Precursor Frequency and Affinity Determine B Cell Competitive Fitness in Germinal Centers,Tested with Germline-Targeting HIV Vaccine Immunogens

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HCV avidity as a tool for detection of recent HCV infection: Sensitivity depends on HCV genotype

Accurate detection of incident hepatitis C virus (HCV) infection is required to target and evaluate public health interventions, but acute infection is largely asymptomatic and difficult to detect using traditional methods. Our aim was to evaluate a previously developed HCV avidity assay to distinguish acute from chronic HCV infection. Plasma samples collected from recent seroconversion subjects in two large Australian cohorts were tested using the avidity assay, and the avidity index (AI) was calculated. Demographic and clinical characteristics of patients with low/high AI were compared via logistic regression. Sensitivity and specificity of the assay for recent infection and the mean duration of recent infection (MDRI) were estimated stratified by HCV genotype. Avidity was assessed in 567 samples (from 215 participants), including 304 with viraemia (defined as ≥250 IU/mL). An inverse relationship between AI and infection duration was found in viraemic samples only. The adjusted odds of a low AI (<30%) decreased with infection duration (odds ratio [OR] per week of 0.93; 95% CI:0.89‐0.97), and were lower for G1 compared with G3 samples (OR = 0.14; 95% CI:0.05‐0.39). Defining recent infection as <26 weeks, sensitivity (at AI cut‐off of 20%) was estimated at 48% (95% CI:39‐56%), 36% (95% CI:20‐52%), and 65% (95% CI:54‐75%) and MDRI was 116, 83, and 152 days for all genotypes, G1, and G3, respectively. Specificity (≥52 weeks infection duration, all genotypes) was 96% (95% CI:90‐98%). HCV avidity testing has utility for detecting recent HCV infection in patients, and for assessing progress in reaching incidence targets for eliminating transmission, but variation in assay performance across genotype should be recognized.     

Optimizing T-cell receptor avidity with somatic hypermutation

Adoptive transfer of T cells that have been genetically modified to express an antitumor T-cell receptor (TCR) is a potent immunotherapy, but only if TCR avidity is sufficiently high. Endogenous TCRs specific to shared (self) tumor-associated antigens (TAAs) have low affinity due to central tolerance. Therefore, for effective therapy, anti-TAA TCRs with higher and optimal avidity must be generated. Here, we describe a new in vitro system for directed evolution of TCR avidity using somatic hypermutation (SHM), a mechanism used in nature by B cells for antibody optimization. We identified 44 point mutations to the Pmel-1 TCR, specific for the H-2D^b-gp100_25-33 melanoma antigen. Primary T cells transduced with TCRs containing two or three of these mutations had enhanced activity in vitro. Furthermore, the triple-mutant TCR improved in vivo therapy of tumor-bearing mice, which exhibited improved survival, smaller tumors and delayed or no relapse. TCR avidity maturation by SHM may be an effective strategy to improve cancer immunotherapy.     

Positive selection of B cells expressing low densities of self-reactive BCRs

B cell tolerance or autoimmunity is determined by selective events. Negative selection of self-reactive B cells is well documented and proven. In contrast, positive selection of conventional B cells is yet to be firmly established. Here, we demonstrate that developing self-reactive B cells are not always highly sensitive to the deletion mechanisms imposed by membrane-bound self-antigens. At low amounts, membrane-bound antigens allow survival of B cells bearing a single high affinity self-reactive B cell receptor (BCR). More importantly, we show that forced allelic inclusion modifies B cell fate; low quantities of self-antigen induce the selection and accumulation of increased numbers of self-reactive B cells with decreased expression of antigen-specific BCRs. By directly measuring antigen binding by intact B cells, we show that the low amounts of self-antigen select self-reactive B cells with a lower association constant. A fraction of these B cells is activated and secretes autoantibodies that form circulating immune complexes with self-antigen. These findings demonstrate that conventional B cells can undergo positive selection and that the fate of a self-reactive B cell depends on the quantity of self-antigen, the number of BCRs engaged, and on its overall antigen-binding avidity, rather than on the affinity of individual BCRs.     

