Abstract
SummaryIn addition to helper and regulatory potential, CD4+ T cells also acquire cytotoxic activity marked by granzyme B (GzmB) expression and the ability to promote rejection of established tumors. Here, we examined the molecular and cellular mechanisms underpinning the differentiation of cytotoxic CD4+ T cells following immunotherapy. CD4+ transfer into lymphodepleted animals or regulatory T (Treg) cell depletion promoted GzmB expression by tumor-infiltrating CD4+, and this was prevented by interleukin-2 (IL-2) neutralization. Transcriptional analysis revealed a polyfunctional helper and cytotoxic phenotype characterized by the expression of the transcription factors T-bet and Blimp-1. While T-bet ablation restricted interferon-γ (IFN-γ) production, loss of Blimp-1 prevented GzmB expression in response to IL-2, suggesting two independent programs required for polyfunctionality of tumor-reactive CD4+ T cells. Our findings underscore the role of Treg cells, IL-2, and Blimp-1 in controlling the differentiation of cytotoxic CD4+ T cells and offer a pathway to enhancement of anti-tumor activity through their manipulation.
Highlights
After the definition of the classical T helper (Th) type 1 (Th1) and type 2 (Th2) lineages (Mosmann et al, 1986), it was reported that mycobacterial antigens could induce the development of cytotoxic CD4+ T cells (Mustafa and Godal, 1987; Ottenhoff et al, 1988)
CD4+ T cell receptor (TCR) Transgenic T Cells Acquire a Polyfunctional Th-Cytotoxic Phenotype upon Transfer into TumorBearing Lymphopenic Mice Upon transfer into tumor-bearing lymphodepleted animals, melanoma-reactive tyrp-1-specific TCR transgenic CD4+ T cells (Trp1 cells) produce IFN-g, tumor necrosis factor a (TNF-a), and granzyme B (GzmB) and acquire potent cytotoxic activity in vitro and in vivo (Quezada et al, 2010; Xie et al, 2010). To confirm whether this activity was specific to the Trp1 TCR or driven by therapeutic modality, we analyzed the activity of Trp1 cells in the context of host lymphodepletion combined with aCTLA-4 treatment or in response to a granulocyte-macrophage colony-stimulating factor (GM-CSF)-expressing tumor cell based vaccine (GVAX) combined with aCTLA-4, which induces effective Trp1 cell activation and IFN-g secretion in vivo (Simpson et al, 2013)
Only Trp1 CD4+ T cells primed in the lymphopenic environment (RT + Trp1 + aCTLA-4) increased GzmB expression, revealing a polyfunctional Th and cytotoxic phenotype (Figure 1C)
Summary
After the definition of the classical T helper (Th) type 1 (Th1) and type 2 (Th2) lineages (Mosmann et al, 1986), it was reported that mycobacterial antigens could induce the development of cytotoxic CD4+ T cells (Mustafa and Godal, 1987; Ottenhoff et al, 1988). Such cytotoxic CD4+ T cells are found in both mice and humans in a wide range of pathological conditions (Juno et al, 2017), including murine cancer models where melanomareactive CD4+ T cells acquire cytotoxic activity and eliminate large transplantable and spontaneous mouse melanoma tumors (Quezada et al, 2010; Xie et al, 2010). Perforin (PFR1)- expressing human CD4+ T cells produce tumor necrosis factor a (TNF-a), interferon-g (IFN-g), and granzyme A (GzmA) (Appay et al, 2002)
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