Collaboration of helper and cytotoxic T lymphocytes

Recycled addition of CD4+ T cell-rich population for induction of human autologous cytotoxic T lymphocytes: A practically efficient method

When CD4(+) T cell-rich population appears in theinitial trial in induction cultures of humanautologous cytotoxic T lymphocytes (CTL), the cultureresults frequently in no or weak killing activity andtherefore usually be discarded as an ;unsuccessful'CTL induction culture. However, addition of theinitial CD4(+) T cell-rich population enabledefficient induction of the autologous CTL in theensuing trials. The CTL thus generated exhibitedstronger killing activities against autologous braintumor cells and ovarian tumor cells than previouslyobserved. This simple recycling of the primed butinert CD4(+) T cell-rich population for CTLinduction will promote clinical practice of adoptiveimmunotherapy of human tumors with autologous CTL.

Highly conserved cross-reactive CD4+ T-cell HA-epitopes of seasonal and the 2009 pandemic influenza viruses

Please cite this paper as: Duvvuri et al. (2010) Highly conserved cross‐reactive CD4+ T‐cell HA‐epitopes of seasonal and the 2009 pandemic influenza viruses. Influenza and Other Respiratory Viruses 4(5), 249–258.

Background The relatively mild nature of the 2009 influenza pandemic (nH1N1) highlights the overriding importance of pre‐existing immune memory. The absence of cross‐reactive antibodies to nH1N1 in most individuals suggests that such attenuation may be attributed to pre‐existing cellular immune responses to epitopes shared between nH1N1 virus and previously circulating strains of inter‐pandemic influenza A viruses.

Results We sought to identify potential CD4+ T cell epitopes and predict the level of cross‐reactivity of responding T cells. By performing large‐scale major histocompatibility complex II analyses on Hemagglutinin (HA) proteins, we investigated the degree of T‐cell cross‐reactivity between seasonal influenza A (sH1N1, H3N2) from 1968 to 2009 and nH1N1 strains. Each epitope was examined against all the protein sequences that correspond to sH1N1, H3N2, and nH1N1. T‐cell cross‐reactivity was estimated to be 52%, and maximum conservancy was found between sH1N1 and nH1N1 with a significant correlation (P < 0·05).

Conclusions  Given the importance of cellular responses in kinetics of influenza infection in humans, our findings underscore the role of T‐cell assays for understanding the inter‐pandemic variability in severity and for planning treatment methods for emerging influenza viruses.

Potent CTL induction by a whole cell pertussis vaccine in anti-tumor peptide immunotherapy

Promising yet limited clinical responses have been reported for peptide based immunotherapy against tumors. In order to induce more potent cytolytic CD8 T cell responses, we investigated the use of Bordetella pertussis vaccine as an adjuvant for peptide immunization. A whole cell (Wc) vaccine has been known to induce a Th1 biased immune response while an acellular (Ac) vaccine tends to induce that of the Th2 type. Natural infection by B. pertussis helps to maintain a robust Th1 memory in the host population. To examine the adjuvant activity of the pertussis vaccine, we immunized mice with an ovalbumin peptide as a model tumor antigen, and monitored the development of anti-tumor activities. The addition of either the Ac or the Wc vaccine helped expand the specific CD8 T cells. However, there was a marked difference in the induced cytolytic activity where the Wc vaccine was superior to the Ac. The Wc vaccine was also more effective in inducing in vivo tumor rejection. The adjuvant activity was not only effective against ovalbumin, but was also evident when an endogenous tumor antigen, Wilms' tumor 1 gene product, was targeted. These results indicate that, although the Wc vaccine does not share the same antigen specificity with tumor cells, it can aid in the development of highly cytolytic CD8 T cells as an adjuvant at the site of peptide immunization.

Hybrid cell vaccination resolves Leishmania donovani infection by eliciting a strong CD8+ cytotoxic T-lymphocyte response with concomitant suppression of interleukin-10 (IL-10) but not IL-4 or IL-13

There is an acute dearth of therapeutic interventions against visceral leishmaniasis that is required to restore an established defective cell-mediated immune response. Hence, formulation of effective immunotherapy requires the use of dominant antigen(s) targeted to elicit a specific antiparasitic cellular immune response. We implemented hybrid cell vaccination therapy in Leishmania donovani-infected BALB/c mice by electrofusing dominant Leishmania antigen kinetoplastid membrane protein 11 (KMP-11)-transfected bone marrow-derived macrophages from BALB/c mice with allogeneic bone marrow-derived dendritic cells from C57BL/6 mice. Hybrid cell vaccine (HCV) cleared the splenic and hepatic parasite burden, eliciting KMP-11-specific major histocompatibility complex class I-restricted CD8+ cytotoxic T-lymphocyte (CTL) responses. Moreover, splenic lymphocytes of HCV-treated mice not only showed the enhancement of gamma interferon but also marked an elevated expression of the Th2 cytokines interleukin-4 (IL-4) and IL-13 at both transcriptional and translational levels. On the other hand, IL-10 production from splenic T cells was markedly suppressed as a result of HCV therapy. CD8+ T-cell depletion completely abrogated HCV-mediated immunity and the anti-KMP-11 CTL response. Interestingly, CD8+ T-cell depletion completely abrogated HCV-induced immunity, resulting in a marked increase of IL-10 but not of IL-4 and IL-13. The present study reports the first implementation of HCV immunotherapy in an infectious disease model, establishing strong antigen-specific CTL generation as a correlate of HCV-mediated antileishmanial immunity that is reversed by in vivo CD8+ T-cell depletion of HCV-treated mice. Our findings might be extended to drug-nonresponsive visceral leishmaniasis patients, as well as against multiple infectious diseases with pathogen-specific immunodominant antigens.

Mimotope vaccines for cancer immunotherapy

Cancer vaccines need to be designed to effectively induce tumor-specific CD8(+) T cells, the key effector cells in immune responses against tumors. These T cells recognize peptides generated from cellular proteins by limited proteolysis, and bound and presented at cell surfaces by MHC class I molecules. Mimotopes, mimetics of T cell epitopes, have been derived from known epitopes by sequence modification, or developed de novo using combinatorial peptide libraries to scan the entire sequence space for peptides that induce the desired T cell responses. Mimotopes of both types have been tested in clinical vaccination trials for treatment of cancer.

Therapeutic vaccination for the treatment of malignant melanoma

With increasing knowledge of tumor-associated antigens and T cell epitopes, and the mechanisms of induction and regulation of T-cellular immune responses, therapeutic vaccination is increasingly being explored as a treatment option for cancer. Several clinical cancer vaccination trials, the majority of them with melanoma patients, have demonstrated efficient induction of tumor-specific cellular immune responses in patients. However, these immune responses, in most cases, do not translate into clinical responses. The clinical response rates in these trials are relatively low. The most likely causes for the lack of correlation of immunological and clinical responsiveness are loss of antigenicity and immune suppression. Nonetheless, many patients in the vaccination trials have experienced extended survival compared to clinical experience. Therapeutic vaccination thus appears suited for maintenance therapy where cure is not possible and is an interesting option for adjuvant therapy after surgical tumor resection. While the clinical efficacy of vaccination is expected to be better for early-stage cancer, advancement of the treatment of advanced-stage disease will require combination with other therapeutic principles.

