Lineage-specific expression of a T cell receptor variable gene promoter controlled by upstream sequences.

We have characterized the sequence contribution of DNA 5' of a functionally rearranged TCR promoter (V beta 8.1) on its T lineage-specific expression through the use of the chloramphenicol acetyl-transferase (CAT) reporter gene. A 230-bp fragment located 570 bp upstream of the determined transcription start site of the V beta 8.1 promoter confers a T lineage specificity of expression to a heterologous promoter. The inability of the V beta 8.1 promoter and its associated elements to function in B cells suggests the existence of a mechanism to prevent inappropriate V beta gene expression in B cells. Of considerable interest is the fact that both a B cell-specific and a nontissue-specific enhancer element were incapable of stimulating significant expression of this promoter in B cells. We discuss the implication of these results on the process of rearrangement of both Ig and TCR genes, and the differentiation of the lymphoid system.

Inhibition or activation of human T cell receptor transfectants is controlled by defined, soluble antigen arrays.

We present evidence that direct T cell receptor (TCR) occupancy by antigen can either activate or inhibit T cells, depending upon whether or not a threshold number of local TCRs are crosslinked by multivalent arrays of the antigen. Variants of Jurkat cells were previously transfected with TCR alpha and beta chains that bind fluorescein, yielding FL-TCR+ human T cells. The transfectants are activated upon binding soluble multivalent antigen arrays at concentrations well below those required for monovalent interactions. This activation, measured by calcium fluxes and interleukin 2 (IL-2) production, indicates the superior binding avidity of multivalent ligands. Smaller, less multivalent arrays do not activate the cells, but antagonize larger arrays, demonstrating that antigen can bind TCR as either agonist or antagonist. The balance between activation and inhibition depends upon antigen array size, ligand valence, and concentration, indicating that a threshold extent of receptor crosslinking, and not individual perturbations of single TCR, is required for activation by antigen. Approximately 100 stimulatory arrays specifically bind per FL-TCR+ cell at concentrations where IL-2 production is half-maximal.

Major histocompatibility complex independent T cell receptor-antigen interaction: functional analysis using fluorescein derivatives.

We have isolated T cell receptor (TCR) cDNAs from fluorescein (FL)-specific human T cell clones (alpha FL beta FL), and transferred them to TCR beta- Jurkat cells in order to study direct FL-binding to the TCR. Using either FL-conjugated polymers (FL-polymer) or FL-substituted Sepharose beads, we are able to demonstrate the direct binding of antigen to the T cell surface, and the functional activation of the T cell transfectants. We present evidence against the involvement of major histocompatibility complex (MHC) molecules or antigen presentation in the interaction of FL with the alpha FL beta FL transfectants. Additionally, we have examined the effect of ring substitutions on the FL molecule as well as specific alterations of substituents attached to the 5' position, and we have found that all of them interfere with the functional recognition of the alpha FL beta FL TCR. These experiments demonstrate that TCRs like antibodies have intrinsic affinities for antigen, even without the involvement of MHC molecules.

Programmed death-1 receptor and interleukin-10 in liver transplant recipients at high risk for late cytomegalovirus disease.

Despite significant advances in antiviral treatment, solid organ transplant (SOT) recipients remain at heightened risk for developing late cytomegalovirus (CMV) disease. Elevated inhibitory immune signaling suggests a state of immune impairment in SOT recipients, who do not control CMV infection and develop severe clinical symptoms after discontinuation of antiviral prophylaxis. We longitudinally monitored the negative immune modulator programmed death (PD)-1 receptor on both CD4 and CD8 T cells, co-expressing the CD137 surface marker of recent activation, in a liver transplant cohort. Liver recipients who progressed to CMV disease expressed elevated levels of PD-1 on CD137(+) CD4 and CD8 T cells, following stimulation with either full-length peptide libraries or CMV lysate. This novel approach, applicable to a multitude of human leukocyte antigen types, enhances the usefulness of the PD-1 measurements as a clinical strategy to predict late CMV disease. In parallel, we detected an increased level of the immunosuppressive cytokine interleukin (IL)-10, in plasma of liver recipients diagnosed with CMV disease. CMV-specific T cells were still functional when both PD-1 and IL-10 were upregulated; however they showed a marked proliferation deficit, which may limit their ability to contain viremia and lead to CMV disease. Our preliminary observations support further investigation of dual monitoring of PD-1 and IL-10, as potential immune markers of CMV disease.

