Synthetic peptides and beta-chain gene rearrangements reveal a diversified T cell repertoire for a lambda light chain third hypervariable region

CD4+ T cells indirectly kill tumor cells via induction of cytotoxic macrophages in mouse models

It is well recognized that CD4⁺ T cells may play an important role in immunosurveillance and immunotherapy against cancer. However, the details of how these cells recognize and eliminate the tumor cells remain incompletely understood. For the past 25 years, we have focused on how CD4⁺ T cells reject multiple myeloma cells in a murine model (MOPC315). In our experimental system, the secreted tumor-specific antigen is taken up by tumor-infiltrating macrophages that process it and present a neoepitope [a V region-derived idiotypic (Id) peptide] on MHC class II molecules to Th1 cells. Stimulated Th1 cells produce IFNγ, which activates macrophages in a manner that elicits an M1-like, tumoricidal phenotype. Through an inducible nitric oxide synthetase (iNOS)-dependent mechanism, the M1 macrophages secrete nitric oxide (NO) that diffuses into neighboring tumor cells. Inside the tumor cells, NO-derived reactive nitrogen species, including peroxynitrite, causes nitrosylation of proteins and triggers apoptosis by the intrinsic apoptotic pathway. This mode of indirect tumor recognition by CD4⁺ T cells operates independently of MHC class II expression on cancer cells. However, secretion of the tumor-specific antigen, and uptake and MHCII presentation on macrophages, is required for rejection. Similar mechanisms can also be observed in a B-lymphoma model and in the unrelated B16 melanoma model. Our findings reveal a novel mechanism by which CD4⁺ T cells kill tumor cells indirectly via induction of intratumoral cytotoxic macrophages. The data suggest that induction of M1 polarization of tumor-infiltrating macrophages, by CD4⁺ T cells or through other means, could serve as an immunotherapeutic strategy.

A Nonadjuvanted IgG2a Monoclonal Antibody against Nucleosomes Elicits Potent T Cell-Dependent, Idiotype-Specific IgG1 Responses and Glomerular IgG1/IgG2a Deposits in Normal Mice

Idiotypes (Ids) are unique epitopes of Ab V regions and can trigger anti-Id immune responses, but immunization with several nonadjuvanted isologous IgG mAbs has induced tolerance to their Ids. We immunized non-lupus-prone mice with 11 allotype "a" of IgG2a (IgG2a^a) and 4 IgG2c nonadjuvanted, isologous mAbs purified from serum-free medium. Of five IgG2a^a mAbs with specificity for nucleosomes, the repeating histone-DNA subunit of chromatin, four elicited an IgG1 anti-mAb response and one mAb was nonimmunogenic. In contrast, none of six IgG2a^a mAbs with unknown specificity triggered anti-mAb responses. The data suggested a link between immunogenicity and specificity for nucleosomes. One anti-nucleosome IgG2a^a mAb, termed 3F7.A10, copurified with self-histones and was a potent immunogen for BALB/c mice. The response against IgG2a^a 3F7.A10 was CD4⁺ Th cell-dependent, dominated by the IgG1 subclass, and Id specific. Ultracentrifugation converted the purified 3F7.A10 mAb into a weak immunogen, suggesting that the mAb had formed immunogenicity-enhancing immune complexes (ICs) with nucleosomal Ags during cell culture. BALB/c mice injected with viable MHC-incompatible 3F7.A10 hybridoma cells grown in serum-free medium mounted strong anti-Id responses. TLR9-deficient mice responded significantly weaker to Id-3F7.A10 than did TLR9-sufficient mice, suggesting that the cognate BCR efficiently internalizes the Id in an IC with nucleosomes. Passive transfer of IgG2a^a 3F7.A10 to BALB/c mice with high titers of IgG1 anti-3F7.A10 led to glomerular deposits of IgG1/IgG2a complexes. The immunogenicity of Id-3F7.A10 raises the possibility that diverse Ids of nucleosome-specific Abs form ICs with nucleosomes released from dying cells and elicit spontaneous formation of anti-Id Abs in vivo.

Naive idiotope-specific B and T cells collaborate efficiently in the absence of dendritic cells

Anti-idiotope (anti-Id) Abs have a role in therapy against B cell lymphomas, as inhibitors of pathogenic autoantibodies, and as surrogate Ags for immunization. Despite these observations, the mechanism by which Id(+) Ig generates anti-Id Abs is essentially unknown. To address this issue, we generated a double knock-in mouse that expresses V regions of a somatically mutated anti-Id mAb with intermediate affinity (affinity constant [Ka] = 0.77 × 10(7) M(-1)) for the myeloma protein M315. The anti-Id mice have normal peripheral B cell populations, and allelic exclusion is efficient. Anti-Id B cells from BCR knock-in mice, together with Id-specific CD4(+) T cells from previously established TCR-transgenic mice, enabled us to study Id-specific T cell-B cell collaboration by dilution of transferred cells into syngeneic BALB/c recipients. We show that previously unstimulated (naive) Id-specific B and T cells collaborate efficiently in vivo, even at low frequencies and in the presence of low amounts of Id(+) Ig, resulting in germinal center formation, plasma cell development, and secretion of isotype-switched anti-Id Abs. We further demonstrate that Id-specific T cell-B cell collaboration occurs readily in the absence of adjuvant and is not dependent on Id-presentation by dendritic cells. The results underscore the potency of anti-Id B cells in MHC class II-restricted presentation of Id(+) Ig and suggest that Id-specific T cell-B cell collaboration is of physiological relevance.

Recognition of the Self Idiotype by T Cells: Induction of a Rapid Increase in Cytoplasmic Free Calcium in T Cells Recognizing a Variable L Chain Determinant

To investigate the initial stages of recognition of the self idiotype (Id) by T cells, we examined the early increase in cytoplasmic free calcium ([Ca2+]i) occurring in murine CD4+ T cells specific for a model Id, Id315, following their interaction with the Id. The changes in [Ca2+]i were monitored with stopped-flow fluorometry by loading T cells with fura 2, a Ca(2+)-binding fluorescent dye. An increase of [Ca2+]i in the Id-specific T cell line was dependent on the presence of both antigen-presenting cells (APC) and Id315. When T cells were mixed with APC pulsed with M315 for 90 min at 37 C, a significant increase in T cell [Ca2+]i was observed within one second. A pronounced elevation in [Ca2+]i was also observed in T cells after their interaction with APC which had been pulsed for 90 min with VL-315 Id-containing proteins (such as VL-315, L315, Fv-315 or Fab'-315 fragments). In contrast, pulsing APC for 5 min with the VL fragment produced little or no change in the [Ca2+]i. These results suggest that VL must be further processed by APC before it can be recognized by T cells. Indeed, a synthetic VL region peptide (positions 91-108, designated as P18) produced an elevation in T cell [Ca2+]i when mixed with APC without pulsing.

