P147 Unexpected things flow crossmatch can reveal

Abstract

Aim Flow cytometric crossmatch (FCXM) has become the preferred method of crossmatching due to its superior sensitivity and specificity over the traditional complement-dependent cytotoxicity-assays. Here we report a case of undiagnosed lymphoma identified during a routine living kidney donor FCXM. Methods FCXM was performed on a BD FACSCanto II flow cytometer using pronase-treated donor peripheral blood mononuclear cells (PBMC). Staining included CD45 for leukocytes, CD3 for T-cells, CD19 for B-cells, and goat anti-human IgG for the detection of surface-bound donor-specific antibody. G46-2.6 and Tu39 were included to measure the expression level of HLA class I and II antigens on donor cells. Immunophenotyping was performed by a reference lab. Results A 65-year-old Caucasian female with unremarkable medical history was evaluated for living kidney donation to an unrelated recipient candidate. In the initial allo crossmatch, while the gated donor lymphocyte population displayed a typical FSC/SSC architecture, normal staining profile with all the cell surface markers and normal HLA expression level, the cell type composition appeared grossly altered. Specifically, the T-cell to B-cell ratio was reversed at 1 to 4.4 (typically observed between 4 to 1 and 9 to 1, based on a retrospective analysis of 44 living donor crossmatches). The allo crossmatch was repeated using freshly collected donor blood and the findings were identical. Morphological examination of donor PBMC with Wright’s stain revealed many disrupted mononuclear cells, and immunophenotyping showed the PBMC consisted of primarily abnormal B cells stained dimly for CD19 and CD20 and negative for CD3, CD5, CD10, CD11c, CD23, and CD38, with the light chain displaying a lambda restriction with a complete absence of kappa chain (normal lambda-to-kappa ratio = 1:2). Taken together, the immunophenotypic profile suggested a diagnosis of B-cell marginal zone non-Hodgkin lymphoma or lymphoplasmacytic lymphoma, with lambda light-chain restriction. The donor was subsequently deferred and referred for follow up. Conclusion This case report illustrates the possibility of identifying undiagnosed hematological malignancies using the conventional histocompatibility crossmatch setup even with limited lymphocyte markers.