Elucidation of virus-host interaction using animal models towards vaccine development

Toward an effective AIDS vaccine development

The history of successful vaccination against severe viral diseases such as smallpox poliomyelitis or measles led to the initial hope that a vaccine against AIDS would be developed quickly. However an effective vaccine against HIV needs to overcome substantial obstacles that emerged as research progressed. Due to life cycle HIV can effectively hide from the host immune response integrating itself as proviral DNA in the host cell genome. A strategy pursued to deal with this difficulty is to include early viral regulatory proteins such as Tat Rev or Nef as vaccine antigens for induction of immune responses that can recognize and destroy HIV-infected cells as soon as the virus life cycle is activated [12]. The virus preferentially targets and destroys host immune cells such as T-helper lymphocytes macrophages and dendritic cells that are probably essential to maintain an effective antiviral immune response. This would imply that vaccine-elicited immunity unlikely to be able to prevent infection itself must be able to quickly control virus replication to prevent harm to the immune system. The high antigenic variability of HIV can be considered as an extremely effective immune-evasion strategy. Because of the low fidelity of the viral RNA polymerase virus progeny always represents a collection of RNA genomes (quasi-species) with random mutations. In vivo selection of immunodeficiency virus variants that can evade the recognition of neutralizing antibodies is common and strong virus-specific cytotoxic T-cell responses can select for escape variants already during resolution of primary viremia [3]. Most HIV infections are acquired sexually via the genital or rectal mucosae; however at these entry sites it appears difficult to induce strong antiviral immunity by vaccination. Finally HIV infection is a poverty-related disease that is particularly threatening health in societies of the developing world. Therefore vaccine candidates must be safe and feasible in production and administration to be eligible for use where most needed. (excerpt)

Will There Be a Vaccine to Protect Against the Hepatitis C Virus?

HIV-1/AIDS vaccine development: are we in the darkness before the dawn?

Neutralizing Antibodies Against Hepatitis C Virus and Their Role in Vaccine Immunity

SARS-CoV-2-specific antibody and T-cell responses 1 year after infection in people recovered from COVID-19: a longitudinal cohort study

Certain major histocompatibility complex class I (MHC-I) alleles (e.g., HLA-B*27) are enriched among human immunodeficiency virus type 1 (HIV-1)-infected individuals who suppress viremia without treatment (termed "elite controllers" [ECs]). Likewise, Mamu-B*08 expression also predisposes rhesus macaques to control simian immunodeficiency virus (SIV) replication. Given the similarities between Mamu-B*08 and HLA-B*27, SIV-infected Mamu-B*08(+) animals provide a model to investigate HLA-B*27-mediated elite control. We have recently shown that vaccination with three immunodominant Mamu-B*08-restricted epitopes (Vif RL8, Vif RL9, and Nef RL10) increased the incidence of elite control in Mamu-B*08(+) macaques after challenge with the pathogenic SIVmac239 clone. Furthermore, a correlate analysis revealed that CD8(+) T cells targeting Nef RL10 was correlated with improved outcome. Interestingly, this epitope is conserved between SIV and HIV-1 and exhibits a delayed and atypical escape pattern. These features led us to postulate that a monotypic vaccine-induced Nef RL10-specific CD8(+) T-cell response would facilitate the development of elite control in Mamu-B*08(+) animals following repeated intrarectal challenges with SIVmac239. To test this, we vaccinated Mamu-B*08(+) animals with nef inserts in which Nef RL10 was either left intact (group 1) or disrupted by mutations (group 2). Although monkeys in both groups mounted Nef-specific cellular responses, only those in group 1 developed Nef RL10-specific CD8(+) T cells. These vaccine-induced effector memory CD8(+) T cells did not prevent infection. Escape variants emerged rapidly in the group 1 vaccinees, and ultimately, the numbers of ECs were similar in groups 1 and 2. High-frequency vaccine-induced CD8(+) T cells focused on a single conserved epitope and therefore did not prevent infection or increase the incidence of elite control in Mamu-B*08(+) macaques. Since elite control of chronic-phase viremia is a classic example of an effective immune response against HIV/SIV, elucidating the basis of this phenomenon may provide useful insights into how to elicit such responses by vaccination. We have previously established that vaccine-induced CD8(+) T-cell responses against three immunodominant epitopes can increase the incidence of elite control in SIV-infected Mamu-B*08(+) rhesus macaques—a model of HLA-B*27-mediated elite control. Here, we investigated whether a monotypic vaccine-induced CD8(+) T-cell response targeting the conserved "late-escaping" Nef RL10 epitope can increase the incidence of elite control in Mamu-B*08(+) monkeys. Surprisingly, vaccine-induced Nef RL10-specific CD8(+) T cells selected for variants within days after infection and, ultimately, did not facilitate the development of elite control. Elite control is, therefore, likely to involve CD8(+) T-cell responses against more than one epitope. Together, these results underscore the complexity and multidimensional nature of virologic control of lentivirus infection.