A public T cell receptor recognized by a monoclonal antibody specific for the D-J junction of the β-chain

It is becoming increasingly clear that T cell responses against many antigens are dominated by public α/β T cell receptors (TCRs) with restricted heterogeneity. Because expression of public TCRs may be related to resistance, or predisposition to diseases, it is relevant to measure their frequencies. Although staining with tetrameric peptide/major histocompatibility complex (pMHC) molecules gives information about specificity, it does not give information about the TCR composition of the individual T cells that stain. Moreover, next-generation sequencing of TCR does not yield information on pairing of α- and β-chains in single T cells. In an effort to overcome these limitations, we have here investigated the possibility of raising a monoclonal antibody (moAb) that recognizes a public TCR. As a model system, we have used T cells responding to the 91-101 CDR3 peptide of an Ig L-chain (λ2³¹⁵), presented by the MHC class II molecule I-E(d). The CD4⁺ T cell responses against this pMHC are dominated by a receptor composed of Vα3Jα1;Vβ6DβJβ1.1. Even the V(D)J junctions are to a large extent shared between T cell clones derived from different BALB/c mice. We here describe a murine moAb (AB10) of B10.D2 origin that recognizes this public TCR, while binding to peripheral T cells is negligible. Binding of the moAb is abrogated by introduction of two Gly residues in the D-J junction of the CDR3 of the β-chain. A model for the public TCR determinant is presented.

Targeted DNA vaccines for enhanced induction of idiotype-specific B and T cells

Background: Idiotypes (Id) are antigenic determinants localized in variable (V) regions of Ig. Id-specific T and B cells (antibodies) play a role in immunotherapy of Id⁺ tumors. However, vaccine strategies that enhance Id-specific responses are needed. Methods: Id⁺ single-chain fragment variable (scFv) from multiple myelomas and B cell lymphomas were prepared in a fusion format that bivalently target surface molecules on antigen-presenting cells (APC). APC-specific targeting units were either scFv from APC-specific mAb (anti-MHC II, anti-CD40) or chemokines (MIP-1α, RANTES). Homodimeric Id-vaccines were injected intramuscularly or intradermally as plasmids in mice, combined with electroporation. Results: (i) Transfected cells secreted plasmid-encoded Id⁺ fusion proteins to extracellular fluid followed by binding of vaccine molecules to APC. (ii) Targeted vaccine molecules increased Id-specific B and T cell responses. (iii) Bivalency and xenogeneic sequences both contributed to enhanced responses. (iv) Targeted Id DNA vaccines induced tumor resistance against challenges with Id⁺ tumors. (v) Human MIP-1α targeting units enhanced Id-specific responses in mice, due to a cross reaction with murine chemokine receptors. Thus, targeted vaccines designed for humans can be quality tested in mice. (vi) Human Id⁺ scFv from four multiple myeloma patients were inserted into the vaccine format and were successfully tested in mice. (vii) Human MIP-1α vaccine proteins enhanced human T cell responses in vitro. (viii) A hypothetical model for how the APC-targeted vaccine molecules enhance Id-specific T and B cells is presented. Conclusion: Targeted DNA Id-vaccines show promising results in preclinical studies, paving the way for testing in patients.

Heterodimeric barnase-barstar vaccine molecules: influence of one versus two targeting units specific for antigen presenting cells

It is known that targeting of antigen to antigen presenting cells (APC) increases immune responses. However, it is unclear if more than one APC-specific targeting unit in the antigenic molecule will increase responses. To address this issue, we have here made heterodimeric vaccine molecules that each express four different fusion subunits. The bacterial ribonuclease barnase and its inhibitor barstar interact with high affinity, and the barnase-barstar complex was therefore used as a dimerization unit. Barnase and barstar were fused N-terminally with single chain fragment variable (scFv)s targeting units specific for either MHC class II molecules on APC or the hapten 5-iodo-4-hydroxy-3-nitrophenylacetyl (NIP). C-terminal antigenic fusions were either the fluorescent protein mCherry or scFv³¹⁵ derived from myeloma protein M315. The heterodimeric vaccine molecules were formed both in vitro and in vivo. Moreover, the four different fused moieties appeared to fold correctly since they retained their specificity and function. DNA vaccination with MHC class II-targeted vaccine induced higher mCherry-specific IgG1 responses compared to non-targeted control. Since mCherry and MHC class II are in trans in this heterodimer, this suggests that heterodimeric proteins are formed in vivo without prior protein purification. Surprisingly, one targeting moiety was sufficient for the increased IgG1 response, and addition of a second targeting moiety did not increase responses. Similar results were found in in vitro T cell assays; vaccine molecules with one targeting unit were as potent as those with two. In combination with the easy cloning strategy, the heterodimeric barnase-barstar vaccine molecule could provide a flexible platform for development of novel DNA vaccines with increased potency.

DeltaPhage--a novel helper phage for high-valence pIX phagemid display

Phage display has been instrumental in discovery of novel binding peptides and folded domains for the past two decades. We recently reported a novel pIX phagemid display system that is characterized by a strong preference for phagemid packaging combined with low display levels, two key features that support highly efficient affinity selection. However, high diversity in selected repertoires are intimately coupled to high display levels during initial selection rounds. To incorporate this additional feature into the pIX display system, we have developed a novel helper phage termed DeltaPhage that allows for high-valence display on pIX. This was obtained by inserting two amber mutations close to the pIX start codon, but after the pVII translational stop, conditionally inactivating the helper phage encoded pIX. Until now, the general notion has been that display on pIX is dependent on wild-type complementation, making high-valence display unachievable. However, we found that DeltaPhage does facilitate high-valence pIX display when used with a non-suppressor host. Here, we report a side-by-side comparison with pIII display, and we find that this novel helper phage complements existing pIX phagemid display systems to allow both low and high-valence display, making pIX display a complete and efficient alternative to existing pIII phagemid display systems.

Periplasmic expression of soluble single chain T cell receptors is rescued by the chaperone FkpA

Background

Efficient expression systems exist for antibody (Ab) molecules, which allow for characterization of large numbers of individual Ab variants. In contrast, such expression systems have been lacking for soluble T cell receptors (TCRs). Attempts to generate bacterial systems have generally resulted in low yields and material which is prone to aggregation and proteolysis. Here we present an optimized periplasmic bacterial expression system for soluble single chain (sc) TCRs.

Results

The effect of 1) over-expression of the periplasmic chaperon FkpA, 2) culture conditions and 3) molecular design was investigated. Elevated levels of FkpA allowed periplasmic soluble scTCR expression, presumably by preventing premature aggregation and inclusion body formation. Periplasmic expression enables disulphide bond formation, which is a prerequisite for the scTCR to reach its correct fold. It also enables quick and easy recovery of correctly folded protein without the need for time-consuming downstream processing. Expression without IPTG induction further improved the periplasmic expression yield, while addition of sucrose to the growth medium showed little effect. Shaker flask yield of mg levels of active purified material was obtained. The Vαβ domain orientation was far superior to the Vβα domain orientation regarding monomeric yield of functionally folded molecules.

Conclusion

The general expression regime presented here allows for rapid production of soluble scTCRs and is applicable for 1) high yield recovery sufficient for biophysical characterization and 2) high throughput screening of such molecules following molecular engineering.

