Toripalimab, a therapeutic monoclonal anti-PD-1 antibody with high binding affinity to PD-1 and enhanced potency to activate human T cells

Over the past decade, US Food and Drug Administration (FDA)-approved immune checkpoint inhibitors that target programmed death-1 (PD-1) have demonstrated significant clinical benefit particularly in patients with PD-L1 expressing tumors. Toripalimab is a humanized anti-PD-1 antibody, approved by FDA for first-line treatment of nasopharyngeal carcinoma in combination with chemotherapy. In a post hoc analysis of phase 3 studies, toripalimab in combination with chemotherapy improved overall survival irrespective of PD-L1 status in nasopharyngeal carcinoma (JUPITER-02), advanced non-small cell lung cancer (CHOICE-01) and advanced esophageal squamous cell carcinoma (JUPITER-06). On further characterization, we determined that toripalimab is molecularly and functionally differentiated from pembrolizumab, an anti-PD-1 mAb approved previously for treating a wide spectrum of tumors. Toripalimab, which binds the FG loop of PD-1, has 12-fold higher binding affinity to PD-1 than pembrolizumab and promotes significantly more Th1- and myeloid-derived inflammatory cytokine responses in healthy human PBMCs in vitro. In an ex vivo system employing dissociated tumor cells from treatment naïve non-small cell lung cancer patients, toripalimab induced several unique genes in IFN-γ and immune cell pathways, showed different kinetics of activation and significantly enhanced IFN-γ signature. Additionally, binding of toripalimab to PD-1 induced lower levels of SHP1 and SHP2 recruitment, the negative regulators of T cell activation, in Jurkat T cells ectopically expressing PD-1. Taken together, these data demonstrate that toripalimab is a potent anti-PD-1 antibody with high affinity PD-1 binding, strong functional attributes and demonstrated clinical activity that encourage its continued clinical investigation in several types of cancer.

IL-1R1-dependent signaling coordinates epithelial regeneration in response to intestinal damage

Repair of the intestinal epithelium is tightly regulated to maintain homeostasis. The response after epithelial damage needs to be local and proportional to the insult. How different types of damage are coupled to repair remains incompletely understood. We report that after distinct types of intestinal epithelial damage, IL-1R1 signaling in GREM1+ mesenchymal cells increases production of R-spondin 3 (RSPO3), a Wnt agonist required for intestinal stem cell self-renewal. In parallel, IL-1R1 signaling regulates IL-22 production by innate lymphoid cells and promotes epithelial hyperplasia and regeneration. Although the regulation of both RSPO3 and IL-22 is critical for epithelial recovery from Citrobacter rodentium infection, IL-1R1-dependent RSPO3 production by GREM1+ mesenchymal cells alone is sufficient and required for recovery after dextran sulfate sodium-induced colitis. These data demonstrate how IL-1R1-dependent signaling orchestrates distinct repair programs tailored to the type of injury sustained that are required to restore intestinal epithelial barrier function.

Distinct Mesenchymal Cell Populations Generate the Essential Intestinal BMP Signaling Gradient

Intestinal stem cells (ISCs) are confined to crypt bottoms and their progeny differentiate near crypt-villus junctions. Wnt and bone morphogenic protein (BMP) gradients drive this polarity, and colorectal cancer fundamentally reflects disruption of this homeostatic signaling. However, sub-epithelial sources of crucial agonists and antagonists that organize this BMP gradient remain obscure. Here, we couple whole-mount high-resolution microscopy with ensemble and single-cell RNA sequencing (RNA-seq) to identify three distinct PDGFRA⁺ mesenchymal cell types. PDGFRA(hi) telocytes are especially abundant at the villus base and provide a BMP reservoir, and we identified a CD81⁺ PDGFRA(lo) population present just below crypts that secretes the BMP antagonist Gremlin1. These cells, referred to as trophocytes, are sufficient to expand ISCs in vitro without additional trophic support and contribute to ISC maintenance in vivo. This study reveals intestinal mesenchymal structure at fine anatomic, molecular, and functional detail and the cellular basis for a signaling gradient necessary for tissue self-renewal.

Fibroblastic reticular cells enhance T cell metabolism and survival via epigenetic remodeling

Lymph node fibroblastic reticular cells (FRCs) respond to signals from activated T cells by releasing nitric oxide, which inhibits T cell proliferation and restricts the size of the expanding T cell pool. Whether interactions with FRCs also support the function or differentiation of activated CD8⁺ T cells is not known. Here we report that encounters with FRCs enhanced cytokine production and remodeled chromatin accessibility in newly activated CD8⁺ T cells via interleukin-6. These epigenetic changes facilitated metabolic reprogramming and amplified the activity of pro-survival pathways through differential transcription factor activity. Accordingly, FRC conditioning significantly enhanced the persistence of virus-specific CD8⁺ T cells in vivo and augmented their differentiation into tissue-resident memory T cells. Our study demonstrates that FRCs play a role beyond restricting T cell expansion-they can also shape the fate and function of CD8⁺ T cells.