Editorial: Time to explore the missing links: the cross-talk between COVID infection and cancer cells; lingering questions on the longitudinal efficacy of the front line immunotherapies against unpredictable “Omicron ghosts” and insights from CAR-T cell therapy pointing toward better clinical outcomes

Over the past decade, tumour immunology has progressed enormously, as a result of the application of a range of new technologies. Screening of tumour gene expression libraries using cancer patients' sera and cancer-specific T lymphocytes has defined a large number of tumour-specific antigenic proteins. The repertoire of known tumour antigens is rapidly expanding as a consequence of these advances. In addition, over the last few years the analysis of human T-cell responses specific for several tumour antigens in cancer patients has been made possible by the use of novel staining reagents (i.e. tetramers). This has allowed the characterization and monitoring of specific tumour responses, and has provided an opportunity to greatly accelerate the development of new anticancer vaccines. Recent results have demonstrated that the immune system can detect the presence of malignant cells in cancer patients, and have raised hopes for the use of antigenic cancer proteins as vaccines to induce tumour-specific cell-mediated immunity. Tumour immunology is now on solid technical and conceptual footing. However, the challenge remains to apply to patients the results obtained in the laboratories. Pioneering work carried out by Thierry Boon and colleagues in carcinogen-induced mouse tumours showed that T cells are capable of recognizing tumour cells containing unique genetic point mutations.1 Subsequent work by many laboratories has led to an ever-increasing list of known tumour-specific antigens in spontaneously arising tumours (reviewed by Renkvist et al.2). To date, identification of tumour antigens has been focused almost exclusively on antigens recognized by tumour-specific HLA class I restricted cytotoxic T lymphocytes (CTL). Recently, the role of HLA class II restricted CD4+ T cells has been increasingly recognized, and the list of known HLA class II epitopes is now rapidly expanding.3–5 HLA class I and class II epitopes are the tools with which tumour-specific immunotherapies can be designed, and as our understanding of the complexity of the immune system expands we are provided with an ever-increasing number of possible therapeutic strategies. Melanoma has been the tumour type particularly studied by tumour immunologists, as melanoma cell lines can be generated relatively easily for assays of cytolytic activity. Several laboratories have demonstrated the presence of melanoma-specific CTL in tumour infiltrated lymph nodes, peripheral blood lymphocytes and skin metastases,6–8 raising hopes for immunotherapeutic strategies for melanoma. However, although these results are consistent with an active tumour-specific immune response in melanoma patients, it remains unclear whether melanoma-specific CTL are capable of slowing tumour progression. Three main approaches have been used to identify tumour antigens. The ‘genetic’ approach, by which the first human tumour antigen was recognized, is based on isolating cytotoxic T-cell clones with specificity for autologous tumour cells and identifying the genes coding for the T-cell-recognized epitopes by cDNA expression cloning.9 Although the genetic approach has mainly been used to characterize HLA class I restricted epitopes, a similar protocol has recently been used to identify tumour antigens recognized by CD4+ cells in the context of HLA class II molecules.10 This novel approach involves cloning the tumour-derived cDNA library down-stream of a gene fragment encoding the first 80 amino acids of the invariant chain, and channelling tumour antigens through the HLA class II presentation pathway. More recently, serological analysis of recombination expression libraries (SEREX) has been shown to be a powerful method to identify tumour antigens. SEREX is based on the recognition by cancer patients' autologous sera of tumour antigens expressed by a λ-phage library.11,12 A large collection of tumour antigens recognized by antibodies, as detected by the SEREX technology, is now available in the database of the Ludwig Institute for Cancer Research (http://www.licr.org/SEREX.htm). The fact that many of the antigens isolated using SEREX correspond to those identified in melanoma patients using CTL-based techniques suggests that antibody responses against tumour antigens may be closely associated with CTL responses. Hence the new antigens defined by SEREX may also sensitize tumours for lysis by CTL. Representational difference analysis (RDA) is a PCR-based subtractive hybridization technique which can effectively isolate differentially expressed genes from a given cDNA population (tester) compared to another (driver). New tumour antigens have also been identified by searching DNA databases for homologous gene