Hybrid-cell vaccines for cancer immune therapy

Hybrid cells generated by fusing allogenic-presenting cells, such as dendritic cells, with tumor cells are a new tool in cancer immunotherapy which are designed to enhance the immunogenicity of antigenic tumors by presenting the whole spectrum of tumor-associated antigens, by providing the co-stimulatory molecules required for T-cell activation, and by the expression of allogenic MHC molecules for recruitment and activation of T-cell help. This approach has been successfully tested in animal models as well as in clinical phaseI/II trials with various tumors. Besides clinical repsonses, induction of tumor-specific cytolytic Tcells were observed. The electrofusion protocol described here has the advantage of high fusion efficiency, high hybrid-cell viability, as well as high reproducibility, and can be used for various tumor cell types after minor adjustments are made to the instrument settings in order to process large numbers of dendritic cells with consistent efficiencies.

Kinetic evolution of a diabetogenic CD8+ T cell response

Nonobese diabetic (NOD) mice develop overt diabetes following prolonged periods of pancreatic islet inflammation involving both CD4+ and CD8+ T cells. The initiation and progression of autoimmune diabetes require the recruitment of beta cell-reactive CD8+ T cells to the pancreatic lymph nodes, their activation by antigen, and their subsequent migration into pancreatic islets. We and others have shown that a significant fraction of NOD islet-associated CD8+ T cells express highly homologous TCRalpha chains (Valpha17 and Jalpha42 joined by the same N-region sequence) and that they recognize the peptide NRP-A7 in the context of the MHC class I molecule H-2K(d). We have also shown that this T cell subpopulation undergoes a process of "avidity maturation" that is associated with progression of benign insulitis to overt diabetes. This paper will summarize our current understanding of the mechanisms that drive the recruitment and activation of this CD8+ T cell subpopulation.

Vaccination with hybrids of tumor and dendritic cells induces tumor-specific T-cell and clinical responses in melanoma stage III and IV patients

Hybrid cell vaccination was developed as therapeutic approach that aims at stimulating tumor-specific cytotoxic T-cell responses in cancer patients using hybrids of autologous tumor and allogeneic dendritic cells. We tested this concept and the efficacy of the vaccines in inducing clinical and immunologic responses in a clinical trial with melanoma stage III and IV patients. Of the 17 patients evaluated, 1 experienced a complete response, 1 a partial response and 6 stable disease with remarkably long survival times. In 11 of 14 patients analyzed, high-frequency T-cell responses to various tumor-associated T-cell epitope were induced and detectable in the peripheral blood. These immune responses were detected in clinical response patients as well as nonresponders. Failures of clinical responses in all the cases investigated correlated with loss of antigen expression and presentation. Hybrid cell vaccination thus proves effective in inducing tumor-specific T-cell responses in cancer patients.

The future of vaccination as a treatment strategy in dermatological diseases

Vaccination approaches are increasingly explored as means for both prevention and therapy of skin diseases. These development are boosted by the rapidly accumulating knowledge of the molecular and cellular bases of these disease and the antigens involved, on the one hand, and of the components and mechanisms of cellular and humoral immune responses, on the other. In a number of cases these newly developed vaccination strategies are already tested in clinical trials. Although most of them are still in very early stages of the development, it is foreseeable that vaccination will emerge as an important option for prevention and treatment of infectious skin diseases as well as of cancer, allergies and maybe, auto-immune disorders.

Identification of T-cell epitopes in the structural and non-structural proteins of classical swine fever virus

To identify new T-cell epitopes of classical swine fever virus (CSFV), 573 overlapping, synthetic pentadecapeptides spanning 82% of the CSFV (strain Glentorf) genome sequence were synthesized and screened. In proliferation assays, 26 peptides distributed throughout the CSFV viral protein sequences were able to induce specific T-cell responses in PBMCs from a CSFV-Glentorf-infected d/d haplotype pig. Of these 26 peptides, 18 were also recognized by PBMCs from a CSFV-Alfort/187-infected d/d haplotype pig. In further experiments, it could be shown that peptide 290 (KHKVRNEVMVHWFDD), which corresponds to amino acid residues 1446-1460 of the CSFV non-structural protein NS2-3 could induce interferon-gamma secretion after secondary in vitro restimulation. The major histocompatibility complex (MHC) restriction for stimulation of T-cells by this pentadecapeptide was identified as being mainly MHC class II and partially MHC class I. In cytolytic assays, CSFV-specific cytotoxic T-lymphocytes (CTLs) were able to lyse peptide 290-loaded target cells. These findings indicate the existence of a CSFV-specific helper T-cell epitope and a CTL epitope in this peptide.

Simian virus 40 large-T-antigen-specific rejection of mKSA tumor cells in BALB/c mice is critically dependent on both strictly tumor-associated, tumor-specific CD8(+) cytotoxic T lymphocytes and CD4(+) T helper cells

Protective immunity of BALB/c mice immunized with simian virus 40 (SV40) large T antigen (TAg) against SV40-transformed, TAg-expressing mKSA tumor cells is critically dependent on both CD8(+) and CD4(+) T lymphocytes. By depleting mice of T-cell subsets at different times before and after tumor challenge, we found that at all times, CD4(+) and CD8(+) cells both were equally important in establishing and maintaining a protective immune response. CD4(+) cells do not contribute to tumor eradication by directly lysing mKSA cells. However, CD4(+) lymphocytes provide help to CD8(+) cells to proliferate and to mature into fully active cytotoxic T lymphocytes (CTL). Depletion of CD4(+) cells by a single injection of CD4-specific monoclonal antibody at any time from directly before injection of the vaccinating antigen to up to 7 days after tumor challenge inhibited the generation of cytolytic CD8(+) lymphocytes. T helper cells in this system secrete the typical Th-1 cytokines interleukin 2 (IL-2) and gamma interferon. Because in this system TAg-specific CD8(+) cells secrete only minute amounts of IL-2, it appears that T helper cells provide these cytokines for CD8(+) T cells. Moreover, this helper effect of CD4(+) T cells in mKSA tumor rejection in BALB/c mice does not simply improve the activity of TAg-specific CD8(+) CTL but actually enables them to mature into cytolytic effector cells. Beyond this activity, the presence of T helper cells is necessary even in the late phase of tumor cell rejection in order to maintain protective immunity. However, despite the support of CD4(+) T helper cells, the tumor-specific CTL response is so weak that only at the site of tumor cell inoculation and not in the spleen or in the regional lymph nodes can TAg-specific CTL be detected.

