Frequency and Intensity of Antibody Responses to Antigens Encoded by KDM5D (SMCY) and Other H-Y Genes After Allogeneic Hematopoietic Cell Transplantation,

Abstract 4028

Male recipients of female hematopoietic cell grafts (F->M HCT), when compared with other donor/recipient gender combinations, face an increased risk for both acute and chronic graft-versus-host disease (GVHD), but also have a significantly decreased risk of posttransplant relapse. F->M HCT is characterized at the cellular level by female donor T cell responses against male-specific minor histocompatibility (H-Y) antigens, which can contribute to both GVHD and graft-versus-leukemia (GVL) activity. Data from both murine models and clinical studies of allogeneic HCT demonstrate that the protein product of the Y chromosome gene KDM5D (previously known as SMCY) is one of the major targets of H-Y-specific T cell responses. CD8⁺ T cell responses against KDM5D peptides have been associated with GVHD and GVL in male recipients of female grafts, and with rejection of male grafts by female recipients.

A subset of Y chromosome-encoded proteins, including several that are targets for CD8⁺ and CD4⁺ T cell responses after F->M HCT, are also the targets of antibody responses in this setting (Miklos et al., Blood 2005; 105:2973). Antibody responses to the protein products of DDX3Y and UTY, in particular, have been detected in up to 50% of F->M HCT recipients. Moreover, antibody responses to these Y chromosome gene products have been associated with the development of chronic GVHD as well as the maintenance of remission. T cell responses to KDM5D in F->M HCT recipients have been extensively studied, but KDM5D-reactive antibody responses have not been thoroughly evaluated. We hypothesized that KDM5D -reactive antibodies would also develop in a significant fraction of F->M HCT recipients, and undertook an exploratory study to define the frequency and intensity of antibody responses to KDM5D in both allogeneic HCT patients and healthy adult male and female control subjects.

Plasma samples were obtained from 39 male HCT patients with female donors, 16 HCT patients with other donor/recipient gender combinations, 12 healthy female controls, and 9 healthy male controls, and assessed for IgG responses against an array of 84 different protein targets by ELISA. The target panel included partial (SMCY and UTY) or whole (DDX3Y, ZFY RPS4Y, and E1F1AY) recombinant H-Y proteins and their X chromosome-encoded homologues that had been expressed in and purified from E. coli, as well as synthetic overlapping peptides of length 15–21 residues derived from the KDM5D and DDX3Y protein sequences or from their X chromosome-encoded homologues KDM5C (SMCX) and DDX3X. Of the 55 samples acquired from HCT recipients, 49 came from recipients who had previously been diagnosed with cGVHD and were receiving immunosuppressive therapy.

Reactivity with KDM5D-derived peptides or recombinant KDM5D protein fragments was observed in HCT recipients of all four donor-recipient gender combinations and also in some healthy control males and females. Amongst male patients with female donors, 7 of 39 (18%) samples were reactive with more than 3 KDM5D peptides, and 2 of 16 (13%) samples from patients with other donor/recipient gender combinations were reactive with 3 or more KDM5D peptides. Significant differences in the frequency of reactivity with individual peptides were observed, with a high frequency of responses to peptides corresponding to sequences within the interval KDM5D_281–375, a region of the protein where there is significant nonidentity with the sequence of its X chromosome-encoded homologue KDM5C. This region also contains the sequence FIDSYICQV, which comprises the epitope recognized by CD8⁺ HLA-A*0201-restricted T cell clones that have frequently been isolated from HLA-A*0201⁺ F->M HCT recipients and have been associated with both GVHD and GVL. Antibody reactivity to KDM5D was correlated with reactivity to several DDX3Y-derived peptides previously shown to be the targets of antibody responses in F->M HCT recipients, but weakly associated with responses to UTY protein fragments, which were observed in 11 of 39 (28%) F->M patients and 1 of 16 (6%) patients with other donor/recipient gender combinations. These results suggest that KDM5D is a frequent target of posttransplant antibody responses in allogeneic HCT recipients. Current studies are evaluating in a larger cohort of patients the relationship of KDM5D-reactive antibody responses to H-Y-specific T cell responses and to the development of acute and chronic GVHD.