sequences.13 These latter two approaches have been used to identify new tumour antigens beyond those that are isolated on the basis of their immunogenicity. The use of DNA micro arrays is also likely to increase the number of known genes over-expressed on tumour cells. The ‘biochemical’ approach involves acid-elution of peptides bound to the HLA class I molecules of tumour cells, and fractionation of the peptides with reverse-phase high-performance liquid chromatography. Peptide fractions are then tested for their ability to sensitize HLA class I matched target cells for lysis by tumour-specific CTL. In some cases the amount of peptide in the positive fraction is sufficient to obtain its sequence by Edman degradation, but in most instances the amount of peptide is too low and the sequence can only be obtained by mass spectroscopy. The peptide sequence can then be used to search databases in order to find the gene encoding the antigenic peptide.14 The ‘reverse immunology’ approach is the reverse of the first two strategies. The starting point is a protein that is known to be over-expressed or mutated in tumour cells. Peptides from within the protein are selected for their high binding affinity to a given HLA class I molecule, and are loaded on to antigen-presenting cells, to stimulate lymphocytes in vitro. To demonstrate that the peptide is a genuine tumour antigen epitope, these CTL must then be demonstrated to kill tumour cells expressing the putative tumour antigen and the relevant class I molecule. There are now several computer algorithms, available on the Internet, for predicting peptide sequences that are likely to bind to a given HLA molecule (http://bimas.dcrt.nih.gov/molbio/hla_bind/). More recently, an algorithm has been developed that will predict efficiency of peptide presentation at the cell surface based on what is known about preferred proteasomal cleavage sites (http://www.paproc.de). The number of known tumour antigens expressed in tumour types other than melanoma is now expanding with the development of these new technologies. Renkvist et al. have recently published an exhaustive list of tumour antigens that have been shown to be recognized by T cells.2 They have listed all HLA class I and class II restricted T-cell epitopes encoded by tumour antigens published by 31 July 2000. The use of the techniques described above has led to the identification of a large number of melanoma antigenic proteins, which can be divided into three main categories. These genes are expressed on a variety of tumour types as well as melanoma, and are not expressed on normal tissues, with the exception of spermatogonia, which do not express HLA class I molecules and do not represent targets for class I restricted immune response. The mechanisms responsible for the expression of this group of antigens in tumours and testis remain unclear. One possibility is that their expression results from de-methylation of genes that are normally silenced in non-germ cells.15 Since many of these antigens occur in a wide variety of tumours, they offer the prospect of ‘broad spectrum’ anticancer vaccines aimed at inducing CTL attack. Cancer-testis antigens include the MAGE family (with now over 20 members),13,16,17 as well as BAGE,18 GAGE19 and NY-ESO-1.20 NY-ESO-1 is one of the most promising of the cancer-testis antigens. It is expressed in a high proportion of breast (30%), prostate (25%), and ovarian (25%) cancer, as well as melanoma (45%), but not in normal tissues.20 NY-ESO-1 appears to be the most immunogenic of cancer-testis antigens known to date, and combined NY-ESO-1-specific T-cell and antibody responses are seen in a high percentage of patients with advanced NY-ESO-1-expressing tumours.21,22 This group of proteins includes antigens that are expressed in melanomas and normal melanocytes. An immune response specific to these antigens may cross-react between melanomas and normal melanocytes. This group of antigens includes melan-A protein (whose function is unknown), tyrosinase, glycoprotein 100 (gp100), gp75/tyrosinase related protein 1 (TRP-1) and TRP-2, which are melanosomal enzymes involved in the melanin biosynthetic pathway. Amongst the known melanoma antigens recognized by CTL, melan-A is probably the best studied. It has been established that, in a significant proportion of HLA-A2 positive melanoma patients and healthy controls, CTL specific for the melan-A epitope 26–35 can be detected ex vivo by tetramer staining.6,8,23 This work has also shown that CTLs detected in healthy individuals and many melanoma patients are of a naïve phenotype, whereas activated cells tend to be seen in patients with more advanced disease.8,23 Tumour antigens can arise from point mutations in normal genes as a result of the inherent genetic instability of malignant transformation. These antigens are expressed only in the individual tumour where they were identified, since it is unlikely that the same mutation will occur in two different tumours, unless