Involvement of both T cell receptor V alpha and V beta variable region domains and alpha chain junctional region in viral antigen recognition

T Cell Receptor Chain Centricity: The Phenomenon and Potential Applications in Cancer Immunotherapy

T cells are crucial players in adaptive anti-cancer immunity. The gene modification of T cells with tumor antigen-specific T cell receptors (TCRs) was a milestone in personalized cancer immunotherapy. TCR is a heterodimer (either α/β or γ/δ) able to recognize a peptide antigen in a complex with self-MHC molecules. Although traditional concepts assume that an α- and β-chain contribute equally to antigen recognition, mounting data reveal that certain receptors possess chain centricity, i.e., one hemi-chain TCR dominates antigen recognition and dictates its specificity. Chain-centric TCRs are currently poorly understood in terms of their origin and the functional T cell subsets that express them. In addition, the ratio of α- and β-chain-centric TCRs, as well as the exact proportion of chain-centric TCRs in the native repertoire, is generally still unknown today. In this review, we provide a retrospective analysis of studies that evidence chain-centric TCRs, propose patterns of their generation, and discuss the potential applications of such receptors in T cell gene modification for adoptive cancer immunotherapy.

MHC I tetramer staining tends to overestimate the number of functionally relevant self-reactive CD8 T cells in the preimmune repertoire

Previous studies that used peptide-MHC (pMHC) tetramers (tet) to identify self-specific T cells have questioned the effectiveness of thymic-negative selection. Here, we used pMHCI tet to enumerate CD8 T cells specific for the immunodominant gp33 epitope of lymphocytic choriomeningitis virus glycoprotein (GP) in mice transgenically engineered to express high levels of GP as a self-antigen in the thymus. In GP-transgenic mice (GP+ ), monoclonal P14 TCR+ CD8 T cells that express a GP-specific TCR could not be detected by gp33/Db -tet staining, indicative of their complete intrathymic deletion. By contrast, in the same GP+ mice, substantial numbers of polyclonal CD8 T cells identifiable by gp33/Db -tet were present. The gp33-tet staining profiles of polyclonal T cells from GP+ and GP-negative (GP- ) mice were overlapping, but mean fluorescence intensities were ∼15% lower in cells from GP+ mice. Remarkably, the gp33-tet+ T cells in GP+ mice failed to clonally expand after lymphocytic choriomeningitis virus infection, whereas those of GP- mice did so. In Nur77GFP -reporter mice, dose-dependent responses to gp33 peptide-induced TCR stimulation revealed that gp33-tet+ T cells with high ligand sensitivity are lacking in GP+ mice. Hence, pMHCI tet staining identifies self-specific CD8 T cells but tends to overestimate the number of truly self-reactive cells.

T Cell Receptor Profiling in Type 1 Diabetes

PURPOSE OF REVIEW

The genetic susceptibility and dominant protection for type 1 diabetes (T1D) associated with human leukocyte antigen (HLA) haplotypes, along with minor risk variants, have long been thought to shape the T cell receptor (TCR) repertoire and eventual phenotype of autoreactive T cells that mediate β-cell destruction. While autoantibodies provide robust markers of disease progression, early studies tracking autoreactive T cells largely failed to achieve clinical utility.

RECENT FINDINGS

Advances in acquisition of pancreata and islets from T1D organ donors have facilitated studies of T cells isolated from the target tissues. Immunosequencing of TCR α/β-chain complementarity determining regions, along with transcriptional profiling, offers the potential to transform biomarker discovery. Herein, we review recent studies characterizing the autoreactive TCR signature in T1D, emerging technologies, and the challenges and opportunities associated with tracking TCR molecular profiles during the natural history of T1D.

Perivascular Arrest of CD8+ T Cells Is a Signature of Experimental Cerebral Malaria

There is significant evidence that brain-infiltrating CD8⁺ T cells play a central role in the development of experimental cerebral malaria (ECM) during Plasmodium berghei ANKA infection of C57BL/6 mice. However, the mechanisms through which they mediate their pathogenic activity during malaria infection remain poorly understood. Utilizing intravital two-photon microscopy combined with detailed ex vivo flow cytometric analysis, we show that brain-infiltrating T cells accumulate within the perivascular spaces of brains of mice infected with both ECM-inducing (P. berghei ANKA) and non-inducing (P. berghei NK65) infections. However, perivascular T cells displayed an arrested behavior specifically during P. berghei ANKA infection, despite the brain-accumulating CD8⁺ T cells exhibiting comparable activation phenotypes during both infections. We observed T cells forming long-term cognate interactions with CX₃CR1-bearing antigen presenting cells within the brains during P. berghei ANKA infection, but abrogation of this interaction by targeted depletion of the APC cells failed to prevent ECM development. Pathogenic CD8⁺ T cells were found to colocalize with rare apoptotic cells expressing CD31, a marker of endothelial cells, within the brain during ECM. However, cellular apoptosis was a rare event and did not result in loss of cerebral vasculature or correspond with the extensive disruption to its integrity observed during ECM. In summary, our data show that the arrest of T cells in the perivascular compartments of the brain is a unique signature of ECM-inducing malaria infection and implies an important role for this event in the development of the ECM-syndrome.

Cerebral malaria is the most severe complication of Plasmodium falciparum infection. Utilizing the murine experimental model of cerebral malaria (ECM), it has been found that CD8⁺ T cells are a key immune cell type responsible for development of cerebral pathology during malaria infection. To identify how CD8⁺ T cells cause cerebral pathology during malaria infection, in this study we have performed detailed in vivo analysis (two photon imaging) of CD8⁺ T cells within the brains of mice infected with strains of malaria parasites that cause or do not cause ECM. We found that CD8⁺ T cells appear to accumulate in similar numbers and in comparable locations within the brains of mice infected with parasites that do or do not cause ECM. Importantly, however, brain accumulating CD8⁺ T cells displayed significantly different movement characteristics during the different infections. CD8⁺ T cells interacted with myeloid cells within the brain during infection with parasites causing ECM, but this association was not required for development of cerebral complications. Furthermore, our results suggest that CD8⁺ T cells do not cause ECM through the widespread killing of brain microvessel cells. The results in this study significantly improve our understanding of the ways through which CD8⁺ T cells can mediate cerebral pathology during malaria infection.

TCR affinity for thymoproteasome-dependent positively selecting peptides conditions antigen responsiveness in CD8(+) T cells

In the thymus, low-affinity T cell antigen receptor (TCR) engagement facilitates positive selection of a useful T cell repertoire. Here we report that TCR responsiveness of mature CD8(+) T cells is fine tuned by their affinity for positively selecting peptides in the thymus and that optimal TCR responsiveness requires positive selection on major histocompatibility complex class I-associated peptides produced by the thymoproteasome, which is specifically expressed in the thymic cortical epithelium. Thymoproteasome-independent positive selection of monoclonal CD8(+) T cells results in aberrant TCR responsiveness, homeostatic maintenance and immune responses to infection. These results demonstrate a novel aspect of positive selection, in which TCR affinity for positively selecting peptides produced by thymic epithelium determines the subsequent antigen responsiveness of mature CD8(+) T cells in the periphery.

Functional expression cloning identifies COX-2 as a suppressor of antigen-specific cancer immunity

The efficacy of immune surveillance and antigen-specific cancer immunotherapy equally depends on the activation of a sustained immune response targeting cancer antigens and the susceptibility of cancer cells to immune effector mechanisms. Using functional expression cloning and T-cell receptor (TCR) transgenic mice, we have identified cyclooxygenase 2/prostaglandin-endoperoxide synthase 2 (COX-2) as resistance factor against the cytotoxicity induced by activated, antigen-specific T cells. Expressing COX-2, but not a catalytically inactive COX-2 mutant, increased the clonogenic survival of E1A-transformed murine cancer cells when cocultured with lymphocytes from St42Rag2^−/− mice harboring a transgenic TCR directed against an E1A epitope. COX-2 expressing tumors established in immune-deficient mice were less susceptible to adoptive immunotherapy with TCR transgenic lymphocytes in vivo. Also, immune surveillance of COX-2-positive tumor cells in TCR transgenic mice was less efficient. The growth of murine MC-GP tumors, which show high endogenous COX-2 expression, in immunocompetent mice was effectively suppressed by treatment with a selective COX-2 inhibitor, celecoxib. Mechanistically, COX-2 expression blunted the interferon-gamma release of antigen-specific T cells exposed to their respective cellular targets, and increased the expression of interleukin-4 and indoleamine 2,3-dioxygenase by tumor cells. Addition of interferon-gamma sensitized COX-2 expressing cancer cells to tumor suppression by antigen-specific T cells. In conclusion, COX-2, which is frequently induced in colorectal cancer, contributes to immune evasion and resistance to antigen-specific cancer immunotherapy by local suppression of T-cell effector functions.

