The need for reliable tools to predict likelihood of HLA-antibody responses to treatment and to monitor efficacy of antibody removal therapies manifests itself on two fronts: the individual patient level, and the population level, specifically for evaluating new drugs. Unfortunately, currently used approached to measure HLA antibody strength fall short from providing quantitative measures.

Serum samples from 40 patients (total of 58 assays including class I and II tests; >2200 positive data points) undergoing antibody removal therapies (desensitization or treatment of antibody mediated rejection) were tested prior to initiation of treatment and at the end of treatment protocol. Solid phase luminex assays were run on sample-pairs, pre- and post-treatment, at the same time using same lot of reagents. MFI values of the routine IgG and the C1q single-antigen-bead HLA-antibody assays were compared with antibody titer values obtained by serial dilution studies. Antibody reduction patterns were tracked and the difference in pre- to post-treatment values were calculated as delta reduction of antibody levels.

Our results clearly show that while delta reduction of antibody values in both IgG and C1q tests exhibited a significant level of variability between different antibodies, titration studies indicated a rather uniform reduction of all antibodies within a serum sample; %CV of 15 for titration studies versus >100 for IgG and C1q MFI variations. Analyzing antibody results using alternative approaches (only C1q positive, only higher MFI values) did not change the overall magnitude of results. Our data also suggest that the superiority of titration studies is due to its ability to overcome some of the serum-inherent issues that led to known limitations of the solid-phase assays. Specifically, given the dynamics of titration studies compared with a one-time measure for the IgG or C1q assays, better estimate of antibody-binding strength is achieved; serum-inherent inhibitory factors are diluted, thus eliminating prozone effects; and over-saturation of targets is no longer an issue as the serum is diluted until a negative response is achieved.

Our results strongly support the use of titration studies as a better tool to quantify HLA-antibody strength, provide guidance to desensitization approaches, monitor success of antibody-removal treatment, and potentially aid in evaluating drug efficacy.

CITATION INFORMATION: Tambur A, Glotz D, Herrera N, Chatroop E, Roitberg T, Friedewald J, Gjertson D. Measuring Efficacy of Antibody Removal Therapies: Back to Titers. Am J Transplant. 2016;16 (suppl 3).

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