The Roles of CD8+ and CD4+ Cells in Tumor Rejection

In vivo administrations of anti-Lyt-2.2 (CDS) mAb and anti-L3T4 (CD4) mAb selectively eliminated CD8⁺ cells amd CD4⁺ cells, respectively. The relative potencies of CD8⁺ cells and CD4⁺ cells and their roles in primary tumor rejections were studied by investigating the effects of these mAbs on tumor growth. CD8⁺ cells were themselves fully capable of mediating rejection in 5 different tumor rejection systems: two radiation leukemia virus (RadLV)-induced leukemias, B6RV2 and BALBRVD, a radiation-induced leukemia BALBRL♂1, and a plasmacytoma BALBMOPC-70A in CB6F₁ mice, and a Friend virus-induced leukemia B6FBL-3 in B6 mice. On the other hand, CD4⁺ cells were capable of resisting tumor growth of B6FBL-3, but not of the other four tumors. Furthermore, for efficient rejection of CB6F₁UV+^˚l sarcoma by CB6F₁ mice, synergy of CDS⁺ and CD4⁺ cells was necessary. Blocking of UV+^˚ 1 rejection was abrogated by delayed administration of anti-L3T4 (CD4) mAb but not anti-Lyt-2.2 (CDS) mAb, indicating the involvement of CD4⁺ cells in only the initial phase of rejection.     

Regression of intestinal adenomas by vaccination with heat shock protein 105-pulsed bone marrow-derived dendritic cells in Apc(Min/+) mice

Heat shock protein (HSP) 105 is overexpressed in various cancers, but is expressed at low levels in many normal tissues, except for the testis. A vaccination with HSP105-pulsed bone marrow-derived dendritic cells (BM-DC) induced antitumor immunity without causing an autoimmune reaction in a mouse model. Because Apc^Min/+ mice develop multiple adenomas throughout the intestinal tract by 4 months of age, the mice provide a clinically relevant model of human intestinal tumor. In the present study, we investigated the efficacy of the HSP105-pulsed BM-DC vaccine on tumor regression in the Apc^Min/+ mouse. Western blot and immunohistochemical analyses revealed that the tumors of the Apc^Min/+ mice endogenously overexpressed HSP105. Immunization of the Apc^Min/+ mice with a HSP105-pulsed BM-DC vaccine at 6, 8, and 10 weeks of age significantly reduced the number of small-intestinal polyps accompanied by infiltration of both CD4⁺ and CD8⁺ T cells in the tumors. Cell depletion experiments proved that both CD4⁺ and CD8⁺ T cells play a critical role in the activation of antitumor immunity induced by these vaccinations. These findings indicate that the HSP105-pulsed BM-DC vaccine can provide potent immunotherapy for tumors that appear spontaneously as a result of the inactivation of a tumor suppressor gene, such as in the Apc^Min/+ mouse model. ( Cancer Sci 2007; 98: 1930–1935)     

Cytotoxic Activity of CD4+ T Cells against Autologous Tumor Cells

The ⁵¹Cr-release assay is mostly applied to detecting the cytotoxic activity of CD8⁺ T cells, and little is known about the activity of CD4⁺ T cells. Therefore, the correlation between the cytotoxic activity of CD4⁺ or CD8⁺ T cells and the incubation period with autologous tumor cells was analyzed by two methods. The incubation periods were 4 and 20 h (4 h and 20 h assay) for the ⁵¹Cr-release assay. Eight pairs of tumor cells and T cells were assayed. T cells were fractionated into CD4⁺ and CD8⁺ T cells by using magnetic beads and panning methods, and those cells were activated by culture with recombinant interleukin-2 and immobilized anti-CD3 monoclonal antibody. In 6 out of 8 cases, no cytotoxic activity of CD4⁺ T cells was detected by the 4 h assay, whereas cytotoxic activity was detected in all cases in the 20 h assay. The cytotoxic activities in 20 h assay of CD4⁺ T cells were increased 67-fold in comparison with the activities in 4 h assay (range: 5–197). In the case of CD8⁺ T cells, cytotoxic activities were detected in 6 out of 8 cases in the 4 h assay. The lytic unit ratio of CD4⁺ and CD8⁺ T cells was calculated as 1.5 in the 20 h assay (range: 0.2->7.2) versus 0.4 in the 4 h assay (range: < 0.1–1.3). Cytotoxic activities in colorimetric assay using Crystal Violet with a 24 h incubation were similar to those in the 20 h ⁵¹Cr-release assay in all eight cases. These results indicate that CD4⁺ T cells have cytotoxic activity as strong as that of CD8⁺ T cells towards autologous tumor cells.     

