P1224: PATIENT-DERIVED XENOGRAFT (PDX) IS A USEFUL TOOL FOR EVALUATING 5-AZACYTIDINE SENSITIVITY IN TFH LYMPHOMAS (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: TFH lymphomas (TFH PTCL) constitute the most frequent non-cutaneous PTCL entity and are characterized by chemoresistance and a poor prognosis. The main obstacles in therapeutic innovations are the rarity of the disease, the difficulty of diagnosis, and the lack of relevant in vitro/in vivo models which make preclinical studies laborious to perform. 5-azacytidine is a hypomethylating agent associated with prolonged survival (Dupuis et al. ASH2022) in relapsed or refractory TFH PTCL patients, but biomarkers of response and synergistic therapeutic combinations are unknown. Patient-Derived Xenograft (PDX) mouse model allow performing preclinical studies in various cancers, but data on TFH PTCL PDX, and how they recapitulate the patient sensitivity to the drug are limited. Aims: To develop and characterize TFH PTCL PDXs and to evaluate their capacity to anticipate the in vivo sensitivity to 5-azacytidine. Methods:1. PDX Generation: Fresh or viable frozen TFH PTCL biopsies were implanted subcutaneously into immunodeficient NSGTM mice. Body weight change and clinical signs of pain or disease were monitored, and blood was collected weekly for flow cytometry analysis to detect human CD45+ cells. Mice were sacrificed when they reached the humane endpoint, and organs and tumor cell suspension were collected. A new passage was generated by injecting cells in suspension intraperitoneally or implanting a piece of tumor subcutaneously. PDX was characterized by flow cytometry (spleen and blood), histological examination and immunohistochemistry, Next Generation Sequencing, and T-cell clonality, and was compared to the primary tumors. 2. 5-azacytidine (5-aza) treatment: After detection of human CD45+ cells in the blood, mice were treated with 2,5 mg/kg 5-aza every 2 days for 5 doses or with vehicle. This treatment was repeated every 28 days until reaching the humane endpoint. Results: We implanted 17 tumors subcutaneously and generated 12 PDX, 8 with at least 3 passages, 4 with currently ongoing in different passages (1 to 3). In addition, one PDX was generated by intravenous injection of circulating tumor cells. The median time to the first detection of human CD45 cells was 11.6 days (Inter quartile range: 7-20), and for reaching the sacrifice point was 43.3 days (IQR: 25-90). Reactive cells from the microenvironment (B cells and CD8 T cells) were detected in the first passages, but decreased over time, as reflected by immunohoistochemical analysis and the evolution of the variant allele frequencies (VAF) in the mutated tumors. To test the correlation between PDX model response and human in vivo response to 5-aza, we selected 5 PDX models generated from patients who subsequently received 5-azacytidine. Two of the patients had a response to 5-aza, one patient had stable disease for 6 cycles before progressing and 2 patients were refractory to 5-aza. In the 2 PDXs (#12 and #18), generated from responding patients, we observed both a decrease of circulating cells and prolonged survival after 5-aza treatment. Whereas in PDX11 generated from the patient with stable disease, we observed a decrease of circulating cells during treatment, with limited survival benefit. By contrast, no effect of treatment with 5-aza was detected in the 2 PDXs (PDX#13 and #6) generated from the resistant patients (see Figure). Summary/Conclusion: PDX can be generated from TFH PTCL in a significant proportion of cases. PDX recapitulates the patient’s sensitivity to 5-azacytidine, allowing a better understanding of the markers of response and development of synergistic treatment combinations. Further studies are required to validate this model in combination with other drugs.Figure. Generation of PDX and Results of 5-aza Treatment Keywords: Angioimmunoblastic T-cell lymphoma, Animal model, DNA methylation, Xenotransplantation