Development of 111In-labeled tumor-associated antigen peptides for monitoring dendritic-cell-based vaccination

P. Laverman, I. de Vries, N. Scharenborg, A. de Boer, M. Broekema, W. Oyen, C. Figdor, G. Adema and O. Boerman

Department of Nuclear Medicine, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
May, 2006



Dendritic cells (DC) are professional antigen-presenting cells capable of inducing potent immune responses. In our ongoing clinical trials, human leukocyte antigen (HLA)-A2.1+ melanoma patients are vaccinated with mature DC, presenting tumor-derived peptides in major histocompatibility complexes (MHC) to naive T cells. Previously, we have shown that both intradermally and intranodally injected (111)In-labeled mature DC migrate to draining lymph nodes. However, little is known about the fate of the MHC-peptide complex after injection of these peptide-loaded DC. The aim of the present study was to develop radiolabeled, tumor-derived peptides to monitor their binding to MHC Class I.The HLA-A2.1 binding peptide gp100:154-162mod (gp100:154m) was conjugated with diethylenetriamine pentaacetic acid (DTPA) either at the N-terminus (alpha-DTPA-gp100:154m) or at the epsilon amino group of the Lys(154) residue (epsilon-DTPA-gp100:154m) and labeled with (111)In.The maximum specific activity for both peptides was 13 GBq/micromol. The IC50 of the alpha-[(111)In]DTPA-gp100:154m peptide was >75 microM. The IC50 of the (111)In-labeled epsilon-DTPA-gp100:154m was 3 microM, similar to the unconjugated peptide. MHC binding studies showed specific binding of the epsilon-[(111)In]DTPA-gp100:154m peptide to the JY cells at 4 degrees C. Interestingly, no specific binding was observed for the alpha-[(111)In]DTPA-gp100:154m peptide. In contrast to the alpha-[(111)In]DTPA-gp100:154m peptide, the epsilon-[(111)In]DTPA-gp100:154m peptide was recognized by cytotoxic T cells.When DTPA was conjugated to the epsilon NH2 group of the Lys(154) residue, MHC binding of the peptide was preserved and could still be recognized by cytotoxic T cells. These studies allow the noninvasive determination of the behavior of MHC-peptide complexes on DC in vivo.