Direct Activation of Human CD8+ Cytotoxic T Lymphocytes by Interleukin-18

Direct activation of human cytotoxic T lymphocytes (CTL) by interleukin (IL)-18 was observed in a system in which CTL effective against autologous tumor cells were generated. Peripheral blood mononuclear cells (PBMC) from tumor-bearing patients, after removal of natural killer (NK) cells, were cultured in a medium containing IL-1, -2, -4, and -6, with or without IL-18, and stimulated with autologous tumor cells. IL-18 increased the activity of the CTL and the proportion of autologous CD8⁺ T cells present after 28 days in the induction culture. When purified CD8⁺ T cells were cultured in the presence of IL-18 and IL-2 for 7 days, the CTL showed enhanced cytotoxic activity against autologous tumor cells. Moreover, a purified CD8⁺ T cell population, which did not exhibit any apparent cytotoxic activity against autologous tumor cells, displayed cytotoxic activity after 7-day incubation with IL-18. These results suggest that IL-18 may be useful to generate autologous CTL in humans and may thereby contribute to adoptive immunotherapy for tumors.     

Solid-phase Anti-CD3 Antibody Activation and Cryopreservation of Human Tumor-infiltrating Lymphocytes Derived from Epithelial Ovarian Cancer

The effect of solid-phase anti-CD3 antibody activation and cryopreservation was evaluated on thirteen samples of tumor-infiltrating lymphocytes (TILs) derived from epithelial ovarian cancer. Seven preparations of TILs were cultured with or without solid-phase anti-CD3 antibody in addition to 100 units/ml of recombinant interleukin-2 (rIL-2). The proliferation rate of all of the seven TIL preparations stimulated by anti-CD3 antibody on the fourth or fifth day of culture was 3.4 to 9.8 times greater than that of lymphocytes cultured with rIL-2 alone. Furthermore, in an experiment with five TIL samples activated with anti-CD3 antibody, three of them showed augmented cytotoxic activity against autologous fresh tumor cells. The population of CD3⁺/CD8⁺ TILs was increased after 4–5 weeks of cultivation and CD8⁺ lymphocytes amounted to over 70% in all of seven preparations tested, whereas two of seven preparations not activated by anti-CD3 antibody were CD3⁺/CD4⁺-dominant. In addition, nine preparations of TILs cultured with rIL-2 were cryopreserved for several weeks; after recovery from cryopreservation, no major change was observed in cell surface markers, in growth rate or in cytotoxic activity. These results suggest that cryopreserved and/or anti-CD3 antibody-activated lymphocytes could conveniently be employed in a clinical trial of adoptive immunotherapy employing TIL.     

Interleukin-12 Augments the Generation of Autologous Tumor-reactive CD8+ Cytotoxic T Lymphocytes from Tumor-infiltrating Lymphocytes

Human tumor-infiltrating lymphocytes (TIL) were obtained from breast cancer, renal cancer or neuroblastoma to investigate the generation of autologous tumor-reactive CD8⁺ cytotoxic T lymphocytes (CTL). When TIL were cultured with interleukin (IL)-2 (100 U/ml), the growth of TIL peaked around 8–10 days after the initiation of culture. In contrast, the proliferation of TIL cultured with IL-2 plus IL-12 peaked around 4–5 days after culture and tumor cells rapidly disappeared from the culture. To determine the generation of autologous tumor-reactive CD8⁺ CTL, TIL-derived CD8⁺ T cells were separated by FACStar. Both IL-2-activated and IL-2 plus IL-12-activated TIL-CD8⁺ T cells showed the same level of lymphokine-activated killer activity against a variety of tumor cells. However, TIL-CD8⁺ T cells activated with IL-2 plus IL-12 revealed greatly augmented cytotoxicity against autologous tumor cells compared with that induced by IL-2 alone. The autologous tumor cell-killing activity of TIL-CD8⁺ CTL was significantly inhibited by the addition of F(ab)₂ anti-CD3 monoclonal antibody, indicating that these CTL recognize autologous tumor antigen through T cell receptor. These results imply that IL-12 is a novel cytokine which facilitates the generation of autologous tumor-reactive CD8⁺ CTL from TIL.     

