Recent evidence has revealed that oncogenic mutations may confer immune escape. A better understanding of how an oncogenic mutation affects immunosuppressive programmed death ligand 1 (PD-L1) expression may help in developing new therapeutic strategies. We show that oncogenic JAK2 (Janus kinase 2) activity caused STAT3 (signal transducer and activator of transcription 3) and STAT5 phosphorylation, which enhanced PD-L1 promoter activity and PD-L1 protein expression in JAK2^V617F-mutant cells, whereas blockade of JAK2 reduced PD-L1 expression in myeloid JAK2^V617F-mutant cells. PD-L1 expression was higher on primary cells isolated from patients with JAK2^V617F–myeloproliferative neoplasms (MPNs) compared to healthy individuals and declined upon JAK2 inhibition. JAK2^V617F mutational burden, pSTAT3, and PD-L1 expression were highest in primary MPN patient–derived monocytes, megakaryocytes, and platelets. PD-1 (programmed death receptor 1) inhibition prolonged survival in human MPN xenograft and primary murine MPN models. This effect was dependent on T cells. Mechanistically, PD-L1 surface expression in JAK2^V617F-mutant cells affected metabolism and cell cycle progression of T cells. In summary, we report that in MPN, constitutive JAK2/STAT3/STAT5 activation, mainly in monocytes, megakaryocytes, and platelets, caused PD-L1–mediated immune escape by reducing T cell activation, metabolic activity, and cell cycle progression. The susceptibility of JAK2^V617F-mutant MPN to PD-1 targeting paves the way for immunomodulatory approaches relying on PD-1 inhibition.

Checkpoint-blocking antibodies like those targeting the PD-1/PD-L1 pathway have revolutionized oncology. We developed radiotracers based on therapeutic checkpoint-blocking antibodies permitting sensitive and high-resolution PET imaging of both PD-1 and PD-L1 in immunocompetent mice. ImmunoPET of naive mice revealed similar overall expression patterns for PD-1 and PD-L1 in secondary lymphoid organs (spleen and lymph nodes). Interestingly, PD-L1 was also detected in brown adipose tissue (BAT), confirming the notion that BAT is immunologically relevant. Under pathophysiological conditions, strong expression of the receptor/ligand pair was also found in non-lymphoid tissues. Both were specifically detected in malignant tumors. PD-1 was readily detected after combined immunoradiotherapy causing massive tumor infiltration by PD-1+ lymphocytes. PD-L1 tracer uptake was reduced in PD-L1 knockout tumors. Moreover, monitoring the expression changes of PD-L1 in response to its main inducer, the effector T cell cytokine IFN-γ, revealed robust upregulation in the lung. This suggests that T cell responses in the lung, a vital organ continuously exposed to a variety of antigens, are strongly restrained by the PD-1 checkpoint. In turn, this could explain the association of PD-1 checkpoint inhibition with potentially fatal immune-mediated pneumonitis and partially also its efficacy in lung cancer.

Radiolabeled biomolecules can be used to visualize a variety of diseases through interaction with specific cell receptors. A key step is the introduction of a molecular entity that allows facile labeling with the medically useful radionuclide ^99mTc without significant alteration of the structure and function of the biomolecule. One strategy focuses on the design of single amino acid chelates (SAACs), novel bifunctional chelators constructed from derivatized amino acids or amino acid analogues. The chelating terminus of the SAAC has been designed for effective coordination to the {^99mTc(CO)₃}⁺ core, while the other terminus allows incorporation into any position along a peptide sequence or into a variety of biomolecules. In applications to peptidic materials, the approach affords significant flexibility in the choice of donors for ^99mTc coordination combined with the considerable advantages of routine solid phase synthetic techniques. The methodology allows libraries of peptide-based ^99mTc(I) and ^186,188Re(I) radiopharmaceuticals to prepared using conventional automated peptides synthesis. Other biomolecules, including nucleosides, carbohydrates, folic acid and vitamin B12 are also readily modified using analogous methods. The approach also allows the preparation of isostructural ^99mTc and Re complexes for the correlation of in vivo and in vitro imaging studies.

Introduction: The gastrin-releasing peptide receptor (GRPR) is overexpressed in breast cancer. The present study evaluates GRPR imaging as a novel imaging modality in breast cancer by employing positron emission tomography (PET) and the GRPR antagonist ⁶⁸Ga-RM2.