Development of therapeutic monoclonal antibodies against DKK1 peptide-HLA-A2 complex to treat human cancers

BACKGROUND

Targeted immunotherapy with monoclonal antibodies (mAbs) is an effective and safe method for the treatment of malignancies. Development of mAbs with improved cytotoxicity, targeting new and known tumor-associated antigens, therefore continues to be an active research area. We reported that Dickkopf-1 (DKK1) is a good target for immunotherapy of human cancers based on its wide expression in different cancers but not in normal tissues. As DKK1 is a secreted protein, mAbs binding directly to DKK1 have limited effects on cancer cells in vivo.

METHODS

The specificity and antibody-binding capacity of DKK1-A2 mAbs were determined using indirect ELISA, confocal imaging, QIFIKIT antibody-binding capacity and cell surface binding assays. The affinity of mAbs was determined using a surface plasmon resonance biosensor. A flow cytometry-based cell death was performed to detect tumor cell apoptosis. Antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays were used to evaluate the ability of DKK1-A2 mAbs to mediate ADCC and CDC activities against tumor cells in vitro. Flow cytometry data were collected with an FACSymphony A3 cell analyzer and analyzed with FlowJo V.10.1 software. Human cancer xenograft mouse models were used to determine the in vivo therapeutic efficacy and the potential safety and toxicity of DKK1-A2 mAbs. In situ TUNEL assay was performed to detect apoptosis in tumors and mouse organs.

RESULTS

We generated novel DKK1-A2 mAbs that recognize the DKK1 P20 peptide presented by human HLA-A*0201 (HLA-A2) molecules (DKK1-A2 complexes) that are naturally expressed by HLA-A2+DKK1+ cancer cells. These mAbs directly induced apoptosis in HLA-A2+DKK1+ hematologic and solid cancer cells by activating the caspase-9 cascade, effectively lysed the cancer cells in vitro by mediating CDC and ADCC and were therapeutic against established cancers in their xenograft mouse models. As DKK1 is not detected in most human tissues, DKK1-A2 mAbs neither bound to or killed HLA-A2+ blood cells in vitro nor caused tissue damage in tumor-free or tumor-bearing HLA-A2-transgenic mice.

CONCLUSION

Our study suggests that DKK1-A2 mAbs may be a promising therapeutic agent to treat human cancers.

Orthopoxvirus-Specific T-Cell Responses in Convalescent Mpox Patients

Orthopoxvirus-specific T-cell responses were analyzed in 10 patients who had recovered from Mpox including 7 people with human immunodeficiency virus (PWH). Eight participants had detectable virus-specific T-cell responses, including a PWH who was not on antiretroviral therapy and a PWH on immunosuppressive therapy. These 2 participants had robust polyfunctional CD4+ T-cell responses to peptides from the 121L vaccinia virus (VACV) protein. T-cells from 4 of 5 HLA-A2-positive participants targeted at least 1 previously described HLA-A2-restricted VACV epitope, including an epitope targeted in 2 participants. These results advance our understanding of immunity in convalescent Mpox patients.

Exopolysaccharide-Treated Dendritic Cells Effectively Ameliorate Acute Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a primary and often lethal complication of allogenic hematopoietic stem cell transplantation (HSCT). Prophylactic regimens for GVHD are given as standard pretransplantation therapy; however, up to 50% of these patients develop acute GVHD (aGVHD) and require additional immunosuppressive intervention. Using a mouse GVHD model, we previously showed that injecting mice with exopolysaccharide (EPS) from Bacillus subtilis prior to GVHD induction significantly increased 80-day survival after transplantation of complete allogeneic major histocompatibility complex-mismatched cells. To ask whether EPS might also inhibit GVHD in humans, we used humanized NSG-HLA-A2 mice and induced GVHD by i.v. injection of A2neg human peripheral blood mononuclear cells (PBMCs). Because we could not inject human donors with EPS, we transferred EPS-pretreated dendritic cells (DCs) to inhibit aGVHD. We derived these DCs from CD34+ human cord blood cells, treated them with EPS, and then injected them together with PBMCs into the NSG-HLA-A2 mice. We found that all mice that received untreated DCs were dead by day 35, whereas 25% of mice receiving EPS-treated DCs (EPS-DCs) survived. This DC cell therapy could be readily translatable to humans, because we can generate large numbers of human EPS-DCs and use them as an "off the shelf" treatment for patients undergoing HSCT.

Prediction and identification of HLA-A*0201-restricted epitopes from cancer testis antigen CT23

Cancer-testis antigen CT23 is a class of tumor-associated antigens (TAA) characterized by restricted expression in male germ cells and a variety of tumor tissues. Numerous studies have shown that CT23 is closely related to tumor cell viability, proliferation, metastasis and invasion. CT23 is immunogenic and can cause specific immune response in tumor patients. Therefore, it is considered to be one of the best target antigens for designing therapeutic tumor vaccines and T-cell-mediated tumor immunotherapy. In this study, we initially obtained seven HLA-A*0201-restricted CT23 epitope candidate peptides through the T cell epitope prediction program. Subsequently, a T2 cell binding assay revealed the potential binding of all candidate peptides with HLA-A2 molecules. Notably, peptide P7 (ALLVLCYSI) exhibited the highest affinity, as evidenced by a fluorescence index (FI) of 2.19. Dendritic cells (DCs) loaded with CT23 candidate peptide can stimulate CD8+T cell activation and proliferation, and compared with other candidate peptides, candidate peptide P7 is superior. The cytotoxic T lymphocytes (CTLs) stimulated by the peptide P7 had killing effect on tumor cells (HLA-A*0201+, CT23+), but no killing effect on tumor cells (HLA-A*0201-, CT23+). The CTLs induced by the peptide P7 also had a specific killing effect on T2 cells bearing the peptide P7. In summary, our findings suggest that the CT23 peptide P7 (ALLVLCYSI) can induce immune responses and holds potential for tumor-specific CTL therapy.

Thioamide Analogues of MHC I Antigen Peptides

Short, synthetic peptides that are displayed by major histocompatibility complex I (MHC I) can stimulate CD8 T cells in vivo to destroy virus-infected or cancer cells. The development of such peptides as vaccines that provide protective immunity, however, is limited by rapid proteolytic degradation. Introduction of unnatural amino acid residues can suppress MHC I antigen proteolysis, but the modified peptides typically display lower affinity for MHC I and/or diminished ability to activate CD8 T cells relative to native antigen. Here, we report a new strategy for modifying MHC I antigens to enhance resistance to proteolysis while preserving MHC I affinity and T cell activation properties. This approach, replacing backbone amide groups with thioamides, was evaluated in two well-characterized antigens presented by HLA-A2, a common human MHC I. For each antigen, singly modified thioamide analogues retained affinity for HLA-A2 and activated T cells specific for the native antigen, as measured via interferon-γ secretion. In each system, we identified a highly potent triply substituted thioamide antigen ("thio-antigen") that displayed substantial resistance to proteolytic cleavage. Collectively, our results suggest that thio-antigens may represent a general and readily accessible source of potent vaccine candidates that resist degradation.

Surveillance of SARS-CoV-2 immunogenicity: loss of immunodominant HLA-A*02-restricted epitopes that activate CD8+ T cells

Introduction and methods

In this present work, coronavirus subfamilies and SARS-CoV-2 Variants of Concern (VOCs) were investigated for the presence of MHC-I immunodominant viral peptides using in silico and in vitro tools.

Results

In our results, HLA-A*02 haplotype showed the highest number of immunodominant epitopes but with the lowest combined prediction score. Furthermore, a decrease in combined prediction score was observed for HLA-A*02-restricted epitopes when the original strain was compared to the VOCs, indicating that the mutations on the VOCs are promoting escape from HLA-A2-mediated antigen presentation, which characterizes a immune evasion process. Additionally, epitope signature analysis revealed major immunogenic peptide loss for structural (S) and non-structural (ORF8) proteins of VOCs in comparison to the Wuhan sequence.

Discussion

These results may indicate that the antiviral CD8+ T-cell responses generated by original strains could not be sufficient for clearance of variants in either newly or reinfection with SARS-CoV-2. In contrast, N epitopes remain the most conserved and reactive peptides across SARS-CoV-2 VOCs. Overall, our data could contribute to the rational design and development of new vaccinal platforms to induce a broad cellular CD8+ T cell antiviral response, aiming at controlling viral transmission of future SARS-CoV-2 variants.

Vaccination with post-translational modified, homocitrullinated peptides induces CD8 T-cell responses that mediate antitumor immunity

BACKGROUND

Post-translational modification of proteins has the potential to alter the ability of T cells to recognize major histocompatibility complex (MHC) class -I and class-II restricted antigens, thereby resulting in altered immune responses. One such modification is carbamylation (homocitrullination) that results in the formation of homocitrulline (Hcit) residues in a non-enzymatic reaction of cyanate with the lysine residues in the polypeptide chain. Homocitrullination occurs in the tumor microenvironment and CD4-mediated immune responses to Hcit epitopes can target stressed tumor cells and provide a potent antitumor response in mouse models.

METHODS

Homocitrullinated peptides were identified and assessed in vitro for HLA-A2 binding and in vivo in human leukocyte antigen (HLA) transgenic mouse models for immunogenicity. CD8 responses were assessed in vitro for cytotoxicity and in vivo tumor therapy. Human tumor samples were analyzed by targeted mass spectrometry for presence of homocitrullinated peptides.