Cytotoxicity of Histocompatibility Leukocyte Antigen–DR8–restricted CD4+ Killer T Cells against Human Autologous Squamous Cell Carcinoma

Although CD8⁺ killer T cells reacting against human autologous tumor cells have recently been studied in detail, little is known about the cytotoxic mechanism of CD4⁺ T cells against such tumor cells. In order to investigate this, we have established CD4⁺ cytotoxic T lymphocyte TcOSC–20 lines. TcOSC–20 showed selective cytotoxic activity against autologous OSC–20 cells, derived from a cancer of the tongue, in an HLA–DR–restricted fashion. HLA–DR8 (DRB1* 08032) is the only DR molecule expressed on OSC–20 cells, and anti–DRS monoclonal antibody could inhibit the Cytotoxicity, suggesting that HLA–DRB1^★ 08032 is the tumor rejection antigen–presenting moleculeto TcOSC–20. The Fas ligand was expressed on TcOSC–20 lines, and its expression was induced upon mixed lymphocyte–tumor cell culture of autologous peripheral blood lymphocytes. Furthermore, the Cytotoxicity of TcOSC–20 was inhibited by anti–Fas ligand antibody.These data imply that TcOSC–20 lines recognize the tumor antigenic peptide presented by HLA–DR8, and exert Cytotoxicity against autologous tumor cells via a Fas–mediated cytotoxic pathway.     

Adult T-cell leukemia/lymphoma cells from blood and skin tumors express cytotoxic T lymphocyte-associated antigen-4 and Foxp3 but lack suppressor activity toward autologous CD8+ T cells

Adult T cell leukemia/lymphoma (ATL) cells share the CD4⁺CD25⁺ phenotype with regulatory T (Treg) cells. However, it is still controversial whether ATL cells are Treg cells. The aim of the present study was to investigate the Treg nature of ATL cells obtained from peripheral blood and skin tumors in terms of their phenotype and function. By flow cytometry and immunohistochemistry, the expression of the Treg-associated molecule cytotoxic T lymphocyte-associated antigen (CTLA)-4 and Foxp3 was examined in freshly isolated circulating and skin-infiltrating tumor cells from 21 ATL patients with skin eruptions. The expression of CTLA-4 on freshly isolated circulating tumor cells was elevated in two of 15 patients, and Foxp3 was expressed intracytoplasmically at high levels in three of nine patients. In five of the patients examined, skin-infiltrating tumor cells bore variously elevated CTLA-4 with high Foxp3 expression. The potentiality of ATL cells as Treg cells was further addressed by stimulating ATL cells with anti-CD3/CD28 monoclonal antibodies and monitoring CTLA-4 expression. With the stimulation, even CTLA-4-low ATL cells expressed higher levels of CTLA-4 than normal CD4⁺CD25⁺ cells. To study function, ATL cells isolated from blood and skin tumors were tested for their ability to suppress the proliferation of autologous CD8⁺ T cells stimulated with allogeneic lymphocytes. Despite the expression of CTLA-4 and Foxp3, these tumors were incapable of suppressing the proliferation of autologous CD8⁺ T cells. ATL cells are phenotypically Treg cells in at least some patients, but lack immunoregulatory functions, at least toward CD8⁺ T cells. ( Cancer Sci 2008; 99: 98–106)     

Expression of Tumor-associated Glycoantigen, Sialyl Lewisa, in Human Head and Neck Squamous Cell Carcinoma and Its Application to Tumor Immunotherapy

