Recognition by major histocompatibility complex class I-restricted cytolytic T lymphocytes of cells expressing vaccinia-encoded viral and class I proteins

High peptide affinity for MHC class I does not correlate with immunodominance

Cytotoxic T (Tc)-cell responses against influenza virus infection in BALB/c (H-2d) mice are dominated by Tc clones reactive to the viral nucleoprotein (NP). Here, we report investigations using recombinant vaccinia viruses (VV) encoding major histocompatibility complex (MHC) class I H-2Kd molecules differing by a single amino acid from glutamine (wild-type, Kdw) to histidine (mutant, Kdm) at position 114 located in the floor of the peptide-binding groove. Influenza-infected target cells expressing Kdw were strongly lysed by Kd-restricted Tc cells against A/WSN influenza virus or the immunodominant peptide of viral NP (NPP147-155), whereas infected Kdm-expressing targets gave little or no lysis, respectively, thus showing the immunodominance of NPP147-155. Kdm-expressing target cells saturated with synthetic NPP147-155 (10-5 M) were lysed similarly to Kdw-expressing targets by NPP147-155-specific Tc cells. Thus the defect in influenza-infected Kdm-expressing targets was quantitative; insufficient Kdm-peptide complexes were expressed. Tc-cell responses against four other viruses or alloantigens showed no effect of Kdm. When peptide transport-defective cells were infected with VV-Kdw or VV-Kdm and co-infected with a recombinant VV encoding an endoplasmic reticulum-targeted viral peptide, two influenza haemaglutinin peptides caused higher expression of Kdw than NPP147-155 indicating their higher affinity for Kdw. These results are inconsistent with the hypothesis that immunodominance in the anti-influenza response reflects high affinity of the immunodominant peptide, but are consistent with skewing of the Tc-cell receptor repertoire.

Spontaneous mutation at position 114 in H-2Kd affects cytotoxic T cell responses to influenza virus infection

Vaccinia virus (VV)-encoded MHC class I Kd molecules which differ by a single amino acid change from glutamine (Kdw, wild type) to histidine (Kdm, mutant) at position 114 located in the floor of the peptide binding groove were compared in terms of peptide binding and cytotoxic T (Tc) cell recognition. Most anti-viral Tc cells were not affected or only marginally affected. However, the Kdm molecule did not detectably present the immunodominant peptide (NPP147-155) of influenza virus nucleoprotein (NP), encoded by the full-length NP gene either in influenza A virus or recombinant VV. This defect could be overcome by using exogenous synthetic NPP147-155 or translation from a minigene encoding NPP147-155 in VV. Kdw presented NPP147-155 encoded by the full-length NP gene, but Kdw-NPP147-155 complexes were at least 100-fold less abundant than after translation from a minigene.

Hypothesis: MHC class I, rather than just a flagpole for CD8+ T cells is also a protease in its own right

Ever since the discovery of MHC class I restriction and the onslaught of the dual receptor hypothesis, MHC class I has been perceived as a passive entity in TCR recognition and the appropriate antigen processing and presentation pathways. However, numerous experimental observations and theoretical considerations are difficult or unable to be explained by the accepted mechanism of class I antigen presentation. Proteases within and outside the endoplasmic reticulum (ER) are evoked to be solely responsible for the generation of the appropriate 8-10 amino acid-long peptides associated with MHC class I. A MHC class I with site-restricted ER protease activity would overcome most of the present difficulties in explaining MHC class I antigen presentation.

The generation of memory antigen-specific cytotoxic T cell responses by CD28/CD80 interactions in the absence of antigen

The interaction of co-stimulatory molecules CD80/CD86 on antigen-presenting cells with CD28 on naive CD8+ cytotoxic T (Tc) cells is understood to be critical in the induction of Tc effectors. CD80 is capable of providing signal 2 for the activation of Tc cells, but has no effect if encountered in the absence of specific peptide/MHC complexes (signal 1). We have found that CD80 presented in vitro to resting memory viral-immune or alloimmune Tc cells can provide sufficient stimulus for the generation of effector Tc cells in the absence of specific antigen, the peptide/MHC class I complex. Effector Tc cells generated in vitro from influenza- or class I alloantigen-primed mice by co-stimulation in the absence of antigen require exogenous interleukin (IL)-2 signaling via the cell surface-expressed IL-2 receptor or, under conditions of IL-2 blockade, exogenous IL-7. Activation of memory Tc cells by signal 1 and 2 is independent of IL-2 and IL-7. Although memory influenza-immune Tc cells did respond to CD80 in the absence of antigen, the presence of antigen +CD80 enabled an earlier induction of these Tc cells and they retained their lytic activity in vitro over a longer time period. The capacity of memory Tc cells to be activated by signal 2 alone provides one explanation for the observed heterogeneity of phenotype of memory T cells in vivo and a possible mechanism for the maintenence of memory in the absence of persisting antigen.

