Variable HLA expression on deceased donor lymphocytes: Not all crossmatches are created equal

Flow cytometric crossmatch tests are used to detect donor-specific antibody and determine eligibility for transplantation. Crossmatch sensitivity is dependent on lymphocyte quality, to include HLA expression on the cell surface. The impact of HLA expression variability on crossmatch reactivity was examined using lymphocytes isolated from different donor types: deceased donor (DD) versus living donor (LD) and tissue sources (blood, spleen, or lymph nodes). HLA class I expression was similar on B cells isolated from LD blood, DD spleen, and DD lymph nodes, but significantly lower on B cells isolated from DD blood (p = 0.0004). In contrast, class II expression on B cells and class I on T cells were significantly higher in LD blood than all DD tissues. Within DD tissues, spleen provided the highest expression of class II on B cells and class I on T cells. HLA expression on B cells, but not T cells, was impacted by memory (CD27+) versus non-memory status. Importantly, HLA expression differences on lymphocytes isolated from the same donor but different tissues impacted crossmatch outcomes. HLA expression is impacted by multiple factors and should be routinely monitored to ensure crossmatch sensitivity and to reconcile crossmatch strength with solid phase HLA antibody analyses.