Antiviral cytotoxic T cell response induced by in vivo priming with a free synthetic peptide

Delivery of pseudorabies virus envelope antigens enclosed in immunostimulating complexes (ISCOMs); elicitation of neutralizing antibody and lymphoproliferative responses in swine and protection in mice

An experimental subunit vaccine that consisted of pseudorabies virus (PRV) envelope glycoproteins enclosed into immunostimulating complexes (PRVenv/ISCOM) was constructed, and evaluated in DBA/2 mice and inbred swine of the SLA haplotype c/c. Two to three weeks after the first vaccine dose, specific anti-PRV antibodies could be demonstrated by ELISA or virus neutralization (VN) assays. Booster PRVenv/ISCOM vaccinations resulted in rapid and significant increases in antibody titres in both mice and swine. In addition, a week after receiving the third PRVenv/ISCOM vaccine dose swine peripheral blood mononuclear cells exhibited significant proliferation in response to stimulation with PRV virion antigen. Moreover, two doses of vaccine sufficed to protect mice fully against lethal virus challenge. Therefore, the data presented here support the ISCOM as a viable antigen delivery system for subunit PRV vaccines.

The cell-binding carboxyterminal undecapeptide of SV40 tumour antigen provides protective cell-dependent immunity

This paper describes the use of the synthetic carboxyterminal undecapeptide of large SV40 tumour antigen, lys698-thr708 (KT) to protect Balb/c mice against growth of subcutaneously transplanted tumorigenic SV40-transformed cells (VLM). The vaccine was prepared by conjugation of KT with 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide (SPDP). Addition of the SPDP-derivative of KT to syngeneic spleen cells rendered KT covalently linked to free thiol-groups of the cell membranes by the formation of -S-S-CH2-CH2-CO-epsilon-NH-lys698 bonds. Vaccination with KT-conjugated cells was intraperitoneal. Alternatively, KT-conjugated cells were generated in the peritoneum by injection of PDP-KT ((2-pyridyldithio)propionic acid-KT). As a control 60Co-irradiated VLM cells were used. In five experiments all VLM-vaccinated and the majority of the PDP-KT-(or KT-spleen cell)-vaccinated mice were protected against tumour growth. However, mice pretreated with saline, unconjugated spleen cells, free KT, KT conjugated to bovine serum albumin, or KT with incomplete Freund's adjuvant developed tumours. Treatment of PDP-KT-vaccinated mice with anti-CD4 or anti-CD8 immunoglobulin abolished tumour immunity completely. Thus, covalent binding of the carboxyterminal undecapeptide of SV40 tumour antigen to viable, untransformed cells yielded a vaccine which protects Balb/c mice against SV40 tumours.

Induction of feline immunodeficiency virus-specific cytotoxic T cells in vivo with carrier-free synthetic peptide

The role of cellular immunity in the establishment and progression of immunosuppressive lentivirus infection remains equivocal. To develop a model system with which these aspects of the host immune response can be studied experimentally, we examined the response of cats to a hybrid peptide containing predicted T-and B-cell epitopes from the gag and env genes of feline immunodeficiency virus (FIV). Cats were immunized with an unmodified 17-residue peptide incorporating residues 196 to 208 (from gag capsid protein p24) and 395 to 398 (from env glycoprotein gp120) of the FIV Glasgow-8 strain by using Quil A as an adjuvant. Virus-specific lymphocytotoxicity was measured by chromium-51 release assays. The target cells were autologous or allogeneic skin fibroblasts either infected with recombinant FIV gag vaccinia virus or pulsed with FIV peptides. Effector cells were either fresh peripheral blood mononuclear cells or T-cell lines stimulated with FIV peptides in vitro. Cytotoxic effector cells from immunized cats lysed autologous, but not allogeneic, target cells when they were either infected with recombinant FIV gag vaccinia virus or pulsed with synthetic peptides comprising residues 196 to 205 or 200 to 208 plus 395. Depletion of CD8+ T cells, from the effector cell population abrogated the lymphocytotoxicity. Immunized cats developed an antibody response to the 17-residue peptide immunogen and to recombinant p24. However, no antibodies which recognized smaller constituent peptides could be detected. This response correlated with peptide-induced T-cell proliferation in vitro. This study demonstrates that cytotoxic T lymphocytes specific for FIV can be induced following immunization with an unmodified short synthetic peptide and defines a system in which the protective or pathological role of such responses can be examined.

Multispecific and heterogeneous recognition of the gag protein by cytotoxic T lymphocytes (CTL) from HIV-infected patients: factors other than the MHC control the epitopic specificities

The HIV gag polyprotein is a major target for recognition by CTL in infected humans. Using recombinant vaccinia viruses (rVV) expressing truncations of the p24gag, and the p18gag, p15gag and HIV-2 p56gag proteins, the characterization of epitope regions recognized by in vitro-stimulated peripheral blood mononuclear cells (PBMC) from 18 infected patients has been studied. The gag-specific response of most individuals is polyclonal and multispecific, and interindividual variations between target epitope regions were frequently observed, despite shared MHC alleles. As CTL may play an important role in the control of HIV replication in infected hosts, these results have important implications for designing vaccine strategies.

Insertion signal sequence fused to minimal peptides elicits specific CD8+ T-cell responses and prolongs survival of thymoma-bearing mice

CD8+ T-lymphocytes (TCD8+) recognize minimal peptides of 8-10 residues which are the products of intracellularly processed proteins and are presented at the cell surface by major histocompatibility complex class I molecules. An important step in this process is the translocation of processed proteins from the cytosol across the endoplasmic reticulum membrane, mediated by transporter associated with antigen-processing proteins or alternatively by endoplasmic reticulum-insertion signal sequences located at the NH2-terminus of the precursor molecules. We report here that the addition of an endoplasmic reticulum-insertion signal sequence at the NH2-terminus of TCD8+ epitopes from chicken ovalbumin (amino acids 257-264) or a naturally occurring tumor antigen expressed by the murine mastocytoma P815 (P1A amino acids 35-43) significantly enhanced the priming of specific TCD8+ in vivo. The signal sequence did not enhance peptide immunogenicity by merely increasing the hydrophobicity of the peptide, since ovalbumin amino acids 257-264 peptide with the signal sequence at its COOH-terminus did not demonstrate enhanced efficacy. The signal sequence did not act as a helper epitope, since TCD8+ responses were not diminished in class II-deficient transgenic mice or in mice depleted of CD4+ T-cells in vivo. Importantly, a single immunization with the fusion peptide significantly prolonged survival of mice challenged with E.G7OVA, a thymoma transfected with the complementary DNA of chicken ovalbumin.

