Universal cytotoxic activity of a HTLV-1 Tax-specific T cell clone from an HLA-A*24:02⁺ patient with adult T-cell leukemia against a variety of HTLV-I-infected T-cells

Gene expression and TCR amino acid sequences selected by HLA-A02:01-restricted CTLs specific to HTLV-1 in ATL patients

Adult T-cell leukaemia/lymphoma (ATL) is an aggressive malignancy of peripheral T cells caused by human T-cell lymphotropic virus type-1 (HTLV-1). Tax is the most important regulatory protein for HTLV-1. We aimed to reveal a unique amino acid sequence (AA) of complementarity-determining region 3 (CDR3) of the T-cell receptor (TCR)β and TCRα chains of HLA-A*02:01-restricted Tax11-19 -specific cytotoxic T cells (Tax-CTLs). The gene expression profiles (GEP) of Tax-CTLs were assessed by the next-generation sequence (NGS) method with SMARTer technology. Tax-CTLs seemed to be oligoclonal, and their gene compositions were skewed. The unique motifs of 'DSWGK' in TCRα and 'LAG' in TCRβ at CDR3 were observed in almost all patients. Tax-CTL clones harbouring the 'LAG' motif with BV28 had a higher binding score than those without either of them, besides a higher binding score associated with longer survival. Tax-CTLs established from a single cell showed killing activities against Tax-peptide-pulsed HLA-A2+ T2 cell lines. GEP of Tax-CTLs revealed that genes associated with immune response activity were well preserved in long-term survivors with stable status. These methods and results can help us better understand immunity against ATL, and should contribute to future studies on the clinical application of adoptive T-cell therapies.

Live attenuated VZV vaccination induces antitumor immunity in ATLL patients

Adult T cell leukemia/lymphoma (ATLL) is a CD4-positive peripheral T cell lymphoma caused by human T cell lymphotropic virus type 1 (HTLV-1). Although ATLL is quite difficult to be cured, up-regulation of cellular immunity such as HTLV-1 Tax-specific cytotoxic T lymphocytes (CTLs) has been proved to be important to obtain long-term survival. At present, no efficacious method to activate ATLL-specific cellular immunity is available. This study aimed to investigate whether live attenuated varicella-zoster virus (VZV) vaccination to ATLL can activate HTLV-1 Tax-specific cellular immune response. A total of 3 indolent- and 3 aggressive-type ATLL patients were enrolled. All aggressive-type patients had the VZV vaccination after completing anti-ATLL treatment including mogamulizumab, which is a monoclonal antibody for C-C chemokine receptor 4 antigen, plus combination chemotherapy, whereas all indolent-type patients had the VZV vaccination without any antitumor treatment. Cellular immune responses including Tax-specific CTLs were analyzed at several time points of pre- and post-VZV vaccination. After the VZV vaccination, a moderate increase in 1 of 3 indolent-type patients and obvious increase in all 3 aggressive-type patients in Tax-specific CTLs percentage were observed. The increase in the cell-mediated immunity against VZV was observed in all indolent- and aggressive-type patients after VZV vaccination. To conclude, VZV vaccination to aggressive-type ATLL patients after mogamulizumab plus chemotherapy led to the up-regulation of HTLV-1 Tax-specific CTLs without any adverse event. Suppression of regulatory T lymphocytes by mogamulizumab may have contributed to increase tumor immunity in aggressive-type ATLL patients. Japan Registry of Clinical Trials number, jRCTs051180107.

