The Long-term Effects of Acute Total-Body Irradiation on Pre-irradiation Measles-vaccine-induced Immunological Memory

Acute total-body irradiation (TBI) leads to transient dose-dependent lymphopenia. While lymphocyte numbers gradually recover, there remain subtle but long-lasting changes to B and T cell populations years after radiation exposure. The degree to which immunological memory is retained after TBI is unknown; however, it is conceivable that vaccine-induced protective immunity is jeopardized. To test this hypothesis, samples were collected from a cohort of rhesus macaques that were vaccinated against measles virus, irradiated, and then allowed to recover from the acute radiation effects for at least a year. Animals received 0 to 7.5 Gy TBI or 10 Gy with 5% bone marrow shielding. Plasma from 109 animals were evaluated for measles-binding antibodies and the ability to neutralize live measles virus. Females exhibited higher measles binding and neutralizing titers, and irradiated animals of both sexes exhibited significant radiation-dose dependent reductions in measles binding IgG and neutralizing titers. Peripheral blood mononuclear cells (PBMC) from the vaccinated, irradiated animals were then stimulated in vitro with measles antigens to evaluate cellular responses. No radiation-dose effects on CD8 T cell responses to measles antigens were detected. In contrast, PBMC from vaccinated, irradiated males exhibited radiation dose-dependent reductions in the percentages of CD4 T cells expressing activation-associated markers and cytokines in response to measles antigens. There were also significant dose- or dose/sex-interacting effects on the levels of IP10, MIP1β, and IL-6 present in the antigen-stimulated PBMC cultures. Cells from animals receiving 10 Gy with 5% bone marrow shielding exhibited signs of T-cell anergy. PBMC from females exhibited only weak responses to measles antigen stimulation regardless of radiation exposure. Collectively, these in vitro studies indicate that radiation can cause protracted dose- and sex-dependent damage to established humoral and cellular immunological memories of measles.