Specific recognition of human leukemic cells by allogeneic T cell lines

Clinical and experimental data suggest a role for the immune response in preventing leukemic relapses following allogeneic bone marrow transplantation the graft-versus-leukemia (GVL) effect. In the context of an allogeneic BMT, a number of different immune mechanisms mediated by donor cells may be responsible for the GVL effect. We have approached this question by using limiting dilution cultures of alloactivated human lymphocytes to analyze the in vitro allogeneic cytolytic response against fresh allogeneic leukemia. Initial results in the limiting dilution assays with split culture analyses demonstrated frequent alloreactive cytolytic T lymphocyte precursors that destroyed remission peripheral blood lymphocytes and leukemic cells from the allogeneic leukemic patient. These assays also demonstrated frequent lymphokine-activated killer (LAK) cell precursors that lysed both the LAK sensitive Daudi line and the allogeneic leukemia. In these experiments, isolated cultures also showed cytolytic activity directed against the allogeneic leukemic blasts without activity against remission PBL, or the LAK-sensitive Daudi cell line. Two T cell lines (ABL1 and ABL2) isolated from an LDA, demonstrated this form of specificity, mediating destruction specifically against the allogeneic acute lymphoblastic leukemic cells. Both cell lines ABL1 and ABL2 were CD3+, TCR alpha beta +, and CD4+. These 2 cell lines mediated little or no cytotoxicity against a large panel of other targets tested (natural killer sensitive and resistant cell lines, allogeneic PBL, and allogeneic fresh leukemic blasts). Antibody-blocking experiments revealed a role for the CD3-TCR receptor of both cell lines in lysis of leukemic cells; the CD4 and MHC class II molecules were clearly involved in the lysis by the ABL1 cell line. Specificity of recognition for the allogeneic leukemic blasts was further confirmed by unlabeled target competitive inhibition studies. The mechanism of the preferential lysis of leukemia by the alloactivated T cell lines described in this paper remains uncertain. Nevertheless, these leukemic-specific populations provide a means by which the human GVL effect may be further studied in vitro.     

Naturally occurring prostate cancer antigen-specific T cell responses of a Th1 phenotype can be detected in patients with prostate cancer

BACKGROUND: Cytotoxic T cells (CTL) are considered one of the primary effector cell populations in antitumor immunity. Recent studies, however, have demonstrated the critical importance of helper T cells (Th), specifically interferon gamma (IFN gamma)-secreting Th1 cells, either by supporting an appropriate CTL environment or by recruiting other effector cells. We evaluated whether patients with prostate cancer have naturally occurring Th-cell responses specific for two prostate cancer-associated antigens, prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP), and whether Th1-type responses to these antigens could be detected. METHODS: Peripheral blood mononuclear cells (PBMC) were collected from 80 patients with prostate cancer and 20 male controls without prostate disease. Th-cell responses were evaluated by measuring antigen-specific proliferation. IFN gamma and IL-5 secretion in response to antigen stimulation was determined by enzyme-linked immunosorbent assay. RESULTS: T cell proliferative responses specific for PSA and PAP could be detected in patients with prostate cancer. Six percent (5/80) of patients had T cell responses specific for PSA and 11% (9/80) for PAP. T cell responses specific for PSA were more prevalent in patients with metastatic disease (P = 0.02), whereas responses specific for PAP could be detected in patients irrespective of disease stage. IFN gamma-producing Th cells, specific for both PSA and PAP, could be identified in patients with prostate cancer. CONCLUSIONS: Patients with prostate cancer can have detectable Th-cell responses specific for the prostate cancer-associated proteins PSA and PAP. The presence of antigen-specific Th1 immune responses in prostate cancer patients suggests that an immune environment capable of supporting antigen-specific CTL may exist in vivo. Prostate 47:222-229, 2001.     

