Proc. Natl. Acad. Sci. USA Vol. 96, pp. 9781–9786, August 1999 Immunology An inverse relationship between T cell receptor affinity and antigen dose during CD4؉ T cell responses in vivo and in vitro WILLIAM REES*, JEREMY BENDER†,T.KENT TEAGUE*, ROSS M. KEDL*, FRANCES CRAWFORD*, ࿣ PHILIPPA MARRACK*†‡§, AND JOHN KAPPLER*†‡¶ *Howard Hughes Medical Institute, Division of Basic Immunology, National Jewish Medical and Research Center, Denver, CO 80206; and Departments of †Immunology, ‡Medicine, §Biochemistry, Biophysics and Genetics, and ¶Pharmacology, University of Colorado Health Sciences Center, Denver, CO 80262 Contributed by John Kappler, June 15, 1999 ABSTRACT Multimeric peptide͞class II MHC staining MATERIALS AND METHODS reagents were synthesized and shown to bind with appropriate ͞ specificity to T cell hybridomas. A small, expanded population Mice and Immunizations. C57BL 10 SnJ mice were pur- of T cells detected with one of these reagents in peptide- chased from The Jackson Laboratory and housed in the immunized C57BL͞10 mice persisted for several months. This Animal Care Facility at the National Jewish Medical and population expanded further on secondary immunization. Research Center. Synthetic 3K peptide (3Kp; ASFEAQKAK- Equating the extent of binding of this reagent to T cell receptor ANKAVD, 15-mer), 2W peptide (2Wp; AWGALAN- WAVDS, 12-mer), and 4Sp (ASFEASGASANSAVDSA, 15- affinity, we saw little correlation of immunizing peptide dose mer) peptides were prepared, purified by reverse-phase chro- to T cell receptor affinity at the peak of the primary response. matography, and analyzed by MS by the Biological Resource However, there was an inverse relation between peptide dose Center at the National Jewish Center. Mice 8–14 weeks old and the apparent receptor affinity of the T cells that were were injected s.c. between the shoulder blades with 100 ␮lof present several months after a primary response or after a emulsified complete Freund’s adjuvant (CFA) containing 50 secondary stimulation either in vivo or in vitro. ␮gor0.5␮g synthetic peptide. For analysis of the secondary immune response, mice were injected s.c. with 50 ␮gor0.5␮g Tracking the cellular dynamics of antigen-specific T cell re- peptide in incomplete Freund’s adjuvant (IFA) at two sites sponses in vivo has been difficult, not only because the along the back 9 weeks after the primary immunization. responding precursors occur at low frequency, but also because Draining lymph nodes were harvested 8 days after the primary ͞ the peptide MHC ligand for the T cell receptor (TCR) is cell immunization and 5 days after the secondary immunization for bound and of low affinity. These latter problems have been further analyses. overcome by methods for producing soluble MHC molecules In Vitro T Cell Stimulation and Hybridoma Production. For bearing single peptides (1–4) and for producing fluorescent the analysis of multimer-specific staining of T cells expanded multimeric versions of these molecules (5–10). The coopera- in vitro,4ϫ 106 lymph node cells from immunized mice were tive binding achieved with these multivalent ligands produces incubated with various concentrations of 3Kp or a control an avidity high enough that antigen-specific T cells can be peptide that binds IAb avidly, 4Sp, in 1-ml cultures containing detected by flow cytometry. In examining the binding of these 1% mouse serum in Click’s medium for 4.5 days. Cells from types of reagents to T cells with receptors of known affinity for 1-ml cultures were stained as described below. monovalent peptide͞MHC, we observed a direct correlation For production of T cell hybridomas, lymph node cells between the extent of multimer binding and receptor affin- harvested 8 days after primary immunization with either 50 ␮g ity (10). or 0.5 ␮g peptide were stimulated in vitro for 5 days with 100 The phenomenon of affinity maturation is well established or 0.1 ␮g͞ml 3Kp, respectively. Surviving viable T cells were in B cell responses. With multiple immunizations of T cell- expanded an additional 3 days with IL-2 before fusion with the dependent antigens, B cells bearing Ig receptors of steadily BW5147 ␣–␤– thymoma as described (21). Hybridomas were increasing affinity grow to dominate the B cell pool (11, 12). screened for antigen specificity by testing for IL-2 produced in These cells appear to arise by selection of somatically mutated response to C57BL͞10 splenocytes with or without the immu- receptors as antigen becomes limiting (13–15). Recent studies nizing peptide at 25 ␮g͞ml as described (22). have demonstrated that T cells having higher average affinity Production of Soluble Peptide-IAb Molecules and Multi- for peptide͞MHC are selected after multiple exposures to meric Staining Reagents. Soluble IAb molecules were pro- antigen (16, 17). Whether this affinity maturation is primarily duced in High Five (Invitrogen) insect cells by using a deriv- the result of the experience of repeated exposure to antigen or ative of the dual-promoter vector pAcUW51 (PharMingen) a shaping of the T cell repertoire during