Abstract Chimeric antigen receptor (CAR) T cell therapy has transformed the treatment landscape for B cell malignancies and multiple myeloma, delivering unprecedented clinical outcomes. However, its application to T cell malignancies remains challenging due to the scarcity of tumor-specific antigen targets and the potential morbidity related to sustained T cell aplasia. In this landscape, killer cell immunoglobulin-like receptor, three Ig domains, and long cytoplasmic tail two (KIR3DL2/CD158k) has recently emerged as a compelling target for immunotherapy in cutaneous T cell lymphomas (CTCL), particularly Sézary syndrome (SS) and transformed mycosis fungoides (tMF). Lacutamab, a first-in-class humanized monoclonal antibody targeting KIR3DL2, has demonstrated potent antitumor activity in vitro via antibody-dependent cell-mediated cytotoxicity (ADCC) and encouraging early clinical efficacy in relapsed/refractory CTCL. Additionally, recent studies have identified elevated KIR3DL2 expression in up to 38% of peripheral T-cell lymphoma (PTCL) cases, particularly in aggressive subtypes such as hepatosplenic T cell lymphoma (HSTCL), monomorphic epitheliotropic intestinal T cell lymphoma (MEITL), peripheral T cell lymphoma not otherwise specified (PTCL-NOS), and others. KIR3DL2 is highly expressed on malignant cells, whereas in normal tissues it is largely confined to a minor subset of NK cells and rare T cells. This selective distribution potentially mitigates on-target, off-tumor toxicity, substantially reduces the risk of fratricide, eliminates the necessity for gene editing in therapeutic effector cells, and preserves critical immune cell populations. We generated a novel murine monoclonal antibody (mAb) targeting KIR3DL2 via hybridoma technology and confirmed its specificity in binding assays by testing it against KIR3DL2-positive T cell lymphoma cell lines (HUT-78, MAC-2A) and their isogenic KIR3DL2 knockout counterparts. Building on the variable heavy (VH) and light (VL) chains of this antibody, we engineered a single-chain variable fragment (scFv)-based CAR construct with CD28 and CD3ζ signaling domains. Following lentiviral transduction of the constructs into primary healthy donor T cells, we demonstrated that the CAR molecules bound recombinant human KIR3DL2 protein, with over 40% of T cells expressing the CAR. CAR expression remained stable for at least 14 days post-transduction, and CAR T cells expanded at rates comparable to untransduced T cells (UTC) suggesting absence of fratricide. Anti-KIR3DL2 CAR T cells exhibited robust in vitro cytotoxic activity against the HH CTCL cell line, which was lentivirally transduced to express KIR3DL2. This effect was significantly greater than that exhibited by UTC, which were stimulated and expanded under comparable in vitro conditions. Notably, sustained cytotoxicity was maintained even at effector-to-target (E:T) ratios as low as 1:10 (p0.0001) and following multiple rounds of tumor rechallenge (p0.0001). In contrast, no substantial lysis was observed against the parental HH cell line, which lacks KIR3DL2 expression. Anti-KIR3DL2 CAR T cells also exhibited significantly enhanced proliferation (p0.0001) and degranulation (p0.0001) compared to donor-matched UTC. In vivo efficacy was evaluated in a xenograft mouse model bearing luciferase-labeled HH-KIR3DL2+ tumors. Mice treated with anti-KIR3DL2 CAR T cells showed complete tumor regression and prolonged disease control for 60 days relative to mice receiving UTC (p0.01 for total flux). No overt signs of toxicity or weight loss were observed during the study period. Overall, our results indicate that the anti-KIR3DL2 CARs developed from our proprietary mAb are specific, safe, and effective against KIR3DL2+ T cell lymphoma cell lines in vitro and in vivo. Studies in additional xenograft models are ongoing. If confirmed, this approach holds promise for treating aggressive and therapy-resistant T cell lymphomas including SS, tMF, HSTCL, MEITL, and PTCL-NOS which, despite their rarity, have dismal survival outcomes and represent a major unmet clinical need.
Cheng et al. (Mon,) studied this question.