The cellular mechanism by which complementary Id+ and anti-Id antibodies communicate: T cells integrated into idiotypic regulation

The V region antigenic determinants (idiotopes (Ids)) of antibodies (Abs) have been suggested to be involved in regulating the immune system. Certain diseases such as diabetes mellitus have recently been associated with a disequilibrium between Id(+) and anti-Id Abs. However, it is unknown how Abs carrying complementary idiotypes (that is, Id(+) and anti-Id Abs) regulate each other at the level of B and T cells. In this study, we show that B lymphoma cells genetically equipped with anti-Id BCR V regions receive a signal when exposed to Id(+)Ig. Moreover, they become x 10(4) more efficient at presenting exogenous Id(+) Ab to CD4(+) T cells in vitro. Activated Id-specific T cells in turn regulated the Id-specific B lymphoma cells. Similar results were obtained in vivo in a surrogate model in which an Id-peptide was incorporated genetically into the C-region of a recombinant Ab that targeted IgD on B cells. The findings suggest that conventional T-B collaboration can explain communication between complementary Id(+) and anti-Id Ab at the cellular level. A model is suggested that integrates present and previous data on B-cell regulation by Id-specific T cells.

Review: to what extent are T cells tolerant to immunoglobulin variable regions?

During the last 25 years it has become increasingly clear that short peptides derived from Ig V-regions are displayed on MHC class II molecules. Recognition of such idiotypic(Id)-peptide/MHC class II complexes by Id-specific CD4(+) T cells plays a role in (1) Id-driven T-B collaboration, (2) immunosurveillance of B cell cancers and (3) Id-vaccination. A crucial question is then: to what extent are T cells tolerized to Ig V-region sequences? Or rephrased: how large is the T-cell repertoire for Ig V-region sequences presented by MHC class II molecules? We argue that T cells are to a large extent tolerant to germline-encoded V-region sequences but that there is a T-cell repertoire for rare Id-sequences that arise as a consequence of somatic hyper mutation or N-region diversity. Moreover, when otherwise rare Id-sequences increase in concentration, T-cell tolerance is induced (Fig. 1). For these reasons, T cells that recognize rare Id-peptides, arising as a consequence of somatic genetic events unique to each B cell, may play a special importance in Id-driven T-B collaboration, immunosurveillance of B-cell malignancies, and Id-vaccination.

The idiotype connection: linking infection and multiple sclerosis

B cells present idiotopes (Id) from their B cell receptor to Id-specific CD4(+) T cells. Chronic Id-driven T-B cell collaboration can cause autoimmune disease in mice. We propose that Id-driven T-B cell collaboration mediates the development of multiple sclerosis by perpetuating immune responses initiated against infectious agents. During germinal centre reactions, B cells express a multitude of mutated Ids. While most mutations lead to decreased affinity and deletion of the B cell, some B cells could be rescued by Id-specific T cells. Such Id-connected T-B cell pairs might initiate inflammatory foci in the central nervous system. This model may explain the intrathecal synthesis of low-avidity IgG against viruses, and the synthesis of oligoclonal IgG with unknown specificity in multiple sclerosis.

DNA vaccines increase immunogenicity of idiotypic tumor antigen by targeting novel fusion proteins to antigen-presenting cells

Naked DNA vaccines have a number of advantages over conventional vaccines, but induce only weak immune responses. We have here investigated if this inadequacy may be overcome by inducing muscle to secrete fusion proteins with the ability to target antigen-presenting cells (APC). The novel targeted vaccines are homodimers with (i) two identical single-chain fragment variable (scFv) targeting units specific for MHC class II molecules on mouse APC, (ii) a human Ig hinge and C(H)3 dimerization unit, and (iii) two identical scFv tumor antigenic units (idiotypes) from B cell cancers. After plasmid injection and electroporation of mouse muscle, secreted vaccine proteins (vaccibodies) delivered idiotypic tumor antigen to APC in draining lymph nodes for induction of T and B cell responses that protected mice against tumor challenges with a multiple myeloma (MOPC315) and a B cell lymphoma (A20). Targeting to APC was essential for these effects. The results show that immunogenicity of plasmid DNA vaccines can be increased by inducing muscle to secrete proteins that target antigen to APC.

Systemic autoimmune disease caused by autoreactive B cells that receive chronic help from Ig V region-specific T cells

B cells present BCR V region-derived Id-peptides on their MHC class II molecules to Id-specific CD4+ T cells. Prolonged Id-driven T-B collaboration could cause autoimmune disease, but this possibility is difficult to test in normal individuals. We have investigated whether mice doubly transgenic for an Id+ Ig L chain and an Id-specific TCR develop autoimmune disease. Surprisingly, T cell tolerance was not complete in these mice because a low frequency of weakly Id-reactive CD4+ T cells accumulated with age. These escapee Id-specific T cells provided chronic help for Id+ B cells, resulting in a lethal systemic autoimmune disease including germinal center reactions, hypergammaglobulinemia, IgG autoantibodies, glomerulonephritis, arthritis, skin affection, and inflammatory bowel disease. Inflamed tissues contained foci of Id-driven T-B collaboration, with deposition of IgG and complement. The disease could be transferred with B and T cells. The results demonstrate a novel mechanism for development of autoimmune disease in which self-reactive Id+ B cells receive prolonged help from Id-specific T cells, thus bypassing the need for help from T cells recognizing conventional Ag.

Cerebrospinal fluid T cell clones from patients with multiple sclerosis: recognition of idiotopes on monoclonal IgG secreted by autologous cerebrospinal fluid B cells

Due to somatic recombination and hypermutation, Ig variable heavy (V(H)) and light (V(L)) regions contain unique immunogenic determinants, idiotopes (Id), which can stimulate T cells. To address the relevance of this in a human disease, monoclonal IgG (mAb)-secreting B cell clones were established from the cerebrospinal fluid (CSF) of two patients with multiple sclerosis (MS). HLA-DR-restricted CD4(+) T cell lines and clones from CSF of both patients specifically recognized autologous CSF mAb. The CSF T cell clones produced IFN-gamma; some also produced TNF-alpha, IL-10 and IL-5. V(H) and V(L) on the monoclonal IgG derived from CSF B cells expressed amino acid replacements due to somatic mutations. A T cell epitope was mapped to a V(H) framework region, where an amino acid replacement was critical for the T cell recognition. The finding of Id-specific T cells and Id-bearing B cells in the CSF indicates that they coexist within the diseased organ, and provide a basis for the study of Id-driven T-B cell collaboration in a human autoimmune disease.

Prolonged and increased expression of soluble Fc receptors, IgG and a TCR-Ig fusion protein by transiently transfected adherent 293E cells

In studies of the relation between structure and function of proteins of the immune system, there is a continuous need for screening of a large number of protein variants. To optimise the yield following transient gene expression in small or medium culture volumes, several parameters were investigated. First, secretion levels of a soluble form of human Fcgamma receptor IIA (FcgammaRIIA) were measured after transfection of 293, 293E, 293T as well as COS-7 cell lines. The transgene was under cytomegalovirus (CMV) promoter control on the expression vector pcDNA3, which also contains an SV40 origin of replication (SV40 ori). All 293 cell lines secreted more protein than COS-7 cells. Introduction of the Epstein Barr virus (EBV) origin of replication (oriP) greatly increased the protein expression from the 293E cells, both the amount of protein produced per day and the duration of production. At best, 293E cells secreted fully functional protein for 3-4 weeks provided supernatant was harvested every 2-3 days followed by medium replacement. This method was then used for expression of soluble forms of human FcgammaRI, FcgammaRIIB, the human neonatal Fc receptor (FcRn), a T cell receptor (TCR)-immunoglobulin (Ig) fusion protein, and human IgG3. With an initial culture volume of 5 ml, the yield was approximately 200 microg for FcgammaRIIA, 1.5 microg for FcgammaRI, 5 microg for FcRn, 20 microg for FcgammaRIIB, 40 microg for the TCR-Ig fusion protein and 850 microg for IgG3. Culture expansion during the 3 weeks of culture further increased the yield. Protein yield was also improved by scaling up the initial volume. This approach can provide sufficient amounts of protein for screening experiments, and in the case of antibody, milligrams of recombinant protein for extensive structural analysis can be obtained from one single transient transfection. The approach should be of interest to laboratories that do not have access to a bioreactor but still have a requirement for reasonable amounts of protein to be produced in an easy and cost-effective manner.