RESULTS

Homocitrullinated peptides from aldolase and cytokeratin were identified, that stimulated CD8-mediated responses in vivo. Modified peptides showed enhanced binding to HLA-A2 compared with the native sequences and immunization of HLA-A2 transgenic mice generated high avidity modification specific CD8 responses that killed peptide expressing target cells. Importantly, in vivo the homocitrullinated aldolase specific response was associated with efficient CD8 dependent antitumor therapy of the aggressive murine B16 tumor model indicating that this epitope is naturally presented in the tumor. In addition, the homocitrullinated aldolase epitope was also detected in human tumor samples.

CONCLUSION

This is the first evidence that homocitrullinated peptides can be processed and presented via MHC-I and targeted for tumor therapy. Thus, Hcit-specific CD8 T-cell responses have potential in the development of future anticancer therapy.

Human A2-CAR T Cells Reject HLA-A2 + Human Islets Transplanted Into Mice Without Inducing Graft-versus-host Disease

BACKGROUND

Type 1 diabetes is an autoimmune disease characterized by T-cell-mediated destruction of pancreatic beta-cells. Islet transplantation is an effective therapy, but its success is limited by islet quality and availability along with the need for immunosuppression. New approaches include the use of stem cell-derived insulin-producing cells and immunomodulatory therapies, but a limitation is the paucity of reproducible animal models in which interactions between human immune cells and insulin-producing cells can be studied without the complication of xenogeneic graft-versus-host disease (xGVHD).

METHODS

We expressed an HLA-A2-specific chimeric antigen receptor (A2-CAR) in human CD4 + and CD8 + T cells and tested their ability to reject HLA-A2 + islets transplanted under the kidney capsule or anterior chamber of the eye of immunodeficient mice. T-cell engraftment, islet function, and xGVHD were assessed longitudinally.

RESULTS

The speed and consistency of A2-CAR T-cell-mediated islet rejection varied depending on the number of A2-CAR T cells and the absence/presence of coinjected peripheral blood mononuclear cells (PBMCs). When <3 million A2-CAR T cells were injected, coinjection of PBMCs accelerated islet rejection but also induced xGVHD. In the absence of PBMCs, injection of 3 million A2-CAR T cells caused synchronous rejection of A2 + human islets within 1 wk and without xGVHD for 12 wk.

CONCLUSIONS

Injection of A2-CAR T cells can be used to study rejection of human insulin-producing cells without the complication of xGVHD. The rapidity and synchrony of rejection will facilitate in vivo screening of new therapies designed to improve the success of islet-replacement therapies.

Immune-infiltrated kidney organoid-on-chip model for assessing T cell bispecific antibodies

T cell bispecific antibodies (TCBs) are the focus of intense development for cancer immunotherapy. Recently, peptide-MHC (major histocompatibility complex)-targeted TCBs have emerged as a new class of biotherapeutics with improved specificity. These TCBs simultaneously bind to target peptides presented by the polymorphic, species-specific MHC encoded by the human leukocyte antigen (HLA) allele present on target cells and to the CD3 coreceptor expressed by human T lymphocytes. Unfortunately, traditional models for assessing their effects on human tissues often lack predictive capability, particularly for "on-target, off-tumor" interactions. Here, we report an immune-infiltrated, kidney organoid-on-chip model in which peripheral blood mononuclear cells (PBMCs) along with nontargeting (control) or targeting TCB-based tool compounds are circulated under flow. The target consists of the RMF peptide derived from the intracellular tumor antigen Wilms' tumor 1 (WT1) presented on HLA-A2 via a bivalent T cell receptor-like binding domain. Using our model, we measured TCB-mediated CD8+ T cell activation and killing of RMF-HLA-A2-presenting cells in the presence of PBMCs and multiple tool compounds. DP47, a non-pMHC-targeting TCB that only binds to CD3 (negative control), does not promote T cell activation and killing. Conversely, the nonspecific ESK1-like TCB (positive control) promotes CD8+ T cell expansion accompanied by dose-dependent T cell-mediated killing of multiple cell types, while WT1-TCB* recognizing the RMF-HLA-A2 complex with high specificity, leads solely to selective killing of WT1-expressing cells within kidney organoids under flow. Our 3D kidney organoid model offers a platform for preclinical testing of cancer immunotherapies and investigating tissue-immune system interactions.

Global analysis of HLA-A2 restricted MAGE-A3 tumor antigen epitopes and corresponding TCRs in non-small cell lung cancer

Background: Advanced non-small cell lung cancer (NSCLC) is the most common type of lung cancer with poor prognosis. Adoptive cell therapy using engineered T-cell receptors (TCRs) targeting cancer-testis antigens, such as Melanoma-associated antigen 3 (MAGE-A3), is a potential approach for the treatment of NSCLC. However, systematic analysis of T cell immune responses to MAGE-A3 antigen and corresponding antigen-specific TCR is still lacking. Methods: In this study, we comprehensively screened HLA-A2 restricted MAGE-A3 tumor epitopes and characterized the corresponding TCRs using in vitro artificial antigen presentation cells (APC) system, single-cell transcriptome and TCR V(D)J sequencing, and machine-learning. Furthermore, the tumor-reactive TCRs with killing potency was screened and verified. Results: We identified the HLA-A2 restricted T cell epitopes from MAGE-A3 that could effectively induce the activation and cytotoxicity of CD8+ T cells using artificial APC in vitro. A cohort of HLA-A2+ NSCLC donors demonstrated that the number of epitope specific CD8+ T cells increased in NSCLC than healthy controls when measured with tetramer derived from the candidate MAGE-A3 epitopes, especially epitope Mp4 (MAGE-A3: 160-169, LVFGIELMEV). Statistical and machine-learning based analyses demonstrated that the MAGE-A3-Mp4 epitope-specific CD8+ T cell clones were mostly in effector and proliferating state. Importantly, T cells artificially expressing the MAGE-A3-Mp4 specific TCRs exhibited strong MAGE-A3+ tumor cell recognition and killing effect. Cross-reactivity risk analysis of the candidates TCRs showed high binding stability to MAGE-A3-Mp4 epitope and low risk of cross-reaction. Conclusions: This work identified candidate TCRs potentially suitable for TCR-T design targeting HLA-A2 restricted MAGE-A3 tumor antigen.

Durable control of metastases in an HLA-A2+ patient with refractory melanoma after low-dose radiotherapy in combination with MAGE-A4 T cell therapy: a case report

There is no currently approved adoptive cellular therapy for solid tumors. Pre-clinical and clinical studies have demonstrated that low-dose radiotherapy (LDRT) can enhance intratumoral T cell infiltration and efficacy. This case report describes a 71-year-old female patient with rectal mucosal melanoma that had developed metastases to liver, lung, mediastinum, axillary nodes, and brain. After systemic therapies had failed, she enrolled in the radiation sub-study of our phase-I clinical trial exploring the safety and efficacy of afamitresgene autoleucel (afami-cel), genetically engineered T cells with a T cell receptor (TCR) targeting the MAGE-A4 tumor antigen in patients with advanced malignancies (NCT03132922). Prior to the infusion of afami-cel, she received concurrent lymphodepleting chemotherapy and LDRT at 5.6 Gy/4 fractions to the liver. Time to partial response was 10 weeks, and duration of overall response was 18.4 weeks. Although the patient progressed at 28 weeks, the disease was well controlled after high-dose radiotherapy to liver metastases and checkpoint inhibitors. As of the last follow-up, she remains alive over two years after LDRT and afami-cel therapy. This report suggests that afami-cel in combination with LDRT safely enhanced clinical benefit. This provides evidence for further exploring the benefit of LDRT in TCR-T cell therapy.

A luminescence-based method to assess antigen presentation and antigen-specific T cell responses for in vitro screening of immunomodulatory checkpoints and therapeutics

Investigations into the strength of antigen-specific responses in vitro is becoming increasingly relevant for decision making in early-phase research of novel immunotherapeutic approaches, including adoptive cell but also immune checkpoint inhibitor (ICI)-based therapies. In the latter, antigen-specific rapid and high throughput tools to investigate MHC/antigen-specific T cell receptor (TCR) activation haven't been implemented yet. Here, we present a simple and rapid luminescence-based approach using the human papillomavirus 16 (HPV16) E711-20 peptide as model antigen and E7-TCR transgenic Jurkat.NFAT-luciferase reporter cells. Upon E7 peptide pulsing of HLA-A2+ cell lines and macrophages, an effector to target ratio dependent increase in luminescence compared to non-pulsed cells was observed after co-incubation with E7-TCR expressing Jurkat, but not with parental cells. Analogous experiments with cells expressing full-length HPV16 identified that E7-specific activation of Jurkat cells enabled detection of endogenous antigen processing and MHC-I presentation. As proof of concept, overexpression of established checkpoints/inhibitory molecules (e.g., PD-L1 or HLA-G) significantly reduced the E7-specific TCR-induced luminescence, an effect that could be restored after treatment with corresponding targeting antagonistic antibodies. Altogether, the luminescence-based method described here represents an alternative approach for the rapid evaluation of MHC-dependent antigen-specific T cell responses in vitro. It can be used as a rapid tool to evaluate the impact of the immunosuppressive tumor microenvironment or novel ICI in triggering effective T cell responses, as well as speeding up the development of novel therapeutics within the immune-oncology field.

