H-2 antigen-specific cytotoxic T cells induced by concanavalin A: estimation of their relative frequency

Secreted heat shock protein gp96-Ig: next-generation vaccines for cancer and infectious diseases

Over the past decade, our laboratory has developed a secreted heat shock protein (HSP), chaperone gp96, cell-based vaccine that generates effective anti-tumor and anti-infectious immunity in vivo. Gp96-peptide complexes were identified as an extremely efficient stimulator of MHC I-mediated antigen cross-presentation, generating CD8 cytotoxic T-lymphocyte responses detectable in blood, spleen, gut and reproductive tract to femto-molar concentrations of antigen. These studies provided the first evidence that cell-based gp96-Ig-secreting vaccines may serve as a potent modality to induce both systemic and mucosal immunity. This approach takes advantage of the combined adjuvant and antigen delivery capacity of gp96 for the generation of cytotoxic immunity against a wide range of antigens in both anti-vial and anti-cancer vaccination. Here, we review the vaccine design that utilizes the unique property/ability of endoplasmic HSP gp96 to bind antigenic peptides and deliver them to antigen-presenting cells.

Theories and quantification of thymic selection

The peripheral T cell repertoire is sculpted from prototypic T cells in the thymus bearing randomly generated T cell receptors (TCR) and by a series of developmental and selection steps that remove cells that are unresponsive or overly reactive to self-peptide–MHC complexes. The challenge of understanding how the kinetics of T cell development and the statistics of the selection processes combine to provide a diverse but self-tolerant T cell repertoire has invited quantitative modeling approaches, which are reviewed here.

License to kill: Formulation requirements for optimal priming of CD8(+) CTL responses with particulate vaccine delivery systems

Induction of CD8(+) T-cell responses is critical for the immunological control of a variety of diseases upon vaccination. Modern subunit vaccines are based on highly purified recombinant proteins. The high purity represents a major advancement in terms of vaccine safety compared to previous vaccination strategies with live attenuated or whole killed pathogens, but typically renders vaccine antigens poorly immunogenic and insufficient in mobilizing protective immunity. Adjuvants are therefore needed in vaccine formulations to enhance, direct and maintain the immune response to vaccine antigens. However, a weakness of many adjuvants is the lack of induction of CD8(+) T-cell responses against protein antigens, which are required for protection against challenging and difficult infectious diseases such as AIDS and for therapeutic cancer vaccination. Within the last decade, adjuvant systems that can induce CD8(+) T-cell responses have been developed and the first clinical trials demonstrating the clinical relevance of such formulations have been performed. This paper reviews the current status of lipid- and polymer-based particulate antigen delivery systems capable of stimulating CD8(+) T-cell immunity with special focus on mechanisms of priming and pharmaceutical requirements for optimal activation of cytotoxic T-lymphocytes that can kill virus-infected or abnormal (cancer) cells.

Lipid-dependent cytotoxicity by the lipase PLRP2 and by PLRP2-positive cytotoxic T lymphocytes (CTLs)

IL-4 induces a lipase, pancreatic lipase related protein 2 (PLRP2), in cytotoxic T lymphocytes (CTLs). Because PLRP2 in semen can mediate lipid-dependent toxicity to sperm, we questioned whether CTL-derived PLRP2 could support similar cytotoxicity toward tumor cells. Recombinant PLRP2 was toxic to P815 tumor cells in 48 h when lipid and another protein, colipase, were present. However, PLRP2-positive CTLs (induced with many lots of IL-4) were unable to mediate lipid-dependent cytotoxicity. Notably, CTLs induced with only one lot of IL-4 had lipid-dependent cytotoxicity. The exceptional lot of IL-4 was effective in multiple experiments at inducing lipid-dependent cytotoxicity. The lipid-dependent cytotoxicity it induced was determined to be perforin-independent. CTLs induced with IL-4 that was unable to induce lipid-dependent cytotoxicity had mRNA for PLRP2 but not mRNA for colipase. Therefore, we added exogenous colipase to the CTL assays but still cytotoxicity was unchanged. We conclude (1) that lipid-dependent cytotoxicity, promoted by the lipase PLRP2 and colipase, will kill tumor cells and (2) that more than PLRP2 alone is required for lipid-dependent cytotoxicity mediated by CTLs.

Pancreatic lipase-related protein 2 (PLRP2) induction by IL-4 in cytotoxic T lymphocytes (CTLs) and reevaluation of the negative effects of its gene ablation on cytotoxicity

Pancreatic lipase-related protein 2 (PLRP2) is induced by IL-4 in vitro in cytotoxic T lymphocyte (CTL) clones and CTLs from immunized wild-type (WT) PLRP2(+/+) are more cytotoxic than PLRP2(-/-) CTLs, suggesting to previous investigators that the lipase PLRP2 might support CTL functions. Here, we further evaluate PLRP2 in CTLs. We found that PLRP2 was optimally induced in splenocytes by 3.5 x 10(-8) M IL-4 by day 6 after activation and was restricted to CD8(+) T cells. PLRP2 mRNA was detected inconsistently (and at low levels) after activation in the presence of IL-2. Cytotoxicity in 4 h (51)Cr assays of WT CTLs was approximately 3-fold the activity of PLRP2(-/-) CTLs cultured with IL-4 and, with IL-2, was unexpectedly approximately 2 fold the activity of PLRP2(-/-) CTLs. Thus, PLRP2 gene ablation affected short-term (perforin-dependent) cytotoxicity, even under the IL-2 conditions. Other variables failed to account for the reduced cytotoxicity. Granzyme B levels, activation markers, and CD8(+) T cell frequencies were similar for WT vs. PLRP2(-/-) CTLs (with either cytokine). Addition of rPLRP2 to IL-4 induced PLRP2(-/-) CTLs (or to cytotoxic granule extracts) failed to increase lysis, suggesting that the missing mediator is more than released PLRP2. Cytotoxicity of WT and PLRP2(-/-) CTLs was similar in 2-day tumor survival assays with IL-4, which can be mediated by perforin-independent mechanisms. We conclude that extracellular PLRP2 lipase is unable to directly augment the cytotoxicity that was lost by PLRP2 ablation and that after reevaluation, the question of what is PLRP2's role in CD8 T cells is still unanswered.