Construction and characterisation of a recombinant vaccinia virus expressing human papillomavirus proteins for immunotherapy of cervical cancer

The presence and consistent expression of the genes encoding the human papillomavirus (HPV) E6 and E7 proteins in the great majority of cervical tumours presents the opportunity for an immunotherapeutic approach for control of the disease. This report describes the construction and characterisation of a recombinant vaccinia virus designed to express modified forms of the E6 and E7 proteins from HPV16 and HPV18, the viruses most commonly associated with cervical cancer. The recombinant virus (designated TA-HPV) was based on the Wyeth vaccine strain of vaccinia, and was shown to express the desired gene products. Studies in mice indicated that the recombinant virus was less neurovirulent than the parental virus and was capable of inducing an HPV-specific CTL response. This pre-clinical evaluation has provided a basis for the initiation of human trials in cervical cancer patients.

Identification of two cytotoxic T lymphocyte-recognized epitopes in the Ras protein

We have investigated the possibility of inducing cytotoxic T lymphocytes (CTL) to Ras containing a mutation at position 61 or to normal Ras, using recombinant vaccinia viruses expressing these proteins. CTL from C57Bl/10 mice immunized with vaccinia expressing mutant Ras showed specificity for the mutant Ras protein and recognition of normal Ras was inefficient. The opposite specificity was observed after immunization with vaccinia expressing normal Ras, since CTL isolated from these mice recognized normal Ras well and mutant Ras inefficiently. Levels of endogenous Ras expression were insufficient for lysis by these CTL. One CTL epitope mapped to amino acids 60-67 and residue 61 was critical for T cell recognition. CTL generated against mutant Ras protein recognized peptide 60-67 containing mutant residue 61, while anti-normal Ras CTL recognized the wild-type 60-67 sequence. A second epitope mapped to residues 152-159 of Ras and was recognized equally well by CTL raised to normal or mutant Ras. The murine data raise the possibility of exploiting Ras-specific CTL for targeted immunotherapy of certain human cancers.

Recognition of vaccinia virus-encoded major histocompatibility complex class I antigens by virus immune cytotoxic T cells is independent of the polymorphism of the peptide transporters

In the cytotoxic T-cell response to viruses, peptide antigens of cytoplasmic origin are presented at the cell surface by the highly polymorphic major histocompatibility complex (MHC) class I molecules to CD8+ T-lymphocyte receptors. Peptide transporter molecules and other MHC-linked gene products have been implicated in the generation and import of antigenic peptides into the lumen of the endoplasmic reticulum for assembly with MHC class I glycoproteins. These accessory molecules in the antigen-presentation pathway map to a polymorphic region in the class II MHC, and the possibility of their allele-specific selectivity in antigen presentation has been raised. Here we show that additional, functionally polymorphic components are not apparent in an in vitro mouse MHC class I-restricted cytotoxic T-cell response to vaccinia and influenza viruses. When the mouse H-2Kd molecule was expressed via a recombinant vaccinia virus in target cells of different mouse MHC haplotypes or cells of rat, Syrian hamster, monkey, and human origin, efficient Kd-restricted and vaccinia virus-specific lysis was observed as measured with bulk effectors and at the clonal level. In addition, human transporters efficiently processed peptides originating from influenza virus nucleoprotein and hemagglutinin antigens as recognized by mouse influenza immune cytotoxic T cells.