Evaluation of safety and efficacy of p53MVA vaccine combined with pembrolizumab in patients with advanced solid cancers.

BACKGROUND: Vaccination of cancer patients with p53-expressing modified vaccinia Ankara virus (p53MVA) has shown in our previous studies to activate p53-reactive T cells in peripheral blood but without immediate clinical benefit. We hypothesized that the immunological responses to p53MVA vaccine may require additional immune checkpoint blockade to achieve clinically beneficial levels. We therefore conducted a phase I trial evaluating the combination of p53MVA and pembrolizumab (anti-PD-1) in patients with advanced solid tumors. PATIENTS AND METHODS: Eleven patients with advanced breast, pancreatic, hepatocellular, or head and neck cancer received up to 3 triweekly vaccines in combination with pembrolizumab given concurrently and thereafter, alone at 3-week intervals until disease progression. The patients were assessed for toxicity and clinical response. Correlative studies analyzed p53-reactive T cells and profile of immune function gene expression. RESULTS: We observed clinical responses in 3/11 patients who remained with stable disease for 30, 32, and 49 weeks. Two of these patients showed increased frequencies and persistence of p53-reactive CD8+ T cells and elevation of expression of multiple immune response genes. Borderline or undetectable p53-specific T cell responses in 7/11 patients were related to no immediate clinical benefit. The first study patient had a grade 5 fatal myocarditis. After the study was amended for enhanced cardiac monitoring, no additional cardiac toxicities were noted. CONCLUSION: We have shown that the combination of p53MVA vaccine with pembrolizumab is feasible, safe, and may offer clinical benefit in select group of patients that should be identified through further studies.

Targeting of human p53-overexpressing tumor cells by an HLA A*0201-restricted murine T-cell receptor expressed in Jurkat T cells.

A potent anti-human (hu) p53 CD8+ CTL response develops in HLA A*0201 transgenic (Tg) mice after immunization with peptides corresponding to HLA A*0201 motifs from hu p53. Mice immunized with the hu P53(149-157) peptide develop a CTL response that is of moderately high affinity and is capable of recognizing hu tumor cells expressing mutated p53. In this report, the mRNAs encoding the predominantly expressed T-cell receptor (TCR) sequences were molecularly cloned from a murine (mu) CTL clone derived from immunized Tg mice, which recognized endogenously processed hu p53 restricted by HLA A*0201. The separate A and B chain TCR cDNAs were transfected in the corresponding TCR A- and B- Jurkat-CD3- mutant T-cell lines, and each rescued CD3 surface expression. Both TCR chains were simultaneously introduced into Jurkat-CD3+ cells, and the transfected Jurkat cells recognized hu T2 cells sensitized with the p53(149-157) CTL epitope but not T2 cells sensitized with a nonspecific CTL epitope. Breast, pancreatic, and sarcoma tumor cell lines, which overexpress endogenous mutated p53, were recognized in the presence of anti-CD28 costimulation, only if they also expressed HLA A*0201. Normal hu fibroblasts established from skin cultures were not recognized. These results represent the first time that a p53-specific TCR capable of recognizing hu cancer cells was heterologously expressed in a naive recipient cell, converting that cell to one recognizing hu tumor cells with mutated p53. This TCR represents a candidate molecule for a genetic strategy in combating hu cancer by an adoptive immunotherapy approach, which uses the strong xenorecognition of hu p53 in mice.