HDAC1 controls CD8+ T cell homeostasis and antiviral response

Reversible lysine acetylation plays an important role in the regulation of T cell responses. HDAC1 has been shown to control peripheral T helper cells, however the role of HDAC1 in CD8⁺ T cell function remains elusive. By using conditional gene targeting approaches, we show that LckCre-mediated deletion of HDAC1 led to reduced numbers of thymocytes as well as peripheral T cells, and to an increased fraction of CD8⁺CD4^– cells within the CD3/TCRβ^lo population, indicating that HDAC1 is essential for the efficient progression of immature CD8⁺CD4^– cells to the DP stage. Moreover, CD44^hi effector CD8⁺ T cells were enhanced in mice with a T cell-specific deletion of HDAC1 under homeostatic conditions and HDAC1-deficient CD44^hi CD8⁺ T cells produced more IFNγ upon ex vivo PMA/ionomycin stimulation in comparison to wild-type cells. Naïve (CD44^l°CD62L⁺) HDAC1-null CD8⁺ T cells displayed a normal proliferative response, produced similar amounts of IL-2 and TNFα, slightly enhanced amounts of IFNγ, and their in vivo cytotoxicity was normal in the absence of HDAC1. However, T cell-specific loss of HDAC1 led to a reduced anti-viral CD8⁺ T cell response upon LCMV infection and impaired expansion of virus-specific CD8⁺ T cells. Taken together, our data indicate that HDAC1 is required for the efficient generation of thymocytes and peripheral T cells, for proper CD8⁺ T cell homeostasis and for an efficient in vivo expansion and activation of CD8⁺ T cells in response to LCMV infection.

Duality of the murine CD8 compartment

CD8αβ plays crucial roles in the thymic selection, differentiation, and activation of some, but not all, CD8(+) T cells, whereas CD8αα does not. To investigate these roles, we produced mice that expressed transgene P14 T-cell receptor β (TCRβ) chain and CD8β or did not (WT and KO mice, respectively). The primary CD8(+) T-cell response to acute lymphocytic choriomeningitis virus (LCMV) infection was predominantly D(b)/GP33 specific and CD8 independent in KO mice and was mostly CD8 dependent in WT mice. Cytotoxic T lymphocytes (CTL) from KO mice failed to mobilize intracellular Ca(2+) and to kill via perforin/granzyme. Their strong Fas/FasL-mediated cytotoxicity and IFN-γ response were signaled via a Ca(2+)-independent, PI3K-dependent pathway. This was also true for 15-20% of CD8-independent CTL found in WT mice. Conversely, the perforin/granzyme-mediated killing and IFN-γ response of CD8-dependent CTL were signaled via a Ca(2+), p56(lck), and nuclear factor of activated T cells-dependent pathway. Deep sequencing of millions of TCRα chain transcripts revealed that the TCR repertoires of preimmune CD8(+) T cells were highly diverse, but those of LCMV D(b)/GP33-specific CTL, especially from KO mice, were narrow. The immune repertoires exhibited biased use of Vα segments that encoded different complementary-determining region 1α (CDR1α) and CDR2α sequences. We suggest that TCR from WT CD8-independent T cells may engage MHC-peptide complexes in a manner unfavorable for efficient CD8 engagement and Ca(2+) signaling but permissive for Ca(2+)-independent, PI3K-dependent signaling. This duality of the CD8 compartment may provide organisms with broader protective immunity.

Estimating the diversity, completeness, and cross-reactivity of the T cell repertoire

In order to recognize and combat a diverse array of pathogens the immune system has a large repertoire of T cells having unique T cell receptors (TCRs) with only a few clones specific for any given antigen. We discuss how the number of different possible TCRs encoded in the genome (the potential repertoire) and the number of different TCRs present in an individual (the realized repertoire) can be measured. One puzzle is that the potential repertoire greatly exceeds the realized diversity of naïve T cells within any individual. We show that the existing hypotheses fail to explain why the immune system has the potential to generate far more diversity than is used in an individual, and propose an alternative hypothesis of “evolutionary sloppiness.” Another immunological puzzle is why mice and humans have similar repertoires even though humans have over 1000-fold more T cells. We discuss how the idea of the “protecton,” the smallest unit of protection, might explain this discrepancy and estimate the size of “protecton” based on available precursor frequencies data. We then consider T cell cross-reactivity – the ability of a T cell clone to respond to more than one epitope. We extend existing calculations to estimate the extent of expected cross-reactivity between the responses to different pathogens. Our results are consistent with two observations: a low probability of observing cross-reactivity between the immune responses to two randomly chosen pathogens; and the ensemble of memory cells being sufficiently diverse to generate cross-reactive responses to new pathogens.

T cells maintain an exhausted phenotype after antigen withdrawal and population reexpansion

During chronic infection, pathogen-specific CD8(+) T cells upregulate expression of molecules such as the inhibitory surface receptor PD-1, have diminished cytokine production and are thought to undergo terminal differentiation into exhausted cells. Here we found that T cells with memory-like properties were generated during chronic infection. After transfer into naive mice, these cells robustly proliferated and controlled a viral infection. The reexpanded T cell populations continued to have the exhausted phenotype they acquired during the chronic infection. Thus, the cells underwent a form of differentiation that was stably transmitted to daughter cells. We therefore propose that during persistent infection, effector T cells stably differentiate into a state that is optimized to limit viral replication without causing overwhelming immunological pathology.

Intrinsic defects in CD8 T cells with aging contribute to impaired primary antiviral responses

Aging is associated with altered immune responses, particularly with a diminished CD8 T cell response. Although both intrinsic and extrinsic factors are hypothesized to impact this decreased T cell response, the direct evidence of an intrinsic deficiency in virus-specific CD8 T cells is limited. In this study, a TCR transgenic (Tg) P14 mouse model was utilized to compare the activation and proliferation of the Tg CD8 T cells of young and aged P14 mice upon stimulation with antigen or infection with virus. The proliferation of purified Tg CD8 T cells of aged mice was significantly lower than that of young mice when cultured in vitro with both the LCMV specific peptide and antigen presenting cells from young wild type mice. In addition, expression of the activation markers, CD69, CD25, and CD44, was delayed on Tg T cells of aged mice after stimulation. Importantly, while adoptive transfer of purified Tg CD8 T cells of young or aged mice into young wild type mice resulted in expansion of the Tg CD8 T cells of both ages after LCMV infection, the expansion of the Tg T cells from aged mice was significantly decreased compared with that of the Tg T cells from young mice. However, while the number of IFN-γ secreting Tg CD8 T cells from aged mice was significantly decreased compared to that of young mice, the percentages of Tg CD8 T cells producing IFN-γ were similar in young and aged mice, demonstrating that proliferation, but not function, of the Tg CD8 T cells of aged mice was impaired. Importantly, chronological age alone was not sufficient to predict an altered proliferative response; rather, expression of high levels of CD44 on CD8 T cells of aged mice reflected a decreased proliferative response. These results reveal that alterations intrinsic to CD8 T cells can contribute to the age-associated defects in the primary CD8 T cell response during viral infection.