Efficient induction of peptide-specific cytotoxic T lymphocytes by LPS-activated spleen cells

Lipopolysaccharides of gram-negative bacteria are potent activators of B cells, dendritic cells and monocytes/macrophages. We have investigated the use of LPS-activated spleen cells as antigen-presenting cells to induce CD8+ cytotoxic T lymphocytes in vivo that are reactive to MHC class I binding peptides. Compared with resting spleen cells, CTL induction was more efficient and less variable for different peptides with LPS-activated spleen cells. Cytotoxic responses were specific for the immunized peptides and contained high affinity CD8+ T cells. The removal of dendritic cells and monocytes/macrophages by Sephadex G10 column did not show profound effects on CTL induction, indicating that B-cell blasts were largely responsible. This easily accessible method should facilitate the screening of MHC class I binding peptides to determine whether or not the host's T-cell repertoire contains reactive T cells.

Hybrid cell vaccination for cancer immune therapy: first clinical trial with metastatic melanoma

Hybrid cell vaccination is a new cancer immune therapy approach that aims at recruiting T cell help for the induction of tumour specific cytolytic immunity. The vaccines are generated by fusion of the patients' tumour cells with allogeneic MHC class II bearing cells to combine the tumour's antigenicity with the immunogenicity of allogeneic MHC molecules. Safety and anti-tumour activity of this treatment were assessed in a clinical trial that has yielded one complete and one partial remission, and 5 cases of stable disease among 16 patients with advanced stage metastatic melanoma. As evidenced by histology, the vaccination induced T cell relocation into tumour nodules. Stable disease could be maintained by repeated booster injections for more than 24 months in some patients. The side effects were minor. Occasional occurrences of vitiligo spots after vaccination were indicative of a restricted therapy induced auto-immune reactivity. The results suggest that hybrid cell vaccination is a safe cancer immune therapy potentially effective for induction of acute anti-tumour response as well as long-term maintenance.

Natural analogue peptides of an HIV-1 GP120 T-helper epitope antagonize response of GP120-specific human CD4 T-cell clones

Neutralizing antibodies and specific cytotoxic T lymphocytes (CTL) may contribute to controlling viral spread, and ideally, to virus clearance in HIV infection. Both effector mechanisms depend on specific CD4 T-helper (Th) cells. Nevertheless, HIV hypervariability facilitates appearance of escape mutants for antibodies and for CTL responses. Here we also show that natural mutations (i.e., from sequences of different HIV strains) in an immunodominant Th epitope recognized by human CD4 clones specific for the envelope glycoprotein gp120 escape CD4 T-cell recognition. Furthermore, several natural analogue peptides exert an antagonistic function by inhibiting proliferative response of T cells specific to gp120 with a wild-type sequence. If similar events occur in vivo, they may represent an additional escape mechanism for HIV. In fact, antagonism for CD4 Th response may occur during superinfection with a different strain, or with the appearance of a variant carrying a mutated antagonistic sequence. In both cases, impaired Th cell function could lead to reduced immune control of HIV infection by interfering with CTL and antibody response.

Involvement of CD4(+) Th1 cells in systemic immunity protective against primary and secondary challenges with Trypanosoma cruzi

In general, gamma interferon (IFN-gamma)-producing CD4(+) Th1 cells are important for the immunological control of intracellular pathogens. We previously demonstrated an association between parasite-specific induction of IFN-gamma responses and resistance to the intracellular protozoan Trypanosoma cruzi. To investigate a potential causal relationship between Th1 responses and T. cruzi resistance, we studied the ability of Th1 cells to protect susceptible BALB/c mice against virulent parasite challenges. We developed immunization protocols capable of inducing polarized Th1 and Th2 responses in vivo. Induction of parasite-specific Th1 responses, but not Th2 responses, protected BALB/c mice against virulent T. cruzi challenges. We generated T. cruzi-specific CD4(+) Th1 and Th2 cell lines from BALB/c mice that were activated by infected macrophages to produce their corresponding cytokine response profiles. Th1 cells, but not Th2 cells, induced nitric oxide production and inhibited intracellular parasite replication in T. cruzi-infected macrophages. Despite the ability to inhibit parasite replication in vitro, Th1 cells alone could not adoptively transfer protection against T. cruzi to SCID mice. In addition, despite the fact that the adoptive transfer of CD4(+) T lymphocytes was shown to be necessary for the development of immunity protective against primary T. cruzi infection in our SCID mouse model, protective secondary effector functions could be transferred to SCID mice from memory-immune BALB/c mice in the absence of CD4(+) T lymphocytes. These results indicate that, although CD4(+) Th1 cells can directly inhibit intracellular parasite replication, a more important role for these cells in T. cruzi systemic immunity may be to provide helper activity for the development of other effector functions protective in vivo.

Prevalent CD8(+) T cell response against one peptide/MHC complex in autoimmune diabetes

Spontaneous autoimmune diabetes in nonobese diabetic (NOD) mice is the result of a CD4(+) and CD8(+) T cell-dependent autoimmune process directed against the pancreatic beta cells. CD8(+) T cells play a critical role in the initiation and progression of diabetes, but the specificity and diversity of their antigenic repertoire remain unknown. Here, we define the structure of a peptide mimotope that elicits the proliferation, cytokine secretion, differentiation, and cytotoxicity of a diabetogenic H-2K(d)-restricted CD8(+) T cell specificity (NY8.3) that uses a T cell receptor alpha (TCRalpha) rearrangement frequently expressed by CD8(+) T cells propagated from the earliest insulitic lesions of NOD mice (Valpha17-Jalpha42 elements, often joined by the N-region sequence M-R-D/E). Stimulation of splenic CD8(+) T cells from single-chain 8. 3-TCRbeta-transgenic NOD mice with this mimotope leads to preferential expansion of T cells bearing an endogenously derived TCRalpha chain identical to the one used by their islet-associated CD8(+) T cells, which is also identical to the 8.3-TCRalpha sequence. Cytotoxicity assays using islet-derived CD8(+) T cell clones from nontransgenic NOD mice as effectors and peptide-pulsed H-2K(d)-transfected RMA-S cells as targets indicate that nearly half of the CD8(+) T cells recruited to islets in NOD mice specifically recognize the same peptide/H-2K(d) complex. This work demonstrates that beta cell-reactive CD8(+) T cells mount a prevalent response against a single peptide/MHC complex and provides one peptide ligand for CD8(+) T cells in autoimmune diabetes.