Efficacy of synthetic vaccines in the induction of cytotoxic T lymphocytes. Comparison of the costimulating support provided by helper T cells and lipoamino acid

Synthetic vaccines that specifically induce active immunity mediated by cytotoxic T lymphocytes (CTL) are of great interest considering the central role of these cells in immune responses against intracellular antigens. The influence of specific T helper (Th) cell recruitment and of the potent immunostimulating lipoamino acid tripalmitoyl-S-glycerylcysteine (P3C) on CTL mediated immunity induced by CTL epitopes was analysed and compared. Synthetic peptides that represent CTL epitopes were found to be inefficient for CTL priming. However, when combined with peptides that contain Th cell epitopes, with proteins that carry multiple Th cell epitopes or with P3C, efficient priming of CTL was obtained. The costimulating support by P3C and proteins resulted in high cytolytic activities already after 9 days whereas, in the case of single helper epitopes, incubation periods of about 4 weeks were required. The effects of P3C and helper epitopes were additive.

Influenza virus-infected dendritic cells stimulate strong proliferative and cytolytic responses from human CD8+ T cells

Antigen-specific, CD8+, cytolytic T lymphocytes (CTLs) could potentially provide resistance to several infectious and malignant diseases. However, the cellular requirements for the generation of specific CTLs in human lymphocyte cultures are not well defined, and repetitive stimulation with antigen is often required. We find that strong CD8+ CTL responses to influenza virus can be generated from freshly isolated blood T cells, as long as dendritic cells are used as antigen presenting cells (APCs). Small numbers of dendritic cells (APC:T cell ratio of 1:50-1:100) induce these CTL responses from most donors in 7 d of culture, but monocytes are weak or inactive. Whereas both dendritic cells and monocytes are infected with influenza virus, the former serve as effective APCs for the induction of CD8+ T cells while the latter act as targets for the CTLs that are induced. The strong CD8+ response to influenza virus-infected dendritic cells is accompanied by extensive proliferation of the CD8+ T cells, but the response can develop in the apparent absence of CD4+ helpers or exogenous lymphokines. CD4+ influenza virus-specific CTLs can also be induced by dendritic cells, but the cultures initially must be depleted of CD8+ cells. These findings should make it possible to use dendritic cells to generate human, antigen-specific, CD8+ CTLs to other targets. The results illustrate the principle that efficient T cell-mediated responses develop in two stages: an afferent limb in which dendritic cells are specialized APCs and an efferent limb in which the primed T cells carry out an immune response to many types of presenting cells.

Mutations inside but not outside the peptide binding cleft of the H-2 Ld molecule affect CTL recognition and binding of the nucleoprotein peptide from the lymphocytic choriomeningitis virus

In order to investigate the role of residues inside and outside the peptide binding cleft of the Ld molecule in peptide presentation to cytotoxic T lymphocytes (CTL), we constructed a series of point mutations in the Ld gene. We determined the effects of the mutations in the Ld molecule on the binding and recognition of an Ld-restricted CTL epitope derived from the nucleoprotein (NP) of the lymphocytic choriomeningitis virus (LCMV). Each of the mutations within the Ld peptide binding cleft resulted in a complete loss of CTL recognition. Addition of the LCMV NP peptide to cells expressing these mutants did not increase surface Ld expression, suggesting that the mutations altered peptide binding. Mutations involving pockets D and E within the cleft affected LCMV peptide binding and recognition as drastically as those in pocket B, which was predicted to interact with a main anchor residue of the peptide. In striking contrast, the mutations located outside the cleft did not change either recognition or binding. These results demonstrate that the Ld residues in the peptide binding cleft are the main determinants dictating LCMV NP peptide binding, and that the residues in each of the pockets within the cleft play a role in this interaction. Surprisingly, one mutation outside the peptide binding cleft, T92S, abrogated CTL lysis of target cells treated with the LCMV NP peptide, but not virus-infected cells. These data show that this mutation selectively altered the presentation of the LCMV NP peptide introduced to the cell exogenously, but not endogenously. This implies that the pathway by which peptides associate with class I molecules within the cell differs from that of exogenous peptide binding.

Induction of a cytotoxic T cell response by co-injection of a T helper peptide and a cytotoxic T lymphocyte peptide in incomplete Freund's adjuvant (IFA): further enhancement by pre-injection of IFA alone

We have previously demonstrated that it is possible to induce a consistent and strong cytolytic T lymphocyte (CTL) response to synthetic peptides, corresponding to poorly immunogenic malaria CTL epitopes, by co-injecting them with peptides representing defined T helper (Th) epitopes in incomplete Freund's adjuvant (IFA). In this study we have tested different immunization protocols to improve further the elicitation of the CTL response. We show that the CTL response to a mixture of Th + CTL peptides administered in IFA was further enhanced by a previous injection of the Th epitope peptide in IFA. Moreover, we found that the response could be significantly augmented by a pre-injection of IFA alone. This enhancement was observed only if the Th epitope was also present in the second injection. The number of lymph node cells recovered was 2-3-fold higher in mice pre-injected with IFA, but the increase in specific CTL activity, expressed as lytic units per animal, by pre-injection of IFA was at least 10-20-fold. Thus, pre-injection of IFA clearly increases the magnitude of a subsequent CTL response.

