Correlation of screening and confirmatory results in tiered immunogenicity testing by solution-phase bridging assays.

Biotherapeutic proteins induce undesired immune responses that can affect drug efficacy and safety. For this reason, immunogenicity assessment is an integral part of drug development and is mandated by the regulatory authorities. Immunogenicity is typically evaluated by a tiered approach consisting of a screening assay followed by a competitive inhibition with unlabeled drug serving as confirmatory assay and additional characterization of the immune response. The confirmatory assay is intended to reduce the number of false positive responses generated in the screening tier and ensure that all samples are correctly classified as positive or negative. The positive-negative sample decisions are based on screening and confirmatory assay cut points that are statistically derived through evaluation of drug-naive samples. In this paper, we describe the analysis of cut point data for the presence of statistical correlation between the screening and confirmatory results. Data were obtained from validations of solution-phase bridging assays for detection of anti-drug antibodies against monoclonal antibody therapeutics. All data sets showed moderate to strong positive correlation, indicating that the screening and confirmatory assays were not independent and were likely to generate similar information. We present theoretical evidence that correlated results may be a general feature of the tiered approach when the same test platform is used for both screening and confirmatory assays. The competitive inhibition test, therefore, may be of limited value beyond reduction of the overall false positive rate. Our results indicate that similar sample results could be obtained by using just the screening assay with the false positive rate set to 1%.

Human leukocyte antigens A*3001 and A*3002 show distinct peptide-binding patterns of the Mycobacterium tuberculosis protein TB10.4: consequences for immune recognition.

High-tuberculosis (TB)-burden countries are located in sub-Saharan Africa. We examined the frequency of human leukocyte antigen (HLA) alleles, followed by recombinant expression of the most frequent HLA-A alleles, i.e., HLA-A*3001 and HLA-A*3002, to study differences in mycobacterial peptide presentation and CD8(+) T-cell recognition. We screened a peptide library (9-mer peptides with an 8-amino-acid overlap) for binding, affinity, and off-rate of the Mycobacterium tuberculosis-associated antigen TB10.4 and identified only three TB10.4 peptides with considerable binding to HLA-A*3001. In contrast, 22 peptides bound to HLA-A*3002. This reflects a marked difference in the binding preference between the two alleles, with A*3002 tolerating a more promiscuous peptide-binding pattern and A*3001 accommodating only a very selective peptide repertoire. Subsequent analysis of the affinity and off-rate of the binding peptides revealed a strong affinity (8 nM to 7 µM) and moderate off-rate (20 min to 3 h) for both alleles. Construction of HLA-A*3001 and HLA-A*3002 tetramers containing selected binding peptides from TB10.4, including a peptide which was shared among both alleles, QIMYNYPAM (TB10.4(3-11)), allowed us to enumerate epitope-specific T cells in HLA-A*3001- and HLA-A*3002-typed patients with active TB. HLA-A*3001 and HLA-A*3002 major histocompatibility complex-peptide complexes were recognized in individuals with active TB, irrespective of their homozygous HLA-A*3001 or HLA-A*3002 genetic background. The antigen-specific T cells exhibited the CD45RA(+) CCR7(+) precursor phenotype and the interleukin-7 receptor (CD127), which were different from the phenotype and receptor exhibited by the parental CD8(+) T-cell population.

Antitumorigenic effects of HIV protease inhibitor ritonavir: inhibition of Kaposi sarcoma.

Treatment of patients with human immunodeficiency virus (HIV) protease inhibitors such as ritonavir can result in increases in CD4(+) T-cell counts that are independent of a reduction in HIV-1 viral load. This lack of correlation between the 2 has led to the identification of additional effects of ritonavir that potentially alter HIV disease pathogenesis. Our previous studies indicated that ritonavir directly affects immune cell activation, proliferation, and susceptibility to apoptosis. We show here that ritonavir inhibited the activation and proliferation of primary endothelial cells and decreased the production of tumor necrosis factor alpha (TNF-alpha) interleukin 6 (IL-6), IL-8, and vascular endothelial growth factor, factors that all contribute to tumor neovascularization and to the development of Kaposi sarcoma (KS) lesions. Ritonavir also suppressed the expression of vascular cell adhesion molecule 1, intercellular adhesion molecule 1, and E-selectin, which correlated with a functional decrease in leukocyte adhesion. Transcriptional activation of nuclear factor-kappaB, as induced by the KS-promoting factor TNF-alpha, the HIV-1 Tat protein, or the human herpesvirus 8 protein ORF74, was inhibited by ritonavir. KS-derived cell lines underwent apoptosis in vitro after treatment with ritonavir at concentrations that are obtained in clinical therapy (3-15 microM). In a KS mouse xenotransplantation model, ritonavir inhibited tumor formation and progression by KS-derived cells. Taken together, these data suggest that ritonavir has antineoplastic effects that are independent from its ability to inhibit the HIV protease.