Raquel S. Laureano

Despite the success of immunotherapy, overcoming immunoresistance in cancer remains challenging. We identified a unique niche of tumor-associated macrophages (TAMs), coexpressing T cell immunoglobulin and mucin domain–containing 3 (TIM3) and V-domain immunoglobulin suppressor of T cell activation (VISTA), that dominated human and mouse tumors resistant to most of the currently used immunotherapies. TIM3 ⁺ VISTA ⁺ TAMs were sustained by IL-4–enriching tumors with low (neo)antigenic and T cell–depleted features. TIM3 ⁺ VISTA ⁺ TAMs showed an anti-inflammatory and protumorigenic phenotype coupled with inability to sense type I interferon (IFN). This was established with cancer cells succumbing to immunogenic cell death (ICD). Dying cancer cells not only triggered autocrine type I IFNs but also exposed HMGB1/VISTA that engaged TIM3/VISTA on TAMs to suppress paracrine IFN-responses. Accordingly, TIM3/VISTA blockade synergized with paclitaxel, an ICD-inducing chemotherapy, to repolarize TIM3 ⁺ VISTA ⁺ TAMs to proinflammatory TAMs that killed cancer cells via tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) signaling. We propose targeting TIM3 ⁺ VISTA ⁺ TAMs to overcome immunoresistant tumors.

Summary: The cellular stress and immunity cycle is a cornerstone of organismal homeostasis. Stress activates intracellular and intercellular communications within a tissue or organ to initiate adaptive responses aiming to resolve the origin of this stress. If such local measures are unable to ameliorate this stress, then intercellular communications expand toward immune activation with the aim of recruiting immune cells to effectively resolve the situation while executing tissue repair to ameliorate any damage and facilitate homeostasis. This cellular stress‐immunity cycle is severely dysregulated in diseased contexts like cancer. On one hand, cancer cells dysregulate the normal cellular stress responses to reorient them toward upholding growth at all costs, even at the expense of organismal integrity and homeostasis. On the other hand, the tumors severely dysregulate or inhibit various components of organismal immunity, for example, by facilitating immunosuppressive tumor landscape, lowering antigenicity, and increasing T‐cell dysfunction. In this review we aim to comprehensively discuss the basis behind tumoral dysregulation of cellular stress‐immunity cycle. We also offer insights into current understanding of the regulators and deregulators of this cycle and how they can be targeted for conceptualizing successful cancer immunotherapy regimen.

Clinically relevant immunological biomarkers that discriminate between diverse hypofunctional states of tumor-associated CD8 ⁺ T cells remain disputed. Using multiomics analysis of CD8 ⁺ T cell features across multiple patient cohorts and tumor types, we identified tumor niche–dependent exhausted and other types of hypofunctional CD8 ⁺ T cell states. CD8 ⁺ T cells in “supportive” niches, like melanoma or lung cancer, exhibited features of tumor reactivity–driven exhaustion (CD8 ⁺ T _EX ). These included a proficient effector memory phenotype, an expanded T cell receptor (TCR) repertoire linked to effector exhaustion signaling, and a cancer-relevant T cell–activating immunopeptidome composed of largely shared cancer antigens or neoantigens. In contrast, “nonsupportive” niches, like glioblastoma, were enriched for features of hypofunctionality distinct from canonical exhaustion. This included immature or insufficiently activated T cell states, high wound healing signatures, nonexpanded TCR repertoires linked to anti-inflammatory signaling, high T cell–recognizable self-epitopes, and an antiproliferative state linked to stress or prodeath responses. In situ spatial mapping of glioblastoma highlighted the prevalence of dysfunctional CD4 ⁺ :CD8 ⁺ T cell interactions, whereas ex vivo single-cell secretome mapping of glioblastoma CD8 ⁺ T cells confirmed negligible effector functionality and a promyeloid, wound healing–like chemokine profile. Within immuno-oncology clinical trials, anti–programmed cell death protein 1 (PD-1) immunotherapy facilitated glioblastoma’s tolerogenic disparities, whereas dendritic cell (DC) vaccines partly corrected them. Accordingly, recipients of a DC vaccine for glioblastoma had high effector memory CD8 ⁺ T cells and evidence of antigen-specific immunity. Collectively, we provide an atlas for assessing different CD8 ⁺ T cell hypofunctional states in immunogenic versus nonimmunogenic cancers.

Tumour-associated macrophages (TAMs) are essential players in the tumour microenvironment (TME) and modulate various pro-tumorigenic functions such as immunosuppression, angiogenesis, cancer cell proliferation, invasion and metastasis, along with resistance to anti-cancer therapies. TAMs also mediate important anti-tumour functions and can clear dying cancer cells via efferocytosis. Thus, not surprisingly, TAMs exhibit heterogeneous activities and functional plasticity depending on the type and context of cancer cell death that they are faced with. This ultimately governs both the pro-tumorigenic and anti-tumorigenic activity of TAMs, making the interface between TAMs and dying cancer cells very important for modulating cancer growth and the efficacy of chemo-radiotherapy or immunotherapy. In this review, we discuss the interface of TAMs with cancer cell death from the perspectives of cell death pathways, TME-driven variations, TAM heterogeneity and cell-death-inducing anti-cancer therapies. We believe that a better understanding of how dying cancer cells influence TAMs can lead to improved combinatorial anti-cancer therapies, especially in combination with TAM-targeting immunotherapies.