Hapten-specific, class II-restricted killing by cloned T cells: direct lysis and production of a cytotoxic factor

DNP-specific, class II-restricted cloned T cells were shown to kill DNP-bearing A20.2J (A20-DNP) antigen-presenting cells. This killing was DNP-specific and was restricted by IA. Results from bystander cytotoxicity, cold-target inhibition, and protein and lymphokine inhibition experiments indicated that killing of A20-DNP targets was mediated by direct lysis. In addition to the direct lysis, antigen stimulation of the T cells also resulted in production of a soluble cytolytic factor which killed bystander L929 fibroblast cells. This killing was sensitive to inhibition of protein synthesis and lymphokine production but was not affected by the addition of cold A20-DNP target cells. Additional studies showed that other antigen-presenting cells, i.e., DNP-bearing P388D1 and splenic macrophages, were also lysed by the cloned T cells. These findings may indicate that lysis of target cells by nominal antigen-specific, class II-restricted T cells plays a role in immune regulation and/or immune protection.     

Does apoptosis contribute to CD4 T cell depletion in human immunodeficiency virus infection ?

Despite an extensive knowledge of the molecular characteristics of the human immunodeficiency virus (HIV) identified more than ten years ago as the cause of AIDS (acquired immune deficiency syndrome) (Barre-Sinoussi et al. 1983) some critical questions have not been answered yet: Is the progressive disappearance of CD4+ helper T lymphocytes, the hallmark of AIDS, directly related to the killing of infected cells by the virus? If not, how do CD4+T cells die? Is HIV using its viral factory to kill uninfected bystander cells? What causes the immune system collapse in HIV infection? In the past three years some important studies have provided stimulating clues suggesting that AIDS is not only related to the killing of host cells by HIV but is also a consequence of mechanisms of misactivation of the immune system, leading to anergy or apoptosis of non-infected effector cells. We discuss some of the in vivo and in vitro models providing evidence that HIV is able to kill and cripple the immune system either by acting directly on its targets or indirectly in bystander T cells keeping in mind that HIV disease must be considered as a multifactorial process.     

Inducer T-cell-mediated killing of antigen-presenting cells

L3T4+ inducer/helper T-cell clones, once activated by antigen-presenting cells (APC) expressing the appropriate Ia allele and antigen, autonomously kill their target APC. All 13 L3T4+ inducer T-cell clones tested demonstrated this cytolytic activity. In addition, 11 different target cells representing the three major APC types, namely, macrophages, B cells, and dendritic cells, were all sensitive to this cytolytic activity. Moreover, normal macrophages which were treated with interferon-gamma to increase Ia expression were also killed. These observations convincingly demonstrate that the cytolytic activity of L3T4+ inducer T-cell clones is a general phenomenon. In contrast to other reports, lysis of target APC could not be detected following 4-6 hr of incubation. Marginal lysis was observed after 9 hr and a 20-hr incubation period was required to achieve maximal killing. The kinetics of killing paralleled other parameters of T-cell activation such as IL-2 release and cell proliferation. Activation of T cells for cytolysis of APC requires the interaction of T-cell receptors with Ia and antigen. Monoclonal antibody to Ia, L3T4 and the T-cell receptor inhibited the cytolysis of APC. The ability to mediate nonspecific bystander killing was variable depending on both the T-cell clone and the target. The implications of these findings to immune regulation and autoimmunity are discussed.     

Selective activation of helper and cytolytic T-cell functions of L3T4+ clones with either antireceptor antibody or phorbol ester and ionophore