The glycoantigen sialyl Lewis^a (sLe^a) is widely expressed on a variety of gastrointestinal tumor cells. Here, we immunohistochemically demonstrated the expression of sLe^a antigen in 54% (7 out of 13) of human head and neck squamous cell carcinoma (H-NSCG) samples. Frequent expression of sLe^a antigen was also demonstrated on a variety of H-NSCC cell lines using flow cytometry. Both CD4⁺ and CD8⁺ T cells, which were activated with immobilized OKT3 monoclonal antibody plus inter-leukin-2, showed augmented cytotoxicity against sLe^a-positive H-NSCC, including autologous tumor cells, on targeting with anti-CD3 x anti-sLe^a bispccific antibody, suggesting that sLe^a antigen is a good target molecule for bispecific antibody-dependent adoptive tumor immunotherapy of human head and neck cancer.     

Effects of Interleukin-12 on the Induction of Cytotoxic T Lymphocytes from the Regional Lymph Node Lymphocytes of Patients with Lung Adenocarcinoma

Lung cancer-specific cytotoxic T lymphocytes (CTL) were induced by repeated stimulations of regional lymph node lymphocytes (RLNL) in lung cancer patients with either autologous or HLA-A-locus-matched tumor cells. To investigate the effect of interleukin-12 (IL-12), IL-12 was added during the stimulation of RLNL from HLA A24 / adenocarcinoma patients with either autologous tumor cells or HLA A24-positive adenocarcinoma cells (PC-9) in combination with, or instead of interleukin-2 (IL-2), and then the cytotoxic activity, cytokine production and populations of the lymphocyte subsets were examined. The addition of IL-12, or the substitution of IL-2 by IL-12 was found to enhance the cytotoxic activity and the cytokine production (IFN-γ, GM-CSF) of the CTL as compared with IL-2 alone. The cytotoxic activity and cytokine production were both partially inhibited by anti-MHC-class I monoclonal antibody. The CTL thus induced by IL-12 had a higher proportion of CD3⁺/CD56⁺ cells than the CTL induced with IL-2 alone. The positively selected CD8⁺/CD56^– lymphocytes showed PC-9-specific cytotoxic activity, because the population did not show any cytotoxicity to K562 or A549 (HLA-A26/A30). However, the CD3⁺/CD56⁺ lymphocytes were cytotoxic to both PC-9 and K562. In conclusion, IL-12 is considered to be a useful cytokine for both the induction of lung-cancer specific CTL and the augmentation of non-MHC-restricted cytotoxicity against tumor cells, and may be applicable for adoptive immunotherapy using CTL.     

Analysis of CD8 T-cell response by IFNgamma ELISPOT and H-2L(d)/pRL1a tetramer assays in pRL1a multiple antigen peptide-immunized and RL male 1-bearing BALB/c and (BALB/c x C57BL/6) F(1) mice

We previously identified an H-2L^d-binding peptide pRL1a (IPGLPLSL) on RL male 1 that is predominantly recognized by cytotoxic T-lymphocytes (CTLs). MAP is a multibranched lysine core with antigenic peptides. Immunization of BALB/c mice with pRL1a MAP effectively induced pRL1a CTLs. Here, we demonstrate the presence of pRL1a-recognizing CD8⁺ T-cells in pRL1a MAP-immunized and RL male 1-bearing BALB/c and (BALB/ cxC57BL/6)F₁ mice by using IFNγ ELISPOT and H-2L^d/pRL1a tetramer assays. A few IFNγ ELISPOTs and no tetramer-positive cells were detected ex vivo in spleen cells from BALB/c mice immunized with pRL1a MAP. After a single in vitro stimulation with RL male 1, 432 and 741 IFNγ ELISPOTs/10⁵ cells were detected and tetramer-positive CD8⁺ T-cells occurred at relative frequencies of 5.7% and 30.8% in splenic CD8⁺ T-cells from mice that had been doubly and triply immunized, respectively, against pRL1a MAP. Tetramer-positive cells displayed two distinct cell populations, CD62L^low and CD62L^high. Secondary in vitro stimulation expanded CD62L^high cells more efficiently than CD62L^low cells. Furthermore, a higher frequency of IFNγ-producing and tetramer-positive CD8⁺ T-cells was detected ex vivo in RL male 1-bearing semi-allogeneic (BALB/cxC57BL/6)F₁ than in BALB/c mice on day 14 after tumor inoculation.     