the mutation results in an obligatory step in malignant transformation. In mouse models, these unique antigens have been shown to be more immunogenic than the other groups of antigens. This group includes some of the most specific targets for immunotherapy, but this potential advantage must be balanced against the impracticality for clinical use if they can only be used against the original tumour in which they were found. Recent studies have shown that the immune system can recognize products from alternative transcripts, including those from cryptic start-sites and alternative reading frames.24 The standard chromium release assay remains one of the assays most widely used, but it is only semiquantitative and relies on the measurement of cytolytic function of a population of cells. The most quantitative method used until recently was the limiting dilution analysis (LDA). This protocol, which is based on cloning in multiple microcultures, requires the CTL precursors (CTLp) to undergo several cycles of replication prior to determining CTL activity by chromium release for individual culture wells. The LDA approach suffers from major limitations such as high variability and failure to measure activated CTL, possibly because already activated CTL undergo apoptosis on further stimulation. Several new techniques have been developed that allow quantification of antigen-specific T cells. These approaches are simple and allow meaningful comparisons of different clinical trials, as well as an improved understanding of spontaneous immune responses. One new approach is the enumeration of cytokine-releasing lymphocytes. Although this is also indirect and involves the measurement of an effector function, it has certain advantages. Cytokine production can be measured at a single-cell level and so there is no need for antigen-specific T cells to be expanded prior to the assay in order to be detected. Two experimental methods have been developed based on this approach. The ELISPOT assay, which measures cytokine secreted from individual cells captured on antibody-coated nitrocellulose membrane.8 Each ‘spot’ represents one cytokine-secreting cell, which appears after labelling with a secondary antibody. Cytokine intracellular staining allows cytokine-producing cells to be identified and counted by flow cytometry.25 This technique requires the stimulation of T cells for a few hours with antigen, prior to their intracellular staining with fluorochrome-labelled antibody specific for intracellular cytokines. To date, the most sensitive protocol to monitor T-cell responses is based on the use of tetrameric HLA class I/peptide complexes (‘tetramers’).26 Fluorochrome-labelled tetrameric HLA class I/peptide complexes can be used to stain cells, which are subsequently analysed by flow cytometry, allowing for the first time enumeration of specific T cells without an indirect functional assay. This technique allows a detailed phenotypic analysis of specific T cells using the large panel of markers already available and has been used to further characterize T-cell responses in melanoma patients.6,8,23,27 Tetramer technology also enables rapid and sensitive separation of homogenous populations of antigen-specific T cells by flow cytometry cell sorting. Tetramer-sorted lines or clones provide a unique source of cells for TCR repertoire analysis and, potentially, for antigen-targeted adoptive transfer therapy.7 Progress in tumour immunotherapy has been hampered by the lack of reliable protocols to measure vaccine-driven T-cell responses. The development of tetramer and ELISPOT assays provides an opportunity to greatly accelerate the development of new anticancer vaccines, as rapid comparison of immunization protocols is now possible. We will attempt to categorize tumour immune-therapeutic interventions according to their therapeutic modality, discussing potential advantages and disadvantages of different therapeutic approaches. This analysis will be focused on antigen-specific immunotherapeutic approaches, as only these protocols ensure an accurate analysis of the tumour-specific immune responses. Early findings that human tumour-infiltrating lymphocytes (TILs) derived from patients with a variety of types of cancer (including metastatic melanoma, breast cancer, colon cancer and ovarian cancer) can exhibit specific tumour lysis or cytokine release in vitro contributed to early optimism about the future role of antitumour immunotherapy. When expanded in vitro with IL-2, TILs were found to maintain antitumour activity, and the adoptive transfer of TILs was demonstrated to treat murine malignancies effectively, leading to early trials of adoptive transfer of TILs plus IL-2 in humans.28–30 In 1994, Rosenberg and colleagues transferred in vitro-expanded TILs and IL-2 in 86 patients with metastatic melanoma.31 The overall response rate was 34%. Although this is similar to response rates achieved with IL-2 alone, there was no difference between patients who had never