Angioimmunoblastic T-cell lymphoma: Characterization of clonal T and B cells and a patient-derived xenograft study of coexisting T- and B-cell proliferation

Abstract

Introduction: Angioimmunoblastic T-cell lymphoma (AITL) is a rare and aggressive lymphoma with a poor prognosis. AITL is associated with Epstein-Barr virus (EBV)-positive B cells in most cases, suggesting a possible role for the virus in the pathobiology of AITL. Cell lines from AITL patients do not exist and models of human AITL are needed. We aim to establish such a model and use it for preclinical therapeutic evaluation.

Methods: Primary lymph node tissue from an AITL patient was used for tumor cell isolation and injection to NSG mice. The established patient-derived xenograft (PDX) model was characterized by immunophenotyping, whole-exome sequencing (WES), and T/B-cell receptor gene rearrangement studies. In vivo AITL PDX trials were performed with elotuzumab, romidepsin, and rituximab.

Results: An AITL PDX mouse model that includes a coexisting EBV+ B-cell proliferation was established. We confirmed clonal identity of the engrafted T cells with the primary T-lymphoma cells. WES on DNA from xenografted sorted T and B cells identified eight and three mutations previously reported in the COSMIC database, respectively. Primary tumor cells could be passaged serially in NSG mice with an increasing percentage of monoclonal B cells that mimic the human condition in which the clonal B-cell component in some cases may mask an underling T-cell lymphoma. In this PDX mouse study, single agent elotuzumab or rituximab significantly improved mice survival. Survival was further improved when elotuzumab or romidepsin was combined with rituximab.

Conclusion: To our knowledge, this is the first molecular characterization of AITL model coexisting with associated EBV+ B cells, and use of such a PDX model for therapeutic evaluation of agents targeting both malignant T cells and B cells simultaneously.

Keywords: AITL; EBV; PDX model; SLAMF7.

FIGURE 1

Engraftment of primary AITL cells in NSG mouse. (A) Gross image of harvested spleens. The AITL engrafted spleen is markedly enlarged compared to the control spleen. (B) Flow cytometry of the passage 1 (P1) engrafted mouse tissues. Human CD45 expressing cells are present in blood, bone marrow, and spleen consisting of predominantly T cells (gate 2) with fewer B cells (gate 3). (C) The percentage of human T and B cells in various sites of the P1 mouse. A predominance of T cells was seen. (D) The primary relapsed lymph node showed atypical Tfh phenotype T cells (CD4⁺/PD1⁺/BCL6⁺) with scattered large EBV+ B cells. Note the large immunoblastic morphology by CD20 staining. SLAMF7 is expressed in a subset of cells. (E) IHC of the engrafted P1 spleen shows mixed lymphomatous T cells expressing CD3, CD4, PD1, and BCL6. Numerous EBV+ large cells are present. SLAMF7 is seen in many of the small to intermediately sized cells compatible with the T cells.

FIGURE 2

In vivo treatment of AITL PDX mice. (A) Treatment with single agent of rituximab, elotuzumab, and two‐drug combined groups extended survival compared to control supported by statistical analysis (p < 0.05). The combination of rituximab with either elotuzumab or romidepsin further prolonged survival compared to each single agent significantly (p < 0.05). (B) IHC staining of cleaved PARP in control, and each indicated mouse spleen tissue. No detectable staining in control sample, while cleaved PARP‐positive cells show in rituximab‐treated mouse spleen, and more positive cells presented in mice samples treated with rituximab combined with either elotuzumab or romidepsin.