Identification of a Homeobox-Like Protein Immune Response in Bone Marrow Transplant Patients

The identification of novel immune targets following hematopoietic cell transplantation (HCT) promises to identify clinically important graft-v-leukemia and graft-v-host disease targets. High-density protein microarrays present thousands of human proteins and facilitate broad-band multiplexed quantitative auto and alloreactive antibody screening. Our studies utilized both male and female patient plasma which were collected pre-transplant and one year post-transplant to identify new immune response targets. The tetra-peptide repeat homeobox-like protein (TPRXL) was initially identified by protein microarray as a potential biomarker in one MDS and four AML transplant patients. We developed an ELISA assay by affinity purifying TPRXL expressed in E.coli, and tested plasma samples collected from 80 HCT patients 1–2 years after HCT. A 42% sero-positive incidence was found across the group of post transplant samples (p-value <0.001). Located at 3p25.1 of the human genome, TPRXL encodes a 257 amino acid and 25 kDa protein containing a significant percentage of serine tetra-peptide repeats. Being a member of the TPRX homeobox gene family, the protein’s secondary structure and function lead to direct interaction with DNA and tight regulation of gene expression. Presently, of the 18 reported TPRXL transcript variants a majority are nearly identical and are found to be highly expressed in early embryonic development, in the placenta, oral tissues and the ascites. Results indicate disease specificity with prevalence of post transplant response in patients with Mantle cell lymphoma (MCL). In addition, patients with chronic GVHD of the oral pharyngeal tissues are predominant in our analysis. In silico studies show that TPRXL is indeed differentially expressed in acute pro-myelocytic leukemia (PML) and acute lymphocytic lymphoma (ALL) cell lines as compared to controls. Since bioinformatics expression data available for MCL cell lines are scarce, perhaps due to fewer reports or studies in this area, it is clear that our novel findings will contribute to currently available information for this disease type. In sum, protein microarray technology represents a powerful tool in facilitating the identification of novel disease associated antigenic targets and that TPRXL is potentially one such prognostic marker.