GRAPEVINE, TEXAS—An analysis of more than 8000 patients provides insights regarding HLA disparity that may help optimize outcomes in individuals undergoing unrelated-donor hematopoietic stem cell transplant.
The study showed that a single allele- or antigen-level HLA mismatch (7/8) increased the risk for acute and chronic graft-vs-host disease (GVHD) and worsened survival rates.
However, there were no locus-specific effects on survival, and there was no impact of allele- vs antigen-level mismatch on survival.
In addition, patients with an 8/8 matched graft had an increased risk of acute GVHD if they had a DQB1 mismatch or a DPB1 mismatch. DPB1 mismatch also decreased the risk of relapse, and nonpermissive DPB1 mismatch was associated with worse survival.
“Thus, we believe that consideration of DPB1 in donor selection may permit skewing toward donors with permissive DPB1 mismatch and may improve outcomes,” said study investigator Joseph Pidala, MD, of the H. Lee Moffitt Cancer Center in Tampa, Florida.
He presented these findings at the 2014 BMT Tandem Meetings as abstract 5, which was designated one of the meeting’s “Best Abstracts.”
Dr Pidala and his colleagues evaluated data from 8003 adult and pediatric patients who had undergone their first myeloablative, unrelated transplant between 1999 and 2011. The patients had been diagnosed with acute myeloid leukemia, acute lymphoblastic leukemia, chronic myeloid leukemia, or myelodysplastic syndrome.
Patients and their donors had high-resolution typing for HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1. Most cases were 8/8 matched (n=5449), followed by 7/8 (n=2071) and 6/8 (n=483).
“Those with a greater extent of HLA mismatch were younger, less likely to be Caucasian, they differed according to disease indication for transplant, and had a greater proportion of advanced disease stage,” Dr Pidala noted.
“Additionally, those with a greater extent of HLA mismatch were more likely to receive bone marrow grafts in comparison to peripheral blood, total body irradiation, and also to receive in vivo T-cell depletion.”
Furthermore, there was a declining proportion of 6/8 match over time. It decreased from 49% (1999-2002) to 37% (2003-2006) to 14% (2007-2011).
Effects of HLA mismatch
In all analyses, the researchers considered findings significant if the P value was less than 0.01.
Compared to an 8/8 matched graft, receiving a 7/8 graft was significantly associated with an increase in acute grade 2-4, acute grade 3-4, and chronic GVHD; higher transplant-related mortality (TRM); lower disease-free survival (DFS) among patients with early stage or intermediate (but not advanced) disease; and lower overall survival (OS) regardless of disease stage.
Receiving a 6/8 graft was significantly associated with an increase in acute grade 2-4 and 3-4 GVHD, increased TRM, decreased DFS (early stage or intermediate disease), and decreased OS (early stage or intermediate disease).
“In no cases did we find [that mismatch had] an impact on the incidence of primary disease relapse,” Dr Pidala said. “Comparing 7/8 to 6/8 cases, we found that those with 7/8 had improved transplant-related mortality and disease-free and overall survival [only] in the context of early stage disease.”
The team also confirmed these findings in an analysis of 5846 unique cases. In this cohort, 2528 patients were 8/8 matched, 882 were 7/8, and 157 were 6/8.
Mismatch at HLA-A (n=743) was significantly associated with an increase in acute grade 2-4/3-4 and chronic GVHD, increased TRM, decreased DFS, and decreased OS.
Mismatch at HLA-B (n=345) was significantly associated with an increase in grade 2-4/3-4 acute GHVD, chronic GVHD, and TRM. And mismatch at HLA-C (n=766) was significantly associated with an increase in acute grade 3-4 GVHD and TRM and a decrease in DFS and OS.
There were no significant differences in the case of DRB1 mismatch. However, Dr Pidala noted that this group had the smallest number of patients, at 217.
“I’d also like to point out that in direct, pair-wise comparisons across the mismatched loci, we did not observe any significant differences in overall survival,” Dr Pidala said. “Similarly, we found no impact of allele- vs antigen-level mismatch on overall survival.”
DP and DQ mismatch
Among 8/8 matched cases, DPB1 mismatch led to a significantly increased risk for acute grade 2-4 and 3-4 GHVD, as well as a significant reduction in the risk of relapse. This was the case whether patients had a single- or double-allele mismatch.
The addition of DQB1 mismatch significantly increased the risk of grade 2-4 acute GVHD among 8/8 matched cases only if it was a single-antigen mismatch.
Neither DPB1 nor DQB1 mismatch had a significant effect on OS, DFS, or TRM in 8/8 matched cases. And neither DPB1 nor DQB1 mismatch had a significant effect on outcomes of patients who received 7/8 matched grafts.
Among 8/8 matched cases, those with permissive DPB1 mismatch had a significantly lower risk of acute grade 2-4 and 3-4 GVHD and a significantly higher risk of relapse than patients with nonpermissive DPB1 mismatch. Patients with nonpermissive mismatch also had significantly higher TRM and significantly lower DFS and OS.
However, there were no significant differences between permissive and nonpermissive mismatches for patients with 7/8 matched grafts.
Based on these results and those of previous studies, Dr Pidala said we can conclude that 8/8 matched grafts confer better survival than mismatched grafts. And a permissive DPB1 mismatch can further improve survival in 8/8 cases.
Among patients receiving a 7/8 matched graft, it is preferable to identify those with HLA-C 03:03/03:04 mismatches, as these patients appear to have mortality rates comparable to 8/8 matched cases.
Among 7/8 matched cases, we should avoid nonpermissive DPB1 mismatch, having 3 or more low-expression loci mismatches (DP, DQ, DRB3/4/5), and nonpermissive allele combinations and amino acid substitutions.