Beta 2-microglobulin-, CD8+ T-cell-deficient mice survive inoculation with high doses of vaccinia virus and exhibit altered IgG responses

Transgenic mice lacking an intact beta 2-microglobulin (beta 2m) gene fail to express major histocompatibility complex (MHC) class I proteins on the cell surface and, as a result, are virtually devoid of CD4- CD8+ lymphocytes. These animals provide a unique model system for directly assessing the role of CD8+ lymphocytes in the modulation of viral infection in vivo. beta 2m- CD8- mice and their normal littermates were inoculated at the base of the tail with the WR strain of vaccinia virus and monitored for serum antibody and lesion formation. Both groups developed similar lesions in response to a broad virus dose range, and all animals had completely recovered by day 28 after inoculation. Isotype-specific immunoglobulin levels were determined for each animal on day 7 and day 14 after primary inoculation, and again 7 days after a virus challenge. The virus-specific IgG1, IgG2a, and IgG2b levels were significantly different in the beta 2m-/- group (20-, 9-, and 30-fold lower, respectively, on day 7 after challenge) compared with the beta 2m+/- group. Virus-specific serum IgM levels for both groups remained similar throughout the experiment. In a separate experiment, beta 2m-/- mice were immunized with a nonviral antigen, 2,4,6-trinitrophenyl-conjugated keyhole limpet hemocyanin, and both total and antigen-specific isotype-specific immunoglobulin titers were determined. Total IgG1, IgG2a, IgG2b, and IgG3 tended to be lower overall in the beta 2m-/- mice compared with beta 2m+/- littermates. In contrast, total and antigen-specific IgE titers were similar in the two groups. These data indicate that CD8+ lymphocytes are not required to clear high doses of vaccinia virus, and they suggest that beta 2m-/- mice are less efficient at antigen-specific IgG production than their beta 2m+/- littermates.

Restoration of the LFA-3 adhesion pathway in Burkitt's lymphoma cells using an LFA-3 recombinant vaccinia virus: consequences for T cell recognition

Conjugate formation between cytotoxic T lymphocytes (CTL) and target B cells, as observed in vitro, is mediated by interactions between adhesion molecules on the two cell surfaces rather than involving immune recognition through the T cell receptor. It is still not clear to what extent such adhesive contacts facilitate the process of immune recognition and target cell lysis. However, work on the Epstein-Barr virus (EBV)-associated malignancy Burkitt's lymphoma (BL) has suggested that down-regulation of one particular adhesion molecule, the lymphocyte function-associated antigen LFA-3, on the tumor cell surface is a key factor in allowing these target cells to escape EBV-specific T cell surveillance. To examine this directly, we used a cDNA for the full-length transmembrane form of LFA-3 to construct a recombinant vaccinia virus (Vacc-LFA 3), which is capable of restoring surface LFA-3 in adhesion molecule-negative BL cell lines to levels as high as seen in EBV-transformed lymphoblastoid cell lines (LCL); biochemical studies confirmed expression of the authentic N-glycosylated protein. The recombinant vaccinia-encoded LFA-3 was functional as an adhesion molecule since BL cells acutely infected with Vacc-LFA-3 then acquired the ability to form conjugates with activated T cells in vitro. However, there was no clear dependence upon LFA-3 when such BL cell lines were tested as targets for cytotoxic T lymphocytes (CTL). Firstly, LFA-3- BL cells could be killed by allospecific CTL recognizing HLA class I alloantigens, in some cases as efficiently as the corresponding LCL. In other cases where lysis was slightly below that of the LCL, Vacc-LFA-3 infection of the BL cells increased lysis up to, but never beyond, LCL values. Secondly, we studied the sensitivity of BL to EBV-specific HLA class I-restricted CTL using a BL target line which was LFA-3- but which expressed the same spectrum of EBV target proteins as an LCL. This line was not recognized by appropriately HLA-matched effectors, even after restoration of LFA-3 expression. We conclude that the LFA-3 status of BL cells influences their conjugate forming ability in in vitro assays but not necessarily their sensitivity to immune T cell-mediated cytolysis.

A general method for the construction of recombinant vaccinia viruses expressing multiple foreign genes

Plasmid vectors with multiple cloning sites adjacent to a vaccinia virus (VV) promoter were constructed and used to insert a protein coding sequence and a dominant selectable marker into a non-essential region of the VV genome. Recombinant viruses, selected on the basis of expression of the herpes simplex virus (HSV) thymidine kinase gene (tk), were shown to express in infected cells the model gene product, murine major histocompatibility complex (MHC) antigen H-2Kd, by cell-surface binding of antibody and by MHC-restricted recognition by cytotoxic T lymphocytes. Double recombinant VVs with insertions at two sites (in the VV tk gene and in the VV HindIII-F region) were constructed and shown to express influenza A/PR/8/34 haemagglutinin and H-2Kd antigen in addition to the HSV tk gene. The plasmids described allow the construction of recombinant VV expressing two genes of interest under the control of the same VV promoter. Such recombinant VVs can be used to study the interaction of immunologically important antigens simultaneously expressed.