Therapeutic effect of idiotype-specific CD4+ T cells against B-cell lymphoma in the absence of anti-idiotypic antibodies

Immunoglobulin (Ig) variable (V) region idiotypes (Id's) are highly tumor-specific antigens produced by B-lymphoma cells and are promising targets for immunotherapy. Id vaccination has proven effective in experimental mouse models and may possibly prevent recurrence of B lymphomas in humans. It has previously been shown that anti-Id antibodies protect against B-cell lymphoma in the absence of T cells. We here demonstrate in a T-cell-receptor transgenic mouse model that the contrary is also true: Id-specific CD4+ T cells can protect against Id+ B-lymphoma cells in the absence of B cells, antibodies, and CD8+ T cells. Moreover, Id-specific CD4+ T cells have a curative potential since they could be transferred as late as 17 days after subcutaneous tumor cell injection of severe combined immunodeficiency (SCID) mice and still abrogate tumor development in about 50% of mice. Such mice undergo an acute inflammatory swelling with infiltration of neutrophils at the site of tumor injection, which subsides over weeks, with some mice cured and delayed emergence of lymphomas in other mice. Adoptively transferred CD4+ T cells accumulated in the tumor and were activated (CD69+). In vitro experiments demonstrated that memory, but not naive, Id-specific CD4+ T cells kill Id+ B-lymphoma cells. The results show that Id-specific CD4+ T cells, in the absence of antibodies home to subcutaneous Id+ B lymphoma, become activated, induce inflammation, and prevent tumor development.

T cells in myeloma

The current trend to develop immunotherapy strategies for patients with myeloma and other B cell malignancies has stimulated considerable interest in the functional state of the T cell population in these patients. Expanded clones of T cells exist in many patients with myeloma and their presence is associated with an improved survival. However, isolating T cells with tumour specificity has proven to be a difficult task and clinical immunization trials have so far failed to achieve a significant response. There is now evidence that tumour specific T cells are either tolerized or deleted following antigen presentation and that idiotype-derived, immunodominant tumour peptides may not exist in all patients. In order to develop more effective immunotherapy strategies for patients with myeloma, further studies are urgently required to identify the most appropriate tumour antigen, the nature of the interactions which take place during antigen presentation, and how to promote the cytotoxicity of autologous T cells.

The primary IgM antibody repertoire: a source of potent idiotype immunogens

A widely held view is that, to elicit adaptive immune responses, most protein antigens must be given with adjuvants that activate the innate immune system. It has also been proposed that the immune system is tolerant to idiotypes (Id) of the syngeneic primary antibody (Ab) repertoire. We now show that among 73 purified noncomplexed secretory IgM monoclonal antibodies (mAb), 4 (5.5%) elicited high levels of IgG Ab against the Id even though no adjuvant was added. The responses were controlled by H2-linked immune response genes. IgG1, but no IgG2a or IgG2b, anti-Id Ab were detected, indicating involvement of T helper type 2 (Th2) cells. All 4 IgM mAb are likely germ-line gene-encoded, and 1 was shown to represent a recurrent Id. After endotoxin depletion the most potent immunogen of the 4 still provoked robust humoral anti-Id responses. The results suggest that a natural protein of the primary IgM Ab repertoire can be immunogenic without an adjuvant.

Phagocytic dendritic cells from myelomas activate tumor-specific T cells at a single cell level

Antigen-presenting cells (APCs) from subcutaneous mouse MOPC315 plasmacytoma phagocytosed immunoglobulin G-coated magnetic beads, enabling efficient isolation within 2 hours by magnetic separation (APC-MB). Cell morphology was heterogeneous, with some of the cells having dendrites. The surface phenotype of purified tumor APCs-MB was CD11b(+), CD11c(+), CD40(+), CD80(+), CD86(+), and MHC class II(+). Tumor APCs-MB expressed messenger RNA for fractalkine and ABCD-1 chemokines, and for CC-type chemokine receptors CCR5 and CCR7, indicating the presence of mature dendritic cells (DCs). Visualized at a single cell level within 4 hours after disruption of the tumor, APCs-MB induced rapid Ca(++) mobilization in MHC class II-restricted tumor idiotype (Id)-specific cloned CD4(+) T cells. In long-term assays, tumor APCs-MB induced proliferation of naive T cells from Id-specific T-cell receptor transgenic mice. The results suggest that tumor APCs-MB represent a heterogeneous cell population that includes myeloid-derived DCs of various stages of maturation. A considerable fraction (> or = 15%) of DCs is spontaneously primed with tumor-specific antigen.

Deletion of idiotype (Id)-specific T cells in multiple myeloma

Mycloma cells secrete monoclonal immunoglobulin (Ig), called myeloma protein. The variable (V) regions of myeloma proteins are unique to each plasma cell tumor, and therefore contain highly tumor-specific antigenic determinants called idiotopes (Id). T cells with specificity for Id are thought to be of importance in eradication of multiple myeloma. In ongoing clinical trials, myeloma patients are vaccinated against the Id of their own myeloma protein, with the aim of inducing Id-specific T cells. However, this strategy will only succeed if Id-specific T cells are present in patients, and are able to respond. In an experimental animal model, we have shown that [d-specific T cells become progressively deleted as the myeloma protein serum concentration exceeds 50 microg/ml. This indicates that the ability of multiple myeloma patients to respond to Id-vaccination might be seriously handicapped. We suggest that Id-vaccination should be reserved for eradication of minimal residual disease, e.g. after high-dose chemotherapy and stem-cell transplantation.

Resting small B cells present endogenous immunoglobulin variable-region determinants to idiotope-specific CD4(+) T cells in vivo

Antigenic determinants localized within the highly diversified V-regions of Ig are called idiotopes (Id). Processed Id-peptides can be presented on MHC class II molecules to CD4(+) T cells. If B cells present their endogenous Id-peptides, T cell activation could occur in the absence of nominal antigen, a potentially important process in T-B cooperation and immune regulation. To test this idea, we used mice made transgenic for a lambda2 L-chain (Id(+) mice). Another transgenic mouse strain expresses TCR transgenes with specificity for the Id (lambda2), presented on MHC class II molecules. When highly purified sorted Id(+) B cells and Id-specific T cells were sequentially injected into MHC syngeneic SCID host, T cell became blastoid, CD69(+) and proliferated. To exclude any role of host APC, MHC incompatible Rag2(- / -) mice (H-2(b)) were used as recipients for the Id(+) B and Id-specific T cells, with similar results. Exposure to extracellular Id(+) immunoglobulin (Ig) was not sufficient for Id priming of B cells in vivo, highlighting the preferential presentation of Id peptides derived from endogenous Ig, by B cells. The results suggest that B cells presenting Id self-peptides generated by V(D)J recombinations or somatic mutations may directly stimulate T cell in vivo in the absence of conventional antigen.