Efficient in vivo induction of CTL by cell-associated covalent H-2Kd-peptide complexes

A novel procedure is presented describing the induction of antigen-specific cytolytic T lymphocytes (CTL) in vivo, that uses as immunogen syngeneic Concanavalin A stimulated spleen cells expressing H-2Kd (Kd) molecules photocrosslinked with a photoreactive peptide derivative. The Kd restricted Plasmodium berghei circumsporozoite (PbCS) peptide 253-260 (YIPSAEKI) was conjugated with photoreactive iodo-4-azidosalicylic acid (IASA) at the NH2-terminus and with 4-azidobenzoic acid (ABA) at the TCR contact residue Lys259 to make IASA-YIPSAEK(ABA)I. Selective photoactivation of the IASA group allowed specific photoaffinity labeling of cell-associated Kd molecules. Optimal peptide derivative binding to Kd molecules of concanavalin A stimulated spleen cells was obtained upon 4-6 h incubation at 26 degrees C in the presence of human beta 2 microglobulin. Photocrosslinking prevented the rapid dissociation of cell-associated Kd-peptide derivative complexes at 37 degrees C. The photoaffinity labeled cells were injected i.p. into syngeneic recipients. After 10 days, the peritoneal exudate lymphocytes were harvested and in vitro stimulated with peptide derivative pulsed P815 mastocytoma cells. The resulting bulk cultures displayed high cytolytic activity that was specific for IASA-YIPSAEK(ABA)I and YIPSAEK(ABA)I. In contrast, peritoneal exudate lymphocytes from mice inoculated with concanavalin A blasts that were pulsed, but not photocrosslinked, with IASA-YIPSAEK(ABA)I expressed only marginal levels of IASA-YIPSAEK(ABA)I-specific cytolytic activity. This immunization strategy, using neither adjuvants nor potentially hazardous transfected/transformed cells, is safe and should be universally applicable.

Vaccination with T cell receptor peptides primes anti-receptor cytotoxic T lymphocytes (CTL) and anergizes T cells specifically recognized by these CTL

We selected three peptides from the germ-line sequence of the V beta 8.2 and J beta 2.3 gene segments of the murine T cell receptor for antigen (TCR) which contained putative Kd- and Ld-restricted epitopes. Immunization of BALB/c (H-2d) mice with the V beta 8.2(67-90) 23-mer peptide 1 as well as the 15-mer V beta 8.2(95-108)-peptide 2 efficiently primed specific CD8+ cytotoxic T lymphocyte (CTL) responses in vivo against natural TCR-V beta 8.2 epitopes. V beta 8.2+ T cells were not deleted in TCR peptide-immunized mice because the fractions of V beta 8.2+ CD4+ and V beta 8.2+ CD8+ T cells in spleen and lymph nodes were not altered. The proliferative response of V beta 8.2+ T cells to stimulation by monoclonal antibody F23.2 was selectively suppressed (by 60-80%) in peptide-immunized BALB/c mice, indicating partial anergy of this T subset. Immunization of BALB/c mice with the J beta 2.3-derived peptide 3 stimulated a CD8+ CTL response against a class I-restricted epitope within this J beta segment that was also generated during natural "endogenous" processing of this self antigen. These data confirm the predictive value of major histocompatibility complex class I allele-specific motifs. The described experiments indicate that TCR peptide-primed CD8+ CTL recognize class I-restricted, natural V beta/J beta-TCR epitopes. Such anti-TCR CTL may, thus, operate in V beta-specific immunoregulation of the T cell system suppressing their functional reactivity without deleting them.

The immunodominant peptide from listeriolysin in Quil A liposomes vaccinates CD8+ cytolytic T cells and confers protection to infection

Cytolytic T-cell vaccination with immunodominant MHC class I-restricted peptides contained within Quil A liposomes has been previously demonstrated. In recent years, Quil A has been under consideration for use as an adjuvant in humans. We assessed the possible use of peptide inoculation in the context of Quil A liposomes to be protective in a mouse model. Listeria monocytogenes was used as the challenge pathogen and the previously identified listeriolysin 91-99 peptide as the immunogen. The listeriolysin 91-99 Quil A liposome inoculum showed significant enhancement of survival after challenge with up to 10 times the L. monocytogenes LD50.

Expression of mage genes by non-small-cell lung carcinomas

Human gene MAGE-I codes for an antigen that is recognized on melanoma cells by autologous cytolytic T lymphocytes (CTL). This antigen is potentially useful as a target for cancer immunotherapy because gene MAGE-I is not expressed in any normal tissues except the testis. We tested 46 surgical samples of non-small-cell lung carcinomas and observed MAGE-I expression in 16 of them (35%). Genes MAGE-2 and 3, which are closely related to MAGE-I, were expressed by a similar proportion of these tumors. Some small-cell lung tumors also express MAGE genes. The proportion of tumors expressing MAGE-I suggests that lung tumor patients may constitute the largest group of patients potentially eligible for pilot studies involving MAGE-I immunization.

Direct involvement of extracellular HIV-1 virions in the apoptosis of CD8+ lymphocytes: a two-step model

Lymphocytes of the CD8 phenotype play an important role in controlling viral burden in HIV-1 infection. Cytotoxic CD8+ T lymphocytes (CTL) can kill HIV-infected cells and in addition, are able to secrete a soluble factor that inhibits HIV replication. In most cases, HIV-infected individuals experience an unexplained CD8+ lymphopenia during the advanced stage of the disease that particularly affect HIV-1-specific CTL. It has been reported that CD8+ lymphocytes in HIV-infected individuals undergo programmed cell death or apoptosis. We now present a two-step model to explain CD8+ apoptosis, based on anchorage of HIV-1-associated MHC class 1 antigen into the envelope of extracellular viral particles.

Peptide-induced T-cell tolerance to prevent autoimmune diabetes in a transgenic mouse model

A synthetic peptide corresponding to an immunodominant epitope of lymphocytic choriomeningitis virus glycoprotein (LCMV GP) was used to prime or to tolerize CD8+ T cells in vivo, dependent on mode of immunization. Peptide-specific tolerance was then examined in transgenic mice expressing LCMV GP in the beta islet cells of the pancreas; these mice develop CD8+ T-cell-mediated diabetes within 8-14 days after LCMV infection. Specific peptide-induced tolerance prevented autoimmune destruction of beta islet cells and diabetes in this transgenic mouse model.