Th2-polarised PrP-specific transgenic T-cells confer partial protection against murine scrapie

Several hurdles must be overcome in order to achieve efficient and safe immunotherapy against conformational neurodegenerative diseases. In prion diseases, the main difficulty is that the prion protein is tolerated as a self protein, which prevents powerful immune responses. Passive antibody therapy is effective only during early, asymptomatic disease, well before diagnosis is made. If efficient immunotherapy of prion diseases is to be achieved, it is crucial to understand precisely how immune tolerance against the prion protein can be overcome and which effector pathways may delay disease progression. To this end, we generated a transgenic mouse that expresses the ß-chain of a T cell receptor recognizing a PrP epitope presented by the class II major histocompatibility complex. The fact that the constraint is applied to only one TCR chain allows adaptation of the other chain according to the presence or absence of tolerogenic PrP. We first show that transgene-bearing T cells, pairing with rearranged α-chains conferring anti-PrP specificity, are systematically eliminated during ontogeny in PrP+ mice, suggesting that precursors with good functional avidity are rare in a normal individual. Second, we show that transgene-bearing T cells with anti-PrP specificity are not suppressed when transferred into PrP+ recipients and proliferate more extensively in a prion-infected host. Finally, such T cells provide protection through a cell-mediated pathway involving IL-4 production. These findings support the idea that cell-mediated immunity in neurodegenerative conditions may not be necessarily detrimental and may even contribute, when properly controlled, to the resolution of pathological processes.

It is generally accepted that prion-specific antibodies can protect against mouse scrapie infection. However, passive antibody therapy is limited to the lymphoinvasion stage of the disease. Active immunization has been attempted but the results have been disappointing. There is therefore a need for developing analytical models that will allow a fine dissection of the immune mechanisms at play in prion diseases and help distinguish between protective effects mediated by B cells and antibodies, and the effect of T cells. The aim of our study was to thoroughly examine T cell tolerance to the prion protein and to evaluate whether a pure specific population of T cells adoptively transferred to a normal host could proliferate and confer protection against scrapie. We designed a transgenic mouse in which the majority of T lymphocytes recognize the prion protein. Our key findings are that prion-specific T cells remain functional when transferred to normal recipients, even more so when the host is infected with scrapie, and confer partial protection against the disease by slowing down prion replication, in complete absence of anti-prion antibodies. Anti-prion T cells may therefore be considered as a therapeutic tool in the future.

Blockade of LTB(4) /BLT(1) pathway improves CD8(+) T-cell-mediated colitis

BACKGROUND

Leukotriene B4 (LTB(4) ) has chemotactic properties for activated T cells expressing the high-affinity receptor BLT(1) . This study investigated whether the LTB(4) antagonist (CP-105,693), selective for BLT(1) receptor, could protect mice from colitis mediated by specific cytotoxic CD8(+) T lymphocytes (CTL).

METHODS

Virus-specific colitis was induced in C57Bl/6 mice transferred with lymphoid cells from P14 TcR Tg mice which are specific to class I GP33 peptide of LCMV. Mice were immunized with GP33-pulsed dendritic cells and colitis was elicited by intrarectal administration of the peptide. Colitis was evaluated by body weight loss and macroscopic and histological analysis of colon. In vivo priming of specific CD8(+) CTL was determined using interferon (IFN)-γ ELISPOT and in vivo CTL assays. In some experiments mice were treated with a selective LTB(4) receptor antagonist.

RESULTS

Immunization with GP33-pulsed dendritic cells (DCs) induced priming of specific CD8(+) CTL, as shown by the presence of IFN-γ-producing CD8(+) T cells in colon draining lymph nodes and in vivo CTL assays. Intrarectal challenge with GP33 induced severe colitis and recruitment of granzyme B(+) P14 CD8(+) cells in colon. Treatment with the specific LTB(4) receptor antagonist before elicitation of colitis reduced the severity of colitis and decreased the frequency of specific effectors.

CONCLUSIONS

Colitis can be induced by IFN-γ-producing cytotoxic CD8(+) CTL specific for viral antigen. Blockade of the LTB(4) /BLT(1) pathway by a selective BLT(1) receptor antagonist attenuates colitis by inhibiting CD8(+) effectors recruitment in colon. These data illustrate the therapeutic potential of LTB(4) receptor selective antagonists in protection from CD8(+) T-cell-mediated intestinal inflammation.

Nck adaptors are positive regulators of the size and sensitivity of the T-cell repertoire

The size and sensitivity of the T-cell repertoire governs the effectiveness of immune responses against invading pathogens. Both are modulated by T-cell receptor (TCR) activity through molecular mechanisms, which remain unclear. Here, we provide genetic evidence that the SH2/SH3 domain containing proteins Nck lower the threshold of T-cell responsiveness. The hallmarks of Nck deletion were T-cell lymphopenia and hyporeactivity to TCR-mediated stimulation. In the absence of the Nck adaptors, peripheral T cells expressing a TCR with low avidity for self-antigens were strongly reduced, whereas an overall impairment of T-cell activation by weak antigenic stimulation was observed. Mechanistically, Nck deletion resulted in a significant decrease in calcium mobilization and ERK phosphorylation upon TCR engagement. Taken together, our findings unveil a crucial role for the Nck adaptors in shaping the T-cell repertoire to ensure maximal antigenic coverage and optimal T cell excitability.

Essential role for TLR9 in prime but not prime-boost plasmid DNA vaccination to activate dendritic cells and protect from lethal viral infection

One of the requirements for efficient vaccination against infection is to achieve the best combination of an adequate adjuvant with the antigenic information to deliver. Although plasmid DNA is a promising tool bearing the unique potential to activate humoral and cellular immunity, an actual challenge is to increase plasmid immunogenicity in human vaccination protocols in which efficacy has proven rather limited. Previous work showed that the bacterial DNA backbone of the plasmid has potent adjuvant properties because it contains CpG motifs that are particular activating nucleotidic sequences. Among TLRs, which are key sensors of microbial products, TLR9 can detect CpG motifs and confer activation of APCs, such as dendritic cells. However, whether the immunogenic properties of plasmid DNA involve TLR9 signaling has not been clearly established. In the current study, we demonstrate that TLR9 determines the effectiveness of vaccination against lethal lymphocytic choriomeningitis virus infection using plasmid DNA in a prime, but not prime-boost, vaccination regimen. Furthermore, we provide evidence that the presence of TLR9 in dendritic cells is necessary for effective and functional priming of virus-specific CD8+ T cells upon plasmid exposure in vitro or single-dose vaccination in vivo. Therefore, at single or low vaccine doses that are often used in human-vaccination protocols, CpG/TLR9 interactions participate in the immunogenicity of plasmid DNA. These results suggest that the TLR9 signaling pathway is involved in the efficacy of plasmid vaccination; therefore, it should remain a focus in the development or amelioration of vaccines to treat infections in humans.

Gads-deficient thymocytes are blocked at the transitional single positive CD4+ stage

Positive selection of T-cell precursors is the process by which a diverse T-cell repertoire is established. Positive selection begins at the CD4(+)CD8(+) double positive (DP) stage of development and involves at least two steps. First, DP thymocytes down-regulate CD8 to become transitional single positive (TSP) CD4(+) thymocytes. Then, cells are selected to become either mature single positive CD4(+) or mature single positive CD8(+) thymocytes. We sought to define the function of Gads during the two steps of positive selection by analyzing a Gads-deficient mouse line. In Gads(+/+) mice, most TSP CD4(+) thymocytes are TCR(hi)Bcl-2(hi)CD69(+), suggesting that essential steps in positive selection occurred in the DP stage. Despite that Gads(-/-) mice could readily generate TSP CD4(+) thymocytes, many Gads(-/-) TSP CD4(+) cells were TCR(lo)Bcl-2(lo)CD69(-), suggesting that Gads(-/-) cells proceeded to the TSP CD4(+) stage prior to being positively selected. These data suggest that positive selection is not a prerequisite for the differentiation of DP thymocytes into TSP CD4(+) thymocytes. We propose a model in which positive selection and differentiation into the TSP CD4(+) stage are separable events and Gads is only required for positive selection.

Transforming growth factor-beta suppresses the activation of CD8+ T-cells when naive but promotes their survival and function once antigen experienced: a two-faced impact on autoimmunity

OBJECTIVE

Transforming growth factor-beta (TGF-beta) can exhibit strong immune suppression but has also been shown to promote T-cell growth. We investigated the differential effect of this cytokine on CD8(+) T-cells in autoimmunity and antiviral immunity.

RESEARCH DESIGN AND METHODS

We used mouse models for virally induced type 1 diabetes in conjunction with transgenic systems enabling manipulation of TGF-beta expression or signaling in vivo.