Gag protein epitopes recognized by CD4(+) T-helper lymphocytes from equine infectious anemia virus-infected carrier horses

Antigen-specific T-helper (Th) lymphocytes are critical for the development of antiviral humoral responses and the expansion of cytotoxic T lymphocytes (CTL). Identification of relevant Th lymphocyte epitopes remains an important step in the development of an efficacious subunit peptide vaccine against equine infectious anemia virus (EIAV), a naturally occurring lentivirus of horses. This study describes Th lymphocyte reactivity in EIAV carrier horses to two proteins, p26 and p15, encoded by the relatively conserved EIAV gag gene. Using partially overlapping peptides, multideterminant and possibly promiscuous epitopes were identified within p26. One peptide was identified which reacted with peripheral blood mononuclear cells (PBMC) from all five EIAV-infected horses, and three other peptides were identified which reacted with PBMC from four of five EIAV-infected horses. Four additional peptides containing both CTL and Th lymphocyte epitopes were also identified. Multiple epitopes were recognized in a region corresponding to the major homology region of the human immunodeficiency virus, a region with significant sequence similarity to other lentiviruses including simian immunodeficiency virus, puma lentivirus, feline immunodeficiency virus, Jembrana disease virus, visna virus, and caprine arthritis encephalitis virus. PBMC reactivity to p15 peptides from EIAV carrier horses also occurred. Multiple p15 peptides were shown to be reactive, but not all infected horses had Th lymphocytes recognizing p15 epitopes. The identification of peptides reactive with PBMC from outbred horses, some of which encoded both CTL and Th lymphocyte epitopes, should contribute to the design of synthetic peptide or recombinant vector vaccines for EIAV.

Shaping the Repertoire of Cytotoxic T-Lymphocyte Responses: Explanation for the Immunodominance Effect Whereby Cytotoxic T Lymphocytes Specific for Immunodominant Antigens Prevent Recognition of Nondominant Antigens

The immunodominance effect, whereby the presence of immunodominant epitopes prevents recognition of nondominant determinants presented on the same antigen-presenting cell (APC) considerably restricts the repertoire of cytotoxic T lymphocyte (CTL) responses. To elucidate the molecular basis of the immunodominance effect, we compared the interactions of a dominant (B6dom1) and a nondominant epitope (H-Y) with their restricting class I molecule (H2-Db), and their ability to trigger cognate CTLs. We found that B6dom1/Db complexes behaved as optimal T-cell receptor (TCR) ligands and triggered a more rapid in vivo expansion of cognate CTLs than H-Y/Db complexes. The superiority of the dominant epitope was explained by its high cell surface density (1,012 copies/cell for B6dom1v 10 copies/cell for H-Y) and its optimal affinity for cognate TCRs. Based on these results, we conclude that dominant class I–associated epitopes are those that have optimal ability to trigger TCR signals in CTLs. We propose that the rapid expansion of CTLs specific for dominant antigens should enable them to compete more successfully than other CTLs for occupancy of the APC surface.

Shaping the Repertoire of Cytotoxic T-Lymphocyte Responses: Explanation for the Immunodominance Effect Whereby Cytotoxic T Lymphocytes Specific for Immunodominant Antigens Prevent Recognition of Nondominant Antigens

The immunodominance effect, whereby the presence of immunodominant epitopes prevents recognition of nondominant determinants presented on the same antigen-presenting cell (APC) considerably restricts the repertoire of cytotoxic T lymphocyte (CTL) responses. To elucidate the molecular basis of the immunodominance effect, we compared the interactions of a dominant (B6dom1) and a nondominant epitope (H-Y) with their restricting class I molecule (H2-Db), and their ability to trigger cognate CTLs. We found that B6dom1/Db complexes behaved as optimal T-cell receptor (TCR) ligands and triggered a more rapid in vivo expansion of cognate CTLs than H-Y/Db complexes. The superiority of the dominant epitope was explained by its high cell surface density (1,012 copies/cell for B6dom1v 10 copies/cell for H-Y) and its optimal affinity for cognate TCRs. Based on these results, we conclude that dominant class I–associated epitopes are those that have optimal ability to trigger TCR signals in CTLs. We propose that the rapid expansion of CTLs specific for dominant antigens should enable them to compete more successfully than other CTLs for occupancy of the APC surface.

Deletions in the hepatitis B virus core gene may influence the clinical outcome in hepatitis B e antigen-positive asymptomatic healthy carriers

To address the significance of mutations within the hepatitis B virus (HBV) core gene in chronic HBV infection, we followed prospectively HBe-antigen-positive asymptomatic healthy carriers, documented the onset of their disease based on serum alanine transaminase (ALT) concentrations, and analyzed sequentially serum samples from a quiescent phase through to an active phase of the chronic infection. In three female carriers, the first flare-up was documented during the follow-up period. Serial analysis by polymerase chain reaction, cloning, and sequencing of the HBV precore/core open reading frame genome demonstrated that clones with core gene deletions emerged during the quiescent phase and persisted subsequently during the active phase in two patients, who failed to seroconvert to anti-HBe and had persistently increased ALT levels despite interferon (IFN) therapy. The deletions were various, overlapping, and located in the mid-core region ranging from amino acid (aa) position 64 to 128. The remaining patient, who seroconverted with IFN therapy, did not have a core-gene-deletion HBV variant during follow-up, but had aa substitutions clustered in some restricted core regions. Two control asymptomatic carriers, who had no change in biochemical or virologic markers over a 15- to 19-year period, had no core-gene-deletion variants and few aa changes. These findings indicate that the mid-portion of the core gene is subject to deletion even during the quiescent phase. Thus, the immunologic interaction between the host and virus may occur insidiously, and the emergence of a core-gene-deletion HBV variant during the quiescent phase may be involved in the onset of hepatitis and the subsequent outcome of chronic infection.

Structural Aspects of the Interaction Between Heterogeneic Human Papillomavirus Type 1 E4-Specific T Cell Receptors and the Same Peptide/HLA-DQ8 Complex

TCR usage has been studied in a panel of Th cell clones specific for the same peptide epitope (P N S Q D R G R P R R S D), derived from the human papillomavirus type 1 (HPV1) E4 protein, and restricted through HLA-DQ8. After identifying the V, D, and J genes used by the TCRs and sequencing across the V(D)J junctions, five different α-chain sequences and five different β-chain sequences, comprising six independent clones, were identified. A structural model of our E4 peptide/HLA-DQ8 complex predicted that the guanidinyl side chain on the arginine residue at position 6 of the peptide could exist in different orientations. An intramolecular interaction between this arginine and the glutamine residue at position four appeared to control this orientation. Interacting HPV1 E4-specific TCRs would therefore have to recognize the complex in different conformations, and molecular modeling of the TCRs suggested that this could be achieved by changing the dimensions of the central pocket formed where the CDR3 loops of the TCR α- and β-chains converge. It is known that interactions between bound peptide and amino acid residues lining the peptide-binding cleft of HLA molecules are important for determining the conformation and orientation of the peptide/MHC complex. The suggestion here that intramolecular interactions between amino acids of close proximity on the bound peptide are also important adds a further level of complexity to the mechanism by which TCRs interact with Ag.

