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Chimeric antigen receptor (CAR) T cells are an adoptive cell immunotherapy genetically synthesized to reprogram T cells for antigen recognition and intracellular signaling to target tumor cells for destruction. A sensitive and reproducible assay to evaluate CAR T cell function is essential to research and develop novel therapies, optimize manufacturing, and evaluate efficacy in the clinical and non-clinical settings. However, conventional methods, such as cytotoxicity assays and in vitrocytokine production, require a long cell culture processing time with a less quantitative and more time-consuming variability. In the present study, we analyzed the change in localization of CAR molecules immediately following antigen recognition using molecular imaging flow cytometry (MI-FCM) to establish a quantitative method to evaluate the immune functionality of CAR T cells, which is correlated with cytotoxic activity. Anti-CD19 CAR (FMC63-28z) was constructed using anti-CD19 scFv (FMC63) based on the method described by Kochenderfer et al. (J Immunol, 2009). CAR T cells were generated by isolating human peripheral blood mononuclear cells from nine healthy donors (21-69 years old). They were then stimulated on plates pre-coated with CD3 and CD28 antibodies in ALys505N-7 medium containing 700 IU/mL IL-2, transfected with anti-CD19 CAR using a lentivirus on day 3, and subsequently expanded on plates pre-coated with CD3 and CD28 antibodies for maximum to 18 days. Second, each CAR T cell was stimulated with or without CD19 antigen, as well as the K562 cell line stably transfected with CD19 (K562-CD19), fixed with paraformaldehyde, and immunostained with anti-CAR, CD4, and CD8 antibodies. We defined the decrease in the CAR molecule area of expression on the cell surface as concentrated CAR. The existence and number of spots of concentrated CAR on CD4- or CD8-positive CAR T cells were analyzed using MI-FCM. The concentration of superficial CAR antigens on some CAR T cells was observed in every lot from the nine healthy donors when they were stimulated with K562-CD19 cells or CD19 antigen. In contrast, this was not observed in the unstimulated controls. When each lot of CAR T cells was stimulated with CD19 antigen and then quantitatively assessed using MI-FCM, the proportion of cells with concentrated CAR among the CD4-positive and CD8-positive CAR T cells was 83.1 ± 11.7% and 81.3 ± 8.1%, respectively, while the proportion of cells with a single spot fraction of concentrated CAR was 31.2 ± 4.0% and 33.8 ± 6.1%, respectively. Third, the cytotoxic activity of each lot of CAR T cells co-cultured with K562-CD19 cells transfected with the firefly luciferase reporter gene for 15 h was evaluated using a luciferase-mediated bioluminescence imaging assay. Importantly, the proportion of single-spot concentrated CAR among CD8-positive CAR T cells was very strongly positively correlated with killing activity (R = 0.916; 95% CI: 0.644-0.982), while the proportion of single-spot concentrated CAR among CD4-positive CAR T cells was significantly positive correlated (R = 0.693; 95% CI: 0.053-0.930). These results suggest that quantifying the CAR concentration in CAR T cells using MI-FCM could be used to evaluate their immune function.

The transcription co-activator P300 regulates gene expression by histone H3 lysine 27 acetylation (H3K27ac) of chromatin and transcriptional regulators. P300 has been suggested to control a variety of biological functions, including differentiation, cell-cycle control, proliferation, apoptosis, and DNA damage response. The clinicopathologic/prognostic importance of P300 in multiple myeloma (MM) is unknown to date. P300 has been linked to the induction of epithelial-to-mesenchymal transition (EMT) and metastasis in a variety of solid tumor malignancies. Like EMT in solid tumors, extra-medullary disease (EMD) in MM relates to a poor prognosis and resistance to treatment. Similarly, the molecular changes concerning EMD in MM are poorly understood, and the role of P300 in MM EMD is yet to be investigated.

Polyclonal anti-thymocyte globulins (ATGs) are widely used in allogeneic stem cell transplantation (allo-SCT) for GvHD prophylaxis. ATGs exerted anti-tumor effects in in vitro experiments, but in vivo studies are lacking. We experienced a case of relapsed AML with cells positive for CD7 who underwent haploidentical SCT and unexpectedly achieved a significant reduction of AML cells in the peripheral blood after receiving ATGs before the administration of other drugs in the conditioning regimen. This patient achieved long-term survival after haploidentical SCT. To assess the impact of ATGs on clinical outcomes in patients with AML, we performed a retrospective analysis of allo-SCT for relapsed/refractory AML and divided 132 patients into four groups according to the expression of CD7 in AML cells and use of ATGs as part of the conditioning regimen, as follows: CD7-positive ATG group (n= 15), CD7-positive no-ATG group (n= 32), CD7-negative ATG group (n= 19), and CD7-negative no-ATG group (n= 66). The overall survival rates in the CD7-positive ATG group were significantly higher than those in the CD7-positive no-ATG group, whereas these rates did not differ statistically between the CD7-negative ATG and CD7-negative no-ATG groups. Our results indicate a possible anti-leukemic effect of ATGs against CD7-positive AML in humans.

The donor-dependent supply of platelets is frequently insufficient to meet transfusion needs. To address this issue, we developed a clinically applicable strategy for the derivation of functional platelets from human pluripotent stem cells (PSCs). This approach involves the establishment of stable immortalized megakaryocyte progenitor cell lines (imMKCLs) from PSC-derived hematopoietic progenitors through the overexpression of BMI1 and BCL-XL to respectively suppress senescence and apoptosis and the constrained overexpression of c-MYC to promote proliferation. The resulting imMKCLs can be expanded in culture over extended periods (4–5 months), even after cryopreservation. Halting the overexpression of c-MYC, BMI1, and BCL-XL in growing imMKCLs led to the production of CD42b+platelets with functionality comparable to that of native platelets on the basis of a range of assays in vitro and in vivo. The combination of robust expansion capacity and efficient platelet production means that appropriately selected imMKCL clones represent a potentially inexhaustible source of hPSC-derived platelets for clinical application.