High-throughput identification of T-lymphocyte antigens from Anaplasma marginale expressed using in vitro transcription and translation

The ability to rapidly screen a complex pathogen proteome for proteins that elicit recall T-lymphocyte responses from immune individuals would accelerate vaccine development. An outer membrane fraction of the rickettsia] pathogen Anaplasma marginale induces protective immunity against infection and disease in cattle. We have used this immunization model to evaluate high-throughput screening of proteins expressed by in vitro transcription and translation (IVTT) for recognition by memory CD4(+) T-lymphocytes. Fifty selected vaccine candidate antigens identified from the A. marginale genome were expressed from transcriptionally active PCR products using an Escherichia coli-based IVTT system, and bead-affinity purified using antibodies to His and FLAG epitope tags. IVTT-expressed bead-bound antigens were processed and presented by antigen presenting cells to T-lymphocytes from outer membrane immunized animals and evaluated for immunogenicity in proliferation assays. Antigens that consistently stimulated responses were known T-cell antigens major surface protein (MSP)2, MSP3, VirB9, and VirB10 and newly identified T-cell antigens outer membrane protein (OMP)4, OMP9, elongation factor-Tu, Ana29, and OMA87. Specific T-cell stimulation was achieved even at low antigen concentration, and was highly sensitive when compared with unbound IVTT reaction products. This method allows rapid expression and identification of T-lymphocyte antigens for any pathogen for which the genome sequence is available. (C) 2008 Elsevier B.V. All rights reserved.