HIV-1 NEF ligands predominate in the HLA class I of infected CD4+ T cells (APP2P.108)

Class I HLA reveal virus-derived ligands to cytotoxic T lymphocytes (CTL) whose function is to eliminate infected cells. The Los Alamos National Laboratory (LANL) database reports numerous HIV-1 CTL epitopes, none of which have elicited protective immunity in vaccine testing. The goal of this study was to determine the number and nature of HIV-1 ligands available for CTL targeting through presentation by the HLA class I of virus-infected cells. Class I presented peptides were recovered from immunoaffinity purified HLA-A*11:01 gathered from HIV-1 (NL4-3)-infected human CD4+ SUP-T1 T cells. These peptides were fractionated by RP-HPLC and mapped by tandem mass spectrometry (MS/MS). Seven HIV-derived peptides were confirmed by MS/MS as unique to infected cells. Twelve LANL HIV epitopes, including the well-studied Gag p24 epitope ACQGVGGPGHK (AK11), were clearly absent from the HLA-A*11:01 of infected cells. Of the 7 HIV-1 ligands found to be presented by A*11:01, 4 were derived from Nef, 2 from Gag, and 1 from Pol. When these 7 ligands were tested for T cell reactivity in a gamma interferon ELISPOT assay using PBMC from HIV-1 infected individuals (including elite controllers), the Nef-derived peptides were found to be highly reactive. These data demonstrate that the class I HLA of HIV-1 infected CD4+ T cells present a handful of viral peptide ligands for recognition by CTL and that reported HIV-1 CTL epitopes might not be presented by the HLA class I of infected cells.

Peptide presentation by different HLA-Class I molecules during viral infection (APP2P.106)

Class I Human Leukocyte Antigens reveal intracellular viruses to the immune system by presenting viral epitopes at the cell surface. In this study we hypothesized that during infection particular HLA class I alleles consistently present more virus-derived peptide ligands to virus-specific CD8+ T cells than do other HLA class I. To test this hypothesis, we infected cells with West Nile virus (WNV) and directly identified and enumerated the virus specific peptides presented by various HLA class I molecules. Cells expressing a number of different HLA-A and HLA-B class I were cultured in bioreactors and infected with WNV. HLA/peptide complexes were harvested from infected and uninfected cells, peptides were eluted from affinity-purified HLA, comparatively mapped by mass spectroscopy, and sequenced. Twenty-four peptides, 20 eluted from HLA-A complexes (HLA-A*02:01, A*01:01, A*11:01 and A*24:02) and 4 from HLA-B complexes (HLA-B*27:05, B*07:02 and B*35:01), were identified as unique to infected cells. Ligands represented different parts of the viral polyprotein demonstrating that peptides sampled by class I HLA are distributed widely throughout the WNV proteome. These data indicate that, in WNV-infected cells, HLA-A present more virus-specific peptides than do HLA-B suggesting a potentially different role for HLA class I loci in developing immune responses that control WNV infection whereby HLA-A is responsible for diverse reactivity and HLA-B leads to more focused immunity.

Profiling class II HLA alloantibodies in transplant patient sera (P2222)

Allogeneic immunizing events including pregnancy, blood transfusion, and transplantation promote strong antibody responses to HLA. Such anti-HLA antibodies preclude organ transplantation, foster hyperacute rejection, and contribute to chronic transplant failure. Diagnostic antibody-screening assays can detect alloreactive antibodies and determine their HLA specificity, yet a number of key antibody attributes remain unexplored. The goal here was to provide the first detailed profile of antibodies directed to allogeneic HLA. Methodologically, sixteen sensitized patients were identified with alloantibodies to HLA-DR11, antibodies reactive with this class II HLA antigen were purified using a novel immunoaffinity column constructed with milligram quantities of native DR11, and these purified DR11 specific antibodies were categorized. Results show that allogeneic antibodies to DR11 were found in the serum at a median concentration of 2.3ug/ml and consisted of the IgM, IgG, IgA, and IgE isotypes. IgG2, IgM, and IgE were elevated while IgG1 was decreased in sensitized patients and, in most patients, these antibodies fixed complement. In conclusion, we show that HLA alloantibody responses are consistently comprised of multiple isotypes, that these alloantibodies reach an appreciable serum concentration, and that these alloantibodies fix complement.

Determination of cellular lipids bound to human CD1d molecules

CD1 molecules are glycoproteins that present lipid antigens at the cell surface for immunological recognition by specialized populations of T lymphocytes. Prior experimental data suggest a wide variety of lipid species can bind to CD1 molecules, but little is known about the characteristics of cellular ligands that are selected for presentation. Here we have molecularly characterized lipids bound to the human CD1d isoform. Ligands were eluted from secreted CD1d molecules and separated by normal phase HPLC, then characterized by mass spectroscopy. A total of 177 lipid species were molecularly identified, comprising glycerophospholipids and sphingolipids. The glycerophospholipids included common diacylglycerol species, reduced forms known as plasmalogens, lyso-phospholipids (monoacyl species), and cardiolipins (tetraacyl species). The sphingolipids included sphingomyelins and glycosylated forms, such as the ganglioside GM3. These results demonstrate that human CD1d molecules bind a surprising diversity of lipid structures within the secretory pathway, including compounds that have been reported to play roles in cancer, autoimmune diseases, lipid signaling, and cell death.