Modulation of immune responses after portal venous injection of antigen

BACKGROUND: How the localization of antigen to the liver, through means such as oral ingestion, induces tolerance is poorly understood. METHODS: To elucidate potential mechanisms we used an adoptive transfer system wherein ova-specific T cells were infused into a syngeneic host, and antigen-specific T-cell responses after delivery of soluble antigen into the liver were monitored. RESULTS: After infusion of antigen into the portal vein, the frequency of antigen-specific T cells in lymph nodes draining the liver was lower than the frequency in peripheral lymph nodes. These findings were the reverse of what is typically observed after subcutaneous injection of antigen with adjuvant. Infusion of antigen with adjuvant into the portal vein did not alter this pattern of antigen-specific T-cell localization; however, an increased frequency of T cells, compared with antigen alone, was observed in peripheral lymph nodes and spleen. After exposure to antigen via the portal vein, T cells isolated from lymph nodes draining the liver and challenged with antigen in vitro exhibited a diminished proliferative response compared with T cells isolated from nondraining lymph nodes. This hyporesponsiveness was not observed when the antigen was administered with adjuvant. CONCLUSIONS: Our findings suggest that the influence of the liver on immune responses might reflect two processes: (1) loss of antigen-specific T cells after primary antigen injection, and (2) hyporesponsiveness on reexposure to antigen. These mechanisms may contribute to the prevention of undesirable immune responses to foods and enteric bacteria in the gastrointestinal tract. Furthermore, these results underscore the importance of minimizing inflammation in circumstances such as islet transplantation, if endogenous mechanisms of tolerance induction are to be maximized.     

Immunology and immunotherapy approaches for prostate cancer

Several mechanisms that impair the immune response to promote tumour progression are reported. These mechanisms aim to reduce the ability of antigen-presenting cells to present antigen and activate na?ve T cells to support an active immune response or to create a suppressive environment that induce non-functional tumour-associated antigen-specific T cells. Prostate cancer (PC) alone accounts for 33% of incident cancer cases and about 9% of all cancer-related deaths among men in the USA during 2006. Whereas androgen deprivation has remained the first line of therapy for advanced PC, other therapies are still required due to progression to an androgen-resistant state and eventually loss of control in patients receiving hormonal therapy. Immunotherapy seems to be a promising approach to enhance tumour-specific T-cell responses in different cancers including prostate. More importantly, clinical trials in advanced PC patients have shown that immunotherapy may generate significant clinical responses. Immunology and immunotherapy aspects of PC with focus on prostate-specific antigen will be presented.     

What is the role of T-lymphocyte surveillance in neoplastic disease?

Dramatic advances have recently been made in our comprehension of how thymus-derived (T) lymphocytes function. Principles of both antigen-specific and nonspecific modes of their action in cell-mediated immunity are summarized as follows. First, different functions are carried out by distinct, separable populations of T lymphocytes. Second, all T-cell responses depend on interaction between cells of different functional subclasses. Thus, target cell killing of cytotoxic T lymphocytes depends on separate, coincident recognition of antigen by pre-cytotoxic T lymphocytes and by amplifier T cells that supply a nonspecific but critical lymphokine. Immunosuppressive drugs such as cyclosporin A and dexamethasone block this interaction at different points.Antigen-specific amplifier T cells also secrete various polypeptide factors that augment the impact of macrophage cytotoxicity, and immune interferon, which stimulates natural killer (NK) cells. Thus, even in cases where T cells are not the effectors, activation of T cells can potentiate host defenses. However, immune paralysis can result from stimulation of antigen-specific suppressor T cells. These act on effector cells directly or on their amplifier cells. The route of immunization often influences the balance between suppression and activation. Suppressor and amplifier T cells may be killed differentially by drugs like cyclophosphamide.Other cases of nonresponsiveness result from the way T cells actually recognize antigen. T cells only react with antigen in cell-surface complexes with self-histocompatibility antigen. Some otherwise-stimulatory antigens cannot form immunogenic complexes with the products of certain histocompatibility alleles, so that nonresponsiveness to those antigens is genetically predetermined. Overall, the centrality of T-lymphocyte surveillance in controlling spontaneous neoplasms is challenged by the low incidence of malignancy in T cell-deficient animals. This controversy will be examined both with reference to the lesions in T-cell development in these cases and with reference to the auxiliary roles played by T cells in amplifying the responses of non-T effector cells.     

