Infection of leucocytes by measles vaccine viruses Edmonston—Zagreb and Enders—Moraten has different consequences: potential mechanism for increased vaccine efficacy or aberrant activity in field trials

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The abilities of two measles vaccine virus strains, Edmonston—Zagreb (E—Z) and Enders—Moraten (E—M), to infect and modify the activities of U937 monocytoid and peripheral blood mononuclear leucocytes (PBMLs) were compared with each other and with changes resulting from infection of these cells by a wild-type measles virus (MV). Both the E—Z and wild-type MV were shown to infect U937 and PBMLs and (1) to markedly increase expression of leucocyte function antigen 1 (LFA-1) on leucocytes present in infected cultures; (2) to increase cell—cell interaction; (3) to grow and disseminate readily in both types of leucocyte cultures; and (4) to persist for more than 7 days in these cultures despite the presence of MV-specific neutralizing antibodies. In contrast, the E—M virus did not grow well in unstimulated PBMLs and, although it did grow well in U937 cells, it did not noticeably alter the expression of LFA-1 on these cells, did not induce significant cell—cell interaction, and was rapidly eliminated from these cultures if MV-specific neutralizing antibodies were present. The possible relationship of these findings to the increased protective efficacy and untoward effects associated with the E—Z MV vaccine is discussed.