IL-12 controls cytotoxicity of a novel subset of self-antigen-specific human CD28+ cytolytic T cells

The Era of Cytotoxic CD4 T Cells

In 1986, Mosmann and Coffman identified 2 functionally distinct subsets of activated CD4 T cells, Th1 and Th2 cells, being key in distinct T cell mediated responses. Over the past three decades, our understanding of CD4 T cell differentiation has expanded and the initial paradigm of a dichotomic CD4 T cell family has been revisited to accommodate a constantly growing number of functionally distinct CD4 T helper and regulatory subpopulations. Of note, CD4 T cells with cytotoxic functions have also been described, initially in viral infections, autoimmune disorders and more recently also in cancer settings. Here, we provide an historical overview on the discovery and characterization of cytotoxic CD4 T cells, followed by a description of their mechanisms of cytotoxicity. We emphasize the relevance of these cells in disease conditions, particularly in cancer, and we provide insights on how to exploit these cells in immunotherapy.

Tumor-specific cytolytic CD4 T cells mediate immunity against human cancer

CD4 T cells have been implicated in cancer immunity for their helper functions. Moreover, their direct cytotoxic potential has been shown in some patients with cancer. Here, by mining single-cell RNA-seq datasets, we identified CD4 T cell clusters displaying cytotoxic phenotypes in different human cancers, resembling CD8 T cell profiles. Using the peptide-MHCII-multimer technology, we confirmed ex vivo the presence of cytolytic tumor-specific CD4 T cells. We performed an integrated phenotypic and functional characterization of these cells, down to the single-cell level, through a high-throughput nanobiochip consisting of massive arrays of picowells and machine learning. We demonstrated a direct, contact-, and granzyme-dependent cytotoxic activity against tumors, with delayed kinetics compared to classical cytotoxic lymphocytes. Last, we found that this cytotoxic activity was in part dependent on SLAMF7. Agonistic engagement of SLAMF7 enhanced cytotoxicity of tumor-specific CD4 T cells, suggesting that targeting these cells might prove synergistic with other cancer immunotherapies.

Quantitative TCR:pMHC Dissociation Rate Assessment by NTAmers Reveals Antimelanoma T Cell Repertoires Enriched for High Functional Competence

Experimental models demonstrated that therapeutic induction of CD8 T cell responses may offer protection against tumors or infectious diseases providing that T cells have sufficiently high TCR/CD8:pMHC avidity for efficient Ag recognition and consequently strong immune functions. However, comprehensive characterization of TCR/CD8:pMHC avidity in clinically relevant situations has remained elusive. In this study, using the novel NTA-His tag-containing multimer technology, we quantified the TCR:pMHC dissociation rates (koff) of tumor-specific vaccine-induced CD8 T cell clones (n = 139) derived from seven melanoma patients vaccinated with IFA, CpG, and the native/EAA or analog/ELA Melan-A(MART-1)(26-35) peptide, binding with low or high affinity to MHC, respectively. We observed substantial correlations between koff and Ca(2+) mobilization (p = 0.016) and target cell recognition (p < 0.0001), with the latter independently of the T cell differentiation state. Our strategy was successful in demonstrating that the type of peptide impacted on TCR/CD8:pMHC avidity, as tumor-reactive T cell clones derived from patients vaccinated with the low-affinity (native) peptide expressed slower koff rates than those derived from patients vaccinated with the high-affinity (analog) peptide (p < 0.0001). Furthermore, we observed that the low-affinity peptide promoted the selective differentiation of tumor-specific T cells bearing TCRs with high TCR/CD8:pMHC avidity (p < 0.0001). Altogether, TCR:pMHC interaction kinetics correlated strongly with T cell functions. Our study demonstrates the feasibility and usefulness of TCR/CD8:pMHC avidity assessment by NTA-His tag-containing multimers of naturally occurring polyclonal T cell responses, which represents a strong asset for the development of immunotherapy.

Expression of cytolytic protein-perforin in peripheral blood lymphocytes in severe traumatic brain injured patients

PURPOSE

The purpose of this study was to investigate the changes of cytotoxic protein-perforin in peripheral blood lymphocytes in severe TBI patients and possible correlation between severity of TBI and perforin expression.

METHODS

Flow cytometry was used for simultaneous detection of intracellular perforin and cell surface antigens of peripheral blood lymphocytes of 20 severe TBI patients on day 1, 4 and 7 after the onset of injury. Peripheral blood mononuclear cells from 20 healthy volunteers were used as control. Clinical and laboratory parameters were also recorded.

RESULTS

There was a statistically significant decrease of perforin-positive lymphocytes including T, natural killer (NK) and NKT cells on day 4 as compared with day 1 after the brain injury or healthy controls. On day 7, perforin expression was restored in lymphocyte of cytotoxic phenotype (CD8(+) T lymphocytes, NK cells, and NKT cells) compared with day 1. High positive correlation was found between the severity of TBI and frequency of perforin-positive cells on day 4 when the occurrence of the intra-hospital infections was the highest.