Phase II Trial of Nelipepimut-S Peptide Vaccine in Women with Ductal Carcinoma In Situ

NeuVax is a vaccine comprised of the HER2-derived MHC class I peptide E75 (nelipepimut-S, NPS) combined with GM-CSF. We completed a randomized trial of preoperative vaccination with NeuVax versus GM-CSF alone in patients with ductal carcinoma in situ (DCIS). The primary objective was to evaluate for NPS-specific cytotoxic T lymphocyte (CTL) responses. Patients with human leukocyte antigen (HLA)-A2-positive DCIS were enrolled and randomized 2:1 to NeuVax versus GM-CSF alone and received two inoculations prior to surgery. The number of NPS-specific CTL was measured pre-vaccination, at surgery, and 1 and 3 to 6 months post-operation by dextramer assay. Differences in CTL responses between groups and between pre-vaccination and 1-month post-operation were analyzed using a two-sample t test or Wilcoxon rank sum test. The incidence and severity of adverse events were compared between groups. Overall, 45 patients were registered; 20 patients were HLA-A2 negative, 7 declined participation, 1 withdrew, and 4 failed screening for other reasons. The remaining 13 were randomized to NeuVax (n = 9) or GM-CSF alone (n = 4). Vaccination was well-tolerated with similar treatment-related toxicity between groups with the majority (>89%) of adverse events being grade 1. The percentage of NPS-specific CTLs increased in both arms between baseline (pre-vaccination) and 1-month post-operation. The increase was numerically greater in the NPS+GM-CSF arm, but the difference was not statistically significant. NPS+GM-CSF is safe and well-tolerated when given preoperatively to patients with DCIS. In patients with HLA-A2-positive DCIS, two inoculations with NPS+GM-CSF can induce in vivo immunity and a continued antigen-specific T-cell response 1-month postsurgery.

PREVENTION RELEVANCE

This trial showed that vaccination of patients with HLA-A2-positive DCIS with NeuVax in the preoperative setting can induce a sustained antigen-specific T-cell response. This provides proof of principle that vaccination in the preoperative or adjuvant setting may stimulate an adaptive immune response that could potentially prevent disease recurrence.

Validation of Ligand Tetramers for the Detection of Antigen-Specific Lymphocytes

The study of Ag-specific lymphocytes has been a key advancement in immunology over the past few decades. The development of multimerized probes containing Ags, peptide:MHC complexes, or other ligands was one innovation allowing the direct study of Ag-specific lymphocytes by flow cytometry. Although these types of study are now common and performed by thousands of laboratories, quality control and assessment of probe quality are often minimal. In fact, many of these types of probe are made in-house, and protocols vary between laboratories. Although peptide:MHC multimers can often be obtained from commercial sources or core facilities, few such services exist for Ag multimers. To ensure high quality and consistency with ligand probes, we have developed an easy and robust multiplexed approach using commercially available beads able to bind Abs specific for the ligand of interest. Using this assay, we have sensitively assessed the performance of peptide:MHC and Ag tetramers and have found considerable batch-to-batch variability in performance and stability over time more easily than using murine or human cell-based assays. This bead-based assay can also reveal common production errors such as miscalculation of Ag concentration. This work could set the stage for the development of standardized assays for all commonly used ligand probes to limit laboratory-to-laboratory technical variation and experimental failure caused by probe underperformance.

Diversity of HLA-A2-Restricted and Immunodominant Epitope Repertoire of Human T-Lymphotropic Virus Type 1 (HTLV-1) Tax Protein: Novel Insights among N-Terminal, Central and C-Terminal Regions

The present study sought to search for the immunodominance related to the N-terminal, Central and C-terminal regions of HTLV-1 Tax using novel, cutting-edge peptide microarray analysis. In addition, in silico predictions were performed to verify the presence of nine amino acid peptides present along Tax restricted to the human leukocyte antigen (HLA)-A2.02*01 haplotype, as well as to verify the ability to induce pro-inflammatory and regulatory cytokines, such as IFN-γ and IL-4, respectively. Our results indicated abundant dose-dependent reactivity for HLA-A*02:01 in all regions (N-terminal, Central and C-terminal), but with specific hotspots. Furthermore, the results of fold-change over the Tax11–19 reactivity obtained at lower concentrations of HLA-A*02:01 reveal that peptides from the three regions contain sequences that react 100 times more than Tax11–19. On the other hand, Tax11–19 has similar or superior HLA-A*02:01 reactivity at higher concentrations of this haplotype. The in silico analysis showed a higher frequency of IFN-γ-inducing peptides in the N-terminal portion, while the C-terminal portion showed a higher frequency of IL-4 inducers. Taken together, these results shed light on the search for new Tax immunodominant epitopes, in addition to the canonic Tax11–19, for the rational design of immunomodulatory strategies for HTLV-1 chronic diseases.

Persistent CD8 T Cell Marks Caused by the HCMV Infection in Seropositive Adults: Prevalence of HLA-E-Reactive CD8 T Cells

This study investigated the frequency and peptide specificity of long-lasting HCMV-specific CD8 T cells in a cohort of 120 cytomegalovirus seropositive (HCMV+) healthy carriers with the aim of deciphering the relative contribution of unconventional HLA-E- versus conventional HLA-A2-specific CD8 T cells to long-term T cell memory expansion in HCMV immunity. The presence of HCMV-specific CD8 T cells was investigated by flow cytometry using five MHC/peptide tetramer complexes (HLA-A2/pp65, HLA-A2/IE1 and three different HLA-E/UL40). Here, we report that 50% of HCMV+ healthy individuals possess HCMV-specific CD8 T cells, representing ≥0.1% of total blood CD8 T cells years post-infection. Around a third (30.8%) of individuals possess HLA-A2-restricted (A2pp65 or A2IE1) and an equal proportion (27.5%) possess an HLA-E/UL40 CD8 T response. Concomitant HLA-E- and HLA-A2-reactive CD8 T cells were frequently found, and VMAPRTLIL peptide was the major target. The frequency of HLA-E/VMAPRTLIL among total blood CD8 T cells was significantly higher than the frequency of HLA-A2pp65 T cells (mean values: 5.9% versus 2.3%, p = 0.0354). HLA-EUL40 CD8 T cells display lower TCR avidity but similar levels of CD3 and CD8 coreceptors. In conclusion, HLA-E-restricted CD8 T cells against the VMAPRTLIL UL40 peptide constitute a predominant subset among long-lasting anti-HCMV CD8 T cells.

In silico and in vitro arboviral MHC class I-restricted-epitope signatures reveal immunodominance and poor overlapping patterns

INTRODUCTION

The present work sought to identify MHC-I-restricted peptide signatures for arbovirus using in silico and in vitro peptide microarray tools.

METHODS

First, an in-silico analysis of immunogenic epitopes restricted to four of the most prevalent human MHC class-I was performed by identification of MHC affinity score. For that, more than 10,000 peptide sequences from 5 Arbovirus and 8 different viral serotypes, namely Zika (ZIKV), Dengue (DENV serotypes 1-4), Chikungunya (CHIKV), Mayaro (MAYV) and Oropouche (OROV) viruses, in addition to YFV were analyzed. Haplotype HLA-A*02.01 was the dominant human MHC for all arboviruses. Over one thousand HLA-A2 immunogenic peptides were employed to build a comprehensive identity matrix. Intending to assess HLAA*02:01 reactivity of peptides in vitro, a peptide microarray was designed and generated using a dimeric protein containing HLA-A*02:01.

RESULTS

The comprehensive identity matrix allowed the identification of only three overlapping peptides between two or more flavivirus sequences, suggesting poor overlapping of virus-specific immunogenic peptides amongst arborviruses. Global analysis of the fluorescence intensity for peptide-HLA-A*02:01 binding indicated a dose-dependent effect in the array. Considering all assessed arboviruses, the number of DENV-derived peptides with HLA-A*02:01 reactivity was the highest. Furthermore, a lower number of YFV-17DD overlapping peptides presented reactivity when compared to non-overlapping peptides. In addition, the assessment of HLA-A*02:01-reactive peptides across virus polyproteins highlighted non-structural proteins as "hot-spots". Data analysis supported these findings showing the presence of major hydrophobic sites in the final segment of non-structural protein 1 throughout 2a (Ns2a) and in nonstructural proteins 2b (Ns2b), 4a (Ns4a) and 4b (Ns4b).

DISCUSSION

To our knowledge, these results provide the most comprehensive and detailed snapshot of the immunodominant peptide signature for arbovirus with MHC-class I restriction, which may bring insight into the design of future virus-specific vaccines to arboviruses and for vaccination protocols in highly endemic areas.

Identification of HLA class I-restricted immunogenic neoantigens in triple negative breast cancer

Immune checkpoint inhibitor (ICI)-based immunotherapy in triple negative breast cancer (TNBC) is achieving limited therapeutic results, requiring the development of more potent strategies. Combination of ICI with vaccination strategies would enhance antitumor immunity and response rates to ICI in patients having poorly infiltrated tumors. In heavily mutated tumors, neoantigens (neoAgs) resulting from tumor mutations have induced potent responses when used as vaccines. Thus, our aim was the identification of immunogenic neoAgs suitable as vaccines in TNBC patients. By using whole exome sequencing, RNAseq and HLA binding algorithms of tumor samples from a cohort of eight TNBC patients, we identified a median of 60 mutations/patient, which originated a putative median number of 98 HLA class I-restricted neoAgs. Considering a group of 27 predicted neoAgs presented by HLA-A*02:01 allele in two patients, peptide binding to HLA was experimentally confirmed in 63% of them, whereas 55% were immunogenic in vivo in HLA-A*02:01⁺ transgenic mice, inducing T-cells against the mutated but not the wild-type peptide sequence. Vaccination with peptide pools or DNA plasmids expressing these neoAgs induced polyepitopic T-cell responses, which recognized neoAg-expressing tumor cells. These results suggest that TNBC tumors harbor neoAgs potentially useful in therapeutic vaccines, opening the way for new combined immunotherapies.