Bispecific Antibody-directed Antitumor Activity of Human CD4+ Helper/Killer T Cells Induced by Anti–CD3 Monoclonal Antibody plus Interleukin 2

Freshly isolated human CD4⁺ T cells can not respond to recombinant interlenkin 2 (rIL–2) because of their lack of p75 IL–2 receptor expression. However, we succeeded In inducing a marked proliferation of purified CD4⁺ T cells by activation with rIL–2 plus anti–CD3 monoclonal antibody (mAb) cross–linked to a plastic plate. The proliferated CD4⁺ T cells produced a significant amount of IL–2 upon stimulation with phorbol ester plus A23187. Interestingly, CD4⁺ T cells activated with anti–CD3 mAb plus rIL–2 revealed a strong cytotoxic activity against Fc receptor (FcR)–positive tumor cells in the presence of anti–CD3 mAb. Moreover, the CD4⁺ T cells could lyse FcR–negative glioma cells by targeting with bispecific mAb containing anti–CD3 mAb and anti–glioma mAb. Thus, we demonstrated that rIL–2 and immobilized anti–CD3 mAb allowed the rapid generation of human CD4⁺ helper/killer T cells, which may be useful for the development of a new adoptive tumor immunotherapy.     

Histocompatibility Leukocyte Antigen-A2-restricted and Tumor-specific Cytotoxic T Lymphocytes from Tumor-infiltrating Lymphocytes of a Patient with Testicular Embryonal Cancer

T lymphocytes play an important role in tumor rejection. To understand T cell-mediated specific immunity at the tumor site of testicular embryonal cancer, we investigated whether interleukin-2 (IL-2)-activated tumor-infiltrating lymphocytes (TIL) of a patient with testicular embryonal cancer show histocompatibility leukocyte antigen (HLA)-class I-restricted and tumor-specific cytotoxicity. We established a CD3⁺CD4^-CD8⁺ cytotoxic T lymphocyte (CTL) line from the IL-2-activated TIL of a 37-year-old patient with testicular embryonal cancer. A 6 h ⁵¹Cr-release assay was performed to measure the cytotoxicity of the CTL. The CD3⁺CD4^-CD8⁺ CTL line showed cytotoxicity against HLA-A2⁺ tumor cells, including freshly isolated autologous tumor cells, adenocarcinoma cell lines from various organs (lung, breast, pancreas, colon and kidney) and squamous cell carcinomas (esophagus and oral cavity). No other cell lines examined, including an autologous tumor cell line and HLA-A2" tumor cell lines, were lysed by this CTL line. These results suggest the existence of HLA-A2-restricted and tumor-specific CTL at the tumor site of testicular embryonal cancer.     

Sequential T Cell Response Involved in Tumor Rejection of Sarcoma, Meth A, in Syngeneic Mice

We investigated the type of T cell response involved in Meth A tumor rejection in primary immune and hyperimmune syngeneic mice. It was found that a CD4⁺ T cell-mediated delayed-type hypersensitivity (DTH) response activating non-specific killer cells such as macrophages, NK and LAK cells, without a specific CD8⁺ cytotoxic T lymphocyte (CTL) response, was the major immune response leading to Meth A tumor rejection in primary immune mice. In contrast, the specific CD8⁺ CTL response was the major response leading to the tumor rejection, in addition to CD4⁺ T cell-mediated DTH response, in hyperimmune mice. Analysis of CD4⁺ T cell clones established from primary immune and hyperimmune spleen cells indicated that a CD4⁺ T cell clone (C9) of primary immune mice (although only one clone was established) was of Th1 type, and induced cytotoxicity in accessory cells by classic DTH in vitro. Eight CD4⁺ T cell clones were established from hyperimmune spleen cells. Six out of the eight clones were of the Th2 type and two were Th0-like. However, no Th1-type CD4⁺ T cell clone was established from hyperimmune spleen cells. All of these CD4⁺ T cell clones, even the Th2-type clones, were capable of inducing cytotoxicity in vitro in T cell-depleted accessory cells, as in an in vitro DTH response. We postulate on the basis of these results that the T cell response leading to Meth A tumor rejection in vivo sequentially changed from a CD4⁺ T cell-mediated classic DTH response to a CD8⁺ CTL response, in addition to a cellular response mediated probably by Th2-type cells, during the process of repeated immunization.     

