Case of yellow fever vaccine--associated viscerotropic disease with prolonged viremia, robust adaptive immune responses, and polymorphisms in CCR5 and RANTES genes.

BACKGROUND: The live attenuated yellow fever vaccine 17D (YF-17D) is one of the most effective vaccines. Despite its excellent safety record, some cases of viscerotropic adverse events develop, which are sometimes fatal. The mechanisms underlying such events remain a mystery. Here, we present an analysis of the immunologic and genetic factors driving disease in a 64-year-old male who developed viscerotropic symptoms. METHODS: We obtained clinical, serologic, virologic, immunologic and genetic data on this case patient. RESULTS: Viral RNA was detected in the blood 33 days after vaccination, in contrast to the expected clearance of virus by day 7 after vaccination in healthy vaccinees. Vaccination induced robust antigen-specific T and B cell responses, which suggested that persistent virus was not due to adaptive immunity of suboptimal magnitude. The genes encoding OAS1, OAS2, TLR3, and DC-SIGN, which mediate antiviral innate immunity, were wild type. However, there were heterozygous genetic polymorphisms in chemokine receptor CCR5, and its ligand RANTES, which influence the migration of effector T cells and CD14+CD16bright monocytes to tissues. Consistent with this, there was a 200-fold increase in the number of CD14+CD16bright monocytes in the blood during viremia and even several months after virus clearance. CONCLUSION: In this patient, viscerotropic disease was not due to the impaired magnitude of adaptive immunity but instead to anomalies in the innate immune system and a possible disruption of the CCR5-RANTES axis.

Human effector and memory CD8+ T cell responses to smallpox and yellow fever vaccines.

To explore the human T cell response to acute viral infection, we performed a longitudinal analysis of CD8(+) T cells responding to the live yellow fever virus and smallpox vaccines--two highly successful human vaccines. Our results show that both vaccines generated a brisk primary effector CD8(+) T cell response of substantial magnitude that could be readily quantitated with a simple set of four phenotypic markers. Secondly, the vaccine-induced T cell response was highly specific with minimal bystander effects. Thirdly, virus-specific CD8(+) T cells passed through an obligate effector phase, contracted more than 90% and gradually differentiated into long-lived memory cells. Finally, these memory cells were highly functional and underwent a memory differentiation program distinct from that described for human CD8(+) T cells specific for persistent viruses. These results provide a benchmark for CD8(+) T cell responses induced by two of the most effective vaccines ever developed.

Monkeypox-induced immunity and failure of childhood smallpox vaccination to provide complete protection.

Following the U.S. monkeypox outbreak of 2003, blood specimens and clinical and epidemiologic data were collected from cases, defined by standard definition, and household contacts of cases to evaluate the role of preexisting (smallpox vaccine-derived) and acquired immunity in susceptibility to monkeypox disease and clinical outcomes. Orthopoxvirus-specific immunoglobulin G (IgG), IgM, CD4, CD8, and B-cell responses were measured at approximately 7 to 14 weeks and 1 year postexposure. Associations between immune responses, smallpox vaccination, and epidemiologic and clinical data were assessed. Participants were categorized into four groups: (i) vaccinated cases, (ii) unvaccinated cases, (iii) vaccinated contacts, and (iv) unvaccinated contacts. Cases, regardless of vaccination status, were positive for orthopoxvirus-specific IgM, IgG, CD4, CD8, and B-cell responses. Antiorthopoxvirus immune responses consistent with infection were observed in some contacts who did not develop monkeypox. Vaccinated contacts maintained low levels of antiorthopoxvirus IgG, CD4, and B-cell responses, with most lacking IgM or CD8 responses. Preexisting immunity, assessed by high antiorthopoxvirus IgG levels and childhood smallpox vaccination, was associated (in a nonsignificant manner) with mild disease. Vaccination failed to provide complete protection against human monkeypox. Previously vaccinated monkeypox cases manifested antiorthopoxvirus IgM and changes in antiorthopoxvirus IgG, CD4, CD8, or B-cell responses as markers of recent infection. Antiorthopoxvirus IgM and CD8 responses occurred most frequently in monkeypox cases (vaccinated and unvaccinated), with IgG, CD4, and memory B-cell responses indicative of vaccine-derived immunity. Immune markers provided evidence of asymptomatic infections in some vaccinated, as well as unvaccinated, individuals.

Immune responses to Bacillus anthracis protective antigen in patients with bioterrorism-related cutaneous or inhalation anthrax.

Anti-protective antigen (PA) immunoglobulin (Ig) G, toxin neutralization, and PA-specific IgG memory B cell responses were studied in patients with bioterrorism-related cutaneous or inhalation anthrax and in a patient with laboratory-acquired cutaneous anthrax. Responses were determined for >1 year after the onset of symptoms. Eleven days after the onset of symptoms (15 days after likely exposure), anti-PA IgG was detected in 16 of 17 patients with confirmed or suspected clinical anthrax who were tested. Anti-PA IgG remained detectable 8-16 months after the onset of symptoms in all 6 survivors of inhalation anthrax and in 7 of 11 survivors of cutaneous anthrax who were tested. Anti-PA IgG levels and serum toxin neutralizing activity were strongly associated (R2=0.83). PA-specific IgG memory B cells were detectable in all 6 survivors of inhalation anthrax but in only 2 of 7 patients with cutaneous anthrax who were tested. Anti-PA IgG is an important diagnostic marker of anthrax, a predictor of serum anti-toxin activity, and a marker of immunological memory against anthrax.

Tracking human antigen-specific memory B cells: a sensitive and generalized ELISPOT system.

In the interest of better understanding the role of human memory B cells in protection against disease, we developed an assay to quantitate antigen-specific memory B cells in human blood. This assay utilizes a 6-day polyclonal stimulation of PBMC followed by an antigen-specific ELISPOT for the detection of memory B cells that have differentiated into antibody secreting cells (ASC) in vitro. We have used this assay to demonstrate that the anthrax vaccine (AVA; BioThrax) elicits a substantial population of protective-antigen (PA) specific memory B cells, and these B cells satisfy the canonical surface phenotype of human memory B cells: CD19(+)CD20(+)Ig(+)CD27(+). These anti-PA antigen-specific memory B cells are IgG(+) and represent up to 2% of circulating IgG(+) B cells. Furthermore, these results confirm that vaccine-elicited memory B cells reside in the CD27(+) B cell population. This ELISPOT-based system has been designed in a generalized manner, such that the assay can be rapidly adapted to detect human antigen-specific memory B cells of any given specificity. This method should be useful for quantitatively assessing the potency of vaccines and the longevity of B cell immunological memory to various vaccines or infectious diseases.

Cutting edge: long-term B cell memory in humans after smallpox vaccination.

Memory B cells are a central component of humoral immunity, and yet little is known about their longevity in humans. Immune memory after smallpox vaccination (DryVax) is a valuable benchmark for understanding the longevity of B cell memory in the absence of re-exposure to Ag. In this study, we demonstrate that smallpox vaccine-specific memory B cells last for >50 years in immunized individuals. Virus-specific memory B cells initially declined postimmunization, but then reached a plateau approximately 10-fold lower than peak and were stably maintained for >50 years after vaccination at a frequency of approximately 0.1% of total circulating IgG(+) B cells. These persisting memory B cells were functional and able to mount a robust anamnestic Ab response upon revaccination. Additionally, virus-specific CD4(+) T cells were detected decades after vaccination. These data show that immunological memory to DryVax vaccine is long-lived and may contribute to protection against smallpox.