Antigen-guided depletion of anti-HLA antibody-producing cells by HLA-Fc fusion proteins

Platelet transfusion and transplantation of allogeneic stem cells and solid organs are life-saving therapies. Unwanted alloantibodies to nonself human leukocyte antigens (HLAs) on donor cells increase the immunological barrier to these therapies and are important causes of platelet transfusion refractoriness and graft rejection. Although the specificities of anti-HLA antibodies can be determined at the allelic level, traditional treatments for antibody-mediated rejection nonselectively suppress humoral immunity and are not universally successful. We designed HLA-Fc fusion proteins with a bivalent targeting module derived from extracellular domains of HLA and an Fc effector module from mouse IgG2a. We found that HLA-Fc with A2 (A2Fc) and B7 (B7Fc) antigens lowered HLA-A2- and HLA-B7-specific reactivities, respectively, in sera from HLA-sensitized patients. A2Fc and B7Fc bound to B-cell hybridomas bearing surface immunoglobulins with cognate specificities and triggered antigen-specific and Fc-dependent cytotoxicity in vitro. In immunodeficient mice carrying HLA-A2-specific hybridoma cells, A2Fc treatment lowered circulating anti-HLA-A2 levels, abolished the outgrowth of hybridoma cells, and prolonged survival compared with control groups. In an in vivo anti-HLA-A2-mediated platelet transfusion refractoriness model, A2Fc treatment mitigated refractoriness. These results support HLA-Fc being a novel strategy for antigen-specific humoral suppression to improve transfusion and transplantation outcomes. With the long-term goal of targeting HLA-specific memory B cells for desensitization, further studies of HLA-Fc's efficacy in immune-competent animal models are warranted.

Case report: A persistently expanded T cell response in an exceptional responder to radiation and atezolizumab for metastatic non-small cell lung cancer

Most patients with advanced non-small cell lung cancer (NSCLC) do not achieve a durable remission after treatment with immune checkpoint inhibitors. Here we report the clinical history of an exceptional responder to radiation and anti-program death-ligand 1 (PD-L1) monoclonal antibody, atezolizumab, for metastatic NSCLC who remains in a complete remission more than 8 years after treatment. Sequencing of the patient’s T cell repertoire from a metastatic lesion and the blood before and after anti-PD-L1 treatment revealed oligoclonal T cell expansion. Characterization of the dominant T cell clone, which comprised 10% of all clones and increased 10-fold in the blood post-treatment, revealed an activated CD8⁺ phenotype and reactivity against 4 HLA-A2 restricted neopeptides but not viral or wild-type human peptides, suggesting tumor reactivity. We hypothesize that the patient’s exceptional response to anti-PD-L1 therapy may have been achieved by increased tumor immunogenicity promoted by pre-treatment radiation therapy as well as long-term persistence of oligoclonal expanded circulating T cells.

Liraglutide protects β-cells in novel human islet spheroid models of type 1 diabetes

To enable accurate, high-throughput and longer-term studies of the immunopathogenesis of type 1 diabetes (T1D), we established three in-vitro islet-immune injury models by culturing spheroids derived from primary human islets with proinflammatory cytokines, activated peripheral blood mononuclear cells or HLA-A2-restricted preproinsulin-specific cytotoxic T lymphocytes. In all models, β-cell function declined as manifested by increased basal and decreased glucose-stimulated insulin release (GSIS), and decreased intracellular insulin content. Additional hallmarks of T1D progression such as loss of the first-phase insulin response (FFIR), increased proinsulin-to-insulin ratios, HLA-class I expression, and inflammatory cytokine release were also observed. Using these models, we show that liraglutide, a glucagon-like peptide 1 receptor agonist, prevented loss of GSIS under T1D-relevant stress, by preserving the FFIR and decreasing immune cell infiltration and cytokine secretion. Our results corroborate that liraglutide mediates an anti-inflammatory effect that aids in protecting β-cells from the immune-mediated attack that leads to T1D.

Anti-HLA-A2-CAR Tregs prolong vascularized mouse heterotopic heart allograft survival

Alloantigen-specific regulatory T cell (Treg) therapy is a promising approach for suppressing alloimmune responses and minimizing immunosuppression after solid organ transplantation. Chimeric antigen receptor (CAR) targeting donor alloantigens can confer donor reactivity to Tregs. However, CAR Treg therapy has not been evaluated in vascularized transplant or multi-MHC mismatched models. Here, we evaluated the ability of CAR Tregs targeting HLA-A2 (A2-CAR) to prolong the survival of heterotopic heart transplants in mice. After verifying the in vitro activation, proliferation, and enhanced suppressive function of A2-CAR Tregs in the presence of A2-antigen, we analyzed the in vivo function of Tregs in C57BL/6 (B6) mice receiving A2-expressing heart allografts. A2-CAR Treg infusion increased the median survival of grafts from B6.HLA-A2 transgenic donors from 23 to 99 days, whereas median survival with polyclonal Treg infusion was 35 days. In a more stringent model of haplo-mismatched hearts from BALB/cxB6.HLA-A2 F1 donors, A2-CAR Tregs slightly increased median graft survival from 11 to 14 days, which was further extended to >100 days when combined with a 9-day course of rapamycin treatment. These findings demonstrate the efficacy of CAR Tregs, alone or in combination with immunosuppressive agents, toward protecting vascularized grafts in fully immunocompetent recipients.

Human stem cell derived beta-like cells engineered to present PD-L1 improve transplant survival in NOD mice carrying human HLA class I

There is a critical need for therapeutic approaches that combine renewable sources of replacement beta cells with localized immunomodulation to counter recurrence of autoimmunity in type 1 diabetes (T1D). However, there are few examples of animal models to study such approaches that incorporate spontaneous autoimmunity directed against human beta cells rather than allogenic rejection. Here, we address this critical limitation by demonstrating rejection and survival of transplanted human stem cell-derived beta-like cells clusters (sBCs) in a fully immune competent mouse model with matching human HLA class I and spontaneous diabetes development. We engineered localized immune tolerance toward transplanted sBCs via inducible cell surface overexpression of PD-L1 (iP-sBCs) with and without deletion of all HLA class I surface molecules via beta-2 microglobulin knockout (iP-BKO sBCs). NOD.HLA-A2.1 mice, which lack classical murine MHC I and instead express human HLA-A*02:01, underwent transplantation of 1,000 human HLA-A*02:01 sBCs under the kidney capsule and were separated into HLA-A2 positive iP-sBC and HLA-class I negative iP-BKO sBC groups, each with +/- doxycycline (DOX) induced PD-L1 expression. IVIS imaging showed significantly improved graft survival in mice transplanted with PD-L1 expressing iP-sBC at day 3 post transplantation compared to controls. However, luciferase signal dropped below in vivo detection limits by day 14 for all groups in this aggressive immune competent diabetes model. Nonetheless, histological examination revealed significant numbers of surviving insulin⁺/PD-L1⁺ sBCs cells for DOX-treated mice at day 16 post-transplant despite extensive infiltration with high numbers of CD3⁺ and CD45⁺ immune cells. These results show that T cells rapidly infiltrate and attack sBC grafts in this model but that significant numbers of PD-L1 expressing sBCs manage to survive in this harsh immunological environment. This investigation represents one of the first in vivo studies recapitulating key aspects of human autoimmune diabetes to test immune tolerance approaches with renewable sources of beta cells.

Identification of novel HLA-A0201-restricted T-cell epitopes against thyroid antigens in autoimmune thyroid diseases

PURPOSE

The different mechanisms that trigger the autoimmune attack to the thyroid between Hashimoto's thyroiditis (HT) and Graves' disease (GD) are still unclear. The aim of this study was to recognize thyroid antigens specific CD8+ T-cell epitopes and explore the relationship between these epitopes and thyroid autoantibodies, duration and classification in these two diseases.

METHODS

Free thiiodothyronine, free tetraiodothyronine, thyroid-stimulating hormone, TgAb, and TPOAb were all measured by immunochemiluminometric assays, while TRAb was tested by radioimmunoassay. HLA class I peptide affinity algorithms were applied to predict candidate thyroid autoantigen peptides that blind to HLA-A*0201. The ELISpot assay was used to detect Tg-, TPO-, and TSHR-specific CD8+ T cells.

RESULTS

We demonstrated that TG-6 was a novel HLA-A*0201-restricted CTL epitope in GD. TG-6, TG-7, TG-10, TG-11, and TPO-6 were immunodominant in GD patients compared with HT patients (TG-6: 38.5 vs. 8%, P = 0.034; TG-7, TG-10, TG-11, and TPO-6: 23.1 vs. 0%, P = 0.034). The immunodominance of TG-6 in GD patients was more evident than healthy controls (HC) (TG-6: 35.8 vs. 0%, P = 0.011), but there was no statistically significant difference between HT patients and HC. Subgroup analyses revealed the T-cell responsiveness to TG-6 was stronger in TgAb-negative HT patients (0 vs. 40%, P = 0.033). However, there was no correlation showed for TPOAb, TRAb, medication and duration in both HT and GD patients.

CONCLUSIONS

We report for the first time that both diseases, HT and GD, recognize different antigen-specific CD8-positive T cells. Tg maybe the dominant thyroid autoantigen contributing to breaking tolerance in GD. It could improve our knowledge of autoimmune thyroid diseases pathogenesis as well as offer new therapeutical tools in terms of peptide vaccine therapy.

