Challenges in αCD38-chimeric antigen receptor (CAR)-expressing natural killer (NK) cell-based immunotherapy in multiple myeloma: Harnessing the CD38dim phenotype of cytokine-stimulated NK cells as a strategy to prevent fratricide.

BACKGROUND AIMS: Adoptive cell therapy with chimeric antigen receptor (CAR)-expressing natural killer (NK) cells is an emerging approach that holds promise in multiple myeloma (MM). However, the generation of CAR-NK cells targeting CD38 is met with obstacles due to the expression of CD38 on NK cells. Knock-out of CD38 is currently explored as a strategy, although the consequences of the lack of CD38 expression with regards to engraftment and activity in the bone marrow microenvironment are not fully elucidated. Here, we present an alternative approach by harnessing the CD38dim phenotype occurring during long-term cytokine stimulation of primary NK cells. METHODS: Primary NK cells were expanded from peripheral blood mononuclear cells by long-term IL-2 stimulation. During expansion, the CD38 expression was monitored in order to identify a time point when introduction of a novel affinity-optimized αCD38-CAR confered optimal viability, i.e. prevented fratricide. CD38dim NK cells were trasduced with retroviral vectors encoding for the CAR trasngene and their functionality was assessed in in vitro activation and cytotoxicity assays. RESULTS: We verified the functionality of the αCD38-CAR-NK cells against CD38+ cell lines and primary MM cells. Importantly, we demonstrated that αCD38-CAR-NK cells derived from patients with MM have increased activity against autologous MM samples ex vivo. CONCLUSIONS: Overall, our results highlight that incorporation of a functional αCD38-CAR construct into a suitable NK-cell expansion and activation protocol results in a potent and feasible immunotherapeutic strategy for the treatment of patients with MM.

Generation of NK cells with chimeric-switch receptors to overcome PD1-mediated inhibition in cancer immunotherapy.

Multiple myeloma (MM) is an incurable hematological cancer, in which immune checkpoint inhibition (ICI) with monoclonal antibodies (mAbs) has failed due to uncontrollable immune responses in combination therapies and lack of efficacy in monotherapies. Although NK cell-specific checkpoint targets such as NKG2A and KIRs are currently being evaluated in clinical trials, the clinical impact of NK cells on the PD1 cascade is less well understood compared to T cells. Furthermore, while NK cells have effector activity within the TME, under continuous ligand exposure, NK cell dysfunctionality may occur due to interaction of PD1 and its ligand PD-L1. Due to above-mentioned factors, we designed novel NK cell specific PD1-based chimeric switch receptors (PD1-CSR) by employing signaling domains of DAP10, DAP12 and CD3ζ to revert NK cell inhibition and retarget ICI. PD1-CSR modified NK cells showed increased degranulation, cytokine secretion and cytotoxicity upon recognition of PD-L1+ target cells. Additionally, PD1-CSR+ NK cells infiltrated and killed tumor spheroids. While primary NK cells (pNK), expressing native PD1, showed decreased degranulation and cytokine production against PD-L1+ target cells by twofold, PD1-CSR+ pNK cells demonstrated increased activity upon PD-L1+ target cell recognition and enhanced antibody-dependent cellular cytotoxicity. PD1-CSR+ pNK cells from patients with MM increased degranulation and cytokine expression against autologous CD138+PD-L1+ malignant plasma cells. Taken together, the present results demonstrate that PD1-CSR+ NK cells enhance and sustain potent anti-tumor activity in a PD-L1+ microenvironment and thus represent a promising strategy to advance adoptive NK cell-based immunotherapies toward PD-L1+ cancers.

Total Skin Electron Beam Therapy as Part of Multimodal Treatment Strategies for Primary Cutaneous T-Cell Lymphoma.

Total-skin electron beam therapy (TSEBT) is one of most effective treatments that has been used for cutaneous T-cell lymphoma. Low-dose TSEBT regimens (10-12 Gy) appear to be an effective alternative to conventional-dose TSEBT (30-36 Gy), yielding short-term remission of cutaneous manifestations with minimal toxicity. TSEBT can be administered to patients any time after a diagnosis of mycosis fungoides (MF). Patients requiring rapid relief from cutaneous lesions or symptoms may particularly benefit from TSEBT as an initial therapy. Radiotherapy (RT) dose, boost radiation delivery, maintenance treatment, and radiation tolerability may enhance remission rates and improve relapse-free survival following TSEBT. In addition, salvage local RT or TSEBT may be safely applied with high effectiveness. In this review, we focus on the use of TSEBT in patients with several forms of primary cutaneous T-cell lymphoma, and highlight the potential of low-dose TSEBT as part of a promising therapeutic approach.