OR30. HLA expression on CD34+ stem cells: is a flow cytometric crossmatch a good gatekeeper for mismatched hematopoietic cell transplantion?

Abstract

Aim Primary graft failure associated with donor specific antibody (DSA) is influenced by the level of circulating DSA at time of infusion and by the density of HLA antigens expressed on cell populations needed for engraftment. It is not yet known what HLA antigens are expressed on CD34 + stem and progenitor cells nor what level of DSA, if any, is permissible. We compared surface expression levels of class I (HLA-A, B, C) and class II (HLA-DR, DQ, DP) molecules on CD34+, B, and T cells to determine whether a lymphocyte flow cytometric crossmatch is an adequate method to assess risk of DSA mediated graft failure. Methods Samples consisted of peripheral blood (PB) from PB stem cell donors or an aliquot of bone marrow (BM) aspirate from BM donors. CD34+, CD19+ (B cells) and CD3+ (T cells) were simultaneously analyzed using monoclonal antibodies specific for each HLA target and flow cytometry. Selected samples were analyzed by flow cytometry using dilutions of DSA containing sera and staining with anti-human IgG. Results Despite individual variations, higher levels of HLA-A and B and lower levels of HLA class II were observed on CD34 + cells compared to lymphocytes (Fig. 1). Titration of sera containing antibody specific for donor’s HLA-A antigens revealed higher reactivity of CD34 + cells than of B or T cells (Fig. 2 - representative result). Conclusions Antibodies specific for all class I and II HLA targets may be deleterious given their expression on CD34 + cells. HLA-A and B specific antibodies may be especially harmful given the high expression of these loci. Use of peripheral T and B donor lymphocytes flow cytometric crossmatch may underestimate the risk of graft failure due to the relative lower expression of HLA-A and B loci in these cell populations. Download : Download high-res image (133KB) Download : Download full-size image Download : Download high-res image (77KB) Download : Download full-size image M.P. Bettinotti: 3. Speaker’s Bureau; Company/Organization; One Lambda Thermo Fisher. A.M. Jackson: 3. Speaker’s Bureau; Company/Organization; One Lambda Thermo Fisher.