Measles virus-specific cellular immunity in patients with vaccine failure

The cytotoxic T-lymphocyte (CTL) response to measles virus (MV) was studied in blood samples from 13 acute- and early convalescent-phase patients with measles infection despite previous vaccination with the live-MV vaccine. MV CTL responses were also measured in six healthy peer controls who had live-MV vaccination during childhood and in five healthy adults who had a remote history of natural measles. All patients recovered from illness without complication. Acute MV infection was diagnosed on the basis of the Centers for Disease Control criteria and by measuring MV-specific immunoglobulin G (IgG) and IgM antibodies. Elevated IgG titers occurred in 80% of the patients at 1 to 2 weeks and in 100% at 4 weeks postinfection. IgM antibodies were detectable in all patient tested and were elevated in 60% of the patients at 1 to 2 weeks postinfection. The MV-specific CTL response was enhanced in 10 of the 13 patients tested, with a mean maximal lysis of 48.5% ± 13.3%, compared with that of healthy peer controls who had had live-MV vaccinations during childhood (mean lysis, 14.6% ± 12.9%; n = 6) and healthy adults with a remote history of natural measles (mean, 30.8% ± 12.2%; n = 5). Three patients had low MV CTL levels at two time points following measles, with a mean lysis of 12% ± 1.7%. It is concluded that while there is no evidence for a deficiency in the generation of cellular immunity to MV in the majority of patients with MV vaccine failure, a small number of individuals may fail to develop an enhanced T-cell response following infection.