Extracorporeal photochemotherapy induces bona fide immunogenic cell death

Abstract

Extracorporeal photochemotherapy (ECP) is employed for the management of cutaneous T cell lymphoma (CTCL). ECP involves the extracorporeal exposure of white blood cells (WBCs) to a photosensitizer, 8-methoxypsoralen (8-MOP), in the context of ultraviolet A (UVA) radiation, followed by WBC reinfusion. Historically, the therapeutic activity of ECP has been attributed to selective cytotoxicity on circulating CTCL cells. However, only a fraction of WBCs is exposed to ECP, and 8-MOP is inactive in the absence of UVA light, implying that other mechanisms underlie the anticancer effects of ECP. Recently, ECP has been shown to enable the physiological differentiation of monocytes into dendritic cells (DCs) that efficiently cross-present tumor-associated antigens (TAAs) to CD8 + T lymphocytes to initiate cognate immunity. However, the source of TAAs and immunostimulatory signals for such DCs remains to be elucidated. Here, we demonstrate that 8-MOP plus UVA light reduces melanoma cell viability along with the emission of ICD-associated danger signals including calreticulin (CALR) exposure on the cell surface and secretion of ATP, high mobility group box 1 (HMGB1) and type I interferon (IFN). Consistently, melanoma cells succumbing to 8-MOP plus UVA irradiation are efficiently engulfed by monocytes, ultimately leading to cross-priming of CD8 + T cells against cancer. Moreover, malignant cells killed by 8-MOP plus UVA irradiation in vitro vaccinate syngeneic immunocompetent mice against living cancer cells of the same type, and such a protection is lost when cancer cells are depleted of calreticulin or HMGB1, as well as in the presence of an ATP-degrading enzyme or antibodies blocking type I IFN receptors. ECP induces bona fide ICD, hence simultaneously providing monocytes with abundant amounts of TAAs and immunostimulatory signals that are sufficient to initiate cognate anticancer immunity.

Platelet P-selectin initiates cross-presentation and dendritic cell differentiation in blood monocytes

“…To examine whether phDC could generate anticancer immunity using complex antigen sources, we challenged our platelet-matured mouse and human phDC with apoptotic tumor cells for stimulation assays with tumor antigen-specific T cells. A clinically used ultraviolet A (UVA)photoactivatable chemotherapy agent, 8-methoxysoralen (8-MOP), was used to induce controlled immunogenic tumor cell death (66,67).…”

PT-112 induces immunogenic cell death and synergizes with immune checkpoint blockers in mouse tumor models

“…21 At least in part, this reflects the proficient activation of intracellular stress responses culminating with the emission of adjuvant signals commonly known as damage-associated molecular patterns (DAMPs) 22 by oxaliplatin (which is largely considered as a bona fide ICD inducer) 23,24 but less so by CDDP and carboplatin (whose immunogenicity remains a matter of debate). 25,26 Based on these premises, we set out to investigate the emission of ICD-associated DAMPs including calreticulin (CALR), ATP and high mobility group box 1 (HMBG1) by cancer cells responding to PT-112, as well as the ability of PT-112 to (1) drive bona fide ICD in gold standard vaccination and abscopal models, 27,28 and (2) synergize with ICBs in the eradication of established mouse tumors. Here, we report that PT-112 causes a form of cancer cell death that is immunogenic per se.…”

Extracorporeal Photopheresis: A Case of Immunotherapy Ahead of Its Time

“…ECP-generated DC exceled at stimulating cytotoxic CD8 T cells with melanoma tumor antigens via MHC class I cross-presentation in a mouse model [57]. A recent report suggests that the potency of ECP-generated DC relays on the emission of damage-associated molecular patterns (DAMP) that augment phagocytic, chemotactic, and activation potential [58]. In particular, calreticulin exposure stimulates phagocytic activity.…”

“…In particular, calreticulin exposure stimulates phagocytic activity. HMGB1 is a nuclear protein with adjuvant properties mediated by TLR4 binding, and extracellular ATP secreted during autophagy promotes chemotaxis via P2Y2 receptor [58, 59]. An in vitro study modeling GvHD indicated that pathogenic T cells express calreticulin and release HMGB1 after 8-MOP/UVA exposure, substantially increasing their phagocytosis by DC [60].…”