Expression of SART3 Tumor-rejection Antigen in Gastric Cancers

We previously reported SART3 as a tumor-rejection antigen recognized by histocompatibility leukocyte antigen (HLA)-A24-restricted cytotoxic T lymphocytes (CTLs). In this study, we investigated the expression of the SART3 antigen in gastric cancers, as a candidate for use in specific immunotherapy. The SART3 antigen was detected in 9 of 10 (90%) gastric cancer cell lines, 35 of 52 (67.3%) gastric cancer tissues, and 0 of 20 non-tumorous gastric tissues. SART3-derived peptides corresponding to positions 109–118 and 315–323 induced HLA-A24-restricted and tumorspecific CTLs from peripheral blood mononuclear cells (PBMCs) of gastric cancer patients. These peptide-induced CTLs recognized HLA-A24⁺ SART3⁺ gastric cancer cells, but not HLA-A24⁺ SART3⁻ or HLA-A24⁻ SART3⁺ gastric cancer cells. Therefore, the SART3 peptides could be useful in specific immunotherapy of gastric cancer patients.     

Human epithelial ovarian carcinoma cell-derived cytokines cooperatively induce activated CD4+CD25−CD45RA+ naïve T cells to express forkhead box protein 3 and exhibit suppressive ability in vitro

Regulatory T cells play an important role in tumor escape from host antitumor immunity. Increased frequencies of CD4⁺CD25⁺ regulatory T cells have been documented in the tumor sites, malignant effusions, and peripheral blood of patients with ovarian carcinoma. However, the mechanism involved remains unclear. In the present study, we collected high-purity human CD4⁺CD25⁻CD45RA⁺ naïve T cells by microbead cell separation. These cells did not express FOXP3 by single-cell analysis, and few cells expressed FOXP3 when they were activated with anti-CD3/CD28 dual signal. However, more cells expressed FOXP3 when the supernatant of human epithelial ovarian carcinoma cell culture was added, yet not the supernatant of normal human ovarian surface epithelia cell culture. Neutralization assays revealed that neutralizing antibody against transforming growth factor β (TGF-β), interleukin-10, and interleukin-4 did not abrogate elevated FOXP3 expression induced by carcinoma cell culture supernatant, whereas neutralizing leukemia inhibitory factor (LIF) partially abrogated FOXP3 expression, but LIF alone could not increase FOXP3 expression in activated naïve T cells. Further, an in vitro coculture suppression assay showed that these cells could suppress the proliferation of autologous CD4⁺CD25⁻CD45RA⁻ T cells. In summary, our findings show that ovarian carcinoma cells are able to induce expression of FOXP3 and exhibit suppressive ability in activated naïve T cells by producing soluble substances, and multiple cytokines involve in the induction of FOXP3 expression. ( Cancer Sci 2009)     

RNA-electroporated CD40-activated B cells induce functional T-cell responses against HepG2 cells

Hepatocellular carcinoma (HCC) is one of the incurable tumours in the world. Cell-based immunotherapy, in which antigen-loaded antigen-presenting cells (APCs) are able to elicit T cell responses, has become an alternative treatment for liver cancer. Here, we used HepG2 cells' total RNA-electroporated CD40 ligand-activated B (CD40-B) cells as alternative APC for induction of specific CD8⁺ T-cell responses. The antigen-presenting ability of CD40-B cells was determined by phenotypic analysis, showing a polyclonal, strongly activated B-cell population with high expression of co-stimulatory molecules. To demonstrate the ability of total RNA extracted from HepG2 cells electroporated CD40-B cells to induce CD8⁺ T-cell responses, these RNA-loaded cells were co-cultured with autologous peripheral blood mononuclear cells for 7 days followed by analysis of T-cell antigen specificity. These experiments showed that CD40-B cells electroporated with HepG2 cells' total RNA are capable of activating antigen-specific interferon-γ-producing CD8⁺ T cells, and these T cells activated by CD40-B cells show a killing effect on HepG2 cells. These findings demonstrated that the carcinoma cell derived total RNA-electroporated CD40-B cells could be used as alternative APC for the induction of antigen-specific CD8⁺ T-cell responses, which might be used in HCC immunotherapy.     

