Background:

Since implementation of the current Kidney Allocation System, highly sensitized patients with 98-100% cPRA (HSPs) are receiving ~10% of deceased donor kidneys compared to <2% prior to its implementation. However, those HSPs who possess allele specific antibodies (aAb) (which are antibodies directed against polymorphisms/epitopes/eplets present in some members of an antigenic group but not others) remain a disadvantaged group of candidates. The approach to list as unacceptable the parent antigen to which patients only have antibodies to specific alleles would unnecessarily exclude compatible donors, thereby further reducing an already limited pool of donors. In this study, we present our experience that expands the donor pool for HSPs with aAbs.

Methods:

38 HSPs with 98-100% cPRA were evaluated. When patients displayed aAbs, parent antigens were not listed as unacceptable in UNet. Instead, when otherwise compatible donors who possessed parent antigens were offered to candidates with aAbs, the parent antigen was resolved by high resolution HLA typing and then a vXM was performed. Donor organs whose allelic specificities were not the targets of the aAbs were transplanted.

Results:

27/38 patients (71%) who possessed aAbs were transplanted with kidneys from donors where no potential mismatched targets were involved. 11/38 (29%) recipients with aAbs were transplanted with parent antigen positive/allele specificity negative donor kidneys. All vXMs and their corresponding physical crossmatches were negative. The median MFI value for aAbs was 4528 (range 2314-15603). Transplant outcomes among these patients were compared to the control group of recipients who had no aAbs. Outcomes were identical between the two groups of recipients.

Conclusions:

Among highly sensitized patients with aAbs, the parent antigens to which patients have aAbs do not need to be considered as unacceptable. Rather, combining high resolution typing with vXM successfully predicts donor/recipient compatibility. This approach maximizes the donor offers to a particularly disadvantaged group of highly sensitized patients without negative impact to transplant outcomes.

CITATION INFORMATION: Zhang A., Zaky Z., Africa J., Good D., Bray R., Gebel H. Increasing the Donor Pool for Highly Sensitized Patients with Allele Specific Antibodies: Optimizing the Virtual Crossmatch (vXM) Am J Transplant. 2017;17 (suppl 3).

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