofuranosyl)-5-methylcytosine (l-(18)F-FMAC) to profile tumor lesions for both dCK and CDA enzymatic activities; and to determine whether this PET assay can identify the most effective NA chemotherapy against tumors with differential expression of dCK and CDA.Isogenic murine leukemic cell lines with defined dCK and CDA activities were generated by retroviral transduction. A cell viability assay was used to determine the sensitivity of the isogenic cell lines to the dCK-dependent NA prodrugs gemcitabine and clofarabine. In vitro enzymatic and cell-based tracer uptake assays and in vivo PET with (18)F-FAC and l-(18)F-FMAC were used to predict tumor responses to gemcitabine and clofarabine.dCK and CDA activities measured by kinase and tracer uptake assays correlated with the sensitivity of isogenic cell lines to gemcitabine and clofarabine. Coexpression of CDA decreased the sensitivity of dCK-positive cells to gemcitabine treatment in vitro by 15-fold but did not affect responses to clofarabine. Coexpression of CDA decreased (18)F-FAC but not l-(18)F-FMAC, phosphorylation, and uptake by dCK-positive cells. (18)F-FAC and l-(18)F-FMAC PET estimates of the enzymatic activities of dCK and CDA in tumor implants in mice were predictive of responses to gemcitabine and clofarabine treatment in vivo.These findings support the utility of PET-based phenotyping of tumor nucleoside metabolism for guiding the selection of NA prodrugs.

Project description:BackgroundNon-invasive imaging biomarkers of cellular proliferation hold great promise for quantifying response to personalized medicine in oncology. An emerging approach to assess tumor proliferation utilizes the positron emission tomography (PET) tracer 3'-deoxy-3'[(18)F]-fluorothymidine, [(18)F]-FLT. Though several studies have associated serial changes in [(18)F]-FLT-PET with elements of therapeutic response, the degree to which [(18)F]-FLT-PET quantitatively reflects proliferative index has been continuously debated for more that a decade. The goal of this study was to elucidate quantitative relationships between [(18)F]-FLT-PET and cellular metrics of proliferation in treatment naïve human cell line xenografts commonly employed in cancer research.Methods and findings[(18)F]-FLT-PET was conducted in human cancer xenograft-bearing mice. Quantitative relationships between PET, thymidine kinase 1 (TK1) protein levels and immunostaining for proliferation markers (Ki67, TK1, PCNA) were evaluated using imaging-matched tumor specimens. Overall, we determined that [(18)F]-FLT-PET reflects TK1 protein levels, yet the cell cycle specificity of TK1 expression and the extent to which tumors utilize thymidine salvage for DNA synthesis decouple [(18)F]-FLT-PET data from standard estimates of proliferative index.ConclusionsOur findings illustrate that [(18)F]-FLT-PET reflects tumor proliferation as a function of thymidine salvage pathway utilization. Unlike more general proliferation markers, such as Ki67, [(18)F]-FLT PET reflects proliferative indices to variable and potentially unreliable extents. [(18)F]-FLT-PET cannot discriminate moderately proliferative, thymidine salvage-driven tumors from those of high proliferative index that rely primarily upon de novo thymidine synthesis. Accordingly, the magnitude of [(18)F]-FLT uptake should not be considered a surrogate of proliferative index. These data rationalize the diversity of [(18)F]-FLT-PET correlative results previously reported and suggest future best-practices when [(18)F]-FLT-PET is employed in oncology.

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Dataset Information

Early identification of antigen-specific immune responses in vivo by [18F]-labeled 3'-fluoro-3'-deoxy-thymidine ([18F]FLT) PET imaging.

Publications

Early identification of antigen-specific immune responses in vivo by [18F]-labeled 3'-fluoro-3'-deoxy-thymidine ([18F]FLT) PET imaging.

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