Vaccination with immunodominant peptides encapsulated in Quil A-containing liposomes induces peptide-specific primary CD8+ cytotoxic T cells

Immunostimulating complexes (ISCOMs), containing lipids, the saponin Quil A, and proteinaceous antigens, have been proven to vaccinate effectively CD8+ cytolytic T cells in vivo. However, conventional ISCOM technology is restricted to hydrophobic proteins or fatty acid-derivatized proteins or peptides. We therefore analysed whether Quil A-containing liposomes are an effective vehicle to shuttle hydrophilic proteins or peptides into the MHC class I pathway of antigen presentation resulting in the in vivo induction of antigen-specific cytolytic T cells (CTL). Liposomes were formed by a lipid dry-down method followed by resuspension with an aqueous solution containing protein/peptide and Quil A and then an extrusion step. Quil A-containing liposomes are an effective means to elicit a CD8+ CTL response to peptide antigen in vivo. CTL could be raised in C57B1/6 mice against ovalbumin (OVA) peptide 257-264 and vesicular stomatitis virus nucleoprotein 52-59, as well as in Balb/c mice against listeriolysin peptide 91-99 and cytomegalovirus pp89 168-176, demonstrating the versatility of this approach. The elicited response was peptide-specific, peptide dose-dependent and Quil A was necessary. Vaccination with liposomes entrapping the whole ovalbumin molecule or an extended (OVA) peptide 254-276 also yielded a CTL responsive to the immunodominant OVA peptide 256-264, implying cellular internalization and correct processing. Thus Quil A-containing liposomes appear to be a versatile vehicle to vaccinate CD8+ T cells in vivo; in addition, they could rapidly enhance the understanding of subunit vaccines and rules of antigen processing and peptide-MHC class I binding.

Enhancement of CTL response induced by a viral peptide using cationized BSA, a Th1-stimulating adjuvant

We have recently shown that it is possible to activate cytotoxic T cells (CTL) in vivo with HSV-1 glycoprotein B H-2Kb-restricted peptide (gB peptide) independent of CD4+ T cell help. Here we report that the gB peptide-specific CTL response is significantly enhanced when mice are immunized with a mixture of gB peptide and cationized BSA (cBSA). The latter molecule is a positively charged form of the native BSA molecule that stimulates CD4+ T cells to produce cytokines characteristic of Th1 cells. The cBSA-enhanced CTL response required the presence of CD4+ T cells, but it did not require stimulation in vitro by antigen or exogenous cytokines. gB peptide/cBSA-activated LN cells transcribed IL-2 and IFN-gamma, but only IL-2 was essential for CTL development. Our data demonstrate that while activation of CTL may occur in the absence of CD4+ cells, cytokines produced by CD4+ Th1 cells provide stimulatory signals during CTL maturation. Thus, cotreatment with a substance that activates Th1 CD4+ cells may be useful for achieving maximal CTL responsiveness.

Use of helper T cell-inducing peptides from conserved regions in HIV-1 env in a noncovalent mixture with a CTL-inducing V3-loop peptide for in vivo induction of long-lasting systemic CTL response

Our previous reports established that immunization of mice in the footpad with a 15-amino acid synthetic peptide (R15K) from the V3 loop region in the envelope protein gp120 of human immunodeficiency virus type 1 (HIV-1) resulted in rapid induction of major histocompatability complex (MHC) class I-restricted, CD8+ HIV-1 envelope-specific cytotoxic T lymphocytes (CTLs) in the proximal popliteal lymph node. While efficient CTL activity could be assayed in lymph node cells for 8 to 10 weeks after a single injection, spleen cells from these mice showed low to negligible levels of specific CTLs at 4 to 8 weeks postimmunization. We tested immunizing mice with a noncovalent mixture of a helper T cell (Th) activity-inducing peptide and R15K and observed efficient induction of R15K-specific CTL response that could be assayed up to 8 weeks postimmunization in cells obtained from both lymph node and spleen. Efficient CTL priming was observed when Th peptides from either of two different conserved regions in the HIV env were mixed with R15K, containing a dipalmityl-lysine-glycine-glycine moiety at the amino terminus. These data confirm reports in literature describing requirement of Th activity for efficient priming of CTL response in vivo. Additionally, these studies strongly suggest the possibility of formulating potential vaccine candidates consisting of mixtures of synthetic peptides capable of inducing Th and CTL responses in the context of multiple MHC haplotypes.

Simian virus 40 T antigen as a carrier for the expression of cytotoxic T-lymphocyte recognition epitopes

Simian virus 40 (SV40) large T antigen can immortalize a wide variety of mammalian cells in culture. We have taken advantage of this property of T antigen to use it as a carrier for the expression of cytotoxic T-lymphocyte (CTL) recognition epitopes. DNA sequences corresponding to an H-2Db-restricted SV40 T-antigen site I (amino acids 205 to 215) were translocated into SV40 T-antigen DNA at codon positions 350 and 650 containing EcoRI linkers. An H-2Kb-restricted herpes simplex virus glycoprotein B epitope (amino acids 498 to 505) was also expressed in SV40 T antigen at positions 350 and 650. Primary C57BL/6 mouse kidney cells were immortalized by transfection with the recombinant and wild-type T-antigen DNA. Clonal isolates of cells expressing chimeric T antigens were shown to be specifically susceptible to lysis by CTL clones directed to SV40 T-antigen site I and herpes simplex virus glycoprotein B epitopes, indicating that CTL epitopes restricted by two different elements can be processed, presented, and recognized by the epitope-specific CTL clones. Our results suggest that SV40 T antigen can be used as a carrier protein to express a wide variety of CTL epitopes.

