Analysis details effects of HLA mismatch

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.

Treatment implications

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.