Th1/Th2 patterns and balance in cytokine production in the parents and infants of a large birth cohort

Regulation of human immune cell cytokine production in vivo is not well understood due in part to limitations on imposing experimental conditions. We proposed that life-imposed conditions (pregnancy, birth, age, gender), combined with large sample size, repeat sampling, and family-based recruitment would serve to reveal peripheral blood cell-derived cytokine patterns reflective of in vivo regulation regarding Th1/Th2 balance and familial correlation. Mononuclear cells were obtained from 483 trios in the Tucson Infant Immune Study: from mothers pre- and postpartum, infants at birth and at 3 mo, and fathers. Con A/PMA-stimulated supernatants were assayed by ELISA for IFN-gamma, IL-4, IL-13, IL-5, and IL-10 and allergen-stimulated supernatants for IFN-gamma, IL-4, and IL-13. Mitogen-stimulated prepartum samples were not globally Th2 biased, differing from postpartum only by a modestly reduced IFN-gamma:IL-5 ratio. Prepartum samples actually produced less IL-10 and IL-13 although more IL-5 than paternal samples. Newborns were also not globally Th2 biased, with mitogen stimulation producing approximately 10-fold less IL-4, IL-5, and IFN-gamma than adults but only 2- to 3-fold less IL-13 and IL-10. Despite these group differences, all cytokines showed marked positive intraindividual correlations (all p < 0.001). Allergen stimulation gave results consistent with a lack of global Th2 bias. Mitogen stimulation revealed parent-child and parent-parent correlations. Thus, rather than a global Th2 bias, cytokine production in pregnant mothers and newborns appears regulated so as to maintain a relative balance among the cytokines, with the nature of the balance differing in mothers and infants and with production influenced by familial factors that include shared environment.

Rapid quantification of naive alloreactive T cells by TNF-alpha production and correlation with allograft rejection in mice

Allograft transplantation requires chronic immunosuppression, but there is no effective strategy to evaluate the long-term maintenance of immunosuppression other than assessment of graft function. The ability to monitor naive alloreactive T cells would provide an alternative guide for drug therapy at early, preclinical stages of graft rejection and for evaluating tolerance-inducing protocols. To detect and quantify naive alloreactive T cells directly ex vivo, we used the unique ability of naive T cells to rapidly produce TNF-alpha but not IFN-gamma. Naive alloreactive T cells were identified by the production of TNF-alpha after a 5-hour in vitro stimulation with alloantigen and were distinguished from effector/memory alloreactive T cells by the inability to produce IFN-gamma. Moreover, naive alloreactive T cells were not detected in mice tolerized against specific alloantigens. The frequency of TNF-alpha-producing cells was predictive for rejection in an in vivo cytotoxicity assay and correlated with skin allograft rejection. Naive alloreactive T cells were also detected in humans, suggesting clinical relevance. We conclude that rapid production of TNF-alpha can be used to quantify naive alloreactive T cells, that it is abrogated after the induction of tolerance, and that it is a potential tool to predict allograft rejection.

Constitutive expression of the pre-TCR enables development of mature T cells

Expression and signalling through the pre-TCR and the TCRalphabeta resemble two critical checkpoints during T cell development. We investigated to which extent a pre-TCR can functionally replace mature TCRalpha chains during T cell development. For this purpose, transgenic mice were generated expressing the pre-TCRalpha (pTalpha) under the transcriptional control of TCRbeta regulatory elements. We report here on the interesting finding that constitutive pTalpha expression allows complete T cell maturation. The pre-TCR complex permits a subset of beta-selected thymocytes to mature in the absence of TCRalpha into peripheral T cells (betaT cells) comprising up to 10% of all lymphocytes. Lymphopenia-driven proliferation of these betaT cells is similar to that of conventional alphabetaT cells. Furthermore, betaT cells proliferated and acquired effector function upon stimulation with allogeneic MHC.

Direct visualization of cross-reactive effector and memory allo-specific CD8 T cells generated in response to viral infections

CD8 T cell cross-reactivity between heterologous viruses has been shown to provide protective immunity, induce immunopathology, influence the immunodominance of epitope-specific T cell responses, and shape the overall memory population. Virus infections also induce cross-reactive allo-specific CTL responses. In this study, we quantified the allo-specific CD8 T cells elicited by infection of C57BL/6 (B6) mice with lymphocytic choriomeningitis virus (LCMV). Cross-reactive LCMV-specific CD8 T cells were directly visualized using LCMV peptide-charged MHC tetramers to costain T cells that were stimulated to produce intracellular IFN-gamma in response to allogeneic target cells. The cross-reactivity between T cells specific for LCMV and allogeneic Ags was broad-based, in that it involved multiple LCMV-derived peptides, but there were distinctive patterns of reactivity against allogeneic cells with different haplotypes. Experiments indicated that this cross-reactivity was not due to the expression of two TCR per cell, and that the patterns of allo-reactivity changed during sequential infection with heterologous viruses. The allo-specific CD8 T cells generated by LCMV infection were maintained at relatively high frequencies in the memory pool, indicating that memory allo-specific CD8 T cell populations can arise as a consequence of viral infections. Mice previously infected with LCMV and harboring allo-specific memory T cells were refractory to the induction of tolerance to allogeneic skin grafts.