After activation with specific antigen and antigen presenting cells (APC) L3T4+ inducer T-cell clones can lyse Ia+ APC. The present study characterizes the mechanism of activation and specificity of L3T4+ inducer cell-mediated cytolytic function. Two methods that bypass the physiological stimulus of antigen presented on Ia+ APC were used to activate L3T4+ clones. The first method utilized an antireceptor monoclonal antibody (MAb), KJ16.133, to activate KJ16.133+ clones. The activated clones expressed nonspecific cytolytic activity, killing target cells irrespective of their H-2 haplotype or their ability to express cell surface Ia molecules. The crosslinking of bound KJ16.133 antibody greatly enhanced cytolytic activity. This activation is receptor specific because KJ16.133- clones were not activated under identical conditions. The second method of activation was provided by a synergistic action of phorbol-12-myristate-13-acetate (PMA) and ionophore A23187. These agents nonspecifically activated all L3T4+ clones tested. The simultaneous presence of the two agents is required for maximal activation. Again, the activated clones expressed potent nonspecific cytolytic activity. These observations demonstrated that L3T4+ inducer T-cell-mediated killing can be separated into two stages: an activation step, which can be specifically and nonspecifically triggered and an effector phase which causes nonspecific lysis of bystander targets. The induction of nonspecific cytolytic activity by antireceptor MAb was inhibited by anti-L3T4 MAb (GK1.5). In contrast, activation of nonspecific cytolytic activity by treatment with PMA plus A23187 was not inhibited by anti-L3T4 MAb. Under the above activation conditions, antireceptor MAb selectively induced the secretion of IL-3 and expression of nonspecific cytolytic activity. However, there was little or no concomitant proliferation and production of IL-2. In contrast, activation by PMA plus A23187 coordinately induces expression of nonspecific cytolytic activity, secretion of lymphokines (IL-3 and IL-2), and cell proliferation. Thus, the anticlonotypic activation preferentially induces certain functions whereas activation with PMA plus A23187 is not selective.     

Hierarchy of cytotoxic T cell clones. I. Reversal of resistance to lysis and killing between anti-hapten cytotoxic T cells

Cells from clones of anti-hapten cytotoxic T lymphocytes (CTL) can act as both effector cells and, when treated with the specific hapten, as target cells. Individual clones can kill haptenated cells only from other clones that are less efficient killers. Clones specific for both fluorescein and trinitrophenol could be ordered in a single hierarchy in which resistance to lysis correlated with lytic efficiency. When the killing efficiency was reduced with phorbol myristate acetate (PMA) or the colchicine analogue, Colcemid, the degree of resistance to lysis was also reduced. The use of PMA-treated fluoresceinated targets greatly enhanced intraclonal killing and similarly lead to a repositioning of clones within the hierarchy of normal cells. By the haptenation of appropriate clones, efficient CTL could kill cells from other clones in a direction apparently opposite to recognition. The results demonstrate that effects other than antigen recognition of the target cell may result in variations in the nature of T cell immune responses.     

A cascade of T-T interactions, mediated by the linked recognition of antigen, in the induction of T cells able to help delayed-type hypersensitivity responses

Previous work has shown that specific helper T cells are required for the primary induction of delayed-type hypersensitivity (DTH). Conditions are defined here under which the primary induction by antigen of precursor helper T cells only occurs in the presence of specific, irradiated effector T cells, demonstrating that the induction of helper T cells requires T-T cooperation. The interaction between precursor and effector helper T cells is mediated by the recognition of epitopes that must be physically linked to one another. In more detail, hapten-Ficoll conjugates and xenogeneic red blood cells induce medium-density but not low-density cultures of unprimed murine spleen cells to express antigen-specific DTH. Low-density cultures do not support the induction of DTH unless they are supplemented with specific irradiated helper T cells. These helper T cells are themselves induced when antigen is added to medium-density but not low-density cultures. Precursor helper T cells in low-density cultures are only induced by antigen in the presence of additional specific irradiated T cells. Further experiments were directed at analyzing the nature of this T-T interaction. Irradiated hapten-primed T cells help the induction of precursor helper T cells specific for burro red blood cells (BRBC) in the presence of haptenated BRBC and chicken red blood cells (CRBC), but do not help in the presence of haptenated CRBC and BRBC. These experiments demonstrate that the interaction between precursor and effector T cells is mediated by the linked recognition of antigen. These findings show that the induction of precursor cells for both DTH reactivity, and those T cells able to help in the induction of DTH, require specific helper T cells. It is further shown that the induction of T cells able to help in the induction of helper precursor cells takes place in medium-density but not low-density cultures. In order words, antigen, when added to medium-density cultures of normal spleen cells, induces T cells able to mediate DTH, and T cells able to help in the induction of these helper T cells, whereas antigen induces none of these T cells when added to low-density cultures unless appropriate specific helper T cells are added.(ABSTRACT TRUNCATED AT 400 WORDS)     

