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CD4+ T cells are typically considered as 'helper' or 'regulatory' populations that support and orchestrate the responses of other lymphocytes. However, they can also develop potent granzyme (Gzm)-mediated cytotoxic activity and CD4+ cytotoxic T cells (CTLs) have been amply documented both in humans and in mice, particularly in the context of human chronic infection and cancer. Despite the established description of CD4+ CTLs, as well as of the critical cytotoxic activity they exert against MHC class II-expressing targets, their developmental and memory maintenance requirements remain elusive. This is at least in part owing to the lack of a murine experimental system where CD4+ CTLs are stably induced. Here, we show that viral and bacterial vectors encoding the same epitope induce distinct CD4+ CTL responses in challenged mice, all of which are nevertheless transient in nature and lack recall properties. Consistent with prior reports, CD4+ CTL differentiation is accompanied by loss of TCF-1 expression, a transcription factor considered essential for memory T cell survival. Using genetic ablation of Tcf7, which encodes TCF-1, at the time of CD4+ T cell activation, we further show that, contrary to observations in CD8+ T cells, continued expression of TCF-1 is not required for CD4+ T cell memory survival. Whilst Tcf7-deficient CD4+ T cells persisted normally following retroviral infection, the CD4+ CTL subset still declined, precluding conclusive determination of the requirement for TCF-1 for murine CD4+ CTL survival. Using xenotransplantation of human CD4+ T cells into murine recipients, we demonstrate that human CD4+ CTLs develop and persist in the same experimental conditions where murine CD4+ CTLs fail to persist. These observations uncover a species-specific defect in murine CD4+ CTL persistence with implications for their use as a model system. [ABSTRACT FROM AUTHOR]

Immune checkpoint blockade (ICB) has revolutionized cancer therapy, but varying response rates illustrate the need for biomarkers of response. Studies in mice have identified a subset of CD8 T cells that is essential for response to PD‐1 ICB. These CD8 T cells co‐express CXCR5, PD‐1 and Tcf1, and provide effector T cells upon PD‐1 ICB. It is unknown whether similar T cells play a role in PD‐1 ICB in humans. We studied human peripheral blood and lymph nodes (LNs) for the frequency, phenotype, and functionality of CXCR5+PD‐1+ CD8 T cells. We find that CXCR5+PD‐1+ CD8 T cells are memory‐like cells, express Tcf1, and lack expression of effector molecules. CXCR5+PD‐1+ CD8 T cells produce cytokines upon stimulation, but have limited proliferative capacity. We studied patients with hematologic malignancies with varying response rates to PD‐1 ICB. Specifically in chronic lymphocytic leukemia, in which PD‐1 ICB does not induce clinical responses, CXCR5+PD‐1+ CD8 T cells show loss of the memory phenotype and increased effector differentiation. In conclusion, we identified CXCR5+PD‐1+ CD8 T cells in human peripheral blood and LN, which could play a similar role during PD‐1 ICB. Future studies should analyze CXCR5+PD‐1+ CD8 T cells during PD‐1 ICB and their importance for therapeutic response. [ABSTRACT FROM AUTHOR]

CD4 + T cells are typically considered as 'helper' or 'regulatory' populations that support and orchestrate the responses of other lymphocytes. However, they can also develop potent granzyme (Gzm)-mediated cytotoxic activity and CD4 + cytotoxic T cells (CTLs) have been amply documented both in humans and in mice, particularly in the context of human chronic infection and cancer. Despite the established description of CD4 + CTLs, as well as of the critical cytotoxic activity they exert against MHC class II-expressing targets, their developmental and memory maintenance requirements remain elusive. This is at least in part owing to the lack of a murine experimental system where CD4 + CTLs are stably induced. Here, we show that viral and bacterial vectors encoding the same epitope induce distinct CD4 + CTL responses in challenged mice, all of which are nevertheless transient in nature and lack recall properties. Consistent with prior reports, CD4 + CTL differentiation is accompanied by loss of TCF-1 expression, a transcription factor considered essential for memory T cell survival. Using genetic ablation of Tcf7 , which encodes TCF-1, at the time of CD4 + T cell activation, we further show that, contrary to observations in CD8 + T cells, continued expression of TCF-1 is not required for CD4 + T cell memory survival. Whilst Tcf7 -deficient CD4 + T cells persisted normally following retroviral infection, the CD4 + CTL subset still declined, precluding conclusive determination of the requirement for TCF-1 for murine CD4 + CTL survival. Using xenotransplantation of human CD4 + T cells into murine recipients, we demonstrate that human CD4 + CTLs develop and persist in the same experimental conditions where murine CD4 + CTLs fail to persist. These observations uncover a species-specific defect in murine CD4 + CTL persistence with implications for their use as a model system., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Hofland, Danelli, Cornish, Donnarumma, Hunt, de Carvalho and Kassiotis.)