Targeting p53 for adoptive T-cell immunotherapy.

p53 gene mutations occur in most human cancers and result in an altered protein product that accumulates within the cell. Although the observed endogenous human CTL response to p53 is weak, high-affinity, human p53-specific CTLs have been generated from HLA A2.1 transgenic mice immunized with human CTL epitope peptides. In this study, we examine the ability of HLA A2.1-restricted and human p53-specific CTLs from HLA A2.1 transgenic mice to suppress the growth of p53-overexpressing human tumors in severe combined immunodeficient (SCID) mice. In vitro, murine p53(149-157)-specific CTLs selectively lysed the p53-overexpressing pancreatic carcinoma cell line Panc-1 but did not recognize HLA A2.1- tumor cells or HLA A2.1+ normal human fibroblasts. Furthermore, in vivo, the growth of established human tumor xenografts in SCID mice was significantly reduced and survival was prolonged after the administration of p53-specific CTLs but not after the administration of control CTLs or PBS alone. Following treatment with p53(149-157)-specific CTLs, regressing Panc-1 tumors were infiltrated by the CD8+ CTLs, as demonstrated by immunohistochemistry. These findings suggest that p53(149-157)-specific and HLA A2.1-restricted murine CTLs suppress the growth of established Panc-1 tumors following adoptive transfer into SCID hosts and prolong their survival.

CD56dimCD57+NKG2C+ NK cell expansion is associated with reduced leukemia relapse after reduced intensity HCT.

We have recently described a specialized subset of human natural killer (NK) cells with a CD56(dim)CD57(+)NKG2C(+) phenotype that expand specifically in response to cytomegalovirus (CMV) reactivation in hematopoietic cell transplant (HCT) recipients and exhibit properties characteristic of adaptive immunity. We hypothesize that these cells mediate relapse protection and improve post-HCT outcomes. In 674 allogeneic HCT recipients, we found that those who reactivated CMV had lower leukemia relapse (26% (17-35%), P=0.05) and superior disease-free survival (DFS) (55% (45-65%) P=0.04) 1 year after reduced intensity conditioning (RIC) compared with CMV seronegative recipients who experienced higher relapse rates (35% (27-43%)) and lower DFS (46% (38-54%)). This protective effect was independent of age and graft-vs-host disease and was not observed in recipients who received myeloablative regimens. Analysis of the reconstituting NK cells demonstrated that CMV reactivation is associated with both higher frequencies and greater absolute numbers of CD56(dim)CD57(+)NKG2C(+) NK cells, particularly after RIC HCT. Furthermore, expansion of these cells at 6 months posttransplant independently trended toward a lower 2-year relapse risk. Together, our data suggest that the protective effect of CMV reactivation on posttransplant relapse is in part driven by adaptive NK cell responses.

Regulation of growth hormone messenger RNA synthesis by dexamethasone and triiodothyronine. Transcriptional rate and mRNA stability changes in pituitary tumor cells.

We have characterized the process by which the growth hormone (GH) gene is stimulated in rat pituitary tumor cells (GC or GH3) by the steroid hormone dexamethasone (Dex) and the thyroid hormone, L-triiodothyronine (T3). A primary transcriptional response is detected within 60 minutes of addition of T3 or Dex + T3 to GH-producing cells (GC or GH3). A fivefold transcriptional stimulation of GH nuclear RNA occurs in cells cultured with serum substitute medium and induced with Dex + T3, while T3 alone induces a modest two- to threefold stimulation. The absence of fetal calf serum from the cell culture medium does not decrease the level of transcriptional activity of the GH gene during hormone stimulation. Twenty-four hours after addition of Dex + T3 the cytoplasmic GH mRNA shows a 50-fold increase, as measured by S1 nuclease analysis. This large accumulation of cytoplasmic GH mRNA in contrast to the relatively small changes in GH gene activity is inconsistent with solely a transcriptional mechanism of hormone induction. We suggest that a change in specific GH mRNA stability also takes place in response to Dex + T3. In contrast to other reports, transcriptional stimulation of the GH gene by Dex is insignificant except in the presence of T3.

Immunochemical and molecular analysis of antigen binding to lipid anchored and soluble forms of an MHC independent human alpha/beta T cell receptor.