Antibodies engineered with IgD specificity efficiently deliver integrated T-cell epitopes for antigen presentation by B cells

We have developed a strategy for improving the stimulation of T cells during immune responses by constructing recombinant antibodies that enhance the delivery of antigen to antigen-presenting cells, such as B cells. These antibodies have variable regions specific for surface molecules on B cells, and a constant region with an inserted antigen. In vitro, such antibodies make B cells approximately 1000-fold more efficient at presenting antigen and stimulating specific T cells. In vivo, the antibodies turn B cells of the spleen into potent stimulators of T cells. This approach may be useful for the generation of new vaccines.

Somatic origin of T-cell epitopes within antibody variable regions: significance to monoclonal therapy and genesis of systemic autoimmune disease

During an immune response, specific antibody variable region genes are diversified by a somatic point mutation process that generates de novo "foreign" V-region sequences. This creates an interesting problem in immune regulation because B cells are highly proficient at self-presenting V-region peptides in the context of class II MHC. Though our studies indicate that the corresponding T-cell repertoire attains a state of tolerance to germline-encoded antibody V-region diversity, it is presently unknown whether the same is true of mutationally generated diversity. On the basis of immunoregulatory considerations, we hypothesize that contact exclusion or tolerance normally precludes T cells from helping B cells via self-presented mutant V-region peptides. The lack of recurrent somatic mutations that create known T-cell epitopes in antibody V regions lends some support to this idea. In contrast, our studies of spontaneously autoreactive B cells in systemic autoimmune disease strongly suggest that precursors of such cells are recruited by T-cell help directed to self-presented mutant idiopeptides. Failures in tolerance or contact exclusion mechanisms may be responsible for this apparently abnormal event. In addition to their importance in immune regulation, somatic mutations or other differences from germline-encoded V-region sequence may be largely responsible for undesirable patient responses to therapeutic monoclonal antibodies. These reactions might be averted or diminished by inducing tolerance in the T-cell repertoire with synthetic peptide correlates of non-germline-encoded V-region sequences in humanized antibodies.

Immunoglobulin as a vehicle for foreign antigenic peptides immunogenic to T cells

Antibody (Ab) molecules may serve as targeting vehicles for delivery of foreign antigenic peptides to antigen presenting cells (APC). An attractive strategy is to substitute segments between beta-strands of immunoglobulin (Ig) constant (C)-region domains with antigenic peptides. For this to work, the mutant Ab must maintain its conformation so that it can be secreted from transfected cells. Furthermore, the antigenic peptides must be excised by the processing machinery of APC and loaded onto major histo-compatibility complex (MHC) class II molecules. To test this, we have introduced a peptide of eleven amino acids (a.a.) as either of three different loops in the first C-region domain of the heavy (H) chain (CH1) of human IgG3. When the resulting mutant H chain genes were expressed in a fibroblast cell line equipped with proper class II molecules, the H chains were retained intracellularly, probably due to the light (L) chain deficiency of the fibroblasts. Nevertheless, by the endogenous class II processing pathway, presentation of the epitope to CD4+ cells was observed for all three mutants. The presentation efficiency, however, depended on the position of the peptide in the H chain. This could be due to influence of flanking sequences, which differ in the three loop replacement mutants. When L chain-expressing Chinese hamster ovary (CHO) lambda cells were transfected with the same constructs, two out of the three mutant Ig were secreted. The mutants had the expected antigen specificity and were recognized by anti-IgG Ab. When added exogenously to dendritic cell APC, the mutant IgG3 were processed, and the liberated foreign epitopes presented to T cells. The results suggest that the loops connecting beta-strands in the Ig fold may be replaced by foreign peptides, which upon processing become stimulatory to CD4+ T cells. Combined with the well-known targeting function of antibodies, this principle may be useful for construction of a new generation of vaccines.

Naive CD4+ T cells confer idiotype-specific tumor resistance in the absence of antibodies

CD4+ T cells can recognize a processed idiotypic peptide derived from the mouse lambda 2(315) immunoglobulin light chain. The idiotypic peptide is presented on the I-E(d) class II major histocompatibility complex molecule. Mice made transgenic for a lambda 2(315)-specific alpha beta T cell receptor have been demonstrated to be specifically resistant against a tumor challenge with the MOPC315 (alpha,lambda 2(315)) plasmacytoma (Lauritzsen, G. F., Weiss, S., Dembic, Z. and Bogen, B., Proc. Natl. Acad. Sci. USA 1994, 91: 5700). That study, however, did not rule out a role of either anti-Id antibodies or T cells expressing nontransgenic specificities due to expression of endogenous T cell receptor (TcR) alpha chains. Also, the role of different T cell subsets in protection was unclear. To remove these ambiguities, we have now made the transgenic mice homozygous for the scid mutation, known to inhibit both Ig and TcR gene rearrangements. Such transgenic SCID mice lack B cells and antibodies while they still have plenty of CD4+ and CD4-8- cells expressing the transgenic alpha beta T cell receptor. The number of CD8+ T cell is dramatically reduced. Even so, transgenic SCID mice are protected against a challenge with MOPC315 plasmacytoma cells. Therefore, B cells, as well as novel T cell receptor specificities created by rearrangements of endogenous alpha-chain genes, are both dispensable for effective immunosurveillance in our system. Surprisingly, we found that transgenic CD8+ and CD4-8- cells are idiotype-specific and I-E(d) restricted. However, these T cell subsets are not required for resistance because adoptive transfer experiments demonstrated that highly purified transgenic SCID CD4+ cells suffice for tumor protection.

A syngeneic idiotype is immunogenic when borne by IgM but tolerogenic when joined to IgG

Some syngeneic monoclonal antibodies (mAb) elicit immune responses like conventional T-dependent antigens. To find out whether the heavy chain class (isotype) plays a role for the immunogenicity of an idiotype (Id), we isolated rare subclones of an IgM mAb (termed Id3) in which the variable region of the heavy chain (VH) is associated with a new constant region (CH). The VH-Id3 gene is a member of the murine 36-60 family and probably has three replacement mutations. The light chain V gene is germ-line V lambda 2. IgM, IgG1, IgG2a and IgG2b variants of Id3 were purified from protein-free medium and injected without adjuvant into BALB/c mice. The parental 19S IgM mAb given subcutaneously (s.c.) elicited a vigorous humoral response against Id3; in comparison, monomeric 8S IgM was a much weaker immunogen. Unlike IgM, multiple challenges with the IgG switch variants failed to induce anti-Id3 Ab. IgG variants gained immunogenicity if they were purified from medium containing fetal calf serum, mixed with complete Freund's adjuvant or injected into mice primed with IgM-Id3. Pretreatment with 100 micrograms s.c. + 50 micrograms of the IgG2a variant extinguished the Ab response to parental IgM, but the response to adjuvant-free bovine serum albumin was intact. Therefore, the tolerance induced by the IgG2a switch variant is antigen-specific and not due to toxicity. Significant inhibition of the Ab response to parental IgM was observed after treatment with 4 micrograms of the IgG2a switch variant. Administration of the IgG1 and IgG2b switch variants also inhibited this response significantly. Thus, the outcome of an encounter with Id3 is strongly influenced by the CH isotype to which the Id is joined. This suggests novel ways to minimize unwanted Ab responses against Id of human therapeutic mAb. In the context of the theory of Id networks, we suggest that dominant B cell clones can preempt anti-Id Ab responses against themselves by early switching from IgM to IgG secretion, before immunogenic IgM Ab have had time to activate anti-Id B cells.

