Activated invariant natural killer T cells directly recognize leukemia cells in a CD1d‐independent manner

Abstract

Invariant natural killer T (iNKT) cells are innate‐like CD1d‐restricted T cells that express the invariant T cell receptor (TCR) composed of Vα24 and Vβ11 in humans. iNKT cells specifically recognize glycolipid antigens such as α‐galactosylceramide (αGalCer) presented by CD1d. iNKT cells show direct cytotoxicity toward CD1d‐positive tumor cells, especially when CD1d presents glycolipid antigens. However, iNKT cell recognition of CD1d‐negative tumor cells is unknown, and direct cytotoxicity of iNKT cells toward CD1d‐negative tumor cells remains controversial. Here, we demonstrate that activated iNKT cells recognize leukemia cells in a CD1d‐independent manner, however still in a TCR‐mediated way. iNKT cells degranulated and released Th1 cytokines toward CD1d‐negative leukemia cells (K562, HL‐60, REH) as well as αGalCer‐loaded CD1d‐positive Jurkat cells. The CD1d‐independent cytotoxicity was enhanced by natural killer cell‐activating receptors such as NKG2D, 2B4, DNAM‐1, LFA‐1 and CD2, but iNKT cells did not depend on these receptors for the recognition of CD1d‐negative leukemia cells. In contrast, TCR was essential for CD1d‐independent recognition and cytotoxicity. iNKT cells degranulated toward patient‐derived leukemia cells independently of CD1d expression. iNKT cells targeted myeloid malignancies more than acute lymphoblastic leukemia. These findings reveal a novel anti–tumor mechanism of iNKT cells in targeting CD1d‐negative tumor cells and indicate the potential of iNKT cells for clinical application to treat leukemia independently of CD1d.

Human intestinal and circulating invariant natural killer T cells are cytotoxic against colorectal cancer cells via the perforin–granzyme pathway

“…Murine and human iNKT cells can target and kill solid tumors by either antigen‐dependent or antigen‐independent mechanisms [ 21 , 27 , 33 , 37 , 38 , 39 , 42 , 48 ]. We thus wondered which could be the case for human iNKT cells in the context of colorectal cancer.…”

“…The antitumor functions of iNKT cells have been of particular interest since the emergence of cancer immunotherapies. They are peculiar in several ways, since they are capable of being activated by lipid antigens, innate signals, and cytokines, and not being affected by histocompatibility issues, as CD1d is a nonpolymorphic molecule [ 21 , 37 , 56 , 57 ]. Nonetheless, the mechanisms of human iNKT cell cytotoxicity are still largely unknown.…”

“…Thanks to their cytotoxic activity, iNKT cells are involved in antitumor functions against many types of cancers, showing either a direct or indirect antitumor effect on cancer cells [ 29 , 30 , 31 , 32 , 33 , 34 ]. Murine iNKT cells isolated from liver, thymus, and spleen can kill leukemia, melanoma, lung, breast, and colorectal cancer cells both in vitro and in vivo ; they express Fas ligand (FasL), TNF‐related apoptosis‐inducing ligand (TRAIL), granzyme B (GZMB), and perforin (PRF) and can target tumor cells in a CD1d‐dependent or CD1d‐independent manner [ 29 , 33 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. While hematopoietic tumors express CD1d, many solid tumors are CD1d negative but can nonetheless be targeted by other mechanisms, including NKG2D engagement [ 27 , 37 , 42 ], or by indirect activation of iNKT cells by other CD1d‐expressing, antigen‐presenting cells present within the tumor microenvironment [ 31 ].…”

“…Murine iNKT cells isolated from liver, thymus, and spleen can kill leukemia, melanoma, lung, breast, and colorectal cancer cells both in vitro and in vivo ; they express Fas ligand (FasL), TNF‐related apoptosis‐inducing ligand (TRAIL), granzyme B (GZMB), and perforin (PRF) and can target tumor cells in a CD1d‐dependent or CD1d‐independent manner [ 29 , 33 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ]. While hematopoietic tumors express CD1d, many solid tumors are CD1d negative but can nonetheless be targeted by other mechanisms, including NKG2D engagement [ 27 , 37 , 42 ], or by indirect activation of iNKT cells by other CD1d‐expressing, antigen‐presenting cells present within the tumor microenvironment [ 31 ]. In vitro studies have shown that the preferred killing mechanism adopted by iNKT cells is the granzyme/perforin pathway [ 27 , 36 , 42 , 43 , 44 ].…”

“…A role for iNKT cells in killing human cancers has been demonstrated [ 34 , 36 , 37 , 42 , 45 , 46 ], and Va24+ NKT cell tumor infiltration is considered an independent positive prognostic factor in human CRC [ 47 ]. Nonetheless, the data generated so far in human cancers describe only the cytotoxic activity of blood‐derived iNKT cells [ 21 , 33 , 36 , 39 , 40 , 45 , 48 ], possibly as a consequence of the great difficulty to isolate and perform functional assays with human tissue‐derived iNKT cells.…”