RESULTS

Surprisingly, when expressed selectively in the pancreas, TGF-beta reduced apoptosis of differentiated autoreactive CD8(+) T-cells, favoring their expansion and infiltration of the islets. These results pointed to drastically opposite roles of TGF-beta on naïve compared with antigen-experienced/memory CD8(+) T-cells. Indeed, in the absence of functional TGF-beta signaling in T-cells, fast-onset type 1 diabetes caused by activation of naïve CD8(+) T-cells occurred faster, whereas slow-onset disease depending on accumulation and activation of antigen-experienced/memory CD8(+) T-cells was decreased. TGF-beta receptor-deficient CD8(+) T-cells showed enhanced activation and expansion after lymphocytic choriomeningitis virus infection in vivo but were more prone to apoptosis once antigen experienced and failed to survive as functional memory cells. In vitro, TGF-beta suppressed naïve CD8(+) T-cell activation and gamma-interferon production, whereas memory CD8(+) T-cells stimulated in the presence of TGF-beta showed enhanced survival and increased production of interleukin-17 in conjunction with gamma-interferon.

CONCLUSIONS

The effect of TGF-beta on CD8(+) T-cells is dependent on their differentiation status and activation history. These results highlight a novel aspect of the pleiotropic nature of TGF-beta and have implications for the design of immune therapies involving this cytokine.

Priming of CD8+ T cells during central nervous system infection with a murine coronavirus is strain dependent

Virus-specific CD8(+) T cells are critical for protection against neurotropic coronaviruses; however, central nervous system (CNS) infection with the recombinant JHM (RJHM) strain of mouse hepatitis virus (MHV) elicits a weak CD8(+) T-cell response in the brain and causes lethal encephalomyelitis. An adoptive transfer model was used to elucidate the kinetics of CD8(+) T-cell priming during CNS infection with RJHM as well as with two MHV strains that induce a robust CD8(+) T-cell response (RA59 and SJHM/RA59, a recombinant A59 virus expressing the JHM spike). While RA59 and SJHM/RA59 infections resulted in CD8(+) T-cell priming within the first 2 days postinfection, RJHM infection did not lead to proliferation of naïve CD8(+) T cells. While all three viruses replicated efficiently in the brain, only RA59 and SJHM/RA59 replicated to appreciable levels in the cervical lymph nodes (CLN), the site of T-cell priming during acute CNS infection. RJHM was unable to suppress the CD8(+) T-cell response elicited by RA59 in mice simultaneously infected with both strains, suggesting that RJHM does not cause generalized immunosuppression. RJHM was also unable to elicit a secondary CD8(+) T-cell response in the brain following peripheral immunization against a viral epitope. Notably, the weak CD8(+) T-cell response elicited by RJHM was unique to CNS infection, since peripheral inoculation induced a robust CD8(+) T-cell response in the spleen. These findings suggest that the failure of RJHM to prime a robust CD8(+) T-cell response during CNS infection is likely due to its failure to replicate in the CLN.

T-cell receptor V(alpha) usage by effector CD4+Vbeta11+ T cells mediating graft-versus-host disease directed to minor histocompatibility antigens

T-cell receptor (TCR) Valpha (TRAV) and Vbeta (TRBV) chains provide the T-cell specificity for recognition of major histocompatibility complex (MHC)-bound antigens. However, there is limited information on the diversity of TRAV use within an antigen response. Previous investigation of CD4(+) T-cell-mediated graft-versus-host disease (GVHD) in the minor histocompatibility antigen-mismatched C57BL/6 (B6)-->BALB.B irradiated murine model determined that Vbeta11(+) T cells were associated with disease severity. Polymerase chain reaction (PCR)-based complementarity-determining region 3 (CDR3)-sized spectratype analysis of B6 Vbeta11(+) T cells from the spleens of recipient BALB.B mice undergoing GVHD indicated biased use within the V(alpha)6, 9, 13, 14, 18, and 22 families. To probe deeper into this limited V(alpha) response, the current study was undertaken to further define TRAV-Jalpha (TRAJ) nucleotide sequences found in host-presensitized B6 Vbeta11(+) T cells proliferating in response to in vitro stimulation with BALB.B splenocytes. Using the nonpalindromic adaptor PCR method, we found dominant use of the TRAV13-TRAJ16 transcript combination. Then, using laser capture microdissection, we found use of the identical TRAV-TRAJ nucleotide sequence in areas dominated by infiltrating Vbeta11(+) CD4(+) T cells during the development of GVHD in both the rete-like prominences of the dorsal lingual epithelium and the ileal crypts of the small intestine.

Comparison of CDR3 length among thymocyte subpopulations: impacts of MHC and BV segment on the CDR3 shortening

Thymocytes are thought to be selected on the basis of antigen specificity between TCR and peptide-MHC (pMHC) ligands. The specificity depends primarily on extensive diversities of complementarity determining region 3 (CDR3), whose specificity is considered to be determined through thymocyte selection. We examined the CDR3 length profiles with 20 BV segments in thymocyte subpopulations from C57BL/6 (H-2(b)), C.B10 (Balb/c congenic, H-2(b)) and Balb/c (H-2(d)) mice. The CDR3 length was shorter in both CD4 single positive (SP) and CD8SP than in double positive (DP), but not altered among DP, double negative (DN) 4 and DN3 subpopulations. The CDR3 shortened more prominently in CD4SP than in CD8SP for C57BL/6 and C.B10, but the shortening was only slight for Balb/c. Although the shortening varied considerably among different BV segments, the greater shortening was observed in most BV segments for CD4SP and in several for CD8SP, in particular, the extent was the greatest in BV1, BV2, BV15, BV16, BV23 and BV26 for CD4SP, and in BV13-1 and BV29 for CD8SP. Moreover, the extent and the pattern of CDR3 shortening were basically the same among highly homologous BV segments (e.g. BV12-1 and 12-2; BV13-1, 13-2 and 13-3). These results taken together indicate that (1) the CDR3 shortening occurred between the DP to the SP stages but never earlier, that (2) there would be the MHC class preference for the CDR3 shortening, that (3) it was in part influenced by MHC haplotype, and finally that (4) the primary structure of particular BV segments would possibly affect the CDR3 length in selected thymocytes. It could be deduced from these results that the CDR3 shortening might play roles in ensuring geometrical disposition of CDRs unique to each BV segment and consequently allow CDRs to intimately interact with pMHC ligands.

T-cell receptor Valpha spectratype analysis of a CD4-mediated T-cell response against minor histocompatibility antigens involved in severe graft-versus-host disease

Although CD4(+) T cells can have an important role in mediating lethal graft-versus-host disease (GVHD) directed to multiple minor histocompatibility antigens (miHA) after bone marrow transplantation, their precise characterization and effector function remains elusive. In this regard, T cell receptor (TCR) Vbeta spectratype analysis has been a powerful tool for identifying donor CD4(+) T cell populations expanding to host miHA after bone marrow transplantation in the major histocompatibility complex-matched C57BL/6 (B6) --> C.B10-H2(b) (BALB.B) model of lethal GVHD. Removal of all of the Vbeta(+) T cell families containing these responding cells from the donor inoculum has proven to be an effective means of preventing the development of GVHD. Previous studies have also found that of the 11 miHA-responsive B6 CD4(+) Vbeta(+) T cell families, transplantation of Vbeta2(+) and Vbeta11(+) T cells together into lethally irradiated BALB.B mice appeared to be primarily responsible for the severity of resultant GVHD. Further focusing on these critical CD4 responses, in this study we demonstrate that B6 CD4(+)Vbeta11(+) T cells alone can induce lethal GVHD in BALB.B recipients. In addition, immunohistochemical staining of host lingual and intestinal epithelial tissues supported the capacity of Vbeta11(+) T cells to infiltrate typical GVHD-associated target areas. To further characterize the specific CD4(+)Vbeta11(+) T cells involved in this anti-miHA response, TCR Valpha spectratype analysis was performed and indicated that 6 Valpha chains were used by this reactive population. These results provide further evidence that a restricted repertoire of T cell specificities, presumably recognizing a correspondingly low number of miHA, is sufficient for the induction of severe GVHD.