Antigen-specific and nonspecific mediators of T-cell/B-cell cooperation. VI. Distinct patterns of cross-reactivity by two human gamma-globulin-primed helper T-cell subpopulations.

We have previously characterized the activities, in vitro, of two different helper T-cell subpopulations, primed with human γ-globulin (HGG). One T-cell subpopulation helps the response of B cells to determinants (e.g., haptens) bound to the same antigen to which the T cells are primed (specific help); the other helper T-cell subpopulation responds to the same priming antigen by secreting a nonspecific molecule which helps B-cell responses to erythrocyte antigens co-cultured with the priming antigen (nonspecific help). These subpopulations also differ in their frequency and dose response to antigen, both in vivo and in vitro. They are similarly susceptible to the induction of unresponsiveness to HGG. In order to determine whether these T-cell subpopulations share or differ in their ranges of antigen recognition, we have compared the reaction of these two HGG-primed helper T-cell subpopulations to a number of γ-globulins (γG's) from other species. Plaque-forming cells generated in response to HGG shared little or no cross-reactivity with any of the heterologous (γG's) tested. In contrast, HGG-primed nonspecific helper T cells responded with significant cross-reactivity when challenged in vitro with dog γG, but HGG-primed specific helper T cells did not respond with any such cross-reactivity. No other heterologous γG tested stimulated any significant cross-reactivity from either HGG-primed T-cell subpopulation. Thus, these two T-cell subpopulations differ in their antigenic recognition. Possible explanations of these data include: (i) a difference in receptor specificity; (ii) a difference in the receptor affinity; (iii) a difference in Ia determinants of the two subpopulations.     

Killer dendritic cells and their potential for cancer immunotherapy

Known for years as the principal messengers of the immune system, dendritic cells (DC) represent a heterogeneous population of antigen presenting cells critically located at the nexus between innate and adaptive immunity. DC play a central role in the initiation of tumor-specific immune responses as they are endowed with the unique ability to take up, process and present tumor antigens to naïve CD4⁺ or CD8⁺ effector T lymphocytes. By virtue of the cytokines they produce, DC also regulate the type, strength and duration of T cell immune responses. In addition, they can participate in anti-tumoral NK and NKT cell activation and in the orchestration of humoral immunity. More recent studies have documented that besides their primary role in the induction and regulation of adaptive anti-tumoral immune responses, DC are also endowed with the capacity to directly kill cancer cells. This dual role of DC as killers and messengers may have important implications for tumor immunotherapy. First, the direct killing of malignant cells by DC may foster the release and thereby the immediate availability of specific tumor antigens for presentation to cytotoxic or helper T lymphocytes. Second, DC may participate in the effector phase of the immune response, potentially augmenting the diversity of the killing mechanisms leading to tumor elimination. This review focuses on this non-conventional cytotoxic function of DC as it relates to the promotion of cancer immunity and discusses the potential application of killer DC (KDC) in tumor immunotherapy.     