Deriving quantitative constraints on T cell selection from data on the mature T cell repertoire

The T cell repertoire is shaped in the thymus through positive and negative selection. Thus, data about the mature repertoire may be used to infer information on how TCR generation and selection operate. Assuming that T cell selection is affinity driven, we derive the quantitative constraints that the parameters driving these processes must fulfill to account for the experimentally observed levels of alloreactivity, self MHC restriction and the frequency of cells recognizing a given foreign Ag. We find that affinity-driven selection is compatible with experimental estimates of these latter quantities only if 1) TCRs see more peptide residues than MHC polymorphic residues, 2) the majority of positively selected clones are deleted by negative selection, 3) between 1 and 3.6 clonal divisions occur on average in the thymus after completion of TCR rearrangement, and 4) selection is driven by 103-105 self peptides.

A quantitative theory of affinity-driven T cell repertoire selection

Binding of the T cell antigen receptor (TCR) to peptides presented on molecules encoded by major histocompatibility complex (MHC) genes is the key event driving T cell development and activation. Selection of the T cell repertoire in the thymus involves two steps. First, positive selection promotes the survival of cells binding thymic self-MHC-peptide complexes with sufficient affinity. The resulting repertoire is self-MHC restricted: it recognizes foreign peptides presented on self, but not foreign MHC. Second, negative selection deletes cells which may be potentially harmful because their receptors interact with self-MHC-peptide complexes with too high an affinity. The mature repertoire is also highly alloreactive: a large fraction of T cells respond to tissues harboring foreign MHC. We derive mathematical expressions giving the frequency of alloreactivity, the level of self-MHC restriction, and the fraction of the repertoire activated by a foreign peptide, as a function of the parameters driving the generation and selection of the repertoire: self-MHC and self-peptide diversity, the stringencies of positive and negative selection, and the number of peptide and MHC polymorphic residues that contribute to T cell receptor binding. Although the model is based on a simplified digit string representation of receptors, all the parameters but one relate directly to experimentally determined quantities. The only parameter without a biological counterpart has no effect on the model's behavior besides a trivial and easily preventable discretization effect. We further analyse the role of the MHC and peptide contribution to TCR binding, and find that their relative, rather than absolute value, is important in shaping the mature repertoire. This result makes it possible to adopt different physical interpretations for the digit string formalism. We also find that the alloreactivity level can be inferred directly from data on the stringency of selection, and that, in agreement with recent experiments, it is not affected by thymic selection.

In Vivo T-Lymphocyte Tolerance in the Absence of Thymic Clonal Deletion Mediated by Hematopoietic Cells

Thymic negative selection renders the developing T-cell repertoire tolerant to self-major histocompatability complex (MHC)/peptide ligands. The major mechanism of induction of self-tolerance is thought to be thymic clonal deletion, ie, the induction of apoptotic cell death in thymocytes expressing a self-reactive T-cell receptor. Consistent with this hypothesis, in mice deficient in thymic clonal deletion mediated by cells of hematopoietic origin, a twofold to threefold increased generation of mature thymocytes has been observed. Here we describe the analysis of the specificity of T lymphocytes developing in the absence of clonal deletion mediated by hematopoietic cells. In vitro, targets expressing syngeneic MHC were readily lysed by activated CD8+ T cells from deletion-deficient mice. However, proliferative responses of T cells from these mice on activation with syngeneic antigen presenting cells were rather poor. In vivo, deletion-deficient T cells were incapable of induction of lethal graft-versus-host disease in syngeneic hosts. These data indicate that in the absence of thymic deletion mediated by hematopoietic cells functional T-cell tolerance can be induced by nonhematopoietic cells in the thymus. Moreover, our results emphasize the redundancy in thymic negative selection mechanisms.

In Vivo T-Lymphocyte Tolerance in the Absence of Thymic Clonal Deletion Mediated by Hematopoietic Cells

Thymic negative selection renders the developing T-cell repertoire tolerant to self-major histocompatability complex (MHC)/peptide ligands. The major mechanism of induction of self-tolerance is thought to be thymic clonal deletion, ie, the induction of apoptotic cell death in thymocytes expressing a self-reactive T-cell receptor. Consistent with this hypothesis, in mice deficient in thymic clonal deletion mediated by cells of hematopoietic origin, a twofold to threefold increased generation of mature thymocytes has been observed. Here we describe the analysis of the specificity of T lymphocytes developing in the absence of clonal deletion mediated by hematopoietic cells. In vitro, targets expressing syngeneic MHC were readily lysed by activated CD8+ T cells from deletion-deficient mice. However, proliferative responses of T cells from these mice on activation with syngeneic antigen presenting cells were rather poor. In vivo, deletion-deficient T cells were incapable of induction of lethal graft-versus-host disease in syngeneic hosts. These data indicate that in the absence of thymic deletion mediated by hematopoietic cells functional T-cell tolerance can be induced by nonhematopoietic cells in the thymus. Moreover, our results emphasize the redundancy in thymic negative selection mechanisms.