Impairment of allograft tumor immunity by isotype-like suppression of antigen-specific T cell factors

PCl-F is an antigen-binding factor that is derived from T cells of picryl chloride (PCl) contact-sensitized mice. Intravenous transfer of PCl-F into naive recipients, followed immediately by PCl challenge, results in the ability to elicit an immediate hypersensitivity-like cutaneous response. This PCl-F-dependent early response is an obligatory step in the mediation of a PCl-specific delayed-type hypersensitivity reaction by late-acting, antigen/MHC-restricted effector T cells. These latter cells recruit a local infiltrate of inflammatory cells by producing chemoattractant lymphokines. Injection of PCl-F also induces a T cell-dependent feedback circuit that ultimately suppresses production of PCl-F, and thus suppresses DTH to PCl. This form of regulation is not antigen-specific, since PCl-F induces suppression of DTH to PCl and to other antigens via suppression of the production of antigen-binding T cell factors necessary for initiation of DTH. This form of regulation does not affect classic, late-acting, lymphokine-producing effector T cells of DTH, or helper T cells for antibody responses. We now report that injection of PCl-F is also capable of inducing suppression of cutaneous hypersensitivity responses to allogeneic and syngeneic tumor cells, and of immune resistance to an allogeneic tumor graft. Our results suggest, therefore, that antigen (tumor)-specific T cell factors play a role in initiation of hypersensitivity responses to tumor cells. Injection of PCl-F suppressed, besides tumor-specific cutaneous hypersensitivity, production of the tumor-specific T cell factor that renders macrophages cytotoxic to tumor cells (i.e., specific macrophage-arming factor or SMAF). Thus, PCl-F injection may impair immune resistance to tumor cells by suppressing initiation of hypersensitivity responses that recruit macrophages, and also by inhibiting production of SMAF that renders macrophages cytotoxic. It is therefore tempting to conclude that the antigen-specific T cell factors that initiate DTH, such as PCl-F and SMAF, belong to the same isotype or group of antigen-specific T cell products that can be regulated by a form of feedback suppression that is isotype-like and inhibits production of these related, antigen-specific T cell factors.     

Interleukin-12 from intrinsic cells is an effector of renal injury in crescentic glomerulonephritis

Interleukin-12 (IL-12) directs the cognate nephritogenic T helper type 1 responses that initiate renal injury in murine crescentic glomerulonephritis (GN). The recent demonstration of IL-12 production by intrinsic renal cells, including mesangial and proximal tubular cells, raises the possibility that IL-12 from nonimmune cells may contribute to inflammatory renal injury. To address this possibility, the development of sheep anti-mouse glomerular basement membrane globulin-induced crescentic GN was studied in C57BL/6 wild-type (WT), IL-12-deficient (IL-12 -/-), and IL-12 "chimeric" mice. IL-12 chimeric mice were produced by transplantation of WT bone marrow into IL-12 -/- mice to restore IL-12 production by immune cells, while leaving them deficient in renal IL-12 production. WT and "sham" chimeric mice (normal bone marrow transplanted into WT mice) developed crescentic GN with glomerular T-cell and macrophage recruitment and impaired renal function (elevated proteinuria and serum creatinine) 10 d after initiation of GN. IL-12 -/- mice showed significant protection from GN. Chimeric IL-12 mice showed significant attenuation of crescent formation, glomerular T-cell and macrophage accumulation, and renal impairment, compared with WT and sham chimeric mice, but were not protected to the same extent as IL-12 -/- mice. IL-12 chimeric mice showed no attenuation of their systemic cognate immune response to the nephritogenic antigen (sheep globulin), indicated by antigen-specific circulating antibody and cutaneous delayed-type hypersensitivity. These studies indicate that IL-12 produced by non-bone marrow derived intrinsic renal cells contributes to immune renal injury. They provide the first in vivo demonstration of a proinflammatory role for an intrinsic renal cell-derived cytokine in renal inflammation.     

Induction of tumor-specific cytotoxic T lymphocytes in cancer patients by autologous tumor RNA-transfected dendritic cells