T cell receptor repertoire analysis in HTLV-1-associated diseases

Human T lymphotropic virus 1 (HTLV-1) is a human retrovirus identified as the causative agent in adult T-cell leukemia/lymphoma (ATL) and chronic-progressive neuroinflammatory disorder HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1 is estimated to infect between 5-20 million people worldwide, although most infected individuals remain asymptomatic. HTLV-1 infected persons carry an estimated lifetime risk of approximately 5% of developing ATL, and between 0.25% and 1.8% of developing HAM/TSP. Most HTLV-1 infection is detected in CD4⁺ T cells in vivo which causes the aggressive malignancy in ATL. In HAM/TSP, the increase of HTLV-1 provirus induces immune dysregulation to alter inflammatory milieu, such as expansion of HTLV-1-specific CD8⁺ T cells, in the central nervous system of the infected subjects, which have been suggested to underlie the pathogenesis of HAM/TSP. Factors contributing to the conversion from asymptomatic carrier to disease state remain poorly understood. As such, the identification and tracking of HTLV-1-specific T cell biomarkers that may be used to monitor the progression from primary infection to immune dysfunction and disease are of great interest. T cell receptor (TCR) repertoires have been extensively investigated as a mechanism of monitoring adaptive T cell immune response to viruses and tumors. Breakthrough technologies such as single-cell RNA sequencing have increased the specificity with which T cell clones may be characterized and continue to improve our understanding of TCR signatures in viral infection, cancer, and associated treatments. In HTLV-1-associated disease, sequencing of TCR repertoires has been used to reveal repertoire patterns, diversity, and clonal expansions of HTLV-1-specific T cells capable of immune evasion and dysregulation in ATL as well as in HAM/TSP. Conserved sequence analysis has further been used to identify CDR3 motif sequences and exploit disease- or patient-specificity and commonality in HTLV-1-associated disease. In this article we review current research on TCR repertoires and HTLV-1-specific clonotypes in HTLV-1-associated diseases ATL and HAM/TSP and discuss the implications of TCR clonal expansions on HTLV-1-associated disease course and treatments.

Potential role of HTLV-1 Tax-specific cytotoxic t lymphocytes expressing a unique t-cell receptor to promote inflammation of the central nervous system in myelopathy associated with HTLV-1

Human T-lymphotropic virus 1 (HTLV-1) infection causes two serious diseases: adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy (HAM). Immunological studies have revealed that HTLV-1 Tax-specific CD8⁺ cytotoxic T-cells (Tax-CTLs) in asymptomatic carriers (ACs) and ATL patients play an important role in the elimination of HTLV-1-infected host cells, whereas Tax-CTLs in HAM patients trigger an excessive immune response against HTLV-1-infected host cells infiltrating the central nervous system (CNS), leading to local inflammation. Our previous evaluation of HTLV-1 Tax_301-309 (SFHSLHLLF)-specific Tax-CTLs (Tax_301-309-CTLs) revealed that a unique T-cell receptor (TCR) containing amino acid (AA)-sequence motif PDR, was shared among HLA-A*24:02⁺ ACs and ATL patients and behaved as an eliminator by strong activity against HTLV-1. However, it remains unclear whether PDR⁺Tax_301-309-CTLs also exist in HLA-A*24:02⁺ HAM patients and are involved in the pathogenesis of HAM. In the present study, by high-throughput TCR repertoire analysis technology, we revealed TCR repertoires of Tax_301-309-CTLs in peripheral blood (PB) of HLA-A*24:02⁺ HAM patients were skewed, and a unique TCR-motif PDR was conserved in HAM patients (10 of 11 cases). The remaining case dominantly expressed (-DR, P-R, and PD-), which differed by one AA from PDR. Overall, TCRs with unique AA-sequence motifs PDR, or (-DR, P-R, and PD-) accounted for a total of 0.3-98.1% of Tax_301-309-CTLs repertoires of HLA-A*24:02⁺ HAM patients. Moreover, TCR repertoire analysis of T-cells in the cerebrospinal fluid (CSF) from four HAM patients demonstrated the possibility that PDR⁺Tax_301-309-CTLs and (-DR, P-R, and PD-)⁺Tax_301-309-CTLs efficiently migrated and accumulated in the CSF of HAM patients fostering increased inflammation, although we observed no clear significant correlation between the frequencies of them in PB and the levels of CSF neopterin, a known disease activity biomarker of HAM. Furthermore, to better understand the potential function of PDR⁺Tax_301-309-CTLs, we performed immune profiling by single-cell RNA-sequencing of Tax_301-309-CTLs, and the result showed that PDR⁺Tax_301-309-CTLs up-regulated the gene expression of natural killer cell marker KLRB1 (CD161), which may be associated with T-cell activation and highly cytotoxic potential of memory T-cells. These findings indicated that unique and shared PDR⁺Tax_301-309-CTLs have a potential role in promoting local inflammation within the CNS of HAM patients.