Natural IgE Production in the Absence of MHC Class II Cognate Help

IgE induction by parasites and allergens is antigen driven and cognate T cell help dependent. We demonstrate that spontaneously produced IgE in T cell-deficient and germ-free wild-type (wt) mice is composed of natural specificities and induced by a mechanism independent of MHC class II (MHC II) cognate help. This does not require secondary lymphoid structures or germinal center formation, although some bystander T cell-derived IL-4 is necessary. The pathway of spontaneous IgE production is not inhibited by regulatory T cells and increases with age to constitute significant serum concentrations, even in naive animals.

Increased epitope-specific CD8+ T cells prevent murine coronavirus spread to the spinal cord and subsequent demyelination

CD8+ T cells are important for clearance of neurotropic mouse hepatitis virus (MHV) strain A59, although their possible role in A59-induced demyelination is not well understood. We developed an adoptive-transfer model to more clearly elucidate the role of virus-specific CD8+ T cells during the acute and chronic phases of infection with A59 that is described as follows. C57BL/6 mice were infected with a recombinant A59 virus expressing the gp33 epitope, an H-2Db-restricted CD8+ T-cell epitope encoded in the glycoprotein of lymphocytic choriomeningitis virus, as a fusion with the enhanced green fluorescent protein (RA59-gfp/gp33). P14 splenocytes (transgenic for a T-cell receptor specific for the gp33 epitope) were transferred at different times pre- and postinfection (p.i.). Adoptive transfer of P14 splenocytes 1 day prior to infection with RA59-gfp/gp33, but not control virus lacking the gp33 epitope, RA59-gfp, reduced weight loss and viral replication and spread in the brain and to the spinal cord. Furthermore, demyelination was significantly reduced compared to that in nonrecipients. However, when P14 cells were transferred on day 3 or 5 p.i., no difference in acute or chronic disease was observed compared to that in nonrecipients. Protection in mice receiving P14 splenocytes prior to infection correlated with a robust gp33-specific immune response that was not observed in mice receiving the later transfers. Thus, an early robust CD8+ T-cell response was necessary to reduce virus replication and spread, specifically to the spinal cord, which protected against demyelination in the chronic phase of the disease.

Murine plasmacytoid dendritic cells induce effector/memory CD8+ T-cell responses in vivo after viral stimulation

Like their human counterparts, mouse plasmacytoid dendritic cells (pDCs) play a central role in innate immunity against viral infections, but their capacity to prime T cells in vivo remains unknown. We show here that virus-activated pDCs differentiate into antigen-presenting cells able to induce effector/memory CD8+ T-cell responses in vivo against both epitopic peptides and endogenous antigen, whereas pDCs activated by synthetic oligodeoxynucleotides containing unmethylated cytosine-guanine motifs (CpG) acquire only the ability to recall antigen-experienced T-cell responses. We also show that immature pDCs are unable to induce effector or regulatory CD8+ T-cell responses. Thus, murine pDCs take part in both innate and adaptive immune responses by directly priming naive CD8+ T cells during viral infection.

Immune functions in mice lacking Clnk, an SLP-76-related adaptor expressed in a subset of immune cells

The SLP-76 family of immune cell-specific adaptors is composed of three distinct members named SLP-76, Blnk, and Clnk. They have been implicated in the signaling pathways coupled to immunoreceptors such as the antigen receptors and Fc receptors. Previous studies using gene-targeted mice and deficient cell lines showed that SLP-76 plays a central role in T-cell development and activation. Moreover, it is essential for normal mast cell and platelet activation. In contrast, Blnk is necessary for B-cell development and activation. While the precise function of Clnk is not known, it was reported that Clnk is selectively expressed in mast cells, natural killer (NK) cells, and previously activated T-cells. Moreover, ectopic expression of Clnk was shown to rescue T-cell receptor-mediated signal transduction in an SLP-76-deficient T-cell line, suggesting that, like its relatives, Clnk is involved in the positive regulation of immunoreceptor signaling. Stimulatory effects of Clnk on immunoreceptor signaling were also reported to occur in transfected B-cell and basophil leukemia cell lines. Herein, we attempted to address the physiological role of Clnk in immune cells by the generation of Clnk-deficient mice. The results of our studies demonstrated that Clnk is dispensable for normal differentiation and function of T cells, mast cells, and NK cells. Hence, unlike its relatives, Clnk is not essential for normal immune functions.

Molecular basis of antigen recognition by insulin specific T cell receptor

The TCR alpha/beta chains recognize antigen peptides bound to the groove of the MHC class II molecule. The crystal structure analyses of the TCR/peptide/MHC class II complexes have revealed that the Valpha chains play a significant role in antigen recognition. However, molecular details which amino acid residues of the Valpha chain are able to contribute to fine antigen specificity are not clearly understood. Previously, we have classified a panel of T hybrids specific for insulin isotypes from different species of animals into four groups based on response profiles to these antigens. In particular, the group III (pork insulin > or = beef insulin hierarchy of responsiveness) and IV (pork insulin >> beef insulin hierarchy of responsiveness) T hybrids are interesting, since these TCR alpha/beta chains with marked different antigen specificities demonstrate identical gene usages and very similar sequences. To specifically address the molecular requirements for insulin recognition by TCR, the TCR alpha and beta chain genes from these group III and IV T hybrids were transfected into 58 alpha-beta- T hybrid. The experiments suggested that CDR3alpha dictates the fine antigen specificity. Then, we have introduced a series of mutations into position 95 of CDR3alpha. The mutation experiments clearly indicated that position 95alpha determines the antigen specificity of the group III and IV T hybrids.

Interplay between TCR affinity and necessity of coreceptor ligation: high-affinity peptide-MHC/TCR interaction overcomes lack of CD8 engagement

CD8 engagement is believed to be a critical event in the activation of naive T cells. In this communication, we address the effects of peptide-MHC (pMHC)/TCR affinity on the necessity of CD8 engagement in T cell activation of primary naive cells. Using two peptides with different measured avidities for the same pMHC-TCR complex, we compared biochemical affinity of pMHC/TCR and the cell surface binding avidity of pMHC/TCR with and without CD8 engagement. We compared early signaling events and later functional activity of naive T cells in the same manner. Although early signaling events are altered, we find that high-affinity pMHC/TCR interactions can overcome the need for CD8 engagement for proliferation and CTL function. An integrated signal over time allows T cell activation with a high-affinity ligand in the absence of CD8 engagement.

Prevalent role of TCR alpha-chain in the selection of the preimmune repertoire specific for a human tumor-associated self-antigen

The specificity of recognition of pMHC complexes by T lymphocytes is determined by the V regions of the TCR alpha- and beta-chains. Recent experimental evidence has suggested that Ag-specific TCR repertoires may exhibit a more V alpha- than V beta-restricted usage. Whether V alpha usage is narrowed during immune responses to Ag or if, on the contrary, restricted V alpha usage is already defined at the early stages of TCR repertoire selection, however, has remained unexplored. Here, we analyzed V and CDR3 TCR regions of single circulating naive T cells specifically detected ex vivo and isolated with HLA-A2/melan-A peptide multimers. Similarly to what was previously observed for melan-A-specific Ag-experienced T cells, we found a relatively wide V beta usage, but a preferential V alpha 2.1 usage. Restricted V alpha 2.1 usage was also found among single CD8(+) A2/melan-A multimer(+) thymocytes, indicating that V alpha-restricted selection takes place in the thymus. V alpha 2.1 usage, however, was independent from functional avidity of Ag recognition. Thus, interaction of the pMHC complex with selected V alpha-chains contributes to set the broad Ag specificity, as underlined by preferential binding of A2/melan-A multimers to V alpha 2.1-bearing TCRs, whereas functional outcomes result from the sum of these with other interactions between pMHC complex and TCR.