We have constructed antigen-specific chimeric human T cell receptor (TCR) molecules deleted of the transmembrane domain and containing the signal sequence for the biosynthesis of the phosphatidyl inositol glycan (GPI) linkage. These membrane-anchored forms of the TCR alpha and beta chains have been expressed in non-T cells, and they are recognized by alpha or beta TCR specific monoclonal antibodies. We have utilized both immunochemical methods and flow cytometry to prove that the enzyme phosphatidylinositol phospholipase C (PI/PLC) is able to cleave the GPI anchored TCR as a heterodimer from the CHO cell surface. We have demonstrated that the alpha/beta TCR heterodimer on the surface of CHO cells will recognize and bind polymers containing fluorescein (FL-polymer), and the binding activity is completely eliminated by the enzyme, PI/PLC. Moreover, soluble forms of the alpha/beta heterodimer will bind tightly to FL substituted sepharose, which demonstrates the retention of biological activity by the TCR after solubilization. Molecular modelling of the putative antigen binding site of the alpha FL beta FL TCR was derived from the known atomic coordinates of eight different hapten or peptide specific antibodies. Mutagenesis of several residues predicted from the model to be important in FL binding gave results consistent with involvement of Ig equivalent CDR2 and CDR3 domains in the antigen binding pocket. Therefore, using a model hapten system in studying recognition of the TCR independent of MHC interactions, we conclude that amino acid residues located in similar positions within CDR domains as compared to the case of MHC restricted TCR recognition are used in the binding of either hapten or peptide antigens.

Real-time assessment of relapse risk based on the WT1 marker in acute leukemia and myelodysplastic syndrome patients after hematopoietic cell transplantation.

Relapse is the major cause of treatment failure after allogeneic hematopoietic cell transplantation (alloHCT) for acute leukemia and myelodysplastic syndrome (MDS). Wilms' tumor Ag (WT1) is overexpressed in the majority of acute leukemia and MDS patients and has been proposed as a universal diagnostic marker for detection of impending relapse. Comprehensive studies have shown that WT1 transcript levels have predictive value in acute leukemia patients in CR after chemotherapy. However, the focus of this study is the period after alloHCT for predicting relapse onset. We analyzed the accumulation of WT1 mRNA transcripts in PB of 82 leukemia and MDS patients and defined specific molecular ratios for relapse prediction. The extensively validated WT1/c-ABL ratio was used to normalize increases in WT1 transcript levels. The observed lead time of crossing or exceeding set WT1 levels is presented along with linear interpolation to estimate the calculated day the WT1 thresholds were crossed. The WT1/c-ABL transcript ratio of 50 or above yielded 100% specificity and 75% sensitivity reliably predicting future relapse with an observed average of 29.4 days (s.d.=19.8) and a calculated average of 63 days (s.d.=29.3) lead time before morphologic confirmation. A lower ratio of 20 or above gave lower specificity, but higher sensitivity (84.8% and 87.5%, respectively) identified more patients who relapsed, at earlier times, providing an earlier warning with actual average lead time of 49.1 days (s.d.=30.8) and calculated average of 78 days (s.d.=28.8). WT1 transcript levels serve as a diagnostic relapse test with greater sensitivity than the morphologic approach used in the clinic as a readout.

Effects of rat growth hormone (rGH)-releasing factor and somatostatin on the release and synthesis of rGH in dispersed pituitary cells.