Cutting Edge: Early Attrition of Memory T Cells during Inflammation and Costimulation Blockade Is Regulated Concurrently by Proapoptotic Proteins Fas and Bim

Apoptosis of CD8 T cells is an essential mechanism that maintains immune system homeostasis, prevents autoimmunity, and reduces immunopathology. CD8 T cell death also occurs early during the response to both inflammation and costimulation blockade (CoB). In this article, we studied the effects of a combined deficiency of Fas (extrinsic pathway) and Bim (intrinsic pathway) on early T cell attrition in response to lymphocytic choriomeningitis virus infection and during CoB during transplantation. Loss of Fas and Bim function in Bcl2l11^-/-Fas^lpr/lpr mice inhibited apoptosis of T cells and prevented the early T cell attrition resulting from lymphocytic choriomeningitis virus infection. Bcl2l11^-/-Fas^lpr/lpr mice were also resistant to prolonged allograft survival induced by CoB targeting the CD40-CD154 pathway. These results demonstrate that both extrinsic and intrinsic apoptosis pathways function concurrently to regulate T cell homeostasis during the early stages of immune responses and allograft survival during CoB.

Testosterone is an endogenous regulator of BAFF and splenic B cell number

Testosterone deficiency in men is associated with increased risk for autoimmunity and increased B cell numbers through unknown mechanisms. Here we show that testosterone regulates the cytokine BAFF, an essential survival factor for B cells. Male mice lacking the androgen receptor have increased splenic B cell numbers, serum BAFF levels and splenic Baff mRNA. Testosterone deficiency by castration causes expansion of BAFF-producing fibroblastic reticular cells (FRCs) in spleen, which may be coupled to lower splenic noradrenaline levels in castrated males, as an α-adrenergic agonist decreases splenic FRC number in vitro. Antibody-mediated blockade of the BAFF receptor or treatment with the neurotoxin 6-hydroxydopamine revert the increased splenic B cell numbers induced by castration. Among healthy men, serum BAFF levels are higher in men with low testosterone. Our study uncovers a previously unrecognized regulation of BAFF by testosterone and raises important questions about BAFF in testosterone-mediated protection against autoimmunity.

Testosterone deficiency is associated with autoimmunity and increased B cell numbers, but the underlying mechanism is unclear. Here the authors show that testosterone may modulate the production of B cell survival factor BAFF by fibroblastic reticular cells via regulation of splenic neurotransmitter levels.

Transient expression of ZBTB32 in anti-viral CD8+ T cells limits the magnitude of the effector response and the generation of memory

Virus infections induce CD8⁺ T cell responses comprised of a large population of terminal effector cells and a smaller subset of long-lived memory cells. The transcription factors regulating the relative expansion versus the long-term survival potential of anti-viral CD8⁺ T cells are not completely understood. We identified ZBTB32 as a transcription factor that is transiently expressed in effector CD8⁺ T cells. After acute virus infection, CD8⁺ T cells deficient in ZBTB32 showed enhanced virus-specific CD8⁺ T cell responses, and generated increased numbers of virus-specific memory cells; in contrast, persistent expression of ZBTB32 suppressed memory cell formation. The dysregulation of CD8⁺ T cell responses in the absence of ZBTB32 was catastrophic, as Zbtb32^-/- mice succumbed to a systemic viral infection and showed evidence of severe lung pathology. We found that ZBTB32 and Blimp-1 were co-expressed following CD8⁺ T cell activation, bound to each other, and cooperatively regulated Blimp-1 target genes Eomes and Cd27. These findings demonstrate that ZBTB32 is a key transcription factor in CD8⁺ effector T cells that is required for the balanced regulation of effector versus memory responses to infection.

CD8⁺ T lymphocytes are essential for immune protection against viruses. In response to an infection, these cells are activated, proliferate, and generate antiviral effector cells that eradicate the infection. Following this, the majority of these effector cells die, leaving a small subset of long-lived virus-specific memory T cells. Our study identifies a transcription factor, ZBTB32, that is required for the regulation of CD8⁺ T cell responses. In its absence, antiviral CD8⁺ T cell numbers increase to abnormally high levels, and generate an overabundance of memory T cells. When this dysregulated response occurs following infection with a virus that cannot be rapidly eliminated by the immune system, the infected animals die from immune-mediated tissue damage, indicating the importance of this pathway.