CONCLUSION

Severe TBI significantly decreases perforin expression in T lymphocytes, NK and NKT cells, which indicate a possible mechanism underlying the high susceptibility to infections.

The three main stumbling blocks for anticancer T cells

Memory and effector T cells have the potential to counteract cancer progression, but often fail to control the disease, essentially because of three main stumbling blocks. First, clonal deletion leads to relatively low numbers or low-to-intermediate T cell receptor (TCR) affinity of self/tumor-specific T cells. Second, the poor innate immune stimulation by solid tumors is responsible for inefficient priming and boosting. Third, T cells are suppressed in the tumor microenvironment by inhibitory signals from other immune cells, stroma and tumor cells, which induces T cell exhaustion, as demonstrated in metastases of melanoma patients. State-of-the-art adoptive cell transfer and active immunotherapy can partially overcome the three stumbling blocks. The reversibility of T cell exhaustion and novel molecular insights provide the basis for further improvements of clinical immunotherapy.

Different perforin expression in peripheral blood and prostate tissue in patients with benign prostatic hyperplasia and prostate cancer

Perforin (P) is a prototypical cytotoxic molecule involved in cell-mediated immunity against various pathogens, alloantigens and particularly different tumours. The purpose of this study was to determine P expression in different lymphocyte subpopulations isolated from peripheral blood and prostate tissue of patients with benign prostatic hyperplasia (BPH) and prostate cancer (PCa) and compare it with the P expression found in the control group. Twenty subjects were recruited in each of the groups. Prostate mononuclear cells of the BPH and PCa tissues were isolated by enzymatic digestion and gradient density centrifugation, whereas peripheral blood mononuclear cells were isolated by gradient density centrifugation alone. Cells and tissue samples were labelled using monoclonal antibodies against P and different surface antigens (CD3, CD4, CD8 and CD56) and analysed by immunofluorescence and flow cytometry. Total P expression in peripheral blood lymphocytes did not differ significantly between BPH/PCa patients and control group, although the BPH and PCa tissue showed lower P expression level. A negative correlation between prostate-specific antigen levels and the overall percentage of P(+), CD3(+) CD56(-) P(+) , and CD3(-) CD56(+) P(+) cells in the prostate tissue was observed only in patients with PCa. Our findings indicate that the low frequency of P(+) lymphocytes, including T, NKT and NK cells, in the prostate tissue of patients with BPH and, particularly, PCa could be the consequence of local tissue microenvironment and one of the mechanisms involved in the pathogenesis of prostate hyperplasia following malignant alteration.

Single cell analysis reveals similar functional competence of dominant and nondominant CD8 T-cell clonotypes

Immune protection from infectious diseases and cancer is mediated by individual T cells of different clonal origin. Their functions are tightly regulated but not yet fully characterized. Understanding the contribution of each T cell will improve the prediction of immune protection based on laboratory assessment of T-cell responses. Here we developed techniques for simultaneous molecular and functional assessment of single CD8 T cells directly ex vivo. We studied two groups of patients with melanoma after vaccination with two closely related tumor antigenic peptides. Vaccination induced T cells with strong memory and effector functions, as found in virtually all T cells of the first patient group, and fractions of T cells in the second group. Interestingly, high functionality was not restricted to dominant clonotypes. Rather, dominant and nondominant clonotypes acquired equal functional competence. In parallel, this was also found for EBV- and CMV-specific T cells. Thus, the nondominant clonotypes may contribute similarly to immunity as their dominant counterparts.

Exhaustion of tumor-specific CD8⁺ T cells in metastases from melanoma patients

In chronic viral infections, CD8⁺ T cells become functionally deficient and display multiple molecular alterations. In contrast, only little is known of self- and tumor-specific CD8⁺ T cells from mice and humans. Here we determined molecular profiles of tumor-specific CD8⁺ T cells from melanoma patients. In peripheral blood from patients vaccinated with CpG and the melanoma antigen Melan-A/MART-1 peptide, we found functional effector T cell populations, with only small but nevertheless significant differences in T cells specific for persistent herpesviruses (EBV and CMV). In contrast, Melan-A/MART-1-specific T cells isolated from metastases from patients with melanoma expressed a large variety of genes associated with T cell exhaustion. The identified exhaustion profile revealed extended molecular alterations. Our data demonstrate a remarkable coexistence of effector cells in circulation and exhausted cells in the tumor environment. Functional T cell impairment is mediated by inhibitory receptors and further molecular pathways, which represent potential targets for cancer therapy.