Immunosuppression in murine malaria. IV. The secondary response to bovine serum albumin

The anamnestic antibody response of CBA mice to bovine serum albumin was characterized by a rapid production of high-avidity antibody. After 3 weeks both the total amount of antibody and its avidity declined but still remained above those seen in the primary response for at least 6 weeks. The effects of acute Plasmodium berghei and Plasmodium yoelii yoelii infections upon the induction and the expression of this anamnestic response were studied. Mice infected with these malaria parasites responded poorly to primary immunization and the immunological memory generated was quantitatively subnormal. In addition, presence of the infection during a period between approximately the second and third weeks of the primary response prejudiced the development of high-avidity memory. Optimally primed mice, challenged during a subsequent acute infection, responded well initially, but were unable to maintain the secondary response at a normal level in terms of both quantity and avidity of the antibody. However, if challenge was delayed until after recovery from the infection, a normal secondary response ensued. Antibody concentrations in the sera of primed animals declined rapidly during infection. This was at least partly due to increased catabolism.     

Concurrent detection of human herpesvirus type 6 and measles-specific IgMs during acute exanthematic human parvovirus B19 infection

A familial outbreak of human parvovirus B19 infection is described in which serological tests carried out routinely for determining the causal agent of febrile rashes of viral etiology failed to yield a definitive diagnosis. Concurrent detection of serum IgMs to parvovirus B19 and to heterologous viruses such as human herpesvirus type 6 (HHV-6) and measles virus complicated interpretation of the data. IgG avidity tests and investigation and testing for the presence of viral DNA in sera by PCR were required to confirm parvovirus B19. The study stresses the importance of avidity and PCR tests to obtain a firm diagnosis of febrile exanthematic viral diseases.     

高水平血清HCMV IgM在低龄儿童原发性HCMV感染诊断中的作用

目的：探讨血清人巨细胞病毒（HCMV）IgM水平在低龄儿童中诊断原发性HCMV感染的意义。方法收集临床诊断为HCMV感染的患儿血标本56例,年龄为0.5-1岁,采用全自动化学发光法分别定量检测血清HCMV IgG、IgM抗体水平,以及IgG亲和力指数。结果 HCMV IgG＋患儿亲和力检测结果发现,其中IgM-/IgG＋的5例患者都为高亲和力IgG,而IgM＋/IgG＋的42例患者中25例是低亲和力IgG,占59.5%。根据IgM定量检测结果进一步将此47例HCMV IgG＋患儿由低至高分成5组,分别为IgM阴性组（〈30 AU/mL）,30-100 AU/mL组,100-170 AU/mL组,170-240 AU/mL组以及大于240 AU/mL组。随着IgM抗体水平的增加,低亲和力样本所占比例呈增高趋势,经卡方检验,差异有统计学意义（χ2=12.72,P〈0.05）。结论在0.5-1岁婴儿中,HCMV IgM水平与HCMV原发感染呈正相关,临床同时参考IgM定量检测和HCMV IgG亲合力检测结果,将对0.5-1岁以内婴幼儿近期HCMV感染发生时间的判定起到有益的互补作用。先进行HCMV IgM定量检测,再进行阳性病例的IgG亲和力检测是低龄儿童原发HCMV感染实验室诊断的可行方案。     

IgG avidity to distinguish secondary from primary measles vaccination failures: prospects for a more effective global measles elimination strategy

The nearly 40-year long debate on the relevance of secondary measles vaccination failure has been inconclusive because a feasible method for the assessment of the duration of immunity has been lacking. Even if a two-dose measles vaccination policy is now universally endorsed, WHO still officially adheres to the view that a single successful measles vaccination, without natural boosters, induces a lifelong immunity and deems secondary failures epidemiologically irrelevant – in the belief that the latter are rare and do not participate in the transmission chain. A recently published study on measles-IgG avidity, which allows for separation of secondary from primary vaccination failures, tentatively showed that the official view does not necessarily hold true. The results may have wide implications on global measles eradication efforts. The potential of IgG avidity measurement in complex postvaccination measles epidemiology is discussed.