EFFECTS OF A SOLUBLE RECOMBINANT HUMAN CD40 LIGAND ON HUMAN LYMPHOMAGENESIS AND LYMPHOMA GROWTH

Abstract

CD40 is a 55 kDa integral membrane protein that is a member of the nerve growth factor/tumor necrosis factor receptor superfamily. CD40 is present on normal and neoplastic B cells, monocytes, dendritic cells, endothelial cells, and other various carcinoma cell lines. Stimulation of CD40 results in B cell proliferation and differentiation. It is also required for successful isotype switching. CD40 and B cell Ig receptor activation also lead to induction of phenotypic and functional germinal center features present in lymph nodes. The ligand for CD40 (CD4OL, CD154) is present primarily on T cells, although it is also found on platelets and NK cells. A recombinant soluble version of the CD4OL has been produced recently. Soluble recombinant human CD4OL (srhCD4OL) has been demonstrated to be an active ligand to CD40. It has been previously demonstrated that an antibody to CD40 was able to inhibit the proliferation of human B cell lymphomas by "activation induced cell death", a process by which activation of neoplastic but not normal cells leads to apoptosis, necrosis, and/or cell-cycle arrest. The antibody has been able to inhibit the formation of human B cell lymphomas both in vitro and in vivo. Most antibodies directed towards human determinants are of murine origin. Mouse antibodies can generate human anti-mouse antibodies in a human which lead to inactivation and clearance of the antibodies. For these reasons, srhCD4OL should be a therapeutically superior alternative for the CD40 antibody, as the recombinant ligand is of human origin. The efficacy of a srhCD4OL using both in vitro and in vivo assays was examined. The in vitro experiments demonstrate that srhCD4OL is effective in suppressing growth of an established B cell lymphoma. The inhibition can be augmented with interferon-y. However, srhCD4OL was not effective in inhibiting human EBV-induced lymphomagenesis in vitro, and actually promoted lymphoma development. In agreement with the in vitro assays, srhCD4OL also did not inhibit lymphoma formation in huPBL-SCID mice. Epstein-Barr virus positive human peripheral blood lymphocytes that are given to SCID mice spontaneously develop EBVlymphoproliferative disease. Treatment of these mice with srhCD4OL did increase the engraftment of human PBL in the mice, without increasing the onset of the lymphomas. Other promoters of engraftment increase the incidence of EBV-LPD. Engraftment was confirmed by quantification of human immunoglobulin in the mouse sera and by flow cytometric assessment of human lymphocyte markers on cells removed from the spleen and thymus. These results demonstrate that srhCD4OL is effective in inhibiting aggressive established lymphomas and this is augmented with IFN-y. However, it is not effective as a preventive measure to stop the formation of lymphomas and should be used with caution in instances where the lymphomas can arise.