Combined PET/MRI: Global Warming-Summary Report of the 6th International Workshop on PET/MRI, March 27-29, 2017, Tübingen, Germany.

The 6th annual meeting to address key issues in positron emission tomography (PET)/magnetic resonance imaging (MRI) was held again in Tübingen, Germany, from March 27 to 29, 2017. Over three days of invited plenary lectures, round table discussions and dialogue board deliberations, participants critically assessed the current state of PET/MRI, both clinically and as a research tool, and attempted to chart future directions. The meeting addressed the use of PET/MRI and workflows in oncology, neurosciences, infection, inflammation and chronic pain syndromes, as well as deeper discussions about how best to characterise the tumour microenvironment, optimise the complementary information available from PET and MRI, and how advanced data mining and bioinformatics, as well as information from liquid biomarkers (circulating tumour cells and nucleic acids) and pathology, can be integrated to give a more complete characterisation of disease phenotype. Some issues that have dominated previous meetings, such as the accuracy of MR-based attenuation correction (AC) of the PET scan, were finally put to rest as having been adequately addressed for the majority of clinical situations. Likewise, the ability to standardise PET systems for use in multicentre trials was confirmed, thus removing a perceived barrier to larger clinical imaging trials. The meeting openly questioned whether PET/MRI should, in all cases, be used as a whole-body imaging modality or whether in many circumstances it would best be employed to give an in-depth study of previously identified disease in a single organ or region. The meeting concluded that there is still much work to be done in the integration of data from different fields and in developing a common language for all stakeholders involved. In addition, the participants advocated joint training and education for individuals who engage in routine PET/MRI. It was agreed that PET/MRI can enhance our understanding of normal and disrupted biology, and we are in a position to describe the in vivo nature of disease processes, metabolism, evolution of cancer and the monitoring of response to pharmacological interventions and therapies. As such, PET/MRI is a key to advancing medicine and patient care.

Therapeutic targeting of naturally presented myeloperoxidase-derived HLA peptide ligands on myeloid leukemia cells by TCR-transgenic T cells.

T cells have been proven to be therapeutically effective in patients with relapsed leukemias, although target antigens on leukemic cells as well as T-cell receptors (TCRs), potentially recognizing those antigens, are mostly unknown. We have applied an immunopeptidomic approach and isolated human leukocyte antigen (HLA) ligands from primary leukemia cells. We identified a number of ligands derived from different genes that are restrictedly expressed in the hematopoietic system. We exemplarily selected myeloperoxidase (MPO) as a potential target and isolated a high-avidity TCR with specificity for a HLA-B*07:02-(HLA-B7)-restricted epitope of MPO in the single HLA-mismatched setting. T cells transgenic for this TCR demonstrated high peptide and antigen specificity as well as leukemia reactivity in vitro and in vivo. In contrast, no significant on- and off-target toxicity could be observed. In conclusion, we here demonstrate, exemplarily for MPO, that leukemia-derived HLA ligands can be selected for specific effector tool development to redirect T cells to be used for graft manipulation or adoptive T-cell therapies in diverse transplant settings. This approach can be extended to other HLA ligands and HLA molecules in order to provide better treatment options for this life-threatening disease.

Induction of cytotoxic T-cell responses against immunoglobulin V region-derived peptides modified at human leukocyte antigen-A2 binding residues.

Cytotoxic T-lymphocyte (CTL) responses can be generated against peptides derived from the immunoglobulin (Ig) V region in some but not all patients. The main reason for this appears to be the low peptide-binding affinity of Ig-derived peptides to major histocompatibility complex (MHC) class I molecules and their resulting low immunogenicity. This might be improved by conservative amino acid modifications at the MHC-binding residues of the peptides (heteroclitic peptides). In this study, it was found that in 18 Ig-derived peptides, that heteroclitic peptides from the Ig gene with improved binding to human leukocyte antigen (HLA)-A*0201 can be used to improve CTL responses. Amino acid substitution substantially increased predicted binding affinity, and there was a strong correlation between predicted and actual binding to HLA-A*0201. CTLs generated against the heteroclitic peptide had not only enhanced cytotoxicity against the heteroclitic peptide but also increased killing of antigen-presenting cells pulsed with the native peptide. Surprisingly, no difference was observed in the frequency of T cells detected by MHC class I peptide tetramers after stimulation with the heteroclitic peptide compared with the native peptide. CTLs generated against heteroclitic peptides could kill patients' tumor cells, showing that Ig-derived peptides can be presented by the tumor cell and that the failure to mount an immune response (among other reasons) likely results from the low immunogenicity of the native Ig-derived peptide. These results suggest that heteroclitic Ig-derived peptides can enhance immunogenicity, thereby eliciting immune responses, and that they might be useful tools for enhancing immunotherapy approaches to treating B-cell malignant diseases.

Generation of cytotoxic T lymphocytes against native and altered peptides of human leukocyte antigen-A*0201 restricted epitopes from the human epithelial cell adhesion molecule.

