Lose of lymphoblast immunogenicity and susceptibility to specific ctl lysis following their maintenance in culture

This study deals with possible mechanisms leading to the insensitivity of lymphoblasts (LB) to cellular-mediated lysis acquired upon their in vitro maintenance. LB, induced by either ConA, IL-2 or by sensitization in allogeneic MLC or MLTC, become refractory to CTL-mediated lysis following >7 days culture in the presence of growth promoting lymphokines (IL-2, IL-4, IL-7). However, the cultured LB (CLB), most of which are CD8+, are efficiently lysed by specific antibody and complement or by CTL in the presence of ConA, and do not inhibit cytotoxicity against LB in cold target competition assays. CLB express lower levels of the Fas antigen, H-2D class I antigen, and certain adhesion molecules (ICAM-1, VLA-4), as compared with LB. Consequently, the ability of CLB to form conjugates with specific CTL is diminished, accounting for the decrease in their susceptibility to specific lysis. In addition, CLB were unable to induce an allogeneic immune response both in vitro and in vivo . The reduced immunogenicity of CLB enabled their prolonged survival in an allogeneic host. Supported by The US-Israel Binational Science Foundation and by the Concern Foundation, Los Angeles, CA.