Targeting dendritic cells with CD44 monoclonal antibodies selectively inhibits the proliferation of naive CD4+ T-helper cells by induction of FAS-independent T-cell apoptosis

CD44 is a multifunctional adhesion molecule that has been shown to be a costimulatory factor for T-cell activation in vitro and in vivo. The aim of the present study was to expand these findings by characterizing the role of CD44 during dendritic cell (DC) antigen presentation to naive, resting T cells. Certain monoclonal antibodies (mAbs) directed against all CD44 isoforms (pan CD44), or against the epitope encoded by the alternatively spliced exon v4 (CD44v4), dose-dependently inhibited the capacity of murine DC to induce proliferation of naive alloreactive T cells. Preincubation of the T cells or DC with these CD44 mAbs revealed that the effect was dependent upon mAb binding to DC, but not to T cells. DC treated with anti-pan CD44 and anti-CD44v4 mAbs induced CD4+ T-cell apoptosis, as shown by annexin V staining and TdT-mediated biotin-dUTP nick-end labelling (TUNEL) assays. However, CD4+ T-cell apoptosis was not dependent on the Fas/Fas ligand (Fas/FasL) system, as DC from FasL-deficient (Gld) mice and T cells from Fas-deficient (Lpr) mice were still susceptible to apoptosis induced by CD44-treated DC. To investigate whether CD44 treatment of DC affects early T-cell/DC interactions, time-lapse video microscopy was performed using peptide-specific T cells from T-cell receptor (TCR) transgenic mice. Interestingly, calcium signalling in CD4+ T cells was significantly diminished following interaction with CD44 mAb-treated DC, but this was not observed in CD8+ T cells. Taken together, we found that perturbation of distinct epitopes of CD44 on DC interfere with early Ca2+ signalling events during the activation of CD4+ T cells, resulting in T-cell apoptosis.

Dominant TCR-alpha requirements for a self antigen recognition in humans

TCR-alpha and -beta chains are composed of somatically rearranged V, D, and J germline-encoded gene segments that confer Ag specificity. Recent crystallographic analyses revealed that TCR-alpha has more contacts with peptide than TCR-beta, suggesting the possibility that peptide recognition predominantly relies on TCR-alpha. T cells specific for the self Ag Melan-A/MART-1 possess an exceptionally high precursor frequency in human histocompatibility leukocyte Ag-A2 individuals. This provided a unique situation for assessment of the structural relationship between TCR and peptide/MHC ligand at both the pre- and postimmune levels. Molecular and phenotypic analysis of many different Melan-A-specific T cell populations revealed that a structural constraint is imposed on the TCR for engagement with Melan-A peptides presented by HLA-A2, namely the highly preferential use of a particular TCRAV segment, AV2. Examination of CD8 single-positive thymocytes indicated that this preferential use in forming the Melan-A-specific TCR is mainly imposed by intrathymic positive selection. Our data demonstrate a dominant function of TCRAV2 segment in forming the TCR repertoire specific for the human self Ag Melan-A/MART-1 and support the view that Ag recognition is mediated predominantly by TCR-alpha.

Predominant role of T cell receptor (TCR)-alpha chain in forming preimmune TCR repertoire revealed by clonal TCR reconstitution system

The CDR3 regions of T cell receptor (TCR)-alpha and -beta chains play central roles in the recognition of antigen (Ag)-MHC complex. TCR repertoire is created on the basis of Ag recognition specificity by CDR3s. To analyze the potential spectrum of TCR-alpha and -beta to exhibit Ag specificity and generate TCR repertoire, we established hundreds of TCR transfectants bearing a single TCR-alpha or -beta chain derived from a cytotoxic T cell (CTL) clone, RT-1, specific for HIVgp160 peptide, and randomly picked up TCR-beta or -alpha chains. Surprisingly, one-third of such TCR-beta containing random CDR3 beta from naive T cells of normal mice could reconstitute the antigen-reactive TCR coupling with RT-1 TCR-alpha. A similar dominant function of TCR-alpha in forming Ag-specific TCR, though low-frequency, was obtained for lymphocytic choriomeningitis virus-specific TCR. Subsequently, we generated TCR-alpha and/or -beta transgenic (Tg) mice specific for HIVgp160 peptide, and analyzed the TCR repertoire of Ag-specific CTLs. Similar to the results from TCR reconstitution, TCR-alpha Tg generated CTLs with heterogeneous TCR-beta, whereas TCR-beta Tg-induced CTLs bearing a single TCR-alpha. These findings of Ag recognition with minimum involvement of CDR3 beta expand our understanding regarding the flexibility of the spectrum of TCR and suggest a predominant role of TCR-alpha chain in determining the preimmune repertoire of Ag-specific TCR.

T cells down-modulate peptide-MHC complexes on APCs in vivo

T cells compete in the response to antigen in vivo and this competition may drive the affinity maturation of a secondary T cell response. Here we show that high-affinity T cells out-competed lower affinity T cells during a response to antigenic challenge in vivo. Although competition between T cells specific for different peptide-major histocompatibility complexes (MHC) occurred, it was less efficient than competition between T cells of the same peptide-MHC specificity. In addition, high-affinity T cells efficiently induced antigen loss from the surface of antigen-presenting cells. Thus T cells that responded to the same peptide-MHC competed with each other by lowering the amount of ligand with which the cells could react. As a result, the activation of high-affinity cells was favored. This provides a mechanism for the affinity maturation of a secondary T cell response.

Structural basis of plasticity in T cell receptor recognition of a self peptide-MHC antigen

The T cell receptor (TCR) inherently has dual specificity. T cells must recognize self-antigens in the thymus during maturation and then discriminate between foreign pathogens in the periphery. A molecular basis for this cross-reactivity is elucidated by the crystal structure of the alloreactive 2C TCR bound to self peptide-major histocompatibility complex (pMHC) antigen H-2Kb-dEV8 refined against anisotropic 3.0 angstrom resolution x-ray data. The interface between peptide and TCR exhibits extremely poor shape complementarity, and the TCR beta chain complementarity-determining region 3 (CDR3) has minimal interaction with the dEV8 peptide. Large conformational changes in three of the TCR CDR loops are induced upon binding, providing a mechanism of structural plasticity to accommodate a variety of different peptide antigens. Extensive TCR interaction with the pMHC alpha helices suggests a generalized orientation that is mediated by the Valpha domain of the TCR and rationalizes how TCRs can effectively "scan" different peptides bound within a large, low-affinity MHC structural framework for those that provide the slight additional kinetic stabilization required for signaling.

Functional management of an antiviral cytotoxic T-cell response

Lymphocytic choriomeningitis virus (LCMV) is known to induce strong, polyclonal cytotoxic T-lymphocyte (CTL) responses. Using a set of variant peptides derived from the major CTL epitope of LCMV, we analyzed the functional fine specificity of the LCMV-specific CTL response. During the primary response, almost all the tested peptides were recognized. In contrast, the secondary response was purged of all minor cross-reactivities and very few peptides were significantly recognized. This study is the first demonstration of the functional maturation of a T-cell response and has important clinical and biological implications.

Elimination of T-cell-receptor beta-chain diversity in transgenic mice restricts antigen-specific but not alloreactive responses

The contribution of T-cell-receptor beta-chain diversity to the T-cell antigen-specific repertoire was investigated using single-chain T-cell-receptor transgenic mice. Animals that express the rearranged beta-chain gene from a T hybridoma with specificity for a hen egg lysozyme peptide, designated HEL (85-96) were analysed for their ability to respond to a panel of diverse antigens. Transgenic mice exhibited a significantly elevated response to HEL (85-96) which was shown to be due to an increased frequency of HEL (85-96)-specific T-cell progenitors. This increased frequency of specific progenitors resulted in the ability of transgenic mice to respond to the peptide in the absence of antigen priming. Conversely, transgenic mice failed to respond to any other antigen tested. Furthermore, this apparent deficiency was associated with a significant decrease in the frequency of antigen-specific T-cell progenitors in transgenic mice. Surprisingly, the ability to launch an alloresponse was unaffected by the exclusive expression of the transgene-derived beta-chain. These results indicate that beta-chain diversity is crucial for the ability of the T-cell population to elicit a rapid and robust response to the profusion of different antigen/major histocompatibility complex (MHC) ligands potentially encountered by an individual. Furthermore, these results suggest a lesser role for beta-chain diversity in contributing to allorecognition, and support a model in which the direct recognition of peptide-mediated conformational MHC forms is the major contributor to the alloreactive response exhibited by the majority of T cells.

