Biomedical subjects

Els Blokland

Publications and source records attributed to Els Blokland.

5 recordsLinked to original sources

PubMed2004

Artificial antigen-presenting constructs efficiently stimulate minor histocompatibility antigen-specific cytotoxic T lymphocytes.

Cytotoxic T lymphocytes (CTLs) specific for hematopoietic-restricted minor histocompatibility antigens (mHags) are important reagents for adoptive immunotherapy of relapsed leukemia after allogeneic stem cell transplantation. However, expansion of these CTLs to therapeutic numbers is often hampered by the limited supply of antigen-presenting cells (APCs). Therefore, we evaluated whether cell-sized latex beads coated with HLA/mHag complexes HLA-A2/HA-1 or HLA-A2/HA-2 and recombinant CD80 and CD54 molecules can replace professional APCs. The artificial antigen-presenting constructs (aAPCs) effectively stimulated HA-1- and HA-2-specific CTL clones as shown by ligand-specific expansion, cytokine production, and maintenance of cytotoxic activity, without alteration of CTL phenotype. Furthermore, HA-1-specific polyclonal CTL lines were enriched as efficiently by aAPCs as by autologous HA-1 peptide-pulsed dendritic cells. Thus, aAPCs coated with HLA/mHag complexes, CD80, and CD54 may serve as tools for in vitro enrichment of immunotherapeutic mHag-specific CTL lines.

Antigen Presentation↗

PubMed2003

The minor histocompatibility antigen HA-3 arises from differential proteasome-mediated cleavage of the lymphoid blast crisis (Lbc) oncoprotein.

Minor histocompatibility (H) antigens crucially affect the outcome of human leukocyte antigen (HLA)-identical allogeneic stem cell transplantation (SCT). To understand the basis of alloimmune responses against minor H antigens, identification of minor H peptides and their antigenicity-determining mechanisms is essential. Here we report the identification of HA-3 and its encoding gene. The HA-3 peptide, VTEPGTAQY (HA-3T), is encoded by the lymphoid blast crisis (Lbc) oncogene. We thus show for the first time that a leukemia-associated oncogene can give rise to immunogenic T-cell epitopes that may have participated in antihost and antileukemic alloimmune responses. Genotypic analysis of HA-3- individuals revealed the allelic counterpart VMEPGTAQY (HA-3M). Despite the lack of T-cell recognition of HA-3- cells, the Thr-->Met substitution had only a modest effect on peptide binding to HLA-A1 and a minimal impact on recognition by T cells when added exogenously to target cells. This substitution did not influence transporter associated with antigen processing (TAP) transport, but, in contrast to the HA-3T peptide, HA-3M is destroyed by proteasome-mediated digestion. Thus, the immunogenicity of minor H antigens can result from proteasome-mediated destruction of the negative allelic peptide.

A Kinase Anchor Proteins↗

PubMed2002

The hematopoietic system-specific minor histocompatibility antigen HA-1 shows aberrant expression in epithelial cancer cells.

Allogeneic stem cell transplantation (SCT) can induce curative graft-versus-tumor reactions in patients with hematological malignancies and solid tumors. The graft-versus-tumor reaction after human histocompatibility leukocyte antigen (HLA)-identical SCT is mediated by alloimmune donor T cells specific for polymorphic minor histocompatibility antigens (mHags). Among these, the mHag HA-1 was found to be restricted to the hematopoietic system. Here, we report on the HA-1 ribonucleic acid expression by microdissected carcinoma tissues and by single disseminated tumor cells isolated from patients with various epithelial tumors. The HA-1 peptide is molecularly defined, as it forms an immunogenic peptide ligand with HLA-A2 on the cell membrane of carcinoma cell lines. HA-1-specific cytotoxic T cells lyse epithelial tumor cell lines in vitro, whereas normal epithelial cells are not recognized. Thus, HA-1-specific immunotherapy combined with HLA-identical allogeneic SCT may now be feasible for patients with HA-1(+) carcinomas.

