Potent Activation of Healthy Donor T-Cells Specific for Mantle Cell Lymphoma Immunoglobulin Derived Peptides by CD40- and TLR7/8-Ligand Matured Dendritic Cells in Vitro

Patients with mantle cell lymphoma (MCL) and MRD after intensive radiochemotherapy and autologous stem cell transplantation have a high risk of relapse. Allogeneic stem cell transplantation offers the possibility of cure but is associated with a high risk of severe “graft versus host disease”(GvHD). A way to decrease the risk of GvHD while augmenting the “graft versus lymphoma” effect may be the in vitro activation and subsequent transplantation of allogeneic idiotyp-specific T-cells. This study was set out to determine whether cytotoxic T-cell responses specific for peptides derived from the mantle cell idiotype immunoglobulin can be activated in healthy individuals. In four patients with MCL treated in the European Mantle Cell Lymphoma Study Group the immunoglobulin heavy chain (IgH) gene family was amplified in lymphoma samples by PCR and sequenced. Using bioinformatics, the corresponding aminoacid sequence was analyzed for nonapeptides potentially binding to the individual HLA-haplotype. Peptides with a Rammensee-score >20 were synthesized. To determine whether these peptides could indeed elicit CD8+ T-cell responses they were used for dendritic cell (DC) pulsation and subsequent T-cell activation. The specificity of the CD8+ T-cells was tested against idiotype-pulsed DC and measured by flow cytometric intracellular interferon (IFN)-gamma staining. The lymphoma specific IgH rearrangements were successfully amplified and sequenced in all patients. In a HLA-A3 positive patient who was in remission after intensive radiochemotherapy and autologous hematopoietic stem cell transplantation three different idiotype HLA-matching peptides with a HLA-A3 binding score >20 were predicted from the VH-region, one additional nonapeptide was overlapping to the N-region of the immunoglobulin, rendering this peptide lymphoma-specific. This pool of peptides was synthesized and used for pulsation of monocyte derived dendritic cells (moDC) in two healthy HLA-A3 positive individuals. The maturation of the DC was done according to a standard protocol using proinflammatory cytokines (IL-6, IL-1 beta, TNF-alpha, PGE₂). After 2–3 weekly stimulations of lymphocytes that had been depleted of regulatory T-cells 2.1% idiotype-specific CD8+ T-cells were activated in both healthy donors. Interestingly, T-cell stimulation using moDC matured with CD40− and TLR7/8-ligands was more efficient in comparison to the standard protocol and resulted in 12.3% IFN-gamma positive CD8+ cells. In summary, these data suggest, that idiotype-specific T-cells can be activated from healthy individuals by standard lymphocyte stimulating protocols in vitro. Moreover, the ability of moDC to activate idiotype-specific T-cells is exceeded by DC maturation using CD40− in combination with TLR7/8-ligands. These findings may help to improve immunotherapy in the settings of allogeneic transplantation strategies in relapsed MCL patients.