Viral Infections in HSCT: Detection, Monitoring, Clinical Management, and Immunologic Implications

In spite of an increasing array of investigations, the relationships between viral infections and allogeneic hematopoietic stem cell transplantation (HSCT) are still controversial, and almost exclusively regard DNA viruses. Viral infections per se account for a considerable risk of morbidity and mortality among HSCT recipients, and available antiviral agents have proven to be of limited effectiveness. Therefore, an optimal management of viral infection represents a key point in HSCT strategies. On the other hand, viruses bear the potential of shaping immunologic recovery after HSCT, possibly interfering with control of the underlying disease and graft-versus-host disease (GvHD), and eventually with HSCT outcome. Moreover, preliminary data are available about the possible role of some virome components as markers of immunologic recovery after HSCT. Lastly, HSCT may exert an immunotherapeutic effect against some viral infections, notably HIV and HTLV-1, and has been considered as an eradicating approach in these indications.

Development of a Unique T Cell Receptor Gene-Transferred Tax-Redirected T Cell Immunotherapy for Adult T Cell Leukemia

Adult T cell leukemia/lymphoma (ATL) is an aggressive peripheral T cell neoplasm caused by infection with human T cell lymphotropic virus type-1 (HTLV-1). Its prognosis remains extremely poor. Tax, the most important regulatory protein for HTLV-1, is associated with the aggressive proliferation of host cells and is also a major target antigen for CD8⁺ cytotoxic T cells (CTLs). Based on our previous findings that Tax-specific CTLs with a T cell receptor (TCR) containing a unique amino-acid sequence motif exhibit strong HLA-A*24:02-restricted, Tax_301-309-specific activity against HTLV-1, we aimed to develop a Tax-redirected T cell immunotherapy for ATL. TCR-ɑ/β genes were cloned from a previously established CTL clone and transduced into peripheral blood mononuclear cells (PBMCs) of healthy volunteers using a retroviral siTCR vector. Then the cytotoxic efficacy against HTLV-1-infected T cells or primary ATL cells was assessed both in vitro and in vivo. The redirected CTLs (Tax-siCTLs) produced a large amount of cytokines and showed strong killing activity against ATL/HTLV-1-infected T cells in vitro, although they did not have universal activity against ATL cells. Next, in a xenograft mouse model using an HTLV-1-infected T cell line (MT-2), in all mice treated with Tax-siCTLs, the tumor rapidly diminished and finally disappeared without normal tissue damage, although all mice that were untreated or treated with non-gene-modified PBMCs died because of tumor progression. Our findings confirm that Tax-siCTLs can exert strong anti-ATL/HTLV-1 effects without a significant reaction against normal cells and have the potential to be a novel immunotherapy for ATL patients.

A skewed distribution and increased PD-1+Vβ+CD4+/CD8+ T cells in patients with acute myeloid leukemia

The limited application of immunotherapy in acute myeloid leukemia (AML) may be due to poor understanding of the global T cell immune dysfunction in AML. In this study, we analyzed the distribution characteristics of 24 TCR Vβ subfamilies in CD3+, CD4+, and CD8+ T cells in AML patients and healthy controls. The percentage of TCR Vβ subfamily T cells was predominately lower in most AML cases, while it was increased in some cases. TCR Vβ2+T cells were increased in AML, particularly TCR Vβ2+CD4+T cells, which were significantly higher. To further address the immunosuppression in different Vβ subfamilies, we characterized the distribution of program death-1 (PD-1)+T cells in TCR Vβ subfamilies of CD4+ and CD8+T cells. Significantly higher levels of PD-1+Vβ+T cells were found for most Vβ subfamilies in most AML cases. A higher percentage of PD-1+Vβ2+T cells with a high number of Vβ2+T cells was found in all of the CD3+, CD4+, and CD8+ T cell subsets. Moreover, increasing PD-1+Vβ7.2, Vβ8+, Vβ14+, Vβ16+, and Vβ22+CD8+T cells were distributed in the AML-M5 subtype group compared with the AML-M3 group. In addition, higher PD-1+ Vβ5.2+ and PD-1+ Vβ12+CD8+T cells were associated with AML patients who had a poor response to chemotherapy. In conclusion, increased PD-1+Vβ+T cells is a common characteristic of AML, higher PD-1+Vβ2+T cells may be associated with a low antileukemia effect, and higher PD-1+Vβ5.2+ and PD-1+Vβ12+CD8+T cells may be related to poor prognosis in AML. These characteristics may be worth considering as immune biomarkers for clinical outcome in AML.