Activation of antigen-specific CD8 T cells results in minimal killing of bystander bacteria

Memory CD8 T cells play a critical role in protective immunity against intracellular pathogens. In addition to their ability to specifically recognize and lyse infected targets, activated CD8 T cells secrete cytokines that induce phagocytic cells to engulf and kill bacterial pathogens. In this study, we asked whether activation of Ag-specific CD8 T cells results in nonspecific killing of bystander bacteria during a mixed infection. Mice with epitope-specific memory CD8 T cells were coinfected with two isogenic strains of recombinant Listeria monocytogenes that differ in the cognate epitope. Recall responses by epitope-specific CD8 T cells rapidly inhibited the growth of epitope-bearing bacteria, impeding the course of infection within 6 h after challenge. This rapid inhibition was highly specific and did not affect the growth of coinfecting bacteria without the epitope. CTL recall did not enhance activation of innate immune cells, as evidenced by the absence of inducible NO synthase production in infectious foci. Our observations demonstrate the remarkable specificity of the bactericidal mechanisms of CTL and reveal the possibility for escape mutants to prevail in the hostile environment of a specific immune response. This implication has a bearing on subunit vaccine design strategies and understanding failure of immunization against bacterial infection.     

In vitro generation of human activated lymphocyte killer cells: separate precursors and modes of generation of NK-like cells and "anomalous" killer cells

The activation of human peripheral blood mononuclear cells (PBM) in culture leads to the generation of nonspecific killer cells. These cells, termed activated lymphocyte killer (ALK) cells, can kill fresh tumor cells and tumor cell lines, in addition to the natural killer (NK) cell sensitive target K562. ALK cells have features in common with both T and NK cells, but their nature and origin are unknown. In the present study, it is shown that ALK cells are in fact heterogeneous and can be generated from both large granular lymphocytes with the same phenotype as NK cells and from T cells. Cell populations enriched for NK cells, when cultured with lymphokines, rapidly acquired a T cell phenotype, enhanced cytolytic activity against K562, and the ability to lyse NK-insensitive target cells such as a melanoma cell line LiBr; these ALK cells were described as NK-like cells. On the other hand, of the cloned cells derived from PBM stimulated with irradiated B lymphoblasts and grown in lymphokines, the major proportion of cytolytic T cells (CTC) able to kill the specific stimulator lymphoblasts were also found to kill LiBr but not K562 cells. These ALK cells, which were derived from the same precursors as CTC, were designated anomalous killer (AK) cells. Consistent with this, the presence of the pan T monoclonal antibody UCHT1 from the beginning of mixed cell cultures inhibited the generation of CTC and of the AK-type of ALK cell, which killed melanoma cells, but not the NK type, which killed K562 targets. By contrast, at the effector cell level, the antibodies UCHT1 and OKT8 only blocked specific killing by CTC but did not block the killing of LiBr or of K562 targets by ALK cells. However, at the effector cell level there was additional evidence for the heterogeneity of ALK cells. Thus, monoclonal antibody 9.1C3, which blocks killing by freshly isolated NK cells, also blocked the killing of K562 targets by NK-like cells, but did not block B lymphoblast killing by CTC or melanoma cell killing by AK cells. It is concluded that after mixed lymphocyte culture, the majority of ALK cells measured by the killing of melanoma target cells arise from the same precursors and are under the same influences as classical CTC (AK cells), whereas cells killing K562 targets are derived from NK cells (NK-like cells). Once generated, the AK cells have a different mechanism of killing from both classical CTC and from NK and NK-like cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

T helper cell activation and human retroviral pathogenesis.

T helper (Th) cells are of central importance in regulating many critical immune effector mechanisms. The profile of cytokines produced by Th cells correlates with the type of effector cells induced during the immune response to foreign antigen. Th1 cells induce the cell-mediated immune response, while Th2 cells drive antibody production. Th cells are the preferential targets of human retroviruses. Infections with human T-cell leukemia virus (HTLV) or human immunodeficiency virus (HIV) result in the expansion of Th cells by the action of HTLV (adult T-cell leukemia) or the progressive loss of T cells by the action of HIV (AIDS). Both retrovirus infections impart a high-level activation state in the host immune cells as well as systemically. However, diverging responses to this activation state have contrasting effects on the Th-cell population. In HIV infection, Th-cell loss has been attributed to several mechanisms, including a selective elimination of cells by apoptosis. The induction of apoptosis in HIV infection is complex, with many different pathways able to induce cell death. In contrast, infection of Th cells with HTLV-1 affords the cell a protective advantage against apoptosis. This advantage may allow the cell to escape immune surveillance, providing the opportunity for the development of Th-cell cancer. In this review, we will discuss the impact of Th-cell activation and general immune activation on human retrovirus expression with a focus upon Th-cell function and the progression to disease.     