The effects of rat hypothalamic GH-releasing factor (GRF) and somatostatin (SRIF) on the release and biosynthesis of rat GH were studied by RIA and quantitative immunoprecipitation using monolayer cultures of rat anterior pituitary cells. In kinetic studies, GRF stimulation of GH release appeared at the first sampling time (20-min incubation) and the effect began to diminish after 2-h incubation with GRF. On the other hand, total (cell plus medium) content of GH significantly increased only after 24-h incubation. To examine the GH-synthesizing effect of GRF more directly, newly synthesized GH labeled by [35S]methionine during incubation with GRF was quantified by immunoprecipitation. The amount of immunoprecipitable GH increased significantly and specifically (compared with the total amount of labeled proteins) also only after 24-h incubation. When GH pools were labeled with [35S]methionine under different schedules, the basal release of newly synthesized GH, which was labeled for 1 h immediately before chase incubation was lower during the first 15 min than stored GH which had been labeled earlier. Basal newly synthesized GH secretion exceeded stored GH secretion after 30 min. GRF stimulated the release of GH from both pools but the stimulation of stored GH was greater. In this system, SRIF suppressed both the basal and stimulated release of GH but did not modify GH biosynthesis under either condition. Newly synthesized GH showed significant degradation during 24-h incubation; neither GRF nor SRIF affected the rate of GH degradation during the same incubation period. These results indicate that 1) GRF stimulates both release and synthesis of GH; 2) these two effects have different kinetics and different sensitivities to SRIF; and 3) GRF stimulates the release of GH from heterogeneous pools disproportionally.

Immunohistochemical analysis of T cell phenotypes in patients with graft-versus-host disease following allogeneic bone marrow transplantation.

Allogeneic bone marrow transplantation has become the therapy of choice in many cases of hematologic malignancy. In both matched related donor transplants--and, to a greater degree, in unrelated donor transplant situations--a major complication of the procedure is GVHD. This problem is caused by mature T cells in the graft, which also facilitate engraftment, and mediate an antitumor effect to reduce relapse. In order to further characterize the T cells that are present at the GVHD site of injury, we have studied 134 fresh tissue biopsies using immunohistochemical methods from 50 consecutive ABMT recipients clinically suspected of having acute GVHD. Antibodies specific for T cells, T cell receptor subsets, B cells, and NK cells were used to characterize the lymphocytic infiltrate in the biopsy tissue from GVHD patients. The data showed that the majority of lymphocytes that had infiltrated the epithelium or epidermis were CD3+ T cells. Using antibodies that distinguished the alpha/beta (beta F1) from the gamma/delta TCR (TCR delta 1)-expressing T cells, we observed that the lymphocytic infiltrates from involved tissues of the gastrointestinal tract, skin, and liver are almost exclusively derived from the alpha/beta expressing T cell subset, and are of the memory cell subset of T cells (CD45RO). This is in contrast to some examples from other disease states, in which a significant proportion of the lymphocytes that infiltrate the epidermal layers are of the gamma/delta type.

Induction of CTL response by a minimal epitope vaccine in HLA A*0201/DR1 transgenic mice: dependence on HLA class II restricted T(H) response.

CTL play a pivotal role in the immune response during viral infections. In this study, the HLA class II restricted T(H) requirement for optimal in vivo induction of HLA class I restricted CTL responses has been investigated. Towards this goal, transgenic mice expressing both HLA class I (A*0201 or A2.1) and class II (DRB1*0101 or DR1) molecules have been derived. Immunization of these mice with an HLA A*0201-restricted and CMV-specific CTL epitope (pp65(495-503)), and either of three different tetanus toxin-derived MHC class II-binding T(H) epitopes, resulted in a vigorous CTL response. CTL specific for the pp65(495-503) epitope were dramatically enhanced in mice expressing both the HLA-DR1 and HLA-A*0201 transgenes. Notably, preinjection of three TT peptides (TT(639-652), TT(830-843), and TT(947-967)) increased the capability of HLA A*0201/DR1 Tg mice to respond to subsequent immunization with the T(H) + CTL peptide mixture. These results indicate that the use of HLA A*0201/DR1 Tg mice constitute a versatile model system (in lieu of immunizing humans) for the study of both HLA class I and class II restricted T-cell responses. These studies provide a rational model for the design and assessment of new minimal-epitope vaccines based on their in vivo induction of a pathogen-specific CTL response.

An orthotopic in vivo model of human pancreatic cancer.