Intrahepatic hepatitis C virus-specific cytotoxic T lymphocyte activity and response to interferon alfa therapy in chronic hepatitis C

Hepatitis C virus (HCV)-specific cytotoxic T lymphocytes (CTL) have been shown to play a role in host defense and pathogenesis of chronic HCV infection. Our aim was to test the hypothesis that intrahepatic HCV-specific CTL activity may impact subsequent response to interferon alfa (IFN-alpha) therapy. Of the 37 patients that we have prospectively evaluated for HCV-specific CTL activity in liver, 21 received IFN therapy, and 19 completed a 6-month course and attended 6 to 18 months of follow-up. Intrahepatic CD8+ cells were isolated from liver biopsy tissue and tested against target cells expressing HCV antigens to determine intrahepatic CTL activity. The relationship between treatment response and HCV-specific CTL activity and other factors known to associate with response (genotype, viremia, histology) was analyzed. HCV-specific CTL activity was detected in 9 of 21 patients (and 9 of 19 who completed therapy). After 6 months of IFN therapy, 8 of 19 (42%) patients had normal serum alanine transaminase (ALT) (complete responders). After 18 months of follow-up, only 3 patients (16%) had a sustained biochemical response. Of the 9 patients with detectable HCV-specific CTL activity in their liver before treatment, 7 (78%) developed a complete response. In contrast, only 1 of the 10 patients with no detectable HCV-specific CTL activity developed a complete response to IFN (P < .01). In 6 of 8 patients with a complete response, including the 3 sustained responders, the CTL response appeared to be directed predominately to the HCV core region. These data suggest that the host immune response, particularly that mediated by CD8+ CTL, may be important in determining the outcome of IFN therapy for chronic HCV infection. Further understanding of the mechanism of action of IFN should impact the design of better therapeutic strategies against chronic HCV infection.

Bystander suppression of murine collagen-induced arthritis by long-term nasal administration of a self type II collagen peptide

Oral and more recently nasal tolerance have attracted attention as potential treatments of autoimmune disease. Arthritis induced by bovine type II collagen (CII) is a widely used animal model of rheumatoid arthritis, which is here used to investigate the efficacy of nasal treatment by a short peptide. The peptide spans residues 707-721 (designated p707), an epitope of mouse CII that is most strongly recognized after immunization of mice with this self-protein. The treatment was partially effective, but almost only when the peptide was administered in large doses over a prolonged period. Mice immunized with bovine CII respond mainly to other peptides, located in the CB11 fragment around amino acid residues 256-270. The tolerance effect therefore results from intramolecular suppression, between epitopes located in different parts of this large protein.

Protein kinase C mediates the signal for interferon-gamma mRNA expression in cytotoxic T cells after their adhesion to laminin

A cytotoxic T-cell line, CTLL-2 cells, showed spreading after adhering to extracellular matrix proteins such as fibronectin (FN), laminin (LN) and hyarulonic acid (HA). The adhesion of CTLL-2 cells to LN was mediated by very late activation antigen-6 (VLA-6). Expression of interferon-gamma (IFN-gamma) mRNA was enhanced in CTLL-2 cells, also when they adhered to extracellular matrix proteins; and the enhanced IFN-gamma mRNA expression by adhering to LN was blocked by anti-alpha 6 antibody. Calphostin C, a protein kinase C (PKC) inhibitor, markedly inhibited the enhancement of IFN-gamma mRNA expression in a dose-dependent manner, which suggested that PKC acted as a second messenger in the IFN-gamma mRNA expression mediated by the interaction of VLA-6 with LN in CTLL-2 cells. Furthermore, confocal laser-microscopic analysis and Western blot analysis revealed that PKC-alpha was activated after CTLL-2 cells adhered to LN. PKC activity translocated from the cytosol fraction to the particulate fraction, after CTLL-2 cells adhered to LN. Altogether, we suggest that PKC plays an important role in the signal transduction for IFN-gamma mRNA expression after cytotoxic T cells adhere to LN.

Human CD4+ T lymphocytes recognize a highly conserved epitope of human T lymphotropic virus type 1 (HTLV-1) env gp21 restricted by HLA DRB1*0101

HTLV-1 causes two distinct human diseases, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukaemia/lymphoma (ATL). Persistently infected individuals carry a risk of <1% of developing either disease. These basic epidemiological data imply that virus-host interactions, especially immunogenetic factors, influence the outcome of infection. Several studies showed that the HLA class II DR1 DQ5 haplotype is over-represented in HAM/TSP, but rare in ATL. Therefore, we selected four patients with HAM/TSP and one seronegative control who all carried the HLA DR1 DQ5 haplotype. We analysed the CD4+ T lymphocyte response against eight synthetic peptides of HTLV-1 envelope (env) glycoprotein gp21, a crucial target antigen in HAM/TSP. The first of two immunodominant epitopes corresponded to a domain of the HTLV-1 envelope protein which had previously been shown to be essential for HTLV-1 envelope function. The second immunodominant epitope overlapped a highly conserved sequence of the retroviral transmembrane envelope protein. DR1 (DRB1*0101)-restricted T lymphocytes were activated by the conserved peptide sequence in nanomolar concentrations. In contrast, this conserved sequence can also induce non-specific, cAMP-mediated immunosuppressive effects on T cells when added in micromolar concentrations to culture media, as shown by Haraguchi S, Good RA, James-Yarish M, Cianciolo GJ, Day NK, Proc Natl Acad Sci USA 1995; 92:5568-71. Hence, HTLV-1 env gp21 might exert either stimulating immunological or immunosuppressive effects in HTLV-1-infected individuals, depending on the level of its expression and the presence of HLA DRB1*0101.

Characterization of an overlapping CD8+ and CD4+ T-cell epitope on rubella capsid protein

A synthetic peptide corresponding to rubella virus capsid protein residues 263 to 275 which contains an epitope recognized by a cloned CD4+ cytotoxic T-lymphocyte (CTL) line was used to induce CD8+ T-cell lines specific to this peptide. A peptide-specific CD8+ CTL clone was derived and characterized. This peptide-specific CD8+ CTL clone exhibited cytotoxicity against target cells infected by a vaccinia recombinant virus expressing rubella virus capsid protein, but not by target cells infected by vaccinia recombinant virus expressing rubella virus E1 or E2 envelope proteins. Analysis of HLA class I restriction of the CD8+ CTL clone revealed that A11 and A3 were restrictive elements. Fine mapping with truncated and overlapping peptide analogs revealed a nonamer sequence, C(264-272), as the T-cell epitope eliciting stronger cytotoxicity. Two anchor residues for binding to HLA A11 and A3 were identified at position 2 (isoleucine) and at position 9 (histidine) or at position 8 (arginine) of the epitope sequence. The identification of overlapping CD4+ and CD8+ T-cell epitopes within the capsid protein sequence C(263-275) implicates a strategy for using such epitopes in a candidate peptide-based rubella vaccine.

Donor-specific cytokine production by graft-infiltrating lymphocytes induces and maintains graft vascular disease in human cardiac allografts

BACKGROUND

The development of graft vascular disease (GVD) in the allograft is a major impediment for long-term survival of heart transplant recipients. GVD may be mediated by cellular processes, in response to the transplanted heart, and regulated by cytokines.

METHODS

We studied donor-specific cytokine production patterns in graft-infiltrating lymphocyte cultures propagated from endomyocardial biopsies. The biopsies were derived from patients with and without signs of GVD, as diagnosed by angiography at 1 year after heart transplantation.