Induction of cytolytic and antibody responses using Plasmodium falciparum repeatless circumsporozoite protein encapsulated in liposomes

Plasmodium circumsporozoite (CS) protein-induced antibody and T-cell responses are considered to be important in protective immunity. Since the key repeat determinant of the CS protein may actually restrict the recognition of other potential T- and B-cell sites, a modified Plasmodium falciparum CS protein lacking the central repeat region, RLF, was expressed in Escherichia coli. On purification, RLF was encapsulated into liposomes [L(RLF)] and used for the in vivo induction of cytolytic T lymphocytes (CTL) and antibodies. Immunization of B10.Br (H-2k) mice with L(RLF), but not with RLF, induced CD8+ CTL specific for the P. falciparum CS protein CTL epitope, amino acid residues 368-390. Anti-L(RLF) serum reacted with antigens on intact sporozoites and inhibited sporozoite invasion of hepatoma cells. Antibody specificity studies in New Zealand White rabbits revealed new B-cell sites localized in amino acid residues 84-94, 91-99, 97-106 and 367-375. Although the mechanisms by which liposomes enhance cellular and humoral immune responses remain unknown, liposome-formulated vaccines have been well tolerated in humans; hence, their use in vaccines, when efficacy depends on antibody and CTL responses, may be broadly applicable.

Induction of CD8+ cytotoxic T cells by immunization with killed influenza virus and effect of cholera toxin B subunit

The MHC class I cytotoxic T-lymphocyte (CTL) response in mice given formalin-inactivated influenza whole-virus vaccine (WVV) with or without cholera toxin B subunit (CTB) was studied. Intraperitoneal injection of Balb/c (H-2d) mice with high doses of A/Taiwan/1/86 (H1N1) WVV stimulated influenza A virus-specific CTL response in a dose-dependent manner. A dose of 4.4 or 44 micrograms induced CTL response equal to or greater than live influenza virus infection. Coadministration of vaccine with 5 or 25 micrograms of CTB resulted in a higher level of CTL than with vaccine alone. CTL lysed A/Taiwan and A/Shanghai (H3N2) virus-infected class I-expressing P815 (H-2d) but not virus-infected EL-4 (H-2b) target cells nor B/Yamagata virus-infected target cells. Virus-infected MHC class II- and class I-expressing A20 (H-2d) targets were also lysed. Depletion of Lyt-2+ (CD8+) T cells with monoclonal antibody completely abrogated lysis of P815 target cells and resulted only in a slight reduction of lysis of A20 target cells. Depletion of L3T4+ (CD4+) T cells or NK cells had minimal effect on lysis of either P815 or A20 target cells. Using limiting dilution analysis, the precursor CTL (pCTL) frequency paralleled CTL activity. Significant CTL activity was detected 7 months after immunization. These results demonstrate that adequate doses of influenza WVV with or without CTB can induce long-lasting influenza A cross-reactive MHC class I-restricted CD8+ CTL response in mice. Thus, coadministration of influenza WVV with CTB may lead to an effective vaccine that stimulates both CTL and antibody responses.

T cell immunity after a viral infection versus T cell tolerance induced by soluble viral peptides

The fate of in vivo activated CD8+ cytotoxic T cells was studied in transgenic mice expressing a T cell receptor (TCR) specific for the lymphocytic choriomeningitis virus (LCMV) glycoprotein peptide 33-41 presented by major histocompatibility complex (MHC) class I molecules. LCMV infection of TCR transgenic mice induced LCMV-specific effector and memory T cells whereas injection of soluble LCMV glycoprotein peptide 33-41 resulted in tolerance by peripheral deletion and anergy of LCMV-specific T cells after an initial expansion phase. Similarly, LCMV peptide 33-41-specific tolerance could be achieved in normal C57BL/6 mice and was not abrogated by an LCMV infection. These results obtained with a classically MHC-restricted peptide antigen parallel previous findings with retroviral or bacterial superantigens and indicate a possibility to modulate specifically mature peripheral cytotoxic T lymphocytes in vivo.

Induction of primary, antiviral cytotoxic, and proliferative responses with antigens administered via dendritic cells

Cytotoxic T lymphocytes (CTL) play an essential role in recovery from viral infections, but induction of CTL responses with nonreplicating antigens is difficult to achieve. Exogenous antigens, such as viral proteins and peptides, normally induce CD4+ T-cell responses unless appropriately delivered to the major histocompatibility complex class I antigen presentation pathway. In vitro studies performed to address this issue revealed a similar scenario, and primary CTL induction with nonreplicating antigens has rarely been reported. This study demonstrated primary antiviral CTL induction in vitro with exogenous antigens delivered in vivo to dendritic cells. This study also evaluated the efficacy of glycoprotein B peptide (free or encapsulated in liposomes), peptide-tripalmitoyl-S-glyceryl cysteinyl conjugate (acylpeptide), and glycoprotein B protein encapsulated in pH-sensitive liposomes as antigen delivery vehicles. Our results show that higher levels of cytotoxicity against herpes simplex virus type 1 resulted from exposure of dendritic cells to peptide-tripalmitoyl-S-glyceryl cysteinyl in liposomes. Macrophages treated in a similar manner were not effective stimulators for primary CTL induction. Our data have relevance to the understanding of mechanisms of antigen processing and presentation and the design of antiviral vaccines.

Formalin inactivation of vesicular stomatitis virus impairs T-cell- but not T-help-independent B-cell responses

The effects of formalin on the infectivity and immunogenicity of vesicular stomatitis virus (VSV) serotype Indiana were investigated. We found that formalin inactivation of VSV prevents infection of Vero cells in a concentration- and time-dependent manner, as shown by fluorometric cell analysis and inhibition of plaque formation. Inactivated VSV failed to induce significant cytotoxic T-lymphocyte responses in vivo or after restimulation in vitro. In contrast, the early immunoglobulin M (IgM) response, which is T help independent in the VSV system, was unaltered, suggesting normal antigenicity for and induction of B cells. However, no switch to IgG occurred, demonstrating failure of induction of T help. If cross-reactive T help was provided by previous infection with a second serotype of VSV (New Jersey), the IgG response was almost completely restored, confirming that the absence of IgG was due to lack of T help. A formalin-treated preparation of glycoprotein of VSV led to a delayed but otherwise normal IgG response, whereas treatment of VSV with UV light or beta-propiolactone reduced IgG titers to the same extent as did formalin. These results suggest that loss of infectivity and the ensuing lack of amplification of viral antigens of formaldehyde-inactivated VSV is the major factor impairing induction of specific T-helper cell responses.