Profile of a serial killer: cellular and molecular approaches to study individual cytotoxic T-cells following therapeutic vaccination

T-cell vaccination may prevent or treat cancer and infectious diseases, but further progress is required to increase clinical efficacy. Step-by-step improvements of T-cell vaccination in phase I/II clinical studies combined with very detailed analysis of T-cell responses at the single cell level are the strategy of choice for the identification of the most promising vaccine candidates for testing in subsequent large-scale phase III clinical trials. Major aims are to fully identify the most efficient T-cells in anticancer therapy, to characterize their TCRs, and to pinpoint the mechanisms of T-cell recruitment and function in well-defined clinical situations. Here we discuss novel strategies for the assessment of human T-cell responses, revealing in part unprecedented insight into T-cell biology and novel structural principles that govern TCR-pMHC recognition. Together, the described approaches advance our knowledge of T-cell mediated-protection from human diseases.

Novel soluble HLA-A2/MELAN-A complexes selectively stain a differentiation defective subpopulation of CD8+ T cells in patients with melanoma

Multimeric MHC I-peptide complexes containing phycoerythrin-streptavidin are widely used to detect and investigate antigen-specific CD8+ (and CD4+) T cells. Because such reagents are heterogeneous, we compared their binding characteristics with those of monodisperse dimeric, tetrameric and octameric complexes containing linkers of variable length and flexibility on Melan-A-specific CD8+ T cell clones and peripheral blood mononuclear cells (PBMC) from HLA-A*0201(+) melanoma patients. Striking binding differences were observed for different defined A2/Melan-A(26-35) complexes on T cells depending on their differentiation stage. In particular, short dimeric but not octameric A2/Melan-A(26-35) complexes selectively and avidly stained incompletely differentiated effector-memory T cells clones and populations expressing CD27 and CD28 and low levels of cytolytic mediators (granzymes and perforin). This subpopulation was found in PBMC from all six melanoma patients analyzed and proliferated on peptide stimulation with only modest phenotypic changes. By contrast influenza matrix(58-66) -specific CD8+ PBMC from nine HLA-A*0201(+) healthy donors were efficiently stained by A2/Flu matrix(58-61) multimers, but not dimer and upon peptide stimulation proliferated and differentiated from memory into effector T cells. Thus PBMC from melanoma patients contain a differentiation defective sub-population of Melan-A-specific CD8+ T cells that can be selectively and efficiently stained by short dimeric A2/Melan- A(26-35) complexes, which makes them directly accessible for longitudinal monitoring and further investigation.

Evidence for a TCR affinity threshold delimiting maximal CD8 T cell function

Protective adaptive immune responses rely on TCR-mediated recognition of Ag-derived peptides presented by self-MHC molecules. However, self-Ag (tumor)-specific TCRs are often of too low affinity to achieve best functionality. To precisely assess the relationship between TCR-peptide-MHC binding parameters and T cell function, we tested a panel of sequence-optimized HLA-A(*)0201/NY-ESO-1(157-165)-specific TCR variants with affinities lying within physiological boundaries to preserve antigenic specificity and avoid cross-reactivity, as well as two outliers (i.e., a very high- and a low-affinity TCR). Primary human CD8 T cells transduced with these TCRs demonstrated robust correlations between binding measurements of TCR affinity and avidity and the biological response of the T cells, such as TCR cell-surface clustering, intracellular signaling, proliferation, and target cell lysis. Strikingly, above a defined TCR-peptide-MHC affinity threshold (K(D) < approximately 5 muM), T cell function could not be further enhanced, revealing a plateau of maximal T cell function, compatible with the notion that multiple TCRs with slightly different affinities participate equally (codominantly) in immune responses. We propose that rational design of improved self-specific TCRs may not need to be optimized beyond a given affinity threshold to achieve both optimal T cell function and avoidance of the unpredictable risk of cross-reactivity.

Fine structural variations of alphabetaTCRs selected by vaccination with natural versus altered self-antigen in melanoma patients

Immunotherapy of cancer is often performed with altered "analog" peptide Ags optimized for HLA class I binding, resulting in enhanced immunogenicity, but the induced T cell responses require further evaluation. Recently, we demonstrated fine specificity differences and enhanced recognition of naturally presented Ag by T cells after vaccination with natural Melan-A/MART-1 peptide, as compared with analog peptide. In this study, we compared the TCR primary structures of 1489 HLA-A*0201/Melan-A(26-35)-specific CD8 T cells derived from both cohorts of patients. Although a strong preference for TRAV12-2 segment usage was present in nearly all patients, usage of particular TRAJ gene segments and CDR3alpha composition differed slightly after vaccination with natural vs analog peptide. Moreover, TCR beta-chain repertoires were broader after natural than analog peptide vaccination. In all patients, we observed a marked conservation of the CDR3beta amino acid composition with recurrent sequences centered on a glycyl-leucyl/valyl/alanyl-glycyl motif. In contrast to viral-specific TCR repertoires, such "public" motifs were primarily expressed by nondominant T cell clonotypes, which contrasted with "private" CDR3beta signatures frequently found in T cell clonotypes that dominated repertoires of individual patients. Interestingly, no differences in functional avidity were observed between public and private T cell clonotypes. Collectively, our data indicate that T cell repertoires generated against natural or analog Melan-A peptide exhibited slightly distinct but otherwise overlapping and structurally conserved TCR features, suggesting that the differences in binding affinity/avidity of TCRs toward pMHC observed in the two cohorts of patients are caused by subtle structural TCR variations.