OBJECTIVE: To demonstrate the feasibility of inducing tumor antigen-specific immune responses in patients with metastatic cancer using total tumor RNA-loaded dendritic cells (DCs). SUMMARY BACKGROUND DATA: The authors have shown that DCs transfected with mRNA encoding defined tumor antigens induce tumor antigen-specific T-cell responses in vitro and in vivo. There may be significant advantages to inducing immune responses against the entire repertoire of antigens expressed by a patient's autologous tumor. METHODS: RNA was extracted from a metastatic colon cancer and used to load autologous DCs. The DCs were coincubated with autologous T cells and the cytolytic activity of the T cells was assessed by the ability to lyse the autologous tumor cells. RNA was then extracted from a metastatic lung cancer and used to load autologous DCs, followed by four injections of the DC vaccine given every 4 weeks. Tumor antigen-specific cytotoxic T lymphocyte activity was then evaluated by testing peripheral blood mononuclear cells for their ability to lyse an antigen-expressing target. RESULTS: DCs transfected with the total RNA content of autologous tumor cells stimulated antigen-specific T-cell responses that are capable of recognizing and lysing autologous, primary tumor cells in vitro. Tumor-specific immune responses were induced in a patient with a carcinoembryonic antigen-expressing adenocarcinoma after immunization with autologous DCs transfected with total tumor RNA. CONCLUSIONS: DCs transfected with total tumor RNA may represent a method for inducing immune responses against the entire repertoire of tumor antigens of surgically resected malignancies.     

Antibodies and vaccines–hope or illusion?

The search for target molecules on tumor cells eliciting strong immune responses in cancer patients has been pursued over decades. Growth factors and their respective receptors were discovered as suitable targets for passive or active immunotherapy approaches. Monoclonal antibodies directed against some of these targets like the proto-oncogene HER2/neu have become an accepted standard of therapy in the clinical management of subgroups of HER2/neu overexpressing breast cancer patients and in other malignancies. Antibodies against multiple other target molecules like epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), etc., are explored in ongoing trials in order to enter clinical practice in the near future. More recently, potent techniques have been developed to identify cancer antigens eliciting spontaneous immune responses in cancer patients. Cancer vaccination strategies targeting some of these cancer antigens have also been developed, and are maturing for clinical application. With reliable immunomonitoring techniques in place it has been shown that vaccination with some of these cancer antigens may induce strong integrated (humoral and cellular) immune responses in antigen-positive cancer patients. A prominent example is the cancer testis (CT-) antigen NY-ESO-1, which is expressed in 30% of all breast cancers. NY-ESO-1 is one of the most immunogenic human cancer antigens known to date. The aim of ongoing clinical trials is to induce or augment preexisting immune responses in cancer patients with strong NY-ESO-1 positive disease. There is preliminary evidence that patients with strong NY-ESO-1-specific immune responses have more favorable courses of disease. In several clinical phase I trials targeting HER2/neu it was shown that antigen-specific T cell responses could be induced. Another new cancer antigen explored for cancer vaccination is the breast differentiation antigen NY-BR-1, expressed in 70% of all tested primary breast cancers. Although this cancer antigen is still in preclinical testing, its strong and restricted pattern of expression in breast cancer makes it a promising target for clinical development. For all cancer vaccines there is mounting evidence that the stage of disease to be targeted is minimal residual disease or in adjuvant settings.     

Antibodies and vaccines--hope or illusion?

The search for target molecules on tumor cells eliciting strong immune responses in cancer patients has been pursued over decades. Growth factors and their respective receptors were discovered as suitable targets for passive or active immunotherapy approaches. Monoclonal antibodies directed against some of these targets like the proto-oncogene HER2/neu have become an accepted standard of therapy in the clinical management of subgroups of HER2/neu overexpressing breast cancer patients and in other malignancies. Antibodies against multiple other target molecules like epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), etc., are explored in ongoing trials in order to enter clinical practice in the near future. More recently, potent techniques have been developed to identify cancer antigens eliciting spontaneous immune responses in cancer patients. Cancer vaccination strategies targeting some of these cancer antigens have also been developed, and are maturing for clinical application. With reliable immunomonitoring techniques in place it has been shown that vaccination with some of these cancer antigens may induce strong integrated (humoral and cellular) immune responses in antigen-positive cancer patients. A prominent example is the cancer testis (CT-) antigen NY-ESO-1, which is expressed in 30% of all breast cancers. NY-ESO-1 is one of the most immunogenic human cancer antigens known to date. The aim of ongoing clinical trials is to induce or augment preexisting immune responses in cancer patients with strong NY-ESO-1 positive disease. There is preliminary evidence that patients with strong NY-ESO-1-specific immune responses have more favorable courses of disease. In several clinical phase I trials targeting HER2/neu it was shown that antigen-specific T cell responses could be induced. Another new cancer antigen explored for cancer vaccination is the breast differentiation antigen NY-BR-1, expressed in 70% of all tested primary breast cancers. Although this cancer antigen is still in preclinical testing, its strong and restricted pattern of expression in breast cancer makes it a promising target for clinical development. For all cancer vaccines there is mounting evidence that the stage of disease to be targeted is minimal residual disease or in adjuvant settings.     