Induction of virus-specific cytotoxic T lymphocytes in vivo by liposome-entrapped mRNA

The induction of anti-influenza cytotoxic T lymphocytes (CTL) in vivo by immunizing mice with liposomes containing messenger RNA (mRNA) encoding the influenza virus nucleoprotein (NP) is described. NP mRNA, obtained by in vitro transcription, was encapsulated into simple cholesterol/phosphatidylcholine/phosphatidylserine liposomes by the detergent removal technique. The dependence of the route of mRNA-liposomes delivery on CTL induction was studied. The CTL induced were identical to those obtained in vivo with infectious virus in terms of specificity, lysing both peptide-sensitized and virus-infected targets. Furthermore, with the same mRNA-liposome preparation, virus-specific CTL responses could be also elicited in mice of three different haplotypes each of them known to present a distinct NP peptide in an MHC-restricted fashion. The relevance of these results in the context of vaccine development is discussed.

A pattern search method for putative anchor residues in T cell epitopes

The binding affinity between an antigenic peptide and its particular major histocompatibility complex (MHC) molecule seems to be largely determined by only a few residues. These residues have been called "anchors" because of their property of fitting into "pockets" inside the groove of the MHC molecule. To predict natural antigenic epitopes within a longer sequence, it therefore appears to be important to know the motif or pattern describing the anchors, i.e. the anchors amino acid residue preference and the distance between anchor residues. A large set of MHC class I-restricted peptides has been described. Peptide sequences vary in length and lack an obvious common sequence motif. For a list of peptides belonging to one type of MHC class I molecule, we describe a method to find the most prominent sequence motif with at least two anchor residues. Briefly, antigenic sequences are aligned, and two anchor positions are searched for, where all anchor residues share a high similarity. The alignments are scored according to the similarity of their anchor residues. We show that the motifs predicted for the MHC alleles A2.1, B27, Kb, Kd, Db are in substantial agreement with experimental data. We derive binding motifs for the MHC class I alleles HLA-A1, A11, B8, B14, H-2Ld and for the MHC class II alleles I-Ab and I-As. In some cases, higher scores were obtained by allowing a slight variation in the number of residues between anchors. Therefore, we support the view that the length of epitopes belonging to a particular class I MHC is not uniform. This method can be used to predict the natural short epitope inside longer antigenic peptides and to predict the epitopes anchor residues. Anchor motifs can be used to search for antigenic regions in sequences of infectious viruses, bacteria and parasites.

Identifying strategies for immune intervention

In recent years the molecular basis of antigen recognition by T cells has been unraveled and the various pathways that control T cell activation and functional specialization have been defined. Consequently, it is now possible to delineate various strategies for intervention with the immune system to design protective vaccines, to induce an effective response to tumor antigens, and to control graft rejection and autoimmune diseases.

Definition of a minimal optimal cytotoxic T-cell epitope within the hepatitis B virus nucleocapsid protein

Residues 11 to 27 of the hepatitis B virus nucleocapsid antigen contain a cytotoxic T-cell epitope that is recognized by cytotoxic T cells from virtually all HLA-A2-positive patients with acute hepatitis B virus infection. Using panels of truncated and overlapping peptides, we now show that the optimal amino acid sequence recognized by cytotoxic T cells is a 10-mer (residues 18 to 27) containing the predicted peptide-binding motif for HLA-A2 and that this peptide can stimulate cytotoxic T cells able to recognize endogenously synthesized hepatitis B core antigen. Since patients with chronic hepatitis B virus infection fail to mount an efficient cytotoxic T-cell response to it, this epitope might serve as the starting point for the design of synthetic peptide-based immunotherapeutic strategies to terminate persistent viral infection.

Transfer of CD8+ T cells into SCID mice and activation of memory virus-specific cytotoxic T cells

The requirements for the activation of naive and memory CD8+ cytotoxic T (Tc) cells into effector virus-specific Tc cells after transferring them into SCID mice were investigated. SCID mice reconstituted with splenocytes or purified CD8+ T cells from naive or influenza-immune syngeneic mice and immunized with influenza virus generated effector Tc cells specific for influenza virus-infected target cells in vitro. The kinetics of the response varied between those two populations. The generation of effector Tc cells after transfer of memory CD8+ T cells indicates that there exists no absolute requirement for 'help' in the activation of memory virus-immune T cells. However, under the conditions described here the in vitro immunogenic peptide NPP derived from influenza nucleoprotein is not sufficient to elicit a response in vivo.

A "string-of-beads" vaccine, comprising linked minigenes, confers protection from lethal-dose virus challenge

We have previously demonstrated that induction of antiviral cytotoxic T lymphocytes (CTL), in the absence of antiviral antibodies, can confer protection against a lethal-dose virus challenge. Here we extend those findings as follows. First, three discrete viral CTL epitopes expressed from minigenes encoding peptides as short as 12 amino acids can be recognized when expressed from recombinant vaccinia virus; second, concentrating on two of the three epitopes, we show that these vaccinia virus recombinants can confer protection in a major histocompatibility complex (MHC)-restricted manner; third, the minigenes can be fused to generate a "string of beads," and the close proximity of the two epitopes within one oligopeptide does not disrupt recognition of either epitope; fourth, this string-of-beads vaccine, in contrast to the single epitope vaccines, can protect on both MHC backgrounds; and, fifth, CTL to different epitopes may act synergistically, as protection is improved when the vaccine contains more than one CTL epitope for a given MHC background.

