Minor Histocompatibility Antigen Mismatch and Incidence of Graft Versus Host Disease, Event-Free, and Overall Survival in Patients Undergoing Unrelated Donor Allogeneic Hematopoietic Cell Transplantation

Abstract 4201

Graft versus Host Disease (GvHD) is a potentially devastating complication of allogeneic hematopoietic cell transplantation (HCT) initiated in part due to donor-recipient disparities in immunoreactive proteins, or minor histocompatibility antigens (mHAgs). There are no established prognostic tools to predict which patients will get acute or chronic GvHD. Analysis of mHAg mismatch is a potential predictive tool for GvHD; however, previous studies attempting to establish a relationship between mHAg mismatch and GvHD have been largely equivocal. Here we tested the hypothesis that analysis of an expanded set of mHAgs for mismatch in the GvH direction can be predictive of acute or chronic GvHD by NIH criteria. We additionally analyzed event-free (EFS) and overall survival (OS) in the mHAg matched and mismatched subgroups. Recipient/donor pairs from 45 HLA-A, -B, -C, and DRB1 matched unrelated donor transplants from 2007–2011 were retrospectively typed for 19 mHAgs using an SSP-PCR typing kit (Minor Histocompatibility Antigen Typing Kit; Life Technologies, Carlsbad, CA). Genomic DNA was obtained from peripheral blood mononuclear cells. EFS and OS were estimated using the Kaplan-Meier method. The relationship between mismatch and acute or chronic GvHD was described using Fischer's Exact Test. Cumulative incidence of treatment related mortality (TRM) was calculated using the Gooley Method. Two patients expired of early TRM and were excluded from the GvHD analyses. The rate of acute GvHD grades II-IV was 6 of 14 in those without a mHAg mismatch and 21 of 29 in those with a mismatch (43% versus 72%, P = 0.062). The rate of chronic GvHD was 8 of 14 in those without a mismatch and 10 of 29 in those with a mismatch (53% versus 34%, P = 0.140). The presence of a mismatch did not significantly impact EFS (P = 0.42) or OS (P = 0.26). The cumulative incidence of TRM at 24 months post transplantation was greater in patients with a mismatch (36% versus 13%). Two year OS was superior in patients who were conditioned with alemtuzumab (N = 24) and had a lower degree of mismatch (0–1 mismatch = 72% versus 2+ mismatches = 38%, P = 0.038). This study suggests the possibility of a relationship between mHAg mismatch and acute GvHD and TRM. Further study using this expanded mHAg analysis on a larger cohort of individuals would more adequately define the potential benefit of mHAg mismatch analysis in the context of unrelated donor HCT.