Distinct mechanisms of CD4+ and CD8+ T-cell activation and bystander apoptosis induced by human immunodeficiency virus type 1 virions

Apoptosis of uninfected bystander T cells contributes to T-cell depletion during human immunodeficiency virus type 1 (HIV-1) infection. HIV-1 envelope/receptor interactions and immune activation have been implicated as contributors to bystander apoptosis. To better understand the relationship between T-cell activation and bystander apoptosis during HIV-1 pathogenesis, we investigated the effects of the highly cytopathic CXCR4-tropic HIV-1 variant ELI6 on primary CD4(+) and CD8(+) T cells. Infection of primary T-cell cultures with ELI6 induced CD4(+) T-cell depletion by direct cell lysis and bystander apoptosis. Exposure of primary CD4(+) and CD8(+) T cells to nonreplicating ELI6 virions induced bystander apoptosis through a Fas-independent mechanism. Bystander apoptosis of CD4(+) T cells required direct contact with virions and Env/CXCR4 binding. In contrast, the apoptosis of CD8(+) T cells was triggered by a soluble factor(s) secreted by CD4(+) T cells. HIV-1 virions activated CD4(+) and CD8(+) T cells to express CD25 and HLA-DR and preferentially induced apoptosis in CD25(+)HLA-DR(+) T cells in a CXCR4-dependent manner. Maximal levels of binding, activation, and apoptosis were induced by virions that incorporated MHC class II and B7-2 into the viral membrane. These results suggest that nonreplicating HIV-1 virions contribute to chronic immune activation and T-cell depletion during HIV-1 pathogenesis by activating CD4(+) and CD8(+) T cells, which then proceed to die via apoptosis. This mechanism may represent a viral immune evasion strategy to increase viral replication by activating target cells while killing immune effector cells that are not productively infected.     

Induction of nonspecific cytotoxicity by monoclonal anti-T3 antibodies

The effects of monoclonal anti-T3 antibodies on the effector phase of cytotoxic T lymphocytes (CTL) were studied with respect to antigen-specific and antigen-nonspecific lysis of different target cells. Anti-T3 antibodies inhibited the antigen-specific lysis by CTL generated in mixed lymphocyte cultures (MLC), but they concomitantly augmented the nonspecific killing of third-party cells such as the cell lines Daudi, Raji, and K562. This nonspecific cytotoxicity was induced by various anti-T3 antibodies, whereas antibodies reactive with other antigens expressed on the cytotoxic effector cells lacked any such activity. Anti-T3 antibodies induced nonspecific cytotoxicity only when activated T cells, obtained by primary MLC, by repeated restimulation, or after cloning, were used. The antibodies had no effect on unstimulated peripheral T lymphocytes or thymocytes. The inhibition of the antigen-specific lysis and the induction of nonspecific lysis by anti-T3 was dose dependent, and both effects occurred at the same concentration range of anti-T3. F(ab')2 fragments of anti-T3 inhibited the specific lysis but were not able to induce cytotoxic activity, indicating that this induction is an Fc-dependent process. When different target cells were tested, only Fc receptor-positive cells were susceptible for this nonspecific cytotoxicity. Thus, anti-T3 antibodies have a dual effect on effector CTL: they inhibit antigen-specific lysis and concomitantly induce nonspecific lysis in an Fc-dependent way.     