BACKGROUND: Pancreatic cancer is a highly lethal disease that frequently presents in advanced stages. For most patients, treatment with great clinical efficacy does not exist. Relevant in vivo models to test novel therapies are highly desirable. METHODS: The human pancreatic ductal adenocarcinoma cell line Panc-1 was injected intraperitoneally into SCID mice. The pattern of the resulting peripancreatic as well as metastatic disease was examined. Survival experiments after chemotherapy with gemcitabine or doxorubicin, and after immunotherapy with p53-specific cytotoxic T lymphocytes were performed. RESULTS: All animals developed isolated pancreatic tumor implants within 48 hours after injection. After the formation of invasive pancreatic tumor nodules, peripancreatic and portal adenopathy developed, causing biliary obstruction. All tumor-bearing animals died of disease within 5 to 12 weeks. Survival after gemcitabine treatment and after p53-CTL injection was significantly prolonged, with some animals remaining tumor-free. Doxorubicin treatment did not yield extended survival, but led to significant toxicity. CONCLUSION: Intraperitoneal injection of Panc-1 cells into SCID mice produces a quasi-orthotopic tumor development model that shares many characteristics with human pancreatic cancer. The ease of cell injection, avoidance of cumbersome surgical intervention with its resulting mortality, and the reliable development of obstructive jaundice as a dependent comorbid factor render this a useful model for in vivo testing of novel therapeutic approaches to pancreatic cancer. Our initial therapeutic studies demonstrate that in vitro antitumor efficacy against Panc-1 cancer cells does not necessarily predict the in vivo response, highlighting the preclinical experimental value of this model.

A fusion protein of HCMV IE1 exon4 and IE2 exon5 stimulates potent cellular immunity in an MVA vaccine vector.

A therapeutic CMV vaccine incorporating an antigenic repertoire capable of eliciting a cellular immune response has yet to be successfully implemented for patients who already have acquired an infection. To address this problem, we have developed a vaccine candidate derived from modified vaccinia Ankara (MVA) that expresses three immunodominant antigens (pp65, IE1, IE2) from CMV. The novelty of this vaccine is the fusion of two adjacent exons from the immediate-early region of CMV, their successful expression in MVA, and robust immunogenicity in both primary and memory response models. Evaluation of the immunogenicity of the viral vaccine in mouse models shows that it can stimulate primary immunity against all three antigens in both the CD4(+) and CD8(+) T cell subsets. Evaluation of human PBMC from healthy CMV-positive donors or patients within 6 months of receiving hematopoietic cell transplant shows robust stimulation of existing CMV-specific CD4(+) and CD8(+) T cell subsets.

Characterization of nuclear protein binding to the interferon-gamma promoter in quiescent and activated human T cells.

Nuclear protein binding to the human interferon-gamma (IFN-gamma) promoter was investigated to determine the structural basis for the control of gene expression during T cell activation. DNase I footprinting of gel-shift complexes demonstrated that proteins bind to two downstream (-124 to -114 and -36 to -30) and one upstream (-534 to -486) element in the IFN-gamma gene promoter. Treatment of human peripheral blood lymphocytes or continuous T cell tumors with phorbol 12-myristate 13-acetate (PMA) plus phytohemagglutinin or calcium ionophore results in a pattern of response that is similar when using either the upstream or downstream elements. Upon induction of T cells, the lower mobility gel-shift band disappears. Yet the equivalent band which is also present in non-T cells is unperturbed after PMA + calcium ionophore treatment. The higher mobility band which is modified upon induction is restricted to the T cell lineage. Upstream and downstream elements share similar protein-binding motifs as indicated by the homology of footprinted sequences, the similarity of protein-binding patterns, and the ability of these elements to compete against each other in gel-shift protein-binding assays. Protein binding to the downstream elements appears to be interactive, since both sites are required for complex formation. When either of the two downstream elements is disrupted by site-directed mutagenesis, the higher mobility gel-shift band is diminished by an amount that is consistent with the reduction in reporter (chloramphenicol acetyltransferase) gene expression. Therefore, proteins in the ubiquitous gel-shift band appear to be associated with the inactive state of IFN-gamma, while the modified band is closely associated with the positive regulation of IFN-gamma gene expression.

The human interferon-gamma gene contains an inducible promoter that can be transactivated by tax I and II.