In vivo priming of cytotoxic T lymphocyte responses in relation to in vitro up-regulation of major histocompatibility complex class I molecules by short synthetic peptides

Cytotoxic T lymphocytes (CTL) recognize target antigens as short peptides presented by major histocompatibility complex class I molecules (MHC-I). Externally added peptides can sensitize target cells by binding directly to MHC-I without any need for internal processing. Those which are similar in length to endogenously processed peptides are more potent in this respect than slightly longer peptides. Peptide MHC-I interactions can also be reflected as up-regulation of MHC-I in vitro on certain cells. We have compared the capacity of Db, Kb- and Ld-binding peptides, which are slightly different in length, to up-regulate MHC-I in vitro with their immunogenicity in vivo, in relation to generation of CTL responses. A clear correlation between these two different functions was found. We have also modified a 9-mer Db-binding peptide by adding cystein to the amino terminus and lysine to the amino- or carboxy terminus and studied the effects on MHC-I up-regulation and in vivo immunogenicity. Cystein and lysine contain reactive groups which are likely to influence the binding of modified peptides into the antigen-binding groove of Db. These small modifications of the optimal 9-mer peptide strongly influenced their functions but still there was a correlation between MHC-I up-regulation and CTL responses. Up-regulation of MHC-I in vitro may reflect a capacity of peptides to accumulate on the surface of particular antigen-presenting cells in vivo.

Induction of primary anti-viral cytotoxic T cells by in vitro stimulation with short synthetic peptide and interleukin-7

The present study investigated whether a short synthetic peptide NPP, with a modified sequence (147-158 R156-) derived from influenza A virus nucleoprotein with high affinity for Kd major histocompatibility complex class I molecules, could induce primary influenza virus-specific cytotoxic T (Tc) cells in vitro. Naive BALB/c (H-2d) splenocytes did not respond to the stimulation with only NPP with the generation of effector Tc cells specific for influenza A virus-infected target cells in vitro. However, they were able to do so if cultured with NPP in the presence of IL-7. IL-7 activity in this system differed significantly from IL-2 activity in the specificity of the effect. The use of exogenous IL-2, instead of IL-7, with NPP resulted in the induction of lytic cells that lysed both influenza virus-infected and uninfected syngeneic target cells. These results suggest that IL-7 is a potent regulatory cytokine in the antigen-specific activation of resting naive Tc cell precursors and may provide the necessary conditions for the induction of human primary Tc cells in vitro.

A nonapeptide encoded by human gene MAGE-1 is recognized on HLA-A1 by cytolytic T lymphocytes directed against tumor antigen MZ2-E

We have reported the identification of human gene MAGE-1, which directs the expression of an antigen recognized on a melanoma by autologous cytolytic T lymphocytes (CTL). We show here that CTL directed against this antigen, which was named MZ2-E, recognize a nonapeptide encoded by the third exon of gene MAGE-1. The CTL also recognize this peptide when it is presented by mouse cells transfected with an HLA-A1 gene, confirming the association of antigen MZ2-E with the HLA-A1 molecule. Other members of the MAGE gene family do not code for the same peptide, suggesting that only MAGE-1 produces the antigen recognized by the anti-MZ2-E CTL. Our results open the possibility of immunizing HLA-A1 patients whose tumor expresses MAGE-1 either with the antigenic peptide or with autologous antigen-presenting cells pulsed with the peptide.

T helper epitopes enhance the cytotoxic response of mice immunized with MHC class I-restricted malaria peptides

We have previously derived MHC class I (H-2Kd) restricted cytotoxic T lymphocytes (CTL) from BALB/c mice immunized with irradiated sporozoites from Plasmodium (P.) berghei and P. yoelii. The CTL recognize synthetic peptides corresponding to a region of the circumsporozoite (CS) protein that is homologous in the two species. In the present study, we have attempted to induce CS-specific CTL by immunization with those peptides in incomplete Freund's adjuvant. Only a low level CTL response was detected in BALB/c mice immunized with synthetic peptides corresponding to the Pb or Py CTL epitopes. In contrast, CS-specific CTL responses could be readily detected in mice injected with mixtures of peptides that combined the P. berghei or P. yoelii CTL epitopes with previously defined T helper epitopes. Several different T helper epitopes were shown to enhance the response when injected as separate peptides in a mixture, or when covalently linked to a CTL epitope. These results may have general implications for the elicitation of CTL responses to defined CTL epitopes and for the design of peptide-based synthetic vaccines.

Poliovirus-specific major histocompatibility complex class I-restricted cytolytic T-cell epitopes in mice localize to neutralizing antigenic regions

A major histocompatibility complex (MHC) class I-restricted cytotoxic T-lymphocyte (CTL) response is induced in BALB/c mice upon immunization with poliovirus serotype 1 (Mahoney strain). A similar class I-restricted response is also induced upon immunization with purified VP1 capsid proteins. Thus, poliovirus-specific MHC class I CTL responses can be induced independently of viral infection in murine hosts. In experiments using recombinant vaccinia virus vectors expressing different segments of the poliovirus capsid proteins and synthetic peptides, two regions of the VP1 capsid protein appear to contain epitopes recognized by this bulk CTL population. These epitope regions contain a Kd-restricted peptide-binding motif. Interestingly, each of these CTL epitopes is located near previously defined neutralizing antigenic sites.

Cationic lipids direct a viral glycoprotein into the class I major histocompatibility complex antigen-presentation pathway

Recombinant glycoprotein B (gB) of herpes simplex virus (HSV) was processed and presented by class I major histocompatibility complex (MHC) molecules after delivery into cells by using N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl sulfate (DOTAP), a commercially available cationic lipid used for DNA transfection. Cells treated with DOTAP-associated gB were susceptible to lysis by class I MHC-restricted, HSV-specific cytotoxic T lymphocytes (CTL), and the treated cells restimulated memory gB-specific CTL activity in spleen cells from HSV-infected mice. gB-specific CTL responses were detected in mice immunized with recombinant gB and DOTAP but not in those receiving gB emulsified in complete Freund's adjuvant. Thus, cationic lipids may facilitate induction of CD8+ T-cell responses in vaccinations with recombinant antigens, and they may serve as readily available reagents for dissecting class I MHC immunity to viruses and other intracellular pathogens.

