AUTONOMOUS GROWTH OF EBV TRANSFORMED B CELL LYMPHOMAS IN PATIENTS WITH PTLD MAY INVOLVE CONSTITUTIVELY ACTIVATED CYTOKINE SIGNALING PATHWAYS

Abstract

163 Post transplant lymphoproliferative disease (PTLD) is a major complication of the immunosuppression required for human organ transplantation. The disease encompasses a spectrum of abnormal, EBV-associated B cell proliferations. We have previously shown that EBV-infected spontaneous lymphoblastoid cell lines (SLCL) derived from patients with PTLD secrete IL-10, IL-6, TNF-α and LT-α, and more significant, require autocrine IL-10 for sustained growth. Using a ribonuclease protection assay, we found that these cells also express RNA for IL-9, IL-13, IL-15, and IFN-γ. To determine if cytokine signal transduction is involved in the autonomous growth of the SLCL, the activation states of proteins of the Jak/STAT cytokine signaling pathway were analyzed in three different SLCL, termed JB7, MF4 and VB4. The tyrosine phosphorylation (P-tyr) states of the Janus kinases (Jaks) and signal transducers and activators of transcription (STAT) proteins were examined by immunoprecipitation and immunoblotting. The JB7 line expresses a high level of constitutively P-tyr Jak1. All three SLCL, but not the Daudi Burkitt's lymphoma B cell line also express Jak2, Jak3 and Tyk2 constitutively phosphorylated on tyrosine residues. STAT1 and STAT3, but not STAT2 or STAT5, were also found to be constitutively phosphorylated in each of the SLCL. Activation of the STAT proteins was confirmed by electromobility shift assay. All three SLCL, but not the Daudi line, express DNA-binding STAT complexes that were identified as STAT1 and STAT3 by antibody supershift experiments. These data support the presence of a constitutively active IL-10 autocrine signaling pathway in the SLCL. Many cytokines are known to induce cellular proliferation in different cell types. The constitutive activation of proteins of the Jak/STAT pathway is likely due to autocrine cytokine signaling. Furthermore, this constitutively activated pathway found in all SLCL, but not in the EBV-infected Burkitt's lymphoma B cell line Daudi, may be critical for the autonomous growth of SLCL. Understanding the signal transduction molecules that participate in the cytokine dependent growth of EBV B cell lymphomas in PTLD may aid in the treatment of this disease. Supported by NIH-AI-41769 and the Stanford Immunology Program Fellowship 5T32-AI-07290.