Detection of a novel specificity (CTLA-4) in ATG/TMG globulins and sera from ATG-treated leukemic patients.
BACKGROUND
T-cell costimulation has been shown to provide positive signals for T-cell activation and generation of effector activity. In this study, we analyzed the presence of antibodies (Abs) against the T-lymphocyte costimulatory molecules CD28, CTLA-4, CD80, and CD86 in anti-T-lymphocyte (ATG) and antithymocyte (TMG) globulin preparations to address their mechanism of action. We focused our attention on the role of CTLA-4-specific Abs in the immunosuppressive effect of ATG/TMG, because anti-CTLA-4 agonistic Abs may suppress T-cell proliferation and nonagonistic Abs may lead to T-cell depletion through an Ab-dependent cell cytotoxicity mechanism.


METHODS
ATG/TMG and patients' sera were tested for binding to recombinant human costimulatory molecules by ELISA techniques. CTLA-4 specificity was also analyzed by cytoplasmic immunofluorescence staining of a CTLA-4 transfectant by competitive inhibition immunofluorescence and by cell proliferation assay in allogeneic mixed lymphocyte reaction (MLR).


RESULTS
Either ATG or TMG predominantly contained anti-CTLA-4 Abs, with higher reactivity in ATG followed by anti-CD86 and -CD28 Abs, whereas anti-CD80 Abs were found only in ATG. Anti-CTLA-4 Abs present in ATG/TMG recognized the native form of CTLA-4 molecule, and their removal reduced the effect of ATG in an allogeneic MLR. Kinetic studies indicated that such Abs were present in the sera of 12 ATG-treated leukemic patients up to 21 days after ATG administration.


CONCLUSIONS
These data suggest that the novel anti-CTLA-4 Abs found in ATG may greatly contribute to its immunosuppressive effect, thus accounting for the absence of rejection and exceptionally low incidence of graft-versus-host disease in the group of patients analyzed.
Pistillo
Maria Pia
MP
Immunogenetics Laboratory, National Cancer Research Institute, Advanced Biotechnology Center, Genova, Italy. pistillo@vega.cba.unige.it
Tazzari
Pier Luigi
PL
Bonifazi
Francesca
F
Bandini
Giuseppe
G
Kato
Tomohiro
T
Matsui
Toshihiro
T
Nishioka
Kusuki
K
Conte
Roberto
R
Ferrara
Giovanni Battista
GB
D000069594:Abatacept; D000818:Animals; D000918:Antibody Specificity; D015703:Antigens, CD / Q000276:immunology; D000943:Antigens, Differentiation / Q000276:immunology*; D000961:Antilymphocyte Serum / Q000627:therapeutic use; D018122:B7-1 Antigen / Q000276:immunology; D051940:B7-2 Antigen; D018106:CD28 Antigens / Q000276:immunology*; D060908:CTLA-4 Antigen; D019337:Hematologic Neoplasms / Q000097:blood / Q000276:immunology / Q000628:therapy; D018380:Hematopoietic Stem Cell Transplantation; D006801:Humans; D018796:Immunoconjugates; D007141:Immunoglobulin Fc Fragments / Q000276:immunology; D007166:Immunosuppressive Agents / Q000276:immunology / Q000627:therapeutic use; D008562:Membrane Glycoproteins / Q000276:immunology; D051379:Mice; D009101:Multiple Myeloma / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000276:immunology; D011994:Recombinant Proteins / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology*; D014407:Tumor Cells, Cultured
D015703:Antigens, CD; D000943:Antigens, Differentiation; D000961:Antilymphocyte Serum; D018122:B7-1 Antigen; D051940:B7-2 Antigen; D018106:CD28 Antigens; C497964:CD86 protein, human; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C497965:Cd86 protein, mouse; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D007141:Immunoglobulin Fc Fragments; D007166:Immunosuppressive Agents; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D000069594:Abatacept