Enhancement of cytotoxic T-lymphocyte response in aged mice by a novel treatment with recombinant AdIL-12 and wild-type adenovirus in rapid succession

A decrease in the expression of Th1 cytokines has been associated with age-related decrease in cytotoxic T-lymphocyte (CTL) function. We utilized an E1-deleted adenovirus (Ad) vector to deliver the murine interleukin-12 (IL-12) gene in order to enhance the antivirus CTL response. Wild-type (WT) Ad was administered 3 days after AdIL-12 treatment, when IL-12 production was at its peak and the anti-Ad antibody response had not yet begun to develop. Before receiving AdIL-12 treatment, aged (18 month old) mice exhibited a 58% decrease in the number of virus-specific CTLs, and a 30% decrease in in vivo CTL activity as compared to young (2 month old) mice. After AdIL-12 treatment, aged mice displayed a greater increase in IL-12 expression and endogenous production of interferon-gamma than observed in young mice. When infected with WT Ad, these AdIL-12-treated aged mice exhibited an increased in vivo CTL response and an in vitro proliferative response that was similar to those in young mice. The frequencies of occurrence of D(b)-E1Bp(+)CD8(+) T cells in the spleen, liver, and lung in aged mice were higher than the corresponding values in young mice. These results indicate that IL-12 treatment significantly promotes the virus-specific CTL response in aged mice and, more importantly, specifically targets the virally infected organs, such as the liver and lung, promoting enhanced CTL activity against the virus.

pConsensus peptide induces tolerogenic CD8+ T cells in lupus-prone (NZB x NZW)F1 mice by differentially regulating Foxp3 and PD1 molecules

Systemic lupus erythematosus is an autoimmune disease caused primarily by autoantibodies (including IgG anti-DNA) and immune complexes that cause tissue damage. After tolerization with an artificial peptide (pConsensus, pCons) based on murine anti-DNA IgG sequences containing MHC class I and class II T cell determinants, lupus-prone (NZB x NZW)F(1) female (BWF(1)) mice develop regulatory CD4+CD25+ T cells and inhibitory CD8+ T cells, both of which suppress anti-DNA Ig production and immune glomerulonephritis. In the present work, we show that splenocytes from BWF(1) mice treated with pCons had significant expansion of primarily CD8+ T cells. CD4+ T cells and B cells were each directly suppressed by CD8+ T cells from tolerized mice in a contact-independent manner. Both pCons-induced CD8+CD28+ and CD8+CD28- T cells suppressed production of anti-DNA in vitro. Silencing with small interfering RNA of Foxp3 abrogated the suppression mediated by both CD8+ T cell subsets. Additionally, CD8+ T cells from tolerized mice were weakly cytotoxic against syngeneic B cells from old anti-DNA-producing mice, but not from young mice. Importantly, pCons treatment had dual effects on CD8+ suppressor T cells from tolerized mice, increasing the intracellular expression of Foxp3 while decreasing the surface expression of PD1 molecules. Blocking PD1/PDL1 interactions in the CD8+ T cells from tolerized mice reduced their expression of Foxp3 and their ability to suppress CD4+CD25- proliferation. In contrast, blocking PD1/PDL1 in naive T cells increased Foxp3 expression. Our data suggest that tolerization with pCons activates different subsets of inhibitory/cytotoxic CD8+ T cells whose targets are both CD4+CD25- effector T cells and B cells.

Unmodified self antigen triggers human CD8 T cells with stronger tumor reactivity than altered antigen

Human cancer vaccines are often prepared with altered "analog" or "heteroclitic" antigens that have been optimized for HLA class I binding, resulting in enhanced immunogenicity. Here, we take advantage of CpG oligodeoxynucleotides as powerful vaccine adjuvants and demonstrate the induction of high T cell frequencies in melanoma patients, despite the use of natural (unmodified) tumor antigenic peptide. Compared with vaccination with analog peptide, natural peptide induced T cell frequencies that were approximately twofold lower. However, T cells showed superior tumor reactivity because of (i) increased functional avidity for natural antigen and (ii) enhancement of T cell activation and effector function. Thus, novel vaccine formulations comprising potent immune stimulators may allow to circumvent the need for modified antigens and can induce highly functional T cells with precise antigen specificity.