Highly efficient redirected anti-tumor activity of human lymphocytes transduced with a completely human chimeric immune receptor

BACKGROUND: Novel antibody-based immunotherapeutic strategies exploit chimeric immune receptors (CIR), expressed on the surface of transduced human peripheral blood mononuclear cells (PBMC), to redirect potent non-MHC-dependent cytotoxicity to tumor cells expressing a tumor-associated antigen. However, clinical application of the strategy has been hampered by the potential side effects associated with immunogenicity and by low transduction efficiency. METHODS: A fully human CIR was constructed that triggers immune activation through the zeta chain of CD3 and contains a human single-chain antibody fragment specific for an extracellular epitope of HER2. PBMC were transduced with the CIR using gibbon-ape leukemia virus envelope pseudotyped retroviruses. In vitro cytotoxicity and inhibition assays were carried out using normal and tumor cell lines expressing different levels of HER2. RESULTS: Bulk populations of CIR-transduced PBMC could express high levels of the construct and subcloning ensured stable expression. CIR-mediated killing and growth inhibition of targets expressing high HER2 levels were very efficient at low effector-to-target ratios. Under the same experimental conditions, CIR-mediated activity against normal cells expressing low HER2 levels was marginal. The CIR-mediated recognition of target cells induced the release of soluble factors able to inhibit growth of both HER-positive and HER2-negative bystander tumor cells. CONCLUSIONS: Human CIR-transduced PBMC exert a potent and dose-dependent anti-tumor activity. Target antigen level appeared to be a critical determinant of specificity and delivery of signals leading to redirected effector functions. Soluble factors, released by redirected effectors at the site of antigen-driven activation, mediate potent bystander killing.     

In vitro T cell-mediated killing of Pseudomonas aeruginosa. II. The role of macrophages and T cell subsets in T cell killing

T lymphocytes from immune mice can adoptively transfer protection against infection with the extra-cellular Gram-negative bacterium Pseudomonas aeruginosa to nonimmune recipients, and in vitro, immune T cells are able to kill these bacteria. Earlier studies indicated that this killing is mediated by a bactericidal lymphokine. Those studies also showed that macrophages enhance this in vitro T cell killing but do not directly participate in the bacterial killing, nor do macrophages function to present antigen to T cells. The current studies demonstrate that the ability of macrophages to enhance T cell killing can be replaced by macrophage culture supernatants or by purified recombinant interleukin 1 (IL 1). In addition, the macrophage supernatant-induced enhancement can also be blocked by antibody to purified IL 1. These studies also demonstrate that the T cell subset that serves as the final effector cell in the killing process is the Lyt-1-, 2,3+, I-J+ phenotype.     

Nonspecific cytotoxicity of spleen cells and the specific cytotoxic action of thymus-derived lymphocytes in vitro

Spleen cells removed from immunized mice specifically kill allogeneic lymphoma cells in vitro, but in the presence of specific antigen nonspecific target cell growth inhibition also occurs. Only the specific target cell killing was found to be θ-sensitive, the nonspecific cytotoxicity was caused by a population of θ-resistant, adherent, and AMS-sensitive cells. Nonspecific cytotoxic effects were caused by spleen cells from normal mice after incubation with endotoxin, and these effects were inhibited by removal of the adherent cells.     

Biological response modifiers (BRM) as antigens

In order to investigate tumoricidal effector cells in therapy by biological response modifiers (BRM) such asPropionibacterium acnes, bacillus Calmette-Guérin (BCG),Streptococcus pyogenes and a protein-bound polysaccharide (PSK), we established T cell lines specific for each BRM from BALB/c mice immunized with the corresponding BRM. These T cell lines proliferated and produced interleukin-2-(IL-2) and/or IL-4, but only in the presence of the relevant BRM and BALB/c spleen cells as the antigen and antigen-presenting cells respectively. Cross-functional experiments indicated that each BRM acts as a nominal antigen, but not as a non-specific immunostimulator. In addition, the T cell lines killed Ia-positive syngeneic B lymphoma cells, but only in the presence of the relevant BRM. These experiments excluded the possibility of cytotoxic effects by each BRM. The T cell lines and clones also killed Ia-negative bystander target cells, but only in the presence of both a relevant antigen and antigen-presenting cells. The T cell clones specific forS. pyogenes orP. acnes tested were Thy1⁺, L3T4⁺ and Lyt2^–. These results indicate that some BRM exert tumoricidal activity by inducing T cells that recognize them as an antigen and kill tumor cells in an antigen-specific manner. The T cells killed tumor targets in either a tumor-necrosis-factor(TNF)-dependent or a TNF-independent manner. The mediator of the latter pathway remains to be elucidated.     