RESULTS

In the first year after transplantation, significantly more T-helper (Th) 1 cytokines (interleukin [IL]-2: P=0.04; interferon-gamma: P=0.01), but not Th2 (IL-4 and IL-6) cytokines, were produced by cultures of patients with GVD compared with patients without GVD. Thereafter, the Th1 cytokine levels in patients with GVD normalized to the levels of patients without GVD. Detectable levels of IL-6 were produced significantly more often (P=0.009) by cultures obtained more than 1 year after transplantation from patients with GVD.

CONCLUSIONS

The results suggest that high levels of Th1 cytokines produced by graft-infiltrating lymphocytes early after transplantation may be responsible for activation of vascular endothelium, leading to the migration and proliferation of smooth muscle cells that is characteristic of GVD. IL-6, produced later after transplantation, continues this process by promoting smooth muscle cell proliferation.

Antigen organization regulates cluster formation and induction of cytotoxic T lymphocytes by helper T cell subsets

Generation of effector cytotoxic T lymphocytes (CTLs) is a process tightly governed by regulatory helper T (Th) cells. The nature of cellular interactions as well as the precise role of distinct Th cell subsets involved in efficient CTL activation remains elusive. Employing in vitro cultures for primary induction of human, peptide-specific CTL, a strict requirement for Th cells and linkage of epitopes for helper and CTLs on the surface of antigen presenting cells was found, suggesting a three cell type cluster as minimal immune regulatory entity. Cognate and antigen-driven interactions of T cells were neither essential nor sufficient to override the need for linked epitopes. Within the three cell type cluster complex, keyhole limpit hemocyanin or tetanus toxoid-reactive Th cells promoted generation of MAGE-3- or HIV-gag-specific CTL. Both type 1 and type 2 Th cells were recruited and induced by CTL. Interleukin 2 and interferon gamma were essential in early stages, and interleukin 4 was utilized in later stages, of CTL maturation. Synergistic effects of CD45RA+ and CD45RO+ Th cells were found. The data reported here suggest a critical link between the innate and adaptive immune system in the initiation process of cytolytic immune responses and offers the basis for efficient vaccine strategies.

Antigenicity of HIV-derived T helper determinants in the context of carrier recombinant proteins: effect on T helper cell repertoire selection

T helper (Th) epitopes can be included in a recombinant protein with B and CTL epitopes to create more effective immunogens. To determine whether the antigenicity of HIV Th epitopes is preserved in this altered molecular context, human Th clones specific for peptides of HIV gp120 and reverse transcriptase p66 were challenged with recombinant proteins carrying the antigenic epitopes in different sites. We found that a given epitope was recognized by a specific T cell clone only when it was inserted in a particular position of the carrier. However, the permissive position was not the same for all epitopes. Enzymatic excision from a nonpermissive context or insertion of a polyserine spacer between the epitope and the carrier restored antigenicity. Nevertheless, antigenicity was not abolished in a synthetic peptide encompassing the epitope and the neighboring residues from the nonpermissive location. These data suggest that, in this case, the primary sequence of the chimeric protein flanking the HIV peptide is not responsible for loss of antigenicity. Furthermore, constructs carrying the epitope in a given position were recognized by peptide-specific Th clones raised from some individuals, but not from others. We show that this is due neither to individual modes of processing nor to the use of distinct major histocompatibility complex MHC class II restriction elements, but rather that it is related to the fine specificity of the clones. To study the effect of epitope context on selection of T cell repertoire in a naive individual, T cell lines were generated in vitro by stimulation with different peptide constructs. This resulted in the induction of diverse clonotypes defined by the pattern of recognition of different constructs, by T cell receptor V beta gene usage and by fine epitope mapping.

Liver-infiltrating and circulating CD4+ T cells in chronic hepatitis C: immunodominant epitopes, HLA-restriction and functional significance

The aim was to assess the specificity and functional significance of liver-infiltrating and peripheral blood T cells in chronic hepatitis C. Peripheral blood mononuclear cells hepatitis C virus from 50 of 58 (86.2%) patients with chronic hepatitis C virus infection and 6 of 28 (21.4%) controls showed a proliferative T cell response to at least one of 16 synthetic peptides covering highly conserved regions of the core, envelope (El) and non-structural regions (NS4) of hepatitis C virus. However, six immunodominant peptides were exclusively recognized by the proliferating blood mononuclear cells from 46 patients with chronic hepatitis C virus infection (79.3%). Fine specificity and HLA-restriction were studied with 15 peptide-specific CD4+ T cell lines and 23 T cell clones isolated from liver tissue and peripheral blood of 12 patients with chronic hepatitis C. It was demonstrated that the peptide-specific response of CD4+ T cells was restricted to the presence of autologous accessory cells and HLA-DR and -DP molecules. Eight peptide-specific T cell lines and five T cell clones derived from liver tissue and peripheral blood, released interferon-gamma (200-6600 pg/ml) and tumor necrosis factor-alpha (100-400 pg/ml) and no or little interleukin-4 (< 140 pg/ml) after peptide-specific or mitogeneic stimulation, thus resembling a Th1-like cytokine profile. Patients with active liver disease showed significantly higher proliferative responses to hepatitis C virus core peptides than asymptomatic hepatitis C virus carriers or complete responders to interferon therapy. In conclusion, class II-restricted CD4+ T cell responses to some immunodominant epitopes within the hepatitis core region correlated with disease activity in chronic hepatitis C virus infection. Functionally, liver-infiltrating and peripheral blood T cells released Th1-like cytokines in response to the specific stimulus. Thus, it can be suggested that CD4+ T cells can mediate the pathogenesis of chronic hepatitis C virus induced liver disease.

T cell tolerance and activation to a transgene-encoded tumor antigen

Much has been learned in recent years concerning the nature of tumor antigens recognized by T cells. To apply this knowledge clinically, the nature of the host response to individual and multiple tumor antigens has to be characterized. This will help to define the efficacy of immune surveillance and the immune status of the host following exposure to tumor antigens expressed on pre-neoplastic tissue. To approach these questions, we have developed a transgenic mouse which expresses the tumor-specific antigen P91A. The single amino acid substitution in P91A results in the expression of a new MHC class I (H-2Ld)-binding peptide. In transgenic tissue, the H-2Ld/P91A complex is expressed in isolation from other tumor-associated antigens, allowing definition of the immune response to a single defined tumor antigen, a situation closely analogous to events during tumorigenesis. We show that CD8+ T cell immune surveillance of P91A is ineffective without the introduction of a helper determinant operating through stimulation of CD4+ T cells. Recognition of the isolated P91A tumor antigen on normal tissue by CD8+ T cells is a tolerogenic process. Induction of T cell tolerance suggests tumor antigen-T cell interactions occurring during tumorigenesis may elicit T cell tolerance and hence confound some immunotherapeutic approaches.

