Mapping the binding site on CD8 beta for MHC class I reveals mutants with enhanced binding.
In an effective immune response, CD8+ T cell recognition of virally derived Ag, bound to MHC class I, results in killing of infected cells. The CD8alphabeta heterodimer acts as a coreceptor with the TCR, to enhance sensitivity of the T cells to peptide/MHC class I, and is two orders of magnitude more efficient as a coreceptor than the CD8alphaalpha. To understand the important interaction between CD8alphabeta and MHC class I, we created a panel of CD8beta mutants and identified mutations in the CDR1, CDR2, and CDR3 loops that decreased binding to MHC class I tetramers as well as mutations that enhanced binding. We tested the coreceptor function of a subset of reducing and enhancing mutants using a T cell hybridoma and found similar reducing and enhancing effects. CD8beta-enhancing mutants could be useful for immunotherapy by transduction into T cells to enhance T cell responses against weak Ags such as those expressed by tumors. We also addressed the question of the orientation of CD8alphabeta with MHC class I using CD8alpha mutants expressed as a heterodimer with wild-type CD8alpha or CD8beta. The partial rescuing of binding with wild-type CD8beta compared with wild-type CD8alpha is consistent with models in which either the topology of CD8alphaalpha and CD8alphabeta binding to MHC class I is different or CD8alphabeta is capable of binding in both the T cell membrane proximal and distal positions.
Devine
Lesley
L
Department of Laboratory Medicine, Yale University, New Heaven, CT 06520, USA.
Thakral
Deepshi
D
Nag
Shanta
S
Dobbins
Jessica
J
Hodsdon
Michael E
ME
Kavathas
Paula B
PB
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D016827:CD8 Antigens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D002522:Chlorocebus aethiops; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis
D016827:CD8 Antigens; C477867:CD8beta antigen; D015395:Histocompatibility Antigens Class I