IN-VITRO ACTIVATION OF LOW-GRADE NON-HODGKINS-LYMPHOMA BY MURINE FIBROBLASTS, IL-4, ANTI-CD40 ANTIBODIES AND THE SOLUBLE CD40 LIGAND

The in vitro analysis of growth regulation in low-grade B non-Hodgkin' s lymphoma (B-NHL) is hampered by the rapid apoptotic death of the mal ignant B cells ex vivo. A complex culture system, using murine CDw32 t ransfected fibroblasts (LTK- cells), IL-4 and anti-CD40 mAb, has been established for the propagation of normal mature B cells in vitro. We investigated the influence of the different components of this cocultu re system on cell survival and apoptosis of B-NHL cells. Nine samples from patients with follicular lymphoma and from eight patients with im munocytoma were analyzed. No cell proliferation of B-NHL cells could b e induced in the culture system. However, CDw32-transfected murine fib roblasts most efficiently supported cell viability of B-NHL cells with an increase in cell survival by 114% compared to the control (P=0.047 ). IL-4 alone also had a stimulatory effect on cell survival of B-NHL cells after 6 days. In contrast, the soluble recombinant CD40 ligand g p39 and the anti-CD40 mAbs mAb89 and EA-5 did not prolong cell surviva l. CDw32 transfectants blocked apoptosis of B-NHL cells efficiently fr om 67% in the control to 16% (P=0.001). Reduction in apoptosis was acc ompanied by an elevated bcl-2 protein expression. IL-4 or mAb89 did no t further reduce apoptotic cell death in CDw32 transfectant-dependent cocultures. Our data underline the pivotal role of LTK- cells for cell survival of B-NHL cells in vitro. The efficient blockage of apoptosis associated with increased bcl-2 protein expression causes prolonged c ell viability of the B-NHL cells.