Presentation by a major histocompatibility complex class I molecule of nucleoprotein peptide expressed in two different genes of an influenza virus transfectant

Recombinant influenza virus vectors

Newly optimized reverse genetics techniques have allowed influenza researchers to generate recombinant influenza viruses expressing mutant viral proteins, as well as foreign proteins. Approaches include the insertion of noninfluenza epitopes and polypeptides into viral glycoproteins, foreign open reading frames as additional segments, and the fusion of independent proteins into viral genes encoding glycoproteins or the nonstructural protein 1. These genetically engineered viruses have been demonstrated to be good viral vectors for mounting B- and T-cell responses and are attractive candidates for vaccine development. As the molecular biology of influenza viral infection is more fully understood, influenza vectors can be concurrently manipulated to produce designed chimeric viruses, unveiling the possibility of a prosperous future with cheap, effective and safe vaccines against different human diseases.

A decade after the generation of a negative-sense RNA virus from cloned cDNA - what have we learned?

Since the first generation of a negative-sense RNA virus entirely from cloned cDNA in 1994, similar reverse genetics systems have been established for members of most genera of the Rhabdo- and Paramyxoviridae families, as well as for Ebola virus (Filoviridae). The generation of segmented negative-sense RNA viruses was technically more challenging and has lagged behind the recovery of nonsegmented viruses, primarily because of the difficulty of providing more than one genomic RNA segment. A member of the Bunyaviridae family (whose genome is composed of three RNA segments) was first generated from cloned cDNA in 1996, followed in 1999 by the production of influenza virus, which contains eight RNA segments. Thus, reverse genetics, or the de novo synthesis of negative-sense RNA viruses from cloned cDNA, has become a reliable laboratory method that can be used to study this large group of medically and economically important viruses. It provides a powerful tool for dissecting the virus life cycle, virus assembly, the role of viral proteins in pathogenicity and the interplay of viral proteins with components of the host cell immune response. Finally, reverse genetics has opened the way to develop live attenuated virus vaccines and vaccine vectors.

Generation of influenza A virus from cloned cDNAs--historical perspective and outlook for the new millenium

Influenza virus reverse genetics has reached a level of sophistication where one can confidently generate virus entirely from cloned DNAs. The new systems makes it feasible to study the molecular mechanisms of virus replication and pathogenicity, as well as to generate attenuated live virus vaccines, gene delivery vehicles, and possibly other RNA viruses from cloned cDNAs. During the next decade, one can anticipate the translation of influenza virus reverse genetics into biomedically relevant advances.

Induction of cytotoxic T lymphocytes of heterogeneous specificities by immunization with a single peptide derived from influenza A virus

We examined whether immunization with a single peptide induces cytotoxic T lymphocytes (CTLs) of heterogeneous specificities in vivo. Immunization of BALB/c mice with the peptide H2:529-537, which corresponded to amino acid residues 529-537 on the HA2 subunit transmembrane region of influenza A/Jap virus (H2N2) and possessed an H-2Kd-binding motif, induced CD8+CD4- CTLs. These CTLs lysed influenza A/Jap virus-infected target cells as well as those pulsed with the H2:529-537 peptide. H2:529-537 peptide-induced CTLs also lysed to lower but significant levels the target cells pulsed with the H1:533-541 peptide, which corresponded to amino acid residues 533-541 on the HA2 subunit transmembrane region of influenza A/PR/8 virus (H1N1) and were compatible to H2:529-537. Immunization with the H1:533-541 peptide, which also possessed an H-2Kd-binding motif, induced CTLs in vivo. H1:533-541-induced CTLs lysed influenza A/PR/8 virus-infected target cells and those pulsed with the peptide H1:533-541. Subtype cross-reactive CTLs to the H2:529-537 peptide were not induced by immunization with the H1:533-541 peptide. Two peptides, H2:3S and H2:7S, which had one amino acid substitution, serine at the third and seventh positions, respectively, induced CTLs that lysed target cells pulsed with the respective peptides to the highest levels. These results indicate that immunization with a single peptide induces CTLs of heterogeneous specificities in vivo.

DNA immunization with minigenes: low frequency of memory cytotoxic T lymphocytes and inefficient antiviral protection are rectified by ubiquitination