Immunosuppressive FK506 treatment leads to more frequent EBV-associated lymphoproliferative disease in humanized mice

Post-transplant lymphoproliferative disorder (PTLD) is a potentially fatal complication after organ transplantation frequently associated with the Epstein-Barr virus (EBV). Immunosuppressive treatment is thought to allow the expansion of EBV-infected B cells, which often express all eight oncogenic EBV latent proteins. Here, we assessed whether HLA-A2 transgenic humanized NSG mice treated with the immunosuppressant FK506 could be used to model EBV-PTLD. We found that FK506 treatment of EBV-infected mice led to an elevated viral burden, more frequent tumor formation and diminished EBV-induced T cell responses, indicative of reduced EBV-specific immune control. EBV latency III and lymphoproliferation-associated cellular transcripts were up-regulated in B cells from immunosuppressed animals, akin to the viral and host gene expression pattern found in EBV-PTLD. Utilizing an unbiased gene expression profiling approach, we identified genes differentially expressed in B cells of EBV-infected animals with and without FK506 treatment. Upon investigating the most promising candidates, we validated sCD30 as a marker of uncontrolled EBV proliferation in both humanized mice and in pediatric patients with EBV-PTLD. High levels of sCD30 have been previously associated with EBV-PTLD in patients. As such, we believe that humanized mice can indeed model aspects of EBV-PTLD development and may prove useful for the safety assessment of immunomodulatory therapies.

Immunogenicity of human embryonic stem cell-derived beta cells

AIMS/HYPOTHESIS

To overcome the donor shortage in the treatment of advanced type 1 diabetes by islet transplantation, human embryonic stem cells (hESCs) show great potential as an unlimited alternative source of beta cells. hESCs may have immune privileged properties and it is important to determine whether these properties are preserved in hESC-derived cells.

METHODS

We comprehensively investigated interactions of both innate and adaptive auto- and allo-immunity with hESC-derived pancreatic progenitor cells and hESC-derived endocrine cells, retrieved after in-vivo differentiation in capsules in the subcutis of mice.

RESULTS

We found that hESC-derived pancreatic endodermal cells expressed relatively low levels of HLA endorsing protection from specific immune responses. HLA was upregulated when exposed to IFNγ, making these endocrine progenitor cells vulnerable to cytotoxic T cells and alloreactive antibodies. In vivo-differentiated endocrine cells were protected from complement, but expressed more HLA and were targets for alloreactive antibody-dependent cellular cytotoxicity and alloreactive cytotoxic T cells. After HLA compatibility was provided by transduction with HLA-A2, preproinsulin-specific T cells killed insulin-producing cells.

CONCLUSIONS/INTERPRETATION

hESC-derived pancreatic progenitors are hypoimmunogenic, while in vivo-differentiated endocrine cells represent mature targets for adaptive immune responses. Our data support the need for immune intervention in transplantation of hESC-derived pancreatic progenitors. Cell-impermeable macro-encapsulation may suffice.

Clinically Relevant Reactivation of Polyomavirus BK (BKPyV) in HLA-A02-Positive Renal Transplant Recipients Is Associated with Impaired Effector-Memory Differentiation of BKPyV-Specific CD8+ T Cells

Polyomavirus BK (BKPyV) frequently reactivates in immunosuppressed renal transplant recipients (RTRs) and may lead to graft loss due to BKPyV-induced interstitial nephritis (BKVN). Little is known on the differentiation of CD8⁺ T cells targeting BKPyV in RTRs. Here we investigated whether BKPyV-specific CD8⁺ T cell differentiation differs in RTRs with varying degrees of BKPyV reactivation and/or BKVN.

Using combinatorial encoding with tetramers carrying BKPyV major capsid protein (VP1) and large T antigen protein (LTAG) epitopes, we investigated CD8⁺ T cell responses to BKPyV in longitudinally obtained PBMC samples from 46 HLA-A02-positive RTRs and 20 healthy adults. We were also able to isolate BKPyV-specific CD8⁺ T cells from five renal allografts, two of which were affected by BKVN.

Before transplantation, BKPyV-specific CD8⁺ T cells targeting VP1 and LTAG epitopes appeared predominantly as central-memory and CD27⁺/CD28⁺ effector-memory (T_EM), and naïve-like PD-1-expressing cells, respectively. After viral reactivation, BKPyV-specific CD8⁺ T cells assumed CD28⁻ T_EM and T_EMRA states in patients who were able to control BKPyV, whereas differentiation lagged behind in patients with severe viral reactivation or BKVN. Furthermore, VP1-specific CD69⁺/CD103⁺ tissue-resident memory (T_RM) cells accumulated in BKVN-affected allografts but lacked signs of effector differentiation. In contrast, granzyme B-expressing effector cells were detected in allografts not affected by BKVN.

In conclusion, effector-memory differentiation of BKPyV-specific CD8⁺ T cells in patients with high viral load or BKVN is impaired. Further characterization of the specific mechanisms behind this altered cellular differentiation is necessary to develop therapies that can prevent the emergence of BKVN.

In immunosuppressed renal transplant recipients (RTRs), BKPyV frequently reactivates from latency and may cause severe interstitial nephritis in the allograft (BKVN). Not only is there no effective treatment, it also not understood why BKVN arises in some RTRs but not in all. In the current study we investigated populations of CD8⁺ T cells targeting epitopes from structural and non-structural BKPyV proteins in RTRs over the course of transplantation. In contrast to RTRs who suffered from self-limiting reactivation of BKPyV, patients who developed severe viral reactivation and BKVN were found to have BKPyV-specific CD8⁺ T cells which did not, or less often differentiate into CD28⁻ effector-memory cells during viral reactivation. Moreover, virus-specific CD8⁺ T cell activation and differentiation was not only impaired in the circulation, but possibly also in BKVN-affected renal allografts. In contrast to the CD8⁺ T cells in kidneys from three patients who did not develop BKVN, T cells in two BKVN-affected kidneys did not display typical cytotoxic effector traits. These findings suggest that impaired BKPyV-specific CD8⁺ T cell maturation in response to viral reactivation, possibly owing to inter-individual differences in sensitivity to immunosuppressive medication or to certain viral quasispecies, underlies the emergence of severe viral reactivation and BKVN.

Hepatitis C Virus Subtype 3a Envelope Protein 1 Binding with Human Leukocyte Antigen Class I Types of Pakistani Population: Candidate Epitopes for Synthetic Peptide Vaccine

The object of this cross sectional study was to determine the HCV subtype 3a envelope protein binding affinity with Human Leukocyte Antigen. Envelope 1 (E1) protein is one of the structural proteins responsible for entering the cells through the receptors. The binding affinity of E1 protein epitopes to the selected Human Leukocyte Antigen (HLA) class I alleles was investigated using the computer-based tools. These prediction tools were also used to design the synthetic vaccine's candidate epitopes and to identify the individuals/populations who are likely to be responder to those vaccines.The mean frequency of HLA I antigens in Pakistani population was calculated. Three alleles each from HLA A and B were selected. E1 protein sequence extracted from HCV 3a isolates was retrieved and twenty-four sequences of it were selected. NetMHCcons 1.0 server was used to determine the binding affinities of HLA alleles to the epitope sequences of 10 amino acids in length.A02, A03, A11, A24, A33, B08, B13, B15, B35 and B40 were the first five antigens more prevalent in Pakistan each from HLA A and HLA B.. We did not find any binding affinity between HLA A*201, B*1501 and B*4001 and epitopes from E1 sequences in a threshold of 50 nM. Totally five various epitopes derived from different isolates were characterized.The prediction of HLA-E1 epitope specific bindings and the forthcoming response can be a useful bioinformatics tool to uncover the right synthetic peptides for vaccine design purposes.

[Construction of three HLA-A*0201-peptide tetramers and their preliminary application in detection of vitiligo-specific cytotoxic T lymphocytes]

OBJECTIVE

To construct vitiligo-specific HLA-A*0201-peptide tetramers and to apply the constructed tetramers in detection of vitiligo-specific cytotoxic T lymphocytes (CTL).

METHODS

Proteins HLA-A0201*-BSP and β2M were obtained by effective prokaryotic expression. The purified proteins were refolded with vitiligo antigen peptides MelanA 26-35, gp100 209-217, and tyrosinase 1-9, respectively to form HLA-A*0201-peptide complex. The complex was biotinylated by BirA enzyme and purified by gel-filtration chromatography. The tetramers were generated by mixing the complex with phycoerythrin (PE)-streptavidin at a ratio of 4∶1 and identified by Dot-blot assay. The capacity of tetramer to detect vitiligo-specific CTL was analyzed by flow cytometry.

RESULTS

The biotinylation of vitiligo-specific HLA-A*0201-peptide tetramers were successfully performed by Dot-blot. Flow cytometry analysis indicated that the tetramer effectively bound to specific CTL from peripheral blood of patients with vitiligo.

CONCLUSION

Three kinds of biotinylated vitiligo-specific HLA-A*0201-peptide tetramers have been constructed successfully. The tetramer can detect antigen specific CTL from patients with vitiligo.

Identification and functional studies of HLA-A0201 restricted CTL epitopes in the X protein of hepatitis B virus

Cytotoxic T lymphocyte (CTL) epitopes in the X protein (HBx) of hepatitis B virus (HBV) may play a key role in the viral control and liver damage. The aim of this study was to identify and study the function of HLA-A0201 restricted CTL epitopes in HBx of HBV genotypes B and C that are epidemic in China. Four nonapeptides signed HBx1: VLCLRPVGA, HBx2: CLFKDWEEL, HBx3: VLHKRTLGL, and HBx4: HLSLRGLPV were predicated by computational analysis and manually confirmed by defining the peptide supermotif, extended motif, and quantitative motif. Synthesized peptides were examined for their affinity and binding stability with HLA-A0201. After being analyzed by enzyme-linked immunospot (ELISPOT) and cytolytic activity assays, the HBx2 epitope was selected for a construction of HLA-A0201-peptide tetramers. The tetramer staining method was used to analyze peripheral blood mononuclear cells (PBMCs) isolated from HBV-infected patients at different disease stages (chronic hepatitis, liver cirrhosis, and hepatoma). Compared with CTL epitopes in the HBV envelope or polymerase, HBx2 is also a potential HLA-A0201 restricted CTL epitope, what may have a clinical implication.