In vivo primary induction of virus-specific CTL by immunization with 9-mer synthetic peptides

A primary cytotoxic T lymphocyte (CTL) response in vivo requires antigen presentation by cytosolic processing and can not in general be obtained by vaccination with soluble proteins. In the present work we have found that vaccination of mice with pre-processed synthetic peptides, corresponding to endogenous 9-mers produced in influenza A virus-infected cells, resulted in strong primary CTL responses. The generated CTL efficiently killed virus-infected target cells with preference for viral strains having the identical amino acid sequences to the peptides used for immunization. The optimal conditions for a primary in vivo CTL response was obtained with 100 micrograms peptide dissolved in incomplete Freund's adjuvant and injected s.c. at the base of tail. Spleen cells which had been primed 7-10 days earlier were restimulated for 5 days in vitro, using an optimal low peptide concentration (0.05 microM) and tested against virus-infected and peptide-treated target cells. The peptide-induced CTL were major histocompatibility complex class I restricted and CD8 positive.

Skin test to assess virus-specific cytotoxic T-cell activity

A way to assess specific CD8+ T-cell activity in a skin test analogous to the conventional delayed-type hypersensitivity (DTH) reaction for CD4+ T cells is presented. Local injection of viral class I binding peptides caused a specific CD8+ T-cell-mediated DTH in footpads of virally infected mice. The DTH was inducible only during the acute phase of the infection. Apparently because of the short half-life of locally available peptide, only activated CD8+ effector T cells could mediate the reaction. This skin test may prove to be particularly interesting for use in humans to evaluate the activation status of CD8+ T cells during acute viral infections and of memory CD8+ T cells, for example, in chronically active immunopathological disease or infection.

Malaria vaccines

The development of an effective malaria vaccine is a feasible goal. Most of the vaccines being developed today are subunit vaccines derived from selected parasite antigens or their immunologically active fragments. The precise characterization of protective immune responses against Plasmodium parasites remains a fundamental part of present research aimed at obtaining a malaria vaccine(s).

Rapid in vivo induction of HIV-specific CD8+ cytotoxic T lymphocytes by a 15-amino acid unmodified free peptide from the immunodominant V3-loop of GP120

Efforts to generate a vaccine to prevent infection by human immunodeficiency virus (HIV) have focused on inducing neutralizing antibodies. However, cytotoxic T-lymphocyte (CTL) responses are a major immune defense mechanism required for recovery from many different virus infections. Since CTL epitopes can be defined by short synthetic peptides, we searched for HIV peptides that elicit a viral-specific CTL response in mice. We have developed a new method for screening CTL-inducing peptides involving a single injection into the footpad of mice to prime CTLs in the draining popliteal lymph node of mice within 10 days. Our results demonstrate that a 15-amino acid peptide (aa 315-329) derived from the V3 loop of HIV gp120 caused a rapid induction of peptide-specific and gp160-specific CD8-positive CTLs. Lysis of targets is specific since cells preincubated with unrelated peptides are resistant to lysis as are cells of a different MHC haplotype pretreated with the cognate peptide. Pretreatment of restimulated node cells with complement plus anti-CD8 but not anti-CD4 removed the lytic activity. We also successfully induced in vivo CTL activity with unmodified synthetic peptides from the influenza and Sendai virus nucleoproteins, indicating general applicability of our method for rapid screening of CTL epitopes. Because HIV replication has been reported by several labs to occur mainly in lymph nodes of infected patients, the rapid induction of HIV-specific CTLs in proximal lymph nodes by unmodified peptides emphasizes the physiological significance of our findings toward vaccine and therapeutic approaches.

Extracellular processing of peptide antigens that bind class I major histocompatibility molecules

One problem associated with the use of synthetic peptides as antigens in vivo is their susceptibility to inactivation by proteolytic degradation. A situation is described in which a serum protease, angiotensin-converting enzyme (ACE), is actually responsible for the class I binding activity of a commonly used influenza antigen, nucleoprotein (NP)(147-158R-). This peptide has been reported to be a highly efficient class I antigen. Evidence is presented that demonstrates that the peptide is inactive until cleaved by ACE, which is a normal constituent of serum. The enzyme removes a COOH-terminal dipeptide resulting in the sequence NP(147-155), which is identical to the naturally processed peptide. Such extracellular processing of peptides and proteins may occur for a variety of antigens both in vitro and in vivo, and could have important implications for the design of proteolytically resistant vaccines.

Induction of cytotoxic T lymphocytes in mice against the principal neutralizing domain of HIV-1 by immunization with an engineered T-cytotoxic-T-helper synthetic peptide construct

Peptide constructs were engineered by colinear synthesis of two short synthetic peptide determinants; a determinant recognized by T helper cells (TDh) and a determinant recognized by T cytotoxic cells (TDc). Three types of constructs were synthesized: TDc-TDh, TDh-TDc, and TDh-KK-TDc, where KK are two lysine residues. In vivo immunization with free construct induced cytolytic lymphocytes (CTL) only in the case of TDc-TDh. However, immunization with spleen cells to which these constructs had been internalized by hypertonic shock, induced CTL activity in all three cases. No CTL could be induced after immunization with free TDc in either protocol. These results indicate that cell internalization of the construct might be essential for CTL induction, and also, that "help" from the TDh seems to be required.

Vaccination with a synthetic peptide modulates lymphocytic choriomeningitis virus-mediated immunopathology

Vaccination with a nucleopeptide (NP 118; amino acids 118 to 132) representing a cytotoxic T-cell epitope of lymphocytic choriomeningitis virus (LCMV) can modulate immunopathology. Immunization with NP 118 protected H-2d mice against intracerebral infection with the LCMV-ARMSTRONG isolate. However, when NP 118-primed H-2d mice were challenged intracerebrally with an intermediate dose (5 x 10(4) PFU) of the LCMV-DOCILE strain, all mice primed with NP 118 emulsified in incomplete Freund's adjuvant died, whereas unprimed mice survived. Correspondingly, peptide vaccination enhanced specifically the cytotoxic T-cell response, influencing the critical balance between T-cell response and virus spread.