Alloreactive cytotoxic T-lymphocyte-defined HLA-B7 subtypes differ in peptide antigen presentation

We investigated T-cell-defined HLA-B7 subtypes using cDNA sequencing, analysis of bound peptides, and reactivity with a panel of alloreactive cytotoxic T-lymphocyte (CTL) clones. Three subtypes (HLA-B*0702, HLA-B*0703, and HLA-B*0705) differ in nucleotide and predicted amino acid sequence. CTL reactivity and pooled peptide sequencing show that these three HLA-B7 subtypes bind distinct but overlapping sets of peptides. In particular B*0702 expresses D pocket residue Asp 114 and binds peptides with P3 Arg, whereas B*0705 expresses D pocket residue Asn 114 and binds peptides with P3 Ala, Leu, and Met. Consistent with different peptide-binding specificities, three alloreactive CTL differentiate between cells expressing B*0702, B*0703, and B*0705 by detecting specific peptide/HLA-B7 complexes. In contrast, three other T-cell-defined HLA-B7 subtypes are identical to HLA-B*0702. The B*0702-expressing cell lines are differentiated by two of ten CTL clones. One CTL clone differentiates B*0702-expressing cells by their ability to present peptide antigen. Thus differences in peptide presentation can explain differential CTL recognition of cell lines expressing structurally identical and variant HLA-B7.

Analysis of cytotoxic T lymphocyte responses to SIV proteins in SIV-infected macaques using antigen-specific stimulation with recombinant vaccinia and fowl poxviruses

Methods to analyze CD8+ CTL responses to simian immunodeficiency virus (SIV)-encoded proteins are essential to understand lentivirus immunopathogenesis and protective immune responses. Recombinant infectious shuttle vectors are useful for analyzing CTL responses to many viruses, including HIV. Therefore, CTL responses in SIV-infected Macaca fascicularis to SIV env and SIV gag/pol were evaluated using specific antigen stimulation with recombinant vaccinia (rVV) and fowl poxviruses (rFPV) containing SIV genes. Peripheral blood mononuclear cells from SIV-infected animals were stimulated with autologous cells infected with rVV expressing SIV env/gag/pol, and CTLs specific for SIV env and for SIV gag/pol were detected by testing for lytic activity in target cells expressing these genes separately. Lymphocyte subset purifications from the effector population demonstrated that the CTL response was mediated by CD8+ cells, and the use of brefeldin A to selectively block antigen presentation in association with MHC class I products affirmed this cytolytic activity was class I restricted. The use of rVV to analyze responses to SIV genes is potentially problematic in hosts immunized to vaccinia. Fowl poxvirus is an alternative virus that has many of the molecular advantages of vaccinia virus but is genomically distinct. Therefore, the ability of rFPV to expand and detect SIV-specific CTLs was evaluated. Although there was no cytopathic effect following infection with rFPV, macaque cells infected with this vector did express rFPV gene products, and could be used as stimulator and target cells to detect SIV-specific CD8+ CTLs. The results suggest that these recombinant viral vectors can be used to specifically stimulate CD8+, MHC class I-restricted CTLs reactive to SIV proteins, and should facilitate evaluating CTL responses in both SIV-infected animals and animals vaccinated against SIV.

Expression in transgenic mice of class I histocompatibility antigens controlled by the metallothionein promoter

To study the effects of increased expression of major histocompatibility complex class I molecules on the development of self-tolerance, transgenic mice were produced that expressed the H-2Kb gene under the control of the metallothionein promoter. Administration of zinc enhanced transgene expression in liver, kidney and exocrine pancreas. No evidence suggestive of an autoimmune response was found in transgene-expressing tissues in mice otherwise allogeneic to H-2Kb. Despite this lack of responsiveness in vivo, T cells could be stimulated in vitro to lyse H-2Kb-bearing target cells. No infiltration was detected in transgenic mice after irradiation and reconstitution with bone marrow cells. When spleen cells were used for reconstitution, however, dense lymphocytic infiltration was seen, particularly in the portal tracts of the liver, and this was accompanied by piecemeal necrosis and apoptosis of periportal hepatocytes. This aggressive response progressively diminished with time, and by 12 weeks after reconstitution many of the portal tracts were free of infiltration while the others showed no accompanying necrosis. The picture at this stage was similar to that seen in chronic persistent hepatitis. These results suggest that, in addition to negative selection in the thymus, peripheral mechanisms not involving clonal deletion or permanent clonal anergy can prevent immune responses to self molecules.

Clonal specificity analysis of mitogen-activated murine T lymphoblasts

We have determined the frequencies and specificities of MHC-reactive and MHC-restricted cytotoxic T lymphocyte precursors (CTL-p) in mitogen (ConA)-activated splenocytes of normal unprimed mice. The limiting dilution (LD) system supported the growth of one out of three Lyt2+ T cell blasts. The generated CTL-populations lysed blast cell targets specifically as determined by split well analyses. MHC-gene product expression was necessary for lysis to occur, since MHC-negative F9 teratocarcinoma cells were not lysed. The frequency determinations and split well analyses revealed: 1) equally high numbers (approximately 1/100) of CTL-p that generated specific allo-MHC or self-MHC reactive CTL populations, 2) high frequencies of CTL-p which recognized hapten (TNP) or minor H (MH)-antigens in the context of self MHC or allo-MHC determinants. The results are discussed with respect to antigen, restriction and receptor specificities of mitogen-activated unprimed T cell blasts.

