Determination of Reference Values of MDR‐ABC Transporter Activities in CD3+ Lymphocytes of Healthy Volunteers Using a Flow Cytometry Based Method

Comparison of P-glycoprotein function in peripheral blood mononuclear cells ex vivo in stable Black and White male and female kidney transplant recipients

Kidney allograft survival remains poorer in Black compared to White recipients due to racial differences in calcineurin inhibitor (CNI) pharmacology. P-glycoprotein (P-gp), an ABC efflux transporter expressed in peripheral blood mononuclear cells (PBMCs), modulates CNI pharmacokinetics and intracellular pharmacology. This study investigated P-gp function in PBMC ex vivo at 0 (trough), 4, 8, and 12 h in stable Black and White male and female kidney transplant recipients (n = 67) receiving tacrolimus and mycophenolic acid. Tacrolimus doses were adjusted to troughs of 4-10 ng/ml. P-gp function was quantified with flow cytometric measurement of cyclosporine (CYA; 2.5 μM)-reversible efflux of P-gp substrate, 3,3'-Diethyloxacarbocyanine iodide by determining the percentage change of mean fluorescent intensity (MFI) with CYA (% ΔMFI). The composite parameter of area under the concentration versus time (AUC)0-12h % ΔMFI estimated P-gp function. Data analysis examined race, sex, and race-sex associations to P-gp function. A secondary aim analyzed ABCB1 genotypes: 1236C>T (rs1128503), 2677G>T/A (rs2032582), 3435C>T (rs1045642), and P-gp function. P-gp function (% ΔMFI) was higher in White patients at troughs (p = 0.031) compared to Black counterparts with similar trends at 4 and 8 h. Reduced AUC0-12h % ΔMFI was noted in Black recipients (N = 32) compared with Whites (N = 35, p = 0.029) with notable pairwise adjusted differences between Black and White women (p = 0.021). Higher AUC0-12h % ΔMFI was associated with ABCB1 2677 TT compared to GG variants (p = 0.035). The AUC0-12h % ΔMFI was greater in White than Black subjects. P-gp function was higher at troughs in White subjects and differed between race-sex groups. P-gp function in PBMC may influence intracellular tacrolimus exposure and inter-relating pharmacodynamic responses which may support race and sex pharmacologic differences.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Peripheral Lymphocyte Multidrug Resistance Activity as a Predictive Tool of Biological Therapeutic Response in Rheumatoid Arthritis

Objective.

Multidrug resistance (MDR) transporters may be used as biomarkers to monitor disease progression in RA and as a predictive tool to establish responsiveness to biological therapy. In this multicenter clinical trial, we aimed to assess the predictive value of activity measurement of transporters MDR1, MD resistance protein (MRP)1, and breast cancer resistance protein (BCRP) for biological therapeutic response in RA before the initiation of biological therapy as well as 4 to 6 and 12 weeks after.

Methods.

Peripheral blood samples were collected from 27 responders and 12 nonresponders to biological disease-modifying antirheumatic drugs (bDMARD) at the indicated timepoints as well as from 35 healthy controls. MDR activity factor (MAF) of MDR1, MRP1, and BCRP was measured in CD3+ and CD19+ cells using the Solvo MDQ Kit and cell surface staining by flow cytometry following peripheral blood mononuclear cells isolation.

Results.

At the start of therapy, MAFC (composite MAF of MRP1 and MDR1) and MAFMDR values, and at 4 to 6 weeks of treatment, MAFC, MAFMRP, and MAFMDR values of CD3 cells were higher in nonresponders compared to responders. Receiver-operation characteristic curve analysis revealed that RA patients with MAFC values above 21.3 in CD3 cells at the start of bDMARD therapy are likely to be nonresponders. At 4 to 6 weeks of treatment, these also predict unfavorable response: MAFC values above 20.3, MAFMRP values above 6.0, and MAFMDR values above 13.9 in CD3 cells.

Conclusion.

Our results indicate that the determination of MAFC values in CD3 cells of patients with RA may be of predictive value prior to the initiation of biological therapy, to establish whether the patient will demonstrate sufficient therapeutic response.