One Antigen HLA-Mismatched Related and 8/8 Allele Matched Unrelated Donors Are Associated with Similar Survival after Hematopoietic Cell Transplantation for Acute Leukemia

Patients in need of an allogenetic hematopoietic cell transplant but who lack an HLA genotypically identical sibling donor, are faced with the decision to consider a single HLA antigen mismatched related donor, or a search for a suitable 8/8 matched unrelated donor. We compared the outcomes of adult patients (≥18 years old) receiving a transplant for the treatment of AML or ALL in first or second remission from either a one-antigen mismatched related donor (MMRD group, N=89) reported to the CIBMTR or an 8/8 HLA-A, B, C and DRB1 allele matched unrelated donor (UD group, N=700) facilitated by the NMDP between 1995-2005. MMRD group was typed by serological or DNA-based methods for HLA-A, -B and –DR with all results verified by lab report review. The UD group was retrospectively typed for HLA-A, B, C and DRB1 by high resolution typing methods. Most received myeloablative conditioning regimens (77%), calcineurin inhibitor-based GVHD prophylaxis (100%) and T cell replete grafts (100%). 13% received ATG with the conditioning regimen. Median follow-up was 54 and 38 months in the MMRD and UD groups, respectively. The MMRD group was younger (median age 35 vs 43, p=0.002), had more ALL patients with low-risk cytogenetics (43% vs 18%, p=0.005), had older donors (median age: 38 vs 34, p=0.047), were more likely to receive methotrexate for GVHD prophylaxis (89% vs 77%, p=0.014) and were more likely to be transplanted prior to 2001 (62% vs 24%; p<0.001). There were no differences in patient or donor gender, diagnosis, disease-status, cytogenetic-risk of AML, time from diagnosis to transplant, stem cell source, conditioning regimen, use of ATG and Karnofsky index. Univariate comparisons (MMRD vs. UD) showed: 3-year OS (42% vs 44%, p=0.647), 3-year DFS (41% vs 41%, p=0.931), 3-year TRM (39% vs 31%, p=0.136), 3-year incidence of relapse (20% vs 28%, p=0.094), grade III-IV acute GVHD by 100 days (22% vs. 15%, p=0.147), chronic GVHD by 1 year (35% vs 47%, p=0.029). All multivariate analyses were adjusted for patient and transplant characteristics and are shown in the table below.

Outcome	RR (MMRD vs. UD)	95% CI	p-value
Survival	0.99	0.73-1.34	0.94
Disease-free survival	1.06	0.80-1.41	0.69
Treatment related mortality	1.14	0.77-1.69	0.52
Relapse	0.81	0.50-1.30	0.38
Acute GVHD III-IV	1.53	0.91-2.57	0.11
Chronic GVHD	0.58	0.39-0.85	0.006

In summary, transplants utilizing one-antigen mismatched related and 8/8 allele-matched unrelated donors did not significantly differ in overall survival or disease free survival, but chronic GVHD was more frequent after UD transplantation.