Exposed or not exposed-that is the question: evidence for resolving and abortive hepatitis C virus infections in blood donors

Evaluation of cytomegalovirus "Blips" in high risk kidney/kidney-pancreas transplant recipients

BACKGROUND

Cytomegalovirus (CMV) is a significant cause of morbidity and mortality after solid organ transplantation. While guidelines suggest using highly sensitive QNAT assays for CMV detection, there is no defined viral load to guide initiation of preemptive therapy.^1,2 This study evaluates the progression to quantifiable CMV (DNAemia) following a CMV "blip" in high risk (D+/R) kidney/kidney-pancreas (KP) transplant recipients.

METHODS

This is a single center, retrospective study. A CMV "blip" was defined as the first positive QNAT assay below the level of quantification (< 1.37×10² IU/mL or < 200 viral copies). Subsequent CMV QNAT assays were followed to assess the progression from blip to CMV DNAemia for 1 year following transplant.

RESULTS

134 patients were included in the study. Fifty-three (39.6%) patients had their first positive CMV QNAT value below the level of quantification, a "CMV blip". Of these 53 patients, 69.8% (n = 37) progressed to DNAemia while 30.2% (n = 16) did not. The median time from transplant to the first CMV blip was 68 (46-97) days and most patients with viral blips (71.1%) were on prophylaxis. No differences in patient characteristics were found among those who progressed from blip to DNAemia and those who only had a blip.

CONCLUSIONS

In CMV high risk kidney/KP transplant recipients, CMV blips progressed to CMV DNAemia in the majority of cases. This progression typically occurred 2-3 weeks following the initial blip. CMV blips are common early post-transplant despite prophylaxis and likely represent an early marker of CMV infection. This article is protected by copyright. All rights reserved.

Heterologous Immunity: Role in Natural and Vaccine-Induced Resistance to Infections

The central paradigm of vaccination is to generate resistance to infection by a specific pathogen when the vacinee is re-exposed to that pathogen. This paradigm is based on two fundamental characteristics of the adaptive immune system, specificity and memory. These characteristics come from the clonal specificity of T and B cells and the long-term survival of previously-encountered memory cells which can rapidly and specifically expand upon re-exposure to the same specific antigen. However, there is an increasing awareness of the concept, as well as experimental documentation of, heterologous immunity and cross-reactivity of adaptive immune lymphocytes in protection from infection. This awareness is supported by a number of human epidemiological studies in vaccine recipients and/or individuals naturally-resistant to certain infections, as well as studies in mouse models of infections, and indeed theoretical considerations regarding the disproportional repertoire of available T and B cell clonotypes compared to antigenic epitopes found on pathogens. Heterologous immunity can broaden the protective outcomes of vaccinations, and natural resistance to infections. Besides exogenous microbes/pathogens and/or vaccines, endogenous microbiota can also impact the outcomes of an infection and/or vaccination through heterologous immunity. Moreover, utilization of viral and/or bacterial vaccine vectors, capable of inducing heterologous immunity may also influence the natural course of many infections/diseases. This review article will briefly discuss these implications and redress the central dogma of specificity in the immune system.

Anti-HCV immunoblot indeterminate results in blood donors: non-specific reactivity or past exposure to HCV?

BACKGROUND AND OBJECTIVE

The significance of anti-HCV immunoblot (IB) indeterminate results can be difficult to determine. We analysed results for blood donors tested on the MP Diagnostics HCV Blot 3.0 IB assay to determine whether indeterminate results representing past exposure to HCV could be distinguished from those due to non-specific reactivity.

MATERIALS AND METHODS

Results for all donors tested by IB during the study period (July 2010 to December 2013) were included in this study.

RESULTS

Of 131 donors tested by IB, 34 (26.0%) were negative, 38 (29.0%) were indeterminate, and 59 (45.0%) were positive. There was no significant difference in IB band reactivity strength between indeterminate and positive donors. The PRISM HCV chemiluminescent immunoassay (ChLIA) sample to cut-off (s/co) ratio distribution for the indeterminate donors was significantly higher than for those with biological false reactivity (P = 0·037), but significantly lower than for donors who were IB positive/HCV RNA negative (P < 0·001) or IB not tested/HCV RNA positive (P < 0·001). Of donors available for follow-up, 53.1% of the indeterminate group disclosed a putative risk factor for HCV infection compared to 39.4% (P < 0·001) for the IB-negative group, 76.6% (P = 0·065) for the IB-positive group and 83.4% (P < 0·001) for the HCV RNA-positive group.