Hematopoietic Stem Cell Transplantation↗

PubMed2002

Generation of minor histocompatibility antigen HA-1-specific cytotoxic T cells restricted by nonself HLA molecules: a potential strategy to treat relapsed leukemia after HLA-mismatched stem cell transplantation.

Successful stem cell transplantation (SCT) across HLA barriers can be performed with cord blood, megadoses of stem cells, or with nonmyeloablative conditioning strategies. Because the HLA-mismatched transplants are often T-cell depleted, leukemia relapse rates are high. Treatment of relapsed leukemia after HLA-mismatched SCT is difficult. A novel potential strategy to treat relapsed leukemia after HLA-mismatched SCT is the use of patients' mismatched HLA molecules as antigen-presenting molecules to generate hematopoietic system-specific cytotoxic T cells (CTLs) from the stem cell donor. Adoptive transfer of these hematopoietic system-specific CTLs that are restricted by nonself HLA molecules may eliminate leukemia without affecting the patient's nonhematopoietic cells or donor hematopoietic cells. We investigated the feasibility of this strategy using the hematopoietic system-specific minor histocompatibility antigen HA-1, which is known to induce HLA-A2-restricted CTLs. HLA-A2(-) peripheral blood mononuclear cells were stimulated with HLA-A2(+) T2 cells pulsed with synthetic HA-1 peptide or with dendritic cells transduced with the HA-1 cDNA. Tetrameric HLA-A2/HA-1 peptide complexes were used to monitor and enrich HA-1-specific CTLs. In the alloreactive cultures, HA-1-specific CTLs were enriched up to 7% by 3 rounds of antigen-specific stimulations and up to 87% by fluorescence-activated cell sorting of tetramer-positive T cells. The HA-1-specific CTLs showed specific lysis of the relevant target cells, including leukemic cells. Because the polyclonal CTL cultures also contained natural killer cells and allo-HLA-A2-specific CTLs, CTL clones were generated that showed the expected HA-1 specificity only. Thus, HA-1-specific CTLs restricted by nonself HLA-A2 molecules can be generated in an HLA-A2-mismatched setting.

Cell Culture Techniques↗

PubMed2002

General T-cell receptor antagonists to immunomodulate HLA-A2-restricted minor histocompatibility antigen HA-1-specific T-cell responses.

T-cell receptors (TCRs) of a series of minor histocompatibility antigen (mHag) HA-1-specific cytotoxic T-cell (CTL) clones isolated from 3 unrelated patients have been shown to use the same BV6S4A2 segment with conserved amino acids in the CDR3Vbeta region. This suggests that different HA-1-specific TCRs interact similarly to the HA-1 antigen presented by the HLA-A2 molecule. The mHag HA-1 forms an immunogenic complex with HLA-A2 and induces strong alloimmune responses after stem cell transplantation (SCT). It was questioned, therefore, whether clonal and polyclonal HA-1-specific CTL responses can be antagonized by a single TCR antagonistic peptide. Functional analysis and molecular modeling of single and double amino acid substitutions of TCR contact residues, adjacent residues, and HLA-A2 binding residues resulted in 4 peptides with high affinity for HLA-A2 and with the capacity to inhibit the lysis of endogenously HA-1-expressing EBV-BLCL by 3 different HA-1-specific CTL clones. These peptides also efficiently antagonized HA-1-specific polyclonal CTL lines derived from 3 patients and significantly reduced the number of interferon-gamma-producing HA-1-specific CTL of a patient with graft-versus-host disease after HA-1-mismatched SCT. These data show that general TCR antagonists can be developed that inhibit HLA-A2-restricted HA-1-specific CTL responses on the clonal and the polyclonal level and that TCR antagonists may modulate the immunodominant mHag HA-1 responses.

Adjuvants, Immunologic↗