A growing number of human tumor antigens have been described that can be recognized by CTLs in a MHC class I restricted fashion. The epithelial cell adhesion molecule (Ep-CAM) is expressed in a variety of human tumors and has attracted attention as a therapeutic target for monoclonal antibody serotherapy. We have identified immunogenic peptides derived from Ep-CAM, that bind to human leukocyte antigen-A*0201 and elicit strong peptide-specific human CTL responses, demonstrating that there is an effective T-cell repertoire against these Ep-CAM-derived peptides that can be recruited. Alterations to these peptides were made to increase their binding affinity to MHC class I molecules. The use of such "heteroclitic" peptides allowed generation of cytotoxic T cells that demonstrated increased killing of target cells pulsed not only with the heteroclitic but also with the native peptide. Most important, CTL cell lines that are generated against these peptides specifically lyse epithelial tumor cells expressing Ep-CAM but not normal hematopoietic or bronchial epithelial cells.

Targeting Folates by Carboxypeptidase G2: Potential Applications in Anticancer Therapy.

Carboxypeptidase G2 (CPG2) cleaves folates and folate analogues resulting in alternative routes of folate metabolism. CPG2 is of particular interest in anticancer therapy for several reasons. CPG2 rapidly converts methotrexate (MTX) into less toxic metabolites causing a rapid decline of MTX serum levels in animal models as well as in humans. Thus, CPG2 is a powerful rescue agent in patients receiving high-dose MTX and might circumvent life-threatening toxicity in patients with MTX intoxication. As CPG2 causes a predefined and considerable decline of MTX levels, this substance might be also attractive for MTX dose escalation studies. In addition, CPG2 has been used in antibody-directed enzyme prodrug therapy. Prodrugs have been developed which are cleaved by CPG2, resulting in a release of active cytotoxic agents. The use of these prodrugs, attached to a tumor-specific antibody-CPG2- complex, might enhance concentrations of cytotoxic drugs in tumor tissues. Finally, CPG2 has been investigated in combination with trimetrexate, as it has been shown that trimetrexate is resistant to CPG2 cleavage. In conclusion, CPG2 is a novel drug with promising properties. However, clinical experiences are limited and further studies are necessary to define the role of CPG2 in cancer therapy. Copyright 2000 S. Karger GmbH, Freiburg

Carboxypeptidase G2 rescue in a 79 year-old patient with cranial lymphoma after high-dose methotrexate induced acute renal failure.

A 79 year-old female patient presented with immunoblastic B-cell lymphoma of the ethmoidal sinuses and destruction of the anterior cranial fossa. After 3 cycles of high-dose methorexate (HD-MTX) MTX serum level remained elevated and creatinine serum levels raised. The patient received Carboxypeptidase G2 (CPG2) intravenously. Within one hour the MTX serum level decreased to <1 micromol/l as determined by high pressure liquid chromatography (HPLC). The patient recovered without significant toxicity and attained a long lasting ongoing (>14 months) complete remission. In this case we were able to demonstrate that rescue from HD-MT nephrotoxicity by CPG2 is also safe and effective in patients with advanced age with impaired renal function. With the help of CPG2, sufficient and potentially curative therapy with HD-MTX may also be provided to patients with a high risk of renal failure.

Stem cell transplantation for indolent lymphoma.

Stem cell transplantation (SCT) has become the treatment of choice for patients with relapsed aggressive non-Hodgkin's lymphoma (NHL). The role of SCT in the management of patients with low-grade NHL remains more controversial, although increasing numbers of patients with advanced-stage follicular lymphoma, mantle cell lymphoma, and chronic lymphocytic leukemia are now undergoing SCT. To date, most patients with NHL have been treated with autologous SCT, currently using peripheral blood stem cells (PBSC) mobilized by chemotherapy and recombinant growth factors. There is increasing concern regarding toxicity of autologous SCT, especially the higher than expected long-term risk of development of myelodysplastic syndrome. This, among other factors, has led to renewed interest in the role of allogeneic SCT for patients with NHL. A major advantage of allogeneic SCT is the potential to exploit a graft-versus-lymphoma effect, and many studies are underway exploring the possibility of manipulating donor cells to maximize T cell responsiveness against lymphoma.

Activation of autologous lymphocytes of patients with chronic myelogenous leukemia in the chronic phase with cytokines and CD3 monoclonal antibody results in bcr/abl- blood leukocyte cultures as determined by reverse transcriptase-polymerase chain reaction.

To investigate the potential of autologous lymphocytes to eliminate chronic myelogenous leukemia (CML) cells following activation and targeting by CD3-monoclonal antibody, we cultured Ficoll-isolated peripheral blood cells from 11 patients with CML in the chronic phase in permutated combinations of interleukin (IL)-2, CD3-monoclonal antibody (OKT3), and interferon (IFN)gamma. The efficiency of CML cell elimination was studied by means of flow cytometry and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Cultures containing only OKT3 and IL-2, with or without IFNgamma, resulted in tumor cell reduction to the level of RT-PCR negativity. The length of the culture period required to reach a RT-PCR-negative state ranged from 3 to 33 days. A 1- to 2-log reduction in leukemic cells could be achieved by culture medium alone. In contrast, 3- to 4-log reductions in CML cells were observed following in vitro culture and ex vivo T cell activation with a given sensitivity for RT-PCR detection of 1 bcr/abl+ cell in 10(4). The feasibility of purging chronic myelogenous leukemia cells in a short time was associated with a low number of platelet counts (r=0.6457; p < 0.05). CML cell reduction was associated with expansion of CD25+/CD4+//CD8+/-/CD56+/- lymphocytes. These findings may be of relevance for immunotherapy procedures.