A Unique T-Cell Receptor Amino Acid Sequence Selected by Human T-Cell Lymphotropic Virus Type 1 Tax301-309-Specific Cytotoxic T Cells in HLA-A24:02-Positive Asymptomatic Carriers and Adult T-Cell Leukemia/Lymphoma Patients

We previously reported that the T-cell receptor (TCR) repertoire of human T-cell lymphotropic virus type 1 (HTLV-1) Tax_301-309-specific CD8⁺ cytotoxic T cells (Tax_301-309-CTLs) was highly restricted and a particular amino acid sequence motif, the PDR motif, was conserved among HLA-A*24:02-positive (HLA-A*24:02⁺) adult T-cell leukemia/lymphoma (ATL) patients who had undergone allogeneic hematopoietic cell transplantation (allo-HSCT). Furthermore, we found that donor-derived PDR⁺ CTLs selectively expanded in ATL long-term HSCT survivors with strong CTL activity against HTLV-1. On the other hand, the TCR repertoires in Tax_301-309-CTLs of asymptomatic HTLV-1 carriers (ACs) remain unclear. In this study, we directly identified the DNA sequence of complementarity-determining region 3 (CDR3) of the TCR-β chain of Tax_301-309-CTLs at the single-cell level and compared not only the TCR repertoires but also the frequencies and phenotypes of Tax_301-309-CTLs between ACs and ATL patients. We did not observe any essential difference in the frequencies of Tax_301-309-CTLs between ACs and ATL patients. In the single-cell TCR repertoire analysis of Tax_301-309-CTLs, 1,458 Tax_301-309-CTLs and 140 clones were identified in this cohort. Tax_301-309-CTLs showed highly restricted TCR repertoires with a strongly biased usage of BV7, and PDR, the unique motif in TCR-β CDR3, was exclusively observed in all ACs and ATL patients. However, there was no correlation between PDR⁺ CTL frequencies and HTLV-1 proviral load (PVL). In conclusion, we have identified, for the first time, a unique amino acid sequence, PDR, as a public TCR-CDR3 motif against Tax in HLA-A*24:02⁺ HTLV-1-infected individuals. Further investigations are warranted to elucidate the role of the PDR⁺ CTL response in the progression from carrier state to ATL.IMPORTANCE ATL is an aggressive T-cell malignancy caused by HTLV-1 infection. The HTLV-1 regulatory protein Tax aggressively promotes the proliferation of HTLV-1-infected lymphocytes and is also a major target antigen for CD8⁺ CTLs. In our previous evaluation of Tax_301-309-CTLs, we found that a unique amino acid sequence motif, PDR, in CDR3 of the TCR-β chain of Tax_301-309-CTLs was conserved among ATL patients after allo-HSCT. Furthermore, the PDR⁺ Tax_301-309-CTL clones selectively expanded and showed strong cytotoxic activities against HTLV-1. On the other hand, it remains unclear how Tax_301-309-CTL repertoire exists in ACs. In this study, we comprehensively compared Tax-specific TCR repertoires at the single-cell level between ACs and ATL patients. Tax_301-309-CTLs showed highly restricted TCR repertoires with a strongly biased usage of BV7, and PDR, the unique motif in TCR-β CDR3, was conserved in all ACs and ATL patients, regardless of clinical subtype in HTLV-1 infection.

Striving to cure adult T-cell leukaemia/lymphoma: a role for allogeneic stem cell transplant?

Adult T-cell leukaemia/lymphoma (ATL) is an aggressive HTLV-1-related malignancy, rare outside of regions where the retrovirus is endemic. Although the use of antiviral therapy has improved outcomes, particularly for indolent forms of ATL, response to combination chemotherapy is poor and outcomes for aggressive subtypes remains dismal. Consolidation with allogeneic stem cell transplant (alloSCT) has an increasing role in the management of ATL in eligible patients, offering favourable long-term remission rates. However, relatively high-transplant-related mortality and issues with donor recruitment for certain ethnicities remain problematic. In this review, we discuss the rationale for and issues surrounding alloSCT in ATL in the context of conventional and emerging therapies.