Handling of retroviral antigens by human antigen-presenting cells

Antigen-specific T helper cells play an important role in retroviral infections. Indeed, they provide help for B-cell activation and antibody production and for clonal expansion of cytolytic lymphocytes. Therefore, we used retrovirus-specific human T helper clones in order to define modes of antigen presentation, antigen-presenting cells and the molecular context of Th epitopes that could be exploited in the design of immunogens aimed at optimizing the Th cell response. In particular, we describe several mechanisms of receptor-mediated antigen uptake that enhance the stimulation of human T-cell clones specific for HIV and HTLV-1 antigens; we report on the differential recognition of Th epitopes depending on the molecular-viral context; we show that dendritic cells are the most efficient presenting cells and are essential for the induction of in vitro primary Th cell responses; and finally, we propose that Th cells specific for internal, conserved antigens of HIV such as reverse transcriptase, may be candidates for intrastructural help resulting in induction of envelope specific antibodies.

Modulation by gamma interferon of antiviral cell-mediated immune responses in vivo

Mice were infected with lymphocytic choriomeningitis virus and injected once 24 h later with a monoclonal antibody directed against gamma interferon. In comparison with controls, the increase of numbers of CD8+ T cells and the generation of virus-specific cytotoxic T lymphocytes in spleens and virus clearance from organs were diminished, as was the ability of spleen cells to transmit adoptive immunity to infected recipients. The same treatment slightly but consistently lessened rather than augmented the virus titers early in infection, which was also observed in thymusless nu/nu mice. Injection into infected mice of the lymphokine itself in quantities probably higher than are produced endogenously resulted in lower virus titers in spleens but higher titers in livers. The adoptive immunity in infected mice achieved by infusion of immune spleen cells was not altered by treating the recipients with gamma interferon monoclonal antibody. Such treatment did not measurably affect the production of antiviral serum antibodies. We conclude that in lymphocytic choriomeningitis virus-infected mice, gamma interferon is needed for the generation of antivirally active CD8+ T lymphocytes, and furthermore that in this experimental model, direct antiviral effects of the lymphokine elude detection.

Induction of measles virus-specific cytotoxic T-cell responses after intranasal immunization with synthetic peptides

We have investigated the structural requirements for the induction of cytotoxic T-cell responses (CTL) in vivo after intranasal immunization with an immunodominant CTL epitope from the nucleoprotein of measles virus (MV). For the induction of CTL responses, covalent linkage of the CTL epitope to a helper T-cell epitope was required and the orientation of the epitopes influenced the immunogenicity of the CTL epitope. The presence of two copies as compared with one copy of a T-helper epitope, rendered the CTL epitope more immunogenic and resulted in the in vivo induction of MV-specific CTLs without the need for an adjuvant. The role of CTL responses to this epitope in protection after intranasal administration was evaluated in a mouse model against challenge with a neuroadapted strain of MV. Although a decreased mortality in the peptide immunized compared with that in unimmunized mice was observed, the protection achieved was not significant. These findings highlight the importance of the rational design of synthetic immunogens for the induction of CTL responses and the potential of the intranasal route for immunization.

CD4+ T-lymphocyte lines developed from HIV-1-seropositive patients recognize different epitopes within the V3 loop

To define the epitopes present within the V3 loop sequence recognized by five HIV-1 envelope-specific T-cell lines, a panel of V3 LAI peptides bearing sequential truncations from both the N- and C-terminus was synthesized and tested for their ability to induce proliferation. Each individual T-cell line had a different pattern of response against the truncated V3 peptides, demonstrating the presence of a cluster of CD4+ T-cell epitopes within the V3 loop. To assess the ability of these envelope-specific T-cell lines to recognize and proliferate in response to V3 loops of different viral strains, they were tested against a panel of heterologous V3 loop peptides derived from different viral genotypes within and outside of HIV-1 clade B. There was no proliferative response against heterologous V3 loops by any of the lines, demonstrating that recognition of the V3 epitopes is highly strain specific. One of the defined epitopes was shown to elicit a cytotoxic response as well, suggesting the multifaceted role that the CD4+ T cell might play in HIV-1 disease.

Human T-lymphotropic virus type 1 peptides in chimeric and multivalent constructs with promiscuous T-cell epitopes enhance immunogenicity and overcome genetic restriction

Conventional strategies of viral peptide immunizations often elicit low-affinity antibody responses and have limited ability to elicit immune responses in outbred animals of diverse major histocompatibility (MHC) haplotypes. This genetically restricted T-cell-stimulatory activity of peptides is a serious obstacle to vaccine design. However, the use of promiscuous T-cell epitopes may circumvent this problem. Promiscuous T-cell epitopes from tetanus toxin (amino acids [aa] 580 to 599) and the measles virus F protein (aa 288 to 302) that bind to several isotypic and allotypic forms of human MHC class II molecules have been identified and have been used in highly immunogenic constructs to overcome haplotype-restricted immune responses. Chimeric and beta-template peptide constructs incorporating known human T-lymphotropic virus type 1 (HTLV-1) B- and T-cell epitopes from the surface envelope protein gp46 (SP2 [aa 86 to 107] and SP4a [aa 190 to 209]) and promiscuous T-cell peptides were synthesized, and their immunogenicities were evaluated in both rabbits and mouse strains of divergent haplotypes (C3H/HeJ [H-2k], C57BL/6 [H-2b], and BALB/c [H-2d]). In addition, peptide preparations were structurally characterized by analytical high-performance liquid chromatography, mass spectrometry, and circular dichroism. In contrast to their linear forms, the chimeric constructs of both the SP2 and SP4a epitopes displayed alpha-helical secondary structures. Immunogenicity of the peptide constructs was evaluated by direct and competitive enzyme-linked immunosorbant assay (ELISA), as well as by radioimmunoprecipitation, syncytium inhibition, and antigen-induced lymphocyte proliferation assays. Immunization with the SP4a peptide without conjugation to a carrier protein produced antibodies specific for SP4a in two mouse strains (C3H/HeJ and C57BL/6). However, BALB/c mice failed to respond to the peptide, indicating that the T-cell epitope of the SP4a sequence is MHC restricted. In contrast, the chimeric constructs MVF-SP2 and SP4a-measles virus F protein were highly immunogenic, producing elevated ELISA titers after only two immunizations. Elicited antibodies recognized native forms of gp46 in ELISAs and radioimmunoprecipitation assays, as well as inhibited HTLV-1-mediated syncytium formation. In addition, chimeric constructs were effective at induction of lymphocyte proliferation to the T-cell epitope, SP4a, in each strain of immunized mice. Our data demonstrate that the antibody response to retroviral peptides is enhanced by promiscuous peptide constructs, in part because of the ability of such constructs to promote appropriate secondary structural forms of viral epitopes. In addition, these constructs promote virus-specific helper T-cell responses, thereby overcoming genetically restricted immune responses to the synthetic peptides.