received IL-2 before and those whose treatment with this cytokine had previously failed, suggesting that IL-2 was not the impacting factor. With the discovery of tumour-specific antigen, the opportunity arose for adoptive transfer to evolve into a tumour antigen-specific therapy. More recently, Yee et al. have described a patient with metastatic melanoma, treated with the adoptive transfer of melan-A-specific clones,32 who developed inflammatory lesions around pigmented areas of skin. Analysis of infiltrating lymphocytes in skin and tumour biopsies by tetramer analysis demonstrated a predominance of melan-A-specific T cells. Adoptive transfer therapy has remained limited due to technical difficulties, although it is being studied in Epstein-Barr virus associated malignancies in transplant recipients.33,34 Active immunotherapy is aimed at stimulating an endogenous immune response towards antigen or antigens, resulting in clonal expansion and activation of T and/or B cells. Clinical trials with antigenic peptides have been undertaken with a view to inducing specific immune responses in vivo. This approach is limited by the HLA type of the patient. It has the advantages that peptides are easily produced, stable, free of contaminating material, devoid of oncogenic potential and easy to administer. Many small clinical trials have been performed and, although interpretation and comparison have been limited by the immunoassays used, their results suggest that tumour-associated peptides alone can produce specific delayed type hypersensitivity (DTH) and CD8+ T-cell responses. Variable clinical responses and no severe toxicities have been seen. Combinations of peptides with different cytokines and adjuvants, including interleukin 2 (IL-2)35 and granulocyte-macrophage colony stimulating factor (GM-CSF),36 have also been used; however, the effect of cytokine alone has rarely been compared in the same trial. Some of the best clinical responses have been demonstrated by Marchand et al. A clinical response was demonstrated in 7/25 patients with metastatic melanoma who received three subcutaneous injections of the MAGE-A3 HLA-A1 restricted nonapeptide EVDPIGHLY.37 Responding patients tended to have cutaneous rather than visceral metastases. Three responses were complete and two of these led to a disease-free state, which lasted for more than 2 years. However, no evidence of CTL response was seen by LDA in the four patients who were analysed (including the two who demonstrated complete clinical responses). Jäger et al. have also shown mixed clinical responses in 12 patients with metastatic NY-ESO-1-expressing cancers who received intradermal injections of three HLA-A2 binding NY-ESO-1 peptides.38 The patients had different tumour types, including melanoma, ovarian carcinoma and breast carcinoma. Peptides were injected intradermally once weekly for 4 weeks. Patients with no evidence of disease progression on day 50 received further immunizations, combined with subcutaneous GM-CSF. Primary peptide-specific CD8+ T-cell responses and DTH responses were generated in 4/7 patients who were antibody-negative at the outset. This was associated with disease stabilization and objective regression of single metastases. NY-ESO-1 antibody-positive patients did not develop significant changes in base-line NY-ESO-1 specific T-cell responses; however, stabilization of disease and regression of individual metastases was observed in 3/5 patients. There have been several trials with HLA-A2-restricted gp100 peptides in patients with metastatic melanoma. Specific CTL responses have been demonstrated for two of the peptides: gp100 209–217 (ITDQVPFSY) and gp100 280–289 (YLEPGPVTA).39 A further study compared these two peptides with modified analogues: IMDQVPFSY (gp100 209 2M) or YLEPGPVTV (gp100 280 9V).40 Post-vaccination specific immune responses to gp100 209 2M could be seen in 4/6 patients, measured by ELISPOT. Despite this apparent increased immunogenicity, no clinical responses were seen with modified peptide alone, compared to 1/9 with native peptide alone. A response rate of 13/31 was seen with IL-2 and modified gp100 209, demonstrating the activity of IL-2.35 Adjuvant GM-CSF and IL-12 were shown not to enhance clinical or immune responses.41 The HLA-A2 restricted melan-A peptide (p27–35) AAGIGILTV combined with incomplete Freund adjuvant (IFA) has been shown to result in specific immune responses when given to patients with metastatic42 or high-risk resected43 melanoma; however, no clinical responses were seen. Similarly, the HLA-A2 restricted tyrosinase peptide 368–376 (YMDGTMSQV) administered with the adjuvant Quillaja saponin (QS-21) produced specific immune responses, as measured by ELISPOT assay, in 2/9 patients with metastatic disease.44 Scheibenbogen and colleagues administered different tyrosinase peptides to 18 patients with metastatic melanoma, according to their HLA type. Tyrosinase-specific immune responses as measured by ELISPOT were seen in