The Influence Of Anti-HLA Antibodies On Engraftment and Donor’s Chimerism Following Allogeneic Hematopoietic Stem Cell Transplantation From HLA-Mismatched Unrelated Donors
Authors: Markiewicz Miroslaw , Koclega Anna , Mizia Sylwia , Siekiera Urszula , Dobrowolska Alicja , Dzierzak-Mietla Monika , Zielinska Patrycja , Bialas Krzysztof , Kyrcz-Krzemien Slawomira 
Published: October 2019

Introduction
Although anti-HLA Antibodies (Abs) are considered an important factor of graft failure in solid organ transplants, their role in allogeneic hematopoietic stem cell transplantation (allo-HSCT) is still undiscovered. Large polymorphism and immunogenicity of HLA-antigens and heterogeneity of anti-HLA Abs warrant the need of such investigation. The purpose of this study was to define the presence of anti-HLA Abs before allo-HSCT from HLA-mismatched unrelated donors and their impact on engraftment and post-transplant full donor’s chimerism.

Material and Methods
70 HLA-mismatched donor/recipient pairs entered the study. Indication for allo-HSCT was: ALL, AML, CML, SAA, PNH, MDS and CLL. Preparative regimen was myeloablative in 68pts (97%) and reduced in 2pts (2.3%). Standard GVHD prophylaxis consisted of cyclosporine, methotrexate and pre-transplant anti-thymocyte globulin (69pts) or Alemtuzumab (1pt). HLA A,B,C,DR,DQ alleles were PCR-typed. Single HLA-antigen was mismatched in 46pts, single HLA-allele in 16pts, double antigens or alleles in 2 pts and another 2 pts had combined antigenic/allelic HLA mismatch. Anti-HLA A,B,C,DR,DQ,DP Abs were identified in sera collected prior to the conditioning treatment with use of automated DynaChip assay utilizing microchips bearing purified class I and class II HLA antigens. Post-transplant chimerism was analyzed using STR-PCR method at 30, 100-days and 1-year after allo-HSCT.

Results
Anti-HLA Abs pre-formed before allo-HSCT were detected in 32pts: against class I, II or both in 13(18.6%), 7(10%) and 12(17.1%) pts. Anti-HLA Abs were detected after allo-HSCT in 49pts: against class I, II or both in 22(32.4%), 7(10.3%) and 20(29.4%) pts, respectively. Anti-HLA Abs directed against the mismatched HLA antigens were observed in 4 pts before allo-HSCT. Although no Abs specific to mismatched HLA alleles were detected, Abs belonging to the same Cross-Reactive Groups (CREGs) were present in 5pts.
No graft failure has been observed (graft failure was defined as absence of neutrophil recovery by day 30 after allo-HSCT or loss of donor’s chimerism). The detection of anti-HLA Abs before allo-HSCT was associated with decrease of post-transplant donor’s chimerism (18/31 vs 11/35, p=0.03). Anti-HLA Abs had no significant impact on engraftment of platelets and neutrophils. The median time to neutrophils engraftment was 16.9 days (range 7-31 days) in pts with and 18.9 days (range 13-30 days) in pts without anti-HLA Abs (p=0.188). The median time to platelets engraftment was 16.9 days (range 9-31 days) in patients with and 18.3 days (range 10-32 days) in pts without anti-HLA Abs (p=0.274).

Conclusions
Our preliminary results indicate, that anti-HLA Abs are present before transplantation in mismatched allo-HSCT recipients. They influence the post-transplant full donor’s chimerism, but they did not influence engraftment and graft failure.

Disclosures:
No relevant conflicts of interest to declare.