Allogeneic HLA-A*02-restricted WT1-specific T cells from mismatched donors are highly reactive but show off-target promiscuity

T cells recognizing tumor-associated Ags such as Wilms tumor protein (WT1) are thought to exert potent antitumor reactivity. However, no consistent high-avidity T cell responses have been demonstrated in vaccination studies with WT1 as target in cancer immunotherapy. The aim of this study was to investigate the possible role of negative thymic selection on the avidity and specificity of T cells directed against self-antigens. T cell clones directed against the HLA-A*0201-binding WT1(126-134) peptide were generated from both HLA-A*02-positive (self-HLA-restricted) and HLA-A*02-negative [nonself (allogeneic) HLA [allo-HLA]-restricted] individuals by direct ex vivo isolation using tetramers or after in vitro priming and selection. The functional avidity and specificity of these T cell clones was analyzed in-depth. Self-HLA-restricted WT1-specific clones only recognized WT1(126-134) with low avidities. In contrast, allo-HLA-restricted WT1 clones exhibited profound functional reactivity against a multitude of HLA-A*02-positive targets, even in the absence of exogenously loaded WT1 peptide, indicative of Ag-binding promiscuity. To characterize this potential promiscuity, reactivity of the T cell clones against 400 randomly selected HLA-A*0201-binding peptides was investigated. The self-HLA-restricted WT1-specific T cell clones only recognized the WT1 peptide. In contrast, the allo-HLA-restricted WT1-reactive clones recognized besides WT1 various other HLA-A*0201-binding peptides. In conclusion, allogeneic HLA-A*02-restricted WT1-specific T cells isolated from mismatched donors may be more tumor-reactive than their autologous counterparts but can show specific off-target promiscuity of potential clinical importance. As a result of this, administration of WT1-specific T cells generated from HLA-mismatched donors should be performed with appropriate precautions against potential off-target effects.

Polyfunctionality of a DKK1 self-antigen-specific CD8(+) T lymphocyte clone in lung cancer

Polyfunctionality is the capacity of a T-cell to execute a variety of effector functions mainly mediated by production of cytokines, chemokines, and cytolytic enzymes. Studies in anti-viral immunity have acknowledged the importance of polyfunctionality in the clearance of infections and maintenance of protection. Although accepted in the field, this concept has not been as well characterized in cancer immunology. Here, we report the polyfunctionality profile analysis of a CD8(+) T-cell clone isolated from a lung cancer patient and directed against Dickkopf-1, a potentially new tumor-associated antigen (TAA). The clone showed Tc1/Th1 effector tendencies confirmed by secretion of cytokines such as IFN-γ, IP-10, MIP-1β, MIP-1α, IL-2, GM-CSF, and expression of cytolytic enzyme granzyme B. This secretion profile is of particular interest in the context of an anti-tumor response. Although secretion of IL-5 and IL-13 was also detected, absence of IL-4 and IL-10 opposes the idea of cytokine-dependent Th1 inhibition. Establishing a comprehensive cytokine secretion profile may help predict T cells' specific response against a novel TAA in a peptide vaccination context. It may further help in selecting clones with an optimal functional profile from the peripheral blood of cancer patients for expansion and adoptive cell transfer therapy.

Tapasin discriminates peptide-human leukocyte antigen-A*02:01 complexes formed with natural ligands

A plethora of peptides are generated intracellularly, and most peptide-human leukocyte antigen (HLA)-I interactions are of a transient, unproductive nature. Without a quality control mechanism, the HLA-I system would be stressed by futile attempts to present peptides not sufficient for the stable peptide-HLA-I complex formation required for long term presentation. Tapasin is thought to be central to this essential quality control, but the underlying mechanisms remain unknown. Here, we report that the N-terminal region of tapasin, Tpn(1-87), assisted folding of peptide-HLA-A*02:01 complexes according to the identity of the peptide. The facilitation was also specific for the identity of the HLA-I heavy chain, where it correlated to established tapasin dependence hierarchies. Two large sets of HLA-A*02:01 binding peptides, one extracted from natural HLA-I ligands from the SYFPEITHI database and one consisting of medium to high affinity non-SYFPEITHI ligands, were studied in the context of HLA-A*02:01 binding and stability. We show that the SYFPEITHI peptides induced more stable HLA-A*02:01 molecules than the other ligands, although affinities were similar. Remarkably, Tpn(1-87) could functionally discriminate the selected SYFPEITHI peptides from the other peptide binders with high sensitivity and specificity. We suggest that this HLA-I- and peptide-specific function, together with the functions exerted by the more C-terminal parts of tapasin, are major features of tapasin-mediated HLA-I quality control. These findings are important for understanding the biogenesis of HLA-I molecules, the selection of presented T-cell epitopes, and the identification of immunogenic targets in both basic research and vaccine design.

Impaired tumor antigen processing by immunoproteasome-expressing CD40-activated B cells and dendritic cells

Professional APCs, such as dendritic cells, are routinely used in vitro for the generation of cytotoxic T lymphocytes specific for tumor antigens. In addition to dendritic cells, CD40-activated B cells and variant K562 leukemic cells can be readily transfected with nucleic acids for in vitro and in vivo antigen presentation. However, the expression of immunoproteasome components in dendritic cells may preclude display of tumor antigens such as Mart1/MelanA. Here, we use three target epitopes, two derived from tumor antigens [Mart1(26-34) (M26) and Cyp1B1(239-247) (Cyp239)] and one derived from the influenza A viral antigen [FluM1(58-66) (FluM58)], to demonstrate that CD40-activated B cells, like dendritic cells, have a limited capability to process certain tumor antigens. In contrast, the K562 HLA-A*0201 transfectant efficiently processes and presents M26 and Cyp239 as well as the influenza FluM58 epitopes to T cells. These results demonstrate that the choice of target APC for gene transfer of tumor antigens may be limited by the relative efficacy of proteasome components to process certain tumor epitopes. Importantly, K562 can be exploited as an artificial APC, efficient in processing both M26 and Cyp239 epitopes and presumably, by extension, other relevant tumor antigens.

An HLA-presented fragment of macrophage migration inhibitory factor is a therapeutic target for invasive breast cancer

This report describes a novel HLA/peptide complex with potential prognostic and therapeutic roles for invasive breast cancer. Macrophage migration inhibitory factor (MIF) mediates inflammation and immunity, and MIF overexpression is observed in breast cancer. We hypothesized that the HLA class I of cancerous breast epithelial cells would present MIF-derived peptides. Consistent with this hypothesis, the peptide FLSELTQQL (MIF(19-27)) was eluted from the HLA-A*0201 (HLA-A2) of breast cancer cell lines. We posited that if this MIF(19-27)/HLA-A2 complex was exclusively found in invasive breast cancer, it could be a useful prognostic indicator. To assess the presentation of MIF peptides by the HLA of various cells and tissues, mice were immunized with the MIF(19-27)/HLA-A2 complex. The resulting mAb (RL21A) stained invasive ductal carcinoma (IDC) but not ductal carcinoma in situ, fibroadenoma, or normal breast tissues. RL21A did not stain WBCs (total WBCs) or normal tissues from deceased HLA-A2 donors, substantiating the tumor-specific nature of this MIF/HLA complex. As this MIF/HLA complex appeared specific to the surface of IDC, RL21A was tested as an immunotherapeutic for breast cancer in vitro and in vivo. In vitro, RL21A killed the MDA-MB-231 cell line via complement and induction of apoptosis. In an in vivo orthotopic mouse model, administration of RL21A reduced MDA-MB-231 and BT-20 tumor burden by 5-fold and by >2-fold, respectively. In summary, HLA-presented MIF peptides show promise as prognostic cell surface indicators for IDC and as targets for immunotherapeutic intervention.

A long peptide from MELOE-1 contains multiple HLA class II T cell epitopes in addition to the HLA-A*0201 epitope: an attractive candidate for melanoma vaccination

CD4(+) T cells contribute importantly to the antitumor T cell response, and thus, long peptides comprising CD4 and CD8 epitopes may be efficient cancer vaccines. We have previously identified an overexpressed antigen in melanoma, MELOE-1, presenting a CD8(+) T cell epitope, MELOE-1(36-44), in the HLA-A*0201 context. A T cell repertoire against this epitope is present in HLA-A*0201+ healthy subjects and melanoma patients and the adjuvant injection of TIL containing MELOE-1 specific CD8(+) T cells to melanoma patients was shown to be beneficial. In this study, we looked for CD4(+) T cell epitopes in the vicinity of the HLA-A*0201 epitope. Stimulation of PBMC from healthy subjects with MELOE-1(26-46) revealed CD4 responses in multiple HLA contexts and by cloning responsive CD4(+) T cells, we identified one HLA-DRβ1*1101-restricted and one HLA-DQβ1*0603-restricted epitope. We showed that the two epitopes could be efficiently presented to CD4(+) T cells by MELOE-1-loaded dendritic cells but not by MELOE-1+ melanoma cell-lines. Finally, we showed that the long peptide MELOE-1(22-46), containing the two optimal class II epitopes and the HLA-A*0201 epitope, was efficiently processed by DC to stimulate CD4(+) and CD8(+) T cell responses in vitro, making it a potential candidate for melanoma vaccination.