Proliferative response of CD4+ T cells and hepatitis B virus clearance in chronic hepatitis with or without hepatitis B e-minus hepatitis B virus mutants

To assess the significance of cell-mediated immunity, T cells were derived from the peripheral blood and liver tissue of hepatitis B virus (HBV)-infected patients and controls. The analysis of the 3H-thymidine-uptake in response to a panel of recombinant HBV antigens revealed that peripheral blood mononuclear cells (PBMC) of the 25 viremic patients with inflammatory active, chronic hepatitis B, 16 with wild-type and nine with HBe-minus HBV mutant infection, showed stronger proliferative responses to HBc and HBe antigens than 16 asymptomatic nonviremic HBsAg carriers with normal aminotransferase levels (HBc: SI 19.3 +/- 3.9 vs. 13.0 +/- 3.2 vs. 8.0 +/- 1.2; P < .01 and HBe: SI 16.6 +/- 4.0 vs. 10.7 +/- 3.5 vs. 6.9 +/- 1.5; P < .05). In 15 patients with acute self-limited hepatitis B, however, significantly stronger HBc antigen-specific T-cell responses were observed during HBV clearance and HBe/anti-HBe seroconversion, whereas in nine completely HBV-immunized patients only minor proliferative responses to HBV antigens were observed. Six HBe/HBcAg- and two HBeAg-specific CD4+ T-cell lines could be expanded from liver tissue and peripheral blood of six viremic patients with chronic hepatitis B. Irrespectively of HBV mutations the HBV-specific activation of the T-cell lines was restricted by the presence of HLA-DR molecules and resulted in the release of Th1-like cytokine patterns. Follow-up of interferon (IFN) recipients showed simultaneous short-term increase of HBc/HBe-specific T-cell reactivities in responder patients during HBV clearance and HBe/anti-HBe seroconversion, whereas in nonresponders high virus load and HBV-specific immune responses were in imbalance.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of peptide-specific primary cytotoxic T lymphocyte responses from human peripheral blood

Various protocols were developed and compared for eliciting specific cytotoxic T lymphocyte (CTL) cell lines from the unselected human peripheral blood mononuclear cells of naive donors. Interleukin-7 and CD4+ T cells primed in vitro by keyhole limpet hemocyanin were shown to act together in the generation of these responses. Primary responses were consistently induced with a variety of different HLA class I-binding malarial peptides. Primary CTL responses could be induced from unselected CD8+ and from CD45RA+CD8+ T cells. The CTL lines derived from these naive donors were CD8+ and demonstrated a high level of HLA class I-restricted killing for > 3 months after priming in vitro. They were also able to recognize and kill targets infected with a recombinant vaccinia virus containing the full-length antigen. In addition, this same protocol enhanced up to fourfold the levels of secondary CTL responses induced. The optimal method presented for naive cytotoxic T cell stimulation is simple, rapid and generally applicable and should provide a useful tool for both basic research and human therapy.

The influence of allo-class II MHC-specific Th2 cells on the generation of CD4 and CD8 cytotoxic T cells to associated class I and class II MHC alloantigen

There is considerable interest in whether CD4 T cell function can affect the outcome of allogeneic transplants. In mice tolerant to an isolated class II MHC disparity, the normal Th1 activity in vitro associated with graft rejection is switched to Th2 in tolerant animals. Because clinical transplants involve multiple class I and II MHC disparities we tested how the switch to Th2 activity of tolerant mice would affect the generation of CD4 and CD8 cytotoxic T cells (CTL) against MHC alloantigens to which the mice were not tolerant. A.TH mice (KkIsDd) were rendered neonatally tolerant of A.TL (KkIkDd) and the generation of CD4 or CD8 CTL measured in a mixed lymphocyte reaction (MLR) against (A.TL x B6)F1 stimulators. Normal mice generated CD4 CTL against both A.TL and B6 (KbIbDb), but tolerant mice were unable to generate cytotoxicity against either A.TL or B6. However, tolerant cells were able to generate CD8 CTL against B6. IL-4 inhibited the generation of CD4, but not CD8, CTL by normal cells and anti-IL-4 antibody was shown to increase the generation of CD4 CTL against B6 in F1 stimulated cultures. Overall the results showed that a Th2 response could inhibit the generation of CD4 CTL against concomitant alloantigen in a process at least partially involving IL-4, but that, conversely, tolerant Th2 cells could help in the generation of CD8 CTL. The results suggest that with whole MHC disparities a simple change of CD4 T cells to Th2 would not be enough to procure graft acceptance.

Human T helper cells specific for HIV reverse transcriptase: possible role in intrastructural help for HIV envelope-specific antibodies

Cooperation between B cells specific for an antigen exposed on a viral structure and T helper (Th) cells specific for an internal antigen, as demonstrated with influenza, hepatitis B and rabies viruses, has been termed intrastructural help. Th cells specific for internal proteins of HIV, which are much less mutated than its exposed antigens, may be valuable in vaccine design against this virus. We investigated the human Th repertoire specific for the core HIV antigen reverse transcriptase (p66), and determined whether these cells could be candidate intrastructural T helpers. CD4+ T lines and clones were generated from non-immune individuals by stimulation with p66-pulsed antigen-presenting cells (APC). Specific lines were obtained with p66 from 19 out of 21 (90%) of these individuals, vs. 7 out of 29 (24%) with gp120. Diverse epitopes were recognized by different individuals, and various V beta genes were used by these clones. Clones using the same V beta genes were of diverse origin, according to VDJ region sequence. Of these lines 45% responded to p66 in the context of HIV virions. Moreover, p66-specific clones could respond to APC that had internalized HIV complexed with envelope-specific monoclonal antibodies, suggesting that p66-specific Th cells may participate in intrastructural help. These studies indicate that p66-specific Th cells are detectable in vitro in most naive individuals and exhibit clonal heterogeneity, and that the majority recognize an HIV conserved antigen. They respond to p66 following processing of whole virions and are clearly candidates for intrastructural help. If confirmed in vivo, p66 should be included among vaccine candidates investigated to optimize the anti-HIV Th response.

A helper T-cell antigen enhances generation of hepatitis C virus-specific cytotoxic T lymphocytes in vitro

A T-cell helper for generation of hepatitis C virus-specific cytotoxic T lymphocytes was studied in three patients with chronic hepatitis C. In all three, human leukocyte antigen B44-restricted cytotoxic T lymphocytes recognizing an epitope in hepatitis C virus nucleocapsid protein residues 81-100 were generated from the peripheral blood lymphocytes by repeated stimulation with a synthetic hepatitis C virus nucleocapsid peptide. The proliferative response of peripheral blood lymphocytes to hepatitis C virus nucleocapsid protein residues 1-120 was observed in one patient, and was ascribed to CD4+ T cells. The helper T cells recognized a major epitope in residues 21-40 and a minor epitope(s) in residues 81-110. They produced interferon gamma, but interleukin 4 was not detectable in the T-helper cell culture supernatants. The hepatitis C virus nucleocapsid protein residues 1-120 and the major helper T-cell epitope enhanced generation of hepatitis C virus-specific cytotoxic T lymphocytes in vitro, although the protein alone did not generate them. In the other two patients, the protein did not enhance generation of hepatitis C virus-specific cytotoxic T lymphocytes in vitro. The results suggest that a hepatitis C virus-specific helper T-cell epitope is helpful for inducing a strong specific cytotoxic T-lymphocyte response.