Antibodies specifically target AML antigen NuSAP1 after allogeneic bone marrow transplantation

Identifying the targets of immune response after allogeneic hematopoietic cell transplantation (HCT) promises to provide relevant immune therapy candidate proteins. We used protein microarrays to serologically identify nucleolar and spindle-associated protein 1 (NuSAP1) and chromatin assembly factor 1, subunit B (p60; CHAF1b) as targets of new antibody responses that developed after allogeneic HCT. Western blots and enzyme-linked immunosorbent assays (ELISA) validated their post-HCT recognition and enabled ELISA testing of 120 other patients with various malignancies who underwent allo-HCT. CHAF1b-specific antibodies were predominantly detected in patients with acute myeloid leukemia (AML), whereas NuSAP1-specific antibodies were exclusively detected in patients with AML 1 year after transplantation (P < .001). Complete genomic exon sequencing failed to identify a nonsynonymous single nucleotide polymorphism (SNP) for NuSAP1 and CHAF1b between the donor and recipient cells. Expression profiles and reverse transcriptase-polymerase chain reaction (RT-PCR) showed NuSAP1 was predominately expressed in the bone marrow CD34(+)CD90(+) hematopoietic stem cells, leukemic cell lines, and B lymphoblasts compared with other tissues or cells. Thus, NuSAP1 is recognized as an immunogenic antigen in 65% of patients with AML following allogeneic HCT and suggests a tumor antigen role.