Our previous studies have shown that isolated cytotoxic T lymphocyte (CTL), B-cell, and T-helper epitopes, for which we coined the term minigenes, can be effective vaccines; when expressed from recombinant vaccinia viruses, these short immunogenic sequences confer protection against a variety of viruses and bacteria. In addition, we have previously demonstrated the utility of DNA immunization using plasmids encoding full-length viral proteins. Here we combine the two approaches and evaluate the effectiveness of minigenes in DNA immunization. We find that DNA immunization with isolated minigenes primes virus-specific memory CTL responses which, 4 days following virus challenge, appear similar in magnitude to those induced by vaccines known to be protective. Surprisingly, this vigorous CTL response fails to confer protection against a normally lethal virus challenge, although the CTL appear fully functional because, along with their high lytic activity, they are similar in affinity and cytokine secretion to CTL induced by virus infection. However this DNA immunization with isolated minigenes results in a low CTL precursor frequency; only 1 in approximately 40,000 T cells is epitope specific. In contrast, a plasmid encoding the same minigene sequences covalently attached to the cellular protein ubiquitin induces protective immunity and a sixfold-higher frequency of CTL precursors. Thus, we show that the most commonly employed criterion to evaluate CTL responses-the presence of lytic activity following secondary stimulation-does not invariably correlate with protection; instead, the better correlate of protection is the CTL precursor frequency. Recent observations indicate that certain effector functions are active in memory CTL and do not require prolonged stimulation. We suggest that these early effector functions of CTL, immediately following infection, are critical in controlling virus dissemination and in determining the outcome of the infection. Finally, we show that improved performance of the ubiquitinated minigenes most probably requires polyubiquitination of the fusion protein, suggesting that the enhancement results from more effective delivery of the minigene to the proteasome.

Towards development of T-cell vaccines

Recent studies on the recognition of antigens by CD4+ and CD8+ T cells have revealed new ways of preparing efficient T-cell vaccines. Here, Constantin Bona and colleagues discuss several approaches for the development of T-cell vaccines, with applications ranging from the induction of protective immunity against intracellular parasites to the development of therapeutic agents against autoimmune disorders, allergic diseases and cancer.

Genetically engineered vaccines: an overview

Despite the early success demonstrated with the hepatitis B vaccine, no other recombinant engineered vaccine has been approved for use in humans. It is unlikely that a recombinant vaccine will be developed to replace an existing licensed human vaccine with a proven record of safety and efficacy. This is due to the economic reality of making vaccines for human use. Genetically engineered subunit vaccines are more costly to manufacture than conventional vaccines, since the antigen must be purified to a higher standard than was demanded of older, conventional vaccines. Each vaccine must also be subjected to extensive testing and review by the FDA, as it would be considered a new product. This is costly to a company in terms of both time and money and is unnecessary if a licensed product is already on the market. Although recombinant subunit vaccines hold great promise, they do present some potential limitations. In addition to being less reactogenic, recombinant subunit vaccines have a tendency to be less immunogenic than their conventional counterparts. This can be attributed to these vaccines being held to a higher degree of purity than was traditionally done for an earlier generation of licensed subunit vaccines. Ironically, the contaminants often found in conventional subunit vaccines may have aided in the inflammatory process, which is essential for initiating a vigorous immune response. This potential problem may be overcome by employing one of the many new types of adjuvants that are becoming available for use in humans. Recombinant subunit vaccines may also suffer from being too well-defined, because they are composed of a single antigen. In contrast, conventional vaccines contain trace amounts of other antigens that may aid in conferring an immunity to infectious agents that is more solid than could be provided by a monovalent vaccine. This problem can be minimized, where necessary, by creating recombinant vaccines that are composed of multiple antigens from the same pathogen. These issues are less of a concern with a live attenuated vaccine, since these vaccines are less costly, require fewer steps to manufacture, and elicit long-lived immunity after only a single dose. Unfortunately, live vaccines carry a higher risk of vaccine-induced complications in recipients that make their use in highly developed, litiginous countries unlikely. In lesser developed countries, where the prevalence of disease and the need for effective vaccines outweighs the risk associated with their administration, live vaccines may play an important role in human health. This review has attempted to make the reader aware of some of the current approaches and issues that are associated with the development of these vaccines. Genetically engineered vaccines hold great promise for the future, but the potential of these vaccines to improve human and animal health has yet to be fully realized.

Antigen processing and presentation by the class I major histocompatibility complex

Major histocompatibility complex (MHC) class I molecules bind peptides derived from cellular proteins and display them for surveillance by the immune system. These peptide-binding molecules are composed of a heavy chain, containing an antigen-binding groove, which is tightly associated with a light chain (beta 2-microglobulin). The majority of presented peptides are generated by degradation of proteins in the cytoplasm, in many cases by a large multicatalytic proteolytic particle, the proteasome. Two beta-subunits of the proteasome, LMP2 and LMP7, are inducible by interferon-gamma and alter the catalytic activities of this particle, enhancing the presentation of at least some antigens. After production of the peptide in the cytosol, it is transported across the endoplasmic reticulum (ER) membrane in an ATP-dependent manner by TAP (transporter associated with antigen presentation), a member of the ATP-binding cassette family of transport proteins. There are minor pathways for generating presented peptides directly in the ER, and some evidence suggests that peptides may be further trimmed in this location. The class I heavy chain and beta 2-microglobulin are cotranslationally translocated into the endoplasmic reticulum where their assembly may be facilitated by the sequential association of the heavy chain with chaperone proteins BiP and calnexin. The class I molecule then associates with the lumenal face of TAP where it is retained, presumably awaiting a peptide. After the class I molecule binds a peptide, it is released for exocytosis to the cell surface where cytotoxic T lymphocytes examine it for peptides derived from foreign proteins.