WT1-specific CTL cells of recipient origin may exist in the peripheral blood of patients achieving full donor chimerism soon after nonmyeloablative transplantation

This study was performed to assay whether leukemia-associated antigen (LAA)-specific CTLs of recipient origin existed in the blood of patients who achieved full donor chimerism (FDC) soon after nonmyeloablative transplantation (NST). In 15 patients who received haplo-identical NST, WT1(+) CD8(+) CTLs were detected with WT1/HLA-A*0201 pentamer, and the donor-recipient chimerism levels were analyzed by three methods. Results showed that WT1(+) CD8(+) CTLs could be detected in patients with HLA-A*0201 expressing only in recipient, and cells of recipient origin existed in the blood of patients who achieved FDC, which suggested that LAA-specific CTLs of recipient origin may exist in patients achieving FDC soon after NST.     

IFN-gamma mediates crescent formation and cell-mediated immune injury in murine glomerulonephritis

Features of crescentic glomerulonephritis suggest that it results from a T helper 1 (Th1) nephritogenic immune response. Interferon-gamma (IFN-gamma), produced by Th1 cells, is involved in T cell-directed macrophage activation in effector Th1 responses. The hypothesis that endogenous IFN-gamma contributes to the development of crescentic glomerulonephritis was tested by comparing the development of glomerulonephritis (induced by a planted antigen) and immune responses in normal C57BL/6 mice (IFN-gamma +/+) and in mice genetically deficient in IFN-gamma (IFN-gamma -/-). Ten days after the initiation of glomerulonephritis, IFN-gamma -/- mice developed fewer glomerular crescents (5+/-1% versus 26+/-3%, P<0.005), less severe glomerular injury, and less renal impairment. Effectors of delayed-type hypersensitivity (CD4+ T cells, macrophages, and fibrin) in glomeruli were reduced in IFN-gamma -/- mice. Skin delayed-type hypersensitivity to sheep globulin was reduced. Total antigen-specific Ig and splenocyte interleukin-2 production were unchanged, but antigen-specific serum IgG2a was reduced. Markers of an antigen-specific Th2 response (serum IgG1, splenocyte interleukin-4) were unchanged. Studies 22 d after the initiation of glomerulonephritis showed that IFN-gamma -/- mice still had fewer crescents (11+/-2% versus 22+/-3%, P = 0.02) and glomerular CD4+ T cells and macrophages than IFN-gamma +/+ mice. These studies demonstrate that endogenous IFN-gamma mediates crescentic glomerulonephritis by promoting cell-mediated immune injury. They support the hypothesis that crescentic glomerulonephritis is a manifestation of a Th1 nephritogenic immune response.     

Impaired immune responses and antigen-specific memory CD4+ T cells in hemodialysis patients

Serologic responses to T cell-dependent vaccinations are severely attenuated in patients with ESRD, but the reasons for this is unknown. In this study, a detailed analysis of antigen-specific T cell responses was performed. Patients on hemodialysis and age- and gender-matched healthy control subjects were vaccinated with hepatitis B surface antigen (HBsAg), antigen-specific CD4(+) T cells were monitored at regular intervals with intracellular cytokine staining and proliferation assays. IL-2-and IFN-gamma-producing CD4(+) T cells were identified as either central or effector memory CD4(+) T cells using antibodies directed against CD45RO and the chemokine receptor CCR7. Control subjects mounted a memory T cell response comprising both central and effector memory CD4(+) T cells, with the central memory response occurring 1 wk before the effector memory response. IL-2(+) HBsAg-specific memory CD4(+) T cells were primarily detected within the effector population. Patients with ESRD showed a delayed response of IL-2-and IFN-gamma-producing central memory CD4(+) T cells, but their maximal responses were similar to those of control subjects. In contrast, patients with ESRD produced only 6.3% of the IL-2(+) HBsAg-specific effector memory CD4(+) T cells produced by control subjects (0.5 +/- 0.2 x 10(4)/L versus 8 +/- 3.5 x 10(4)/L; P < 0.001), and this impaired response correlated with antigen-specific T cell proliferation and anti-HBsAg IgG titers. In conclusion, the production of antigen-specific effector memory CD4(+) T cells after vaccination, which is critical to achieve an adequate humoral response, is severely impaired in patients with ESRD.     