antigen waning that has been described (3). For each construct, the ␤ chain (18–20) is unknown. carried a leader sequence followed by an antigenic peptide We examined these questions for CD4ϩ T cells responding sequence and a glycine-rich linker at its amino terminus end to a peptide presented by the mouse class II MHC molecule, (4). The carboxyl terminus of the ␤ chain carried a peptide tag IAb. We tracked the frequency and relative affinities of allowing for biotinylation at a unique position by the birA peptide͞MHC-binding T cells during both primary and sec- enzyme (10, 23). ondary immune responses. Our results show that with repeated Soluble peptide-IAb heterodimers were purified from cul- or prolonged exposure to antigen, limiting doses of antigen ture supernatants by affinity chromatography with the M5͞114 select for T cells with higher-affinity receptors. Abbreviations: TCR, T cell antigen receptor; CFA, complete Freund’s The publication costs of this article were defrayed in part by page charge adjuvant; IFA, incomplete Freund’s adjuvant; PESA, phycoerythrin- conjugated streptavidin; 3Kp, 3K peptide; 2Wp, 2W peptide. payment. This article must therefore be hereby marked ‘‘advertisement’’ in ࿣To whom reprint requests should be addressed at: National Jewish accordance with 18 U.S.C. §1734 solely to indicate this fact. Medical and Research Center, 1400 Jackson Street, K519, Denver, PNAS is available online at www.pnas.org. CO 80206. E-mail: [email protected]. 9781 Downloaded by guest on September 28, 2021 9782 Immunology: Rees et al. Proc. Natl. Acad. Sci. USA 96 (1999) mAb (24). The yield of MHC class II heterodimer in the 0.01- to 1-␮g͞ml range was determined by sandwich ELISA, cap- turing with plate-bound M5͞114 mAb and detecting with biotinylated 17͞227 mAb (25). Biotinylation efficiency was determined by ELISA relative to samples cleared of biotin- ylated protein by using avidin-agarose beads (Vector Labora- tories). Biotinylated, peptide-IAb heterodimers were purified by size-exclusion chromatography on Superdex-200, and fluores- cent multimeric complexes were prepared from peptide-IAb- bio molecules and phycoerythrin-conjugated streptavidin (PESA) as described (10). Flow Cytometric Analysis. Flow cytometry was performed on a FACSCaliber instrument, and analysis used CELL QUEST Software (Becton Dickinson) and MKFLOW histogram analysis software (available on request). Hybridomas were stained and analyzed for TCR and CD4 content by using biotinylated H597 (26) and the APC-conjugated anti-CD4 antibody RM4–5 (PharMingen). Lymph node cells, either freshly isolated or cultured, were washed and incubated with peptide-IAb multimers for 2 hr at 37°C in tissue culture medium containing 10% FCS. Typically, 5–8 ϫ 106 cells were incubated with 40 ␮g͞ml staining reagent ␮ in a final volume of 300 l. The cells were incubated an b additional 45 min with antibodies against CD4 (allophycocya- FIG. 1. Specific binding of peptide-IA staining reagents to T cell hybridomas. (A) Sequences of the antigenic peptide portion of the nin-conjugated RM4–5), B220 (cy-chrome-conjugated RA3– staining reagents 3K-IAb͞PESA, E␣-IAb͞PESA, and 2W-IAb͞PESA. 6B2), and CD44 (fluorescein-conjugated IM7) (PharMingen). (B) T cell hybridomas (3 ϫ 105) specific for 3Kp͞IAb (B3K05.06, Left) 6 Approximately 10 events were analyzed by flow cytometry. and 2Wp͞IAb (B2W01.01, Right) were incubated separately with the three peptide-IAb͞PESA-staining reagents or MCC-IEk͞PESA at 40 ␮g͞ml in 100 ␮l of complete tissue culture medium for 2 hr at 37°C. RESULTS Washed cells were analyzed by flow cytometry for phycoerythrin Multivalent cell-staining complexes of soluble IAb molecules fluorescence, and histograms are shown. In Left and Right the histo- with covalently associated antigenic peptides were prepared as gram of the stain performed with the cognate-staining reagent is the described in Materials and Methods, using procedures that have dotted line and all other histograms are solid lines. been used previously to prepare staining reagents from soluble These T cells are better visualized in Fig. 2b, which shows IAd and IEk molecules (10). Soluble IAb molecules harboring histograms of the binding of the peptide-IAb͞PESA reagents the 3K, 2W, or mouse E␣(52–68) (E␣) peptide sequences (Fig. ϩ to CD4 CD44high T cells. When compared with the T cells 1A) were singly biotinylated in vitro through a sequence tag on ␤ from mice immunized with CFA alone, there was a small, but the C terminus of the chain and assembled into soluble ϩ high multimers with PESA. The three IAb staining reagents, 3K- well-defined, expanded population of CD4 CD44 T cells b͞ IAb͞PESA, 2W-IAb͞PESA, and E␣-IAb͞PESA along with a from the 3Kp-immunized mice that bound the 3K-IA PESA, ␣ b͞ ␮ reagent constructed with a different isotype of MHC class II, but not E -IA PESA, reagent. In mice immunized with 50 g ϩ high MCC-IEk͞PESA (10), were used to stain the T cell hybridomas antigen, these cells represented 1.3% of the CD4 CD44 T B3K05.06 and B2W01.01, which are specific for 3Kp and 2Wp cells.