CONCLUSION

The results of this study indicate that PRISM ChLIA s/co ratios >2·00 with IB indeterminate results predict exposure to HCV, particularly in the presence of putative risk factors for HCV infection. These findings may be applied to optimizing counselling of donors with indeterminate HCV results.

Infectivity in chimpanzees (Pan troglodytes) of plasma collected before HCV RNA detectability by FDA-licensed assays: implications for transfusion safety and HCV infection outcomes

Serial plasma aliquots (50 mL) obtained from 10 commercial donors who converted from hepatitis C virus (HCV) RNA negative to positive were transfused into 2 chimpanzees to assess infectivity during early HCV infection. Plasma, obtained 4 days before HCV RNA detectability by licensed assays, transmitted HCV infection to chimpanzee X355. The infectious PCR-negative plasma was subsequently shown to be positive in 2 of 23 replicates using a sensitive transcription-mediated amplification (TMA) assay, and estimated to contain 1.2 HCV RNA copies/mL (60 copies/50 mL transfused). Plasma units obtained up to 8 weeks earlier were not infectious in a second susceptible chimp, even when from donors with low-level, intermittent HCV RNA detection. Chimp x355 developed acute viremia with subsequent seroconversion, but cleared both virus and Ab in 17 weeks. When rechallenged 38 months later with 6000 RNA copies/mL from the same donor, X355 was transiently reinfected and again rapidly lost all HCV markers. We conclude that: (1) transfusions can transmit HCV infection before RNA detection, but the interval of test-negative infectivity is very brief; (2) early "blips" of HCV RNA appear noninfectious and can be ignored when calculating residual transfusion risk; and (3) markers of HCV infection can be lost rapidly after exposure to low-dose inocula.

Hepatitis C virus-specific cellular immune responses in individuals with no evidence of infection

The detection of hepatitis C virus (HCV)-specific T cell responses in HCV-uninfected, presumably unexposed, subjects could be due to an underestimation of the frequency of spontaneously resolving infections, as most acute HCV infections are clinically silent. To address this hypothesis, HCV-specific cellular immune responses were characterized, in individuals negative for an HCV PCR assay and humoral response, with (n = 32) or without (n = 33) risk of exposure to HCV. Uninfected volunteers (n = 20) with a chronically HCV-infected partner were included as positive controls for potential exposure to HCV and HCV infection, respectively. HCV-specific T cell responses in freshly isolated peripheral blood mononuclear cells were studied ex vivo by ELISPOT and CFSE-based proliferation assays using panels of HCV Core and NS3-derived peptides. A pool of unrelated peptides was used as a negative control, and a peptide mix of human cytomegalovirus, Epstein-Bar virus and Influenza virus as a positive control. Overall, 20% of presumably HCV-uninfected subject tested had detectable T-cell responses to the virus, a rate much higher than previous estimates of HCV prevalence in developed countries. This result would be consistent with unapparent primary HCV infections that either cleared spontaneously or remained undetected by conventional serological assays.

Declining hepatitis C virus (HCV) prevalence in pregnant women: impact of anti-HCV screening of donated blood

BACKGROUND

Screening blood donors for hepatitis C virus (HCV) antibody has effectively mitigated transfusion transmission of HCV. We conducted a post hoc analysis to clarify the impact of donor screening on a general population of reproductive-age females and their offspring.

STUDY DESIGN AND METHODS

Anti-HCV screening in Japan started in late-1989. In a cohort studied between May 1990 and November 2004, a total of 22,664 consecutive serum samples from pregnant women were screened for anti-HCV. Reactive samples were further tested for HCV RNA. Linear structural regression was applied to identify causal relationships.

RESULTS

Anti-HCV-reactive rates declined significantly by two measures. First, among women known to have been transfused, rates fell from 14.8% to 3.1% with the implementation of anti-HCV screening (p < 0.01). Nevertheless, this is 10 times higher than the 0.3% reactive rate seen in a similar cohort of nontransfused women. Second, rates fell from 1.8% among women born in 1955 or before to 0.3% for women born in 1966 or later (p < 0.01). Among 103 anti-HCV-reactive women, 31 (30%) had been transfused and another 17 (17%) had other identifiable risk factors. The remaining 55 (53%) had no clear risk factor. Blood transfusion accounted for 19% of anti-HCV acquisition, by path analysis. Only one infant in this cohort was vertically infected with HCV.

CONCLUSION

Anti-HCV screening of donated blood and hygienic improvements have markedly decreased HCV infection of pregnant women with a transfusion history; however, 70% of anti-HCV-reactive women were deemed to be infected via routes other than transfusion.