Effective antigen cross-presentation by prostate cancer patients' dendritic cells: implications for prostate cancer immunotherapy

Despite the potency with which dendritic cells (DCs) are able to utilize the exogenous MHC I antigen cross-presentation pathway to cross-present antigen for the activation of killer T cells in model systems, concern about defects in immune function in cancer patients has led to uncertainty regarding whether immune cells derived from patients can effectively be used to generate tumor vaccines. We have undertaken a careful analysis of the potency of using DCs obtained from prostate cancer patients to cross-present antigen derived from human prostate tumor cells for the activation of antigen-specific T cells. Such DCs can be matured ex vivo into functionally active cells and are capable of cross-presenting influenza antigen derived from internalized apoptotic prostate tumor cells. Importantly, we demonstrate effective stimulation of both CD4+ and CD8+ T cells, as evident by production of IFN-gamma, and the ability of CD8+ T cells to differentiate into effector CTLs. These results, defining conditions in which prostate cancer patient DCs can efficiently utilize the cross-presentation pathway and in which apoptotic tumor can serve as a source of antigen for DCs to activate T cells, demonstrate that this system warrants clinical study as a potential immunotherapy.     

Presence and specificity of tumor associated lymphocytes from ascites fluid in prostate cancer

BACKGROUND: In the present study, we had the rare opportunity to study immunological responses of TAL from ascites fluid in a patient with hormone-refractory prostate cancer. METHODS: We evaluated tumor antigen-specific T-cell responses, induced by either prostate specific antigen (PSA) pulsed dendritic cells (DCs) or PSA peptides, in TAL and peripheral blood lymphocytes. RESULTS: DC stimulation with PSA protein induced recognition of naturally processed PSA epitopes by both blood and ascites T cells. In contrast, only ascites T cells recognized the PSA-3 peptide, after stimulation with PSA-pulsed DCs or peptides. Finally, although IFNgamma secreting T cells were detectable in both blood and ascites by ELISPOT, multiplex cytokine assay detected the presence of predominantly Th2 cytokines. CONCLUSIONS: Although tumor antigen-specific TAL were detected in ascites fluid, these cells were producing immunosuppressive cytokines which may contribute to tumor escape from recognition and/or destruction by the immune system.     

Antigen-specific tumor vaccine efficacy in vivo against prostate cancer with low class I MHC requires competent class II MHC

BACKGROUND: Cancers can escape immune recognition by means of evading class I major histocompatibility complex (MHC) -mediated recognition by cytotoxic T lymphocytes. However, immunization strategies targeting defined tumor-associated antigens have not been extensively characterized in murine prostate cancer models. Therefore, we evaluated antigen-specific, antitumor immunity after antigen-encoding vaccinia immunization against mouse prostate cancer cells expressing a model tumor-associated antigen (beta-galactosidase) and exhibiting partially deficient class I MHC. METHODS AND RESULTS: Low class I MHC expression in beta-galactosidase-expressing D7RM-1 prostate cancer cells was shown by fluorescence activated cell sorting, and deficient class I MHC-mediated antigen presentation was shown in resistance of D7RM-1 to cytolysis by beta-galactosidase-specific cytotoxic T lymphocytes (CTL). Despite partially deficient class I MHC presenting function, immunization with vaccinia encoding beta-galactosidase conferred antigen-specific protection against D7RM-1 cancer. Antigen-specific immunity was recapitulated in beta(2)m knockout mice (with deficient class I MHC and CTL function), confirming that class I MHC antigen presentation was not required for immunity against tumor partially deficient in class I MHC. Conversely, antigen-specific antitumor immunity was abrogated in A(b)beta knockout mice (with deficient class II MHC and helper T cell function), demonstrating a requirement for functional class II MHC. Resistant tumors from the otherwise effectively immunized beta(2)m knockout mice (among which tumor progression had been reduced or delayed) showed reduced target antigen expression, corroborating antigen-specificity (and showing an alternative immune escape mechanism), whereas antigen expression (like tumor growth) was unaffected among A(b)beta knockout mice. CONCLUSION: Our results demonstrate that class I MHC-restricted antigen presentation and CTL activity is neither necessary nor sufficient for antigen-encoding vaccinia immunization to induce protective immunity against class I MHC-low tumors, whereas host class II MHC-mediated antigen presentation facilitates antigen-specific immunity against prostate cancer in vivo. Reduced expression of the target antigen developed rapidly in vivo as an immune escape mechanism for such cancers.     