Immune checkpoint blockade (ICB) has revolutionized cancer therapy, but varying response rates illustrate the need for biomarkers of response. Studies in mice have identified a subset of CD8 T cells that is essential for response to PD-1 ICB. These CD8 T cells co-express CXCR5, PD-1 and Tcf1, and provide effector T cells upon PD-1 ICB. It is unknown whether similar T cells play a role in PD-1 ICB in humans. We studied human peripheral blood and lymph nodes (LNs) for the frequency, phenotype, and functionality of CXCR5 + PD-1 + CD8 T cells. We find that CXCR5 + PD-1 + CD8 T cells are memory-like cells, express Tcf1, and lack expression of effector molecules. CXCR5 + PD-1 + CD8 T cells produce cytokines upon stimulation, but have limited proliferative capacity. We studied patients with hematologic malignancies with varying response rates to PD-1 ICB. Specifically in chronic lymphocytic leukemia, in which PD-1 ICB does not induce clinical responses, CXCR5 + PD-1 + CD8 T cells show loss of the memory phenotype and increased effector differentiation. In conclusion, we identified CXCR5 + PD-1 + CD8 T cells in human peripheral blood and LN, which could play a similar role during PD-1 ICB. Future studies should analyze CXCR5 + PD-1 + CD8 T cells during PD-1 ICB and their importance for therapeutic response., (© 2020 The Authors. European Journal of Immunology published by Wiley-VCH GmbH.)

Acquired T cell dysfunction is a hallmark of chronic lymphocytic leukemia (CLL), and is linked to an increased risk of infections, but also reduced immune surveillance and disappointing responses to autologous T cell-based immunotherapy. The mechanisms of T cell dysfunction in CLL are not well understood. Studying immunity against chronic viruses allows for detailed analysis of the effect of CLL on T cells chronically exposed to a specific antigen. Cytomegalovirus (CMV) reactivations are rare in CLL, which corroborates with preserved CMV-specific T cell function. Epstein-Barr virus (EBV) is another herpesvirus that results in chronic infection, but unlike CMV, is characterized by subclinical reactivations in CLL patients. Since both herpesviruses induce strong CD8 + T cell responses, but have different clinical outcomes, studying these specific T cells may shed light on the mechanisms of CLL-induced T cell dysfunction. We first analyzed the phenotype of EBV-specific CD8 + T cells in CLL and healthy controls, and found that in CLL EBV-specific CD8 + T cells are in an advanced differentiation state with higher expression of inhibitory receptors. Secondly, CLL-derived EBV-specific CD8 + T cells show reduced cytotoxic potential, in contrast to CMV-specific T cells. Finally, we performed transcriptome analysis to visualize differential modulation by CLL of these T cell subsets. While T cell activation and differentiation genes are unaffected, in EBV-specific T cells expression of genes involved in synapse formation and T cell exhaustion is altered. Our findings on the heterogeneity of antigen specific T cell function in CLL aids in understanding immune-dysregulation in this disease., (Copyright © 2020 the Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the European Hematology Association.)

Allogeneic stem cell transplant-derived T cells have the potential to seek and eliminate sites of residual cancer that escaped primary therapy. Oncolytic myxoma virus (MYXV) exhibits potent anti-cancer efficacy against human cancers like multiple myeloma (MM) and can arm transplant-derived T cells to become more effective cancer killers in vitro and in an immunodeficient xenotransplant murine model. Here, we tested ex vivo MYXV virotherapy against residual murine MM in immunocompetent mice using an allogeneic mouse-mouse model. In contrast to all human MM cell lines previously tested, the murine MM cell line tested here was highly resistant to direct MYXV infection and oncolysis in vitro. Despite this in vitro resistance, we found that ex vivo MYXV-armed allogeneic bone marrow (BM) transplantation dramatically ablated pre-seeded residual MM in vivo. Unexpectedly, we show that both neutrophils and activated T cells from the donor function as virus-armed carrier cells, and MYXV-preloaded cells enhanced MM killing. Our results demonstrate a novel therapeutic paradigm for residual cancer, in which multiple classes of allotransplant leukocytes can be armed by MYXV ex vivo to enhance the graft-versus-tumor effects.