Ca2+ mobilization in physiologically stimulated single T cells gradually increases with peptide concentration (analog signaling)

We have investigated Ca2+ mobilization in single T cells stimulated with their physiological ligand, i.e. antigenic peptide bound to major histocompatibility complex (MHC) molecules on antigen-presenting cells (APC). Fibroblasts expressing I-Ed class II molecules were pulsed with a peptide derived from the lambda 2(315) immunoglobulin light chain. Onto such antigen-pulsed fibroblasts were sedimented cloned Th1 cells loaded with Fura-2. Changes in cytosolic Ca2+ concentration in single T cells were continually monitored by use of an imaging system based on fluorometry. Ca2+ mobilization was both peptide-specific and MHC-restricted. Within seconds of the initial APC-T cell contact, a Ca2+ spike could be observed. The Ca2+ response gradually declined over a 25-min period, during which oscillations were noted. Various parameters characterizing the magnitude of the Ca2+ response (latency, increase rate, max and mean Ca2+ increase, frequency and period of oscillations) all correlated with the amount of peptide used for pulsing the fibroblasts. Thus, Ca2+ mobilization in single T cells appears not to be an all or none phenomenon. Rather, activation is incremental (analog signaling), the degree of Ca2+ mobilization probably being related to the number of stimulatory peptide-MHC complexes on the surface of the APC. The extent of calcium mobilization and lymphokine production (interleukin (IL)-2, IL-3, interferon-gamma) correlated, at least at the population level.

Sequence features that correlate with MHC restriction

Identification of common sequence motifs in antigenic peptides restricted to a specific class II molecule has not been easy due to the large variation in length and sequence that is observed in these peptides. The goal of this study is to develop an automated computerized method for the identification of sequence features and structural determinants that play a role in the MHC restriction of helper T-cell antigenic peptides. For this, we compiled an extended database of helper T-cell sites, including the information on MHC restriction, when available. Two groups of peptides are assigned to each MHC type: (1) peptides that bind to that MHC molecule to elicit a T-cell response, and (2) peptides that were shown experimentally either not to bind to or not to elicit a T-cell proliferative response in association with that MHC molecule. We search for common motifs in the group of binding peptides, and identify significant motifs that are frequent among these peptides but almost absent in the group of non-binding peptides. A motif consists of physical-chemical and structural properties that may be responsible for binding specificity and can be extracted from sequence data, such as, hydrophobicity, charge, hydrogen bonding capability, etc. The first search is performed on the non-aligned binding peptides. Next, the sequences are aligned according to an identified motif and a search for additional, conserved, properties is performed. The statistical significance of the motifs is evaluated as well as their compatibility with published experimental results on substitution effects. Here we demonstrate the general scheme of the analysis and results for I-Ek and I-Ak associated peptides.

Processing and presentation of idiotypes to MHC-restricted T cells

Among the self antigens, immunoglobulins, and in particular idiotypes, are of special interest because of their extreme sequence heterogeneity and their postulated involvement in regulatory interactions in the immune system. We have therefore studied antigen processing and presentation of variable region peptides, processed idiotypes, to MHC class II molecule-restricted T cells. The immunoglobulin used has been the lambda 2(315) light chain produced by the BALB/c MOPC 315 plasmacytoma (alpha, lambda 2). The minimum length of a stimulatory synthetic idiotypic peptide comprises residues 91-101 of lambda 2(315) and is presented by the I-E(d) molecule to CD4+ T cells. T cell clones with specificity for the 91-101(lambda 2(315))/I-E(d) complex utilize a limited TCR repertoire and are of both Th1 and Th2 type. For presentation, extracellular lambda 2(315) requires endocytosis and processing, as previously described for conventional exogenous antigens. In addition, a B lymphoma cell can process and present its own endogenous lambda 2(315). This was shown by transfecting manipulated lambda 2(315) gene variants into B lymphoma cells, followed by evaluation of the APC function of the transfectants. These studies demonstrated that surface expression or secretion of lambda 2(315) is not necessary for presentation and suggested that the endoplasmic reticulum may be a processing compartment. To extend our findings to naive Id+ B cells and anti-Id T cells, we have generated lambda 2(315)-transgenic as well as TCR-transgenic mice. A model is presented for a T-B cell interaction based on presentation of processed idiotypes.

Anti-tumour activity of idiotype-specific, MHC-restricted Th1 and Th2 clones in vitro and in vivo

Idiotypes (Id) can serve as individual markers on B cells; therefore, cytotoxic Id-specific T cells may play a significant role in immunological surveillance of Id+ B-cell tumours. We have investigated the anti-tumour activity of CD4+ BALB/c Th1 and Th2 clones which recognize a processed Id of the syngeneic lambda 2(315) L chain in the context of the class II MHC molecule I-Ed. Id-specific T cells and A20/46 B lymphoma cells transfected with the lambda 2(315) gene were injected s.c. into the same site of BALB/c mice (Winn assay). The results show that both Th1 and Th2 clones can protect against tumour development. The protection was Id-specific because T cells did not influence tumour development by an A20/46 B lymphoma cell line transfected with the pSV2neo expression vector alone. In vitro studies showed that the Th1 clones were cytotoxic to lambda 2(315)-transfected B lymphoma cells; by contrast, the Th2 clone was not cytotoxic in 51Cr-release assay even though the Th2 cells inhibited the growth of lambda 2(315) B lymphoma cells. The anti-lymphoma properties of both the Th1 and Th2 clones appear to involve as yet undefined cytotoxic and growth inhibiting molecules.

Restricted alpha/beta receptor gene usage of idiotype-specific major histocompatibility complex-restricted T cells: selection for CDR3-related sequences

We have sequenced the T cell receptor (TcR) V alpha and V beta genes of seven independent BALB/c CD4+ T cell clones specific for the immunoglobulin lambda 2 light chain produced by the MOPC 315 myeloma (lambda 2(315)). All the clones recognize a peptide of residues 91-101 of lambda 2(315) and are restricted by the major histocompatibility complex (MHC) molecule I-E(d). The results indicate that in BALB/c mice, this anti-idiotypic response uses a very limited number of TcR. The four clones which cross-react between Phe94 and Tyr94 peptide analogues use very similar receptors (V alpha 3, J alpha 1, V beta 6, J beta 1.1). The V alpha 3 gene used by all of these clones is identical and has not been previously described. Although the four clones differ in nucleotide sequence in the V/J borders, two had identical receptors at the amino acid level. One of the cross-reactive clones exhibits a heteroclitic response to the Tyr94 peptide variant resulting from a single amino acid exchange in the V/J junction of the alpha chain. The three remaining clones which recognize only the Phe94 and not the Tyr94 peptide have somewhat more diverse TcR, however, two of these three clones use V beta 6. One of these non-crossreacting clones is alloreactive, the specificity of which can be attributed to differences in the N-D-J sequences. Taken together these data indicate that this T cell response to an immunoglobulin idiotope is very restricted in terms of the TcR used. These data in conjunction with recently published results indicate that, although there can be strong preference for individual V alpha or V beta gene segments, certain V alpha/V beta combinations are preferentially selected for interacting with a given peptide/MHC combination, and that the CDR3-related regions are crucial for antigen fine specificity and alloreactivity.