four patients, and minor clinical responses were also seen.45 The simultaneous injection of a pool of HLA-A2 restricted peptides from melan-A, tyrosinase and gp100 was used to vaccinate six patients with metastatic melanoma. Specific immune responses against melan-A (3/6) and the tyrosinase signal sequence (2/6) were demonstrated.46 No major tumour regressions were seen, however. In a follow-up study, in which systemic GM-CSF was coadministered with the fourth injection, enhanced specific immune responses and objective tumour regressions were observed in all three patients.36 Jäger et al. have since reported the case of a patient who, since 1995, received continued immunization with the above peptides.47 The patient had a partial remission and developed extensive vitiligo, and after eight immunizations developed an increase in CTL activity against the melan-A and tyrosinase peptides. There are now several large multicentre trials underway to further investigate peptide vaccines. The ECOG 1696 trial is examining a polypeptide vaccine, consisting of A2 restricted peptides: melan A 27–35, gp100 209–217 and tyrosinase 368–376. Patients with metastatic melanoma will receive the peptide vaccine, and IFNα, GM-CSF, neither or both. Clinical responses as well as immune responses, measured by tetramers and ELISPOT, will be examined. The Intergroup E4697 trial is using the same vaccine and immune monitoring protocol in patients who are disease free, but who have a > 70% chance of disease recurrence. Dendritic cells (DC) are now recognized to be the pivotal antigen-presenting cells that initiate immune responses. The generation of immature DC requires culturing CD34+ precursor cells or CD14+ monocyte-enriched PBMC in the presence of exogenous GM-CSF and IL-4.48 Additional maturation stimuli of cytokine-derived DC with TNF-α or monocyte-conditioned medium is required to obtain mature DC. Recent published papers have demonstrated that immunostimulatory properties of DC are linked to their maturation state. While injection of mature DC enhances antigen-specific T-cell immunity, injection of immature DC results in antigen-specific inhibition of effector T-cell function49,50 (reviewed by Roncaolo et al.51). It has also been demonstrated that the cryopreservation of DC does not affect the phenotype or function of the cells, further simplifying the production of cells for vaccination purposes.52 Although the introduction DC into the clinic has been hampered by the enormous resources required to generate DC for clinical use, there is an increasing number of clinical trials being published in the literature, involving a wide range of tumour types. Clinical trials have examined methods of generating DC, the maturation status of injected DC and the route of DC injection. Various methods for ‘loading’ tumour antigens onto DC have also been studied, including peptide ‘pulsing’ of DC,53 loading of DC with tumour cell lysates,54 or the fusion of DC with tumour cells. DC-based immunotherapy has been shown to be safe, and clinical and immunological responses have been reported. Nestle and colleagues treated 16 patients with metastatic melanoma with DC pulsed with HLA-A2 tyrosinase, gp100 and melan-A peptides, HLA-A1 MAGE-A1 and MAGEA-3 peptides; or with tumour lysate, if tumour cells were They were also pulsed with as an The DC were injected to a of into lymph with responses were seen in patients, with two complete responses. patients developed a delayed type hypersensitivity (DTH) towards and tumour antigen-specific DTH was seen in patients. and colleagues HLA-A1 patients with metastatic melanoma with of DC pulsed with MAGE-A3 HLA-A1 restricted peptide intradermal and two of MAGE-A3 peptide-specific CTL precursors were observed in patients. of individual metastases was observed in patients, and T-cell were observed in a in gene technology have in the development of new tools with which tumour-specific can be or DNA can be used to express a variety of genes in vivo that tumour antigens, cytokines or can be allowing improved intracellular or of antigen, and the tumour antigen sequence may be modified to enhance of vaccines, in which multiple CTL epitopes are expressed as a of are also with DNA has been shown to result in antibody and T-cell immune responses, including the generation of antigen-specific CD8+ and CD4+ cells in murine studies have demonstrated that immunizations against tumour antigens such as or can result in immune responses, leading to tumour DNA has the advantages that it is defined and can be and produced in large It is neither capable of Several I trials of vaccines encoding a variety of tumour antigens and/or are now being undertaken in several different tumour types. have the advantage that may to cell-mediated responses. Several vaccines are for use in clinical trials including and such as and modified of DNA by with a virus has been shown to result in increased of specific against in murine and this approach has to cancer vaccines.