The molecular basis of alloreactivity in antigen-specific, major histocompatibility complex-restricted T cell clones

We have studied the relationship between major histocompatibility complex (MHC)-restricted antigen recognition and alloreactivity by examining T cell receptor (TCR) alpha and beta gene expression in cytochrome c-specific, Ek alpha:Ek beta (Ek)-restricted helper T cell clones derived from B10.A mice. The clones could be segregated on the basis of four distinct alloreactivity patterns. Clones cross-reactive for three different allogeneic la molecules (As alpha:As beta [As], Ab alpha:Ab beta [Ab], Ek alpha: Eb beta [Eb]) expressed the same V alpha and V beta gene segments, generating the distinct alloreactive specificities via unique V alpha-J alpha and V beta-D beta-J beta joining events. Ek alpha:Es beta (Es)-alloreactive B10.A clones expressed the same V alpha, J alpha, and V beta segments as an Es-restricted, Ek-alloreactive, cytochrome c-specific, H-2-congenic B10.S(9R) clone. This homology between TCRs mediating allorecognition of la molecules and recognition of the same la molecules as restriction elements associated with nominal antigen suggests that MHC-restricted recognition and allorecognition represent differences in the affinity of the TCR-MHC molecule interaction.

The cytotoxic T-cell response to Ia antigens: lack of correlation between the level of specific cytotoxicity obtained in primary mixed lymphocyte reaction and the frequency of specific cytotoxic T lymphocyte

We have investigated the cytotoxic response to allogeneic I-E and I-A antigens in bulk culture and limiting dilution experiments. A high degree of specific killing could be generated from unprimed T cells of I-E-negative strains upon stimulation with cells expressing I-E. In such conditions, cytotoxic T lymphocytes (CTL) were generated in the absence of a specific proliferative response. The frequency determinations by means of limiting dilution experiments showed that I-E-specific CTL precursors were much less frequent than the K and D specific precursors. The results suggest the existence of a population of I-E-specific CTL that failed to grow under conditions that allowed the growth of class I-specific CTL.

Degeneracy of H-2 recognition by cytotoxic T lymphocytes: 10% of the total repertoire is "specific" for a given haplotype and up to 1% is self-H-2 reactive

The frequency of specific cytotoxic T lymphocytes (CTL) precursors in the total CTL pool was analyzed in a lectin-driven limiting dilution system. We found that up to 10% of the expressed CTL repertoire in a normal mouse is "specific" for a given allogeneic H-2 haplotype. Split-well analysis under clonal conditions demonstrates that the antigens recognized by the effector CTL are H-2 encoded. A high frequency of CTL "specific" for self-H-2 antigens was revealed in all the experiments, accounting for about 1% of the total inducible pool of CTL. These results suggest a high degree of degeneracy of H-2 recognition by CTL and the immunocompetence of self-H-2-reactive CTL precursors in normal individuals.

Proliferative kinetics, phenotype and cytotoxic function of thymic and peripheral T-cell colonies

Cells produced in murine T-cell colonies grown in methylcellulose have been studied to evaluate their proliferation, phenotypic differentiation, and ability to give rise to cytotoxic cells. Colony-forming cells from presumably cortical or medullary thymocytes, separated by peanut agglutination, or from lymph nodes, showed rapid proliferation regardless of their origin, although cortical thymic colony cells showed significantly slower proliferation from day 10 to day 12 of culture. Essentially all the colony cells maintained the Lyt-1+2+ phenotype of the colony-forming cells, and no L3T4+ cells were found. The colony cells were characterized as rather mature cells by being strongly H-2-positive, and, except for a few cells, by lacking the TL antigen. Colony cells maintained the Lyt-1+2+ phenotype after expansion in liquid culture, and both cortically and medullary derived colony cells showed lectin-dependent cytotoxic activity against P-815 tumour cells. We conclude that our assay for growing thymus-derived T-cell colonies results in the proliferation of a phenotypically and functionally relatively mature cytotoxic T-lymphocyte progeny.

Maternal immunoregulation: interrelationship between alloreactive and anti-self plus conventional antigen T sets of cells

In a previous paper we reported early immunoregulatory mechanisms involving not only the appearance of progressive suppression but also significant increases in alloreactive T levels in paraaortic lymph nodes (PALN) and spleen, not only in allogeneic but also in syngeneic pregnancies. Taking into account the hypothesis of the superposition of the alloreactive and the anti-self plus conventional antigens T sets of cells, we investigated whether immunization with conventional antigens was able to alter alloreactive T levels. Weekly i.p. doses of rabbit red bloods cells (RRBC) in BALB/c mice resulted in a dose-dependent increase in spleen alloreactivity as determined by graft-versus-host (GvH) assays in strain combinations differing at H-2 level but not in those sharing the same H-2 with BALB/c. The increases could be significantly decreased by an anti-idiotype anti-RRBC serum. Pretreatment with i.p. weekly doses of sheep red blood cells (SRBC) before mating was able to induce dose-dependent fetal damage when the parents differed at the H-2 level. SRBC immunization in one of the uterine horns induced increases in PALN weight which were much higher in progesterone-pseudopregnant than in virgin mice; T alloreactivity was significantly increased in the draining PALN only in pseudopregnant females. These results favour the postulation of the superposition between the alloreactive and the anti-self plus conventional antigens T sets of cells and suggest a possible role for conventional fetal antigens (non H-2) in triggering immunoregulatory mechanisms operating in pregnancy.