Weak positive selection of transgenic T cell receptor-bearing thymocytes: importance of major histocompatibility complex class II, T cell receptor and CD4 surface molecule densities

We have produced alpha beta T cell receptor (TcR)-transgenic mice and studied MHC-dependent positive selection of T cells bearing this receptor. The alpha and beta transgenes were isolated from an I-Ed-restricted, CD4+ BALB/c (H-2d/d) T cell clone specific for a peptide consisting of the 91-101 residues of the lambda 2 immunoglobulin light chain of MOPC315. Mice which carry the transgenes on a BALB/c background, but with H-2d/d, H-2b/d or H-2b/b major histocompatibility complex (MHC) haplotypes, were investigated for TcR expression in thymocytes and peripheral T cells. The thymocytes expressing the transgene-encoded alpha beta receptor are weakly positively selected when compared with previous findings in other TcR-transgenic mice models. Thus, alpha beta thymocytes vary in their efficacy of being positively selected by their restriction element. Furthermore, the density of TcR and CD4 on thymocytes, as well as the density of I-Ed molecules on thymic epithelial cells, appear critical for the extent of positive selection. A possible explanation is that the transgenic TcR has a marginal affinity for self-MHC molecules on thymic epithelium, and that this may be compensated for by an increase in the number of CD4/TcR/MHC ternary complexes forming between the maturing thymocyte and the cortical epithelial cells.

Idiotype-specific, major histocompatibility complex restricted T cells are of both Th1 and Th2 type

The lymphokine secretion patterns of seven independent 91-101.lambda 2(315)/I-Ed specific, CD4+ T-cell clones have been investigated. Six of the clones are of the Th1 type as they secrete IL2 and IFN gamma, but not IL4. Some of these six Th1 clones produce TNF alpha/beta, and some produce minor amounts of IL5 and IL6. One clone is of the Th2 type as it produces IL4, IL5, and large amounts of IL6, but not IL2, IFN gamma or TNF. The Th1/Th2 classification does not have any stringent relationship to immunization protocol, fine specificity and V alpha/V beta gene segment utilization. The immunoregulatory significance of our findings for Id/MHC-dependent T-B cell interaction is discussed.

MHC class II-restricted presentation of intracellular antigen

An endogenously produced immunoglobulin light chain (lambda 2(315] is processed and presented to T cells in association with major histocompatibility complex (MHC) class II molecules. Using transfectants producing variant forms of lambda 2(315) that are neither expressed on the cell surface nor secreted, we demonstrate that intracellular lambda 2(315), which has never been exported outside of the cell, is the source of processed lambda 2(315) idiotype. This challenges the currently accepted paradigm that endogenous antigens are only presented by MHC class I molecules. Variants of lambda 2(315) protein that are retained in the endoplasmic recticulum (ER) are also presented. Variants that are expressed in the cytosol as well as those that are transported into the nucleus rather than the ER are not presented. Thus, the ER is likely to be the processing compartment.

A stimulatory monoclonal antibody detecting T cell receptor diversity among idiotype-specific, major histocompatibility complex-restricted T cell clones

A panel of independent BALB/c T cell clones responding to a peptide of the lambda 2(315) immunoglobulin light chain (residues 91-101), in the context of I-Ed, has previously been described. A monoclonal antibody (mAb; GB113) to the T cell receptor (TcR) of one of the clones, 4B2A1 (V alpha 1, J alpha 19; V beta 8.2, D beta 1.1, J beta 1.2) precipitates the alpha/beta heterodimer from 4B2A1. However, GB113 does not bind DO11-10.2 cells bearing a similar alpha/beta heterodimer (V alpha 1.1, J alpha TT11; V beta 8.2, D beta 1.1, J beta 1.1). GB113 does not cross-react with the TcR of the six other clones in the panel. Furthermore, the mAb does not bind polyclonal lambda 2(315)-specific T cell lines except 4.4% of cells of line 4 from which 4B2A1 was cloned. The mAb only binds a negligible number (0.5%) of BALB/c thymocytes and peripheral T cells. Therefore, the epitope detected by GB113 is very rarely expressed on 91-101. lambda 2(315)-specific TcR or on TcR of normal T cells. Soluble GB113 induces T cell activation [measured as proliferation and interleukin (IL) 2, IL3 and interferon-gamma production]. GB113-induced T cell activation is enhanced by soluble anti-CD4 and anti-Thy-1 mAb.

Flexibility of the T cell repertoire. Self tolerance causes a shift of T cell receptor gene usage in response to insulin

Bovine insulin(BI)-specific I-Ab-restricted T cell clones have been characterized for fine specificity and TCR gene usage. We have demonstrated that mouse strains carrying H-2b on three different genetic backgrounds (C57BL, BALB, and 129) rearrange and express the V beta 6 gene in a large proportion (36%) of insulin-specific clones. In these strains, the non-MHC background did not seem to influence TCR gene usage in response to BI. The V beta 6+ clones appeared to be selected by the antigen. In contrast, no V beta 6+ clones could be isolated from (B6 x DBA/2)F1 mice, where V beta 6+ (and V beta 8.1+) T cells are deleted by self tolerance to Mls-1a. Thus, although a small proportion of residual V beta 6+ cells had been demonstrated in Mls-1a mice, these cells could not be retrieved in a response that uses V beta 6 predominantly. In functional terms, therefore, the deletion of V beta 6 by self tolerance appears to be complete. Instead of V beta 6, the majority (up to 60%) of I-Ab- as well as I-Ad-restricted insulin-specific clones from the (B6 x DBA/2)F1 mice expressed V beta 8.2 and V beta 8.3. This shift of gene usage was not accompanied by any detectable change in the fine specificity pattern of response. Thus, in the insulin-specific response, the flexibility of T cell repertoire fully compensates for deletions caused by self tolerance.

Monoclonal antibodies specific for variable and constant domains of murine lambda chains

Rat monoclonal antibodies directed against the BALB/c myeloma protein M315 (alpha,lambda 2) are described. 9A8 (IgG1) binds the V domain of lambda 2 and cross-reacts with lambda 1 and lambda 3 chains. 2B6 (IgG2a) is directed to the C domain of lambda 2 and cross-reacts with C lambda 3. The antibodies bind isolated chains as well as complete immunoglobulins. The monoclonals detect soluble immunoglobulin (radioimmunoassay), immunoglobulin immobilized on polystyrene (enzyme-linked immunosorbent assay), immunoglobulin bound to nitrocellulose (immunoblotting), and surface immunoglobulin intercalated in cell membranes (immunofluorescence). The antibodies are easily purified on protein G immunosorbents and may be biotinylated or conjugated with fluorescein isothiocyanate without loss of capacity to bind. In addition to the anti-lambda antibodies, a C alpha 2/C alpha 3-specific monoclonal antibody, 8D2 (IgG2a) is described.

