Abstracts / Human Immunology 73 (2012) 1–47
Wednesday, October 10, 2012 4:00 PM - 5:30 PM Abstract Session 6: Immunomodulation
POLYMORPHISMS ALTERING THE RESIDUE TRIAD 97/114/156 CONFER TAPASIN INDEPENDENCY TO HLA CLASS I MOLECULES. Soumya Badrinath, Trevor Huyton, Rainer Blasczyk, Christina Bade-Doeding. Institute for Transfusion Medicine, Hannover Medical School, Hannover, Germany. Aim: Assembly of HLA class I complex is assisted by the peptide loading complex and its determinant Tapasin (TPN). The crucial role of TPN in selecting peptides makes it an ideal target for viral immune escape mechanisms. For instance the immune evasion strategy of HCMV prevents the presentation of viral antigens by targeting TPN. Our recent investigations highlighted the importance of residue 156 within the PBR in determining TPN dependence of assembly and peptide binding speciﬁcities for HLA-B⁄44 allotypes. We extended this work further to HLA-A⁄24 allelic variants which are known to process and present the IE-1 peptides following HCMV infection. Methods: We compared the TPN dependency and peptide repertoire of A⁄24:02Gln156, A⁄24:06Trp156 and ⁄ A 24:13Leu156. Class I negative and class I/TPN negative cells were lentivirally transduced with HLA-A⁄24 full length constructs, mRNA transcripts veriﬁed by real time PCR and surface expression of complexes assessed by ﬂow cytometry. Peptides eluted from soluble HLA-A⁄24 molecules loaded in the presence or absence of TPN were sequenced by LC-ESI-MSMS. Results: Both A⁄24:06 and A⁄24:13 showed high levels of surface expression (75%) in the absence of TPN, while A⁄24:02 exhibited partial independence. Their peptides clearly showed different patterns and features. Structurally, HLA-A⁄24:02 contains the residue triad Met97/His114/Gln156, while A⁄24:06 and A⁄24:13 contain a Trp and Leu polymorphism respectively at 156 that provides TPN independence by stabilizing the triad residues, thus generating an energetically stable and a more peptide receptive environment. Conclusions: TPN independent alleles might help to combat infections. However, presentation of unusual ligands by these alleles could be a risk factor during stem cell transplantation and needs to be considered during donor selection. The future of HSCT relies on our understanding of how successful clinical outcomes can be achieved despite patient-donor allelic mismatches.
RELATIONSHIP BETWEEN HLA RESTRICTED MINOR HISTOCOMPATIBILITY ANTIGENS AND GRAFT VERSUS HOST DISEASE IN PATIENTS FOLLOWING MATCHED UNRELATED PERIPHERAL BLOOD STEM CELL ALLOGRAFTS. Christine A. Tremblay 1, Marcela R. Uribe 1, Daniel Peaceman 2, Rachel B. Salit 2, Steven Pavletic 2, Sharon D. Adams 1, Willy A. Flegel 1. 1 Department of Transfusion Medicine, Clinical Center, National Institutes of Health, Bethesda, MD, USA; 2 National Cancer Institute, National Institutes of Health, Bethesda, MD, USA. Aim: The goal of the study was to evaluate a correlation of an HLA restricted minor histocompatibility antigen (mHAg) with the development of graft versus host disease (GVHD). The objective was to assess whether testing for mHAgs should be done on a prospective basis, to guide donor selection and reduce the high incidence of GVHD in post-transplant allografts when treating hematologic malignancies. Methods: A cohort of 45 patient/unrelated donor pairs, 10/10 HLA match, in the NCI protocol 07-C-0195 were typed for 18 mHAgs using an SSP-PCR typing kit (Minor Histocompatibility Antigen Typing Kit; Life Technologies, Carlsbad, CA). GVHD data was obtained from the clinical protocol database. Patients were determined not evaluable if they relapsed or had residual disease requiring a donor lymphocyte infusion or additional chemotherapy. Due to clinical status, one patient could not be evaluated for acute or chronic GVHD. In addition, 4 patients could not be evaluated for chronic GVHD. Therefore, 44 out of 45 patients were evaluated for acute GVHD and 40 out of 45 patients for chronic GVHD. Statistical analysis was performed using the Fisher exact test. Results: Patients with mHAg mismatches were analyzed for both acute and chronic GVHD. Preliminary analysis demonstrates that out of the 45 patient/donor pairs, 30 pairs had mHAgs mismatched in the GVHD direction. 19 of the 30 patients (63%) with mismatches developed acute GVHD (P = 0.062) and 15 of the 30 patients (50%) with mismatches developed chronic GVHD (P = 0.061). Nine of these patients developed both acute and chronic GVHD. Conclusions: Data suggests some correlation regarding mHAg mismatches and the development of GVHD. Further study and a larger cohort may allow a gauge for the efﬁcacy of testing for the mHAgs on a prospective basis. Testing on a prospective basis could give clinicians more knowledge to select donors with a favorable mHAg constellation to reduce the risk of their transplant patients developing GVHD.