Expanded Antibody Detection: Closing the SAB Gap with the UT Health Histocompatibility and Immunogenetics Laboratory

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Like many labs, the Histocompatibility and Immunogenetics Laboratory team at UT Health San Antonio has long wrestled with the challenge of closing the “SAB gap” or determining a way to test for critical HLA antibody targets not included on standard single antigen bead panels.

In this story, Dr. Kelley Hitchman, Princess Alexis Sattiewhite, and Brittany Rivera share how the UT Health lab adopted an expanded panel for HLA antibody detection to close these gaps. With broader coverage, the team can report on results with greater ease, perform more accurate virtual crossmatches, and provide better service to their clinical teams and patients.

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BRITTANY RIVERA: I like to think of each patient as kind of like a puzzle. And you're with them the whole time, you're there for pre-transplant cross match, post-transplant. So all the testing we do is like a piece of that puzzle. I do think that the expanded panel is like giving you another piece to help solve that.

DR. KELLEY HITCHMAN: Right now, the University Health HLA laboratory is really focused mostly on solid organ transplantation. We support a very robust adult and pediatric kidney transplant program, as well as the second-largest living liver transplant program in the U.S.

When we are assessing a case pre-transplant looking for compatibility between a patient and a donor or when we're looking post-transplant for donor-specific antibodies, it's a huge gap to tell your clinicians, "I just can't look for that and there's nothing that I can do to help you," because I don't feel like that's actually the case.

When we are looking to fill those gaps without reagents, we can analyze the data to see what we have on a base panel that's the most similar antigen on the panel but it's not exactly the antigen it's just antibody reactivity that may be similar. So it's an option, but it's not the most accurate option. We would much rather be able to characterize specifically the potential for antibody reactivity against a specific antigen.

PRINCESS ALEXIS SATTIEWHITE: We first started using the extended panel December 2020. Bridging the gap was somewhat complex; we didn't have as many specificities as the ExPlex panel does now. So for example, we have our allele A*0205, beforehand on the expanded panel we only could report an A*02. We had several A*02 alleles that we just had to report positives or negatives for every single one. Now that we have the A*0205 on the extended panel, we can just report specifically A*0205.

BRITTANY RIVERA: Using the expanded panel with our post-transplant specimens has helped us be able to really identify DSA instead of saying like, "potential" or "serological equivalent," because instead of saying, "oh we have this A*2" and we have four alleles, now we have nine and we can actually rule out certain DSAs using this panel.

DR. KELLEY HITCHMAN: Highly sensitized patients it's very important to be accurate. You want to truly be able to say there is, or is not, donor-specific antibody in this patient rather than basing it on an imputation, or a guess. I feel like with extended options in single antigen testing we feel much more confident about the estimations in our immunologic risk assessments.

The testing is done before the immunologic risk assessment has to be performed, so that when the time comes that a patient comes up for an offer, we don't have to scramble and do a bunch of additional tests in that moment and potentially delay transplantation because we have accurate data at hand.

PRINCESS ALEXIS SATTIEWHITE: The additional information that we have gained from using the extended panel has enabled us to improve our matching of donors to recipients. In a larger sense, we've been able to transplant more patients without the fear of rejection because we have that specificity there. We've also been able to cut down on unnecessary transplants because we can rule out those beforehand.

Many thanks to: 

Dr. Kelley Hitchman, Associate Professor | Section Chief, HLA | Director, Histocompatibility and Immunogenetics Laboratory, UT Health San Antonio

Princess Alexis Sattiewhite, MBASCP, CHT | HLA Laboratory Technical Supervisor | Histocompatibility and Immunogenetics Laboratory, UT Health San Antonio

Brittany Rivera, AMT | HLA Laboratory Technologist | Histocompatibility and Immunogenetics Laboratory, UT Health San Antonio