T cells infected with the HTLV (human T cell leukemia virus)-I and -II retroviruses often express the lymphokine interferon-gamma (IFN-gamma). We sought the molecular explanation for this phenomena by co-transfecting the transactivator genes of these human retroviruses together with 5' flanking sequences of the human IFN-gamma gene linked to a heterologous reporter gene. In the presence of phytohemagglutinin or anti-T cell receptor monoclonal antibodies and phorbol 12-myristate 13-acetate, the IFN-gamma promoter is activated in human T cells, which can be further enhanced by co-transfection of the tax I or II genes. Using Bal-31 deletion analysis, we have found that induction by mitogens can be mapped to a region between -284 to -260 (bp) 5' of the transcriptional start site, which is separable from the sequence(s) further upstream which transmit the synergistic transactivation by tax I or II.

The use of transgenic mice to generate high affinity p53 specific cytolytic T cells.

P53 is an attractive target immunotherapy because it is overexpressed in up to one half of all malignancies, and its overexpression often correlates with a worsened prognosis. We wanted to determine the feasibility of targeting wild-type epitopes p53 on human tumor cells. HLA A2.1 transgenic mice were immunized with the immunodominant wild-type p53 peptide epitopes, p53(149-157) and p53(264-272), along with a pan-DR helper epitope peptide in incomplete Freund's adjuvant (IFA). Twelve days later, splenocytes were harvested and stimulated with syngeneic blast cells that had been acid-treated to remove endogenous peptide and p53 peptide-pulsed. The responding cells were subsequently restimulated weekly with acid washed, peptide-pulsed Jurkat cells transfected with HLA A2.1. Peptide specific activity was tested in a chromium release assay. The resulting cytotoxic T cells (CTL) were cloned by limiting dilution. Peptide specific CTL were generated against both p53(149-157) and p53(264-272. Only p53(149-157) specific CTL were able to recognize and lyse cells that overexpressed endogenous p53. CTL clones derived from the p53(149-157) cell line demonstrated high affinity and specificity for p53(149-157) when presented by HLA A2.1+ cells. The p53(149-157) specific CTL were tested for specificity against a variety of cultured human cell lines. The CTL clones only lysed cells that overexpressed p53 in the context of HLA A2.1 and did not lyse cells with normal p53 expression or cells that lacked HLA A2.1 expression. This study demonstrates the possibility of targeting tumors, which overexpress p53, and raises the possibility transferring the high affinity, p53 specific T cell receptors from the murine CTL to human T cells.

Development of a candidate HLA A*0201 restricted peptide-based vaccine against human cytomegalovirus infection.

The development of a protective cellular immune response against human cytomegalovirus (HCMV) is the most important determinant of recovery from HCMV infection after allogeneic bone marrow transplantation (BMT). The ultimate aim of our study is to develop an antigen-specific and peptide-based vaccine strategy against HCMV in the setting of BMT. Toward this end we have studied the cellular immune response against the immunodominant matrix protein pp65 of HCMV. Using an HLA A*0201-restricted T-cell clone reactive against pp65 from peripheral blood from a seropositive individual, we have mapped the position of the cytolytic T lymphocyte (CTL) epitope from HCMV pp65 to an 84-amino acid segment. Of the four peptides which best fit the HLA A*0201 motif in that region, one nonamer sensitized an autologous Epstein-Barr virus immortalized lymphocyte cell line for lysis. In vitro immunization of PBMC from HLA A*0201 and HCMV seropositive volunteers using the defined nonamer peptide stimulated significant recognition of HCMV infected or peptide-sensitized fibroblasts. Similarly, HLA A*0201 transgenic mice immunized with the nonamer peptide developed CTL that recognize both the immunizing peptide and endogenously processed pp65 in an HLA A*0201 restricted manner. Lipid modification of the amino terminus of the nonamer peptide resulted in its ability to stimulate immune responses without the use of adjuvant. This demonstration of a vaccine function of the nonamer peptide without adjuvant suggests its potential for use in an immunization trial of BMT donors to induce protective CTLs in patients undergoing allogeneic BMT.