Predicting interactions between T cell receptors and MHC-peptide complexes

Conserved interactions between T cell receptors (TCRs) and major histocompatibility complex (MHC) proteins with bound peptide antigens are not well understood. In order to gain a better understanding of the interaction modes of human TCR variable (V) regions, we have performed a structural analysis of the TCRs bound to their MHC-peptide ligands in human, using the available structural models determined by X-ray crystallography. We identified important differences to previous studies in which such interactions were evaluated. Based on the interactions found in the actual experimental structures we developed the first rule-based approach for predicting the ability of TCR residues in the complementarity-determining region (CDR) 1, CDR2, and CDR3 loops to interact with the MHC-peptide antigen complex. Two relatively simple algorithms show good performance under cross validation.

Ipilimumab efficacy and safety in patients with advanced melanoma: a retrospective analysis of HLA subtype from four trials

Ipilimumab is a fully human, monoclonal antibody that blocks cytotoxic T-lymphocyte antigen-4 to potentiate an antitumor T-cell response. This agent improved overall survival in a phase III trial in previously treated patients with advanced melanoma. Because the mechanism of action for ipilimumab is thought to be HLA independent, most trials enrolled patients without regard to HLA subtype. However, enrollment in the phase III trial was restricted to class-I HLA-A*0201-positive patients because two of the three arms contained an HLA-A*0201-restricted gp100 vaccine. HLA typing was also performed prospectively in several phase II trials and was available for 93.5% of patients. In this retrospective analysis, pooled efficacy and safety data are presented according to HLA-A*0201 status and dose from pretreated patients randomized to 0.3, 3, or 10 mg/kg ipilimumab in four phase II trials. Median overall survival (OS) was similar for the 187 HLA-A*0201-positive [9.3 months, 95% CI (confidence interval) 7.4-11.5] and 266 HLA-A*0201-negative patients [11.4 months, 95% CI 9.3-15.1] randomized to ipilimumab at all doses across the four phase II trials. These data are comparable to the OS for the 137 HLA-A*0201-positive patients randomized to ipilimumab in the phase III study [10.1 months, 95% CI 8.0-13.8]. Ipilimumab-induced adverse events and immune-related adverse events (skin, gastrointestinal, hepatic, other) also occurred at similar frequencies among patients in the phase II and III trials, regardless of HLA-A*0201 status. These findings support the hypothesis that ipilimumab-treated patients with advanced melanoma have similar outcomes regardless of their HLA-A*0201 status.

Peptide microarrays for the profiling of cytotoxic T-lymphocyte activity using minimum numbers of cells

The identification of epitopes that elicit cytotoxic T-lymphocyte activity is a prerequisite for the development of cancer-specific immunotherapies. However, especially the parallel characterization of several epitopes is limited by the availability of T cells. Microarrays have enabled an unprecedented miniaturization and parallelization in biological assays. Here, we developed peptide microarrays for the detection of CTL activity. MHC class I-binding peptide epitopes were pipetted onto polymer-coated glass slides. Target cells, loaded with the cell-impermeant dye calcein, were incubated on these arrays, followed by incubation with antigen-expanded CTLs. Cytotoxic activity was detected by release of calcein and detachment of target cells. With only 200,000 cells per microarray, CTLs could be detected at a frequency of 0.5% corresponding to 1,000 antigen-specific T cells. Target cells and CTLs only settled on peptide spots enabling a clear separation of individual epitopes. Even though no physical boundaries were present between the individual spots, peptide loading only occurred locally and cytolytic activity was confined to the spots carrying the specific epitope. The peptide microarrays provide a robust platform that implements the whole process from antigen presentation to the detection of CTL activity in a miniaturized format. The method surpasses all established methods in the minimum numbers of cells required. With antigen uptake occurring on the microarray, further applications are foreseen in the testing of antigen precursors that require uptake and processing prior to presentation.

Structures of native and affinity-enhanced WT1 epitopes bound to HLA-A*0201: implications for WT1-based cancer therapeutics

Presentation of peptides by class I or class II major histocompatibility complex (MHC) molecules is required for the initiation and propagation of a T cell-mediated immune response. Peptides from the Wilms Tumor 1 transcription factor (WT1), upregulated in many hematopoetic and solid tumors, can be recognized by T cells and numerous efforts are underway to engineer WT1-based cancer vaccines. Here we determined the structures of the class I MHC molecule HLA-A*0201 bound to the native 126-134 epitope of the WT1 peptide and a recently described variant (R1Y) with improved MHC binding. The R1Y variant, a potential vaccine candidate, alters the positions of MHC charged side chains near the peptide N-terminus and significantly reduces the peptide/MHC electrostatic surface potential. These alterations indicate that the R1Y variant is an imperfect mimic of the native WT1 peptide, and suggest caution in its use as a therapeutic vaccine. Stability measurements revealed how the R1Y substitution enhances MHC binding affinity, and together with the structures suggest a strategy for engineering WT1 variants with improved MHC binding that retain the structural features of the native peptide/MHC complex.

Generation of robust CD8+ T-cell responses against subdominant epitopes in conserved regions of HIV-1 by repertoire mining with mimotopes

HLA-A 0201-restricted virus-specific CD8(+) CTL do not appear to control HIV effectively in vivo. To enhance the immunogenicity of a highly conserved subdominant epitope, TV9 (TLNAWVKVV, p24 Gag(19-27)), mimotopes were designed by screening a large combinatorial nonapeptide library with TV9-specific CTL primed in vitro from healthy donors. A mimic peptide with a low binding affinity to HLA-A 0201, TV9p6 (KINAWIKVV), was studied further. Parallel cultures of in vitro-primed CTL showed that TV9p6 consistently activated cross-reactive and equally functional CTL as measured by cytotoxicity, cytokine production and suppression of HIV replication in vitro. Comparison of TCRB gene usage between CTL primed from the same donors with TV9 or TV9p6 revealed a degree of clonal overlap in some cases and an example of a conserved TCRB sequence encoded distinctly at the nucleotide level between individuals (a "public" TCR); however, in the main, distinct clonotypes were recruited by each peptide antigen. These findings indicate that mimotopes can mobilize functional cross-reactive clonotypes that are less readily recruited from the naïve T-cell pool by the corresponding WT epitope. Mimotope-induced repertoire diversification could potentially override subdominance under certain circumstances and enhance vaccine-induced responses to conserved but poorly immunogenic determinants within the HIV proteome.

Cytotoxic T lymphocyte epitopes from human heparanase can elicit a potent anti-tumor immune response in mice

Heparanase is expressed in almost all advanced tumors, and therefore it may serve as a potential target for tumor therapy. Our previous study has shown that heparanase can serve as a potential universal tumor-associated antigen (TAA) for the immunotherapy of advanced tumors. Further study demonstrated that the HLA-A*0201-restricted Cytotoxic T lymphocytes (CTL) epitopes Hpa525 (PAFSYSFFV), Hpa277 (KMLKSFLKA) and Hpa405 (WLSLLFKKL) from human heparanase could induce a potent anti-tumor immune response in vitro. The present study was designed to investigate whether the above peptides could induce immune responses in mice. Our results demonstrated that the effectors from heparanase peptide-immunized mice could effectively lyse various tumor cells that were heparanase positive and HLA-A*0201 matched. We also found that these peptide-specific CTLs did not lyse autologous lymphocytes that had low heparanase activity. Further study revealed that Hpa525, Hpa277, and Hpa405 peptides increased the frequency of IFN-gamma-producing T cells as compared to a negative peptide. These results suggest that Hpa525, Hpa277, and Hpa405 peptides are novel HLA-A*0201-restricted CTL epitopes capable of inducing heparanase-specific CTLs in mice. Because heparanase is expressed in most advanced malignant tumors, Hpa525, Hpa277, and Hpa405 peptide-based vaccines may be useful for the immunotherapy of patients with advanced tumors.

A novel cancer vaccine strategy based on HLA-A*0201 matched allogeneic plasmacytoid dendritic cells

Background

The development of effective cancer vaccines still remains a challenge. Despite the crucial role of plasmacytoid dendritic cells (pDCs) in anti-tumor responses, their therapeutic potential has not yet been worked out. We explored the relevance of HLA-A*0201 matched allogeneic pDCs as vectors for immunotherapy.

Methods and Findings

Stimulation of PBMC from HLA-A*0201⁺ donors by HLA-A*0201 matched allogeneic pDCs pulsed with tumor-derived peptides triggered high levels of antigen-specific and functional cytotoxic T cell responses (up to 98% tetramer⁺ CD8 T cells). The pDC vaccine demonstrated strong anti-tumor therapeutic in vivo efficacy as shown by the inhibition of tumor growth in a humanized mouse model. It also elicited highly functional tumor-specific T cells ex-vivo from PBMC and TIL of stage I-IV melanoma patients. Responses against MelA, GP100, tyrosinase and MAGE-3 antigens reached tetramer levels up to 62%, 24%, 85% and 4.3% respectively. pDC vaccine-primed T cells specifically killed patients' own autologous melanoma tumor cells. This semi-allogeneic pDC vaccine was more effective than conventional myeloid DC-based vaccines. Furthermore, the pDC vaccine design endows it with a strong potential for clinical application in cancer treatment.

Conclusions

These findings highlight HLA-A*0201 matched allogeneic pDCs as potent inducers of tumor immunity and provide a promising immunotherapeutic strategy to fight cancer.