Immunodominance of major histocompatibility complex class I-restricted influenza virus epitopes can be influenced by the T-cell receptor repertoire

We have used T-cell receptor beta-chain transgenic mice to determine the effects of a limited T-cell receptor repertoire on major histocompatibility complex class I-restricted epitope selection during the course of an influenza virus infection. Analysis of T-cell hybridomas generated from wild-type and transgenic mice demonstrated that the viral epitope recognized depended on the available T-cell receptor repertoire. Wild-type T-cell hybridomas recognized epitopes derived from the nucleoprotein and basic polymerase molecules, whereas hybridomas generated from transgenic mice recognized epitopes derived from the nonstructural protein and the matrix protein. There was no overlap in specificity between the two panels of hybridomas. This reciprocal pattern of specificity was also apparent in cytoxicity assays with brochoalveolar lavage cells isolated from the lungs of influenza virus-infected mice. T-cell receptor usage in the transgenic hybridomas was very restricted, with only one V alpha element used for ech of the two viral epitopes recognized. In the case of the hybridomas reactive to the nonstructural protein, sequence analysis showed that they all expressed V alpha 4J alpha 32 chains associated with the same junctional amino acids (Leu-Leu) that were encoded by five different nucleotide sequences, indicating a strong selection for T-cell receptor usage. Taken together, these data demonstrate that the available T-cell receptor repertoire can have a profound effect on the immunodominance of class I-restricted epitopes during a viral infection.

T cell development and repertoire of mice expressing a single T cell receptor alpha chain

We examined T cell development and T cell repertoire in transgenic mice expressing a single T cell receptor (TCR) alpha chain derived from the H-2Db-lymphocytic choriomeningitis virus (LCMV)-specific cytolytic T lymphocyte (CTL) clone P14. To generate these alpha P14 mice, mice transgenic for the P14 TCR alpha chain were backcrossed to TCR alpha-deficient mice. Thymi from alpha P14 mice exhibited a marked decrease of mature CD4+8- and CD8+4- single-positive thymocytes comparable to thymi from TCR alpha-deficient mice. Correspondingly, the number of peripheral T cells was reduced in the CD4 (tenfold) and in the CD8 (twofold) subsets when compared to normal mice. T cells from alpha P14 mice generated a primary anti-LCMV CTL response when stimulated in vitro with LCMV in contrast to normal mice which require priming in vivo; elimination of LCMV in vivo was, however, not improved. Flow cytometric analysis of T cells with V beta-specific antibodies showed a diverse endogenous TCR V beta repertoire. Functional analysis of the T cell repertoire, however, revealed a strongly reduced (30-fold) allogeneic and the absence of a vesicular stomatitis virus-specific CTL response and an impaired ability to provide T cell help for antibody isotype switching. Thus, T cell selection in the thymus was impaired and the T cell repertoire was limited in mice expressing only one type of TCR alpha chain.

Role of T helper cell precursor frequency on vesicular stomatitis virus neutralizing antibody responses in a T cell receptor beta chain transgenic mouse

During most immune responses, T cells help antigen-specific B cells to make antibodies against the antigen. One of the contributions of T cells to antibody production is the induction of isotype switching from IgM to IgG, which is the most abundant isotype in blood serum during recall responses. Other features of memory responses are faster kinetics and higher titers of antibody in the serum. What causes a primary immune response to be different from a secondary is not yet very clear and, particularly, the influence of precursor frequencies of T and B cells on memory responses still remains to be answered. To address this issue, a transgenic (tg) mouse line (ADA) was developed; it expresses the beta chain (V beta 2) of a major histocompatibility complex class II-restricted T cell receptor (TcR) specific for the glycoprotein (G) of vesicular stomatitis virus (VSV) serotype Indiana (VSV-IND). These mice exhibit an increased precursor frequency of VSV-specific CD4+ T cells that leads to enhanced neutralizing IgG production against VSV in vivo in unprimed mice. The data indicate that increased frequency of naive specific helper T cells alone may account for features of a memory phenotype such as high titer of antibodies and isotype switching.

The biased V gamma gene usage in the synovial fluid of patients with rheumatoid arthritis

Taking advantage of the reverse transcriptase-polymerase chain reaction (RT-PCR), we have analyzed T cell receptor gamma-chain mRNA of synovial fluid gamma/delta T cells from patients with rheumatoid arthritis (RA) in comparison with those of peripheral blood mononuclear cells (PBMC) from RA patients and healthy individuals. The quantitative RT-PCR method in conjunction with nucleotide sequencing revealed the frequent usage of the V gamma 3 gene segment in RA synovial fluid mononuclear cells (SFMC) (p < 0.01) which in PBMC of healthy individuals occurred rarely. PBMC of most healthy individuals expressed the V gamma 9 gene predominantly (p < 0.01) as expected. However, only half of RA patients showed elevated levels of the V gamma 9 gene expression in their PBMC. The gamma-chain mRNA containing the V gamma 3 gene in RA SFMC showed no conserved junctional sequence (complementarity-determining region 3). To investigate the nature of ligands recognized by the V gamma 3-bearing T cells, we analyzed V gamma gene usage of RA SFMC, RA PBMC, and normal PBMC stimulated with Mycobacterium tuberculosis (MT) or MT plus interleukin-2 since there is mounting evidence of high reactivity of RA SFMC to MT and mycobacterial heat-shock protein 65. However, the V gamma usage appeared to be mostly V gamma 9 in RA SFMC, RA PBMC and normal PBMC. Taken together these results suggest that an as yet unknown antigen(s) (other than MT) might select gamma/delta T cells expressing the V gamma 3 gene in RA SFMC.

Virus-specific CD8+ T-cell responses in mice transgenic for a T-cell receptor beta chain selected at random

The consequences of severely limiting the T-cell receptor (TCR) repertoire available for the response to intranasal infection with an influenza A virus or with Sendai virus have been analyzed by using H-2k mice (TG8.1) transgenic for a TCR beta-chain gene (V beta 8.1D beta 2J beta 2.3C beta 2). Analyzing the prevalence of V beta 8.1+ CD8+ T cells in lymph node cultures from nontransgenic (non-TG) H-2k controls primed with either virus and then stimulated in vitro with the homologous virus or with anti-CD3 epsilon showed that this TCR is not normally selected from the CD8+ T-cell repertoire during these infections. However, the TG8.1 mice cleared both viruses and generated virus-specific effector cytotoxic T lymphocytes (CTL) and memory CTL precursors, though the responses were delayed compared with the non-TG controls. Depletion of the CD4+ T-cell subset had little effect on the course of influenza virus infection but substantially slowed the development of the Sendai virus-specific CTL response and virus elimination in both the TG8.1 and non-TG mice, indicating that CD4+ helpers are promoting the CD8+ T-cell response in the Sendai virus model. Even so, restricting the available T-cell repertoire to lymphocytes expressing a single TCR beta chain still allows sufficient TCR diversity for CD8+ T cells (acting in the presence or absence of the CD4+ subset) to limit infection with an influenza A virus and a parainfluenza type 1 virus.

T-cell receptor usage by melanoma-specific clonal and highly oligoclonal tumor-infiltrating lymphocyte lines

Tumor-infiltrating lymphocytes (TIL) obtained from human melanomas can specifically lyse autologous tumor in vitro and mediate tumor regression in vivo. To develop more effective therapeutic reagents and to further understand the T-cell response to tumors, the diversity of T-cell receptors (TCRs) involved in melanoma antigen recognition has been studied. The TCR variable (V) genes, joining (J) segments, and N diversity regions used by five clonal lines and one highly oligoclonal, melanoma-specific, CD8+ TIL line were examined utilizing PCR amplification with V gene subfamily-specific primers and anchor PCR. The TIL lysed multiple allogeneic melanomas expressing matched surface major histocompatibility complex class I molecules. TCR analysis confirmed the clonal nature of the TIL lines; however, the TCR repertoire was diverse. Even among the three HLA-A2 restricted TIL (TIL 1200, TIL F2-2, and TIL-5), no common V gene usage was found. Comparison of the third complementarity-determining regions of the TCRs from the HLA-A2 restricted TIL revealed no homology. Results presented here identify T-cell clonotypes that recognize epitopes on highly prevalent, shared melanoma tumor-associated antigens presented in the context of HLA-B55, HLA-A1, and HLA-A2. These T cells and the antigens they recognize represent important components for the design of new immunotherapies for patients with advanced melanoma.

