Patient-Derived Xenograft Model in B-Cell Lymphoma: A Platform for a Personalized Clinical Trial
Authors: Bell Taylor , Zhang Hui , Ahmed Makhdum , Guo Hui , Li Carrie J , Liu Yang , Lam Laura T , Chen Zhihong , Wang Jack , Zhang Victoria , Nomie Krystle , Zhang Liang , Wang Michael 
Published: October 2019

Abstract
Background: Imprecise correlation of treatment response in established cell line and cells obtained from patients (i.e., patient-primary) limits the preclinical investigation of novel compounds. Similarly, the "xenograft" models wherein human cancer cell lines are transplanted into immunocompromised mice do not represent the full spectrum of cancers. However, Patient-derived xenograft (PDX) mouse models have been shown to recapitulate the diversity of growth, metastasis, and histopathology of the original tumor. Based on our previously established mantle cell lymphoma (MCL) PDX model, we developed other B-cell lymphoma PDXs recapitulating tumor pathological and clinical characteristics, progression and response to therapeutic agents, this will provide an indispensable model system towards personalized treatment for B-cell lymphoma.
Methods: We developed 34 PDX models with an implanted fetal bone chip for several B-cell lymphomas including marginal zone lymphoma (MZL), follicular lymphoma (FL), Burkitt's lymphoma (BL), and diffuse large B-cell lymphoma (DLBCL), and MCL. We tested the in vitro efficacy of a panel of drugs among freshly isolated tumor cells from patients and tumor cells from the PDX models. We also generated a drug-resistant MCL PDX model, compared the effect of targeted drugs on the tumor burden in the drug-resistant model and identified potential therapeutic opportunity with drug combinations. We validated combination therapy in vivoand conducted next generation sequencing (NGS) using a 1,212 gene panel (OncoPlus®) on DNA from primary patient cells.
Results: We collected clinical samples from 34 patients with several types of B-cell lymphomas including MCL (n=21), DLBCL (n=3), FL (n=2), BL (n=1), and MZL (n=2). Of the 34 patients, 18 (53%) were newly diagnosed and untreated clinically, 11 (32%) patients were relapsed after treatment with 1-3 chemotherapy or targeted therapy treatments, and 5 (15%) patients were treated with one-dose therapy before sample collection. All of the tumor cells, from both the patient and PDXs, showed the same drug response pattern. Consecutive ibrutinib administration to PDX mice from PT1 during G4 induced the development of an ibrutinib-resistant tumor. The cell viability of isolated PDX tumor cells treated with ibrutinib was not significantly different between G1 and G2 nor was it different between G5 and G6 (p>0.05). In addition, histological features were consistent with patient tumor histology. Furthermore, whole exome sequencing revealed fidelity between the patient and PDX tumor cells as well as between subsequent generations of the PDX. [B1] We[Z2] engrafted a patients tumor cells into NSG-hu mice to create an MCL-bearing PDX mouse model (PT28-PDX). G2 PDX cells were isolated and treated with a panel of drugs. We found that G2 PDX cells were most sensitive to bortezomib (BTZ) (Velcade®). Growth inhibition of the G2 PDX cells was significantly higher with BTZ compared to ibrutinib (p=0.002) and cells were most sensitive to BTZ compared with other agents (p≤ 0.002). Based on this finding, the patient was treated with Velcade®, rituximab and dexamethasone and responded to treatment. However, the G3 PDX became resistant to BTZ. She was then treated with a 1 cycle of rituximab and cytarabine. Soon after, we initiated three-drug combination treatment with lenalidomide (Len), rituximab (RTX) and dexamethasone (DEX) in PDX G4. Len+RTX+DEX significantly prolonged mouse survival indicating that this could be an effective regimen for this patient after BTZ relapse. As guided by the PDX, PT28 underwent Len+RTX+DEX regimen and her peripheral lymphocytosis disappeared demonstrating response.
Conclusions: The PDX model with implanted fetal bone chip is a valid experimental platform that recapitulates tumor characteristics of B-cell lymphomas. Leveraging the PDX platform to identify and select drugs that are likely to be efficacious for individual patients and subsequently administering the promising agents to those who relapse after an initial therapy is the next milestone.

Disclosures
Wang: BeiGene: Research Funding; Asana BioSciences: Research Funding; Juno Therapeutics: Research Funding; Pharmacyclics: Research Funding; Celgene: Research Funding; Onyx: Research Funding; Kite Pharma: Research Funding; Acerta Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.