Macrophage–T Cell Interaction Is Essential for the Induction of p75 Interleukin 2 (IL–2) Receptor and IL–2 Responsiveness in Human CD4+ T Cells

Fresh human CD8⁺ T cells showed a strong proliferative response to a high concentration of interleukin 2 (IL–2) in the absence of macrophages. In contrast, CD4⁺ T cells revealed no significant IL–2 responsiveness in the absence of macrophages. However, if CD4⁺ T cells were cocultured with macrophages, they showed higher proliferative response to IL–2 than CD8⁺ T cells. In accordance with the magnitude of IL–2 responsiveness, freshly isolated CD8⁺ T cells expressed significant amounts of p75 IL–2 receptor, while fresh CD4⁺ T cells did not express p75 IL–2 receptor. The expression of p75 IL–2 receptor on CD4⁺ T cells was induced by coculture with macrophages. The macrophage–induced p75 IL–2 receptor acquisition was blocked by monoclonal antibody (inAh) against class II antigen. Moreover, the addition of anti–CD4 mAb or anti–class II mAb to the culture caused a great inhibition of IL–2 responsiveness of CD4⁺ T cells. These results strongly suggest that macrophage–T cell interaction through CD4 and/or class II molecules is essential for the expression of p75 IL–2 receptor and IL–2 responsiveness in human CD4⁺, but not CD8⁺ T cells.     

Murine Asialo GM1+CD8+ T Cells as Novel Interleukin-12-responsive Killer T Cell Precursors

Freshly isolated CD8⁺ T cells, but not CD4⁺ T cells, contained 20–30% of asialo GM1⁺ (ASGM1⁺) T cells which were distinct from ASGM1⁺NK1.1⁺ natural killer cells. This novel ASGM1⁺CD8⁺ T cell subpopulation showed a strong proliferative response to interlenkin-12 (IL-12) in the presence of IL-2. Culture of ASGM1⁺CD8⁺ T cells with IL-12 plus IL-2 allowed the generation of anomalous killer T cells concomitantly with the accumulation of cytolytic molecules. Moreover, ASGM1⁺CD8⁺ T cells produced high levels of interferon-γ (IFN-γ), but not IL-4, upon stimulation with IL-12 plus IL-2. Such immune responses were not observed in ASGM1⁻ CD8⁺ T cell snbpopulations constituting the majority of CD8⁺ T cells. These results demonstrated that ASGM1⁺CD8⁺ T cells are a novel subpopulation of IL-12-responsive and IFN-γ-producing killer T cell precursors.     

Natural Antigenic Peptides from Squamous Cell Carcinoma Recognized by Autologous HLA-DR8–restricted CD4+ T Cells

A large number of human tumor antigens recognized by CD8⁺ cytotoxic T lymphocytes (CTL) have been identified. Some of them have been employed in clinical trials and have achieved some objective responses. However, little is known about those that are recognized by CD4⁺ T cells, except for a very few that were identified from melanomas. Previously, we reported that an oral squamous cell carcinoma (SCC) cell line, OSC–20, was effectively lysed by HLA-DRB1·08032 (HLA-DRS)-restricted autologous CD4⁺ T cell line, TcOSC–20. In this study, we performed two steps of chromatographic purification of the tumor cell lysate in combination with mass spectrometry. We found one reverse-phase high-performance liquid chromatography (RP-HPLC) fraction that was effectively recognized by the T cells. We analyzed the fraction by nano-liquid chromatography/electrospray ionization ion trap mass spectrometry (LC/MS/MS) and found six representative ions. We could determine the primary amino acid sequence of each of the six ions. Three of them contained a potential HLA-DR8 binding motif, and TcOSC–20 showed a rather strong cytotoxic response to one of the synthetic pep tides, namely, amino acid residues 321–336 of human a-enolase. Thus, several gene products of squamous cancer cells are endogenously processed and may be presented on HLA class II molecules, so that they could constitute target molecules for autologous CD4⁺ T cells.