Studies of lymphocyte-dependent antibodies to leukemia-associated antigens using frozen stored leukemia target cells.

The ability of frozen stored leukemia blast cells to participate in a lymphocyte-dependent antibody assay (LDA) is demonstrated. Frozen stored acute myelogenous and lymphocytic blast cells retained antigenicity and high viability (larger than or equal to 80%). High titer LDA reactivity against frozen stored leukemic blasts was demonstrated with heterologous (rabbit) and homologous (leukemic patient) antisera. Similarly, we demonstrated the ability of frozen stored peripheral blood mononuclear cells to mediate effectively the destruction of antibody-coated leukemia blast cells stored frozen in liquid nitrogen before use. These findings will facilitate the study of LDA and antibody-dependent cellular cytotoxicity in human leukemia patients using a completely autogeneic system.     

Transplantation preferentially induces a KLRG-1lo CD127hi differentiation program in antigen-specific CD8+ T cells

Models of infection have shaped our understanding of programmed memory T cell differentiation, yet whether these models apply to memory programming in the context of transplantation has yet to be defined. Previous work has identified differences in the response of antigen-specific CD8⁺ T cells to cognate antigen based on the environment in which the antigen is presented. Thus, we hypothesized that programming of antigen specific CD8⁺ T cells responding to graft and pathogen may be dissimilar. Here we find that antigen-specific CD8⁺ T cells primed by a skin graft contract faster than those primed by gammaherpesvirus (gHV), yet are able to expand more rapidly upon rechallenge. Moreover, graft-primed antigen-specific CD8⁺ T cells exhibited higher frequencies of cells secreting IL-2 and demonstrate lower expression of KLRG-1, which are qualities suggestive of increased recall potential. Additionally, the expression of CD127 at a memory time point suggests graft-elicited CD8⁺ antigen specific T cells are maintained in a less terminally-differentiated state compared to gHV-elicited CD8⁺ antigen specific T cells, despite fewer cells being present at that time point. Taken together, our findings suggest that the surface marker expression and functional profiles of T cells depends on the priming conditions and may be used to predict immunologic risk following transplantation after traditional allosensitization or heterologous immune priming.     

Purified donor T cells alone activate transplantation immunity to the male antigen but induce tolerance in combination with Mac-1+ donor cells.

BACKGROUND: In most experimental systems examined, "professional" antigen-presenting cells (APCs), such as dendritic cells, have been found to activate T cells, whereas "nonprofessional" antigen-bearing cells (nonAPC) may induce tolerance. Some recent studies have suggested that nonAPCs may under certain conditions prime a T-cell immune response. We have attempted to separate the roles of transplanted T cells and monocytic/dendritic cells in activating or tolerizing antigen-specific T cells in vivo, by examining the consequences of parenteral exposure to male antigen in anti-male TCR transgenic female mice. METHODS: Qualitative and quantitative changes in the large population of male-reactive transgenic T cells to various male donor cell populations in transgenic female mice were followed after injections of highly purified male lymphoid cells. Changes in male-reactive T cells with time and the long-term outcome of male skin grafts were measured. RESULTS: When a nonAPC population consisting of highly purified male T cells alone was injected intravenously into H-Y antigen-specific TCR transgenic female mice, the number of host transgenic T cells was sustainably increased, and male graft rejection was accelerated. Injection of a combination of purified T cells and purified Mac-l+ cells induced massive and permanent deletion of the host male-reactive T-cell population and permanent graft tolerance. Mac-l+ cells alone gave no appreciable change in responsive T cells or graft rejection times. CONCLUSIONS: The data indicate that highly purified T cells engrafted alone induce rapid sensitization toward the male antigen. They also show that both male donor T cells and a population of male monocytic/ dendritic cells are required to induce peripheral tolerance toward this antigen and that this tolerance is related to permanent peripheral deletion of male-reactive T cells.