Clonal specificity of concanavalin A-induced cytotoxic T lymphocytes

The specificity of polyclonally induced cytotoxic T lymphocyte (CTL) precursors has been analyzed under clonal conditions. Primary clones of concanavalin A-inducible CTL, if tested on different targets, revealed that they could distinguish between (a) two different allogeneic tumor targets; (b) allogeneic and syngeneic tumor targets, and (c) syngeneic B blasts and tumor targets. No "nonspecific" CTL clones were generated under these culture conditions, and all clones were found to display classical immunological specificity.

Developmental regulation of T-cell receptor gene expression

In contrast to B cells or their antibody products, T lymphocytes have a dual specificity, for both the eliciting foreign antigen and for polymorphic determinants on cell surface glycoproteins encoded in the major histocompatibility complex (MHC restriction). The recent identification of T-cell receptor glycoproteins as well as the genes encoding T-cell receptor subunits will help to elucidate whether MHC proteins and foreign antigens are recognized by two T-cell receptors or by a single receptor. An important feature of MHC restriction is that it appears to be largely acquired by a differentiating T-cell population under the influence of MHC antigens expressed in the thymus, suggesting that precursor T cells are selected on the basis of their reactivity with MHC determinants expressed in the host thymus. To understand this process of 'thymus education', knowledge of the developmental regulation of T-cell receptor gene expression is necessary. Here we report that whereas messenger RNAs encoding the beta-and gamma-subunits are relatively abundant in immature thymocytes, alpha mRNA levels are very low. Interestingly, whereas alpha mRNA levels increase during further development and beta mRNA levels stay roughly constant, gamma mRNA falls to very low levels in mature T cells, suggesting a role for the gamma gene in T-cell differentiation.

A quantitative assay detecting small numbers of effector helper T cells, regardless of clonal specificity

We have developed a new assay for quantitative detection of all helper T cells that can induce normal B lymphocytes to proliferation and Ig secretion. To establish the optimal assay conditions, we have used cloned T helper cells of defined specificities that had previously been shown to activate normal B lymphocytes expressing the specific antigen(s) on direct cellular interactions. As shown in this paper, 'irrelevant' B lymphocytes--that is, those that do not express either antigen or restriction elements recognized by the effector helper T cells--can also be induced in the presence of appropriate concentrations of pokeweed mitogen which are not mitogenic for the 'target' B lymphocytes. 'Nonspecific' plaque-forming cell responses are of the same magnitude as those provided to specifically triggered targets and equal or better than those induced by lipopolysaccharide. The assay is highly sensitive and enables 'semi-quantitative' detection of less than 20-30 effector T cells per culture. Since effector helper T cells can be detected regardless of the clonal specificity, the assay appears useful for quantitative studies of various populations of T helper cells displaying mixed specificities and for the classification of cells with unknown functions.

Regulation of cytotoxic lymphocyte precursors: I. Interactions between concanavalin A and T cell growth factors

The induction of cytotoxic T lymphocytes by concanavalin A has been analyzed under conditions of limit dilution. The dose-response curves deviate from linearity in a way that has been interpreted as revealing successive zones of suppression as the cell concentration was increased. The magnitude of suppression was influenced by both the concentration of concanavalin A and the amount of T cell growth factors added to the culture. These regulatory events involve the cytotoxic T cell clones produced by (CBA X DBA)F1 spleen cells which are detected by DBA mastocytoma (P815) targets at a maximum detectable frequency of 1 in 2000 cells. Similar multiphase dose-response data were also obtained with syngeneic and allogeneic combinations with the same target cell. It is suggested that the successive zones of suppression and activation are a consequence of the relative frequencies of CTL-P, suppressive and helper cells, and the ease with which the cells are activated in limit dilution cultures. The experimental approach illustrates how CTL production can be manipulated to study the balance of signals required to control effector cell production.

Graft-versus-host reactions in F1 hybrid mice: MHC-restriction-independent generalized depression of virus-specific cytotoxic T cell response

A graft-versus-host reaction (GVHR) was induced in F1 hybrid mice by intravenous injection of parental spleen cells. A possible effect generated by recipient F1 mice of a GVHR on the restriction specificities of anti-viral cytotoxic T cells was investigated. (A/J X C57BL/6) F1 recipients were injected with 1 X 10(8) or 2 X 10(7) spleen cells from either parent. Zero to two weeks later during an acute GVHR or 12 to 26 weeks later during a chronic GVHR, spleen cells from these F1 recipients were assayed for their capacity to generate vaccinia (or lymphocytic choriomeningitis) virus-specific cytotoxic T cells. No effect was seen when parental cells were injected with virus on the same day. During the acute phase of the GVHR, recipients of spleen cells of both doses or from either parent injected 7 or 14 days previously generated markedly fewer cytotoxic T cells with respect to both parental restriction specificities. In the more chronic situation only, recipients of 1 X 10(8) parental spleen cells showed depressed virus-specific cytotoxic responses, again both restriction specificities were affected comparably. Therefore, a GVHR depresses generation of virus-specific cytotoxic T cells in a dose- and time-dependent way, but does not measurably disturb the balance of parental 1 versus parental 2 restriction specificity in an F1 recipient.

