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Blood Adv. 2019 Jul 23;3(14):2199-2204. doi: 10.1182/bloodadvances.2019000445.

Recurrent genetic HLA loss in AML relapsed after matched unrelated allogeneic hematopoietic cell transplantation.

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Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
Department of Pathology, Massachusetts General Hospital, Boston, MA.
Broad Institute, Cambridge, MA.
Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
Center for Cancer Genome Discovery, Dana-Farber Cancer Institute, Boston, MA.
Agilent Technologies, Santa Clara, CA.
Ottawa Blood Disease Centre, The Ottawa Hospital, Ottawa, ON, Canada; and.
Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA.


Immune evasion is a hallmark of cancer and a central mechanism underlying acquired resistance to immune therapy. In allogeneic hematopoietic cell transplantation (alloHCT), late relapses can arise after prolonged alloreactive T-cell control, but the molecular mechanisms of immune escape remain unclear. To identify mechanisms of immune evasion, we performed a genetic analysis of serial samples from 25 patients with myeloid malignancies who relapsed ≥1 year after alloHCT. Using targeted sequencing and microarray analysis to determine HLA allele-specific copy number, we identified copy-neutral loss of heterozygosity events and focal deletions spanning class 1 HLA genes in 2 of 12 recipients of matched unrelated-donor HCT and in 1 of 4 recipients of mismatched unrelated-donor HCT. Relapsed clones, although highly related to their antecedent pretransplantation malignancies, frequently acquired additional mutations in transcription factors and mitogenic signaling genes. Previously, the study of relapse after haploidentical HCT established the paradigm of immune evasion via loss of mismatched HLA. Here, in the context of matched unrelated-donor HCT, HLA loss provides genetic evidence that allogeneic immune recognition may be mediated by minor histocompatibility antigens and suggests opportunities for novel immunologic approaches for relapse prevention.

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