Flow cytometry and cell activation

Deficient phosphorylation of Stat1 in leukocytes identifies neutralizing antibodies in multiple sclerosis patients treated with interferon-beta

BACKGROUND

Anti interferon-beta (IFN-β) neutralizing antibodies (NAb) affect efficacy of treatment of multiple sclerosis patients, but exactly when the detrimental effects of NAbs offset therapeutic efficacy is debated. Quantification of intracellular pathway-specific phosphorylation by phospho-specific flow cytometry (phosphoflow) is a promising tool for evaluation of these effects in primary immune cells from treated patients at the single-cell level.

METHOD

Samples for phosphoflow and gene expression changes were collected before administration of IFN-β and at four, six, and eight hours thereafter. Patients were NAb negative (n = 3) or were NAb positive with low/medium (n = 1) or high (n = 2) NAb titers. Levels of phosphorylation of six Stat transcription factors (pStat) in seven cell subtypes and expression levels of 71 pathway-specific genes in whole blood were measured. The data was subjected to principal component analysis (PCA), fifty-fifty MANOVA, ANOVA, and partial least square regression (PLSR).

RESULTS

PCA of pStat levels clustered patients according to NAb class independently of time. PCA of gene expression data clustered patients according to NAb class but was affected by time and treatment. In the fifty-fifty MANOVA, NAb class was significant for both pStat levels and gene expression data. The ANOVA identified pStat1 protein in several cell subtypes as significantly affected by NAb class. The best fitting model for NAb prediction based on PLSR included pStat1 in monocytes, T cells, or lymphocytes and pStat3 in monocytes (r = 0.97). Gene expression data were slightly less predictive of NAb titers.

CONCLUSION

Based on this proof of concept study, we hypothesize that NAb effects can be monitored by evaluation of a single biomarker, pStat1, in either monocytes or T cells by phosphoflow directly after IFN-β administration. The method will significantly reduce cost relative to labor intensive in vitro methods and offers a patient-specific approach to NAb evaluation.

Immunogenic effects of recombinant interferon-beta therapy disrupt the JAK/STAT pathway in primary immune cells from patients with multiple sclerosis

BACKGROUND

Immunogenicity of recombinant interferon-β (IFN-β) is a known complication in the therapy of relapsing-remitting multiple sclerosis (RRMS). Neutralizing antibodies (NAbs) that can interfere with efficacy are quantified using in vitro bioassays; however, these assays do not reveal the immunogenic state of the patient and are not predictive of treatment outcome.

OBJECTIVE

Assessment of the impact of NAbs on IFN-β responsive cells and signalling pathways in peripheral blood mononuclear cells (PBMCs) with phospho-specific flow cytometry.

METHOD

PBMCs from 10 IFN-β-treated patients with RRMS, two untreated patients, and two healthy controls were re-stimulated in autologous sera and media with a serial dilution of IFN-β (0-8000 U/ml) and levels of phosphorylation of STAT1/3/4/5/6 transcription factors were quantified in PBMC subtypes (NAb titres 0 to > 6000 neutralizing units). Data was subjected to principal component analysis, Hotelling's T (2), and partial least squares analysis.

RESULTS

Three significantly distinct clusters of individuals were revealed in autologous sera: therapy-naïve and healthy, treated NAb-negative, and treated NAb-positive. Compared with controls STATs signalling patterns were modulated in treated NAb-negative patients and inhibited in all treated NAb-positive patients independently of NAb titres. In media no clustering of patients could be found. The predictability of NAb titres based on the phospho-flow data was 74%.

CONCLUSION

Phospho-specific flow cytometry can delineate subset-specific cell responses that can act as surrogates for NAb exposure in blood. Immunogenic effects alter the response in primary cells even at low NAb levels. Cell line-based immunogenicity testing is not readily transferable to the immunogenic response in patients.