Thymic cytotoxic T lymphocytes are primed in vivo to minor histocompatibility antigens

Potent cytotoxic T lymphocyte (CTL) activity can be derived from cultures of thymocyte responders and minor H different spleen cell stimulators. As is the case of the spleen cell response previously reported, this cytotoxic activity requires in vivo priming. We performed several experiments designed to determine whether the in vivo priming effect is due to the in situ priming of the thymocyte CTL precursors, to contamination of thymus cell preparations with cells of neighboring lymph nodes, or to the appearance in the thymus of antigen-reactive peripheral T cells. We show by depletion of peripheral cells with antilymphocyte serum and part body irradiation that recent thymic immigrants derived from the bone marrow contribute to the primed thymic response. Thymic CTL were primed in animals in which peripheral T cell responses were completely eliminated by repeated treatment in vivo with monoclonal anti-Thy-1 reagents. Primed, antigen-activated lymph node cells were also demonstrated to contribute to the thymus-derived CTL response. Thus, the minor H-specific thymic CTL response is due both to in situ priming and the immigration of activated peripheral T cells. We discuss the possible significance for models of T cell differentiation of the presence within the thymus of antigen and antigen-reactive mature T cells.

The differential effect of 2-deoxyguanosine on concanavalin A-induced suppressor and cytotoxic activity

The effect of 2-deoxyguanosine (dGuo) on the generation in vitro of nonspecific suppressor cells in murine spleen cell cultures by concanavalin A (Con A) is examined. The experiments indicate that dGuo abrogates the generation of nonspecific suppressor activity by lectin stimulation of murine spleen cells. When comparisons were made between the effect of this nucleoside on the generation of suppressor and cytotoxic cells by Con A stimulation of murine spleen cells, it was found that dGuo only affected the generation of suppressor cells. The development of lectin-stimulated cytotoxicity was not affected by dGuo. In addition it was found that dGuo does not affect the NK activity of murine spleens.

Fetal calf serum-injected F1 mice spontaneously generate specific anti-parental cytotoxic T lymphocytes in in vitro culture

Spleen cells from adult (BALB/c x AKR/J)F1 mice primed in vivo with fetal calf serum (FCS) can spontaneously generate anti-parental AKR/J cytotoxic T cells (CTL) in a 5-day in vitro culture containing 5% FCS. This response is distinguished by the following features: (i) it is anti-parental but not anti-self, and (ii) it has specificity for the Kk parental determinant as shown by mapping studies on a variety of targets and antiserum-blocking experiments. Although specifically elicited by FCS and mediated by FCS-induced T-helper cells, it is ascertained that this cytotoxicity is not directed against Kk components modified by absorbed FCS as shown by cold-target competition studies. Further experiments involved a comparative investigation of the patterns of lysis of allogenically induced CTL, FCS-induced CTL, and natural killer (NK) cytotoxic activities on tumor cell targets. The resistance of BW 5147 tumor targets to NK- and FCS-induced lysis was found to be dramatically overcome by treatment with mitomycin C, and provides circumstantial evidence for a functional relationship between the FCS-induced anti-parental CTL effectors and NK cells based on the observed similarity in lytic patterns of these two effector types. With reference to the work of other authors, the possibility that hybrid resistance and its possible in vitro counterpart, F1 anti-parental CTL cytotoxicity, and NK activity are mediated by similar or common effector mechanisms is discussed.

Study of murine lymphoid cells in situ after stimulation with Concanavalin A

The effects of Concanavalin A (Con A) on the lymphocytes in situ were investigated here by studying the blastogenesis and organization of lymphoid cells in the histological preparations of the spleen and the mesenteric lymph node and the cell death at different hours after iv administration of different doses (10, 20 and 50 micrograms/animal) of the substance. The gradual transformation of the lymphocytes into blasts was observed in the histological preparations of the spleen and the mesenteric lymph node. The rate of the change became higher with higher dose of Con A. It seems that the lymph node was affected more with in vivo Con A treatment than the spleen on account of higher percentage of blast transformation at early hour and lower density of the cells due to cell migration or cell death. Purpose of this study has been discussed.

The segregation of specific clones of cytotoxic lymphocytes in an in vitro primary response against influenza virus

CBA spleen cells have been stimulated in vitro with A/Jap influenza virus-infected CBA spleen cells to generate a 'primary' cytotoxic lymphocyte (CL) response. The culture conditions were devised to allow the segregation of individual clones of CL and cytotoxicity measured by the lysis of infected or non-infected L-929 cells. The specificity was assessed by splitting clones and measuring the ability of the clones to discriminate between pairs of targets. Influenza A/FMI and A/Jap strains were used. Subsets of clones were detected which could lyze either A/Jap-infected or A/FMI-infected target cells. In addition CL clones were found which lyzed uninfected L-929 cells and a fourth category were clones which could not discriminate between A/FMI-and A/Jap-infected targets.

Recognition of polymorphic H-2 domains by T lymphocytes. I. Functional role of different H-2 domains for the generation of alloreactive cytotoxic T lymphocytes and determination of precursor frequencies

In the present communication, the repertoire of alloreactive cytotoxic T lymphocytes (CTL) clones was quantitatively investigated by limiting dilution analysis and by target inhibition with a panel of monoclonal antibodies (mAb). These mAb have previously been shown to define two distinct alloantigenic domains, A and B, on the H-2Kk molecule. The Poisson distribution analysis of H-2Kk-specific CTL clones generated in a limiting dilution system revealed three CTL populations with different precursor frequencies. The high frequent population is suppressed by an unknown suppressive mechanism that allows less frequent CTL populations to become visible. Target inhibition studies with a panel of Kk-specific mAb showed that these CTL populations differ not only in their precursor frequency but also in their specificity for different H-2 epitopes on the Kk molecule. Thus clones of the high frequency population are almost exclusively specific for determinants within domain A. In contrast, the low frequency population displays predominant specificity for determinants of domain B, while the population with medium frequency is blocked equally well by mAb against either domains A or B. Each mAb blocked only a fraction of clones indicating that each CTL subpopulation may consist of a large number of clonotypes with specificity for different H-2 epitopes. The data suggest that CTL recognize basically the same polymorphic domains on the H-2Kk molecule defined by antibodies, and they show that regulatory mechanisms determine the expressed repertoire in CTL populations.