Identification and characterization of a HER-2/neu epitope as a potential target for cancer immunotherapy

Our aim is to develop peptide vaccines that stimulate tumor antigen-specific T-lymphocyte responses against frequently detected cancers. We describe herein a novel HLA-A*0201-restricted epitope, encompassing amino acids 828-836 (residues QIAKGMSYL), which is naturally presented by various HER-2/neu (+) tumor cell lines. HER-2/neu(828-836), [HER-2(9(828))], possesses two anchor residues and stabilized HLA-A*0201 on T2 cells in a concentration-dependent Class I binding assay. This peptide was stable for 3.5 h in an off-kinetic assay. HER-2(9(828)) was found to be immunogenic in HLA-A*0201 transgenic (HHD) mice inducing peptide-specific and functionally potent CTL and long-lasting anti-tumor immunity. Most important, using HLA-A*0201 pentamer analysis we could detect increased ex vivo frequencies of CD8(+) T-lymphocytes specifically recognizing HER-2(9(828)) in 8 out of 20 HLA-A*0201(+) HER-2/neu (+) breast cancer patients. Moreover, HER-2(9(828))-specific human CTL recognized the tumor cell line SKOV3.A2 as well as the primary RS.A2.1.DR1 tumor cell line both expressing HER-2/neu and HLA-A*0201. Finally, therapeutic vaccination with HER-2(9(828)) in HHD mice was proven effective against established transplantable ALC.A2.1.HER tumors, inducing complete tumor regression in 50% of mice. Our data encourage further exploitation of HER-2(9(828)) as a promising candidate for peptide-based cancer vaccines.

[Application of HLA-A*0201/WT1 pentamer combined with intracellular IFNgamma+ staining in detecting circulating WT1 specific T cells in leukemia]

This study was purposed to investigate the value of combination of pentamer and intracellular IFNgamma staining in the qualitative and quantitative detection of circulating antigen-specific T cells. WT1 expressions in 14 HLA-A*0201+ patients and their matched donors were detected by RT-PCR, and circulating WT1 specific T cells were assayed by HLA-A*0201/WT1 pentamer combined with intracellular IFNgamma+ staining. The results showed that the low level of WT1 expression was found only in 2 cases out of 14 donors, but different levels of WT1 expression could be observed in all leukemic patients. The WT1+CD8+ CTL and WT1+IFNgamma+ cells did not detected in all 14 donors, but WT1+CD8+ CTL cells in 2 patients and WT1+IFNgamma+ cells in 3 patients could be detected before transplantation respectively, there was no significant difference between them, while the WT1+CD8+ CTL cells and WT1+IFNgamma+ cells both could be detected in all 14 patients after transplantation, the positive detection rate after transplantation was obviously higher than that before transplantation. The WT1+CD8+ and WT1+ IFNgamma+ cells could be detected within 30 days after transplantation, but the positive detection rate of WT1+IFNgamma+ cells was higher than that of WT1+CD8+ CTL cells (p=0.014). The median peak value of WT1+CD8+ CTL cells was 0.18% in 14 patients, and the median peak value of WT1+IFNgamma+ cells was 0.83% in 14 patients, the later was significantly higher than former. The median peak time of WT1+CD8+ CTL cells was 75 days after transplantation, while the WT1+IFNgamma+ cells was 105 days after transplantation, there was no significant difference between them. It is concluded that pentamer and intracellular IFNgamma staining may effectively detect circulating WT1 specific T cells in leukemic patients, and the combination of these two methods profit to the exact qualitation and quantitation of circulating antigen-specific T cells.

A novel HLA (HLA-A*0201) transgenic rabbit model for preclinical evaluation of human CD8+ T cell epitope-based vaccines against ocular herpes

We introduced a novel humanized HLA-A*0201 transgenic (HLA Tg) rabbit model to assess the protective efficacy of a human CD8(+) T cell epitope-based vaccine against primary ocular herpes infection and disease. Each of the three immunodominant human CD8(+) T cell peptide epitopes from HSV-1 glycoprotein D (gD(53-61), gD(70-78), and gD(278-286)) were joined with a promiscuous human CD4(+) T cell peptide epitope (gD(49-82)) to construct three separate pairs of CD4-CD8 peptides. Each CD4-CD8 peptide pair was then covalently linked to an N(epsilon)-palmitoyl-lysine residue via a functional base lysine amino group to construct CD4-CD8 lipopeptides. HLA Tg rabbits were immunized s.c. with a mixture of the three CD4-CD8 HSV-1 gD lipopeptides. The HSV-gD-specific T cell responses induced by the mixture of CD4-CD8 lipopeptide vaccine and the protective efficacy against acute virus replication and ocular disease were determined. Immunization induced HSV-gD(49-82)-specific CD4(+) T cells in draining lymph node (DLN); induced HLA-restricted HSV-gD(53-61), gD(70-78), and gD(278-286)-specific CD8(+) T cells in DLN, conjunctiva, and trigeminal ganglia and reduced HSV-1 replication in tears and corneal eye disease after ocular HSV-1 challenge. In addition, the HSV-1 epitope-specific CD8(+) T cells induced in DLNs, conjunctiva, and the trigeminal ganglia were inversely proportional with corneal disease. The humanized HLA Tg rabbits appeared to be a useful preclinical animal model for investigating the immunogenicity and protective efficacy of human CD8(+) T cell epitope-based prophylactic vaccines against ocular herpes. The relevance of HLA Tg rabbits for future investigation of human CD4-CD8 epitope-based therapeutic vaccines against recurrent HSV-1 is discussed.

Immunoproteasome LMP2 60HH variant alters MBP epitope generation and reduces the risk to develop multiple sclerosis in Italian female population

Background

Albeit several studies pointed out the pivotal role that CD4+T cells have in Multiple Sclerosis, the CD8+ T cells involvement in the pathology is still in its early phases of investigation. Proteasome degradation is the key step in the production of MHC class I-restricted epitopes and therefore its activity could be an important element in the activation and regulation of autoreactive CD8+ T cells in Multiple Sclerosis.

Methodology/Principal Findings

Immunoproteasomes and PA28-αβ regulator are present in MS affected brain area and accumulated in plaques. They are expressed in cell types supposed to be involved in MS development such as neurons, endothelial cells, oligodendrocytes, macrophages/macroglia and lymphocytes. Furthermore, in a genetic study on 1262 Italian MS cases and 845 controls we observed that HLA-A*02+ female subjects carrying the immunoproteasome LMP2 codon 60HH variant have a reduced risk to develop MS. Accordingly, immunoproteasomes carrying the LMP2 60H allele produce in vitro a lower amount of the HLA-A*0201 restricted immunodominant epitope MBP_111–119.

Conclusion/Significance

The immunoproteasome LMP2 60HH variant reduces the risk to develop MS amongst Italian HLA-A*02+ females. We propose that such an effect is mediated by the altered proteasome-dependent production of a specific MBP epitope presented on the MHC class I. Our observations thereby support the hypothesis of an involvement of immunoproteasome in the MS pathogenesis.

Diverse patterns of T-cell response against multiple newly identified human Y chromosome-encoded minor histocompatibility epitopes

PURPOSE

Donor T cells respond to minor histocompatibility antigens (mHA), resulting in both graft-versus-host disease and graft versus leukemia after allogeneic hematopoietic stem cell transplantation. Because relatively few mHAs are known, we developed a new approach to predict and subsequently validate candidate mHA.

EXPERIMENTAL DESIGN

We developed an algorithm based on genetic disparities between Y chromosome-encoded and X chromosome-encoded proteins and known requirements for binding to HLA class I molecules to predict Y chromosome-derived, HLA A*0201-restricted peptides (HY) and ranked peptides based on potential immunogenicity. We evaluated T-cell responses to 41 candidate peptides in 28 male recipients with female donors (FM), 22 male recipients with male donors (MM), and 26 normal individuals. All patients and donors were HLA A*0201 positive.

RESULTS

Thirteen peptides derived from five proteins elicited significantly greater T-cell responses in FM patients compared with MM patients and in normal females compared with normal males. Six peptides were more immunogenic than the only previously known HLA A*0201-restricted Y-encoded mHA. Twenty-seven of 28 FM patients responded to at least one HY peptide, but despite a common Y chromosome mismatch and expression of HLA A*0201, each patient responded to a unique set of peptides.

CONCLUSIONS

Novel HLA A*0201-restricted HY epitopes can be predicted and validated in patients after allogeneic hematopoietic stem cell transplantation. Highly diverse patterns of T-cell response against these epitopes have been identified. Prospective monitoring of responses to large panels of immunogenic peptides can facilitate the identification of clinically relevant targets of graft-versus-host disease and graft versus leukemia.

Cytomegalovirus-specific CD8(+) T cells targeting different HLA/peptide combinations correlate with protection but at different threshold frequencies

Cytomegalovirus (CMV) causes significant morbidity and mortality in patients after haematopoietic stem cell transplantation (HSCT). Due to limitations of current antiviral therapies, alternative approaches, involving transfer of donor-derived CMV-specific CD8(+) T cells, have been considered. Levels of such cells correlating with protection against CMV infection and disease have only been reported in patients expressing HLA-A*0201 and HLA-B*0702. This is despite an increasing number of reports describing cells targeting CMV peptides presented by other human leucocyte antigens (HLAs). Considering several frequent HLA alleles, our findings suggest that HLA-A*2402/pp65 (341-349)- and HLA-B*3501/pp65 (123-131)-specific CD8+ T cells correlate with protection from CMV reactivation at significantly lower cell levels than HLA-A*0101/pp50 (245-253)- and HLAA* 0201/pp65 (495-503)-specific CD8+ T cells, both in HSCT recipients posttransplant and in healthy CMV seropositive volunteers. This may result from a differing efficiency of the responses restricted by the two sets of HLA alleles. These findings add to the knowledge of immunodominance and differences in antigen processing that are coordinated in individuals with different HLA alleles and have direct implications for therapy and monitoring in patients.