Identification of T-cell epitopes and use in construction of synthetic vaccines

The T cell is central to the immune system response to foreign antigens, and understanding the mechanism of T cell response to antigen is crucial for vaccine development. Short subpeptides of foreign antigen can prime the T cells to respond to the whole antigen, in some cases as well as or better than immunization with the whole antigen itself. Antigenic sites located first in the murine model are also antigenic in the human, suggesting that the structural features of antigenic sites are species-independent. The amphipathic helix hypothesis has proven useful in developing an algorithm that has successfully located immunodominant sites in important proteins, thus reducing substantially the experimental time and effort required to locate those sites. Other algorithms have also been used successfully, but in all cases there are proven T-cell sites not accounted for by the algorithm. A data base showing T-cell response to collections of peptides uniformly distributed along protein antigens would be very useful in subsequent efforts to characterize the physical and chemical properties of T-cell antigenic sites.

B-lymphoma cells process and present their endogenous immunoglobulin to major histocompatibility complex-restricted T cells

Antigen-presenting B-lymphoma cells were transfected with the gene encoding the immunoglobulin lambda 2 light chain of MOPC315 cells (lambda 2(315). The lambda 2 chain is expressed on the cell surface of the transfectants together with the endogenous heavy chain. The transfectants present an idiotope of the lambda 2(315) light chain to class II-restricted T-cell clones. Recognition by the T cells requires processing of the lambda 2(315) light chain. From these data we conclude that B-lymphoma cells constitutively process and present their immunoglobulins. Secretion and reuptake of the light chain was not necessary for the presentation. Thus, B cells bear two types of idiotypes on their membrane, a native form as surface immunoglobulin and a processed form in the context of products of the major histocompatibility complex.

Immune responses to an adjuvant-free native syngeneic myeloma protein (M315)

Myeloma protein 315 (M315; isotype IgA, lambda 2) is used in this report as a model to explore the immunogenicity of a syngeneic Ig under nearly physiological conditions. We have previously shown that a synthetic peptide spanning the mutated HV3 loop of the L-315 chain, when emulsified in complete Freund's adjuvant, elicits T helper cells (Th) that respond to a boost with L-315 or M315, indicating that M315 is recognized as a processed protein antigen. We now show that the adjuvant-free 7S monomer of native or of mildly reduced and alkylated M315, given in divided doses totalling 300 or 800 micrograms to BALB/c mice, induced persistent anti-M315 antibodies (Ab), a large part of which was IgG1 directed mainly to idiotypes (Id) associated with M315's hapten-binding site. Polymers of M315 IgA (800 micrograms) failed to induce Ab, due probably to their rapid clearance into bile. Short-term treatment with anti-CD4 monoclonal Ab GK1.5 at the time of priming with 7S M315 inhibited the responses almost completely. The spleens of M315-immune mice contained Th that recognized the L-chain subunit of M315 as a carrier indicating that these Th did not require an assembled (VH-VL) pair of 315 V regions to be activated. We also observed low amounts of Ab specific for epitopes of the C alpha region. This evidence opens the possibility that a distinct autoimmune pathway exists for elicitation of rheumatoid factor (RF; autoAb to Fc gamma) that involves help to RF-producing B cells by Id-specific Th. We suggest that these Th recognize V-region peptides from IgG that have been captured, processed and presented by these B cells.

Are idiotypic peptides from variable domains critical for T-dependent production of rheumatoid factors?

Studies from this laboratory have indicated that isologous myeloma protein 315 (M315, isotype IgA, lambda 2) elicits T helper cells which recognize processed forms (peptides) of its V-domains and that recognition is controlled by H-2 linked immune-response (Ir) genes (J Exp Med 1982; 155:1587-96; Eur J Immunol 1986; 16:889-93). We now report that adjuvant-free soluble M315, particularly the mildly reduced and alkylated form, stimulates a T-dependent antibody response mainly specific for M315's paired V-domains. A small subset of the antibodies appeared to recognize the C-region of IgA, thus being analogous to rheumatoid factors (RF). On the basis of these observations, we propose that one pathway to RF production depends on T helper cells that interact directly with RF-producing B cells across peptide-MHC bridges. These peptides are envisaged to be derived from hypervariable regions of IgG V-domains, and they are therefore called "idiotypic peptides". This hypothesis assumes that the number of different idiotypic peptides is so large that the immune system has not developed tolerance to all of them.

Two M315 idiotopes defined by isologous monoclonal antibodies: one depends on germline and the other on mutated murine lambda 2 light chain sequences

We have previously reported that T helper cells of BALB/c mice recognize the unique mutated sequence Phe94, Arg95, Asn96 of the lambda 2 L chain of isologous (BALB/c) myeloma protein 315. Here we study two Id (Id-315.1.4 and Id-315.TH) of the DNP-Lys binding M315 defined by two monoclonal isologous anti-Id Ab (Ab 2-1.4 and Ab 2-TH). Both Id were (1) totally expressed by Fv-315, but not by free unpaired V domains, (2) specifically dependent on VH-315, since lambda 2-315 recombined with four other H chains did not express the Id, (3) related to the hapten-binding site because their expression was blocked by the haptens DNP-Lys and DNP-Gly, and (4) topographically related because Ab 2-1.4 and Ab 2-TH competed with each other for binding to M315. The contribution of lambda chain V regions was studied with the aid of reconstituted Ig molecules of H-315 paired with lambda 1, lambda 2, and lambda 3 L chains. Id-315.TH was expressed equally well by reconstituted Ig containing three different lambda 2 chains (lambda 2-5-7, lambda 2-T952, and lambda 2-315), but its expression was profoundly reduced when H-315 was associated with lambda 3-SAPC15 or lambda 1-J558 L chains; it therefore depended upon amino acids encoded by germline lambda 2 genes. By contrast, Id-315.1.4 was only restored by the lambda 2-315 chain paired with H-315. Since lambda 2-5-7 and lambda 2-T952 differ from lambda 2-315 at positions 38, 94, 95, 96, and 98 or 99, respectively, Id-315.1.4 probably requires the unique mutated amino acids Phe94, Arg95, Asn96 of lambda 2-315. This resembles the effects on Id expression of previously reported unique amino acids of the D region. We failed to confirm that hyperimmunization of BALB/c mice with Ab 2-1.4 cross-linked to KLH induced M315-like Ab. The results are discussed in terms of the contribution of the third hypervariable loop of lambda chains to Id and the immunogenicity of isologous Ig.

Idiotope-specific T cell clones that recognize syngeneic immunoglobulin fragments in the context of class II molecules

We have established idiotope (Id)-specific T cell lines and clones derived from at least 4 different BALB/c mice immunized with the light chain (lambda 2(315] of the BALB/c myeloma protein M315 (alpha, lambda 2). Independently derived clones were indistinguishable in that they reacted to V lambda 2(315), one or more of the amino acids corresponding to somatically mutated codons 94, 95 and 96 of the third hypervariable region being essential for expression of the Id. While the Id was efficiently expressed on V lambda 2(315), Fv315 and lambda 2(315) fragments, about a 100-1000-fold higher molar concentration of Fab315 and M315 was needed to induce equivalent responses. Thus, Ig quaternary structure heavily influenced the availability of the Id for T cells. The V lambda 2(315)-specific T cells were Thy-1.2+, L3T4+, Ly-2.2- and I-Ed restricted. Some of the T cell clones produced interleukin 2 (IL2), IL3 and B cell growth and differentiation factors upon activation. In addition, T cells were cytotoxic in long-term assays for Ed beta Ek alpha-, but not Ek beta Ek alpha- transfected L cells in the presence of Id. The cytotoxic effect was the basis for an L cell growth inhibition assay for T cell activation that was at least 10-fold more sensitive than ordinary proliferation assays.