Cultured human T-cell lines kill autologous solid tumours

Lymphocytes from peripheral blood, lymph node, spleen and tumour of 7 patients with various carcinomas (2 lung, 3 colon, 1 gastric and 1 parotid tumour) were cultured for 15 days in conditioned media containing T-cell growth factor (TCGF; Interleukin 2) after which their cytotoxic activity against autologous tumour (and in some instances, autologous normal) cells and allogeneic tumour targets was evaluated in a short-term 51Cr-release assay. Significant cytotoxicity against autologous tumour targets was detected in at least one effector preparation from all of the patients, under conditions where, in some cases, other autologous cells (normal lung, PHA-transformed lymphocytes) were resistant. This cytotoxicity also generally extended to allogeneic tumour targets, but lysis of K562, a cell line sensitive to natural killing, occurred in only 3 of 19 effector cell preparations. The data are consistent with a polyclonal expansion of cytotoxic T-cells of tumour-bearing patients which includes the amplification of a population recognitive of antigens expressed on autologous neoplastic cells.

A one-receptor view of T-cell behaviour

The discovery of T cells and their behaviour has forced a re-evaluation of the immunological relationship between self and not-self. T cells seem to respond against foreign antigens only when the latter are in some form of association with self molecules encoded by the major histocompatibility complex. This has raised the question of whether T-cell recognition may depend on two separate receptors. I present here the case for a model of T-cell behaviour based on a single receptor.

Quantitative studies on T cell diversity. II. Determination of the frequencies and Lyt phenotypes of two types of precursor cells for alloreactive cytotoxic T cells in polyclonally and specifically activated splenic T cells

Two different limiting dilution systems have been applied to compare precursor frequencies of alloreactive cytotoxic T cells (CTL-P) in the polyclonally and specifically activated lymphocyte populations and in selected Lyt T cell subsets. Both systems make use of T cell growth factor for T cell expansion but differ with respect to the activation step in that lymphocytes are either activated directly with allogenetic stimulator cells or are sensitized polyclonally with concanavalin A (Con A) in bulk culture before their expansion under limiting dilution conditions. In polyclonally activated C57BL/6 lymphocyte populations, two types of CTL-P specific for H-2d alloantigens could be identified: a frequent set with a frequency of 1/100-1/300, and a rare set with a frequency of 1/2,000-1/8,000. In contrast, only a single CTL-P set was found in specifically activated populations with a frequency similar to that of the frequent CTL-P found on Con A blasts. In Con A blasts, the frequent at higher cell concentrations by suppressor T cells, whereas rare CTL-P were insensitive to this suppressive mechanism. Whereas in specifically activated T cells, the predominant CTL-P phenotype was Lyt-123, the predominant Lyt phenotypes for the frequent and the rare CTL-P found in Con A blasts were Lyt-123 and Lyt-123, respectively, which suggests that they represent primary and secondary CTL-P, respectively. The results are discussed with respect to previous reports on the involvement of Lyt T cell subsets in the generation of cytotoxic responses and their regulation by T suppressor cells.

T cells respond preferentially to antigens that are similar to self H-2

We have constructed bone marrow irradiation chimeras to investigate the influence of self antigens on the specificity of the T lymphocyte receptor repertoire. Bone marrow cells from (A X B)F1 mice heterozygous for the major histocompatibility genes were allowed to mature into T cells in irradiated parent A or parent B strains. More than 8 weeks after irradiation, when the lymphoid system had regenerated from the F1 stem cells, the degree of T cell reactivity to mutant major histocompatibility antigens, A', was assessed. It was found that T cells that had matured in the irradiated A mice, [F1 leads to A] chimeras, responded better to A' antigen than did T cells from the [F1 leads to B] chimeras. Because the mutant histocompatibility antigen A' is very similar in structure to A, differing only by one or a few residues, this suggests that the T cell repertoire in [F1 leads to parent] chimeras reacts preferentially with foreign antigens that are slight variants of the self antigens expressed on radiation-resistant cells--probably cells in the thymus.

Generation of cytotoxic T-lymphocyte precursor cells in T-cell colonies grown in vitro

The role of the thymus in T-lymphocyte differentiation remains unclear. The demonstration that the thymus can restrict the T-lymphocyte specificity repertoire suggests that T cells acquire specificity within the thymus. However, the demonstrations of immunocompetent helper T cells and cytotoxic T-lymphocyte precursor cells (CLPs) in athymic nude mice suggest that the acquisition of some T-cell reactivity may occur without the thymus. We have been using T-cell colonies grown in vitro as a model system for studying various aspects of T-cell differentiation in both mouse and man. In one study we showed that CLPs can be found in T-cell colonies grown from spleen cells of normal mice, each colony containing CLPs of several different specificities. The colonies containing CLPs are not clonal, appearing to have a colony-forming unit (CFU-T) of two (perhaps three) cells. Here we provide direct evidence that the CLPs are spontaneously produced in the colonies. In addition, the cells of the CFU-T were characterized with antisera directed against the cell-surface marker Thy-1, which is present on all murine T cells, and the cell-surface markers Lyt-1 and Lyt-2, which are differentially distributed on different T-cell subclasses. We found that the CFU-T contains both a Thy-1+ and a Thy-1- cell, neither of which seems to carry either Lyt-1 or Lyt-2 surface markers.