Target cell recognition structures in LDCC and ODCC

Cytotoxic T lymphocyte effector cells specific for a defined class I antigen can kill target cells displaying a wide range of different class I proteins in the presence of certain lectins and oxidizing agents. However, optimal lysis of the target cell (TC) still requires interaction of the CTL with the TC class I proteins. This raises the question of how the lectin or oxidizing agent alters the system in such a way that an "inappropriate" CTL-TC interaction takes place, in a class I-dependent manner. In this study we show that if papain-sensitive molecules are cleared from the TC surface and are allowed to regenerate in the presence of tunicamycin, the cells still serve as targets in direct, class I antigen-specific CTL killing, but not in LDCC or ODCC. Target cells treated in this way display N-linked carbohydrate-less class I proteins, and presumably other N-linked carbohydrate-less, papain-sensitive molecules as well. We present data showing that both types of molecules are important in nonspecific lytic reactions.     

Immunologic functions of isolated human lymphocyte subpopulations. III. Specific allogeneic lympholysis mediated by human T cells alone.

The studies presented herein have evaluated both the specificity and cellular basis of cell-mediated lympholysis (CML) in man. An efficient and quantitative 51Cr release assay was utilized to study the role of highly purified human T and B cells in CML. After in vitro sensitization human T cells develop the capacity to kill specifically allogeneic cells to which they were sensitized. In contrast, B cells were neither triggered to proliferate nor activated to kill allogeneic targets. B cells were not activated to kill even when sensitized in the presence of potentially "helper" T cells, nor did they block T cells from killing during the effector phase. Cell-free supernatants taken from active in vitro sensitization cultures were not lympholytic and did not modulate T cell killing. Hence, these studies show that both the afferent and efferent phases of human CML are T cell functions.     

T-T cell interaction in the induction of delayed-type hypersensitivity (DTH) responses: vaccinia virus-reactive helper T cell activity involved in enhanced in vivo induction of DTH responses and its application to augmentation of tumor-specific DTH responses

The role of antigen-specific helper T cells in augmenting the in vivo development of delayed-type hypersensitivity (DTH) responses was investigated. C3H/HeN mice were inoculated i.p. with vaccinia virus to generate virus-reactive helper T cell activity. These vaccinia virus-primed or unprimed mice were subsequently immunized subcutaneously (s.c.) with either trinitrophenyl (TNP)-modified syngeneic spleen cells (TNP-self), vaccinia virus-infected spleen cells (virus-self), or cells modified with TNP subsequent to virus infection (virus-self-TNP). Seven days later, these mice were tested for anti-TNP DTH responses either by challenging them directly with TNP-self into footpads or by utilizing a local adoptive transfer system. The results demonstrated that vaccinia virus-primed mice failed to generate significant anti-TNP DTH responses when s.c. immunization was provided by either virus-self or TNP-self alone. In contrast, vaccinia virus-primed mice, but not unprimed mice, could generate augmented anti-TNP DTH responses when immunized with virus-self-TNP. Anti-vaccinia virus-reactive helper activity was successfully transferred into 600 R x-irradiated unprimed syngeneic mice by injecting i.v. spleen cells from virus-primed mice. These helper T cells were found to be antigen specific and were mediated by Thy-1+, Lyt-1+2- cells. DTH effector cells enhanced by helper T cells were also antigen specific and were of the Thy-1+, Lyt-1+2- phenotype. Furthermore, vaccinia virus-reactive helper T cell activity could be applied to augment the induction of tumor-specific DTH responses by immunization with vaccinia virus-infected syngeneic X5563 tumor cells. T-T cell interaction between Lyt-1+ helper T cells and Lyt-1+ DTH effector T cells is discussed in the light of the augmenting mechanism of in vivo anti-tumor-specific immune responses.