SY27-03: Biomarker-guided development of novel multi-peptide cancer vaccines - from discovery to phase lll trials.

Acute infection with a single hepatitis C virus strain in dialysis patients: Analysis of adaptive immune response and viral variability

Coronavirus disease-2019 (COVID-19) bivalent ancestral/Omicron messenger RNA (mRNA) booster vaccinations became available to boost and expand the immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron infections. In a prospective cohort study including 59 healthcare workers, we assessed SARS-CoV-2 ancestral and Omicron BA.5-specific neutralizing antibody and T-cell responses in previously infected and infection-naive individuals. Also, we assessed the effect of an ancestral/Omicron BA.1 bivalent mRNA booster vaccination on these immune responses. 10 months after previous monovalent mRNA vaccinations, ancestral SARS-CoV-2 S1-specific T-cell and anti-RBD IgG responses remained detectable in most individuals and a previous SARS-CoV-2 infection was associated with increased T-cell responses. T-cell responses, anti-RBD IgG, and Omicron BA.5 neutralization activity increased after receiving an ancestral/Omicron BA.1 bivalent booster mRNA vaccination. An Omicron BA.5 infection in addition to bivalent vaccination, led to a higher ratio of Omicron BA.5 to ancestral strain neutralization activity compared to no bivalent vaccination and no recent SARS-CoV-2 infection. In conclusion, SARS-CoV-2 T-cell and antibody responses persist for up to 10 months after a monovalent booster mRNA vaccination. An ancestral/Omicron BA.1 bivalent booster mRNA vaccination increases these immune responses and also induces Omicron BA.5 cross-neutralization antibody activity. Finally, our data indicate that hybrid immunity is associated with improved preservation of T-cell immunity.

Role of neutralizing antibodies in HIV infection.

SARS-CoV-2: an unknown agent and challenges in vaccine development

New perspectives for T-cell-based HCV vaccines