Identification of conserved T cell receptor CDR3 residues contacting known exposed peptide side chains from a major histocompatibility complex class I-bound determinant

We have analyzed the T cell receptor (TCR) repertoire found in the major histocompatibility complex class I-restricted cytotoxic T lymphocyte (CTL) response to the protein ovalbumin (OVA). Despite skewing towards the expression of V beta 5.2+TCR by OVA-specific CTL from C57BL/6 mice, we found a relatively high degree of diversity in V(D)J usage in both TCR alpha- and beta-chains. Closer examination showed that the majority of these sequences encoded negatively and positively charged residues at their respective TCR alpha- and beta-chain VJ or VDJ junctions. These junctions form the third complementarity-determining regions (CDR3) of the TCR polypeptides involved in the direct interaction with the class I-bound peptide. Crystallographic analyses of Kb-peptide complexes predict that the major determinant from OVA, peptide OVA257-264 (SIINFEKL), contains two exposed charged side chains which can contact the TCR. These are the negatively charged glutamic acid at determinant position 6 (P6) and the positively charged lysine at P7. To examine whether the TCR alpha-chain makes contact with P7 lysine, we established a single chain TCR transgenic C57BL/6 mouse line where all T cells express a TCR beta-chain derived from the V beta 5.2+ clone B3. OVA-specific T cells derived from in vivo primed transgenic mice preferentially expressed TCR alpha-chains that also contained negatively charged junctional residues despite some further variation in V alpha and J alpha sequences. Stimulation of naive TCR beta-chain transgenic T cells with a P7 substitution peptide analogue induced a T cell response that was no longer cross-reactive with the wild-type OVA257-264 determinant, suggesting that the TCR alpha-chain from the T cell clone B3 can determine the specificity for this residue. Consequently, these results reveal the existence of conserved residues in the CDR3 of TCR alpha- and beta-chains specific for OVA257-264 and identify their possible orientation over the peptide-class I complex.

Analysis of tetanus toxin peptide/DR recognition by human T cell receptors reconstituted into a murine T cell hybridoma

We have previously reported that human T cell receptors (TcR) selected in the class II-restricted (HLA-DRB1*1302) response to a tetanus toxin peptide (tt830-843) frequently used the V beta 2 germ-line segment which paired with several V alpha segments and that the putative CDR3 of both alpha and beta chains showed remarkable heterogeneity. To analyze the structural basis for recognition of the tt830-843/DR complex, five of these TcR were reconstituted into a murine T cell hybridoma, 58 alpha- beta-, by expressing the human alpha and beta variable regions joined to the mouse alpha and beta constant regions, respectively. The chimeric TcR, expressing the same V beta germ-line segment (V beta 2), two expressing V alpha 21.1, two V alpha 17.1 and one V alpha 8.1 were shown to have the expected antigen specificity and DR restriction. Two lines of evidence suggested that the putative CDR3, although not conserved in these TcR, played a key role in recognition. First, two TcR with identical V germ-line segments but distinct CDR3 showed large difference in their capacity to react with the ligand. Second, interchanging the alpha and beta chains from tt830-843/DR1302-specific TcR which differed in their CDR3 sequences invariably led to loss of recognition. We also asked whether germ-line V alpha 17.1 could functionally replace V alpha 21.1, as they appear to be related in their primary sequence. However, as in the case of CDR3 exchanges, V alpha replacement abrogated TcR reactivity. Taken together, these data underline the fine interdependence of the structural components of the TcR binding site in defining a given specificity. Four of the TcR studied displaying promiscuous recognition were also tested against different DR alleles and site-directed mutants. The results of these experiments suggested that, in spite of their structural heterogeneity, anti-tt830-843 TcR may have a similar orientation with respect to the peptide/DR complex. The reconstitution system described herein should represent a valuable tool for detailed studies of human TcR specificity.

Conservation of T cell receptor usage by HLA B27-restricted influenza-specific cytotoxic T lymphocytes suggests a general pattern for antigen-specific major histocompatibility complex class I-restricted responses

Eight HLA B27-restricted influenza A virus nucleoprotein 383-391-specific cytotoxic T lymphocyte (CTL) clones were obtained from three unrelated donors following natural infection. T cell receptor (TcR) usage was studied using the "anchored" polymerase chain reaction. TcR alpha-chain usage was restricted with three predominant V alpha (V alpha 12.1, 14.1, 22) and two predominant J alpha segments. beta-chain variable-region usage was also conserved, with V beta 7 being used by five clones despite contributing less than 2% of peripheral blood lymphocyte V beta sequences of one individual studied. The TcR beta-chain junctional region was highly conserved even between CTL clones from unrelated individuals, with a negatively charged amino acid, contributed to by N-region addition, encoded at position 97 in all but two clones. This study shows that peptide-specific HLA B27-restricted CTL following influenza virus infection use very similar TcR and, when considered with previous studies, suggests a pattern of TcR conservation for major histocompatibility complex class I-restricted responses. No difference in TcR usage was detected between one healthy donor and two with HLA B27-associated arthritis.

Restricted T cell receptor expression by human T cell clones specific for mycobacterial 65-kDa heat-shock protein: selective in vivo expansion of T cells bearing defined receptors

We have examined the T cell receptor (TcR) expression of clones specific for epitopes of mycobacterial 65-kDa heat-shock protein (hsp65) in the context of two different HLA molecules, and used this system as a model to assess the selection of T cells responsive to this antigen in vivo. DR3-restricted clones were raised from both the synovial fluid (SF) and peripheral blood (PB) of a patient with reactive arthritis in three separate cloning events. Five of five SF-derived clones tested expressed either V beta 5.2 or a closely related beta chain, V beta 5.6. The alpha chains expressed by V beta 5.2+ and V beta 5.6+ clones were from different families, V alpha 2.4 and V alpha 23.2, respectively. Nine of ten clones derived from two cloning procedures on PB taken 3 years later also expressed either V beta 5.2 or V beta 5.6. This suggests that the TcR repertoire for recognizing this major histocompatibility complex/peptide complex is relatively restricted and favors the use of V beta 5. Conservation of the beta chain third complementarity-determining region (CDR3) sequence was not evident, however. Sequencing alpha and beta chains of representative V beta 5.2+ and V beta 5.6+ PB-derived clones revealed TcR which were identical to those utilized by the SF-derived clones, showing that the repertoire for recognition of this antigen is stable over time. Similar studies of TcR expression were carried out on hsp65-specific, DP4-restricted clones derived from the SF of a patient with rheumatoid arthritis by two independent cloning procedures. There was conservation of alpha chain usage, since all clones expressed a member of the V alpha 1 family, but again CDR3 sequence conservation was not apparent. beta chain usage was not restricted since different clones expressed V beta 6.7, V beta 22.3 and V beta 12. Subtle differences in epitope specificity were detected for two clones with differing TcR. Once more, T cell clones with identical alpha and beta TcR chains were obtained from the separate cloning procedures, suggesting oligoclonalty of T cells with this defined specificity in the patient's SF.

Characterization of T cell repertoire changes in acute Kawasaki disease

Kawasaki disease (KD) is an acute multisystem vasculitis of unknown etiology that is associated with marked activation of T cells and monocyte/macrophages. Using a quantitative polymerase chain reaction (PCR) technique, we recently found that the acute phase of KD is associated with the expansion of T cells expressing the V beta 2 and V beta 8.1 gene segments. In the present work, we used a newly developed anti-V beta 2 monoclonal antibody (mAb) and studied a new group of KD patients to extend our previous PCR results. Immunofluorescence analysis confirmed that V beta 2-bearing T cells are selectively increased in patients with acute KD. The increase occurred primarily in the CD4 T cell subset. The percentages of V beta 2+ T cells as determined by mAb reactivity and flow cytometry correlated linearly with V beta expression as quantitated by PCR. However, T cells from acute KD patients appeared to express proportionately higher levels of V beta 2 transcripts per cell as compared with healthy controls or convalescent KD patients. Sequence analysis of T cell receptor beta chain genes of V beta 2 and V beta 8.1 expressing T cells from acute KD patients showed extensive junctional region diversity. These data showing polyclonal expansion of V beta 2+ and V beta 8+ T cells in acute KD provide additional insight into the immunopathogenesis of this disease.